The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
J Llorca - One of the best experts on this subject based on the ideXlab platform.
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a numerical study of the influence of microvoids in the transverse mechanical response of unidirectional composites
Composites Science and Technology, 2014Co-Authors: Danial Ashouri Vajari, Carlos Gonzalez, J Llorca, Brian Nyvang LegarthAbstract:Abstract The effect of porosity on the transverse mechanical properties of unidirectional fiber-reinforced composites is studied by means of computational micromechanics. The composite behavior is simulated by the finite element analysis of a representative volume element of the composite microstructure in which the random distribution of fibers and the voids are explicitly included. Two types of voids – interfiber voids and matrix voids – were included in the microstructure and the actual damage mechanisms in the composite, namely matrix and interface Failure, were accounted for. It was found that porosity (in the range 1–5%) led to a large reduction in the transverse strength and the influence of both types of voids in the onset and propagation of damage throughout the microstructure was studied under transverse tension and compression. Finally, the Failure Locus of the composite lamina under transverse tension/compression and out-of-plane shear was obtained by means of computational micromechanics and compared with the predictions of Puck’s model and with experimental data available in the literature. The results show that the strength of composites is significantly reduced by the presence of voids.
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Failure Locus of polypropylene nonwoven fabrics under in-plane biaxial deformation
Comptes Rendus Mécanique, 2012Co-Authors: Alvaro Ridruejo, Carlos Gonzalez, J LlorcaAbstract:Abstract The Failure Locus, the characteristics of the stress–strain curve and the damage localization patterns were analyzed in a polypropylene nonwoven fabric under in-plane biaxial deformation. The analysis was carried out by means of a homogenization model developed within the context of the finite element method. It provides the constitutive response for a mesodomain of the fabric corresponding to the area associated to a finite element and takes into account the main deformation and damage mechanisms experimentally observed. It was found that the Failure Locus in the stress space was accurately predicted by the Von Mises criterion and Failure took place by the localization of damage into a crack perpendicular to the main loading axis.
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influence of the loading path on the strength of fiber reinforced composites subjected to transverse compression and shear
International Journal of Solids and Structures, 2008Co-Authors: Essam Totry, Carlos Gonzalez, J LlorcaAbstract:The influence of the loading path on the Failure Locus of a composite lamina subjected to transverse compression and out-of-plane shear is analyzed through computational micromechanics. This is carried out using the finite element simulation of a representative volume element of the microstructure, which takes into account explicitly fiber and matrix spatial distribution within the lamina. In addition, the actual Failure mechanisms (plastic deformation of the matrix and interface decohesion) are included in the simulations through the corresponding constitutive models. Two different interface strength values were chosen to explore the limiting cases of composites with strong or weak interfaces. It was found that Failure Locus was independent of the loading path for the three cases analyzed (pseudo-radial, compression followed by shear and shear followed by compression) in the composites with strong and weak interfaces. This result was attributed to the fact that the dominant Failure mechanism in each material was the same in transverse compression and in shear. Failure is also controlled by the same mechanisms under a combination of both stresses and the Failure Locus depended mainly on the magnitude of the stresses that trigger fracture rather than in the loading path to reach the critical condition.
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Prediction of the Failure Locus of C/PEEK composites under transverse compression and longitudinal shear through computational micromechanics
Composites Science and Technology, 2008Co-Authors: Essam Totry, Carlos Gonzalez, J LlorcaAbstract:The potential of computational micromechanics to predict the Failure Locus of a unidirectional C/PEEK composite subjected to transverse compression and longitudinal shear was established. Numerical simulations were compared with the experimental results of Vogler and Kyriakides [Vogler TJ, Kyriakides S. Inelastic behavior of an AS4/PEEK composite under combined transverse compression and shear. Part I: Experiments. Int J Plasticity 1999;15:783–806], which contain detailed information of the matrix and fiber properties as well as the Failure micromechanisms during multiaxial loading. Analyses were based in the finite element analysis of a three-dimensional representative volume element of the lamina microstructure and included the main deformation and Failure mechanisms observed experimentally, namely matrix shear yielding and interface decohesion. In addition, the numerical predictions of the Failure Locus for composites with strong and weak interfaces were compared with those obtained by current phenomenological Failure models to establish the accuracy and range of validity of these criteria
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Failure Locus of fiber-reinforced composites under transverse compression and out-of-plane shear
Composites Science and Technology, 2007Co-Authors: Essam Totry, Carlos Gonzalez, J LlorcaAbstract:The Failure Locus a fiber-reinforced composite lamina, made up of 50 vol.% of carbon fibers embedded in an epoxy matrix, is computed under transverse compression and out-of-plane shear, a stress state whose experimental reproduction is highly complex. The mechanical response was obtained by the finite element method of a representative volume element of the lamina, which explicitly takes into account the fibers and the matrix in the lamina. The actual deformation and Failure mechanisms experimentally observed in the matrix, fibers and interfaces were included in the simulations through the appropriate constitutive equations. Two sets of simulations were performed, assuming that the fiber/matrix interface was either strong or weak. The corresponding Failure loci were compared with those given by three Failure criteria for composites (Hashin, Puck and LaRC) which provide reasonable predictions in other multiaxial stress states. The estimations of the Failure criteria were largely consistent with the numerical simulations in the composites with a strong interface but overestimated the composite strength when the interface was weak because the effect of interface decohesion (which becomes dominant) was not taken into account. These results point out the need to include interface fracture in the Failure criteria for composites.
Imad Barsoum - One of the best experts on this subject based on the ideXlab platform.
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The Sensitivity to the Lode Parameter in Ductile Failure of Tubular Steel Grades
Journal of Pressure Vessel Technology, 2018Co-Authors: Imad Barsoum, Mohamed Al-khaledAbstract:Ductile Failure in steels is highly controlled by the stress state, characterized by the stress triaxiality (T) and the Lode parameter (L). The ASME Boiler and Pressure Vessel Code requires pressure vessels to be designed to resist local ductile Failure. However, the standard does not account for the Lode parameter dependence in its Failure Locus. In this study, the influence of the stress state, characterized T and L, on the ductility of ASME tubular product steel grades is investigated. Two seamless pipes of midstrength carbon steel SA-106 Gr. B and high-strength superduplex steel SA-790 were considered. Ring specimen geometries for plane strain (PS) stress state (L = 0) and tensile stress (TS) state (L = −1) are utilized to establish the ductile Failure Locus in terms of T and L for the two steels. The experimental results (EXP) show that the effect of the Lode parameter on the Failure Locus for the SA-106 Gr. B steel is insignificant, whereas for the SA-790 steel, the effect is rather significant. A parameter SL is introduced in order to quantify the sensitivity of the Failure Locus to the Lode parameter. It is found that for materials with ultimate strength lower than about 550 MPa, the sensitivity to L is insignificant (SL ≈ 1), whereas for materials with ultimate strength higher than 550 MPa, the sensitivity to L could be significant (SL > 1). Scanning electron microscopic (SEM) analysis of the fracture surfaces revealed that the sensitivity to L is closely associated with the rupture micromechanisms involved.
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New Ring Specimen Geometries for Determining the Failure Locus of Tubulars
Journal of Pressure Vessel Technology, 2017Co-Authors: Mohamed Al-khaled, Imad BarsoumAbstract: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 at 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 Lode parameter. The ASME-BPVC local Failure criterion showed close agreement with experimental results (EXP).
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An Experimental Setup for Determining the Failure Locus of ASME Tubular Pressure Vessel Steel Grades
Volume 5: High-Pressure Technology; ASME Nondestructive Evaluation Diagnosis and Prognosis Division (NDPD); SPC Track for Senate, 2017Co-Authors: M. A. Al Khaled, Imad BarsoumAbstract: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 levels. 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.
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Constitutive model and Failure Locus of a polypropylene grade used in offshore intake pipes
Polymer Testing, 2017Co-Authors: D. Yurindatama, Imad BarsoumAbstract:Abstract BorECO®™ BA212E is a polypropylene block co-polymer which has become a common material in the manufacturing of large diameter non-pressurized gravity offshore intake pipelines. These lines are used for transportation of sea water for cooling of petrochemical process plants. The pipe sections are joined by butt heat fusion welding to create the pipeline. Recently a few premature Failures of such pipelines have been reported in the field. Hence, there is a need to characterize the constitutive behavior of the pipe and weld material in order to properly design these pipes. The aim of this work is to determine the material constitutive behaviors of the pipe material and the welded joint material. Uniaxial tensile tests of both the pipe and weld joint material are conducted at various strain rates. Both the pipe and weld material show a rather high strain rate dependency, with the weld material having about half the yield strength than that of the pipe material. An analytical constitutive material model is developed for both the pipe and weld material, incorporating the effect of strain rate. The Failure Locus, expressed in terms of the equivalent plastic strain at Failure vs. the stress triaxiality, for both materials is also determined as part of the constitutive model using notched dumbbell specimens. The constitutive model and Failure loci for the pipe and weld material are implemented in a finite element model (FEM) and are validated by conducting a series of independent four-point bend experiments on both material types. The validation is carried out by comparing the FEM results of the four-point bend model with the experimental results, which show a rather good agreement.
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Ring Specimen Geometry for Determining the Ductility of Tubulars
Volume 9: Mechanics of Solids Structures and Fluids; NDE Diagnosis and Prognosis, 2016Co-Authors: M. A. Al Khaled, Imad BarsoumAbstract: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.
Xuefeng Shu - One of the best experts on this subject based on the ideXlab platform.
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Impact Response of Aluminium Alloy Foams Under Complex Stress States
Latin American Journal of Solids and Structures, 2016Co-Authors: Zhiwei Zhou, Zhihua Wang, Xuefeng Shu, Longmao ZhaoAbstract:A series of dynamic tests were conducted on a closed-cell aluminum alloy foams in order to determine experimental Failure surface under impact loading conditions. Quasi-static tests have also been performed to investigate Failure mechanism under different stress paths. Three typical types of deformation modes can be observed, which corresponds to the different Failure mechanism. The Failure loci of the foam in principal stress plane are explored from quasi-static to dynamic loading conditions. A significant strength enhancement is identified experimentally. The expansion of the Failure Locus from the quasi-static to the dynamic test is almost isotropic. A modified Failure criterion for the metallic foam is proposed to predict Failure Locus as a function of strain rate. This rate-dependence Failure criterion is capable of giving a good description of the biaxial Failure stresses over a wide range of the strain rates.
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Quasi-static Failure behaviour of PMMA under combined shear–compression loading
Polymer Testing, 2015Co-Authors: Tao Jin, Zhiwei Zhou, Zhihua Wang, Zhenguo Liu, Xuefeng ShuAbstract:Abstract Quasi-static shear–compression tests were conducted on polymethyl methacrylate (PMMA) polymer specimens using a universal materials testing machine to investigate their Failure behaviour under quasi-static multi-axial loading. Instead of using confining pressure, cylindrical specimens with bevelled ends of different angles (5°, 10°, 15°, 20°, 25° and 30°) were used to generate different shear stresses. In addition, a cylindrical specimen with no bevelled ends and a hat specimen of PMMA were applied in the quasi-static shear–compression tests to determine the compression and shear strengths of PMMA, respectively. Experimental results show that the Failure force of PMMA decreased as the tilt angle of the specimen increased. Furthermore, the Failure Locus of the material can be predicted using a macroscopic Failure criterion with an elliptical shape. The deformation modes of each type of PMMA specimen under quasi-static loading were determined.
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Shear-compression Failure behavior of PMMA at different loading rates
Materials Letters, 2013Co-Authors: Zhiwei Zhou, Zhihua Wang, Xuefeng Shu, Longmao ZhaoAbstract:Three different types of tests, i.e. uniaxial compression, shear and combined shear-compression have been conducted on PMMA (polymethyl methacrylate) at different loading rates in order to investigate its Failure behavior under different loading conditions. The experiment results show that the material exhibits the rate-dependent Failure and post-Failure behavior. Macroscopic Failure loci of PMMA were was determined experimentally in the shear-normal stress space. Further, a macroscopic Failure criterion was proposed to predict the material's Failure Locus as a function of the loading rate. The capability of the Failure criterion was examined by simulating the Failure behavior of the material at different load rates. The simulation results revealed very good agreement between the experimental data and the responses determined from the proposed Failure criterion.
Tomasz Wierzbicki - One of the best experts on this subject based on the ideXlab platform.
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Crush behavior of thin-walled prismatic columns under combined bending and compression
Computers & Structures, 2001Co-Authors: Heung-soo Kim, Tomasz WierzbickiAbstract:Abstract The objective of this paper is to investigate the crushing response of thin-walled prismatic column under combined loading of compression and bending. Square cross-section beams with two different aspect ratios were subject to a prescribed translational and rotational displacement rate. The nonlinear explicit FE code PAM-CRASH was used to generate the results. The initial and subsequent Failure loci representing interaction between sectional force and moment were constructed from the numerical results. Also analytical solution of the same problem was derived. Shanley nonlinear spring model was used in conjunction with the concept of `superbeam' element to model the generalized plastic hinge. It was shown that the general characteristics of Failure Locus calculated analytically and numerically are quite similar. The present finding can be used to better interpret results of FE calculations of automotive bodies and to develop simplified crash-oriented design tools.
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biaxial bending collapse of thin walled beams filled partially or fully with aluminium foam
International Journal of Crashworthiness, 2000Co-Authors: Tomasz WierzbickiAbstract:Abstract The objective of this paper is the analysis of large planar and biaxial bending rotation response of thin-walled beams with square cross-section filled partially or fully with aluminium foam. The beams were subjected to the cantilever bending, and the characteristics of moment-rotation response were investigated varying the length of foam-filling, the orientation angle, and the adhesive strength. A general purpose nonlinear FE code Pam-Crash was used to generate results. It was shown that the aluminium foam filler retards inward sectional collapse of thin-walled column so that the multiple folds are formed increasing the bending resistance considerably. The initial and subsequent shrinking of Failure Locus were constructed, and the normality rule was checked for the partially or fully foam-filled columns in biaxial bending collapse.
Carlos Gonzalez - One of the best experts on this subject based on the ideXlab platform.
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a numerical study of the influence of microvoids in the transverse mechanical response of unidirectional composites
Composites Science and Technology, 2014Co-Authors: Danial Ashouri Vajari, Carlos Gonzalez, J Llorca, Brian Nyvang LegarthAbstract:Abstract The effect of porosity on the transverse mechanical properties of unidirectional fiber-reinforced composites is studied by means of computational micromechanics. The composite behavior is simulated by the finite element analysis of a representative volume element of the composite microstructure in which the random distribution of fibers and the voids are explicitly included. Two types of voids – interfiber voids and matrix voids – were included in the microstructure and the actual damage mechanisms in the composite, namely matrix and interface Failure, were accounted for. It was found that porosity (in the range 1–5%) led to a large reduction in the transverse strength and the influence of both types of voids in the onset and propagation of damage throughout the microstructure was studied under transverse tension and compression. Finally, the Failure Locus of the composite lamina under transverse tension/compression and out-of-plane shear was obtained by means of computational micromechanics and compared with the predictions of Puck’s model and with experimental data available in the literature. The results show that the strength of composites is significantly reduced by the presence of voids.
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Failure Locus of polypropylene nonwoven fabrics under in-plane biaxial deformation
Comptes Rendus Mécanique, 2012Co-Authors: Alvaro Ridruejo, Carlos Gonzalez, J LlorcaAbstract:Abstract The Failure Locus, the characteristics of the stress–strain curve and the damage localization patterns were analyzed in a polypropylene nonwoven fabric under in-plane biaxial deformation. The analysis was carried out by means of a homogenization model developed within the context of the finite element method. It provides the constitutive response for a mesodomain of the fabric corresponding to the area associated to a finite element and takes into account the main deformation and damage mechanisms experimentally observed. It was found that the Failure Locus in the stress space was accurately predicted by the Von Mises criterion and Failure took place by the localization of damage into a crack perpendicular to the main loading axis.
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influence of the loading path on the strength of fiber reinforced composites subjected to transverse compression and shear
International Journal of Solids and Structures, 2008Co-Authors: Essam Totry, Carlos Gonzalez, J LlorcaAbstract:The influence of the loading path on the Failure Locus of a composite lamina subjected to transverse compression and out-of-plane shear is analyzed through computational micromechanics. This is carried out using the finite element simulation of a representative volume element of the microstructure, which takes into account explicitly fiber and matrix spatial distribution within the lamina. In addition, the actual Failure mechanisms (plastic deformation of the matrix and interface decohesion) are included in the simulations through the corresponding constitutive models. Two different interface strength values were chosen to explore the limiting cases of composites with strong or weak interfaces. It was found that Failure Locus was independent of the loading path for the three cases analyzed (pseudo-radial, compression followed by shear and shear followed by compression) in the composites with strong and weak interfaces. This result was attributed to the fact that the dominant Failure mechanism in each material was the same in transverse compression and in shear. Failure is also controlled by the same mechanisms under a combination of both stresses and the Failure Locus depended mainly on the magnitude of the stresses that trigger fracture rather than in the loading path to reach the critical condition.
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Prediction of the Failure Locus of C/PEEK composites under transverse compression and longitudinal shear through computational micromechanics
Composites Science and Technology, 2008Co-Authors: Essam Totry, Carlos Gonzalez, J LlorcaAbstract:The potential of computational micromechanics to predict the Failure Locus of a unidirectional C/PEEK composite subjected to transverse compression and longitudinal shear was established. Numerical simulations were compared with the experimental results of Vogler and Kyriakides [Vogler TJ, Kyriakides S. Inelastic behavior of an AS4/PEEK composite under combined transverse compression and shear. Part I: Experiments. Int J Plasticity 1999;15:783–806], which contain detailed information of the matrix and fiber properties as well as the Failure micromechanisms during multiaxial loading. Analyses were based in the finite element analysis of a three-dimensional representative volume element of the lamina microstructure and included the main deformation and Failure mechanisms observed experimentally, namely matrix shear yielding and interface decohesion. In addition, the numerical predictions of the Failure Locus for composites with strong and weak interfaces were compared with those obtained by current phenomenological Failure models to establish the accuracy and range of validity of these criteria
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Failure Locus of fiber-reinforced composites under transverse compression and out-of-plane shear
Composites Science and Technology, 2007Co-Authors: Essam Totry, Carlos Gonzalez, J LlorcaAbstract:The Failure Locus a fiber-reinforced composite lamina, made up of 50 vol.% of carbon fibers embedded in an epoxy matrix, is computed under transverse compression and out-of-plane shear, a stress state whose experimental reproduction is highly complex. The mechanical response was obtained by the finite element method of a representative volume element of the lamina, which explicitly takes into account the fibers and the matrix in the lamina. The actual deformation and Failure mechanisms experimentally observed in the matrix, fibers and interfaces were included in the simulations through the appropriate constitutive equations. Two sets of simulations were performed, assuming that the fiber/matrix interface was either strong or weak. The corresponding Failure loci were compared with those given by three Failure criteria for composites (Hashin, Puck and LaRC) which provide reasonable predictions in other multiaxial stress states. The estimations of the Failure criteria were largely consistent with the numerical simulations in the composites with a strong interface but overestimated the composite strength when the interface was weak because the effect of interface decohesion (which becomes dominant) was not taken into account. These results point out the need to include interface fracture in the Failure criteria for composites.
