Study of the response of CFRP composite laminates to a laser-induced shock

Laser-induced shock yields to a local tensile stress within a sample. This high strain rate stress can be used to verify the bond strength between two layers. This method has been applied to Carbon Fibre Reinforced Polymer (CFRP) composite laminates, involved in aeronautic or defense industry. Experiments have been carried out on high power laser facility in the nanosecond regime. A velocimetry interferometer has been used to record the material velocity at the back surface of the samples. This study provides a comprehensive approach of the response of CFRP laminates of different thicknesses to a shock load normal to the fibres direction. The stress waves generation and propagation within the laminate and the induced delamination are key issues of this work. The main result is the ability of the technique to evaluate the out-of-plane strength of these laminate

Shock adhesion test for composite bonded assembly using a high pulsed power generator

In a context of the rising use of composite assemblies in aeronautic or defense fields, the assessment of their strength is a key issue. The method developed in this study attempts to provide solutions. A shock adhesion test based on short compressive loads, obtained by a high pulsed power generator, is proposed as a proof test to ensure the quality of composite bonded assemblies. A calibrated load induces a local tensile stress able to damage the bond interface. The high pulsed power source is the GEnerateur de Pression Isentropique device (Isentropic Pressure Generator), used to generate the required stresses, with a 450 ns pulse duration to test assemblies above the mm thickness range. The understanding of the mechanisms of wave propagation and tensile stress generation within these multilayer assemblies are scientific challenges. The ability of the technique to induce a tensile stress able to disbond the laminates and the assemblies is demonstrated. This paper details the response of carbon epoxy laminates and their bonded assemblies to a shock loading near the damage threshold

Modelling of interaction between a snow mantle and a flexible structure using a discrete element method

International audienceThe search of improvement of protective techniques against natural phenomena such as snow avalanches continues to use classic methods for calculating flexible structures. This paper deals with a new method to design avalanche protection nets. This method is based on a coupled analysis of both net structure and snow mantle by using a Discrete Element Method. This has led to the development of computational software so that avalanche nets can be easily designed. This tool gives the evolution of the forces acting in several parts of the work as a function of the snow situation

Hierarchical Segmentation of Polarimetric SAR Images Using Heterogeneous Clutter Models

International audienceIn this paper, heterogeneous clutter models are used to describe polarimetric synthetic aperture radar (PolSAR) data. The KummerU distribution is introduced to model the PolSAR clutter. Then, a detailed analysis is carried out to evaluate the potential of this new multivariate distribution. It is implemented in a hierarchical maximum likelihood segmentation algorithm. The segmentation results are shown on both synthetic and high-resolution PolSAR data at the X- and L-bands. Finally, some methods are examined to determine automatically the "optimal" number of segments in the final partition