Papers by Keyword: Plastic Strain

Abstract: Properties of materials and their variations in depth direction in the same location could be measured directly by progressive multi-cycle (PMC) nanoindentation method. But influences of strain-hardening on measured results in this process haven’t been researched thoroughly. Measurements on an austenitic steel sample and a fused silica sample were conducted by PMC nanoindentation and standard nanoindentation methods, and differences of the results by two methods of the two materials were analyzed. It was found that hardness of austenitic steel measured by PMC method decreased monotonously with increased depth, while hardness measured by standard method decreased to stable value with increased depth. And properties of fused silica measured by both methods accorded much well. Based on analysis of plastic strain during indentation process, it was deduced that austenitic steel with high plasticity could introduce second convergence of plastic strain and stress in PMC indentation process, which made measured hardness decrease monotonously with increased depth.

Abstract: The corrosion behaviour of titanium alloys is not well understood – especially the role of the microstructure and plastic strain. In this paper, the influence of the microstructure and plastic strain on the corrosion resistance of TiMo10Zr4 and Ti6Al4V alloys was studied in the Ringer’s solution at 37 °C. Measurements were performed for different pH values and in aerated and de-aerated solutions using potentiodynamic polarization techniques. Results obtained on the two alloys were compared. It was shown that in the absence of plastic strain TiMo10Zr4 shows better corrosion resistance than Ti6Al4V (especially for pH = 8). By contrast, the current density in the passive range measured after 8% plastic strain was greater on TiMo10Zr4 than on Ti6Al4V, indicating that the passive film on TiMo10Zr4 is less protective than that formed on Ti6Al4V.

Abstract: As a result of the work of Frank-Read dislocation source the shear zone is formed. It is filled with deformation defects forming as a consequence of the dynamic features of the motion of dislocation loops and due to the interaction of shear forming dislocations with dislocations of non-coplanar slip systems. The accumulation of jogs on screw segments leads to the fact that the edge segments are moving faster than the screw segments so the shear zone is swept out generally by screw segments. The expressions of the intensities of the deformation defects accumulation in shear zones are given in the article. The point defects plays special role in the formation and evolution of misorientation substructures into deformed monocrystals, polycrystals and nanocrystals.

Abstract: Dislocation junctions, formed as a result of dislocation reactions, affect the plastic strain process, at least, for two reasons. First of all, junctions serve as barriers to shear-forming dislocations and restrict their path, therefore, the size of the shear zone. Sizes of the shear zone are determined by the density of reacting dislocations in non-coplanar slip systems, forming long enough barriers in the form of dislocation junctions. Secondly, non-breaking dislocation junctions are accumulated inside the shear zone, which leads to an increase in the intensity of the dislocation density accumulation.The present work is devoted to the study of the influence of dislocation junctions on accumulation of the density of dislocation debris (debris junctions) due to formation of stable junctions. For this purpose, the probability density function of lengths in non-breaking junctions is calculated. The model of dislocation interactions, built by the authors of the paper for FCC single crystals, is used.

Abstract: Different levels of compression plane strain were applied to third generation aluminum alloys to simulate rolling-type deformation following solution heat treatment. The aluminum alloys utilized were extruded production samples provided by Alcoa in a solution heat treated condition (T4). The alloys included in this study are AA2099-T4 containing 1.78 wt% lithium, and AA2055-T4 containing 1.13 wt% lithium and an additional component of 0.45 wt% silver. Following plane strain compression, the samples were isothermally heat treated at 155 °C for times up to about 7 days. Data presented include hardening behavior values and various electron microscopy techniques using conventional TEM to document subsequent precipitate sequence distributions and general kinetics.

Abstract: In order to simulate the large deformation surrounding the rotational tool of friction stir welding (FSW) precisely, the moving particle semi-implicit (MPS) method was employed and the temperature distributions near the tool were obtained. Also, the temperature distributions in the whole model except for the area computed by MPS were calculated by the finite element method (FEM) and then the elastic-plastic analysis was conducted using the temperature distributions obtained by MPS and FEM. The inhomogeneous temperature distributions through the thickness near the joint line could be simulated and the maximum temperature distributions computed had a good agreement with the experiments. In addition, the longitudinal plastic strain distributions indicates that this plastic strain near the tool is not governed by only the temperature distributions and the influence of plastic flow should be taken into account.

Abstract: To model the stress-strain relation of frozen soil under different temperatures, an elasto-plastic constitutive model coupling with temperature variable was proposed. Under axisymmetric condition, elastic strain was calculated by the K-G model coupling with temperature. The plastic strain was calculated by using the DP yield criterion, associated flow rule and isotropic hardening law. All of the elastic and plastic parameters are related to the temperature variable. The simulated results show that the proposed model can predict the deformation behavior of frozen soil under different temperatures.

Abstract: During evaluation of the mechanical properties of tinplate for packaging industry by uniaxial tensile test, a non-uniform plastic strain occurs very often. This phenomenon results from the fact, that the plastic deformation is not uniformly developed throughout the measured section. There is a localization of deformation in one or more places resulting in local changes of the tinplate ́s mechanical properties. This paper deals with local strain hardening and non-uniformity of plastic strain of the tinplate temper TH415CA during uniaxial tensile test. Based on micro hardness measurements in the following locally deformed areas, local changes of mechanical properties of the tinplate were determined. The reasons of early strain localization were assumed by microstructural analysis. In the present work are considering partial aspects of the problem focusing on the properties of the local strain hardening and their consequences for stability of uniform plastic strain.

Abstract: Life of an aero-engine is limited by the life of the turbine blade in particular and that of hot end components in general. Design of aero-engine is always conservative in nature considering the flight safety as paramount important. Earlier engines have been assigned life in hours but the life of the component is limited by LCF cycles particularly during the start-stop cycles. In this paper LCF behaviour of a typical Russian origin nickel base wrought super alloy AP220BD used for turbine blade has been studied at room temperature (RT), 400 °C and 700 °C that corresponds to idle rating and cruise rating of a typical aero-engine. Low cycle fatigue (LCF) tests have been carried out at RT, 400°C and 700 °C at three strain amplitudes of ±0.3%, ±0.5% and ±0.8%. Hysteresis loop have been developed at each strain and temperature. It has been observed that LCF life of the nickel base wrought alloy AP220BD is not influenced significantly at strain amplitude of ±0.3% till it reaches 400° C. Reduction in LCF life with increase in strain amplitude from ±0.3% to ±0.8% is much significant compared to that of increase in temperature up to 700°c.The higher life at intermediate strain of ±0.5% may be due to DSA(dynamic strain aging) of the material. Transgranular fracture has been observed at RT & 400° C while intergranular fracture at 700° C.

Abstract: In order to study the stability of rock-socketed piles in landslide control project, this paper took a practical engineering as example, employed the ANASYS software platform as the implementation tool to establish the finite element analysis model. In this analysis, the Drucker-Prager criterion was selected and several differentiated models were established to research the influence of different socketed depth on rock stability. The result indicates that when the embedding depth is constant, the deformation of rock is growing with the increasing of load. When entering into the plastic response, the crack eventually developed into plastic zone around the rock-socketed pile; the adverse effects of the bottom rock would be smaller complying with the deeper of the pillar embedding into the rock; the cost increases with depth of embedded part in practical engineering, according to this research, it is economical and reasonable to choose triple pile diameter as the embedded depth.