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The influence of heat treatment on the mechanical behavior in terms of true stress-strain and mode of fracture of the deferent non-heat-treatable alloys has been carried out. Hardness, resistivity and the microstructural change of the alloys due to annealing also consider for complying the properties. In this purpose the hot rolled followed by cold rolled alloys samples are isochronally annealed for one hour at different temperatures. The experimental results show that maximum strength can be achieved by 5xxx series alloys followed by 3xxx, 4xxx and the lowest for 1xxx series alloys as attributed to the alloying element performance. Increasing of heat treatment temperature led to decrease in hardness and resistivity of the alloys by reason of recovery and coarsened the grains. The stress-strain curves show the lower strength and higher elongation with annealing temperature. Microstructural study also confirms that cold rolled alloys contents the elongated grain but annealing at 400°C per one hour a recrystallized grains are formed. Fractographic observations also verify that commercially pure aluminum and silicon added alloys are fractured of ductile mechanism, but manganese and magnesium added alloys demonstrate a brittle type of fracture as by reason of formed intermetallic phases. [ABSTRACT FROM AUTHOR]

The mechanical properties of polyvinyl chloride (PVC) geomembrane (GM), particularly its elastic modulus, are of the utmost importance in engineering design and evaluation of performance. The existing test methods make it difficult to provide an accurate elastic modulus of PVC GM. This research presents the establishment of an improved method for analysing the true stress–strain by non-contact measurement technology to determine the elastic modulus. Digital image correlation (DIC) was used to measure the axial and transverse strain, and it was found to give measurements of strain with a high degree of accuracy. The variation of Poisson's ratio is discussed and the true cross-sectional area is determined, allowing the true stress to be calculated theoretically. In accordance with the true stress–strain curve, the elastic modulus and linear range are established, which can provide designers with the tools to evaluate the true performance of GM and help them to select anti-seepage materials in design. [ABSTRACT FROM AUTHOR]

Resistance spot welding studies at varying current with an 8 mm electrode on steel grades DP980, DP690, TRIP980, and TRIP780, established that peak strength with sound weld could be achieved at a current range of 9 to 10 kA, where the nugget diameter was between 6.9 and 7.5 mm. The joint efficiency, measured as hardening ratio was highest in TRIP690 at 2.22 and for higher strength grade it was between 1.37 and 1.51. The softening ratio in the HAZ associated with tempering of preexisting martensite, was 0.86 to 0.9. Higher fusion strength was associated with alloying content that increased resistance that increased weld pool fusion that further enhanced the nugget diameter and hence the strength. The TRIP steel at high cooling rate showed martensite and retained austenite and the DP steel showed martensite content in higher grade and dispersed ferrite with martensite in the lower DP grade. The Tensile shear strength was lowest (16kN) for DP780, while for other grades it was between 20 and 22 kN. The strength enhancement in TRIP steel was due to higher weld diameter at higher current, where partial pull out failure mode was observed. At lower current, the interfacial pull out failure mode was observed with poor fusion and at high currents partial pull out at HAZ was observed. The Coach peel strength was highest at 3.2 kN for DP780, 2.2 kN for DP980, 2 kN for TRIP 690 and 1.7kN for TRIP 980 which followed the trend in TSS. The observed failure may be attributed to the high fusion strength in TRIP steel due to sound nugget and a microstructure of martensite with retained austenite. The lower strength with DP steels was attributed to low alloyed lath martensite in DP 980 and the lower grade DP780 was softer which was associated with ferrite dispersion in martensite. At very high currents, the fusion was good but there was a pull out at HAZ due to the softening associated with the tempering of preexisting martensite that influenced the failure at HAZ failure mode.

Based on the true stress, the ultimate material’s strength, and the fatigue slope b values, the probabilistic percentiles of the S-N curve of ductile materials are formulated. The Weibull β and η parameters used to determine the product’s reliability are determined directly from the material’s strength values corresponding to 103 and 106 cycles. And since in Table corresponding to the properties of this A538 A (b) steel and collected by table 23-A of Shigley Mechanical Engineering Design book; authors present the σt, Sut, and b values of several materials, then the Weibull parameters for each one of these materials as well as the 95% and 5% reliability percentiles of their S-N curves are given. A step-by-step application to the steel A538 A (b) material is presented. And based on the maximum and minimum applied stress values, the corresponding Weibull stress distribution was fitted and used with the Weibull strength distribution, in the stress/strength reliability function to determine the element’s reliability.

Ni3Al-based polycrystalline intermetallic compound is a kind of engineering superalloy, which have been used in the adjustment flaps of aeroengine tail nozzle. In order to explore its mechanical properties and microstructure evolution in service, the high temperature flow characteristics and microstructural changes of alloys were investigated by uniaxial isothermal compression tests on Gleeble-1500. The true stress-true strain curves were obtained and the microstructures were analyzed by OM, SEM, and EBSD. Based on the experimental data, three different constitutive models, belonging to phenomenological model, physical-based model, and radial basis function (RBF) neural network model, separately, were established to predict the deformation stress. The results show that the true stress is very sensitive to temperature and stain rate. Flow instability occurred during the deformation process, which caused some decline in the stress. Microstructure evolution under different deformation conditions indicated that the γ' to γn' phase transformation was also related to the degree of deformation and the four stage evolutionary process was identified. The SEM and EBSD results showed that the DRX appeared at the later stage of the deformation. The prediction capabilities of the three models were assessed by correlation coefficient (R), the absolute value of relative error (ARE), and the absolute average error (AARE). The result demonstrated that the RBF neural network had the best ability to predict the flow stress and the coefficient.

In order to investigate the hot deformation mechanism of a newly development Ni3Al‐based superalloy, hot compression tests at temperatures between 1100 °C–1250 °C and the strain rates of 0.001 s−1–1.0 s−1 were conducted. The results show that the curves of true stress‐strain indicate the thermal deformation is a typical dynamic recrystallization process, which the peak stresses and steady‐state stresses increase with decreasing temperatures and increasing strain rates. The softening mechanism is mainly dynamic recrystallization. The experimental data of peak stresses and steady‐state stresses is employed to calculate the constants in the Arrhenius equation. The steady‐state stresses are considered more reasonable for solving the parameters in the Arrhenius equation. Based on the constitutive equation obtained, the calculated values of steady‐state stresses match well with the experimental values at the strain rates of 0.001 s−1, 0.01 s−1 and 0.1 s−1, whereas there exists much deviation at 1.0 s−1. For the sake of accuracy of predicted results at 1.0 s−1 strain rate, a modified Zener‐Hollomon parameter Z' is introduced. The results show that the modified constitutive equations established in this study could well predict the value of steady‐state stress in hot deformation of the newly development Ni3Al‐based alloy. [ABSTRACT FROM AUTHOR]

The true stress-strain curve of a material should be determined for plastic property input to numerical analysis. This study proposes a simple methodology for determining the true stress-strain curve of SA-508 Grade 3 Class 1 low alloy steel using limited information from a general tensile test with finite element analysis. Measured engineering stresses and strains can be reasonably converted to true stresses and strains under uniform deformation before necking. True stress-strains are difficult to determine after necking because of nonuniform deformation without specialized measurement techniques. Five post-necking strain hardening models are considered, namely, linear, swift, Ludwick, Hollomon-linear (HL) and Hollomon-linear-constant (HLC) models. The equations for each model can be determined using the results of the tensile test, which include the true stress-strain value at the maximum load point and the corrected true stress-strain value at the fracture point plus the Considere instability criterion. The HL and HLC models suggested that the engineering stress-strains from the finite element analysis are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

Sapphire is widely used as optical materials and substrate materials because of its excellent physical and chemical properties. The dynamic mechanical properties under impact loading are very important for the sapphire parts used in extreme conditions. In this study, the dynamic mechanical properties of C -plane sapphire have been tested on the Split Hopkinson Pressure Bar. The true stress-strain curve of sapphire has been obtained at different velocities. The failure process of sapphire has been observed via high-speed photography. And the fracture morphology of sapphire after impact was analyzed. It is found that sapphire undergoes a very small linear section under impact loading. Subsequently the microcrack damage evolution stage occurs and then crack propagation is instability after reaching the compressive limit. It is found that the impact velocity has no effect on the linear elastic section of sapphire, but the compressive strength and fracture of sapphire will increase with increasing impact velocity. The crystal orientation influences the crack path and crack pattern, which lead to different energy consumption during crack propagation. [ABSTRACT FROM AUTHOR]

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The dynamic stress-strain curves obtained by Hopkinson bar testing can be subjected to a variety of possible approximations including hardware-based issues and/or accuracy reductions due to the procedures for the analysis and the post-processing of the experimental data. In order to highlight the possible occurrence of such approximations and to eventually assess their magnitude, quasi-static and dynamic tensile tests have been carried out on a 3 8MnSiVS6 steel, adopting two different Split Hopkinson Tensile Bars (SHTB) adopting different mechanical solutions for the input bars clamping / releasing systems. High speed video acquisition with frames extraction and image analysis delivered the evolving specimen geometry and its dimensions all over the test duration. Slightly different procedures are also adopted for the analysis of the raw experimental data leading to the relationships between stress, strain and strain rate for each test. The stress–strain curves and the strain rate–strain curves are derived from both series of experiments according to the engineering approach and to the true approach, the latter being obtained according to different hypotheses for the post-necking evolution of the true curve. High speed camera helped in measuring via image analysis the current evolving area of the neck section allowing to derive the true strain, true strain rate and true stress to be compared to the similar variables determined from the strain gauges on the bars. [ABSTRACT FROM AUTHOR]

In a tensile test, the precise measurement of the area at the necking section is crucial for predicting the post-necking true stress-strain behavior. In the conventional theoretical method, this area is linked to the engineering strain using the incompressibility criteria, which is not applicable in the post necking domain. The present work proposes a digital image correlation (DIC)-based technique with two cameras for estimating real-time area reduction at a necking section of a rectangular tensile specimen during a uniaxial tensile test. In the current study, the area at a given section is computed by measuring strain synchronously in the width and thickness planes of a tensile specimen and translating the change in lengths in both planes into a global coordinate system. The area computation of the proposed approach is successfully validated by measuring the necking area of a terminated tensile specimen (stopped before fracture) by optical microscope to an error in the range of 0.12–1.10%. Following verification, the post necking behaviors of aluminum alloys such as AA6061-T6 and AA7075-T6 are assessed. The current approach is further implemented to evaluate the area reduction and post necking behavior of similar and dissimilar friction stir welding (FSW) joints of AA6061-T6 and AA7075-T6 that possess process induced microstructural inhomogeneity. The current experimental approach effectively assessed the area reduction of a similar and dissimilar FSW joint influenced by weld inhomogeneity, which is otherwise complicated to contemplate using an analytical approach. [Display omitted] • An experimental method for assessing post-necking behavior has been purposed. • The method calculates the real-time area using a digital image correlation system. • The area calculation from the method is verified using a measuring microscopes. • The post-necking behavior of different aspect ratio specimens has been evaluated. • The post-necking behavior of friction stir welding joints was then assessed. [ABSTRACT FROM AUTHOR]

A ring tensile test with image analysis to measure failure properties, such as failure ring tensile stress ( σ f ) and strain ( ε f ), of surimi ( Itoyori A grade) gels with varying moisture content (76–80%) was developed using Laplace’s law. The novel approach was validated for different inside diameters and thicknesses. Digital image correlation (DIC) was used to identify the validity of Laplace’s law. For normalization, Laplace’s law was applied to eliminate the dependence of the width and inside diameter. The values of σ f by thickness, including the zero point, was accurately described using linear regression analysis ( r 2 > 0.99). This shows that σ f can estimate the reference σ f regardless of thickness. The values of σ f of the ring specimen were best fit with a linear function to moisture content ( r 2 > 0.94). The results of ε f for differing moisture content and thickness showed no significant differences ( p < 0.05). [ABSTRACT FROM AUTHOR]

Synopsis Many studies have presented stress-strain relationship of human hair, but most of them have been based on an engineering stress-strain curve, which is not a true representation of stress-strain behaviour. In this study, a more accurate 'true' stress-strain curve of human hair was determined by applying optical techniques to the images of the hair deformed under tension. This was achieved by applying digital image cross-correlation ( DIC) to 10× magnified images of hair fibres taken under increasing tension to estimate the strain increments. True strain was calculated by summation of the strain increments according to the theoretical definition of 'true' strain. The variation in diameter with the increase in longitudinal elongation was also measured from the 40× magnified images to estimate the Poisson's ratio and true stress. By combining the true strain and the true stress, a true stress-strain curve could be determined, which demonstrated much higher stress values than the conventional engineering stress-strain curve at the same degree of deformation. Four regions were identified in the true stress-strain relationship and empirical constitutive equations were proposed for each region. Theoretical analysis on the necking condition using the constitutive equations provided the insight into the failure mechanism of human hair. This analysis indicated that local thinning caused by necking does not occur in the hair fibres, but, rather, relatively uniform deformation takes place until final failure (fracture) eventually occurs. [ABSTRACT FROM AUTHOR]

Abstract: Cyclic plastic deformation phenomena include the Bauschinger effect, cyclic hardening/softening, strain range effect, loading history memory, ratcheting, mean stress dependent hardening, mean stress relaxation and non-proportional hardening. In this work, different cyclic plastic deformation responses of piping materials (SA333 C–Mn steel and 304LN stainless steel) are experimentally explored. Cyclic hardening/softening is depends upon loading types (i.e. stress/strain controlled), previous loading history and strain/stress range. Pre-straining followed by LCF and mean stress relaxation shows similar kind of material response. Substantial amount of non proportional hardening is observed in SA333 C–Mn steel during 90° out of phase tension-torsion loading. During ratcheting, large amount of permanent strain is accumulated with progression of cycles. Permanent strain accumulation in a particular direction causes cross-sectional area reduction and which results uncontrollable alteration of true stress in engineering stress controlled ratcheting test. In this work, true stress control ratcheting on piping materials has been carried out in laboratory environment. Effects of stress amplitude and mean stress on the ratcheting behaviors are analyzed. A comparison has also been drawn in between the true and engineering stress controlled tests, and massive difference in ratcheting life and strain accumulation is found. [Copyright &y& Elsevier]

Abstract: Low cycle fatigue, ratcheting and dependence of their deformation response on previous deformation histories are investigated at room temperature laboratory environment for SA333 C–Mn steel. It is noticed that cyclic hardening/softening response of low cycle fatigue is considerably influenced by applied strain amplitude, monotonic pre-straining and high to low step loading sequences. Results indicate that ratcheting under high to low step loading has significant effect on its subsequent ratcheting response. However, ratcheting under low to high step loading has very little effect on successive ratcheting responses. [Copyright &y& Elsevier]

Abstract: Low cycle fatigue experiments have been conducted on 304LN stainless steel in ambient air at room temperature. Uniaxial ratcheting behavior has also been studied on this material and in both engineering and true stress controlling modes. It is shown that material’s cyclic hardening/softening behavior in low cycle fatigue and in ratcheting is dependent not only on material but also on the loading condition. Improvement of ratcheting life and mean stress dependent hardening are observed in the presence of mean stress. A method based on the strain energy density (SED) is used to represent cyclic hardening/softening behavior of the material in this work. The decrease of SED with cycles is an indication that the life in low cycle fatigue and in ratcheting is improved. The SED represents the area of the hysteresis loops. [ABSTRACT FROM AUTHOR]

Abstract: Asymmetric cyclic loading in the plastic region can leads to progressive accumulation of permanent strain. True stress controlled uniaxial asymmetric cycling on SA333 steel is conducted at various combinations of mean stress and stress amplitude in laboratory environment. It is investigated that fatigue life increases in the presence of mean stress. Plastic strain amplitude and hysteresis loop area are found to decrease with increasing mean stress. A huge difference of life and ratcheting strain accumulation is found in engineering and true stress controlled tests. [ABSTRACT FROM AUTHOR]

Abstract: The effects of cyclic loading on tensile fracture properties of polycarbonate (PC) and the alloy of polycarbonate and acrylonitrile–butadiene–styrene (PC/ABS) are experimentally investigated in the paper. Two digital cameras are used to record simultaneously the tensile deformation of specimens and the large deformation and the necking process of these polymers are discussed. Two lateral contractions are not identical at the later tensile stages and the contraction ratios in each lateral direction are related with the tensile strains in axial direction on width and thickness surface. The curvature radiuses at the minimum section during necking process are shown. The volume increases during necking process and then decreases gradually. The yield stress and fracture stress of PC/ABS are lower than that of PC. The degradation of the fracture stress and fracture strain due to the application of cyclic loading is larger for PC than that for PC/ABS, and these can be used to explain qualitatively why PC has higher fatigue crack growth rate than PC/ABS. [Copyright &y& Elsevier]

Generally, bulk metallic glasses (BMGs) exhibit a very limited plastic deformation under a compression load at room temperature, often less than 2% before fracturing. In this letter, through an appropriate choice of BMGs' composition, an amorphous rod of ZrM64.80Cu14.85Ni10.35Al10 with a diameter of 2 mm was prepared by using copper mold suction casting. X-ray diffraction and differential scanning calorimetry were utilized to determine its structure and thermal stability, and the uniaxial compression test was adopted to study its plastic deformation behavior at room temperature simultaneously. The results showed that the glass transition temperature and onset temperature of the exothermic reaction of the amorphous rod were 646 and 750 K, respectively, and its micro-hardness was 594.7 Hv. During compression, when the engineering strain and engineering stress arrived at 9.05% and 1732 MPa, respectively, i.e., the true strain and true stress reached 9.42% and 1560 MPa, respectively, the amorphous rod started to yield. After yielding, with the increase of load, the strain increased and the glass rod ultimately were compressed into flake-like form. Although the maximum engineering strain was larger than 70%, i.e., the maximum true strain exceeded by 120%, the amorphous specimen was not fractured, indicating that it has super-plasticity at room temperature. Through the appropriate choice of composition and optimization of the technological process, flexible BMG with super-plasticity at room temperature could be produced. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a novel experimental method of analysis to determine the tensile properties of weldment of the heterogeneous tailor-welded blank (TWB) and its base metal. A real-time microscopic recording system was developed to acquire the true stress–strain data of the weldment during tensile testing. Specially designed tensile specimens of the weldment were cut from the prepared stainless steel (AISI 304) TWBs with a thickness combination of 1mm/1.2mm. With the aid of a newly developed measurement system, the real-time deformation of laser-marked circular grids on the surface of the tensile specimens was captured. The deformation recorded made possible the determination of the stress and strain values of the weldment based on the assumption of plastic incompressibility. The accurately measured tensile data of the weldment is used to determine the localized necking based on the vertex theory. The localized necking criterion is implemented into a computer program, LS-DYNA, which is critical in the numerical simulation of the TWB forming. The simulation makes it possible accurate determination of the strain distributions in TWBs along the centerline perpendicular to the weldment. The predicted strain distributions were compared with those measured and found to be satisfactory, thus demonstrating the validity of the proposed experimental method to accurately determine the true stress–strain values of the weldment and the parent metals. [Copyright &y& Elsevier]

In order to determine the stress–strain response in the diffuse necking for low carbon steels, the evolution of the diffuse necking region and the distributions of stress and strain in the narrowest cross-section are analyzed comprehensively based on 3D-DIC and FE simulation. Three parabolic functions are adopted to simplify the diffuse necking deformation: the shape of the necking region is parabolic, the distributions of stress and strain in the narrowest cross-section are also parabolic. A hardening model for solving the uniaxial tensile true stress and strain in the diffuse necking is established. Uniaxial tensile tests of four kinds of low carbon steel sheets and three typical anisotropic directions have been carried out to verify the reliability of the developed model. The numerical simulation results show that the uniaxial tensile load–elongation curves based on the hardening model are in good agreement with the experimental results, with an error of less than 1.3%. The true stress and strain in the diffuse necking can be determined easily by interpreting the tensile curve and measuring the shape of necking region. It avoids the difficulty and time-consuming of the inverse methods. This study can provide a valuable reference for establishing theoretical models to acquire true stress–strain curves over large range of strains for anisotropic sheet metals. • A diffuse necking hardening model for anisotropic sheet metals is developed. • Three parabolic functions are adopted to simplify the diffuse necking deformation. • Deriving the relationship among the gauge length, and the narrowest cross-sectional width and thickness. • Establishing the mathematical expressions of the distribution of stress and strain in narrowest cross-section. [ABSTRACT FROM AUTHOR]