K. Madani

Elastic-plastic analysis of interaction between an interface and crack in bi-materials

The objective of the present work is to investigate the interaction between interfaces and cracks in metal/alumina bi-materials. The behaviour is analyzed by the determination of the J integral and the plastic zone at the crack tip using the finite-element methods. Different orientations of the crack according to the bi-materials interface were examined such as cracks parallel and perpendicular to the interface and inclined cracks. The effects of the mechanical properties of the joint materials, the crack length and the metal thickness on the extent of plastic zone and the J integral at the crack tip were also highlighted. The obtained results allow us to deduce mathematical relations giving the variation of the J integral and the plastic zone according to the crack position.

Effect of composite hygrothermal aging on the SIF variation in bonded composite repair of aircraft structures

In this study, the finite element method is used to analyze the effect of hygrothermal aging of composite on the stress intensity factor variation for the crack repaired with bonded composite patch. The obtained results show that moisture absorption has a negative effect on the repair performance. Indeed, the stress intensity factor increases with an increase in the water absorption in both mode I and mixed mode of crack propagation. The fatigue life of the repaired structures decreases with the increase in water absorption by the composite patch.

Hygrothermal ageing effect of ADEKIT A140 adhesive on the J-integral of a plate repaired by composite patch

Abstract The effect of an hygrothermal ageing on the mechanical behavior of the bulk adhesive ‘Adekit A140 epoxy’ was investigated. The bulk test specimens of the adhesive were immersed in distilled water at various temperatures (20, 40 and 60 °C). Under these conditions, the tensile properties were determined and used in a numerical study about the behavior of bonded assemblies allowing to calculate the J-Integral. The obtained results illustrate the variation of the mechanical behavior of bulk adhesive depending on the immersion time and environmental temperature. The presence of water in the adhesive decreases the tensile strength and the elastic modulus but also increases the ductility of material. These changes in mechanical properties are more important when the percentage of water absorbed increases. The temperature increases the amount of absorbed water in the adhesive, consequently increases the degradation kinetics with the immersion time and directly affect the load transfer rate of the damaged area to the composite patch and therefore the value of the integral J.

Experiments Method Design Applied to Optimization of Patch Repairs for Cracked Plates

The optimization of the patch shape of bonded composite repair in aircraft structures is an efficient way to improve the repair performance. In this study the three-dimensional nonlinear finite element method is used to determine the J integral variation along the front of repaired crack with bonded composite patch in aircraft structures. The experimental design method was applied to optimize the patch shape and size in order to determine the most influencing dimension on the repair efficiency.

Effects of the composite and adhesive aging on the plasticity in bonded composite repair

In this study, the effects of hygrothermal aging of composite patches and adhesives on the plasticity ahead of repaired crack with bonded composite patch were analyzed. The finite element method was used to compute the size and the shape of the plastic zone for cracks repaired with bonded hygrothermal aged composite patches and adhesives. The obtained results show that moisture absorption has a negative effect on the repair performance. Indeed, the size of plastic zone increases with an increase in the rate of water absorption whether in composite patches or in adhesives. The reduction of the composite patches and adhesive strength by the water absorption leads to a reduction of the repair performances.