Numerical analysis of stress intensity factor and t-stress in pipeline of steel p264gh submitted to loading conditions

Stress singularities occur at crack tips, corners and material interfaces. The stress intensi-ty factors and T-stresses are coefficients of structural components where the active stress singular and first regular stress terms, respectively, are denoted by William's eigen function expansion series. A finite element analysis by CASTEM 2000 have been undertaken in order to determine the evolution of the T-stress and stress intensity factor terms in mode I for an arc of pipeline specimens with an external surface crack. A stress difference method described by Moustabchir et al. (2012) are adapted and, in the following step, the volumetric method is then embedded to compute the SIFs and T-stress near the crack tip. Different crack geometries combined with different length-to-thickness ratios are examined for the T-stress and stress-intensity factor. The revisited stress difference method employed here shows to be an accurate and robust scheme for evaluating the T-stress/SIFs in an arc of the pipeline

An extended finite element method (XFEM) study on the elastic T-stress evaluations for a notch in a pipe steel exposed to internal pressure

The work investigates the importance of the K-T approach in the modelling of pressure cracked structures. T-stress is the constant in the second term of the Williams expression; it is often negligible, but recent literature has shown that there are cases where T-stress plays the role of opening the crack, also T-stress improves elastic modeling at the point of crack. In this research study, the most important effects of the T-stress are collected and analyzed. A numerical analysis was carried out by the extended finite element method (X-FEM) to analyze T-stress in an arc with external notch under internal pressure. The different stress method (SDM) is employed to calculate T-stress. Moreover, the influence of the geometry of the notch on the biaxiality is also examined. The biaxiality gave us a view on the initiation of the crack. The results are extended with a comparison to previous literature to validate the promising investigations

Etude comparative et caractérisations mécaniques des structures sandwichs multicouches

The development of modern technologies requires that one use materials presenting high mechanical properties specific to their employment,but whose densities are low. The composite materials are materials which fulfil the preceding requirements. Because of their interest, the composite materials were initially used in aerospace, automotive, and construction industries. In composites, a class of particular interest ragarding the possibilities of design and development concern the sandwich structures resulting from a general assembly of a skin material with high stiffness and core materials of low density. The final properties of the materials are directly derived to the industry, many developments and studies in recent years have been aimed at optimizing the ratio mechanical performance over density. This thesis was undertaken with the same objective, but by having a strategy of optimization being focused more particulary on core materials. Our process is to reconsider in its entirety core materials and to propose a new concept of core complex which rests on the material stacking of different nature according to a quite precise sequence. The experimental results are correlated with those obtained by a theoretical approach based on a finite element methodLe développement des technologies modernes exige que l'on utilise des matériaux présentant des propriétés mécaniques élevées spécifiques à leur emploi mais dont les masses volumiques soient faibles. Les matériaux composites sont des matériaux qui répondent aux exigences précédentes. En raison de leur intérêt, les matériaux composites ont d'abord été utilisés dans nombreux secteurs d'activité (aérospatiale, automobile, construction, etc.). Dans les matériaux composites, une catégorie nous intéresse plus particulièrement de part ses possibilités de conception et de développement : les structures composites qui résultent d'une manière générale de l'assemblage d'un matériau de peau présentant une grande rigidité et d'un matériau d'âme de faible densité. Ces matériaux montrent un rapport performances mécaniques/densité très intéressant comparé à des matériaux plus classiques. Les propriétés finales de ce type de matériau sont directement dépendantes des propriétés constituantes et de la qualité de leur assemblage. Afin d'apporter des solutions aux industriels, de nombreux développements et études au cours de ces dernières années ont eu pour but l'optimisation du rapport performance mécanique/densité. Ce travail de thèse a été entrepris avec le même objectif, mais en ayant une stratégie d'optimisation se focalisant plus particulièrement sur le matériau d'âme. Notre démarche est de repenser dans son intégralité le matériau d'âme et de proposer un nouveau concept d'âme complexe qui repose sur l'empilement de matériaux de natures différentes suivant une séquence bien précise, Les résultats expérimentaux obtenus sont confrontés à une approche théorique basée sur une méthode d'éléments fini

Comparative study and mechanical characterisation of multi-layer sandwich structures

Le développement des technologies modernes exige que l'on utilise des matériaux présentant des propriétés mécaniques élevées spécifiques à leur emploi mais dont les masses volumiques soient faibles. Les matériaux composites sont des matériaux qui répondent aux exigences précédentes. En raison de leur intérêt, les matériaux composites ont d'abord été utilisés dans nombreux secteurs d'activité (aérospatiale, automobile, construction, etc.). Dans les matériaux composites, une catégorie nous intéresse plus particulièrement de part ses possibilités de conception et de développement : les structures composites qui résultent d'une manière générale de l'assemblage d'un matériau de peau présentant une grande rigidité et d'un matériau d'âme de faible densité. Ces matériaux montrent un rapport performances mécaniques/densité très intéressant comparé à des matériaux plus classiques. Les propriétés finales de ce type de matériau sont directement dépendantes des propriétés constituantes et de la qualité de leur assemblage. Afin d'apporter des solutions aux industriels, de nombreux développements et études au cours de ces dernières années ont eu pour but l'optimisation du rapport performance mécanique/densité. Ce travail de thèse a été entrepris avec le même objectif, mais en ayant une stratégie d'optimisation se focalisant plus particulièrement sur le matériau d'âme. Notre démarche est de repenser dans son intégralité le matériau d'âme et de proposer un nouveau concept d'âme complexe qui repose sur l'empilement de matériaux de natures différentes suivant une séquence bien précise, Les résultats expérimentaux obtenus sont confrontés à une approche théorique basée sur une méthode d'éléments finisThe development of modern technologies requires that one use materials presenting high mechanical properties specific to their employment,but whose densities are low. The composite materials are materials which fulfil the preceding requirements. Because of their interest, the composite materials were initially used in aerospace, automotive, and construction industries. In composites, a class of particular interest ragarding the possibilities of design and development concern the sandwich structures resulting from a general assembly of a skin material with high stiffness and core materials of low density. The final properties of the materials are directly derived to the industry, many developments and studies in recent years have been aimed at optimizing the ratio mechanical performance over density. This thesis was undertaken with the same objective, but by having a strategy of optimization being focused more particulary on core materials. Our process is to reconsider in its entirety core materials and to propose a new concept of core complex which rests on the material stacking of different nature according to a quite precise sequence. The experimental results are correlated with those obtained by a theoretical approach based on a finite element metho

Etude comparative et caractérisations mécaniques des structures sandwichs multicouches

Le développement des technologies modernes exige que l'on utilise des matériaux présentant des propriétés mécaniques élevées spécifiques à leur emploi mais dont les masses volumiques soient faibles. Les matériaux composites sont des matériaux qui répondent aux exigences précédentes. En raison de leur intérêt, les matériaux composites ont d'abord été utilisés dans nombreux secteurs d'activité (aérospatiale, automobile, construction, etc.). Dans les matériaux composites, une catégorie nous intéresse plus particulièrement de part ses possibilités de conception et de développement : les structures composites qui résultent d'une manière générale de l'assemblage d'un matériau de peau présentant une grande rigidité et d'un matériau d'âme de faible densité. Ces matériaux montrent un rapport performances mécaniques/densité très intéressant comparé à des matériaux plus classiques. Les propriétés finales de ce type de matériau sont directement dépendantes des propriétés constituantes et de la qualité de leur assemblage. Afin d'apporter des solutions aux industriels, de nombreux développements et études au cours de ces dernières années ont eu pour but l'optimisation du rapport performance mécanique/densité. Ce travail de thèse a été entrepris avec le même objectif, mais en ayant une stratégie d'optimisation se focalisant plus particulièrement sur le matériau d'âme. Notre démarche est de repenser dans son intégralité le matériau d'âme et de proposer un nouveau concept d'âme complexe qui repose sur l'empilement de matériaux de natures différentes suivant une séquence bien précise, Les résultats expérimentaux obtenus sont confrontés à une approche théorique basée sur une méthode d'éléments finisThe development of modern technologies requires that one use materials presenting high mechanical properties specific to their employment,but whose densities are low. The composite materials are materials which fulfil the preceding requirements. Because of their interest, the composite materials were initially used in aerospace, automotive, and construction industries. In composites, a class of particular interest ragarding the possibilities of design and development concern the sandwich structures resulting from a general assembly of a skin material with high stiffness and core materials of low density. The final properties of the materials are directly derived to the industry, many developments and studies in recent years have been aimed at optimizing the ratio mechanical performance over density. This thesis was undertaken with the same objective, but by having a strategy of optimization being focused more particulary on core materials. Our process is to reconsider in its entirety core materials and to propose a new concept of core complex which rests on the material stacking of different nature according to a quite precise sequence. The experimental results are correlated with those obtained by a theoretical approach based on a finite element methodMETZ-SCD (574632105) / SudocSudocFranceF

Dynamical characterisation and damage mechanisms of E-glass/vinylester woven composites at high strain rates compression

International audienceWithin the EUCLID project, ‘Survivability, Durability and Performance of Naval Composite Structures’, one task is to develop improved fibre composite joints for naval ship superstructures. In many practical situations, the structures are subjected to loading at very high strain rates like slamming, impact, underwater explosions or blast effect. Material and structural response vary significantly under such loading as compared to static loading. In this paper, the results from a series of Split Hopkinson Pressure Bar tests on the woven composites are presented. These tests were done in two configurations: in-plane and out-of-plan compression test. It is observed that the failure strength varies with the different loading directions. The results indicate that the stress–strain curves, maximum engineering stresses and strains evolve as strain rate changes. The woven composites have higher values of engineering stress and dynamic stiffness for in-plane than for out-of-plane compression at the same strain rate; however, the in-plane strain at maximum stress is higher than that of out-of-plane compression. During the experiments, a high speed camera was used to determine the damage mechanisms. The specimens are mainly damaged in a crushing and shear failure mode under out-of-plane loading, as for in-plane test, the failure was dominated by fibre buckling and delamination

Mechanical behavior and damage kinetics of woven E-glass/vinylester laminate composites under high strain rate dynamic compressive loading: Experimental and numerical investigation

International audienceSplit Hopkinson pressure bar (SHPB) is one of the most important and recognized apparatus used for characterizing the dynamic behavior of materials. In the first part of this study, the results from a series of SHPB tests on the woven composites are presented in this paper. The compressive material properties are determined by testing the [0°/90°]26 laminate systems from low to high strain rates. Samples of cubic geometry are tested in in-plane and out-of-plane direction. Preliminary compressive stress–strain vs. strain rates data obtained show that the dynamic material strength increases with increasing strain rates. The tests show a strong material sensitivity to dynamic loading. For in-plane tests, there is a transitional strain rate, reflecting the dependencies on strain rate observed in experiments. The results indicate that the stress–strain curves, maximum compressive stresses and strains evolve as strain rate changes. During the experiments, a high speed camera was used to determine the kinetics of damage. The specimens are mainly damaged in a crushing and shear failure mode under out-of-plane loading, as for in-plane test, the failure was dominated by fiber buckling and delamination. In the second part of this study, numerical models without damage are developed to investigate the validity of assumptions of compression Split-Hopkinson Pressure Bar technique. Abaqus software was used for the numerical simulation. The results obtained by numerical investigation of SHPB are compared with the in-plane and out-of-plane compression test of a woven composite. A good correlation was noted between the experimental and numerical results, which allows validate the numerical approach

Investigation of Thermal and Mechanical Properties of Three-Dimensional Braided Composite Materials

This paper investigates the thermal and mechanical properties of a composite made from a combination of 2063-epoxy resin and three different braided carbon-fiber fabric reinforcements. These fibres consist of HTS carbon, HTS carbon braided with nickel coated carbon and HTS carbon braided with nickel coated copper, respectively. The composites were manufactured through resin transfer molding (RTM) route. The thermal diffusivity of carbon fibers composites was measured at different temperature by using a flash method. The transverse and planar thermal conductivities were determined by measuring the specific heat, density and thermal diffusivities, respectively. The current research highlights the influence of adding nickel coated carbon and nickel-plated copper wires on the braided composites. The evaluation shows that the HTS carbon braided manufactured with nickel-plated copper wires presents higher in-plane thermal conductivity (in direction parallel of the fibres) when comparing to HTS carbon and HTS carbon braided manufactured with nickel coated carbon. The thermal conductivity benefits of those composite were achieved at the expenses of lower mechanical properties of braided composites investigated

Comparative study of mechanical properties and damage kinetics of two- and three-dimensional woven composites under high-strain rate dynamic compressive loading

International audienceThe in-plane compressive behavior of two- and three-dimensional woven composite was investigated at high strain rates. The Split Hopkinson Pressure Bar is employed to test the high strain rate dynamic mechanical properties of E-glass vinylester composite material. For three-dimensional woven composite, two configurations were tested: compression responses along the stitched direction and orthogonal to the stitched direction. Dynamic compression properties for two- and three-dimensional are determined and compared. Experimental results show that the strain rate has a significant effect on the two- and three-dimensional woven composite response. It is observed that the three-dimensional woven composite has higher compression strength and dynamic modulus than the two-dimensional composite at high strain rate. For this study, a high-speed camera was used to determine the damage kinetics under dynamic load. The two-dimensional woven composite is mainly damaged in a mode of matrix cracks and severe delamination, while the mode for three-dimensional woven composite is mainly cracking of matrix and delamination for in-plane along to the stitched direction and shear banding failure for in-plane orthogonal to the stitched direction

Characterization of Fracture Toughness Properties of Aluminium Alloy for Pipelines

Continuous critical loading of pressure equipments can affect the structural stability of these plants. The structural stability and mechanical resistance under pressure loads can also be affected by defects. Fracture mechanics assumptions were applied to aluminium alloys to study their effect on its mechanical behaviours. A 3-point bending standard test was employed and the critical Stress Intensity Factor, K (SIF) in mode I was determined in order to provide a quantitative/qualitative evaluation of the performance. Additional experiments were carried out to validate the numerical results gained from the Finite Element Method (FEM) and the Extended Finite Element Method (X-FEM). The crack propagation process is discussed in this study focussing on the effect of crack tip radius