The main objective of this work is the numerical prediction of the mechanical behaviour up to the damage of the bends of the functionally graded material (FGM) type ceramic/metal pipes. Firstly, the effective elastoplastic proper-ties of bent FGM pipes were determined using the homogenisation law by the Mori–Tanaka models for the elastic part and TTO (Tamura-Tomota-Ozawa) for the plastic part based on a rule of mixtures per function in the form of a power law. Our work also aims at the use of a meshing method (UMM) to predict the behaviour of the FGM by finite element in the mesh of the model. The analysis was performed using the UMM technique for different loading cases and volume fraction distribution. Two stages are necessary for the analysis of the damage: the first is the model of initiation of the damage established by the criterion of maximum deformation named MAXPE and the second is criterion of the energy of the rupture according to the theory Hillerborg used to determine damage evolution. Both stages involve a 3D finite element method analysis. However, for damage, the XFEM technique was used in our UMM method to predict crack initiation and propagation in FGM pipe bends. The results of the numerical analysis concerning the mechanical behavior showed, that if the nature of the bent pipes is in FGM, a good reduction of the various stresses compared to those where the nature of the pipe is metallic material. The results were presented in the form of a force–displacement curve. The validation of the proposed numerical methodology is highlighted by comparisons of current results with results from the literature, which showed good agreement. The analysis took into account the effect of the main parameters in a bent FGM pipe under internal pressure and bending moment on the variation of the force–strain curves.
Nowadays, the adhesive bonding process takes an important place in several industrial fields, especially in aeronautics. Given its advantages over other conventional mechanical processes, this process is being extended to be applied in composite materials and, in recent years, more particularly in the bonding of functional graded materials (FGM). Current research aims to optimize the mechanical properties of the substrates and the adhesive to minimize stress concentrations in the adhesive joint, which is the weak link of the structure. The present work analyzes, by the finite element method (FEM), the mechanical behavior of a single-lap joint with varying nature of the substrates. The analysis takes into account the variation of stresses in the adhesive of a bonded joint of different types (metal/metal, composite/composite, FGM/metal, FGM/FGM). On the other hand, an attempt has been made to introduce an adhesive with graded mechanical properties made up of two types to ensure efficient joining and reduce stress concentrations at the bond edges. The introduction of the FGM substrate mechanical properties is done using a USDFLD subroutine implemented in the ABAQUS computer code. Different damage approaches were used for the adhesive, namely the virtual crack closure technique (VCCT) and cohesive zone models (CZM) techniques. The effect of the mechanical properties of the substrates and adhesive were considered. The results show clearly that the value of the different stresses can be reduced if the mechanical properties of the substrates are optimized. On the other hand, the different techniques used to model the bonded joint converge towards the same results, emphasizing the agreement of the load-displacement curves with the experimental test, and the variation of the stresses according to the lap length with analysis by analytical models.
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