: Qualitative accelerated test methods improve system reliability by identifying and removing ini... more : Qualitative accelerated test methods improve system reliability by identifying and removing initial design flaws. However, schedule and cost constraints often preclude sufficient testing to generate a meaningful reliability estimate from the data obtained in these tests. In this dissertation a modified accelerated life test is proposed to assess the likelihood of attaining a reliability requirement based on tests of early system prototypes. Assuming each prototype contains an unknown number of independent competing failure modes whose respective times to occurrence are governed by a distinct Weibull law, the observed failure data from this qualitative test are shown to follow a poly-Weibull distribution. However, using an agent-based Monte Carlo simulation, it is shown that for typical products subjected to qualitative testing, the failure observations result from a homogenous subset of the total number of latent failure modes and the failure data can be adequately modeled with a ...
: Recent advances in additive manufacturing (3D printing) have introduced new parameters in reduc... more : Recent advances in additive manufacturing (3D printing) have introduced new parameters in reducing cost in manufacturing aircraft components. The additive process provides a possible means to reduce an aircrafts lifecycle cost (LCC), but the effects of changed process parameters of additive manufacturing machines on final material characteristics are not well known. This research explores these effects with the intent to motivate greater use and application in aviation. We conduct this study in two parts. First, focusing on fused filament fabrication (FFF) through Mark Forged, Inc.s Mark One machine, this research creates PA6dog-bone specimens for (1) a design of experiments (DOE) procedure and (2) a destructive test of a continuous fiber composite specimen from the Mark One machine. Second, this paper explores cost modeling issues using in the additive manufacturing industry with a specific focus on energy usage. Taken together, this research effort identifies critical factors in...
Across many industries, systems are exceeding their intended design lives, whether they are ships... more Across many industries, systems are exceeding their intended design lives, whether they are ships, bridges or military aircraft. As a result failure rates can increase and unanticipated wear or failure conditions can arise. Health monitoring research and application has the potential to more safely lengthen the service life of a range of systems through utilization of sensor data and knowledge of failure mechanisms to predict component life remaining. A further benefit of health monitoring when combined across an entire platform is system health management. System health management is an enabler of condition based maintenance, which allows repair or replacement based on material condition, not a set time. Replacement of components based on condition can enable cost savings through fewer parts being used and the associated maintenance costs. The goal of this research is to show the management of system health can provide savings in maintenance and logistics cost while increasing vehi...
: The purpose of the present research was three-fold: 1) gain a more sophisticated understanding ... more : The purpose of the present research was three-fold: 1) gain a more sophisticated understanding of the response of co-cured composite joints with and without through-thickness reinforcement (TTR), 2) compare the behavior of specimens reinforced with various sizes and densities of reinforcement, and 3) use experimental data to verify the existing DYNA3D smeared property model. Double cantilever beam, end-notch flexure and T-section specimens reinforced with 0.011" diameter z-pins at 2% and 4% volume densities were tested to determine the mode I, mode II and mixed mode (I and II) behavior. Results were added to preliminary research in which tests were conducted on previously mentioned specimen geometries reinforced with 0.022" diameter z-pins at similar densities. Experiments were modeled in DYNA3D using shell and cohesive elements. The energy release rate, G, determined through a curve fit developed from beam theory, was smeared across the region of reinforcement treating ...
2017 Annual IEEE International Systems Conference (SysCon)
Aircraft are generally designed and produced to be maintainable. Recently, the U.S. Air Force, du... more Aircraft are generally designed and produced to be maintainable. Recently, the U.S. Air Force, due to increasing aircraft unit costs, began to investigate early conceptual designs for attritable (unmanned) aircraft. Attritability is a system characteristic that trades reliability and maintainability for low-cost of a system meant for reuse — at least a few times. This characteristic is affected by system attributes like reliability, redundancy, reparability and cost. This concept of a trading these attributes for lower cost presents a very interesting design space for systems engineers, but it presents several challenges. This paper introduces the system characteristic of attritability and shows the far-reaching impacts and challenges that this novel attribute presents through the use of reliability modeling and cost estimation techniques.
Traditional testing methods are costly and inefficient for predicting the lifetimes of materials ... more Traditional testing methods are costly and inefficient for predicting the lifetimes of materials that are expected to function reliably over many years, such as components in the nuclear stockpile. Alternatives to traditional tests accelerate the aging of components by subjecting them to conditions outside normal service or storage ranges, which, in principle, provides test data within a compressed time frame. Alternatives include accelerated life testing (ALT), accelerated degradation testing (ADT), highly accelerated life testing (HALT), highly accelerated stress screening (HASS), and variants on these methods. Use of accelerated methods is often hindered by organizational conflicts between testing as part of an iterative process of finding and removing defects and testing as a means of estimating or predicting reliable life. We are developing a taxonomy for classifying types of accelerated tests and a statistical framework for reconciling conflicting objectives and optimizing the use of testing resources. M any systems are subject to requirements for extremely high reliability over long periods of operation or storage—the nuclear stockpile is a prime example. In addition, systems and components often need to be developed within a time frame that is much shorter than their required reliable operating lives. These requirements present a challenge to traditional reliability engineering, in which items are tested to failure under expected operating conditions in order to predict the reliable lifetime of a deployed system. When lifetimes are measured in years or decades, this approach is no longer feasible. Reliability can be defined as " the ability of an item to perform a required function, under given environmental and operational conditions and for a stated period of time " [1]. Formally, if F(t) is the probability of failure at or before time t, the reliability function R(t) = 1–F(t) gives the probability that the item will still be functional at time t. Derived quantities include the probability density of failure, f(t) = dF(t)/dt, and the hazard rate, h(t) = f(t)/R(t). The hazard rate gives the failure rate at time t, given survival up to t—knowing whether h(t) is increasing, decreasing, or constant is helpful in predicting an item's useful life.
: Qualitative accelerated test methods improve system reliability by identifying and removing ini... more : Qualitative accelerated test methods improve system reliability by identifying and removing initial design flaws. However, schedule and cost constraints often preclude sufficient testing to generate a meaningful reliability estimate from the data obtained in these tests. In this dissertation a modified accelerated life test is proposed to assess the likelihood of attaining a reliability requirement based on tests of early system prototypes. Assuming each prototype contains an unknown number of independent competing failure modes whose respective times to occurrence are governed by a distinct Weibull law, the observed failure data from this qualitative test are shown to follow a poly-Weibull distribution. However, using an agent-based Monte Carlo simulation, it is shown that for typical products subjected to qualitative testing, the failure observations result from a homogenous subset of the total number of latent failure modes and the failure data can be adequately modeled with a ...
: Recent advances in additive manufacturing (3D printing) have introduced new parameters in reduc... more : Recent advances in additive manufacturing (3D printing) have introduced new parameters in reducing cost in manufacturing aircraft components. The additive process provides a possible means to reduce an aircrafts lifecycle cost (LCC), but the effects of changed process parameters of additive manufacturing machines on final material characteristics are not well known. This research explores these effects with the intent to motivate greater use and application in aviation. We conduct this study in two parts. First, focusing on fused filament fabrication (FFF) through Mark Forged, Inc.s Mark One machine, this research creates PA6dog-bone specimens for (1) a design of experiments (DOE) procedure and (2) a destructive test of a continuous fiber composite specimen from the Mark One machine. Second, this paper explores cost modeling issues using in the additive manufacturing industry with a specific focus on energy usage. Taken together, this research effort identifies critical factors in...
Across many industries, systems are exceeding their intended design lives, whether they are ships... more Across many industries, systems are exceeding their intended design lives, whether they are ships, bridges or military aircraft. As a result failure rates can increase and unanticipated wear or failure conditions can arise. Health monitoring research and application has the potential to more safely lengthen the service life of a range of systems through utilization of sensor data and knowledge of failure mechanisms to predict component life remaining. A further benefit of health monitoring when combined across an entire platform is system health management. System health management is an enabler of condition based maintenance, which allows repair or replacement based on material condition, not a set time. Replacement of components based on condition can enable cost savings through fewer parts being used and the associated maintenance costs. The goal of this research is to show the management of system health can provide savings in maintenance and logistics cost while increasing vehi...
: The purpose of the present research was three-fold: 1) gain a more sophisticated understanding ... more : The purpose of the present research was three-fold: 1) gain a more sophisticated understanding of the response of co-cured composite joints with and without through-thickness reinforcement (TTR), 2) compare the behavior of specimens reinforced with various sizes and densities of reinforcement, and 3) use experimental data to verify the existing DYNA3D smeared property model. Double cantilever beam, end-notch flexure and T-section specimens reinforced with 0.011" diameter z-pins at 2% and 4% volume densities were tested to determine the mode I, mode II and mixed mode (I and II) behavior. Results were added to preliminary research in which tests were conducted on previously mentioned specimen geometries reinforced with 0.022" diameter z-pins at similar densities. Experiments were modeled in DYNA3D using shell and cohesive elements. The energy release rate, G, determined through a curve fit developed from beam theory, was smeared across the region of reinforcement treating ...
2017 Annual IEEE International Systems Conference (SysCon)
Aircraft are generally designed and produced to be maintainable. Recently, the U.S. Air Force, du... more Aircraft are generally designed and produced to be maintainable. Recently, the U.S. Air Force, due to increasing aircraft unit costs, began to investigate early conceptual designs for attritable (unmanned) aircraft. Attritability is a system characteristic that trades reliability and maintainability for low-cost of a system meant for reuse — at least a few times. This characteristic is affected by system attributes like reliability, redundancy, reparability and cost. This concept of a trading these attributes for lower cost presents a very interesting design space for systems engineers, but it presents several challenges. This paper introduces the system characteristic of attritability and shows the far-reaching impacts and challenges that this novel attribute presents through the use of reliability modeling and cost estimation techniques.
Traditional testing methods are costly and inefficient for predicting the lifetimes of materials ... more Traditional testing methods are costly and inefficient for predicting the lifetimes of materials that are expected to function reliably over many years, such as components in the nuclear stockpile. Alternatives to traditional tests accelerate the aging of components by subjecting them to conditions outside normal service or storage ranges, which, in principle, provides test data within a compressed time frame. Alternatives include accelerated life testing (ALT), accelerated degradation testing (ADT), highly accelerated life testing (HALT), highly accelerated stress screening (HASS), and variants on these methods. Use of accelerated methods is often hindered by organizational conflicts between testing as part of an iterative process of finding and removing defects and testing as a means of estimating or predicting reliable life. We are developing a taxonomy for classifying types of accelerated tests and a statistical framework for reconciling conflicting objectives and optimizing the use of testing resources. M any systems are subject to requirements for extremely high reliability over long periods of operation or storage—the nuclear stockpile is a prime example. In addition, systems and components often need to be developed within a time frame that is much shorter than their required reliable operating lives. These requirements present a challenge to traditional reliability engineering, in which items are tested to failure under expected operating conditions in order to predict the reliable lifetime of a deployed system. When lifetimes are measured in years or decades, this approach is no longer feasible. Reliability can be defined as " the ability of an item to perform a required function, under given environmental and operational conditions and for a stated period of time " [1]. Formally, if F(t) is the probability of failure at or before time t, the reliability function R(t) = 1–F(t) gives the probability that the item will still be functional at time t. Derived quantities include the probability density of failure, f(t) = dF(t)/dt, and the hazard rate, h(t) = f(t)/R(t). The hazard rate gives the failure rate at time t, given survival up to t—knowing whether h(t) is increasing, decreasing, or constant is helpful in predicting an item's useful life.
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