scholarly journals Study of localization in a void-sheet under stress states near pure shear

2015 ◽  
Vol 75-76 ◽  
pp. 134-142 ◽  
Author(s):  
Viggo Tvergaard
Keyword(s):  
Pure Shear ◽  
Stress States ◽  
Void Sheet

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.

scholarly journals Behavior of the Abaqus CDP model in simple stress states

2019 ◽  
Vol 52 (2) ◽  
pp. 87-113
Author(s):  
Alexis Fedoroff ◽  
Kim Calonius ◽  
Juha Kuutti
Keyword(s):  
Pure Shear ◽  
Material Model ◽  
Sensitivity Study ◽  
Stress States ◽  
Tension State ◽  
Impact Simulations ◽  
Parameter Values ◽  
Shear State ◽  
Element Removal ◽  
Simple Stress

In order to use the Abaqus Concrete Damaged Plasticity (CDP) material model in simulations of reinforced concrete structures, one has to understand the effect of various parameters of the material model. Although most of the material parameters can be determined from standard concrete tests, some parameters need more advanced tests to be determined. In impact simulations, one often has only limited material data available, and it makes therefore sense to study the parameter sensitivity of the material model in order to fix realistic parameter values. In this paper, the sensitivity of the simulation response with respect to two modelparameters is studied: the dilation angle and the tensile to compressive meridian ratio. The sensitivity study is performed in three simple but representative stress states: the uniaxial tension state, the confined uniaxial compressive state and the pure shear state. Finally, it is discussed how these simple stress states relate to the element removal criteria, which is necessary in simulations involving fragmentation.

Simplified phenomenological model of the nonlinear behavior of FRPs under combined stress states

2017 ◽  
Vol 52 (4) ◽  
pp. 475-485 ◽  
Author(s):  
Siegfried Galkin ◽  
Fabian J Schirmaier ◽  
Luise Kärger
Keyword(s):  
Shear Stress ◽  
Phenomenological Model ◽  
Pure Shear ◽  
Nonlinear Behavior ◽  
Strain Curve ◽  
Shear Loading ◽  
Material Behavior ◽  
Nonlinear Material ◽  
Combined Stress ◽  
Stress States

Nonlinear material behavior of FRPs under shear loading is widely observed and investigated. In case of combined stress states under tension and shear, an interaction between the macroscopic shear stress–strain curve evolution and the applied tension has been observed and described by several publications in the past. In the present work, the available experimental data with combined stress states are evaluated and a specific threshold shear stress is found, above which nonlinear material behavior occurs for all stress states. Further, a new simplified phenomenological model is derived to model the nonlinear behavior of FRPs when the threshold shear stress is exceeded. This simplified model only needs the threshold shear stress and one evolution parameter, both derived from a pure shear test, to model nonlinear behavior for all combined stress states. A comparison with the available experimental results and with the predictions of the WWFE-III participants for WWFE-III test case 1 shows a very good agreement.

Multiaxial Nonlinear Viscoelastic Characterization and Modeling of a Structural Adhesive

1997 ◽  
Vol 119 (3) ◽  
pp. 205-210 ◽  
Author(s):  
C. F. Popelar ◽  
K. M. Liechti
Keyword(s):  
Free Volume ◽  
Time Scale ◽  
Pure Shear ◽  
Polymeric Materials ◽  
Displacement Fields ◽  
Free Volume Theory ◽  
Global Response ◽  
Nonlinear Viscoelastic ◽  
Stress States ◽  
Structural Adhesive

Many polymeric materials, including structural adhesives, exhibit a nonlinear viscoelastic response. The nonlinear free volume approach is based on the Doolittle concept that the “free volume” controls the mobility of polymer molecules and, thus, the inherent time scale of the material. It then follows that factors such as temperature and moisture, which change the free volume, will influence the time scale. Furthermore, stress-induced dilatation will also affect the free volume and, hence, the time scale. However, during this investigation dilatational effects alone were found to be insufficient in describing the response of near pure shear tests performed on a bisphenol A epoxy with an amido amine hardener. Thus, the free volume approach presented here has been modified to include distortional effects in the inherent time scale of the material. In addition to predicting the global response under a variety of multiaxial stress states, the modified free volume theory also accurately predicts the local displacement fields, including those associated with a localized region, as determined from geometric moire´ measurements at various stages of deformation.

scholarly journals Influence of Residual Stresses of Sputtered Thin Film Electrodes for Dielectric Elastomer Applications

Proceedings ◽  
2020 ◽  
Vol 64 (1) ◽  
pp. 2
Author(s):  
Jonas Hubertus ◽  
Sipontina Croce ◽  
Julian Neu ◽  
Gianluca Rizzello ◽  
Stefan Seelecke ◽  
...  
Keyword(s):  
Thin Film ◽  
Residual Stress ◽  
Residual Stresses ◽  
Pure Shear ◽  
Dielectric Elastomer ◽  
Film Stress ◽  
Electromechanical Properties ◽  
Residual Stress State ◽  
Thin Film Electrodes ◽  
Stress States

This paper focuses on the electromechanical properties of novel sub-micron compliant metallic thin film electrodes for dielectric elastomer membranes. Electrodes with thicknesses within the range of 10–20 nm and different residual stress states are explored. Both pure nickel films and sandwiches of nickel (Ni) and carbon (C) are deposited by direct current (DC) magnetron sputtering onto pre-stretched silicone elastomer membranes. Both 37.5% biaxial pre-stretch and 57.5% uniaxial pre-stretch under pure shear condition (PSC) are considered in the conducted investigation. After the coating process is completed, the elastomer is allowed to relax. In the contracted configuration, it exhibits a wrinkled surface. After this state is reached, the electromechanical characterization is performed. All types of films reveal a low initial resistance (around 100 Ω/square). Depending on the kind of pre-stretch and the electrode material, a strain of 100% without any major degradation is achieved. It is also shown how the residual stress of the layers can be influenced by suitable sputtering parameters. As a result, low residual film stress significantly improves the electromechanical properties of PSC pre-stretched elastomers, but have only a minor influence on the biaxially pre-stretched ones, regarding the Ni and the Ni + C thin films. This phenomenon is directly connected to the failure mechanisms observed on the two types of pre-stretched membranes. With reversed layer order, i.e., C + Ni electrodes, the residual stress state of Ni does not influence the electromechanical properties for both the biaxially pre-stretched and the PSC pre-stretched coated membranes. The results are of fundamental importance for understanding the role of residual stresses for the creation of electromechanically stable and highly conductive electrode films, to be used in dielectric elastomer (DE) applications.

Experimental study of cemented interfaces for applications in CO2 storage re-using depleted oil and gas reservoirs

2021 ◽  
Author(s):  
Frédérique Rossillon ◽  
Vivien Esnault ◽  
Eléonore Roguet
Keyword(s):  
Oil And Gas ◽  
Pure Shear ◽  
Co2 Storage ◽  
Fem Analysis ◽  
Mechanical Tests ◽  
Stress Pattern ◽  
Pull Out ◽  
Stress States ◽  
The Impact ◽  
Push Out

<p>The European ERA-ACT REX-CO<sub>2</sub> project aims to develop a tool to assess the compatibility of existing wells for CO<sub>2</sub> sequestration. Indeed, the reuse of existing wells for storage in depleted reservoirs is an attractive medium-term solution for geological sequestration of CO<sub>2</sub>.</p><p>The mechanical integrity of the wells is a critical point in term of storage durability. A variety of flow paths that could lead to a migration of the stored CO<sub>2</sub> to surrounding geological layers or the surface have been identified. Among those, operational feedback shows that a likely leakage route are along the interfaces of the well structure. These potential flow path can be generated by the debonding of the cement sheath from the steel casing or surrounding rocks. One ambition of REX-CO<sub>2 </sub>project is to ultimately predict the wells integrity as a function of the variations in undergone mechanical loadings. In order to reach this objective, it appears relevant to characterize the mechanical strength of these interfaces.</p><p>IFPEN work consists in carrying out mechanical tests on bimaterial specimens to study cement/steel or cement/rock interfaces in different configurations representative of downhole conditions. Two types of tests are performed allowing the characterization of the bonding in two different stress states: the pull-out test and the push-out test. Combined with simulations, these results can either be used directly or feed a damage interface models. The authors are currently running an extensive parametric study, to explore the impact of various downhole conditions, such as pressure or environment, and to CO<sub>2</sub> exposure.</p><p>The presentation focuses on the mechanical testing methodology. The pull-out test is a tension test performed on a cylinder made of two materials. In this case, the stress pattern is obvious, the interface is loaded in tension. This test is difficult to carry out perfectly due to the weak and scattered behaviour in tension, and finding proper gluing solutions. The push-out test, commonly used in the literature, consists in pushing a plug (steel or rock) into a cement ring to measure the bonding resistance. Despite other push-out tests, a surrounding steel ring ensures the cement confinement and avoid radial cracks. FEM analysis shows stress pattern is more complex than a pure shear at the interface, as often assumed in the literature. An analysis of loading curves enables to understand the different damage stages of the interfaces.</p>

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.

Comparison of Substructures Between Uniaxial and Biaxial Deformation in 1100-0 Aluminum

1981 ◽  
Vol 39 ◽  
pp. 52-53
Author(s):  
D. L. Rohr ◽  
S. S. Hecker
Keyword(s):  
Plastic Strain ◽  
Cell Walls ◽  
Room Temperature ◽  
Mechanical Response ◽  
Biaxial Tension ◽  
Initial Deformation ◽  
Uniaxial Deformation ◽  
Biaxial Deformation ◽  
Stress States ◽  
Comprehensive Study

As part of a comprehensive study of microstructural and mechanical response of metals to uniaxial and biaxial deformations, the development of substructure in 1100 A1 has been studied over a range of plastic strain for two stress states.Specimens of 1100 aluminum annealed at 350 C were tested in uniaxial (UT) and balanced biaxial tension (BBT) at room temperature to different strain levels. The biaxial specimens were produced by the in-plane punch stretching technique. Areas of known strain levels were prepared for TEM by lapping followed by jet electropolishing. All specimens were examined in a JEOL 200B run at 150 and 200 kV within 24 to 36 hours after testing.The development of the substructure with deformation is shown in Fig. 1 for both stress states. Initial deformation produces dislocation tangles, which form cell walls by 10% uniaxial deformation, and start to recover to form subgrains by 25%. The results of several hundred measurements of cell/subgrain sizes by a linear intercept technique are presented in Table I.

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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