13th International Conference on the Technology of Plasticity (ICTP 2021): Characterization of Plasticity and Ductile Fracture of Metals under Proportional and Non-proportional Loading I
Program Organizers: Glenn Daehn, Ohio State University; Libby Culley, The Ohio State University; Anupam Vivek, Ohio State University; Jian Cao, Northwestern University; Brad Kinsey, University of New Hampshire; Erman Tekkaya, TU Dortmund; Yoshinori Yoshida, Gifu University

Monday 9:15 AM
July 26, 2021
Room: Virtual: Room E
Location: Virtual

Session Chair: Yanshan Lou, Xi'an Jiaotong University


Experimental Study on Uniaxial Strain Cyclic Behavior of GS-20Mn5: Zongyuan Zou1; Shuting Han1; Hongzhong Wang1; Qun Li1; Baofeng Guo1; Shiyan Zhao1; 1Yanshan University
    Due to the common discontinuity of the structure and non-uniform load, local high stress phenomenon tends to be appeared in the mechanical structure under repeated loading, and even local small plastic deformation maybe occur. In this case, the cyclic elastic-plastic mechanical properties of the structural steel are the key elements for the reasonable and accurate assessment of structural safety. In order to study the cyclic mechanical properties of GS-20Mn5, which is a commonly used steel in load bearing mechanical equipment, corresponding strain cyclic loading tests were performed. The cyclic elastoplastic deformation characteristics under strain-controlled cyclic loading with different strain ratios (R=-1,0.5) are studied, and the cyclic hardening/softening and mean stress relaxation features are revealed. The results show that the cyclic hardening/softening features are affected by the strain amplitude and cycles. This test material tends to show cyclic hardening at higher strain amplitudes. The cyclic stress-strain curve is obtained by the incremental step test, and the corresponding yield strength is about 4.8% larger than that under uniaxial tension. When R=0.5, the test material exhibits obvious mean stress relaxation. When the strain amplitude is 0.16%, 0.30% and 0.40%, the mean stress decreases then stabilizes at about 25 MPa, -3 MPa and -6 MPa, respectively. For the mechanical equipment made of GS-20Mn5 with local small plastic deformation under cyclic loading, the obtained cyclic mechanical performance of GS-20Mn5 can provide reference for the analysis and evaluation of the structural safety.

Experimental Study on the In-plane Torsion Test for Sheet Metal: Chong Zhang1; Yanshan Lou1; 1Xi'an Jiaotong University
    In-plane torsion tests attract a lot of attention recently since it can avoid unwanted reaction torque compared with the traditional in-plane shear test. In this study, the in-plane torsion tests are used to strain different types of specimens to characterize plastic behaviors of sheet metals. For specimens with slits, strain hardening is calibrated up to large deformation by the finite element model updating (FEMU) technology with the experimental torque-torsion angle curves. Fracture strain is measured under shear by the in-plane torsion test. Cyclic shear loading tests are also carried out for multiple in-plane torsion test specimens to characterize the kinematic hardening behavior of sheet metals. This study shows that the in-plane torsion tests are a proper testing method to experimentally study the fracture in pure shear, the strain hardening at large deformation, and the kinematic hardening behavior under cyclic loading.

Strain Hardening of AA5182-O Considering Strain Rate and Temperature Effect: Hongchun Shang1; Pengfei Wu1; Yanshan Lou1; 1Xi'an Jiaotong University
    Strain hardening properties of AA5182-O metal sheet are experimentally studied and analytically modelled in this research. A notched specimen is used to characterize the strain hardening properties of the alloy at different strain rate and temperature up to large strain until fracture. The strain hardening behaviors are then modeled by popular analytical models to consider the strain rate and thermal effects. The high nonlinear strain hardening with the effect of strain rate and temperature is also illustrated by artificial neural network. The results show that the strain hardening with strain rate and thermal effect can be accurately modelled by the neural network compared with the conventional models, but its computation efficiency is much lower than the analytical models.

Plastic and Fracture Characteristics of WE43 Mg Alloy Under Complex Stress States: Pengfei Wu1; Chong Zhang1; Yanshan Lou1; Qiang Chen2; Haiqing Ning2; 1Xi'an Jiaotong University; 2Southwest Technology and Engineering Research Institute
    This paper investigates the deformation behavior and fracture characteristics of WE43 Mg alloy under complex stress states, including uniaxial tension, plane strain tension, uniaxial compression, shear, etc. With the digital image correlation technique and a hybrid experimental-numerical method, experimental data are obtained for the stress-strain curves and fracture strain for different tests. The results indicate the effect of loading conditions on both yielding and fracture. The effect of loading condition on yielding and fracture is modeled by popular yield functions and fracture criteria. The predicted yield surfaces and fracture envelopes are predicted by experimental results to evaluate their accuracy on the modeling of plasticity and fracture for the WE43 Mg alloy.

Evaluation of isotropic and anisotropic constitutive models on plasticity prediction of AA7075 extruded tube under Tension-Tension and Tension-Compression: Sobhan Alah Nazari Tiji1; Amir Asgharzadeh1; Taejoon Park1; Madhura Athale1; Farhang Pourboghrat1; 1The Ohio State University
    Plasticity of AA7075-O extruded tube under tension-tension (T-T) and tension-compression (T-C) was characterized using multiaxial tube expansion test method. Three different yield functions, von-Mises, Hill’s 1948, and Yld2004 were considered to model the anisotropic plasticity of the AA7075-O tubes under T-T and T-C. The anisotropic models were calibrated based on the measured biaxial stresses and the conjugate plastic strain rates as strain-rate potential based on plastic work equivalency. As shown, this calibration method is an accurate and more flexible way of calibrating the advanced yield functions with no necessity for having proportional loading paths. It was also shown that the three yield functions predict the strain paths under T-C conditions almost similarly, however, the strain paths under T-T conditions are predicted better as the number of anisotropy parameters in the yield functions increases.

On Edge Crack Initiation of an Aluminum Sheet Metal: Jie Sheng1; Seung-Yong Yang2; Mohammad Alharbi1; Wei Tong1; 1Southern Methodist University; 2Korea University of Technology and Education
    Edge crack initiation and growth in an aluminum sheet metal were investigated experimentally under overall uniaxial tension, plane strain tension and shearing loading conditions along its RD, DD and TD directions. A simple edge crack initiation criterion was formulated from the local strain measurement results. Nonlinear finite element analysis was carried out to analyze the deformation of the same aluminum sheet metal in a hole expansion operation using a quartic polynomial quartic yield function with the associate flow rule. The calibrated anisotropic plasticity model and edge crack initiation criteria were evaluated in terms of the predicted locations of necking and potential crack initiation in the hole expansion of the aluminum sheet metal.

Estimation and Prevention of Strain Localization in Shear Tests: Heinrich Traphöner1; Till Clausmeyer1; A. Erman Tekkaya1; 1TU Dortmund University
    The localization of strain in conventional shear tests and in-plane torsion tests is analysed for three different materials, namely CP1000, DP1000, and DC04. The influence of material properties, such as strength, strain hardening, and strain gauge length on the measurement of shear strains is investigated experimentally and by a new analytical approach. The weakly hardening high-strength complex-phase steel CP1000 shows experimental and analytical deviations up to 25% of the determined strain depending on the evaluation strategy. Such devia-tions will lead to crucial errors for the calibration of fracture curves and damage models. By a new grooved in-plane torsion test specimen shear tests can be performed without the influence of the localization of strain. Strain measurements can thus be performed more exactly nearly regardless of the strain gauge length and hard-ening behavior. In first experimental results the deviation is below 4.6% for CP1000 and below 0.5% for DC04.

Heterogeneous Deformation in (α+β) Titanium Alloys: Iin-situ Explorations of Strain Localization and Its Governing Deformation Micro-events: Shaolou Wei1; Cem Tasan1; 1Massachusetts Institute of Technology
    The diverse microstructural combinations in two-phase titanium alloys have enabled a profuse platform in tailoring the corresponding mechanical performances. The plastic deformation coordination between α and β phases is of fundamental significance in affecting the macroscopic load-bearing responses, yet, the underlying deformation micro-events especially their contribution to strain localization and partition still remain elusive and deem detailed considerations. In this presentation, by studying a Ti-Al-V-Fe (α+β) alloy via integrated in-situ digital image correlation (DIC), in-situ synchrotron X-ray diffraction, and crystallographic calculation, we aim to showcase the exploration of the following three fundamental topics: (1) what are the deformation micro-events that governing strain localization inception? (2) how do strain localization and/or its partition evolve with respect to plastic straining? (3) how do the foregoing deformation micro-events affect damage nucleation and thereby macroscopic failure? Broader indications for mechanistically-guided microstructural design will also be included.

A New Criterion for Triclinic-asymmetric Yielding: Implicitly Describing Anisotropy and Distortional Asymmetry: Zachary Brunson1; Aaron Stebner2; Michael Wakin1; 1Colorado School of Mines; 2Georgia Institute of Technology
    With every industry striving to reduce the weight of components and structures from aerospace and automotive to wind and solar power, structural materials with anisotropic and asymmetric behavior are becoming more popular. Since an accurate and efficient description of the elastic limit is necessary to describe both the deformation during manufacturing and the final component strength, we propose a new yield criterion for pressure-insensitive anisotropic and anisotropically asymmetric solids. Previous orthotropic yield criteria were extended using a fully implicit description for the anisotropy in both the strengths and strength differential effects (asymmetry). This provides for the modeling of asymmetry in shear for orthotropic materials and applications to lower symmetry materials such as triclinic. This presentation will explore the world of implicit and explicit models of anisotropic and asymmetric yielding, introduce our proposed yield criterion, and provide experimental case studies for various applications.