Hocine Kebir

A new singular boundary element for crack problems Application to bolted joints

Abstract The present paper is concerned with the effective numerical implementation of the two-dimensional Dual Boundary Element Method to analyse the mixed-mode crack growth in bolted joints. All the boundaries are discretized with discontinuous quadratic boundary elements and the crack-tip is modeled by singular elements that exactly represent the strain field singularity 1/ r . The Stress Identity Factors can be computed very accurately from the crack opening displacement at collocation points extremely close to the crack tip. Furthermore, the analysis of two-dimensional elastic contact problems is developed, with an iterative procedure. The contact equations are written explicitly with both transactions and displacements retained as unknowns. The computed results show that the proposed approach for Stress Intensity Factors evaluation is simple, produces very accurate solutions and has little dependence on the size of the elements near the crack tip. The algorithm is applied to several two-dimensional examples and the results obtained are in very good agreement with analytical solutions and experimental results carried out at the AEROSPATIALE Research Centre.

Monte-Carlo simulations of life expectancy using the dual boundary element method

Abstract Ageing aircraft structures are susceptible to a very typical and dangerous form of fatigue damage named “multiple site damage”. An overall assessment method has been developed in order to improve the understanding of this phenomenon and to provide inspection programs. A full deterministic approach has been completed first. An automatic numerical process, using the dual boundary element method and fracture mechanics laws, computes the crack evolution until failure of the structure. Then, in order to take materials scatter into account, a probabilistic approach has been developed based on Monte-Carlo simulations. Initial cracks scenarios are randomly defined and cracks evolution is computed for each of them. Thus statistical results are provided. The results obtained are in good agreement with experimental tests carried out at the Aerospatiale Matra research center.

Simulation de la propagation de fissures dans les solides élastiques en modes mixtes par la méthode des équations intégrales duales

ABSTRACT The present paper is concerned with the effective numerical implementation of the two dimensional Dual Boundary element method to analyse the mixed-mode crack growth All the boundaries are discretized with discontinuous quadratic boundary elements and the crack-tip is modeled by singular elements that exactly represent the strain field singularity 1/√r The Stress Intensity Factors can be computed very accurately from the crack opening displacement at collocation points extremely close to the crack tip The algorithm is applied to several two dimensional examples and the results obtained are in very good agreement with experimental results.

Numerical Simulation of the Ductile Fracture Growth Using the Boundary Element Method

This work aims at simulating the ductile fracture phenomenon occurring in thin cracked structures thanks to the boundary element method. A process based on the dual integral formulation of the problem has been developed so as to solve elastoplastic cracked problems. Since this method provides accurate mechanical fields at the crack tip, the Rice and Tracey criterion for ductile fracture can be evaluated during the post-processing step. The validity of the method is at last addressed with the comparison between numerical and experimental results for a test on a CCT specimen.

Simulation of Forming Processes, with Friction, Coupling Finite Elements and Boundary Elements

Nowadays, the simulation of forming process is rather well integrated in the industrial numerical codes. However, in order to take into account the possible modifications of the tool during rates of working, a dedicated numerical software is currently developed within the Laboratory Roberval. This one more uses coupling finite elements and boundary elements for the respective modelling of the part and the tool. This software will more particularly allow the identification of the fatigue criteria of the tool. The optimal shapes of tools could also be conceived for increase their lifespan and the manufactured part could have the required quality.

Probability Based Computations Of Life Expectancy Of Mechanical Structures

Ageing aircraft structures are susceptible to a very typical and dangerous form of fatigue damage named Multiple Site Damage. An overall assessment method has been developed in order to improve the understanding of this phenomenon. A full deterministic approach has been completed first. An automatic numerical process, using the Dual Boundary Element Method and Fracture Mechanics laws, computes the crack evolution until failure of the structure. Then, in order to take materials scatter into account, a probabilistic approach has been developed based on Monte-Carlo simulations. Initial cracks scenarios are randomly defined and cracks evolution is computed for each of them. Thus statistical results are provided. The results obtained are in good agreement with experimental results carried out at the AEROSPATIALE research center.