scholarly journals Effect of the Triaxiality in Plane Stress Conditions. Triaxiality Effect in a PVC Material

2013 ◽  
Vol 3 (1) ◽  
pp. 373-380
Author(s):  
N. Selini ◽  
M. Elmeguenni ◽  
M. Benguediab
Keyword(s):  
Pure Shear ◽  
Stress Triaxiality ◽  
Volumetric Strain ◽  
Experimental Tests ◽  
Plastic Instability ◽  
Pressure Vessels ◽  
Polymer Materials ◽  
Plastic Behavior ◽  
Anisotropic Plastic ◽  
Plastic Volumetric Strain

Polymer materials are gaining more and more importance in engineering applications. A new methodology of analysis is required in order to assess the capability of such material in withstanding complex loads. Therefore, the behavior of these materials currently arouses a great research interest. The use of PVC plastic pipes in pressure vessels and pipelines has increased rapidly in the last decade. In order to determine the plastic behavior of PVC, an experimental method is presented. Through the results obtained from experimental tests, in the first part of this paper, we investigate the use of a phenomenological model proposed by G’Sell and Jonas. The true stress-strain response under large plastic deformation was investigated in different stress triaxiality frameworks. Particular attention was given to volumetric strain evolution, separation resulting from elastic volumetric strain, plastic volumetric strain and pure shear. The effect of stress triaxiality on plastic instability and fracture strain was also examined. The deformation process should be considered as explained, and the anisotropic plastic response induced by the deformation could be introduced in constitutive equations of G’Sell.

The Stress Triaxiality Effect under Large Plastic Deformation of a Polybutylene Terephthalate (PBT)

2018 ◽  
Vol 34 ◽  
pp. 13-28
Author(s):  
Abdel Nour Zaim ◽  
Benattou Bouchouicha ◽  
Hadj Miloud Meddah ◽  
El Bahri Ould Chikh
Keyword(s):  
Plastic Deformation ◽  
Pure Shear ◽  
Stress Triaxiality ◽  
Volumetric Strain ◽  
Plastic Instability ◽  
Large Plastic Deformation ◽  
Polybutylene Terephthalate ◽  
New Generation ◽  
Plastic Volumetric Strain ◽  
Strain Responses

In this work, we focus on a new generation of polymer named Polybutylene terephthalate (PBT). In order to analyse and determine true behaviour of this polymer, a special experimental method was used. Hence, the true stress/strain responses are investigated under a large plastic deformation in different stress triaxiality frameworks with a particular attention on the volumetric strain evolution, with their decomposition to an elastic volumetric strain, plastic volumetric strain and the pure shear. Moreover, the effect of stress triaxiality on the plastic instability and the fracture strain is also examined. With the plastic instability analysis, it was found that plastic strain hardening increases gradually with the triaxiality. Finally, in order to evaluate the damage of this polymer, a theoretical damage formula is proposed.

Plasticity Effect on the Mechanical Behavior of an Amorphous Polymer

2019 ◽  
Vol 43 ◽  
pp. 1-19
Author(s):  
Boudjellel Moulai Ali ◽  
El Bahri Ould Chikh ◽  
Hadj Miloud Meddah ◽  
Bel Abbès Bachir Bouiadjra
Keyword(s):  
Fracture Strain ◽  
Amorphous Polymer ◽  
Stress Triaxiality ◽  
Volumetric Strain ◽  
Plastic Instability ◽  
Pressure Vessels ◽  
Large Plastic Deformation ◽  
Know How ◽  
Plasticity Effect ◽  
And Performance

In the process of forming solid materials, the plastic instability phenomena often control the appearance and performance of the finished product. The study of these phenomena is therefore of great scientific and technological importance. Polymers materials, for example, polyvinyl chloride (PVC) are frequently used in the plastic pipes in pressure vessels and pipelines, which require details that are more serious, it is therefore essential to understand the mechanisms of plastic instability in polymers in order to know how to control them. In order to determine the plastic behaviour of PVC, the true stress-strain response under large plastic deformation was investigated in different stress triaxiality frameworks. A particular attention was given on the volumetric strain evolution and the damage. The effect of stress triaxiality on the fracture strain was also examined. In the second part of this paper, an elasto-viscoplastic behaviour model is presented, with non associated plasticity, damage and coalescence, which represents the observed behaviours of a PVC material under different triaxialities and for three initial void shapes

Inverse Identification of CDM Model Parameters for DP1000 Steel Sheets Using a Hybrid Experimental-Numerical Methodology Spanning Various Stress Triaxiality Ratios

2013 ◽  
Vol 554-557 ◽  
pp. 2103-2110 ◽  
Author(s):  
Zhen Ming Yue ◽  
Celal Soyarslan ◽  
Houssem Badreddine ◽  
Khemais Saanouni ◽  
A. Erman Tekkaya
Keyword(s):  
Constitutive Model ◽  
Pure Shear ◽  
Stress Triaxiality ◽  
Experimental Tests ◽  
Image Correlation ◽  
Material Surface ◽  
Model Parameters ◽  
Mixed Hardening ◽  
Steel Sheets ◽  
Strain Paths

A hybrid experimental-numerical methodology is presented for the identification of the model parameters regarding a mixed hardening anisotropic finite plasticity fully coupled with isotropic ductile damage in which the micro-crack closure effect is given account for, for steel sheets made of DP1000. The experimental tests involve tensile tests with smooth and pre-notched specimens and shear tests with specimen morphologies recently proposed by D.R. Shouler, J.M. Allwood (Design and use of a novel sample design for formability testing in pure shear, Journal of Materials Processing Technology, Volume 210, Issue 10, 1 July 2010, Pages 1304-1313). These tests cover stress triaxiality ratios lying between 0 (pure shear) and 1/√3 (plane strain). To neutralize machine stiffness effects displacements of the chosen material surface pixels are kept track of using the digital image correlation system ARAMIS, where recorded inputs are synchronized with force measurements. On the numerical part, developed constitutive model is implemented as user defined material subroutine, VUMAT, for ABAQUS/Explicit. FE models for the test cases are built using 3D brick elements (rather than thin shells) and devising developed VUMAT for the constitutive model, model parameters are identified using an inverse parameter identification procedure where the objective function relies on the difference of experimentally observed-numerically predicted forces for the selected pixel displacements. The validity of the material model and transferability of its parameters are tested using tests involving complex strain paths.

scholarly journals Study of Influence of Width to Thickness Ratio in Sheet Metals on Bendability under Ambient and Superimposed Hydrostatic Pressure

2021 ◽  
Vol 2 (3) ◽  
pp. 542-558
Author(s):  
Mohammadmehdi Shahzamanian ◽  
David Lloyd ◽  
Amir Partovi ◽  
Peidong Wu
Keyword(s):  
Hydrostatic Pressure ◽  
Stress Ratio ◽  
Fracture Strain ◽  
Stress Triaxiality ◽  
Volumetric Strain ◽  
Thickness Ratio ◽  
Sheet Metals ◽  
The Finite Element Method ◽  
Bending Strain ◽  
Good Agreement

The effect of the width to thickness ratio on the bendability of sheet metal is investigated using the finite element method (FEM) employing the Gurson–Tvergaard–Needleman (GTN) model. Strain path changes in the sheet with change in the width/thickness ratio. It is shown that bendability and fracture strain increase significantly by decrease in the width/thickness ratio. The stress state is almost uniaxial when the stress ratio (α) is close to zero for narrow sheets. Stress ratio is nothing but the major stress to minor stress ratio. This delays the growth and coalescence of micro-voids as the volumetric strain and stress triaxiality (pressure/effective stress) decrease. On the other hand, ductility decreases with increase in α for wider sheets. Fracture bending strain is calculated and, as expected, it increases with decrease in the width/thickness ratio. Furthermore, a brief study is performed to understand the effect of superimposed hydrostatic pressure on fracture strain for various sheet metals with different width/thickness ratios. It is found that the superimposed hydrostatic pressure increases the ductility, and that the effect of the width/thickness ratio in metals on ductility is as significant as the effect of superimposed hydrostatic pressure. Numerical results are found to be in good agreement with experimental observations.

Thermo-Elasto-Plastic Analysis of Thick-Walled Spherical Pressure Vessels Made of Functionally Graded Materials

2016 ◽  
Vol 08 (04) ◽  
pp. 1650054 ◽  
Author(s):  
Zeinab Mazarei ◽  
Mohammad Zamani Nejad ◽  
Amin Hadi
Keyword(s):  
Heat Flux ◽  
Functionally Graded Materials ◽  
Poisson’S Ratio ◽  
Pressure Vessels ◽  
Functionally Graded ◽  
Material Behavior ◽  
Poisson's Ratio ◽  
Uniform Heat Flux ◽  
Plastic Behavior ◽  
Graded Materials

An exact closed-form analytical solution is presented to solve the thermo-elasto-plastic problem of thick-walled spherical vessels made of functionally graded materials (FGMs). Assuming that the inner surface is exposed to a uniform heat flux, and that the outer surface is exposed to an airstream. The heat conduction equation for the one-dimensional problem in spherical coordinates is used to obtain temperature distribution in the sphere. Material properties are graded in the thickness direction according to a power law distribution, whereas the Poisson’s ratio is kept constant. The Poisson’s ratio due to slight variations in engineering materials is assumed constant. The plastic model is based on von Mises yield criterion and its associated flow rules under the assumption of perfectly plastic material behavior. For various values of inhomogeneity constant, the so-obtained solution is then used to study the distribution of limit heat flux, displacement and stresses versus the radial direction. Moreover, the effect of increasing the heat flux and pressure on the propagation of the plastic zone are investigated. Furthermore, the effect of change in Poisson’s ratio on the value of the critical material parameter is demonstrated. The present study is also validated by comparing the numerical results for thick elasto-plastic spherical shells available in the literature. To the best of the authors’ knowledge, in previous studies, exact thermo-elasto-plastic behavior of FGM thick-walled sphrical pressure vessels has not investigated.

Numerical Investigation of Ductile Fracture in Pipelines Under Complex Loading Using a Phenomenological Damage Model

2021 ◽  
Author(s):  
Iago S. Santos ◽  
Diego F. B. Sarzosa
Keyword(s):  
Ductile Fracture ◽  
Mechanical Response ◽  
Numerical Study ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Numerical Procedure ◽  
Complex Loading ◽  
Experimental Tests ◽  
Compact Tension ◽  
Axial Tensile

Abstract This paper presents a numerical study on pipes ductile fracture mechanical response using a phenomenological computational damage model. The damage is controlled by an initiation criterion dependent on the stress triaxiality and the Lode angle parameter, and a post-initiation damage law to eliminate each finite element from the mesh. Experimental tests were carried out to calibrate the elastoplastic response, damage parameters and validate the FEM models. The tested geometries were round bars having smooth and notched cross-section, flat notched specimens under axial tensile loads, and fracture toughness tests in deeply cracked bending specimens SE(B) and compact tension samples C(T). The calibrated numerical procedure was applied to execute a parametric study in pipes with circumferential surface cracks subjected to tensile and internal pressure loads simultaneously. The effects of the variation of geometric parameters and the load applications on the pipes strain capacity were investigated. The influence of longitudinal misalignment between adjacent pipes was also investigated.

scholarly journals THE BEHAVIOR CHARACTERISTICS OF A RESERVOIR LEVEE SUBJECTED TO INCREASING WATER LEVELS

2017 ◽  
Vol 23 (1) ◽  
pp. 15-27
Author(s):  
Chung-Won LEE ◽  
Yong-Seong KIM ◽  
Sung-Yong PARK ◽  
Dong-Gyun KIM ◽  
Gunn HEO
Keyword(s):  
Hydraulic Fracturing ◽  
Real Time ◽  
Pore Water ◽  
Volumetric Strain ◽  
Water Levels ◽  
The Core ◽  
The Stability ◽  
Centrifugal Model ◽  
Behavior Characteristics ◽  
Plastic Volumetric Strain

Centrifugal model testing has been widely used to study the stability of levees. However, there have been a limited number of physical studies on levees where the velocity of increasing water levels was considered. To investigate the behavior characteristics of reservoir levees with different velocities of increasing water levels, centrifugal model tests and seepage-deformation coupled analyses were conducted. Through this study, it was confirmed that increasing water levels at higher velocities induces dramatic increases in the displacement, plastic volumetric strain and risk of hydraulic fracturing occurring in the core of the levee. Hence, real-time monitoring of the displacement and the pore water pres­sure of a levee is important to ensure levee stability.

Modeling of Anisotropic Plastic Behavior of Advanced High Strength Steel Sheet TRIP 780

2011 ◽  
Vol 410 ◽  
pp. 232-235 ◽  
Author(s):  
Sansot Panich ◽  
Vitoon Uthaisangsuk ◽  
Surasak Suranuntchai ◽  
Suwat Jirathearanat
Keyword(s):  
High Strength Steel ◽  
Steel Sheet ◽  
Plastic Anisotropy ◽  
High Strength ◽  
Uniaxial Tensile ◽  
Plastic Behavior ◽  
Biaxial Test ◽  
Advanced High Strength Steel ◽  
Yield Criteria ◽  
Anisotropic Plastic

Anisotropic plastic behavior of advanced high strength steel sheet of grade TRIP780 (Transformation Induced Plasticity) was investigated using three different yield functions, namely, the von Mises’s isotropic, Hill’s anisotropic (Hill’48), and Barlat’s anisotropic (Yld2000-2d) criterion. Uniaxial tensile and balanced biaxial test were conducted for the examined steel in order to characterize flow behavior and plastic anisotropy for different stress states. Especially, disk compression test was performed for obtaining balanced r-value. All these data were used to determine the anisotropic coefficients. As a result, yield stresses and r-values for different directions were calculated according to these yield criteria. The results were compared with experimental data. To verify the modelling accuracy, tensile tests of various notched samples were carried out and stress-strain distributions in the critical area were characterized. By this manner, the effect of stress triaxiality due to different notched shapes on the strain localization calculated by the investigated yield criteria could be studied.

Ring Specimen Geometry for Determining the Ductility of Tubulars

2016 ◽  
Author(s):  
M. A. Al Khaled ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Plane Strain ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
Pressure Vessels ◽  
Ring Specimen ◽  
Lode Parameter ◽  
Wide Range ◽  
Failure Locus

Pressure vessels designed in accordance with the ASME BPVC code are protected against local ductile failure. Recent work has shown that local ductile failure highly depends on the stress state characterized by both stress triaxiality (T) and the Lode parameter (L). In this paper, the effect of stress state on the ductility of a tubular steel is studied. Two ring specimen configurations were optimized to allow the determination of the ductile failure locus of both tensile and plane strain loadings. The geometry of both ring specimen configurations was optimized to achieve a plane strain (L = 0) condition and a generalized tension (L = −1) condition. Notches with different radii were machined on both types to achieve a wide range of stress triaxiality. Specimens were manufactured from SA-106 carbon tubular steel and were tested to determine the ductile failure loci as a function of T and L. Failure locus of SA-106 steel was constructed based on the failure instants and was found to be independent of the variation in the Lode parameter. The ASME-BPVC local failure criterion showed close agreement with experimental results.

Using Thermoplastic (HDPE) Liners and Glass Fiber Reinforced Thermosetting and Thermoplastic Structural Wall Matrices to Produce Filament Wound Pressure Vessels

2010 ◽  
Author(s):  
Joao F. Silva ◽  
Joao P. Nunes ◽  
Joao C. Velosa
Keyword(s):  
Glass Fiber ◽  
Composite Laminates ◽  
Large Scale ◽  
Service Condition ◽  
Pressure Vessels ◽  
Filament Winding ◽  
Plastic Behavior ◽  
Fiber Reinforced ◽  
Structural Wall ◽  
Glass Fiber Reinforced

Polymer composites are an excellent alternative to replace more traditional materials in the fabrication of pressure cylinders for common applications. They minimize the weight and improve the mechanical, impact and corrosion behavior, which are relevant characteristics for almost all current and future large scale pressure cylinder applications, such as liquid filters and accumulators, hydrogen cell storage vessels, oxygen bottles, etc. A new generation of composite pressure vessels has been studied in this work. The vessels consist on a thermoplastic liner wrapped with a filament winding glass fiber reinforced polymer matrix structure. A conventional 6-axis CNC controlled filament winding equipment was used to manufacture the thermosetting matrix composite vessels and adapted for production of thermoplastic matrix based composite vessels. The Abaqus 6.4.2 FEM package was used to predict the mechanical behavior of pressure vessels with capacity of approximately of 0.068 m3 (68 liters) for a 0.6 MPa (6 bar) pressure service condition according to the requirements of the EN 13923 standard, namely, the minimum internal burst pressure. The Tsai-Wu and von-Mises criteria were used to predict composite laminate and thermoplastic liner failures, respectively, considering the elasto-plastic behavior of the HDPE liner and the lamina properties deducted from the micromechanical models for composite laminates. Finally, the results obtained from the simulations were compared with those obtained from the experimental pressure tests made on the thermoplastic liners and final composite vessels.

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