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Yeqing Wang

Syracuse University, Mechanical and Aerospace Engineering, Faculty Member

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Research interests include multiphysics analysis, composite materials and structures, hypersonic re-entry ablation problems, directed energy (e.g., laser and lightning strike) effects on solid materials, laser-matter interaction, laser subtractive and additive machining, laser-induced breakdown spectroscopy
Address: 263 Link Hall, Syracuse University, Syracuse, NY 13244

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Mississippi State University

Beijing Institute of Technology

Sasmeeta Tripathy

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Papers by Yeqing Wang

Modeling the lightning continuing current electric arc discharge and material thermal damage: Effects of combinations of amplitude and duration

International Journal of Thermal Sciences, 2021

The damage depth of a material is a key parameter for industrial objects in consideration of the ... more The damage depth of a material is a key parameter for industrial objects in consideration of the lightning threat. The continuing current component in a multiple lightning sequence features a large charge transfer, which often leads to the dominant damage depth for electrically conductive materials. Laboratory simulation of the lightning continuing current is prone to misinterpretation due to various combinations of the current amplitude and duration in fulfillment of the fixed charge requirement of 200 C (±20%) in standards. This study employs a Unified Plasma-Material Finite Element Model (UPM-FEM) that is developed based on the classical magnetohydrodynamics method to analyze the influence of the current amplitude-duration combinations on the arcmaterial interactions. The energy originated from different physical processes, the heat flux and current density on material surface, and the material damage response are predicted using the UPM-FEM and compared for different amplitude-duration combinations at a fixed transfer charge. We report that the Joule heating, thermal conduction, radiative emission, and electronic enthalpic flux jointly determine the energy budget injected to materials at low current levels (≤300 A). While at higher currents (≥500 A), the thermal conduction contributes less significantly compared to the other energy items. The more pronounced increase of radiative emission heat loss will bring a saturation trend in arc properties and the material damage. A combination with a big current amplitude is recommended for achieving consistent arc properties and material damage in lightning continuing current test.

Low velocity impact behavior of auxetic CFRP composite laminates with in-plane negative Poisson's ratio

Journal of Composite Materials, 2023

Introducing auxeticity or negative Poisson's ratio is one potential solution to mitigate the low ... more Introducing auxeticity or negative Poisson's ratio is one potential solution to mitigate the low velocity impact damage of fiber reinforced polymer matrix composites, which can be achieved by tailoring the layup of an anisotropic composite laminate. This study aims to investigate the effect of laminate-level in-plane negative Poisson's ratio on the low velocity impact behavior of carbon fiber reinforced polymer (CFRP) matrix composites using numerical simulations. The layups of the auxetic composites that allow them to produce negative Poisson's ratios are identified based on the Classical Lamination Theory and verified through fundamental coupon-level experimental tests. To ensure meaningful comparisons, the non-auxetic counterpart composites are designed by allowing them to produce positive in-plane Poisson's ratio while closely matching the longitudinal effective modulus of the auxetic laminate. The simulation results indicate that the auxetic laminates suffer smaller (12.6% on average) delamination area in top and bottom interfaces, much smaller (38% on average) matrix compressive damage in the top and bottom plies, and smaller (14.6% on average) fiber tensile damage area in each ply of the laminate at relatively higher impact energies (5 and 8 J).

Three-dimensional modeling of frontal polymerization for rapid, efficient, and uniform thermoset composites manufacturing

Composites Part B, 2023

Due to the incapability of one-dimensional (1D) and two-dimensional (2D) models in simulating the... more Due to the incapability of one-dimensional (1D) and two-dimensional (2D) models in simulating the frontal polymerization (FP) process in laminated composites with multiple fiber angles (e.g., cross-ply, angle-ply), modeling a three-dimensional (3D) domain, which is more representative of practical applications, provides critical guidance in the control and optimization of the FP process. In this paper, subroutines are developed to achieve the 3D modeling of FP in unidirectional and cross-ply carbon fiber laminates with finite element analysis, which are validated against the experimental data. The 3D model is employed to study the effect of triggering direction in relevance to the fiber direction on the FP process, which cannot be studied using traditional 1D/2D models. Our findings suggest that triggering in the fiber direction leads to a higher front velocity, in comparison to cases where front was triggered in the direction perpendicular to the fiber. Moreover, the average front velocity in cross-ply laminates is on average 20-25% lower than that in unidirectional laminates. When triggered using two opposite fronts in the in-plane direction, the maximum temperature of the thermal spike in the crossply laminate, when two fronts merge, is about 100 • C lower than that in the unidirectional laminate. In cross-ply laminates, a sloped pattern forms across the thickness direction as the front propagates in the in-plane direction, as opposed to the traditionally observed uniform propagation pattern in unidirectional cases. Furthermore, the effect of thermal conductivity is studied using two additional composite laminates with glass (1.14 W/m⋅K) and Kevlar fibers (0.04 W/m⋅K). It is shown that the frontal velocity, degree of cure, and the thermal spike temperature decrease as the thermal conductivity reduces.

Tension buckling and postbuckling of nanocomposite laminated plates with in-plane negative Poisson's ratio

Nanotechnology Reviews, 2024

Mechanical metamaterials with negative Poisson's ratio (NPR) have emerged as a novel class of eng... more Mechanical metamaterials with negative Poisson's ratio (NPR) have emerged as a novel class of engineering material, and have attracted increasing attention in various engineering sectors. Most studies available on the buckling problem of laminated plates with positive or NPR are those under uniaxial compression. Here, we report that the buckling phenomenon may occur for auxetic nanocomposite laminated plates under uniaxial tension when the unloaded edges of the plates are immovable. Two types of nanocomposites are considered, including graphene/Cu and carbon nanotube/Cu composites. Governing equations of the auxetic nanocomposite laminated plates are formulated based on the framework of Reddy's higher-order shear deformation theory. In modeling, the von Kármán nonlinear straindisplacement relationship, temperature-dependent material properties, thermal effects, and the plate-substrate interaction are considered. The explicit analytical solutions for postbuckling of auxetic nanocomposite laminated plates subjected to uniaxial tension are obtained for the first time by employing a two-step perturbation approach. Numerical investigations are performed for tension buckling and postbuckling behaviors of auxetic nanocomposite laminated rectangular plates with in-plane NPR rested on an elastic substrate under temperature environments.

Challenges and Future Recommendations for Lightning Strike Damage Assessments of Composites: Laboratory Testing and Predictive Modeling

Materials, 2024

Lightning strike events pose significant challenges to the structural integrity and performance o... more Lightning strike events pose significant challenges to the structural integrity and performance of composite materials, particularly in aerospace, wind turbine blade, and infrastructure applications. Through a meticulous examination of the state-of-the-art methodologies of laboratory testing and damage predictive modeling, this review elucidates the role of simulated lightning strike tests in providing inputs required for damage modeling and experimental data for model validations. In addition, this review provides a holistic understanding of what is there, what are current issues, and what is still missing in both lightning strike testing and modeling to enable a robust and high-fidelity predictive capability, and challenges and future recommendations are also presented. The insights gleaned from this review are poised to catalyze advancements in the safety, reliability, and durability of composite materials under lightning strike conditions, as well as to facilitate the development of innovative lightning damage mitigation strategies.

Negative Poisson's ratio can enhance stability of layered composite structures

Thin-Walled Structures, 2024

Composite laminates with negative Posson's ratios (i.e., auxetic composite laminates) were experi... more Composite laminates with negative Posson's ratios (i.e., auxetic composite laminates) were experimentally found to demonstrate a threefold increase in buckling strength under uniaxial compression in comparison with the equivalent non-auxetic ones. To investigate whether the enhancement is genuinely due to the negative Poisson's ratio (i.e., the auxeticity) or merely caused by the concurrent change in the bending stiffness matrix as the composite layup changes, a novel monoclinic plate-based composite laminate approach is proposed, which for the first time, allows to isolate the auxeticity effect from the concurrent change of the stiffness matrix. Results provided theoretical proof that the auxeticity plays an active role in enhancing the critical buckling strength of layered composite structure. However, such a role is dynamically sensitive to elements in the bending stiffness matrix, especially the bending-twisting ratio and the anisotropy of the bending stiffness between the longitudinal and lateral directions. Insights are expected to provide guidance in exploiting negative Poisson's ratio for improving the stability of layered composite structures.

UV-induced frontal polymerization for optimized in-situ curing of epoxy resin for excellent tensile and flexural properties

Composites Communications, 2024

UV-induced frontal polymerization is an emergent rapid curing method for thermoset resin and its ... more UV-induced frontal polymerization is an emergent rapid curing method for thermoset resin and its fiber composites which features the generation of a self-sustaining front that propagates within the entire material. This is different from using the commercially available UV curable resin which prohibited the curing of thermoset composites with opaque fibers (e.g., carbon fiber) due to the UV light being blocked by the fibers. In this study, we experimentally demonstrate that using the UV-induced frontal polymerization allows us to reduce the curing time of a standard tensile specimen of epoxy resin from traditionally 15 h using the oven curing method to only less than 1.5 min. The frontal polymerized epoxy specimens showed comparable and even superior tensile and flexural properties when compared to the traditional oven cured specimens. Moreover, we experimentally investigated the influence of the weight content of the photoinitiator, the UV light intensity, and the specimen geometry on the characteristics of the frontal polymerization process (i.e., front temperature, front velocity, and degree of cure) and the resulting tensile and flexural properties. The results and discussions are expected to provide guidance in scaling up this UV-induced frontal polymerization technique for the sustainable and additive manufacturing and repair of thermoset resin and its fiber composites.

Stiff, lightweight, and programmable architectured pyrolytic carbon lattices via modular assembling Check for updates

Communications Materials, 2025

Recent advances in additive manufacturing have enabled the creation of three-dimensional (3D) arc... more Recent advances in additive manufacturing have enabled the creation of three-dimensional (3D) architectured pyrolytic carbon (PyC) structures with ultrahigh specific strength and energy absorption capabilities. However, their scalability is limited by reduced strength at larger sizes. Here we introduce a modular assembling approach to scale up PyC lattice structures while retaining strength. Three assembling mechanisms-adhesive, Lego-adhesive, and mechanical interlocking-are explored, demonstrating notably increased specific compressive strength and modulus as size increases, driven by energy release from assembly joint fractures. Practical application is demonstrated by using assembled PyC lattices as the core of an aerospace sandwich structure, significantly enhancing indentation resistance compared to conventional aramid paper honeycomb core. The method also enables versatile designs, including curved structures for space debris protection and bio-scaffold applications. This scalable approach offers a promising pathway for integrating PyC structures into large-scale engineering applications requiring superior mechanical properties and programmability in complicated shape design.

Balancing Strength and Extreme Thermal Resilience in Lunar Regolith Composites: The Role of Multi-Walled Carbon Nanotubes

Small, 2025

The National Aeronautics and Space Administration's (NASA) Artemis program stands at the forefron... more The National Aeronautics and Space Administration's (NASA) Artemis program stands at the forefront of commercial space initiatives, aiming to establish sustainable lunar habitats, demanding resilient construction materials with minimal reliance on Earth-based resources. In response to these demands, this study explores the feasibility of reinforcing lunar regolith with multi-walled carbon nanotubes (MWCNTs) while relying on minimal water and additives for composite fabrication as a potential solution for building semi-permanent Moon bases. Composites incorporating 0.00, 0.25, 0.50, and 1.00 wt.% MWC-NTs are subjected to freeze-thaw cycles, vacuum pressures, ambient environments, and oven-curing methods to emulate the Moon's harsh environment. Results show that ambient-cured composites containing MWCNTs achieve compressive strengths exceeding 35 MPa, resulting in a 44.44% increase compared to the sample without MWCNTs, highlighting the reinforcing potential of carbon nanotubes (CNTs) for extraterrestrial applications. However, thermal cycling reveals performance limitations due to mismatched coefficients of thermal expansion between MWCNTs and the regolith matrix, causing microcracking. In contrast, vacuum-cured MWCNT-free samples surpass 45 MPa, indicating that curing protocols can significantly influence densification and mechanical properties. These findings underscore the trade-offs between material composition, curing approaches, and thermal stability, offering key insights into designing robust, resource-efficient lunar construction.

Rapid Curing of Epoxy Resin Using Self- Sustained Frontal Polymerization Towards the Additive Manufacturing of Thermoset Fiber Composites

American Society for Composites 2022, Sep 19, 2022

The demand for lightweight and high-performance thermoset fiber composites, such as the carbon fi... more The demand for lightweight and high-performance thermoset fiber composites, such as the carbon fiber reinforced epoxy resin composites, has been rapidly increasing in a wide variety of industries. However, thermoset composites require cross linking for curing and consolidation, which is time consuming and can often take several hours. Additionally, the associated capital, operation, and maintenance costs are immense. The major challenge in the additive manufacturing and repair of thermoset-matrix fiber composites is an issue with the in-situ curing. To address this challenge, one of the promising solutions is to use the frontal polymerization technique to significantly reduce the curing time, from several hours to only a few seconds, while simultaneously obviating the need for external heating sources. In this work, the frontal polymerization of the epoxy resin, i.e., one of the most used thermoset resins for fiber composites, is investigated. Specifically, the frontal polymerization is initiated by the ultraviolet LED light. Then, with the help of a thermal co-initiator, the exothermic heating released due to the photopolymerization triggers the thermal polymerization, leading to a selfsustained polymerization front to form and propagate through the epoxy resin. Preliminary experimental results on the effect of weight fraction of the thermal coinitiator on the performance of the frontal polymerization of epoxy resin are presented and discussed. Results include the temperature measurements, SEM images showing the surface morphology of the cured epoxy resin specimens, and the tensile properties of the cured epoxy resin. The tensile properties of the epoxy resin specimens cured using the frontal polymerization technique are also compared with those of a conventional thermoset epoxy resin.

Effect of Negative Poisson’s Ratio on the Tensile Properties of Auxetic CFRP Composites

American Society for Composites 2022, Sep 19, 2022

Carbon fiber reinforced polymer (CFRP) matrix composites have become increasingly popular across ... more Carbon fiber reinforced polymer (CFRP) matrix composites have become increasingly popular across industries such as aerospace and automotive industries due to its outstanding mechanical properties and significant weight saving capability. CFRP composites are also widely known to be highly tailorable. For instance, different laminate-level mechanical properties for CFRP composites can be achieved by varying the individual carbon fiber laminar arrangements, among one of them is the Poisson’s ratio. Conventional materials have a positive Poisson’s ratio (PPR), visualize any conventional materials in a 2D block shape, when stretching that material in longitudinal direction, contraction follows on the transverse direction, whereas for materials with a negative Poisson’s ratio (NPR), stretching in the longitudinal direction leads to expansion in the transverse direction. Materials with NPRs have been shown to improve the indentation and impact resistances, when compared to equivalent materials with PPRs. However, producing NPRs could potentially compromise other properties, such as tensile properties, which has not been reported. The current work investigates the effects of NPR on the tensile properties of CFRP composites. Specifically, a laminatelevel NPR of -0.4094 in the in-plane direction is achieved through ply arrangement of CFRP composites using classical lamination theory (CLT). The non-auxetic counterpart CFRP composites are designed to produce an PPR of 0.1598 in the in-plane direction while simultaneously match their elastic moduli in three directions with those of the auxetic composites. Results show that the predicted tensile modulus and in-plane Poisson’s ratio were in excellent agreement with the experiment results. It was found that the ultimate tensile strength and failure strain or ductility of auxetic specimens were on average 40% lower than those of the conventional CFRP composites.

Low velocity impact behavior of auxetic CFRP composite laminates with in-plane negative Poisson’s ratio

Journal of Composite Materials, Apr 6, 2023

Introducing auxeticity or negative Poisson’s ratio is one potential solution to mitigate the low ... more Introducing auxeticity or negative Poisson’s ratio is one potential solution to mitigate the low velocity impact damage of fiber reinforced polymer matrix composites, which can be achieved by tailoring the layup of an anisotropic composite laminate. This study aims to investigate the effect of laminate-level in-plane negative Poisson’s ratio on the low velocity impact behavior of carbon fiber reinforced polymer (CFRP) matrix composites using numerical simulations. The layups of the auxetic composites that allow them to produce negative Poisson’s ratios are identified based on the Classical Lamination Theory and verified through fundamental coupon-level experimental tests. To ensure meaningful comparisons, the non-auxetic counterpart composites are designed by allowing them to produce positive in-plane Poisson’s ratio while closely matching the longitudinal effective modulus of the auxetic laminate. The simulation results indicate that the auxetic laminates suffer smaller (12.6% on average) delamination area in top and bottom interfaces, much smaller (38% on average) matrix compressive damage in the top and bottom plies, and smaller (14.6% on average) fiber tensile damage area in each ply of the laminate at relatively higher impact energies (5 and 8 J).

Reliability Analysis of Wind Turbine Blades Considering Lightning Strike

Journal of physics, 2020

Lightning strike damage accounts for a significant amount of wind turbines failure. An accurate e... more Lightning strike damage accounts for a significant amount of wind turbines failure. An accurate evaluation of wind turbines' reliability considering lightning strike is thus of critical importance. This research develops two novel lightning stepped leader models considering the stochastic properties and the branching geometry of lightning. In the framework of the reliability analysis of wind turbine blades, the finite element analyses including the two new leader models are conducted and then the electric field in the wind turbine blades are studied. The results show that the branched model adds extra increment of the electric field in the wind turbine blades which is more practical for the wind turbine lightning protection, wind farm siting, and operations and maintenance of wind farms.

Reliability Analysis of Offshore Wind Turbines Using Copula

Offshore structures are subject to severe environmental conditions and require high operating and... more Offshore structures are subject to severe environmental conditions and require high operating and maintenance costs. At the design stage of an offshore structure, it is necessary to perform load analysis and to consider representative environmental conditions characterized by statistical models. However, many available joint distribution models of the environmental parameters can only describe the correlation of these parameters in a very restricted form. The use of simple probabilistic models without correctly addressing their correlation may lead to significant bias in the reliability analysis. Here, the correlation between three offshore environmental parameters including the significant wave height, wave peak period, and mean wind speed is described by copula. The copula density functions and theoretical derivations of copula correlation parameters using actual sea state data are provided for general applications of reliability analysis of offshore structures. Hindcast data of two representative sites are used to fit the best copula. The developed copula-based joint distribution can be used for accurate reliability analysis of offshore structures considering long-term fatigue loads and extreme responses.

Modeling of Lighning Strike Effects in the Fiber-Reinforced Polymer Matrix Composites

Enhanced through-thickness electrical conductivity and lightning strike damage response of interleaved vertically aligned short carbon fiber composites

Composites Part B-engineering, Mar 1, 2023

Through-thickness electrical conductivity of carbon fiber reinforced polymers (CFRPs) is a key ch... more Through-thickness electrical conductivity of carbon fiber reinforced polymers (CFRPs) is a key characteristic that determines the severity of lighting strike-induced damage. Carbon Fibers (CFs) are inherently electrically conductive and therefore provide high conductivity in the direction of the fiber orientation. However, electrical conductivities through the thickness and orthogonal to the CF orientation in CFRPs are governed by the insulating polymer matrix present between CFs. In this work, through the thickness alignment of short CFs in between layers of CFRP laminates is demonstrated to improve the through-thickness electrical conductivity. Composites with interleaved vertically aligned short CF fibers (<150 μm) will be referred as V-fiber composites hereafter. The effect of the V-fiber on the lightning strike damage is evaluated against an artificial lightning strike of 100 kA (modified waveform A of SAE ARP-5412B standard). The improved through-thickness electrical conductivity of CFRP laminates (1.15 S/cm) through vertical alignment of short CFs was compared to reference CFRP laminates (0.13 S/cm) and was found to dissipate the artificial lightning strike current more efficiently. The surface damage after the artificial lightning strike in the V-fiber composites was reduced to 12.69 cm 2 compared to the reference CFRP surface damage of 57.67 cm 2 , a 78% reduction. It was also demonstrated that Joule heat generated due to lightning strike on the composites was significantly less than the reference sample using infrared (IR) thermography. A high retention (up to 78%) of flexural properties (modulus and strength) was observed in V-fiber composites post lightning strike impact as compared to only 47% retention in the reference panel.

Ablation Characteristics of Nanosecond Laser Pulsed Ablation of Aluminum

This research presents laser ablation characteristics of an aluminum alloy after nanosecond pulse... more This research presents laser ablation characteristics of an aluminum alloy after nanosecond pulsed laser ablation (PLA) with a 1064 nm Nd:YAG laser. White light interferometry and scanning electron microscopy were used to establish relationships between laser ablation characteristics and the number of pulses at different beam energies. Laser ablation features studied in this research are crater profiles, radii and depth, and extent of surface damage. An extensive damaged area around the laser ablation crater was found and is believed to be produced by the laser-induced plasma generated during PLA. Spectroscopic analysis showed that there is a correlation between the plasma formation threshold and the initiation of the plasma-affected area, and laser ablation at different angles of incidence between the beam and the sample showed a correlation between the plasma shape and the shape of the damaged area around the ablation crater. However, the variables influencing the occurrence of the plasma-affected and the extent of plasma-induced damage are not yet fully recognized and understood.

Lightning Analysis of Wind Turbines

Springer eBooks, 2018

Lightning strike damage accounts for one of the greatest number of losses for wind turbines and i... more Lightning strike damage accounts for one of the greatest number of losses for wind turbines and is among the top two most frequently reported causes of loss in the wind energy insurance claims in the United States (USA). The Midwest and Texas area, where the most wind power is produced in the USA, are subjected to high lightning flash activities. Also, since multi-MW wind turbines are pursued in the recent years, the corresponding wind turbine blades are becoming longer than before. The longer the blade, the greater its risk of being hit by the lightning. An increase in the blade size and extensive use of composite materials lead to significant challenges in the development of lightning strike protection systems for wind turbine blades, and a better understanding of the response of polymer-matrix composites to a lightning strike is essential for such developments. In this chapter, the basic physics of lightning strike and lightning interaction with the wind turbines are discussed. The common lightning strike protections for wind turbines as well as typical lightning damage mechanisms are introduced. In addition, the analytical and finite element numerical approach of predicting the lightning strike-induced electric field is presented. The obtained electric fields are used to estimate the lightning dielectric breakdown of the composite wind turbine blade. Furthermore, the other forms of lightning damage for wind turbine blades, including the rapid heat transfer, thermal ablation, and delamination, are also discussed. Future recommendations for such lightning research of wind turbines are provided.

Discharge and ground electrode design considerations for the lightning strike damage tolerance assessment of CFRP matrix composite laminates

Composites Part B-engineering, Oct 1, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Assessment of a one-dimensional finite element charring ablation material response model for phenolic-impregnated carbon ablator

Aerospace Science and Technology, Aug 1, 2019

In this study, mathematical formulations to model charring ablation problems were numerically imp... more In this study, mathematical formulations to model charring ablation problems were numerically implemented using finite element analysis (FEA) with ABAQUS, which account for the material decomposition and progressive surface removal in the heat conduction and the surface energy balance equations. FEA was performed for a one-dimensional model to predict the temperature and ablation histories of a phenolic-impregnated carbon ablator sample (i.e., a common heat shield material for hypersonic vehicles and spacecraft) subjected to oxy-acetylene torch flame (i.e., 0.8 SLPM acetylene gas to 2.7 SLPM oxygen gas). The recovery enthalpy and convective heat transfer coefficient for the ablation model were calculated based on gas compositions and two assumed surface conditions (i.e., equilibrium and frozen). Simulations using the calculated recovery enthalpy and convective heat transfer coefficient resulted in a recession rate of 6.38 times (equilibrium) and 14.08 times (frozen) higher than the experimental data, despite fair agreement of the surface temperature. In addition, the effect of the heat transfer coefficient was investigated through a steady-state ablation analysis. The results of the analysis indicate that there is not one single value for the heat transfer coefficient that would allow the prediction to match both measured recession rate and surface temperature. Possible reasons for such an inconsistency are provided and discussed.

Modeling the lightning continuing current electric arc discharge and material thermal damage: Effects of combinations of amplitude and duration

International Journal of Thermal Sciences, 2021

The damage depth of a material is a key parameter for industrial objects in consideration of the ... more The damage depth of a material is a key parameter for industrial objects in consideration of the lightning threat. The continuing current component in a multiple lightning sequence features a large charge transfer, which often leads to the dominant damage depth for electrically conductive materials. Laboratory simulation of the lightning continuing current is prone to misinterpretation due to various combinations of the current amplitude and duration in fulfillment of the fixed charge requirement of 200 C (±20%) in standards. This study employs a Unified Plasma-Material Finite Element Model (UPM-FEM) that is developed based on the classical magnetohydrodynamics method to analyze the influence of the current amplitude-duration combinations on the arcmaterial interactions. The energy originated from different physical processes, the heat flux and current density on material surface, and the material damage response are predicted using the UPM-FEM and compared for different amplitude-duration combinations at a fixed transfer charge. We report that the Joule heating, thermal conduction, radiative emission, and electronic enthalpic flux jointly determine the energy budget injected to materials at low current levels (≤300 A). While at higher currents (≥500 A), the thermal conduction contributes less significantly compared to the other energy items. The more pronounced increase of radiative emission heat loss will bring a saturation trend in arc properties and the material damage. A combination with a big current amplitude is recommended for achieving consistent arc properties and material damage in lightning continuing current test.

Low velocity impact behavior of auxetic CFRP composite laminates with in-plane negative Poisson's ratio

Journal of Composite Materials, 2023

Introducing auxeticity or negative Poisson's ratio is one potential solution to mitigate the low ... more Introducing auxeticity or negative Poisson's ratio is one potential solution to mitigate the low velocity impact damage of fiber reinforced polymer matrix composites, which can be achieved by tailoring the layup of an anisotropic composite laminate. This study aims to investigate the effect of laminate-level in-plane negative Poisson's ratio on the low velocity impact behavior of carbon fiber reinforced polymer (CFRP) matrix composites using numerical simulations. The layups of the auxetic composites that allow them to produce negative Poisson's ratios are identified based on the Classical Lamination Theory and verified through fundamental coupon-level experimental tests. To ensure meaningful comparisons, the non-auxetic counterpart composites are designed by allowing them to produce positive in-plane Poisson's ratio while closely matching the longitudinal effective modulus of the auxetic laminate. The simulation results indicate that the auxetic laminates suffer smaller (12.6% on average) delamination area in top and bottom interfaces, much smaller (38% on average) matrix compressive damage in the top and bottom plies, and smaller (14.6% on average) fiber tensile damage area in each ply of the laminate at relatively higher impact energies (5 and 8 J).

Three-dimensional modeling of frontal polymerization for rapid, efficient, and uniform thermoset composites manufacturing

Composites Part B, 2023

Due to the incapability of one-dimensional (1D) and two-dimensional (2D) models in simulating the... more Due to the incapability of one-dimensional (1D) and two-dimensional (2D) models in simulating the frontal polymerization (FP) process in laminated composites with multiple fiber angles (e.g., cross-ply, angle-ply), modeling a three-dimensional (3D) domain, which is more representative of practical applications, provides critical guidance in the control and optimization of the FP process. In this paper, subroutines are developed to achieve the 3D modeling of FP in unidirectional and cross-ply carbon fiber laminates with finite element analysis, which are validated against the experimental data. The 3D model is employed to study the effect of triggering direction in relevance to the fiber direction on the FP process, which cannot be studied using traditional 1D/2D models. Our findings suggest that triggering in the fiber direction leads to a higher front velocity, in comparison to cases where front was triggered in the direction perpendicular to the fiber. Moreover, the average front velocity in cross-ply laminates is on average 20-25% lower than that in unidirectional laminates. When triggered using two opposite fronts in the in-plane direction, the maximum temperature of the thermal spike in the crossply laminate, when two fronts merge, is about 100 • C lower than that in the unidirectional laminate. In cross-ply laminates, a sloped pattern forms across the thickness direction as the front propagates in the in-plane direction, as opposed to the traditionally observed uniform propagation pattern in unidirectional cases. Furthermore, the effect of thermal conductivity is studied using two additional composite laminates with glass (1.14 W/m⋅K) and Kevlar fibers (0.04 W/m⋅K). It is shown that the frontal velocity, degree of cure, and the thermal spike temperature decrease as the thermal conductivity reduces.

Tension buckling and postbuckling of nanocomposite laminated plates with in-plane negative Poisson's ratio

Nanotechnology Reviews, 2024

Mechanical metamaterials with negative Poisson's ratio (NPR) have emerged as a novel class of eng... more Mechanical metamaterials with negative Poisson's ratio (NPR) have emerged as a novel class of engineering material, and have attracted increasing attention in various engineering sectors. Most studies available on the buckling problem of laminated plates with positive or NPR are those under uniaxial compression. Here, we report that the buckling phenomenon may occur for auxetic nanocomposite laminated plates under uniaxial tension when the unloaded edges of the plates are immovable. Two types of nanocomposites are considered, including graphene/Cu and carbon nanotube/Cu composites. Governing equations of the auxetic nanocomposite laminated plates are formulated based on the framework of Reddy's higher-order shear deformation theory. In modeling, the von Kármán nonlinear straindisplacement relationship, temperature-dependent material properties, thermal effects, and the plate-substrate interaction are considered. The explicit analytical solutions for postbuckling of auxetic nanocomposite laminated plates subjected to uniaxial tension are obtained for the first time by employing a two-step perturbation approach. Numerical investigations are performed for tension buckling and postbuckling behaviors of auxetic nanocomposite laminated rectangular plates with in-plane NPR rested on an elastic substrate under temperature environments.

Challenges and Future Recommendations for Lightning Strike Damage Assessments of Composites: Laboratory Testing and Predictive Modeling

Materials, 2024

Lightning strike events pose significant challenges to the structural integrity and performance o... more Lightning strike events pose significant challenges to the structural integrity and performance of composite materials, particularly in aerospace, wind turbine blade, and infrastructure applications. Through a meticulous examination of the state-of-the-art methodologies of laboratory testing and damage predictive modeling, this review elucidates the role of simulated lightning strike tests in providing inputs required for damage modeling and experimental data for model validations. In addition, this review provides a holistic understanding of what is there, what are current issues, and what is still missing in both lightning strike testing and modeling to enable a robust and high-fidelity predictive capability, and challenges and future recommendations are also presented. The insights gleaned from this review are poised to catalyze advancements in the safety, reliability, and durability of composite materials under lightning strike conditions, as well as to facilitate the development of innovative lightning damage mitigation strategies.

Negative Poisson's ratio can enhance stability of layered composite structures

Thin-Walled Structures, 2024

Composite laminates with negative Posson's ratios (i.e., auxetic composite laminates) were experi... more Composite laminates with negative Posson's ratios (i.e., auxetic composite laminates) were experimentally found to demonstrate a threefold increase in buckling strength under uniaxial compression in comparison with the equivalent non-auxetic ones. To investigate whether the enhancement is genuinely due to the negative Poisson's ratio (i.e., the auxeticity) or merely caused by the concurrent change in the bending stiffness matrix as the composite layup changes, a novel monoclinic plate-based composite laminate approach is proposed, which for the first time, allows to isolate the auxeticity effect from the concurrent change of the stiffness matrix. Results provided theoretical proof that the auxeticity plays an active role in enhancing the critical buckling strength of layered composite structure. However, such a role is dynamically sensitive to elements in the bending stiffness matrix, especially the bending-twisting ratio and the anisotropy of the bending stiffness between the longitudinal and lateral directions. Insights are expected to provide guidance in exploiting negative Poisson's ratio for improving the stability of layered composite structures.

UV-induced frontal polymerization for optimized in-situ curing of epoxy resin for excellent tensile and flexural properties

Composites Communications, 2024

UV-induced frontal polymerization is an emergent rapid curing method for thermoset resin and its ... more UV-induced frontal polymerization is an emergent rapid curing method for thermoset resin and its fiber composites which features the generation of a self-sustaining front that propagates within the entire material. This is different from using the commercially available UV curable resin which prohibited the curing of thermoset composites with opaque fibers (e.g., carbon fiber) due to the UV light being blocked by the fibers. In this study, we experimentally demonstrate that using the UV-induced frontal polymerization allows us to reduce the curing time of a standard tensile specimen of epoxy resin from traditionally 15 h using the oven curing method to only less than 1.5 min. The frontal polymerized epoxy specimens showed comparable and even superior tensile and flexural properties when compared to the traditional oven cured specimens. Moreover, we experimentally investigated the influence of the weight content of the photoinitiator, the UV light intensity, and the specimen geometry on the characteristics of the frontal polymerization process (i.e., front temperature, front velocity, and degree of cure) and the resulting tensile and flexural properties. The results and discussions are expected to provide guidance in scaling up this UV-induced frontal polymerization technique for the sustainable and additive manufacturing and repair of thermoset resin and its fiber composites.

Stiff, lightweight, and programmable architectured pyrolytic carbon lattices via modular assembling Check for updates

Communications Materials, 2025

Recent advances in additive manufacturing have enabled the creation of three-dimensional (3D) arc... more Recent advances in additive manufacturing have enabled the creation of three-dimensional (3D) architectured pyrolytic carbon (PyC) structures with ultrahigh specific strength and energy absorption capabilities. However, their scalability is limited by reduced strength at larger sizes. Here we introduce a modular assembling approach to scale up PyC lattice structures while retaining strength. Three assembling mechanisms-adhesive, Lego-adhesive, and mechanical interlocking-are explored, demonstrating notably increased specific compressive strength and modulus as size increases, driven by energy release from assembly joint fractures. Practical application is demonstrated by using assembled PyC lattices as the core of an aerospace sandwich structure, significantly enhancing indentation resistance compared to conventional aramid paper honeycomb core. The method also enables versatile designs, including curved structures for space debris protection and bio-scaffold applications. This scalable approach offers a promising pathway for integrating PyC structures into large-scale engineering applications requiring superior mechanical properties and programmability in complicated shape design.

Balancing Strength and Extreme Thermal Resilience in Lunar Regolith Composites: The Role of Multi-Walled Carbon Nanotubes

Small, 2025

The National Aeronautics and Space Administration's (NASA) Artemis program stands at the forefron... more The National Aeronautics and Space Administration's (NASA) Artemis program stands at the forefront of commercial space initiatives, aiming to establish sustainable lunar habitats, demanding resilient construction materials with minimal reliance on Earth-based resources. In response to these demands, this study explores the feasibility of reinforcing lunar regolith with multi-walled carbon nanotubes (MWCNTs) while relying on minimal water and additives for composite fabrication as a potential solution for building semi-permanent Moon bases. Composites incorporating 0.00, 0.25, 0.50, and 1.00 wt.% MWC-NTs are subjected to freeze-thaw cycles, vacuum pressures, ambient environments, and oven-curing methods to emulate the Moon's harsh environment. Results show that ambient-cured composites containing MWCNTs achieve compressive strengths exceeding 35 MPa, resulting in a 44.44% increase compared to the sample without MWCNTs, highlighting the reinforcing potential of carbon nanotubes (CNTs) for extraterrestrial applications. However, thermal cycling reveals performance limitations due to mismatched coefficients of thermal expansion between MWCNTs and the regolith matrix, causing microcracking. In contrast, vacuum-cured MWCNT-free samples surpass 45 MPa, indicating that curing protocols can significantly influence densification and mechanical properties. These findings underscore the trade-offs between material composition, curing approaches, and thermal stability, offering key insights into designing robust, resource-efficient lunar construction.

Rapid Curing of Epoxy Resin Using Self- Sustained Frontal Polymerization Towards the Additive Manufacturing of Thermoset Fiber Composites

American Society for Composites 2022, Sep 19, 2022

The demand for lightweight and high-performance thermoset fiber composites, such as the carbon fi... more The demand for lightweight and high-performance thermoset fiber composites, such as the carbon fiber reinforced epoxy resin composites, has been rapidly increasing in a wide variety of industries. However, thermoset composites require cross linking for curing and consolidation, which is time consuming and can often take several hours. Additionally, the associated capital, operation, and maintenance costs are immense. The major challenge in the additive manufacturing and repair of thermoset-matrix fiber composites is an issue with the in-situ curing. To address this challenge, one of the promising solutions is to use the frontal polymerization technique to significantly reduce the curing time, from several hours to only a few seconds, while simultaneously obviating the need for external heating sources. In this work, the frontal polymerization of the epoxy resin, i.e., one of the most used thermoset resins for fiber composites, is investigated. Specifically, the frontal polymerization is initiated by the ultraviolet LED light. Then, with the help of a thermal co-initiator, the exothermic heating released due to the photopolymerization triggers the thermal polymerization, leading to a selfsustained polymerization front to form and propagate through the epoxy resin. Preliminary experimental results on the effect of weight fraction of the thermal coinitiator on the performance of the frontal polymerization of epoxy resin are presented and discussed. Results include the temperature measurements, SEM images showing the surface morphology of the cured epoxy resin specimens, and the tensile properties of the cured epoxy resin. The tensile properties of the epoxy resin specimens cured using the frontal polymerization technique are also compared with those of a conventional thermoset epoxy resin.

Effect of Negative Poisson’s Ratio on the Tensile Properties of Auxetic CFRP Composites

American Society for Composites 2022, Sep 19, 2022

Carbon fiber reinforced polymer (CFRP) matrix composites have become increasingly popular across ... more Carbon fiber reinforced polymer (CFRP) matrix composites have become increasingly popular across industries such as aerospace and automotive industries due to its outstanding mechanical properties and significant weight saving capability. CFRP composites are also widely known to be highly tailorable. For instance, different laminate-level mechanical properties for CFRP composites can be achieved by varying the individual carbon fiber laminar arrangements, among one of them is the Poisson’s ratio. Conventional materials have a positive Poisson’s ratio (PPR), visualize any conventional materials in a 2D block shape, when stretching that material in longitudinal direction, contraction follows on the transverse direction, whereas for materials with a negative Poisson’s ratio (NPR), stretching in the longitudinal direction leads to expansion in the transverse direction. Materials with NPRs have been shown to improve the indentation and impact resistances, when compared to equivalent materials with PPRs. However, producing NPRs could potentially compromise other properties, such as tensile properties, which has not been reported. The current work investigates the effects of NPR on the tensile properties of CFRP composites. Specifically, a laminatelevel NPR of -0.4094 in the in-plane direction is achieved through ply arrangement of CFRP composites using classical lamination theory (CLT). The non-auxetic counterpart CFRP composites are designed to produce an PPR of 0.1598 in the in-plane direction while simultaneously match their elastic moduli in three directions with those of the auxetic composites. Results show that the predicted tensile modulus and in-plane Poisson’s ratio were in excellent agreement with the experiment results. It was found that the ultimate tensile strength and failure strain or ductility of auxetic specimens were on average 40% lower than those of the conventional CFRP composites.

Low velocity impact behavior of auxetic CFRP composite laminates with in-plane negative Poisson’s ratio

Journal of Composite Materials, Apr 6, 2023

Introducing auxeticity or negative Poisson’s ratio is one potential solution to mitigate the low ... more Introducing auxeticity or negative Poisson’s ratio is one potential solution to mitigate the low velocity impact damage of fiber reinforced polymer matrix composites, which can be achieved by tailoring the layup of an anisotropic composite laminate. This study aims to investigate the effect of laminate-level in-plane negative Poisson’s ratio on the low velocity impact behavior of carbon fiber reinforced polymer (CFRP) matrix composites using numerical simulations. The layups of the auxetic composites that allow them to produce negative Poisson’s ratios are identified based on the Classical Lamination Theory and verified through fundamental coupon-level experimental tests. To ensure meaningful comparisons, the non-auxetic counterpart composites are designed by allowing them to produce positive in-plane Poisson’s ratio while closely matching the longitudinal effective modulus of the auxetic laminate. The simulation results indicate that the auxetic laminates suffer smaller (12.6% on average) delamination area in top and bottom interfaces, much smaller (38% on average) matrix compressive damage in the top and bottom plies, and smaller (14.6% on average) fiber tensile damage area in each ply of the laminate at relatively higher impact energies (5 and 8 J).

Reliability Analysis of Wind Turbine Blades Considering Lightning Strike

Journal of physics, 2020

Lightning strike damage accounts for a significant amount of wind turbines failure. An accurate e... more Lightning strike damage accounts for a significant amount of wind turbines failure. An accurate evaluation of wind turbines' reliability considering lightning strike is thus of critical importance. This research develops two novel lightning stepped leader models considering the stochastic properties and the branching geometry of lightning. In the framework of the reliability analysis of wind turbine blades, the finite element analyses including the two new leader models are conducted and then the electric field in the wind turbine blades are studied. The results show that the branched model adds extra increment of the electric field in the wind turbine blades which is more practical for the wind turbine lightning protection, wind farm siting, and operations and maintenance of wind farms.

Reliability Analysis of Offshore Wind Turbines Using Copula

Offshore structures are subject to severe environmental conditions and require high operating and... more Offshore structures are subject to severe environmental conditions and require high operating and maintenance costs. At the design stage of an offshore structure, it is necessary to perform load analysis and to consider representative environmental conditions characterized by statistical models. However, many available joint distribution models of the environmental parameters can only describe the correlation of these parameters in a very restricted form. The use of simple probabilistic models without correctly addressing their correlation may lead to significant bias in the reliability analysis. Here, the correlation between three offshore environmental parameters including the significant wave height, wave peak period, and mean wind speed is described by copula. The copula density functions and theoretical derivations of copula correlation parameters using actual sea state data are provided for general applications of reliability analysis of offshore structures. Hindcast data of two representative sites are used to fit the best copula. The developed copula-based joint distribution can be used for accurate reliability analysis of offshore structures considering long-term fatigue loads and extreme responses.

Modeling of Lighning Strike Effects in the Fiber-Reinforced Polymer Matrix Composites

Enhanced through-thickness electrical conductivity and lightning strike damage response of interleaved vertically aligned short carbon fiber composites

Composites Part B-engineering, Mar 1, 2023

Through-thickness electrical conductivity of carbon fiber reinforced polymers (CFRPs) is a key ch... more Through-thickness electrical conductivity of carbon fiber reinforced polymers (CFRPs) is a key characteristic that determines the severity of lighting strike-induced damage. Carbon Fibers (CFs) are inherently electrically conductive and therefore provide high conductivity in the direction of the fiber orientation. However, electrical conductivities through the thickness and orthogonal to the CF orientation in CFRPs are governed by the insulating polymer matrix present between CFs. In this work, through the thickness alignment of short CFs in between layers of CFRP laminates is demonstrated to improve the through-thickness electrical conductivity. Composites with interleaved vertically aligned short CF fibers (<150 μm) will be referred as V-fiber composites hereafter. The effect of the V-fiber on the lightning strike damage is evaluated against an artificial lightning strike of 100 kA (modified waveform A of SAE ARP-5412B standard). The improved through-thickness electrical conductivity of CFRP laminates (1.15 S/cm) through vertical alignment of short CFs was compared to reference CFRP laminates (0.13 S/cm) and was found to dissipate the artificial lightning strike current more efficiently. The surface damage after the artificial lightning strike in the V-fiber composites was reduced to 12.69 cm 2 compared to the reference CFRP surface damage of 57.67 cm 2 , a 78% reduction. It was also demonstrated that Joule heat generated due to lightning strike on the composites was significantly less than the reference sample using infrared (IR) thermography. A high retention (up to 78%) of flexural properties (modulus and strength) was observed in V-fiber composites post lightning strike impact as compared to only 47% retention in the reference panel.

Ablation Characteristics of Nanosecond Laser Pulsed Ablation of Aluminum

This research presents laser ablation characteristics of an aluminum alloy after nanosecond pulse... more This research presents laser ablation characteristics of an aluminum alloy after nanosecond pulsed laser ablation (PLA) with a 1064 nm Nd:YAG laser. White light interferometry and scanning electron microscopy were used to establish relationships between laser ablation characteristics and the number of pulses at different beam energies. Laser ablation features studied in this research are crater profiles, radii and depth, and extent of surface damage. An extensive damaged area around the laser ablation crater was found and is believed to be produced by the laser-induced plasma generated during PLA. Spectroscopic analysis showed that there is a correlation between the plasma formation threshold and the initiation of the plasma-affected area, and laser ablation at different angles of incidence between the beam and the sample showed a correlation between the plasma shape and the shape of the damaged area around the ablation crater. However, the variables influencing the occurrence of the plasma-affected and the extent of plasma-induced damage are not yet fully recognized and understood.

Lightning Analysis of Wind Turbines

Springer eBooks, 2018

Lightning strike damage accounts for one of the greatest number of losses for wind turbines and i... more Lightning strike damage accounts for one of the greatest number of losses for wind turbines and is among the top two most frequently reported causes of loss in the wind energy insurance claims in the United States (USA). The Midwest and Texas area, where the most wind power is produced in the USA, are subjected to high lightning flash activities. Also, since multi-MW wind turbines are pursued in the recent years, the corresponding wind turbine blades are becoming longer than before. The longer the blade, the greater its risk of being hit by the lightning. An increase in the blade size and extensive use of composite materials lead to significant challenges in the development of lightning strike protection systems for wind turbine blades, and a better understanding of the response of polymer-matrix composites to a lightning strike is essential for such developments. In this chapter, the basic physics of lightning strike and lightning interaction with the wind turbines are discussed. The common lightning strike protections for wind turbines as well as typical lightning damage mechanisms are introduced. In addition, the analytical and finite element numerical approach of predicting the lightning strike-induced electric field is presented. The obtained electric fields are used to estimate the lightning dielectric breakdown of the composite wind turbine blade. Furthermore, the other forms of lightning damage for wind turbine blades, including the rapid heat transfer, thermal ablation, and delamination, are also discussed. Future recommendations for such lightning research of wind turbines are provided.

Discharge and ground electrode design considerations for the lightning strike damage tolerance assessment of CFRP matrix composite laminates

Composites Part B-engineering, Oct 1, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Assessment of a one-dimensional finite element charring ablation material response model for phenolic-impregnated carbon ablator

Aerospace Science and Technology, Aug 1, 2019

In this study, mathematical formulations to model charring ablation problems were numerically imp... more In this study, mathematical formulations to model charring ablation problems were numerically implemented using finite element analysis (FEA) with ABAQUS, which account for the material decomposition and progressive surface removal in the heat conduction and the surface energy balance equations. FEA was performed for a one-dimensional model to predict the temperature and ablation histories of a phenolic-impregnated carbon ablator sample (i.e., a common heat shield material for hypersonic vehicles and spacecraft) subjected to oxy-acetylene torch flame (i.e., 0.8 SLPM acetylene gas to 2.7 SLPM oxygen gas). The recovery enthalpy and convective heat transfer coefficient for the ablation model were calculated based on gas compositions and two assumed surface conditions (i.e., equilibrium and frozen). Simulations using the calculated recovery enthalpy and convective heat transfer coefficient resulted in a recession rate of 6.38 times (equilibrium) and 14.08 times (frozen) higher than the experimental data, despite fair agreement of the surface temperature. In addition, the effect of the heat transfer coefficient was investigated through a steady-state ablation analysis. The results of the analysis indicate that there is not one single value for the heat transfer coefficient that would allow the prediction to match both measured recession rate and surface temperature. Possible reasons for such an inconsistency are provided and discussed.