Analysis Of Stress-strain Curves Research Articles

Hot Deformation Behavior of a New-Generation 980 MPa Grade TRIP Steel for Automobiles

Using a Gleeble 1500 thermo-mechanical simulator, the behavior of the dynamic recrystallization (DRX) of a low-silicon TRIP steel containing phosphorus and vanadium for automobiles is studied systematically. By the analysis of ture stress-strain curves, critical stress(σc) and strain(εc) are determined at different deformation conditions. The deformation activation energy Qdef is 323 kJ/mol. The ratios of εc/εp and σc/σp of the tested TRIP steel are 0.553 and 0.89, respectively. The equation for describing the Zener–Hollomn formula for tested steel is derived. A linear equation between σc, σp, εc, εp and lnZ have been established through regression analysis, respectively.

Mechanical Behavior and Microstructural Change of a High Nitrogen CrMn Austenitic Stainless Steel during Hot Deformation

The hot deformation behavior of a high nitrogen CrMn austenitic stainless steel in the temperature range 1173 to 1473 K (900 to 1200 °C) and strain rate range 0.01 to 10 s−1 was investigated using optical microscopy, stress-strain curve analysis, processing maps, etc. The results showed that the work hardening rate and flow stress decreased with increasing deformation temperature and decreasing strain rate in 18Mn18Cr0.5N steel. The dynamic recrystallization (DRX) grain size decreased with increasing Z value; however, deformation heating has an effect on the DRX grain size under high strain rate conditions. In the processing maps, flow instability was observed at higher strain rate regions (1 to 10 s−1) and manifested as flow localization near the grain boundary. Early in the deformation, the flow instability region was at higher temperatures, and then the extent of this unstable region decreased with increasing strain and was restricted to lower temperatures. The hot deformation equation as well as the quantitative dependence of the critical stress for DRX and DRX grain size on Z value was obtained.

Mechanisms of Ductility in CoTi and CoZr B2 Intermetallics

The present research is conducted in order to elucidate the operative deformation mechanisms allowing ductility in the B2 (CsCl) intermetallics CoTi and CoZr. A twofold approach combines in-situ neutron diffraction during uniaxial compression with elastoplastic self-consistent (EPSC) polycrystal modeling. Tensile and compression tests of CoZr and CoTi confirm that both intermetallics are ductile at room temperature. Low compressive yield points of −62 and −50 MPa are identified for CoTi and CoZr, respectively. Analysis of stress-strain curves, in-situ neutron diffraction internal strain measurements, and EPSC modeling confirm that the initial plasticity is accommodated via the established $$ \left\langle { 100} \right\rangle \left\{ {0 1 1} \right\} $$ slip mode. However, a sudden decrease in the hardening rate observed in the macroscopic stress-strain curve and apparent in the internal stress developments signals the activation of a secondary mechanism, which helps to explain the anomalous ductility. The EPSC simulations involving either $$ \left\langle { 1 10} \right\rangle \left\{ {\overline{1} 10} \right\} $$ or $$ \left\langle { 1 1 1} \right\rangle \left\{ {1\overline{1} 0} \right\} $$ slip mechanisms coupled with $$ \left\langle { 1 0 0} \right\rangle $$ slip can reproduce the observed transitions at −350 and −250 MPa for CoTi and CoZr, respectively. Implications related to previous observations of a yield strength anomaly and the possible influence of kink banding are discussed.

Dynamic Properties of Plain Concrete in Triaxial Stress State

There was experimental investigation of plain concrete dynamic behavior at high strain rates using a custom-designed, triaxial, servo-hydraulic controlled testing machine with over 60 cubic specimens in this study. A gradually increasing force was used for axial loading of each specimen at a constant strain rate at 10 supra -5 second supra -1, 10 supra -4 second supra -1, or 10 supra -3 second supra -1 and laterally confined at a 0, 4, 8, 12, or 16 MPa (0, 0.58, 1.16, 1.74, or 2.32 ksi) constant pressure. At each strain rate, there was analysis and discussion of axial stress-strain curves under confining pressures. Test results indicated that there were significant increases according to confining pressure of both ultimate strength and its corresponding strain. There was development of empirical equations accounting for triaxial stress and strain rate effects. There is substantial ultimate strength increases under low confinement and moderate increases under high confinement with increasing strain rate.

Constitutive Analysis of Stress-Strain Curves of a High-Nitrogen Austenitic Stainless Steel

Abstract The Ni content in the conventional austenitic stainless steel tends to be lowered by alloying of high amount of N so that the production cost can be significantly reduced. In this paper, the flow stress curves for a high-nitrogen alloyed stainless steel of 1Cr22Mn15N were investigated by the thermo-mechanical simulator, which show typical characteristics of appearance of dynamic recrystallization. Besides, a numerical model based on Zener-Holloman parameter has been established to simulate the flow stress curves with quite good agreement. It was found that the activation energy for 1Cr22Mn15N is much more than that for the other 300 series stainless steels possible, indicating that strengthening resulting from interstitial solution of N atoms is stronger that for substitutional solution of other elements.

STUDY OF DYNAMIC RECRYSTALLIZATION OF LOW CARBON STEEL IN THIN SLAB CONTINUOUS ROLLING PROCESS

Combined with the technological characteristics of thin slab continuous rolling process (TSCR), dynamic recrystallization of an extremely coarse austenite of low carbon steel is studied by Thermecmaster-Z hot simulator. By the analysis of true stress-strain curves and the observation of microstructures at different deformation stages, the critical stress and critical strain are determined under different deformation conditions. The effect of Z parameter on dynamic recrystallization of coarse austenite is studied. The microstructure evolution in real production is also discussed.

The Modified Super-Ellipsoid Yield Criterion for Human Trabecular Bone

Despite the importance of multiaxial failure of trabecular bone in many biomechanical applications, to date no complete multiaxial failure criterion for human trabecular bone has been developed. By using experimentally validated nonlinear high-resolution, micromechanical finite-element models as a surrogate for multiaxial loading experiments, we determined the three-dimensional normal strain yield surface and all combinations of the two-dimensional normal-shear strain yield envelope. High-resolution finite-element models of three human femoral neck trabecular bone specimens obtained through microcomputed tomography were used. In total, 889 multiaxial-loading cases were analyzed, requiring over 41,000 CPU hours on parallel supercomputers. Our results indicated that the multiaxial yield behavior of trabecular bone in strain space was homogeneous across the specimens and nearly isotropic. Analysis of stress-strain curves along each axis in the 3-D normal strain space indicated uncoupled yield behavior whereas substantial coupling was seen for normal-shear loading. A modified super-ellipsoid surface with only four parameters fit the normal strain yield data very well with an arithmetic error +/-SD less than -0.04 +/- 5.1%. Furthermore, the principal strains associated with normal-shear loading showed excellent agreement with the yield surface obtained for normal strain loading (arithmetic error +/- SD < 2.5 +/- 6.5%). We conclude that the four-parameter "Modified Super-Ellipsoid" yield surface presented here describes the multiaxial failure behavior of human femoral neck trabecular bone very well.

High temperature compressive deformation and fracture characteristics of the activated sintered W–Ni compacts

In order to determine the working conditions for the Ni-activated sintered W compact, a wide range of compression test was carried out under controlled temperature conditions between 900 and 1100 °C and a constant true strain rate of 1 × 10 −3–1 × 10 0/s. A moderate true strain up to 0.6 was obtained without a fracture at the testing temperature of 900 °C irrespectively of the strain rate for the specimen of an appropriate porosity and controlled grain size, being comparable to that of the pure W specimen. The relationship between the brittle features and the segregated Ni phase was able to be discussed on the basis of the microstructural analysis on the fracture surface and the true stress–strain curve analysis.

Elastic energy storage in human articular cartilage: estimation of the elastic modulus for type II collagen and changes associated with osteoarthritis.

The viscoelastic mechanical properties of normal and osteoarthritic articular were analyzed based on data reported by Kempson [in: Adult Articular Cartilage (1973)] and Silver et al. (Connect. Tissue Res., 2001b). Results of the analysis of tensile elastic stress-strain curves suggest that the elastic modulus of cartilage from the superficial zone is approximately 7.0 GPa parallel and 2.21 GPa perpendicular to the cleavage line pattern. Collagen fibril lengths in the superficial zone were found to be approximately 1265 microm parallel and 668 microm perpendicular to the cleavage line direction. The values for the elastic modulus and fibril lengths decreased with increased extent of osteoarthritis. The elastic modulus of type II collagen parallel to the cleavage line pattern in the superficial zone approaches that of type I collagen in tendon, suggesting that elastic energy storage occurs in the superficial zone due to the tensile pre-tension that exists in this region. Decreases in the elastic modulus associated with osteoarthritis reflect decreased ability of cartilage to store elastic energy, which leads to cartilage fibrillation and fissure formation. We hypothesize that under normal physiological conditions, collagen fibrils in cartilage function to store elastic energy associated with weight bearing and locomotion. Enzymatic cleavage of cartilage proteoglycans and collagen observed in osteoarthritis may lead to fibrillation and fissure formation as a result of impaired energy storage capability of cartilage.

Stress-strain behavior and tensile dilatometry of glass bead-filled polypropylene and polyamide 6

The mechanical behavior of multiphase materials is closely related to the interfacial adhesion between their various components. There is considerable interest in the development of simple experimental techniques for characterization of interfacial debonding during mechanical loading. Probably the best known method is tensile dilatometry, in which the onset and progression of debonding are related to the volume of microvoids generated in the material as it undergoes mechanical loading. Several authors have suggested that equivalent information can also be extracted from stress-strain data generated during a simple constant strain rate test. In practice, however, the transition between the initially well-bonded and the debonded state is obscured by the strain-induced softening of the matrix, which is usually observed in the same strain range as the debonding. In this work the filler/matrix debonding in polypropylene and polyamide 6 filled with up to 50 vol % of glass beads is examined using both tensile dilatometry and an analysis of tensile stress-strain curves. It was found that, depending on the level of adhesion, either a complete or partial debonding occurs in the strain range studied (0–8%). It appears that the volume change due to debonding is a small part of the total volume strain recorded. Therefore, the accuracy of the tensile dilatometry is not sufficient to detect the onset of debonding. The loss of stiffness of the composite, particularly when compared to the loss of stiffness of the matrix offers a more promising way to follow the debonding process. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 653–665, 1997

Prediction of Fracture Resistance Curves for Nuclear Piping Materials(III)

In order to perform leak-before-break design of nuclear piping systems and integrity evaluation of reactor vessels, full stress-strain curves and fracture resistance (J-R) curves are required. However it is time-consuming and expensive to obtain J-R curves experimentally. The objective of this paper is to modify two J-R curve prediction methods previously proposed by the authors and to propose an additional J-R curve prediction method for nuclear piping materials. In the first method which is based on the elastic-plastic finite element analysis, a blunting region handling procedure is added to the existing method. In the second method which is based on the empirical equation, a revised general equation is proposed to apply to both carbon steel and stainless steel. Finally, in the third method, both full stress-strain curve and finite element analysis results are used for J-R curve prediction. A good agreement between the predicted results based on the proposed methods and the experimental ones is obtained.

二次元弾塑性有限要素法による粒界に気泡を含む材料の応力-歪み曲線の解析

二次元弾塑性有限要素法による粒界に気泡を含む材料の応力-歪み曲線の解析

Analysis of stress-strain curves in the rat molar periodontal ligament after application of orthodontic force

Previous studies have shown that the mechanical strength of the periodontal ligament decreased markedly after application of an orthodontic force to the rat molars.13 However, an analysis of stress-strain curves obtained from transverse sections of the rat molars has not been made. The present study analyzed the stress-strain curves obtained from the mesial root of the rat mandibular first molar to evaluate the changes of the mechanical properties of the ligament after application of an orthodontic force. An elastic band was inserted between the mandibular first and second molars for 7 days. The maximum shear stress, elastic stiffness, and failure strain energy density were significantly less in the experimental group than in the control group, but the maximum strain was significantly greater. Histologic examinations of the transverse section after mechanical testing showed that the area of the ligament adhering to the mesial surface (compression side) of the socket bone was significantly less in the experimental group. It is suggested that orthodontic forces may cause changes in the constitution of the periodontal collagen, in osteoclastic activity in alveolar bone, and in mineralization patterns of Sharpey's fibers followed by reductions of the mechanical strength of the ligament, particularly on the compression side of alveolar bone.

Analysis of stress-strain curves of filled polymer composites

The stress-strain curves of polymeric composites with dispersed fillers are described with a 5% accuracy by a simple formula containing two readily determinable parameters, having a clearly physical significance. These parameters are closely related to the morphology of the composite and the degree of interaction of the filler particles with the matrix, and are therefore useful for a quantitative description of both mechanical and other physical properties of filled composites. Thus, by using one of the stress-strain diagram parameters-the heterogeneity coefficient — the heat conductivity of the composite and its dependence on the degree of filling can be readily and unequivocally determined.

Analysis of stress-strain curves at fast and slow velocities of loading in vitro in the transverse section of the rat incisor periodontal ligament following the administration of β-aminopropionitrile

The in vitro mechanical properties of this ligament were examined by analysing the stress-strain curve obtained from a transverse section of the mandible. Mechanical measures were compared between normal rats and lathyritic rats given drinking water containing 0.2% of β-aminopropionitrile (BAPN) for 20 days, and between the velocity of loading at 10 4 and 1 mm/24 h. The daily dose of BAPN decreased gradually because the body weight increased gradually. At the velocity of 10 4 mm/24 h, the maximum shear stress, elastic stiffness and failure strain energy density in the experimental subgroup fell to 43–50% of the control values, and at 1 mm/24 h to 71–80%. The maximum strains were not significantly different between the control and experimental subgroups either at 10 4 or at 1 mm/24 h. In the control subgroups, the maximum shear stress, elastic stiffness and failure strain energy density at 1 mm/24 h fell to 0.04 – 0.30% of those at 10 4 mm/24 h. and in the experimental subgroups to 0.08 – 0.43%. The maximum strains at 1 mm/24 h were 1.7 – 1.8 times greater than those at 10 4 mm/24 h in both the control and experimental subgroups. It is assumed that changes in the mechanical properties of the periodontal ligament were caused by inhibition of maturation of the periodontal collagen fibres. Assuming that the periodontal ligament is viscoelastic in nature, it is suggested that the main component reacting at 10 4mm/24 h was an elastic one and that both components, with emphasis on the viscous one, interact at 1 mm/24 h. It is also suggested that the elastic component was more severely affected by the drug than the viscous component.

Prediction of Mechanical Properties of Multi-phase Steels Based on Stress-Strain Curves.

An approach to predict mechanical properties of hot-rolled multi-phase steels referring to the stress-strain curves is proposed. Different from a conventional approach of regression analysis about the relationships between properties and chemical compositions and processing factors, a proposed one is based on the analysis and application of stress-strain curve: several commonly used mechanical properties such as yield strength, tensile strength, uniform elongation, total elongation, work-hardening exponent (n) and Vickers hardness, are derived systematically from the stress-strain curve of a multi-phase steel, which is calculated by using concentration factor, i.e., strain partition ratio and stress-strain curves of constituent phases. Stress-strain curves of individual component structures such as ferrite, pearlite, bainite, and martensite are expressed by Swift's equation. Physical background of the concentration factor is discussed by examining theoretical models of deformation for two-phase materials. Evaluation of plastic relaxation related to microstructural topology might be the most difficult point of this approach and some trials are presented.

Hydrogen effects on low-cycle fatigue of the single-crystal nickel-base superalloy CMSX-2

The effects of hydrogen on the low-cycle fatigue behavior of CMSX-2 [001]-oriented single crystals were examined. Fatigue tests were conducted under constant plastic strain amplitude control. Cyclic stress-strain curves and fatigue life data at different plastic strain amplitudes were determined for hydrogen-free and hydrogen-charged specimens. Two charging procedures, leading to different hydrogen concentrations, were applied. Hydrogen was found to decrease significantly the number of cycles to failure under the various experimental conditions. The increasing hydrogen concentration and ratio of the hydrogen to nonhydrogen-containing volume were found to shorten fatigue life in hydrogen-charged specimens. Based on the analysis of cyclic stress-strain curves and optical and transmission electron microscopy (TEM), it was established that hydrogen enhanced strain localization and promoted crystallographic, stage I cracking, leading to embrittlement. The overall fracture mechanism is discussed in conjunction with Duquette and Gell’s stage I fracture model.[16]

Analysis of Stress-Strain Curve of Polyethylene Films by Toda-Lattice Model

Stress-strain curves of high density- and linear low density-polyethylenes and their blend films were analyzed by Toda-lattice model which has asymmetric interaction potential. Parameters in Toda-lattice model were experimentally determined from Young’s modulus and Gruneisen parameter. Young’s modulus was estimated from the initial slope of stress-strain curves, and Gruneisen parameter from the initial slope of ultrasonic velocity-strain curves. Using the parameters, we obtained the theoretical stress-strain curves at different temperatures for all the films. For all the films, the theoretical stress-strain curve was in good agreement with the experimental one except in the yielding region. Thus, nonlinear nature of polyethylene films can be ascribed mainly to the asymmetry of the interaction potential curve.

β‐Ａｍｉｎｏｐｒｏｐｉｏｎｉｔｒｉｌｅ（ＢＡＰＮ）投与ラットにおける臼歯歯根膜の応力―歪曲線の解析

To understand the function of the periodontal ligament as a tooth support, stress-strain curves obtained from the transverse section of the mesial root of the rat mandibular first molar were analyzed following administration of BAPN, known as an inhibitor of collagen cross-linking. An experimental group of rats took drinking water containing 0.2% of BAPN ad libitum for 20 days. Radiographs of the transverse section of the molar root were processed by an image analyzer. Mechanical testing was performed by pushing the tooth out of the surrounding alveolar bone at a loading speed of 7 mm/min in an extrusive direction. Doses of BAPN ranged from 19 to 29 mg/100 g bw/day during the experimental period. By the analysis of stress-strain curves, it was found that the maximum shear stress, the elastic stiffness and the failure strain energy density decreased respectively to 42, 43 and 43 percent of the control values following administration of BAPN. However BAPN did not cause a significant change in the maximum strain. It is supposed that the changes in the mechanical properties of the ligament were caused by the inhibition of cross-linking of periodontal collagen fibers.

Effect of alcohols on the mechanical and transport properties of asymmetric cellulose acetate membranes

The tensile properties and rejection performance of cellulose acetate membranes in the presence of alcohol-water solutions are reported. The analysis of experimental results indicates that cellulose acetate membranes can be used to recover alcohols from waste water via reverse osmosis. The analysis of stress-strain curves of both virgin membranes conditioned in alcohol solution can be used to assess the potentiality of this cellulose acetate membranes in alcohol recovery processes.