M. Wali

NONLINEAR DYNAMICS ANALYSIS OF FGM SHELL STRUCTURES WITH A HIGHER ORDER SHEAR STRAIN ENHANCED SOLID-SHELL ELEMENT

IN THIS PAPER, NON-LINEAR DYNAMICS ANALYSIS OF FUNCTIONALLY GRADED MATERIAL (FGM) SHELL STRUCTURES IS INVESTIGATED USING THE HIGHER ORDER SOLID-SHELL ELEMENT BASED ON THE ENHANCED ASSUMED STRAIN (EAS). WITH THIS ELEMENT, A QUADRATIC DISTRIBUTION OF THE SHEAR STRESS THROUGH THE THICKNESS IS CONSIDERED IN AN ENHANCING PART. MATERIAL PROPERTIES OF THE SHELL STRUCTURE ARE VARIED CONTINUOUSLY IN THE THICKNESS DIRECTION ACCORDING TO THE GENERAL FOUR-PARAMETER POWER-LAW DISTRIBUTION IN TERMS OF THE VOLUME FRACTIONS OF THE CONSTITUENTS. PERFORMANCE AND ACCURACY OF THE PRESENT HIGHER ORDER SOLID-SHELL ELEMENT ARE CONFIRMED BY COMPARING THE NUMERICAL RESULTS OBTAINED FROM FINITE ELEMENT ANALYSES WITH RESULTS FROM THE LITERATURE.

NUMERICAL ANALYSIS OF GEOMETRICALLY NON-LINEAR BEHAVIOR OF FUNCTIONALLY GRADED SHELLS

IN THIS PAPER, A GEOMETRICALLY NONLINEAR ANALYSIS OF FUNCTIONALLY GRADED MATERIAL (FGM) SHELLS IS INVESTIGATED USING ABAQUS SOFTWARE. A USER DEFINED SUBROUTINE (UMAT) IS DEVELOPED AND IMPLEMENTED IN ABAQUS/STANDARD TO STUDY THE FG SHELLS IN LARGE DISPLACEMENTS AND ROTATIONS. THE MATERIAL PROPERTIES ARE INTRODUCED ACCORDING TO THE INTEGRATION POINTS IN ABAQUS VIA THE UMAT SUBROUTINE. THE PREDICTIONS OF STATIC RESPONSE OF SEVERAL NON-TRIVIAL STRUCTURE PROBLEMS ARE COMPARED TO SOME REFERENCE SOLUTIONS IN ORDER TO VERIFY THE ACCURACY AND THE EFFECTIVENESS OF THE NEW DEVELOPED NONLINEAR SOLUTION PROCEDURES. ALL THE RESULTS INDICATE VERY GOOD PERFORMANCE IN COMPARISON WITH REFERENCES.

Geometrically nonlinear analysis of elastoplastic behavior of functionally graded shells

A geometrically nonlinear analysis of elastoplastic ceramic/metal functionally graded material (FGM) shells is investigated in this paper based on the first-order shear deformation theory. The elastoplastic behavior of the ceramic particle-reinforced metal matrix FGM shell is assumed to follow Ludwik hardening law. The elastoplastic material properties are assumed to vary smoothly through the thickness of the shells. The Mori–Tanaka model and self-consistent formulas of Suquet are employed to locally evaluate effective elastoplastic parameters of the ceramic/metal FGM composite. The homogenization formulation and numerical algorithms are implemented into ABAQUS/Standard via a user material subroutine (UMAT) developed to study the FG shells in large displacements and rotations. With the aim of demonstrating the accuracy of the present method, current numerical results are compared to experimental and numerical ones considering geometrically nonlinear elastoplastic FGMs and show very good agreement. The overall robustness of the new developed solution taking into account both geometric and material nonlinearities is demonstrated through several non-trivial benchmark problems taken from the literature. The effect of the constituent distribution on the deflections is analyzed.

The Extended Finite Element Method for Cracked Incompressible Hyperelastic Structures Analysis

This paper aims to examine the contribution of the extended finite element method (XFEM) in finite strain fracture mechanics problems. A generalized neo-Hookean hyperelastic material is considered in an incompressible plane stress approximation. The accuracy of the implementation is demonstrated by a series of numerical tests.

Low Velocity Impact Behavior of Glass Fibre-Reinforced Polyamide

The low velocity impact behavior of composites made of polyamide (PA) as matrix and glass fibre as reinforcement has been investigated. The assessment of the impact behavior has driven the need to perform tensile tests to determine the elasto-plastic behavior of the composites. The specimens were manufactured by injection molding techniques for the experimental tensile testing. ABAQUS/EXPLICIT for finite element modeling is employed in order to predict the impact behavior of glass fibre-reinforced polyamide. The determinations of the impact force history and elasto-plastic structure deflection are the most important objectives in impact engineering structures design.

Dynamic Analysis of the Perforation of Aluminum Alloy at Low Velocity Impact

A finite element implementation of an anisotropic plasticity model for aluminum AA5754-O in impact simulations was performed, particularly for the case of perforation on low velocity (up to about 25 m/s). The elasto-viscoplastic model includes isotropic elasticity, anisotropic yielding, associated plastic flow and mixed non-linear isotropic/kinematic hardening. Coupling between elasto-viscoplastic model and isotropic ductile damage is investigated. Strain rate is integrated in numerical modeling. The material model is implemented into a user-defined material (VUMAT) subroutine for the commercial finite element code ABAQUS/Explicit to predict the numerical response of circular aluminum plate subjected to low velocity impact. Results include the effect of anisotropy on the material behavior. It is shown that anisotropy plays a significant role in penetration of the present plate material.

On the Use of NC Milling and Turning Machines in SPIF Process of Asymmetric Parts: Numerical Investigation

Incremental sheet forming is a flexible process that benefits from the evolution of CNC machine tools; it usually uses a three-axis NC milling machine even for asymmetric parts. This paper presents a numerical simulation of single point incremental forming (SPIF) process of asymmetric part, manufactured using two types of NC machines: NC milling machine and NC turning machine. A finite element model (FEM) is developed by using the commercial FE code ABAQUS/Explicit. An elastoplastic constitutive model with quadratic yield criterion of Hill’48 and isotropic hardening behavior has been considered for the sheet metal. A user material subroutine (VUMAT) is used to implement this material behavior. Results including thickness variation, deformed shape, and forming force along Z-axis are presented. A remarkable difference has been observed in the results obtained from the use of these two machines. In fact, NC lathe machine is a good alternative to manufacture asymmetric parts and many advantages can be mentioned, such as the remarkable decrease of thinning and vertical force which improves formability during the ISF operation.

Effects of Using Flexible Die Instead of Flexible Punch in Rubber Pad Forming Process

Flexible forming with rubber pad is a forming technique that is commonly used in the aeronautic and automotive industries to produce parts with complex shapes from thin sheet metal. The purpose of this chapter is to compare between using flexible punch or flexible die in sheet metal forming with rubber pad. A finite element simulation is carried out to predict the behavior of the flexible stamping process of aluminum sheet metal with the two techniques of forming. For the sheet metal, an elastoplastic constitutive model is adopted and implemented in ABAQUS/Standard software via UMAT subroutine. However, a Mooney–Rivlin hyperelastic model is adopted for the rubber pad. Results predicted numerically consist of comparing the variation of some key parameters process using two deformation styles in order to produce safety parts without localized severe deformation. It was found that using rubber as flexible die may reduce the thinning rate and values of equivalent plastic strain in the formed part. Also, based on the Forming Limit Diagram (FLD) analysis, using flexible die instead of flexible punch may successfully form part without necking and micro crack and without localized severe deformation that can lead to fracture.

A New Cumulative Fatigue Damage Model for Short Glass Fiber-Reinforced Polyamide 66

Fatigue damage of short glass fiber-reinforced composite is a quite complex phenomenon, and a large research effort is being spent on it these days. Furthermore, fatigue damage in such materials, fatigue damage kinetic exhibits three stages, namely: (i) matrix microcracking and damage initiation, (ii) coalescence and propagation of microcracks and (iii) macroscopic cracks propagation up to material failure. The proposed model is based on the stiffness degradation rule of short glass fibers-reinforced polyamide 66. This new versatile phenomenological fatigue damage model attempts to predict fatigue damage growth in its three stages. The characteristics of damage growth and accumulation of short glass fiber-reinforced polyamide 66 under fatigue bending loading were studied in this paper. Experimental data from bending fatigue tests were used to identify the model parameters. Results showed that this model is capable of describing the three stages of damage evolution of theses composite materials. Furthermore, the predicted fatigue life is in good agreement with the experimental ones.

A Higher Order Shear Strain Enhanced Solid-Shell Element for Laminated Composites Structures Analysis

This paper presents a free from locking higher order solid-shell element based on the Enhanced Assumed Strain (EAS) for laminated composite structures analysis. The transverse shear strain is divided into two parts: the first one is independent of the thickness coordinate and formulated by the Assumed Natural Strain (ANS) method; the second part is an enhancing part which ensures a quadratic distribution through the thickness. This permit to remove the shear correction factors and improves the accuracy of transverse shear stresses. Also, volumetric locking is completely avoided by using the optimal parameters in the EAS method. Comparisons of numerical results with those extracted from literature show the performance of the developed finite element.