scholarly journals Correlation of Macroscopic Fracture Behavior with Microscopic Fracture Mechanism for AHSS Sheet

Materials ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 900 ◽  
Author(s):  
Lingyun Qian ◽  
Xiaocan Wang ◽  
Chaoyang Sun ◽  
Anyi Dai
Keyword(s):  
Fracture Mechanism ◽  
Fracture Behavior ◽  
Pure Shear ◽  
Stress Triaxiality ◽  
High Strength ◽  
Numerical Approach ◽  
Fracture Mechanisms ◽  
Macroscopic Fracture ◽  
Shear Slip ◽  
Stress States

This research aims to correlate the macroscopic fracture phenomenon with its microscopic fracture mechanism for an advanced high-strength steel (AHSS) TRIP 780 sheet by applying a combined experimental-numerical approach. Six specimens with different shapes were tensioned to fracture and the main deformation areas of specimens were subjected to stress states ranging from lower to higher stress triaxiality. The final fracture surface feature for each specimen was obtained to characterize the macroscopic fracture modes at different stress states. The scanning electron microscope (SEM) fractographies of fracture surfaces were detected to reveal the microscopic fracture mechanisms. The stress triaxiality evolution was applied to correlate of fracture mode and fracture mechanism by comparing the macroscopic fracture features as well as micro-defect changes. An increase of stress triaxiality leads to voids extension and then results in a voids-dominant fracture. The micro-shear-slip tends to appear in the stress triaxiality level lower than that of pure shear stress state. The fracture behavior of a practice deformation process was the result of interplay between shear-slip fracture and void-dominant fracture. The unified relationship between average void sizes and stress triaxiality was obtained. The void growth was predicted by the Rice–Tracey model with higher precision.

scholarly journals Tensile Fracture Mechanism of Masonry Wallettes Parallel to Bed Joints: A Stochastic Discontinuum Analysis

Modelling ◽  
2020 ◽  
Vol 1 (2) ◽  
pp. 78-93
Author(s):  
Bora Pulatsu ◽  
Semih Gonen ◽  
Ece Erdogmus ◽  
Paulo B. Lourenço ◽  
Jose V. Lemos ◽  
...  
Keyword(s):  
Material Properties ◽  
Fracture Mechanism ◽  
Equations Of Motion ◽  
Constitutive Models ◽  
Numerical Approach ◽  
Tensile Fracture ◽  
Fracture Mechanisms ◽  
Contact Points ◽  
Statistical Variations ◽  
Modeling Strategy

Nonhomogeneous material characteristics of masonry lead to complex fracture mechanisms, which require substantial analysis regarding the influence of masonry constituents. In this context, this study presents a discontinuum modeling strategy, based on the discrete element method, developed to investigate the tensile fracture mechanism of masonry wallettes parallel to the bed joints considering the inherent variation in the material properties. The applied numerical approach utilizes polyhedral blocks to represent masonry and integrate the equations of motion explicitly to compute nodal velocities for each block in the system. The mechanical interaction between the adjacent blocks is computed at the active contact points, where the contact stresses are calculated and updated based on the implemented contact constitutive models. In this research, different fracture mechanisms of masonry wallettes under tension are explored developing at the unit–mortar interface and/or within the units. The contact properties are determined based on certain statistical variations. Emphasis is given to the influence of the material properties on the fracture mechanism and capacity of the masonry assemblages. The results of the analysis reveal and quantify the importance of the contact properties for unit and unit–mortar interfaces (e.g., tensile strength, cohesion, and friction coefficient) in terms of capacity and corresponding fracture mechanism for masonry wallettes.

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.

scholarly journals Temperature Dependence of Fracture Characteristics of Variously Heat-Treated Grades of Ultra-High-Strength Steel: Experimental and Modelling

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5875
Author(s):  
Jaroslav Pokluda ◽  
Ivo Dlouhý ◽  
Marta Kianicová ◽  
Jan Čupera ◽  
Jana Horníková ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Temperature Dependence ◽  
High Stress ◽  
Stress Triaxiality ◽  
High Strength ◽  
Fracture Mechanisms ◽  
Temperature Range ◽  
Heat Treated ◽  
Shape Ratio ◽  
Standard Steel

The temperature dependence of tensile characteristics and fracture toughness of the standardly heat-treated low-alloyed steel OCHN3MFA along with three additionally heat-treated grades was experimentally studied. In the temperature range of ⟨−196; 22⟩ °C, all the additional heat treatments transferred the standard steel from a high- to ultra-high strength levels even with improved tensile ductility characteristics. This could be explained by a reduction of the inclusion content, refinement of the martensitic blocks, ductile retained austenite content, and homogenization of the shape ratio of martensitic laths as revealed by metallographic, X-ray, and EBSD techniques. On the other hand, the values of the fracture toughness of all grades were found to be comparable in the whole temperature range as the cause of a high stress triaxiality in the pre-cracked Charpy V-notch samples. The values of the fracture toughness of the standard steel grade could be predicted well using the fracture model proposed by Pokluda et al. based on the tensile characteristics. Such a prediction failed in the case of additionally heat-treated grades due to the different temperature dependence of the fracture mechanisms occurring in the tensile and fracture-toughness tests. While the tensile samples fractured in a ductile-dimple mode at all temperatures, the fracture-toughness specimens exhibited a transition from the ductile to quasi-brittle fracture mode with decreasing temperature. This transition could be interpreted in terms of a transfer from the model proposed by Rice and Johnson to the model of Tvergaard and Hutchinson.

scholarly journals A Fracture Criterion for Prediction of Fracture Initiation of Metal Materials at Various Stress States for Nuclear Waste Storage

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Zhihui Li ◽  
Xue Yang ◽  
Anmin Tang
Keyword(s):  
Fracture Criterion ◽  
Shear Fracture ◽  
Stress Triaxiality ◽  
Fracture Initiation ◽  
Initiation Site ◽  
Fracture Mechanisms ◽  
Nuclear Waste Storage ◽  
Maximal Shear Stress ◽  
Stress States ◽  
New Criterion

A fracture criterion is newly proposed to evaluate fracture behavior and predict fracture initiation of metal materials in different complicated stress states for four different fracture mechanisms including quasicleavage fracture, normal fracture with void, shear fracture with void, and shear fracture without void. The dominant factors of these four different mechanisms are distinct, so it is impossible to capture all features of fracture initiation under different stress states with a single criterion, and different functions are necessary to predict fracture initiation of different mechanisms. In the new fracture criterion, different branches of the fracture criterion have been proposed corresponding to different fracture mechanisms. Quasicleavage fracture and normal fracture with void are described as a function of the principal stress, shear fracture with void is a function of the stress triaxiality and maximal shear stress, and shear fracture without void is only controlled by the maximal shear stress. The new fracture criterion is applied to predict the fracture initiation site and the fracture direction of nodular cast iron QT400-15 in combined tension-torsion tests. Predicted results are compared with experimental results to validate the performance of the new criterion in the intermediate stress triaxiality between 0 and 1/3. The new criterion is also applied to predict the crack initiation site and the direction of crack initiation of LY12 aluminium alloy and HY130 mild steel in mixed mode fracture tests to validate the performance of the new criterion in the high stress triaxiality. The new fracture criterion gives consistent results for these materials in a wide stress triaxiality range. It is shown that the new fracture criterion is a better supplement to the deficiency of fracture mechanics and also a better amendment to traditional strength theory in complicated stress states. Therefore, the new fracture criterion is recommended to be utilized to evaluate the fracture initiation of metal structures in nuclear waste storage and other engineering applications.

Study of Damage Mechanism on Aluminum Alloy under Two Kinds of Stress States and FEM Simulation

2007 ◽  
Vol 353-358 ◽  
pp. 1157-1160 ◽  
Author(s):  
Hao Zhu ◽  
Liang Zhu ◽  
Jian Hong Chen
Keyword(s):  
Aluminum Alloy ◽  
Shear Test ◽  
Volume Fraction ◽  
Pure Shear ◽  
Shear Bands ◽  
Stress Triaxiality ◽  
Damage Mechanism ◽  
Critical Value ◽  
Stress States ◽  
Test Stress

In order to study the damage mechanism under different stress states of aluminum alloy components, two kinds of representative triaxial stress states were adopted, namely notch tensile and pure shear. The results of study showed: During the notch tensile test, stress triaxiality in the least transverse-section was relatively higher. With increasing applied stress, the volume fraction of the microvoid in notch root was increasing constantly. When microvoid volume fraction reached the critical value, the specimen fractured. During the pure shear test, stress triaxiality almost came up to zero, and there was almost no micro-void but localized shear bands within the specimen. The shear bands resulted from non-uniform deformation constantly under the shear stress. With stress concentrating, the cracks were produced in the shear bands and later coalesced. When the equivalent plastic strain reached the critical value, the specimen fractured. The modified Gurson damage model and the Johnson-Cook model were used to simulate the notch tensile and shear test respectively. Simulated engineering stress-strain curves fit the measured engineering stress-strain curves very well. In addition, the empirical damage evolution equation for the notch specimen was obtained from the experiment data and FEM simulations.

Influence of Zr on the Microstructure and Mechanical Properties of an Al-Zn-Mg-Cu Alloy

2007 ◽  
Vol 546-549 ◽  
pp. 1069-1076 ◽  
Author(s):  
Shou Jie Yang ◽  
You Hua Xie ◽  
Sheng Long Dai ◽  
Ming Gao Yan
Keyword(s):  
Mechanical Properties ◽  
Fracture Mechanism ◽  
Mass Fraction ◽  
Fracture Behavior ◽  
High Strength ◽  
Age Hardening ◽  
Cu Alloy ◽  
Microstructure And Mechanical Properties ◽  
Peak Value

Recently, a new super-high-strength Al-Zn-Mg-Cu alloy with Zr bearing was developed in BIAM. In this paper, the effect of microalloying element Zr on the microstructure and mechanical properties of the alloy was investigated. It was found that the influence of Zr on the microstructure and age-hardening behaviors was remarkable. The strength of the alloy increases with increasing the content of zirconium, and the peak value of the elongation appeared when the content of Zr was 0.06%(mass fraction) and then decreases. The fracture behavior was also studied. The result shows that the fracture mechanism of the alloy was converted from intergranular brittle to transgranular ductile model with increasing the content of zirconium. Finally, the optimum contents of Zr in the alloy were proposed as 0.10%~0.14%.

A Comparative Study on Various Ductile Crack Formation Criteria

2004 ◽  
Vol 126 (3) ◽  
pp. 314-324 ◽  
Author(s):  
Yingbin Bao ◽  
Tomasz Wierzbicki
Keyword(s):  
Crack Formation ◽  
Stress Triaxiality ◽  
Tensile Tests ◽  
Equivalent Strain ◽  
Fracture Mechanisms ◽  
Ductile Crack ◽  
Fracture Criteria ◽  
Wide Range ◽  
Mechanical Models ◽  
Stress States

Various fracture criteria, based on different assumptions and different mechanical models, have been proposed in the past to predict ductile fracture. The objective of this study is to assess their effectiveness and accuracy in a wide range of process parameters. A series of tests on 2024-T351 aluminum alloy, including upsetting tests and tensile tests is carried out. It is found that none of the existing fracture criteria give consistent results. Two totally different fracture mechanisms are clearly observed from microfractographs of upsetting and tensile specimens. This observation confirms that it is impossible to capture all features of ductile crack formation in different stress states with a single criterion. It is shown that different functions are necessary to predict crack formation for different ranges of stress triaxiality. Weighting functions in a wide range of stress states can be obtained by determining the fracture locus in the space of equivalent strain to fracture and stress triaxiality.

scholarly journals Numerical-Experimental Plastic-Damage Characterisation of Additively Manufactured 18Ni300 Maraging Steel by Means of Multiaxial Double-Notched Specimens

2021 ◽  
Vol 5 (3) ◽  
pp. 84
Author(s):  
Tiago Silva ◽  
Afonso Gregório ◽  
Filipe Silva ◽  
José Xavier ◽  
Ana Reis ◽  
...  
Keyword(s):  
Maraging Steel ◽  
High Stress ◽  
Stress Triaxiality ◽  
High Strength ◽  
Viable Option ◽  
Notched Specimens ◽  
Stress States ◽  
Data Gap ◽  
Structural Parts ◽  
High Degree

Additive manufacturing (AM) has become a viable option for producing structural parts with a high degree of geometrical complexity. Despite such trend, accurate material properties, under diversified testing conditions, are scarce or practically non-existent for the most recent additively manufactured (AMed) materials. Such data gap may compromise component performance design, through numerical simulation, especially enhanced by topological optimisation of AMed components. This study aimed at a comprehensive characterisation of laser powder bed fusion as-built 18Ni300 maraging steel and its systematic comparison to the conventional counterpart. Multiaxial double-notched specimens demonstrated a successful depiction of both plastic and damage behaviour under different stress states. Tensile specimens with distinct notch configurations were also used for high stress triaxiality range characterisation. This study demonstrates that the multiaxial double-notched specimens constitute a viable option towards the inverse plastic behaviour calibration of high-strength additively manufactured steels in distinct state of stress conditions. AMed maraging steel exhibited higher strength and lower ductility than the conventional material.

Effect of Prestrain at Elevated Temperature on the Fracture Behavior of High Strength Steels

1983 ◽  
Vol 105 (1) ◽  
pp. 16-20 ◽  
Author(s):  
K. Satoh ◽  
M. Toyoda ◽  
Y. Mutoh
Keyword(s):  
Elevated Temperature ◽  
Cleavage Fracture ◽  
Fracture Mechanism ◽  
Strain Aging ◽  
Fracture Behavior ◽  
Present Report ◽  
High Strength Steels ◽  
High Strength ◽  
Fracture Initiation ◽  
Initiation And Propagation

It is well known that fracture initiation behavior is influenced by weld thermal straining. In the present report, attention is focused on the influence of weld thermal straining on the fracture mechanism. The influence of prestrain at elevated temperature or strain-aging on the initiation and propagation behaviors of ductile and cleavage fracture in KD32 and HT80 steels is investigated. A relationship between the increase in the lowest temperature at which a tear dimple region can be observed (Ti) or the decrease in stretched zone width and the increase in hardness at the notch tip is found.

Sign in / Sign up

Export Citation Format

Share Document