Analysis of a dry friction problem under small displacements: application to a bolted joint

This study presents an analysis of the problem of macroscopic contact of steel upon steel with dry friction, in the specific case of a bolted joint. The configurations of these types of joints result in very small displacements and interface sliding velocities. To understand how the system formed by the two surfaces in contact works, an experiment was carried out. The analysis of the results obtained made it possible to define the behavior of the system and to model the variations of the main parameters by original and continuous laws. These laws accurately correlate to all the results of the tests effectuated

Study of impact on helicopter blade

This article presents a study of damage in structures that are similar to helicopter blade sections, subjected to an impact. These complex composite structures were impacted by a steel ball of 125 g at impact speed ranging from 30 to 130 m/s. This led to properly highlight the kinematics of the impact and to define the sequence of the damage’s mechanisms. An explicit FE model is also presented. The damage modelling of the roving is performed through a scale change. It allows a good representation of observed experimental behaviour. As the mesh density is low, it can be used for the modelling of a real structure

Combined shear/compression structural testing of asymmetric sandwich structures

Asymmetric sandwich technology can be applied in the design of lightweight, non-pressurized aeronautical structures such as those of helicopters. A test rig of asymmetric sandwich structures subjected to compression/shear loads was designed, validated, and set up. It conforms to the standard certification procedure for composite aeronautical structures set out in the “test pyramid”, a multiscale approach. The static tests until failure showed asymmetric sandwich structures to be extremely resistant, which, in the case of the tested specimen shape, were characterized by the absence of buckling and failure compressive strains up to 10,000 μ strains. Specimens impacted with perforation damage were also tested, enabling the original phenomenon of crack propagation to be observed step-by-step. The results of the completed tests thus enable the concept to be validated, and justify the possibility of creating a much larger machine to overcome the drawbacks linked to the use of small specimens

Impacts on foam stabilised composite structures: Experimental and numerical study

A dropweight tester is used to make low velocity tests on specific sandwich type structures. Sandwich are made of glass-epoxy skin and polyurethane foam core. The skins can be straight or little curved, and impact direction is the global skin direction. The aim of these tests is to study the initiation of rupture in such structures: local buckling of skin and foam core rupture. Experimental results are given. They show the evolution of buckling critical stress in the skin when impact velocity increases. The rupture mode in curved skin specimen is also studied: rupture is no more provoked by buckling. A numerical analysis is proposed to model the behaviour of the structure and the rupture initiation. Finally, a method is developed, in order to predict the propagation of skin debonding during impact: an element layer under the skin is damaged with a specific law to simulate debonding

Stacking sequence optimization of composite tubes submitted to crushing using the discrete ply model

International audienceThe purpose of this study is to study the applicability of Discrete Ply Modeling (DPM) to crushing of composite tubes and to study the effect of stacking sequence and trigger geometry on the Specific Energy Absorption (SEA). The model was first validated with experimental results after which various stacking sequences were simulated to optimize it with an aim to increase the SEA.The stacking sequence [90/02/90/03/90/0/90] performed the best in terms of SEA value. As a result, the confidence of the DPM has been proven for some draping sequences but seems to be less confident to simulate the trigger effect

A comparison of three wood species (poplar, birch and oak) for crash application

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Discrete ply modelling of impact and compression after impact on composite laminates

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