Influence of the stress state on void nucleation and subsequent growth around inclusion in ductile material

2015 ◽  
Vol 193 (1) ◽  
pp. 43-57 ◽  
Author(s):  
Q. M. Yu
Keyword(s):  
Stress State ◽  
Void Nucleation ◽  
Ductile Material ◽  
Subsequent Growth

Numerical Simulation of Void Nucleation in S355 Steel

2016 ◽  
Vol 250 ◽  
pp. 244-249
Author(s):  
Wiktor Wcislik
Keyword(s):  
Numerical Simulation ◽  
Stress State ◽  
Civil Engineering ◽  
Void Nucleation ◽  
Iron Carbide ◽  
High Stress ◽  
Nucleation Process ◽  
Engineering Structures ◽  
The Matrix

The study presents the numerical simulation of the void nucleation process due to decohesion of the interface between the matrix and inclusion of iron carbide Fe3C, under high stress state triaxiality ratio, which is equal to 1.345. The analysis was conducted for S355J2G3 steel, commonly used in civil engineering structures. Special attention was paid to the determination of the value of void nucleation strain.

Influence of Lode Angle on the ASME Local Strain Failure Criterion

2016 ◽  
Author(s):  
Kumarswamy Karpanan ◽  
William Thomas
Keyword(s):  
Experimental Data ◽  
Stress State ◽  
Tensile Testing ◽  
Failure Strain ◽  
Axial Stress ◽  
Equivalent Stress ◽  
Ductile Material ◽  
Uniaxial Tensile ◽  
Lode Angle ◽  
Triaxiality Factor

Failure strain at any point on a structure is not a constant but is a function of several factors, such as stress state, strain rate, and temperature. Failure strain predicted from the uniaxial tensile testing cannot be applied to the bi-axial or tri-axial stress state. ASME Sec VIII-Div-2, and −3 codes give methods to predict the failure strain for multi-axial stress state by considering the triaxiality factor, which is defined as the ratio of mean stress to the equivalent stress. Failure strain predicted by the ASME method (based on the Rice-Tracey ductile failure model) is an exponential curve that relates the failure strain to the triaxiality factor. The ASME VIII-3 method also gives procedures to calculate failure strain for various material types: ferritic, stainless steel, nickel alloy, aluminum, etc. Experimental results of failure strain at various stress states show that the failure strain is not only a function of the triaxiality factor, but also a function of the Lode angle. The Lode angle takes on the value of 1, 0, and −1 for tension, pure shear, and compression stress state, respectively. Experimental data shows that the failure strain is a 3D surface which has an exponential relation with triaxiality and a parabolic relation with the Lode angle. To validate the ASME failure strain prediction, this paper compares experimental failure strain test data from literature with the ASME predictions. The ASME predictions are non-conservative especially for moderately ductile materials such as aluminum and high strength carbon steel. A reduction factor on failure strain for low ductile material is presented using the relation between the R (yield/ultimate) and the stress ratio (shear/tensile stress). The ASME method does not account for the environmental effects while calculating the failure strain. High pressure, high temperature (HPHT) subsea components designed using ASME VIII-3 code are subjected to various environments in subsea, such as seawater, seawater with cathodic protection (CP) and production fluid (crude oil). Experimental data shows that the Elongation (EL) and/or Reduction in Area (RA) from tensile testing decrease in these environments. Therefore, to account for any environment effect on the failure strain, reduced EL and RA can be used to predict the failure strain.

Interfacial Stresses and Void Nucleation in Discontinuously Reinforced Composites

1999 ◽  
Vol 122 (1) ◽  
pp. 86-92 ◽  
Author(s):  
T. C. Tszeng
Keyword(s):  
Stress State ◽  
Bonding Strength ◽  
Volume Fraction ◽  
Void Nucleation ◽  
Matrix Material ◽  
Interfacial Bonding ◽  
Von Mises Stress ◽  
Inclusion Problem ◽  
Matrix Interface ◽  
Interfacial Bonding Strength

This paper presents the theoretical predictions of the stress state at the inclusion-matrix interface in discontinuous metal matrix composites by the generalized inclusion method. In the author’s previous works, this method had been extended to the elastoplastic deformation in the matrix material. The present analysis of the ellipsoidal inclusion problem indicates that the regions at the pole and the equator of the particle/matrix interface essentially remain elastic regardless of the level of deformation, although the size of the elastic region keeps decreasing as deformation becomes larger. It was also found that, when the composite is undergoing a relatively large plastic deformation (strain), the maximum interfacial normal stress is approximately linearly dependent upon the von Mises stress and the hydrostatic stress. Based on the stress criterion for void nucleation, the author determined the void nucleation loci and nucleation strain for a composite subjected to an axisymmetric macroscopic stress state. The influence of interfacial bonding strength, inclusion shape, and volume fraction on the occurrence of void nucleation have been determined. The interfacial bonding strength in a SiC-aluminum system was re-evaluated by using existing experimental evidence. [S0094-4289(00)01301-3]

A Coupled-Constitutive Model for Ductile Fracture: Void Nucleation to Coalescence

2010 ◽  
Author(s):  
Cliff Butcher ◽  
Zengtao Chen
Keyword(s):  
Stress State ◽  
Constitutive Model ◽  
Ductile Fracture ◽  
Mechanical Response ◽  
Volume Fraction ◽  
Void Nucleation ◽  
Homogenization Theory ◽  
Integration Scheme ◽  
Second Phase ◽  
The Matrix

A novel framework and integration scheme has been developed to implement a secant-based homogenization theory for particle-reinforced plasticity into an existing damage-based constitutive model, the well known Gurson-Tvergaard (GT) model. In this approach, the material is treated as a three-phase composite composed of voids and particles embedded in a ductile matrix. Two successive homogenization theories (damage- and particle-based) are then applied to determine the macro-mechanical response of the material as well as the average stress state within the constituents as a function of the particle shape, composition, and volume fraction. By identifying the stress state within the particles and the matrix, void nucleation can be accurately represented and the void growth and coalescence models are improved through knowledge of the stress state within the matrix. The performance of the coupled model is evaluated using a model aluminum alloy. A parametric study is performed to elucidate the influence of the second-phase particles and their shape on damage evolution and ductile fracture.

A Generalized Damage Model Accounting for Instability and Ductile Fracture for Sheet Metals

2014 ◽  
Vol 611-612 ◽  
pp. 106-110 ◽  
Author(s):  
Jun He Lian ◽  
Xiao Xu Jia ◽  
Sebastian Münstermann ◽  
Wolfgang Bleck
Keyword(s):  
Stress State ◽  
Ductile Fracture ◽  
Automotive Industry ◽  
Void Nucleation ◽  
Damage Model ◽  
High Stress ◽  
Forming Limit ◽  
Dual Phase ◽  
Sheet Metals ◽  
Hard Phase

With the requirement of vehicle performance and fuel economy, dual-phase (DP) steels as one of the advanced high stress steels (AHSS) are increasingly used in the automotive industry due to the excellent combination of the tensile strength and ductility. On a microscale the ductile fracture is governed by the void nucleation, growth and coalescence mechanism. In the dual-phase steels this damage mechanism exhibits a rather complex situation: voids are generated by the debonding of the hard phase from the matrix and the inner cracking of the hard phase besides by inclusions. On a macroscale fracture of these materials is observed in the automotive industry with the absence of strain localization or minimal post-necking deformation. Consequently the failure during the forming process is caused by a competitive or combined mechanism of internal damage evolution and metal instability. In this study, the target is to develop a simple and generalized model for metal forming processes accounting for instability, damage and ductile fracture. Theoretical predictions of metal instability by the Hill–Swift necking criterion and the modified maximum force criterion are considered. The damage model is developed by the combination of the prediction of metal instability and ductile fracture of sheet metals. The model is developed in 3D triaxial stress state and the accumulation of damage is stress state dependent. Furthermore, the influence of the hardening curve effected by damage on the forming limit curve is investigated.

In situ observations of electromigration induced void behavior

1995 ◽  
Vol 53 ◽  
pp. 244-245
Author(s):  
T. Marieb ◽  
J. C. Bravman ◽  
P. Flinn ◽  
D. Gardner ◽  
M. Madden
Keyword(s):  
Electron Microscopy ◽  
Void Nucleation ◽  
Plan View ◽  
Transmission Electron ◽  
Nucleation Sites ◽  
Microelectronics Industry ◽  
In Situ Observations ◽  
Backscatter Electron Detector ◽  
Voltage Scanning

Electromigration and stress voiding have been active areas of research in the microelectronics industry for many years. While accelerated testing of these phenomena has been performed for the last 25 years[1-2], only recently has the introduction of high voltage scanning electron microscopy (HVSEM) made possible in situ testing of realistic, passivated, full thickness samples at high resolution.With a combination of in situ HVSEM and post-testing transmission electron microscopy (TEM) , electromigration void nucleation sites in both normal polycrystalline and near-bamboo pure Al were investigated. The effect of the microstructure of the lines on the void motion was also studied.The HVSEM used was a slightly modified JEOL 1200 EX II scanning TEM with a backscatter electron detector placed above the sample[3]. To observe electromigration in situ the sample was heated and the line had current supplied to it to accelerate the voiding process. After testing lines were prepared for TEM by employing the plan-view wedge technique [6].

Short Stress State Questionnaire

2015 ◽  
Vol 31 (1) ◽  
pp. 20-30 ◽  
Author(s):  
William S. Helton ◽  
Katharina Näswall
Keyword(s):  
Stress State ◽  
Factor Structure ◽  
Human Performance ◽  
Self Report ◽  
Confirmatory Factor ◽  
Stress States ◽  
Related Stress ◽  
Using Data ◽  
Task Conditions ◽  
Multiple Samples

Conscious appraisals of stress, or stress states, are an important aspect of human performance. This article presents evidence supporting the validity and measurement characteristics of a short multidimensional self-report measure of stress state, the Short Stress State Questionnaire (SSSQ; Helton, 2004 ). The SSSQ measures task engagement, distress, and worry. A confirmatory factor analysis of the SSSQ using data pooled from multiple samples suggests the SSSQ does have a three factor structure and post-task changes are not due to changes in factor structure, but to mean level changes (state changes). In addition, the SSSQ demonstrates sensitivity to task stressors in line with hypotheses. Different task conditions elicited unique patterns of stress state on the three factors of the SSSQ in line with prior predictions. The 24-item SSSQ is a valid measure of stress state which may be useful to researchers interested in conscious appraisals of task-related stress.

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