Abdelouahed Laksimi

Modelling of damage and failure of glass/epoxy composite plates subject to impact fatigue

An investigation has been carried out to study the impact fatigue damage of glass/epoxy laminated composites. Accumulation of damage, such as matrix cracking, delamination and fibre breakage, with repeated impact of the composite material may reduce the overall stiffness. These damage modes have been combined in a very complicated way to describe damage growth and fracture. A model is proposed for characterising the damage as a function of the normalised impact number. The scalar variable D, which characterises the material damage, is written as a function of the life duration β, using a modified form of the Mankowsky empirical law [Int J Solids Struct 32(11) (1995) 1607]. The macroscopic failure mode and the internal damage in laminated specimens of glass/epoxy as a consequence of impact fatigue are analysed at different levels of incident impact energy. The impact fatigue tests have been conducted on an apparatus built in our laboratory.

Investigation of failure mechanisms in WC–Co coated materials

Abstract WC–Co coated materials are increasingly used in aeronautical applications. The objective of the present study was to develop and validate a method for the characterisation of damage in coated material using a technique involving simultaneous use of both acoustic emission (AE) and scanning electron microscopy observations. Four point bending tests in association with in situ AE were conducted on WC–Co coated specimens prepared with high velocity oxy-fuel technology. Observation of the samples under a microscope shows two types of cracks: transverse cracks, which are regularly spaced on the surface of the coating and interfacial cracks. AE results for these tests were also investigated in terms of amplitude, hits, absolute energy and position of the event. These results show two different types of acoustic event in terms of absolute energy and amplitude. A transverse cracking model within a coating is then presented. This model is obtained by use of the integral equation method.

Damage analysis and the fibre–matrix effect in polypropylene reinforced by short glass fibres above glass transition temperature

Abstract In this paper an experimental and theoretic study of the influence of the fibre–matrix interface on the damage of the polypropylene reinforced with 40% in mass of short glass fibres is described. Tensile tests show the existence of several zones of behaviour, which are linear, non-linear without damage and non-linear with damage for material with treated and untreated short glass fibres. Creep tests with damage were carried out on each material. The number of acoustic emission events characterizing each damage mechanism, is more significant for the material with treated fibres. Also, the kinetics of damage is more pronounced in the first phase of damage for material with untreated fibres.

Caractérisation par émission acoustique de l'adhérence et de l'endommagement d'un revêtement : cas d'un revêtement WC-Co sur acier

Abstract This note presents a characterization method of the ‘adhesion’ of a coating by acoustic emission technique. In situ acoustic emission measurements which were investigated in terms of amplitude, absolute energy, position of the event, etc. were performed on WC–Co coated specimens prepared by HVOF (high velocity oxy fuel) during four-point bending tests. The microscopic observations of the specimens show two types of cracks: transversal cracks (regularly spaced on the coating surface) and interfacial cracks. Acoustic emission results show two different types of acoustic events in terms of absolute energy and amplitude, which are representative of two cracking mechanisms.

Acoustic Emission Analysis of Crack Growth in a Corrosion Product

In the chemical and petrochemical industry the storage tanks under operation are very often subjected to high mechanical stress, fatigue stress, aging and corrosion phenomena reducing their lifespan. Corrosion phenomena related to the aggressiveness of the stored chemical products is often the origin of leaks in this kind of structures. The controls of corrosion activity are required for the maintenance of storage tanks. Various non destructive testing techniques can be used. The most common method consists to empty the tank, to clean it and finally to sand its floor and walls. Thereafter, a visual inspection can be carried out and a control with non destructive methods, such as MFL (Magnetic Flux Leakage), can be performed. The cost of this operation varies according to the size of the storage tank and the possible production breakdown. Acoustic emission technique has major advantages compared to the traditional NDT methods. It’s a global technique which can be applied on line without significant immobilization of the structure. The aim of this work is to analyse the acoustic emission generated by a crack growth in corrosion product and to identify the signature of the AE produced by different damage mechanisms: microcrack, crack growth, coalescences. To carry out this experimental investigation, three point bending tests have been performed using samples taken from a corroded flat bottomed crude oil storage tank.