Local damage in a 5-harness satin weave composite under static tension, part II: meso-FE modelling

International audienceThis study forms the second part of a paper on the local damage analysis in a thermo-plastic 5-harness satin weave composite under uni-axial static tensile load. The experimental observations of Part I are confronted with the meso-FE simulations. Part II describes the following steps regarding the unit cell meso-FE modeling starting from: 1) Construction of the unit cell geometrical model; 2) Estimation of the homogenized elastic constants of the unit cell using different boundary conditions; 3) Evaluation of the local stress and damage behavior of the unit cell using meso-FE simulations. The aim of the numerical analysis is to investigate the dependency of local ply stress and damage profiles on the adjacent layers of the laminate

Endovascular Treatment of the Descending Thoracic Aorta

AbstractObjectives: to report our initial experience with endovascular stent graft repair of a variety of thoracic aortic pathology.Design: retrospective single center study.Material and methods: between February 2000 and January 2002, endovascular stent graft repair was performed in 26 patients: traumatic aortic isthmus rupture (n=3), Type B dissection (n=11) and descending thoracic aortic aneurysm (n=12). The deployed stent graft systems were AneuRx-Medtronic (n=1), Talent-Medtronic (n=13) and Excluder-Gore (n=12).Results: successful deployment of the stent grafts in the intended position was achieved in all patients. No hospital mortality neither paraplegia were observed. Late, non procedure related, death occurred in four patients (15%). Access artery complications with rupture of the iliac artery occurred in two patients and were managed by iliac-femoral bypass. The left subclavian artery was overstented in seven patients (27%). Only the first patient received a carotido-subclavian bypass. The mean maximal aortic diameter decreased significantly in patients treated for descending thoracic aneurysm. Only one patient had an endoleak type II after 6 months without enlargement of the aneurysm. Complete thrombosis of the thoracic false lumen occurred in all but one patient treated for Type B dissection 6 months postoperatively. Two patients underwent a consecutive stent graft placement, due to a large re-entry tear distal to the first stent graft.Conclusions: endovascular stent graft repair for Type B dissection, descending thoracic aneurysm and aortic isthmus rupture is a promising less-invasive alternative to surgical repair. Further studies are mandatory to determine its long-term efficacy

A progressive damage model of textile composites on meso-scale using finite element method: static damage analysis

A meso-scale finite element model for static damage in textile composites was established. The impregnated yarn is taken as homogeneous and transverse isotropic material, whose mechanical properties are calculated using Chamis' equations. The damage modes are determined by using the Tsai-Wu criterion and additional criteria. The Murakami damage tensor is used to calculate the post-damage stiffness matrix. The model has been validated using plain weave and twill weave carbon-epoxy composites. The initiation of inter-fiber matrix cracks and fiber rupture were analyzed using this meso-FE model

Local damage in a 5-harness satin weave composite under static tension, part I: experimental analysis

International audienceThis paper presents an experimental damage analysis of a 5-harness satin weave carbon-PPS (PolyPhenylene Sulphide) composite under uni-axial static tensile load. In order to understand the local damage behaviour, tensile tests were performed and accompanied by acoustic emission (AE) and microscopic analysis of the composite specimen. These tests enable us to detect the damage initiation stress as well as the damage initiation location in the composite. Microscopic observation of the tested composite laminates allowed the characterization of the sequence of intra-yarn transverse damage (perpendicular to the load direction) occurrence at different locations in the laminate, starting from crack initiation to the final failure of the composite

On the nonlinear evolution of the Poisson’s ratio under quasi-static loading for a carbon fabricreinforced thermoplastic, Part I:

a b s t r a c t When observing or describing the damage state in a composite material, often only Young's modulus or residual deformation are considered. Generally, however, the Poisson's ratio is more sensitive to damage than those properties. Rather than observing the Poisson's ratio as function of crack density, the evolution of the Poisson's ratio as function of the longitudinal strain was studied in part I of this research, where a peculiar shape of the evolution was observed and proven to be entirely due to the material itself, rather than the sensors used for the strain measurement. In this article, a theoretical explanation for the peculiar evolution of the Poisson's ratio as function of the longitudinal strain is presented. Based on this explanation, extra experiments were conducted for validation purposes. The material used for this study is a carbon fabric-reinforced PPS

In-situ local strain measurement in textile composites with embedded optical fibre sensors

To understand the local strains inside a textile composite, numerical simulations are typically done on the scale of one repetitive unit cell of the weaving pattern. Periodic boundary conditions are applied to the edges of the unit cell and different load cases can then be applied to the unit cell of the textile composite. Most often, the periodic boundary conditions are applied on all faces of the unit cell, which implies the assumption that the material is repeating itself over an infinite distance in all three orthogonal directions. This assumption is more or less valid for the textile composite material in the midplane of thick laminates, where it is constrained by neighbouring material in all three directions. It is very difficult to validate such simulations, because local strain measurements inside a textile composite have rarely been done, and the interpretation is not straightforward. This paper shows the successful use of embedded optical fibre sensors to measure the local strains inside a satin weave carbon/PPS composite (typically used in aerospace applications). The length of the Bragg grating inside the optical fibre sensor has been chosen such that it is longer than the length of one unit cell of the satin weave architecture (7.4 mm). The read-outs of the optical fibre sensor give the minimum and maximum local strains that occur along the length of the Bragg grating

Local strain variation in the plies of a satin weave composite: experimental vs. numerical

Along with the advantages of multi directional load carrying capabilities, the complicated interlacing pattern of the yarns in a textile composite produce large stress – strain gradients. The stress-strain behavior in a textile composite is influenced by: a) stacking sequence; b) number of plies in the laminate; c) distance of the ply to the surface [1]. From the numerical perspective, the investigation of the free edge and free surface effects in a textile composite unit cell [2] reveals that the local stress behavior changes considerably depending upon the finite/ infinite conditions used for the unit cell FE analysis. In the above context, to capture the variation in local parameters such as strain and damage profiles at different locations (inside/surface) of the satin weave composite under the tensile load, experimental techniques such as strain mapping, Fibre Brag Grating sensors (FBG’s) and the microscopic analysis is used. For the numerical validation, different unit cell stacking models with appropriate boundary conditions are used for the FE analysis. Comparison of the numerical and experimental results (Table 1) provides valuable information regarding the local strain variation (from edge to the centre) in a satin weave composite (Figure 1). In the similar guide lines, local damage variation is also studied using different unit cell stacks

Damage signature of fatigued fabric reinforced plastics in the pulsed ultrasonic polar scan

This study investigates the use of both the amplitude and time-of-flight based pulsed ultrasonic polar scan (P-UPS) for the nondestructive detection and evaluation of fatigue damage in fiber reinforced composites. Several thermoplastic carbon fabric reinforced PPS specimens (CETEX), loaded under various fatigue conditions, have been scanned at multiple material spots according to the P-UPS technique in order to extract material degradation in a quantitative way. The P-UPS results indicate that shear dominated fatigued carbon/PPS goes with a reduction of shear properties combined with large fiber distortions. The P-UPS results of the tension-tension fatigued carbon/PPS samples on the other hand reveal a directional degradation of the stiffness properties, reaching a maximum reduction of -12.8% along the loading direction. The P-UPS extracted damage characteristics are fully supported by simulations, conventional destructive tests as well as visual inspection. The results demonstrate the excellent capability of the P-UPS method for nondestructively assessing and quantifying both shear-dominated and tension-tension fatigue damage in fabric reinforced plastics