Anisotropic Behavior in Plasticity and Ductile Fracture of an Aluminum Alloy

2015 ◽  
Vol 651-653 ◽  
pp. 163-168 ◽  
Author(s):  
Yan Shan Lou ◽  
Jeong Whan Yoon
Keyword(s):  
Plastic Deformation ◽  
Aluminum Alloy ◽  
Ductile Fracture ◽  
Stress Triaxiality ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Anisotropic Plasticity ◽  
Dog Bone ◽  
Associate Flow Rule ◽  
Anisotropic Plastic

Anisotropic mechanical behavior is investigated for an aluminum alloy of 6K21-IH T4 both in plastic deformation and ductile fracture. Anisotropic plastic deformation is characterized by uniaxial tensile tests of dog-bone specimens, while anisotropy in ductile fracture is illustrated with specimens with a central hole, notched specimens and shear specimens. All these specimens are cut off at every 15º from the rolling direction. The r-values and uniaxial tensile yield stresses are measured from the tensile tests of dog-bone specimens. Then the anisotropic plasticity is modeled by a newly proposed J2-J3 criterion under non-associate flow rule (non-AFR). The testing processes of specimens for ductile fracture analysis are simulated to extract the maximum plastic strain at fracture strokes as well as the evolution of the stress triaxiality and the Lode parameter in different testing directions. The measured fracture behavior is described by a shear-controlled ductile fracture criterion proposed by Lou et al. (2014. Modeling of shear ductile fracture considering a changeable cut-off value for stress triaxiality. Int. J. Plasticity 54, 56-80) for different loading directions. It is demonstrated that the anisotropic plastic deformation is described by the J2-J3 criterion with high accuracy in various loading conditions including shear, uniaxial tension and plane strain tension. Moreover, the anisotropy in ductile fracture is not negligible and cannot be modeled by isotropic ductile fracture criteria. Thus, an anisotropic model must be proposed to accurately illustrate the directionality in ductile fracture.

scholarly journals Investigation on the ductile fracture of a high-strength dual-phase steel with anisotropic damage mechanics model

2021 ◽  
Author(s):  
Zinan Li ◽  
Wenqi Liu ◽  
Fuhui Shen ◽  
Sebastian Münstermann ◽  
Junhe Lian
Keyword(s):  
Plastic Deformation ◽  
Ductile Fracture ◽  
Fracture Behavior ◽  
Dual Phase Steel ◽  
High Strength ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Dual Phase ◽  
Plasticity Model ◽  
Anisotropic Plastic

In this study, a hybrid experimental and numerical investigation is implemented to characterize the plasticity and ductile fracture behavior of a high-strength dual-phase steel. Uniaxial tensile tests are conducted along the three typical directions of rolled sheet metals for the anisotropic plastic behavior, while the hydraulic bulge test is applied for the flow behavior under equiaxial biaxial tension. Further tensile tests are conducted on various featured dog-bone specimens to study the fracture behavior of the material from the uniaxial to plane-strain tension. On the numerical side, the evolving non-associated Hill48 (enHill48) plasticity model considering anisotropic hardening and plastic strain ratio evolution is employed to describe the anisotropic plastic deformation. The extended enHill48 model with damage and fracture formulation is further calibrated and validated in the study to describe the ductile fracture behavior of the steel under various stress states. Through a comparison of the results based on the evolving anisotropic model with the isotropic Mises model, it is concluded that even for materials that show only minor initial plastic anisotropy, it could develop a non-negligible influence on the large plastic deformation and the prediction of both deformation and fracture shows profound improvement with the evolving anisotropic plasticity model.

scholarly journals Determination of Forming Limits Based on Finite Element Simulations

2021 ◽  
Author(s):  
Fuhui Shen ◽  
Kai Chen ◽  
Junhe Lian ◽  
Sebastian Münstermann
Keyword(s):  
Finite Element ◽  
Damage Mechanics ◽  
Tensile Tests ◽  
Finite Element Simulations ◽  
Experimental Results ◽  
Uniaxial Tensile ◽  
Anisotropic Plasticity ◽  
Forming Limits ◽  
Dog Bone ◽  
Spatio Temporal

Two categories of experiments have been performed to obtain the experimental forming limits of a ferritic stainless steel from uniaxial to equibiaxial tension, including Nakajima tests and tensile tests of flat specimens with different geometries of the central hole as well as the notched dog bone. The plasticity behavior of the investigated material is described using an evolving non-associated anisotropic plasticity model, which is calibrated based on experimental results of uniaxial tensile tests along different loading directions. A damage mechanics model is calibrated and validated based on the global force and displacement response of tensile tests. Finite element simulations of the Nakajima tests and the tensile tests of various geometries have been performed using the anisotropic material model. A novel spatio-temporal method is developed to evaluate the forming limits under different stress states by quantitatively characterizing the plastic strain distribution on the specimen surface. The forming limits have been independently determined from finite element simulation results of tensile specimens and Nakajima specimens using the spatio-temporal evaluation method. The forming limits obtained from numerical simulations of these two types of experiments are in good agreement with experimental results.

scholarly journals Anisotropic Plastic Behavior of Additively Manufactured PH1 Steel

2021 ◽  
Author(s):  
Wenqi Liu ◽  
Zinan Li ◽  
Sven Bossuyt ◽  
Antti Forsström ◽  
Zaiqing Que ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Thermal History ◽  
Deformation Behavior ◽  
Uniaxial Tensile ◽  
Plastic Behavior ◽  
Geometrical Shape ◽  
Anisotropic Plasticity ◽  
Plastic Deformation Behavior ◽  
Anisotropic Plastic

Metals made by additive manufacturing (AM) have intensely augmented over the past decade for customizing complex structured products in the aerospace industry, automotive, and biomedical engineering. However, for AM fabricated steels, the correlation between the microstructure and mechanical properties is yet a challenging task with limited reports. To realize optimization and material design during the AM process, it is imperative to understand the influence of the microstructural features on the mechanical properties of AM fabricated steels. In the present study, three material blocks with 120×25×15 mm3 dimensions are produced from PH1 steel powder using powder bed fusion (PBF) technology to investigate the anisotropic plastic deformation behavior arising from the manufacturing process. Despite being identical in geometrical shape, the manufactured blocks are designed distinguishingly with various coordinate transformations, i.e. alternating the orientation of the block in the building direction (z) and the substrate plate (x, y). Uniaxial tensile tests are performed along the length direction of each specimen to characterize the anisotropic plastic deformation behavior. The distinctly anisotropic plasticity behavior in terms of strength and ductility are observed in the AM PH1 steel, which is explained by their varied microstructure affected by the thermal history of blocks. It could also be revealed that the thermal history in the AM blocks is influenced by the block geometry even though the same process parameters are employed.

Transformation in Austenitic Stainless Steel Sheet under Different Loading Directions

2011 ◽  
Vol 473 ◽  
pp. 444-451
Author(s):  
A.H. van den Boogaard ◽  
J. Krauer ◽  
Pavel Hora
Keyword(s):  
Phase Transformation ◽  
Martensitic Transformation ◽  
Sheet Material ◽  
Stress Triaxiality ◽  
Austenitic Stainless Steels ◽  
Tensile Tests ◽  
Sheet Forming ◽  
Uniaxial Tensile ◽  
Reference Curve ◽  
Strain Relation

The stress-strain relation for austenitic stainless steels is based on 2 main contributions: work hardening and a phase transformation from austenite to martensite. The transformation is highly temperature dependent. In most models for phase transformation from austenite to martensite, the stress triaxiality plays an important role also. The sensitivity to triaxiality is often investigated based on uniaxial compression and tensile tests. To validate the common formulation for triaxiality dependence of the martensitic transformation, a series of experiments is performed with the Twente biaxial tester for sheet material. A number of deformation directions are prescribed between plane strain and simple shear. Uniaxial tensile tests were performed at different temperatures to get a temperature corrected reference curve for the martensite–strain relation. The current results for typical stress states in sheet forming do not show the dependency on the triaxiality that is given in literature. This means that for sheet forming simulations, changes in stress state affects the martensitic transformation less than expected from tension–compression experiments.

scholarly journals Strain Rate-Dependent Constitutive and Low Stress Triaxiality Fracture Behavior Investigation of 6005 Al Alloy

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Yong Peng ◽  
Xuanzhen Chen ◽  
Shan Peng ◽  
Chao Chen ◽  
Jiahao Li ◽  
...  
Keyword(s):  
Flow Stress ◽  
Plastic Strain ◽  
Strain Rate ◽  
Fracture Behavior ◽  
Equivalent Plastic Strain ◽  
Stress Triaxiality ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Strain Rates ◽  
Stress States

In order to study the dynamic and fracture behavior of 6005 aluminum alloy at different strain rates and stress states, various tests (tensile tests at different strain rates and tensile shearing tests at five stress states) are conducted by Mechanical Testing and Simulation (MTS) and split-Hopkinson tension bar (SHTB). Numerical simulations based on the finite element method (FEM) are performed with ABAQUS/Standard to obtain the actual stress triaxialities and equivalent plastic strain to fracture. The results of tensile tests for 6005 Al show obvious rate dependence on strain rates. The results obtained from simulations indicate the feature of nonmonotonicity between the strain to fracture and stress triaxiality. The equivalent plastic strain reduces to a minimum value and then increases in the stress triaxiality range from 0.04 to 0.30. A simplified Johnson-Cook (JC) constitutive model is proposed to depict the relationship between the flow stress and strain rate. What is more, the strain-rate factor is modified using a quadratic polynomial regression model, in which it is considered to vary with the strain and strain rates. A fracture criterion is also proposed in a low stress triaxiality range from 0.04 to 0.369. Error analysis for the modified JC model indicates that the model exhibits higher accuracy than the original one in predicting the flow stress at different strain rates. The fractography analysis indicates that the material has a typical ductile fracture mechanism including the shear fracture under pure shear and the dimple fracture under uniaxial tensile.

A Model to Predict the Effect of Pre-Strain on the Fracture Toughness of Line Pipe Steel

2002 ◽  
Author(s):  
Andrew Cosham ◽  
Naoto Hagiwara ◽  
Naoki Fukuda ◽  
Tomoki Masuda
Keyword(s):  
Fracture Toughness ◽  
Plastic Deformation ◽  
Theoretical Model ◽  
Plastic Strain ◽  
Ductile Fracture ◽  
Experimental Studies ◽  
Uniaxial Tensile ◽  
Stress Strain ◽  
Line Pipe ◽  
Strained Material

New and existing pipelines can be subjected to high plastic strains. Denting a pipeline causes permanent plastic deformation. Onshore pipelines subject to subsidence, frost heave or earthquake loading can experience significant plastic strain during service. Offshore pipelines that are reeled prior to laying, or are laid in deep water, or are operating at high temperatures and high pressures, can experience significant plastic strain both prior to, and during, service. Experimental studies have indicated that pre-strain (permanent plastic deformation) has a detrimental effect on the fracture toughness of steel; it reduces the resistance to crack initiation, reduces the resistance to crack growth, and increases the transition temperature. Consequently, there is a need for a thorough understanding of the effect of pre-strain on the fracture toughness of line pipe. Accordingly, a theoretical model for predicting the effect of tensile pre-strain on the ductile fracture toughness has been developed using the local approach. The effect of pre-strain is expressed in terms of an equation for the ratio of the fracture toughness of the pre-strained material to that of the virgin (not pre-strained) material. The model indicates that the effect of tensile pre-strain on the material’s fracture toughness can be characterised in terms of the effect of pre-strain on the stress-strain characteristics of the material, the critical fracture strain for a stress state corresponding to that during pre-strain, and several parameters that relate to the conditions for ductile fracture (or cleavage fracture). The implications of the model are that it may be possible to estimate the reduction in toughness caused by pre-strain simply from a full stress-strain curve of the virgin material. The model has been validated against the results of crack tip opening displacement (CTOD) tests conducted by Tokyo Gas on two line pipe steels subject to uniaxial tensile pre-strain. It is shown that the predictions and trends of the theoretical model are in broad agreement with the test results.

Grain Refinement of Magnesium Alloys by CONFORM: A Continuous Severe Plastic Deformation Route?

2012 ◽  
Vol 706-709 ◽  
pp. 1781-1786 ◽  
Author(s):  
You Liang He ◽  
Fei Gao ◽  
Bao Yun Song ◽  
Rong Fu ◽  
Gui Ming Wu ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Severe Plastic Deformation ◽  
Grain Refinement ◽  
Large Scale ◽  
Tensile Tests ◽  
Mg Alloys ◽  
Uniaxial Tensile ◽  
Batch Mode ◽  
Angular Pressing ◽  
Conform Process

Effective grain refinement through equal channel angular pressing (ECAP) for magnesium (Mg) alloys has been demonstrated by many researchers. Although with the capability to achieve superplasticity, the batch mode nature of this method and the required repetitive processing to attain ultrafine grained structure have prohibited it from being widely used in large-scale industrial production. In this study, a well-established metal forming method – the continuous extrusion forming (CONFORM) process – was employed as a severe plastic deformation route to refine the microstructure of Mg alloys. Cast Mg-3%Al-1%Zn (AZ31) rods were used as the feedstock and the cast structure (grain size of ~150 microns) was refined to ~1 micron afteronepass CONFORM extrusion. Uniaxial tensile tests of the as-extruded samples were conducted at a temperature of 473K and an elongation of ~200% was achieved under a strain rate of 1×10-4s-1. The significant grain refinement effect was attributed to the severe shear deformation occurred during the CONFORM process, which is very similar to ECAP but with even higher effective strains. The most important advantage of CONFORM over ECAP is that the former is a continuous route, so it is able to produce long products. It was also shown that CONFORM could be an additional forming method for Mg alloys to conventional rolling, forging and extrusion.

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