Papers by Liviu Palaghian
The Annals of "Dunarea de Jos" University of Galati. Fascicle IX, Metallurgy and Materials Science, 2008
The paper presents the bending fatigue testing for four steel brands. The test showed that the fa... more The paper presents the bending fatigue testing for four steel brands. The test showed that the fatigue strength is decreasing with the increasing of both ingot size and the rolled sheet thickness. The fatigue strength is varying following the ingot area and the orientation of cutting direction versus rolling direction.
Fundamentals of Tribology and Bridging the Gap Between the Macro- and Micro/Nanoscales, 2001
The analysis of fatigue and wear damage in air and corrosive environment has to use different met... more The analysis of fatigue and wear damage in air and corrosive environment has to use different methods of investigation depending on the degradation phase characterizing the surface tested.
DAAAM Proceedings, 2011
The experiments were conducted to investigate the reciprocating wear behavior of an aerospace mat... more The experiments were conducted to investigate the reciprocating wear behavior of an aerospace material (Ti-6Al-4V alloy) under pin/ball-on-plate contact configuration. Results obtained from dry reciprocating wear tests of Ti6Al4V/34CrNiMo6 and Ti6Al4V/AISI420 contact pairs are presented. The results presented in this work show the wear modification via varying normal load. The results provide a comparison between fretting and reciprocating sliding situation.
The Annals of "Dunarea de Jos" University of Galati. Fascicle IX, Metallurgy and Materials Science, 2007
The complex interaction effect of mechanical stress- mechanical systems and aggressive environmen... more The complex interaction effect of mechanical stress- mechanical systems and aggressive environment, leads, at dramatic decreasing of their durability and reliability. The analyze of physical-chemical processes such as: electrode potential evolution, anodic current density evolution, size evolution and growing speed of cracks, allow finding common characteristics of failure due to mechanical stress combined with aggressive environment. Based on the analyze of failure mechanisms by stress cracking corrosion (monotonic mechanical loading), fatigue corrosion (cyclic mechanical loading) and tribocorrosion the paper authors suggest a global model of this kind of failure, based on degradation process of stress cracking corrosion with capability to realize a prediction of damage by these processes.
This paper presents and discusses the mechanism to produce corrosion pits and cracks from corrosi... more This paper presents and discusses the mechanism to produce corrosion pits and cracks from corrosion pits in case of environmentally assisted cracking (EAC). Modeling of corrosion defect growth and possible fracture of the structure implies studies based on the electrochemical, statistical and linear elastic fracture mechanisms. In the work also is presented some possibilities of life prediction of materials in corrosive environment.
The paper presents some surfaces changes aspects in fatigue corrosion damage based on electrochem... more The paper presents some surfaces changes aspects in fatigue corrosion damage based on electrochemical, mechanical profilometry and microscopically analyze of cylindrical and plate steel specimens. The researches have demonstrated that principal cause of damage for rotating specimen is localized pitting corrosion and for plate specimen is generalized surface corrosion, manifested by oscillatory evolution of electrochemical parameters.
This paper studies some aspects of coatings fracture theory and the possibility of extending Lawn... more This paper studies some aspects of coatings fracture theory and the possibility of extending Lawn’s equation from Vickers indenter geometry to the Rockwell one. Indentation tests were performed on stainless steel coatings deposited on 35.CD.4 steel substrate. The stainless steel coatings were nitrogen added in order to improve the fracture toughness. A comparison between different nitrogen concentrations has been made, based on the normal critical load at the first crack appearance. This load was very accurate measured with an acoustic emission state-of-the-art device, Vallen System AMSY4. Based on measured diameters of the ring cracks, the crack length was calculated. The normal critical load was precisely measured, due to acoustic emission method. Thus, it was calculated the fracture coefficient, K. A fracture pattern diagram as a function of normal load was plotted for stainless-nitrogen coating deposited on 35.CD.4 steel substrate.
The paper aims to establish an algorithm for determining the values and evolution of the stress c... more The paper aims to establish an algorithm for determining the values and evolution of the stress concentration factor in corrosive environment, and establish its influence on the fatigue strength of steel required in a corrosive environment. The experimental determinations and theoretical modeling of the process of degradation by corrosion fatigue leads to the conclusion that the stress concentration factor has little influence on the degradation, the principal factor being the surface quality factor.
The paper presents experimental results of the mechanical tests (alternating plane bending and Ch... more The paper presents experimental results of the mechanical tests (alternating plane bending and Charpy impact) performed on samples obtained from X 65 PSL 2 steel slabs. Samples were taken from different batches, cast at the same continuous casting machine. Since metallographic analyses indicates a heterogeneous micro and macrostructure, the samples were collected from different areas of the slabs (surface and middle). In order to highlight the influence of hydrogen embrittlement on mechanical characteristics of steel, some specimens were hydrogenated into hydrogen sulphide environment, for different periods of time. There were calculated the hydrogen embrittlement degree and the structural heterogeneity degree of the slabs structure with data from the two types of the mentioned tests. It is found that the hydrogen embrittlement mainly influences the fatigue characteristics. The structural differences between surface and middle of the slabs are mainly highlighted by the impact tests.
It is found that under the influence of variable loads, the roughness parameters of the surfaces ... more It is found that under the influence of variable loads, the roughness parameters of the surfaces have a certain evolution in dependence with their size. The surface texture resulting from the machining process was characterized using 3D PRO500 profilometer. The surface roughness parameters were used in estimating the effective stress concentration factors Kt using the Arola–Ramulu model. The effective stress concentration factor Kt is an evolutionary process during the fatigue tests corresponding with the roughness parameters evolution.
The results presented in this work show the electrochemical response of a naval steel (grade EN36... more The results presented in this work show the electrochemical response of a naval steel (grade EN36) under corrosion fatigue conditions (3% solution NaCl). The corrosion fatigue tests were carried out using two different specimens: with homogeneous and welded structures. Tafel analysis is performed in order to obtain the variation with time of some kinetic parameters, such as: corrosion potential, polarization resistance, current density, corrosion rate and Tafel slopes. It is found: the oscillatory evolution of these parameters with time (due to the breaking and recovering processes of oxide films); the evolution of the reactivity and stability with time of welded and seamless state; and also, the tendency of pitting degradation of the superficial layer.
This paper presents some theoretical and experimental results regarding the influence of the fric... more This paper presents some theoretical and experimental results regarding the influence of the friction coefficient upon the energy losses in spur gears and worm gears. Tests have been made on medium carbon steel cylindrical specimens for the first case and FcA2 antifriction cast iron - OLC 45 steel and CuSn12T bronze - OLC 45 steel for the second case. They had a pure rolling relative motion and then rolling with sliding motion having different specific sliding degrees. The experimental results showed new aspects of the variation mode of the frictional coefficient in different conditions. This, in its turn, influences the energetic performances of gears.
Based on these experimental observations and on the remark that any small change on the discontin... more Based on these experimental observations and on the remark that any small change on the discontinuity geometry has a significant effect on the stress distribution around it, a stress concentration factor is mandatory to be incorporated into the fatigue models in order to accurately predict the life. In this paper, it is proposed a correlation between the global degradation processes in plain fatigue case and the local degradation process in fretting fatigue case.
This present paper shows the behavior of functional integrity state of a TI6Al4V alloy under reci... more This present paper shows the behavior of functional integrity state of a TI6Al4V alloy under reciprocating wear sliding conditions in a comparative way for two different counter materials, steel and ceramic balls in dry and corrosive environment (3.5% NaCl). The surface integrity analysis of the dry reciprocating wear tests was based on the evolution of the roughness parameters with the applied load. In the case of reciprocating wear tests in corrosive environment the surface integrity analysis was based on electrochemical parameters. Comparative analysis of the evolution of the roughness parameters with the applied load shows a higher stability of the Ti6Al4V/Al2O3 contact pair, while from the point of view of the electrochemical parameters the tribological properties are worst than Ti6Al4V/steel ball contact pair.
This paper presents the results of several tribocorrosion tests conducted on an Al7175/steel ball... more This paper presents the results of several tribocorrosion tests conducted on an Al7175/steel ball and Al7175/alumina ball contact pairs. In order to carry out the tests was used a reciprocating ball on plate tribometer CETR UMT-2. The contact pairs are immersed within an aqueous solution of 3.5% NaCl. An electrochemical cell has been realized that allowed to record the electrochemical parameters. The results showed that the intensity of the tribochemical processes is more pronounced for Al7175/alumina ball contact pairs.
Based on the well known fatigue corrosion effects, the mechanical stress and the corrosive enviro... more Based on the well known fatigue corrosion effects, the mechanical stress and the corrosive environment have a significant effect on the prediction of the lifespan of the equipments that work in corrosive environment, two models are proposed. The first model is dedicated to the evolution of the pits volume that occurs on the specimen surface, while the second one is dedicated to the electrode potential evolution of the material. It was observed a good correlation between the experimental and the predicted results.
DAAAM Proceedings, 2011
Surface finish or roughness has been recognized as being important in various engineering problem... more Surface finish or roughness has been recognized as being important in various engineering problems. The present study uses a microhardness tests for the characterization the influence of roughness surface finish, on the hardness variation and degradation over time in case of the plate specimens were fatigued using constant amplitude loading. The microhardness was measured at different depths and different levels of time with 100 g indentation loads.
Environmental Engineering and Management Journal, 2010
This paper presents some aspects regarding the damage of metal surfaces undergoing mechanical str... more This paper presents some aspects regarding the damage of metal surfaces undergoing mechanical stress corrosive environmental interaction. This interaction is investigated on samples made of two types of low-alloy steel, general use steel type OL524Ak and a shipbuilding steel grade E36, subjected to cyclic load in aqueous solution of 3.5% NaCl. Both electrochemical and fractographic aspects reveal the initiation and development of damage processes on the metal surfaces. It is also highlighted that the processes of damage by corrosion fatigue of the steel structures can be monitored based on recordings of the electrochemical parameters.
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Papers by Liviu Palaghian