Papers by Author: Mohamed Sahnoun

Abstract: Several analytical, numerical and experimental techniques are available to study the stress concentration around the notches. The stress distribution in a rectangular composite laminated plate with a central notch was studied using the finite element method. The objective of this study is to analyze the fibre orientation effect on the variation of stress concentrations at the notch root and the J-integral at the crack-tip emanating from this notch in a plate subjected to tensile loading. The results show that the anisotropic stress concentration factor can be higher or lower than that of a homogeneous material. The area of maximum normal and tangential stresses could shift with fibre orientation with respect to the loading axis. The interaction effect between a crack located on the ligament of the plate and the circular notch of radius is considered.The results indicate that fold sequence influences appreciably the acceleration or the retardation of the crack propagation.

Abstract: In this paper, the evaluation of the SIFof a macrocrack in interaction with one or several microcracks in a material containing a geometrical defect was investigated. Several configurations were considered in order to apprehend the mechanisms induced by the interaction effect and in particular the effects of reduction and/or amplification of the stress field between macro and single or multiple microcracks. The obtained results show that, macro–microcrack spacing is an important parameter if the microscopic crack is relatively close to the macrocrack-tip. The macrocrack has the tendency to accelerate as it propagates towards the microcrack. When the relative distance characterizing this spacing is higher than 0.3, the interaction effect can be neglected and the SIF remains unchanged for both defect types. When this ratio is lower than 0.3, the interaction between the two defects becomes significant and the stress intensity factor at the macrocrack tip strongly increases.

Abstract: Ceramic/metal bimaterials systems are increasingly used in industry owing to the synergetic association of opposite properties of the bonded materials. Discontinuity in these properties can result in crack initiation and stress concentration entailing the bimaterial system failure. A good understanding of damage mechanism at the metal/ceramic interface is crucial to the dimensioning of multilayered systems. In this work the finite element method is used to analyze the stress concentration effect in a linear interface and curved interface. The geometrical configuration of the interface has a great influence the stress concentration on distribution developed near or in the assembly interface. The effect of a circular notch on the behavior of an interfacial crack is highlighted. The results indicate that the interface generates normal and tangential stress concentration resondless of the assembly mechanical properties. The curved geometry of the interface strongly reduces stress concentration in comparison with the linear interface. The reduction is 90%.

Abstract: The real structures are of complex geometrical forms containing numerous zones of stress concentrations. These sites are characterized by weak sections due to the presence of notches which are the main causes of cracks initiation. The knowledge of the distribution of the stress field in the neighborhood of a notch is of an extreme importance for the analysis of the variation of the stress concentration factor with respect to the geometry of the notch. In this paper, the finite element method is used to study the effect of the existence of a microcrack on the behaviour of a notched structure. Then the behaviour of a crack emanating from the notch with the presence of the pre-existing crack is also investigated. It requires estimating the stress intensity factor at the crack tip, the length of the crack, the notch diameter and the angle between its bisecting line and the crack direction.

Abstract: In this study, an analysis of buckling was carried out on composite rectangular plates with and without circular notch by using the finite element method. The graphite/epoxy laminated plates were arranged antisymmetrically in the following ordered way [(θ/-θ)₂]_s. The buckling strength of the asymmetrical laminated plates subjected to uniaxial load is determined as a function of fiber orientation. The results show that whatever the notch radius, the buckling load is almost stable. The cumulated effect due to the presence of the longitudinal and transverse cracks as well as a circular notch reduces the buckling load considerably, which increases the risk of the fracture.