Analysis Of Stress-strain Curves Research Articles

Strain-induced ferrite formation and its effect on mechanical properties of a dual phase steel produced using laboratory simulated strip casting

Thermo-mechanical processing of a strip cast dual phase (DP) steel was carried out using a Gleeble thermo-mechanical simulator. The effect of deformation temperatures in the range from 1050 to 700 °C on the microstructure evolution was investigated using optical, scanning and transmission electron microscopy along with electron backscattering diffraction (EBSD). Strain-induced ferrite (SIF) formation was observed following austenite deformation (∼0.41 reduction) in the 800–700 °C temperature range, leading to a ferrite grain refinement down to 3.1 ± 2.3 μm. A novel segmentation procedure was applied to separate selected EBSD maps into polygonal ferrite, SIF and second phase regions (bainite/martensite). Following this, the microtexture, misorientation angle distribution and the deviation from the Kurdjumov–Sachs and Nishiyama–Wasserman orientation relationships of each microstructure constituent were analysed. Based on iso-work modelling analysis of tensile stress-strain curves, the SIF was found to enhance strength with a slight decrease in ductility compared to polygonal ferrite. The tensile mechanical properties after deformation at 750 °C reached the level of DP 600 produced in industry, highlighting the potential to manufacture DP steels via the strip casting technique.

Dynamic Recrystallization Kinetics of Cu-0.36Cr-0.03Zr Alloy During Hot Compression

Based on compression tests in the temperature range of 800-950 °C and the strain rate range of 0.001-20 s−1 on a Gleeble-3500 thermomechanical simulator, the dynamic recrystallization (DRX) kinetics of Cu-0.36Cr-0.03Zr alloy is developed by further analysis of true stress-strain curves and by investigating microstructures under different deformation conditions. The kinetics of dynamic recrystallization is expressed as the modified JMAK model, and effects of varying strain rate and temperature on the model parameters, including the critical strain, peak strain and materials constant k d , are investigated. The complete DRX grain size is described as a power law function of Zener-Hollomon parameter (Z), and it agrees well with the experimental data.

Investigation of the fracture modes of red sandstone using XFEM and acoustic emissions

Acoustic emissions (AE) and stress–strain curve analysis are accepted methods of analyzing crack propagation and monitoring various failure stages, including crack closure and the crack initiation level, during rock failure under brittle rock loading. This study designed a series of three-point bending tests and shear fracture tests to investigate the features of AE signals for different modes. The Extended Finite Element Method (XFEM) is also adopted to simulate these experiments processes. The obtained results indicate that the maximum load for the shear fracture mode is approximately three times larger than that for the tensile fracture mode and that the displacement in the shear fracture mode is also larger than that in the tensile fracture mode. AE signals had higher AF (average frequency) and lower Rise Angle (RA) (ratio of the rise time to the peak amplitude) values when tensile failure occurred, while they exhibited lower AF and higher RA values when shear failure occurred. Accumulative AE energy for the shear mode is significantly larger than that for type I tensile fracture. The influence of inhomogeneity is also evident, as signals acquired at different distances exhibit distinct characteristics. The results show that AE leads to the characterization of the dominant fracture mode using only two AE descriptors. Note that we also should reasonably arrange AE sensors to monitor large-scale projects in the field.

Power-law scaling between mean stress drops and strain rates in bulk metallic glasses

Discrete, jerky stress-drop bursts (serrated flows) during plastic deformation of a Zr-based bulk metallic glass exhibit different magnitudes in response to variant strain rates. Through the classical statistical analysis of stress-strain curves during serrated flow, plastic dynamic behavior changes from Gauss to the power-law distribution with increasing the strain rates. In addition, a quantitative liner relation between mean stress drops and the logarithm of strain rates is obtained to describe the influence of strain rates on mean amplitudes of the stress drop. The power-law scaling behavior is illustrated in different views including the strain-rate dependence, energy dynamics, the Poisson's ratio of material, and shear-banding operation. These results are helpful for understanding the serration behavior at room temperature.

Hot deformation behavior of high Ti 6061 Al alloy

The hot deformation behavior of a high Ti 6061 aluminum alloy in the temperature range from 350 to 510 °C and strain rate range from 0.001 to 10 s−1 was investigated using stress–strain curve analysis, processing map, transmission electron microscopy and electron backscatter diffraction analysis. The results show that the peak stress decreases with increasing deformation temperatures and decreasing strain rate. The average deformation activation energy is 185 kJ/mol in the parameter range investigated. The flow stress model was constructed. The main softening mechanism is dynamic recovery. The processing map was obtained using dynamic material model, and the suggested processing window is 400–440 °C and 0.001–0.1 s−1.

Space-time scale invariance in dynamically fragmented quasi-brittle materials

The paper reports on a study to investigate the influence of load intensity and material structure on statistical regularities of fragmentation in ZrO2-based ceramics differing in porosity. The study was performed on a modified split Hopkinson pressure bar system and allowed a comparative analysis of dynamic stress-strain curves and statistical characteristics of fragmentation such as distributions of emitted light pulses (fractoluminescence) and fragment sizes. It is shown that increasing the ceramic porosity changes both the form of stress-strain curves and the pulse distribution. In ceramic specimens with up to 45% porosity, the pulse distribution is described by a bimodal power law; in ceramic specimens with 60% porosity, by a power law. The fragment size distribution in the material corresponds to a power law with the exponent dependent on porosity and load intensity.

Constitutive Models for Compressive Deformation of AZ80 Magnesium Alloy under Multiple Loading Directions and Strain Rates

Two constitutive models, the modified Johnson-Cook model and the logarithm linear relation model based on empirical approach and data analysis, were presented to illustrate compressive deformation of magnesium alloys AZ80 under multiple loading directions and strain rates. The results of stress-strain curve analysis and sensitivity index analysis suggested that the stress held large fluctuations in loading direction of 90°. Model testing signified that the logarithm linear relation model was more proper than the modified Johnson-Cook model in view of relative mean square error and correlation coefficients. Moreover, numerical simulation building on established models also indicated that the logarithm linear model is more precise than the modified Johnson-Cook model.

Investigation of the controlling parameters on the bowing phenomenon in ultra-thin crystalline silicon solar cells

A reduction in silicon material consumption in the photovoltaic industry is required for cost reduction. Development of ultra-thin crystalline silicon (c-Si) solar cell (<120 μm) is a promising way to significantly cut down the production cost of the cell modules. However, the ultra-thin c-Si solar cells suffer from the bowing phenomenon, which occurs after thermal sintering process between the silicon and the rear contact aluminum layers due to their distinct material properties. The bowing depth increases exponentially along with the decrease of silicon layer thickness. Since excessive bowing yields irreparable damage to the cell panel, mitigating the bowing depth is essential for commercialization of the thin c-Si solar cells. Here, dominant factors affecting the solar cell bowing are explored to determine the optimal manufacturing conditions for minimizing the bowing displacement. Using a numerical procedure developed in our previous study including three layers of silicon, recrystallized, and aluminum, we performed a design of experiment (DOE) analysis on six important factors. We investigated the sensitivity of the selected parameters and their mutual correlations through the DOE analysis, followed by providing an equation for bowing depth prediction with additional stress-strain curve analysis among the solar cell sub-layers. The agreement of our prediction model with the experimental results was excellent in a broad range of silicon thickness. This study offers a basis for an appropriate design guideline for manufacturing thin c-Si solar cells.

ヒマシ油変性ポリオールを用いた新規熱可塑性ポリウレタンの合成

A Novel linear polyurethane was synthesized by the reaction of 1,6-hexamethylenediisocyanate, Bis(2-hydroxyethyl)terephthalate and castor oil denatured polyol. The polymer was obtained with 51% yield. The molecular weights of the polymer were Mn = 10000, Mw = 16000, by the measurement of gel permeation chromatography. The temperature for 10% weight loss of the polymer was 270°C by thermogravimetric analysis. The stress, strain and Young’s modulus of the polymer was, respectively, 20.19 MPa, 1.43% and 14.11 Mpa by stress-strain curve analysis.

Effect of Nitrogen Content on Hot Deformation Behavior and Grain Growth in Nuclear Grade 316LN Stainless Steel

316LN stainless steel with 0.08%N (08N) and 0.17%N (17N) was compressed at 1073–1473 K and 0.001–10 s−1. The hot deformation behavior was investigated using stress-strain curve analysis, processing maps, and so forth. The microstructure was analyzed through electron backscatter diffraction analysis. Under most conditions, the deformation resistance of 17N was higher than that of 08N. This difference became more pronounced at lower temperatures. The strain rate sensitivity increased with increasing temperature for types of steel. In addition, the higher the N content, the higher the strain rate sensitivity. Hot deformation activation energy increased from 487 kJ/mol to 549 kJ/mol as N concentration was increased from 0.08% to 0.17%. The critical strain for initiation of dynamic recrystallization was lowered with increasing N content. In the processing maps, both power dissipation ratio and unstable region increased with increasing N concentration. In terms of microstructure evolution, N promoted dynamic recrystallization kinetic and decreased dynamic recrystallization grain size. The grain growth rate was lower in 17N than in 08N during heat treatment. Finally, it was found that N favored twin boundary formation.

Fabrication and characterisation of carbon fibre reinforced polymer rods with aluminium foam core

Carbon fibre reinforced polymer composites are high-performance materials that have become the dominant advanced composite materials used for aerospace, automobile, sporting goods and other applications owing to their high strength, high modulus and low density. In this study, a new fabrication technique of aluminium foam was employed where NaCl was used as the space holder and argon gas was injected into the aluminium molten metal. The NaCl particles were then removed by dissolution process. The aluminium foam specimens were then wrapped with carbon fibre pre-preg and cured in a vacuum oven. The compressive properties such as compressive strength, elastic modulus and failure strain were obtained from the analysis of stress-strain curves. The results showed that carbon fibre reinforced polymer composite tubes with aluminium foam core exhibited higher compressive strength and elastic modulus compared with neat aluminium foam rods and neat carbon fibre reinforced polymer rods.

TECHNOLOGY OF MAKING OF ARMATURE WITH HIGH LEVEL OF DURABILITY

Purpose. Assessing the impact of technological parameters on the properties of the complex in the manufacture of valves with a high level of safety. Methodology. Material for the study was selected alloy steel 20ХГС2. Curing rods with a diameter of 6,5 mm was performed rapid cooling from temperatures of 1080…1100 °C. The heating was carried out in Vacation chamber furnaces. Cold plastic deformation was carried out by drawing. Mechanical properties were determined from the analysis of stress-strain curve. The microstructure was studied using light microscopy and methods of quantitative metallographic. The parameter evaluating thin crystalline structure of the metal line width has been used ( ) x-ray interference (220). Findings. Shows the change in the properties of the complex as a function of temperature end of accelerated cooling of steel wire rod, which is being investigated. The analysis of the structural state of rolled after heat strengthening and after various degrees of plastic deformation by drawing. Shown that 20…30 % after deformation rapidly cooled to a temperature of steel 20ХГС2 580…600 °C, elongation is maintained at the level of 6 %, while the strength reaches at values of 2000-2100 MPa. Using the tempering at an intermediate temperature can improve the plastic properties of the pre-heat-strengthened, cold-rolled steel. Originality. The deformation of the thermally bonded low-alloy steel 20ХГС2 accompanied by a monotonic decrease in the line width of x-ray interference (220). Rate of increase in strength during cold deformation of steel martensite-bainite structure is due to the simultaneous development processes from the decay of the softening of martensitic structures and deformation strengthening. Practical value. The research results can be used to develop high-technology manufacturing reinforcing bar in an industrial environment for steel making

Hot Deformation Behavior of As-cast AISI M2 High-speed Steel Containing Mischmetal

The hot deformation behavior of as-cast AISI M2 high-speed steel containing mischmetal (RE) has been investigated on a Gleeble-3500 simulator in the temperature range of 1000–1150 °C and strain rate range of 0. 01 – 10 s−1 at true strain of 1.0. The mechanical behavior has been characterized using stress-strain curve analysis, kinetic analysis, processing maps, etc. Metallographic investigation was performed to evaluate the mechanism of flow instability. The results show that the deformation activation energy decreases with increasing deformation temperature; the efficiency of power dissipation increases with decreasing strain rate and increasing temperature; flow instability is observed at low-to-medium temperature and higher strain rate region when the strain is smaller, but extends to lower strain rate and high temperature regions with the increment of strain, in which it is manifested as flow localization near the grain boundary. Hot deformation equations and processing maps are obtained. The optimal processing window is suggested and the deformation mechanism is dynamic recrystallization (DRX).

Graphene oxide/poly(acrylic acid) hydrogel by γ-ray pre-irradiation on graphene oxide surface

Graphene oxide/poly(acrylic acid) (GO/PAA) hybrid hydrogel was prepared using a γ-ray pre-irradiation technique. The functional groups in graphene oxide were modified to peroxide in an O2 environment with γ-ray radiation. Radical species from the thermal decomposition of peroxides initiated radical polymerization of the acrylic acid monomers. Modified GO and GO/PAA hydrogels were investigated using scanning electron microscopy and Fourier transform infrared (FTIR), Raman, and electron spin resonance spectroscopy. The thermal, mechanical, and swelling properties of GO/PAA hydrogel were studied by a tensile stress-strain curve and thermal gravimetric analysis. A genuine binary hybrid hydrogel of graphene oxide and PAA was obtained from a simple synthetic procedure based on γ-ray pre-irradiation without further additives. Open image in new window

Superelastic Deformation in Polycrystalline Fe-Ni-Co-Ti-Cu Alloys

This article presents the deformation behavior of aged ferromagnetic alloys of Fe-Ni-Co-Ti-Cu system caused by phase transitions. The basic characteristic temperatures of martensitic transformation (MT) of the alloys were determined from temperature dependences of low-field magnetic susceptibility. The coefficients of thermal expansion of high- and low-temperature phases, as well as values of volume effect were obtained from dilatometric data. Peculiarities of deformation behavior were studied from the analysis of stress-strain curves, registered at uniaxial tension. It was found that investigated alloys have a substantial superelastic deformation and a low value of the temperature hysteresis of MT with the volume effect of 2%, which is typical for thermoelastic alloys of Fe-Ni-Co-Ti-Cu system.

The Dynamic Recrystallization of Hot-Deformed Austenite in a Micro-Alloyed Steel

As the dynamic recrystallization (DRX) behavior of hot-deformed austenite is the basis of determining controlled rolling schedule for steel, in the present work, the dynamic recrystallization behavior of austenite of a 0.22%C-1.30%Mn-0.04%Nb micro-alloyed steel was investigated by means of high temperature compression tests on the Thermecmastor-Z simulator. By the analysis of true stress-strain curves at different deformation stages, the hot deformation equation of austenite was established for the steel. As a result, the energy to induce recrystallization of austenite for the steel is 419.1 kJmol-1, as it was influenced by the drag effect of micro-alloyed element Nb in solid solution. The ratio (σc/σp) of critical stress σc (where DRX occurs) to peak stress σp is 0.93 while the ratio (εc/εp) of critical strain εc to peak stress εp is 0.52 for the steel. The austenite grain size of dynamic recrystallization of the micro-alloyed steel is refined by decreasing the deformation temperature and improving the stain rate.

Mechanical Behaviour of Reservoir Rock Under Brine Saturation

Acoustic emissions (AE) and stress–strain curve analysis are well accepted ways of analysing crack propagation and monitoring the various failure stages (such as crack closure, crack initiation level during rock failure under compression) of rocks and rock-like materials. This paper presents details and results of experimental investigations conducted for characterizing the brittle failure processes induced in a rock due to monocyclic uniaxial compression on loading of two types of sandstone core samples saturated in NaCl brines of varying concentration (0, 2, 5, 10 and 15 % NaCl by weight). The two types of sandstone samples were saturated under vacuum for more than 45 days with the respective pore fluid to allow them to interact with the rocks. It was observed that the uniaxial compressive strength and stress–strain behaviour of the rock specimens changed with increasing NaCl concentration in the saturating fluid. The acoustic emission patterns also varied considerably for increasing ionic strength of the saturating brines. These observations can be attributed to the deposition of NaCl crystals in the rock’s pore spaces as well some minor geo-chemical interactions between the rock minerals and the brine. The AE pattern variations could also be partly related to the higher conductivity of the ionic strength of the high-NaCl concentration brine as it is able to transfer more acoustic energy from the cracks to the AE sensors.

Strain Rate and Temperature-Dependent Deformation Behavior for Pb–10wt%Sn Solder Alloy

The mechanical response of Pb–10wt% Sn solder alloy has been tested under four strain rates and three deformation temperatures. The behavior of true stress–true strain of Pb–10wt% Sn solder alloy has been investigated over strain rates of 0.005–0.25% s−1 and deformation temperatures of 383, 413, and 433 K. The deformation behavior and grain growth mechanism were investigated by stress–strain curve analysis and microstructure observations. The results show that the general characteristics of stress–strain curve and microstructure of Pb–10wt% Sn alloy sensitively depend on the deformation temperature and strain rate. New free grains have been nucleated in microstructures in the process of dynamic recrystallization. These grains grow during deformation, forming coarser structure and elongation. The dynamic recrystallization and grain growth increase with increasing deformation temperature and decreasing strain rate.

Hot deformation behavior of an 8% Cr cold roller steel

An 8% Cr cold roller steel was compressed in the temperature range 900–1200 °C and strain rate range 0.01–10 s−1. The mechanical behavior has been characterized using stress–strain curve analysis, kinetic analysis, processing maps, etc. Metallographic investigation was performed to evaluate the microstructure evolution and the mechanism of flow instability. It was found that the work hardening rate and flow stress decreased with increasing deformation temperature and decreasing strain rate in 8% Cr steel; the efficiency of power dissipation decreased with increasing Z value; flow instability was observed at higher Z-value conditions and manifested as flow localization near the grain boundary. The hot deformation equation and the dependences of critical stress for dynamic recrystallization and dynamic recrystallization grain size on Z value were obtained. The suggested processing window is in the temperature range 1050–1200 °C and strain rate range 0.1–1 s−1 in the hot processing of 8% Cr steel.

Hot deformation behavior of a Nb-containing 316LN stainless steel

A Nb-containing 316LN stainless steel was compressed in the temperature range 900–1200 °C and strain rate range 0.01–10 s −1. The mechanical behavior has been characterized using stress–strain curve analysis, kinetic analysis, processing maps, etc. The microstructural evolution was observed and the mechanism of flow instability was discussed. It was found that the work hardening rate and flow stress decreased with increasing deformation temperature and decreasing strain rate. On the contrary, the efficiency of power dissipation increased with them; Flow instability was manifested as cracking and flow localization; The hot deformation equation and the relationships between deformation condition and dynamic recrystallization grain size and fraction were obtained; For Nb-containing 316LN stainless steel, the favorite nucleation sites for dynamic recrystallization are in sequence of triple point, grain boundary, twin boundary and intragranular deformation band; The suggested processing window is given.