scholarly journals Virtual Extensometer Analysis of Martensite Band Nucleation, Growth, and Strain Softening in Pseudoelastic NiTi Subjected to Different Load Cases

Materials ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 1458
Author(s):  
Cagatay Elibol ◽  
Martin Wagner
Keyword(s):  
Strain Softening ◽  
Nucleation Site ◽  
Shear Loading ◽  
Gauge Length ◽  
Surface Strain ◽  
Image Correlation ◽  
Localized Deformation ◽  
Stress Strain ◽  
Softening Behavior ◽  
Characteristic Features

Pseudoelastic NiTi shape memory alloys exhibit different stress–strain curves and modes of deformation in tension vs. compression. We have recently shown that under a combination of compression and shear, heterogeneous deformation can occur. In the present study, we use digital image correlation to systematically analyze how characteristic features of the nominally uniaxial engineering stress–strain curves (particularly the martensite nucleation peak and the plateau length) are affected by extensometer parameters in tension, compression, and the novel load case of shear-compression. By post-experimental analysis of full surface strain field data, the effect of the placement of various virtual extensometers at different locations (with respect to the nucleation site of martensite bands or inhomogeneously deforming regions) and with different gauge lengths is documented. By positioning an extensometer directly on the region corresponding to the nucleating martensite band, we, for the first time, directly record the strain-softening nature of the material—a specific softening behavior that is, for instance, important for the modeling community. Our results show that the stress–strain curves, which are often used as a basis for constitutive modeling, are affected considerably by the choice of extensometer, particularly under tensile loading, that leads to a distinct mode of localized deformation/transformation. Under compression-shear loading, inhomogeneous deformation (without lateral growth of martensite bands) is observed. The effects of extensometer gauge length are thus less pronounced than in tension, yet systematic—they are rationalized by considering the relative impact of differently deforming regions.

Joint Inclination Effect on Strength, Stress-Strain Curve and Strain Localization of Rock in Plane Strain Compression

2005 ◽  
Vol 495-497 ◽  
pp. 69-76 ◽  
Author(s):  
X.B. Wang
Keyword(s):  
Plane Strain ◽  
Strain Softening ◽  
Strain Curve ◽  
Plane Strain Compression ◽  
Peak Strength ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Softening Behavior ◽  
Ideal Plastic ◽  
Joint Inclination

Peak strength, mechanical behavior, and shear band (SB) of anisotropic jointed rock (JR) were modeled by Fast Lagrangian Analysis of Continua (FLAC). The failure criterion of rock was a composite Mohr-Coulomb criterion with tension cut-off and the post-peak constitutive relation was linear strain-softening. An inclined joint was treated as square elements of ideal plastic material beyond the peak strength. A FISH function was written to find automatically elements in the joint. For the lower or higher joint inclination (JI), the higher peak strength and more apparent strain-softening behavior are observed; the failure of JR is due to the slip along the joint and the new generated SBs initiated at joint’s two ends. For the lower JI, the slope of softening branch of stress-strain curve is not concerned with JI since the new and longer SBs’s inclination is not dependent on JI, as can be qualitatively explained by previous analytical solution of post-peak slope of stress-strain curve for rock specimen subjected to shear failure in uniaxial compression based on gradient-dependent plasticity. For the higher JI, the post-peak stress-strain curve becomes steeper as JI increases since the contribution of the new SBs undergoing strain-softening behavior to axial strain of JR increases with JI. For the moderate JI, the lower strength and ideal plastic behavior beyond the elastic stage are found, reflecting that the inclined joint governs the deformation of JR. The present numerical prediction on anisotropic peak strength in plane strain compression qualitatively agrees with triaxial experimental tests of many kinds of rocks. Comparison of the present numerical prediction on JI corresponding to the minimum peak strength of JR and the oversimplified theoretical result by Jaeger shows that Jaeger’s formula has overestimated the value of JI.

Modelling the deformation of a high-hardness armour steel in Taylor rod-on-anvil experiments

2019 ◽  
Author(s):  
Shannon Ryan ◽  
Brodie McDonald ◽  
Nikki Scott ◽  
Rory Bigger ◽  
Sidney Chocron
Keyword(s):  
Experimental Measurement ◽  
High Speed ◽  
Elevated Temperatures ◽  
High Hardness ◽  
Shear Loading ◽  
Surface Strain ◽  
Image Correlation ◽  
High Speed Photography ◽  
Rate Dependency ◽  
Armour Steel

Abstract A high hardness armour steel (HHA) has been subjected to mechanical characterization under tension, compression, and shear loading at quasi-static and dynamic rates incorporating ambient and elevated temperatures. The resulting data has been used to derive constants for four plasticity constitutive models: Johnson-Cook (JC), Zerilli-Armstrong (ZA), modified Johnson-Cook (MJC), and a generalized J2-J3 yield surface (GYS). The resulting models have been used to predict the response of the HHA material during Taylor rod-on-anvil experiments. High speed photography and digital image correlation was used during the rod-on-anvil experiments to capture both transient deformation profiles and maximum principal strain along the surface of the rod (i.e. compression along the length of the rod). The JC, MJC, and GYS models were found to provide the best prediction of the shape of the rod (nose diameter and length), within 2% of the experimental measurement in all four rod-on-anvil experiments which did not result in fracture. The JC and GYS models, furthermore, were found to provide the best agreement with the measured transient surface strain profiles, predicting the experimental measurement to within 10% at all measurement locations and time steps for the experiment resulting in maximum deformation (impact velocity = 208 m/s). The results suggest that the added complexity of models such as the MJC and GYS, which incorporate strain hardening saturation, two-part strain rate dependency, and J3 plasticity effects, are unnecessary for HHA under the loading conditions experienced during rod-on-anvil experiments.

scholarly journals Thermomechanical response of Mg AZ31 at different levels of temperatures and strain rates

2019 ◽  
Vol 304 ◽  
pp. 01025
Author(s):  
Farid Abed ◽  
Wael Abuzaid ◽  
Yomna Morad
Keyword(s):  
True Strain ◽  
Weight Ratio ◽  
High Strength ◽  
Tensile Tests ◽  
Industrial Applications ◽  
Gauge Length ◽  
Image Correlation ◽  
Strain Rates ◽  
Localized Deformation ◽  
The Difference

Magnesium alloys’ mechanical behavior has received increasing attention because of its high strength to weight ratio making them ideal for various industrial applications, such as vehicle components, transportation and aerospace. The objective of this work is to closely investigate the thermo-mechanical properties of magnesium alloy AZ31 at different strain rates and temperatures. Tensile tests are conducted on a 30 mm gauge length MgAZ31 specimens at two quasi-static strain rates (1.11x10−3 s−1 and 0.28 s−1) at a range of temperatures between 25 ºC and 250 ºC. Digital Image Correlation (DIC) system was used to calculate the true strain and provide quantitative assessment of the localized deformation response at high levels of deformation. The stress-strain responses of MgAZ31 show that the yield stress as well as the ultimate stress decreases as temperature increases and strain rate decreases. Moreover, the difference between the yield and ultimate stresses at both strain rates increases rapidly as temperature increases. The material shows a significant increase in ductility as temperature increases while the modulus of elasticity remains independent of change in strain rates.

scholarly journals Experimental Investigation on Shear Failure Mechanism of Rock Mass with Intermittent Joints

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Minghui Ma ◽  
Fenhua Ren ◽  
Wensheng Liu
Keyword(s):  
Rock Mass ◽  
Shear Strain ◽  
Failure Mechanism ◽  
Shear Failure ◽  
Shear Fracture ◽  
Shear Loading ◽  
Surface Strain ◽  
Image Correlation ◽  
Maximum Shear Strain ◽  
Natural Rock

There are a large number of discontinuous weak planes distributed in the natural rock mass, which makes the sliding failure of rock mass along the intermittent structural plane very complex. To investigate the shear failure mechanism of rock mass with intermittent joints and study the influence of different joint heights on the shear failure mode of the rock mass, direct shear tests were carried out by presetting a series of jointed rock specimens with different undulating heights. During the shear loading, digital image correlation (DIC) technology was employed to monitor the surface strain field of the specimens in real time. The results show that the fluctuation height has a significant effect on the evolution of shear strain. With the increase of shear load, the maximum shear strain of the jointed specimens with different undulating heights first increases slowly and then increases rapidly. When the undulating height is 5 mm, the failure of the specimen is dominated by the rock sliding along prefabricated joints. When the undulating height is larger than 10 mm, the shear fracture of the rock becomes dominant. With the increase of the undulating height, more penetrating cracks perpendicular to the preexisting joints appear between the serrated surfaces, and the shear fracture phenomenon is more obvious.

scholarly journals Shear bands in undrained plane strain compression of Norwegian quick clays

2018 ◽  
Vol 55 (1) ◽  
pp. 45-56 ◽  
Author(s):  
Vikas Thakur ◽  
Steinar Nordal ◽  
Gioacchino Viggiani ◽  
Pascal Charrier
Keyword(s):  
Plane Strain ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Shear Bands ◽  
Shear Loading ◽  
Image Correlation ◽  
Localized Deformation ◽  
Excess Pore Water Pressure ◽  
Excess Pore

This work presents the results of plane strain tests carried out at the Laboratoire 3SR Grenoble (France) on undisturbed samples of very sensitive Norwegian soft clay. Discussion of the results focuses on the observed failure mechanisms and zones of localized deformation. The tested clay is defined as quick clay because it liquefies completely upon remolding. Thus, careful handling was necessary, and original procedures were developed to place samples in the plane strain testing device with minimum disturbance. Results show that excess pore-water pressure had developed during shear loading and shear strength was lost after the peak, which is a typical phenomenon in sensitive soils. The sample was held between two glass plates to enable visual tracking of the deformations. A digital image correlation analysis revealed a complex pattern of emerging shear bands, with one or two bands dominating and providing a final failure mechanism. Two local pore-water pressure transducers were attached to the sample boundary and showed differences in local excess pore-water pressure. It is suggested that excess pore-water pressure depends on the distance from the transducers to the zones of concentrated shear strains.

scholarly journals A Proposed Algorithm to Compute the Stress-Strain Plastic Region and Displacement of a Deep-Lying Tunnel Considering Intermediate Stress and Strain-Softening Behavior

2021 ◽  
Vol 12 (1) ◽  
pp. 85
Author(s):  
Jinwang Li ◽  
Xiufeng He ◽  
Caihua Shen ◽  
Xiangtian Zheng
Keyword(s):  
Principal Stress ◽  
Radial Displacement ◽  
Strain Softening ◽  
Plastic Region ◽  
Intermediate Principal Stress ◽  
Surrounding Rock ◽  
Parameter Analysis ◽  
Flow Rule ◽  
Stress Strain ◽  
Softening Behavior

Past studies on deep-lying tunnels under the assumption of plane strain have generally neglected the influence of intermediate principal stress even though this affects the surrounding rocks in the plastic zone. This study proposes a finite difference method to compute the stress strain plastic region and displacement of a tunnel based on the Drucker–Prager (D–P) yield criterion and non-associated flow rule and considering the influences of intermediate principal stress and the strain-softening behavior of surrounding rock. The computed results were compared with those of other well-known solutions and the accuracy and validity of the method were confirmed through some examples. Parameter analysis was conducted to investigate the effects of intermediate principal stress on stress-strain, the plastic region, the ground response curve, and the dilatability of surrounding rock. The results showed that the plastic radius , the residual radius , and radial displacement of surrounding rock first decreased and then increased with increasing intermediate principal stress coefficient b from 0 to 1, with the minimums occurring at b = 0.75. On the contrary, the peak and rate of variation of the dilatancy coefficient first increased and then decreased with increasing b and the dilatancy coefficient gradually transitioned from nonlinear to linear variation. Meanwhile, the inhibition of the plastic radius and radial displacement gradually weakened with increasing support pressure, whereas the dilatancy coefficient of the tunnel opening gradually increased.

Nonlinear Flexural Modeling for Epoxy Resin Materials

2011 ◽  
Author(s):  
Masoud Yekani Fard ◽  
Yingtao Liu ◽  
Aditi Chattopadhyay
Keyword(s):  
Composite Structures ◽  
Strain Softening ◽  
Constitutive Models ◽  
Polymeric Materials ◽  
Local Stress ◽  
Image Correlation ◽  
Flexural Behavior ◽  
Peak Strain ◽  
Stress Strain ◽  
Tension And Compression

Polymer composite structures are usually subjected to large flexural loadings, so the flexural behavior of these structures and their constituents are critical to their use. A novel approach for polymeric materials with strain softening model in tension and compression is developed to investigate the flexural behavior of Epon E 863. The tension and compression model consists of a bilinear ascending curve in pre-peak, strain softening followed by constant plastic flow in the post-peak response. The effects of softening localization on flexural response are considered. Local stress strain tension and compression responses, using digital image correlation system, are used for material characterization. Closed form expressions for flexural behavior are developed. The structural response of beams under three and four point bending and round plate on three symmetrical supports are studied experimentally and analytically. Results show that direct use of uniaxial tension and compression stress strain models underestimates the flexural load carrying capacity. Flexural over-strength factor obtained from inverse analysis of beam under three point bending is conservative and it could be used to modify the constitutive models for analyzing a structural system.

Determination of Weld Metal Mechanical Properties Utilising Novel Tensile Testing Methods

2007 ◽  
Vol 7-8 ◽  
pp. 127-132 ◽  
Author(s):  
M. Kartal ◽  
Rafal M. Molak ◽  
Mark Turski ◽  
S. Gungor ◽  
Michael E. Fitzpatrick ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Weld Metal ◽  
Tensile Test ◽  
Weld Zone ◽  
Local Stress ◽  
Gauge Length ◽  
Image Correlation ◽  
Stress Strain ◽  
Strain Behaviour ◽  
Dic Technique

The aim of this study was to develop a method of extracting local mechanical properties from weld metal by strain mapping using the digital image correlation (DIC) technique. The feasibility of determining local stress-strain behaviour in the weld zone of a 316H stainless steel pipe with a girth weld was investigated by tensile tests of specimens machined from the pipe so that it contained the weld at its centre. The tensile test was recorded using a high resolution digital camera and the DIC technique was used to obtain the complete set of full field displacement maps during the tensile test. The local strain was calculated at every sub-region of 32×32 pixels, which enabled the local stress-strain behaviour for this region to be determined. Results from these tests show the variability of the elastic modulus, yield stress and UTS across the weld. To check the reliability of the technique, a set of micro tensile samples, with gauge length of 3.7mm and crosssectional area of 0.7×0.7 mm2, were machined from the various locations in and around the weld zone. The comparison of stress-strain curves determined from micro-samples to stress-strain curves from the corresponding locations within a larger more conventional tensile specimen shows reasonably good agreement.

scholarly journals An Improved Lagrangian-Inverse Method for Evaluating the Dynamic Constitutive Parameters of Concrete

Materials ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1871
Author(s):  
Xinlu Yu ◽  
Yingqian Fu ◽  
Xinlong Dong ◽  
Fenghua Zhou ◽  
Jianguo Ning
Keyword(s):  
High Speed ◽  
Inverse Method ◽  
Image Correlation ◽  
Analysis Method ◽  
Stress Strain ◽  
Optical Techniques ◽  
Element Simulation ◽  
Non Linear ◽  
Constitutive Parameters ◽  
Inverse Analysis Method

The dynamic constitutive behaviors of concrete-like materials are of vital importance for structure designing under impact loading conditions. This study proposes a new method to evaluate the constitutive behaviors of ordinary concrete at high strain rates. The proposed method combines the Lagrangian-inverse analysis method with optical techniques (ultra-high-speed camera and digital image correlation techniques). The proposed method is validated against finite-element simulation. Spalling tests were conducted on concretes where optical techniques were employed to obtain the high-frequency spatial and temporal displacement data. We then obtained stress–strain curves of concrete by applying the proposed method on the results of spalling tests. The results show non-linear constitutive behaviors in these stress–strain curves. These non-linear constitutive behaviors can be possibly explained by local heterogeneity of concrete. The proposed method provides an alternative mean to access the dynamic constitutive behaviors which can help future structure designing of concrete-like materials.

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