Smoothed finite element method implemented in a resultant eight-node solid-shell element for geometrical linear analysis

International audienceA smoothed finite element method formulation for the resultant eight-node solid-shell element is presented in this paper for geometrical linear analysis. The smoothing process is successfully performed on the element mid-surface to deal with the membrane and bending effects of the stiffness matrix. The strain smoothing process allows replacing the Cartesian derivatives of shape functions by the product of shape functions with normal vectors to the element mid-surface boundaries. The present formulation remains competitive when compared to the classical finite element formulations since no inverse of the Jacobian matrix is calculated. The three dimensional resultant shell theory allows the element kinematics to be defined only with the displacement degrees of freedom. The assumed natural strain method is used not only to eliminate the transverse shear locking problem encountered in thin-walled structures, but also to reduce trapezoidal effects. The efficiency of the present element is presented and compared with that of standard solid-shell elements through various benchmark problems including some with highly distorted meshes

Electric field modelling around an ice-covered insulator using boundary element method

The presence of a thick ice layer on a post insulator can change considerably the distribution of the electric field along this equipment, and that especially when a water film flows on the accumulated ice surface. The main objective of this paper is the modelling of electric field distribution along a post insulator covered with atmospheric ice with air gaps, using the boundary element method (BEM). Moreover, the influence of the presence of a highly conductive water film at the ice surface on the field distribution is also studied. The results contribute to the prediction of flashover on industrial ice-covered insulators

Prediction procedure for hail impact

The constant increase of composite materials’ performances makes them more and more used in recent aircrafts. Structures, as the wings or the fuselage, may suffer from hail impacts that can make critical damages or even perforate them. In order to guaranty the safety of passengers, aircrafts have to be certified and simulations have to demonstrate good agreements with real behaviour of the structures and the hail projectile. The aim of this work is to propose a procedure to analyse the home made manufacturing of the ice generally performed in laboratories, its mechanical characterization and a mechanical model that can predict the time-space profile of the impact force on a rigid structure. Because of the high strain level of the hail during the impact, the Smooth Particle Hydrodynamics (SPH) method will be used. Indeed, the finite elements method needs heavy remeshing that are time consuming to avoid mesh distortion. The SPH is a numerical meshless method that calculates interactions between particles at every time increment. Models available in the literature have been studied and the model of J.D. Tippmann (Tippmann, Kim, et Jennifer D. Rhymer 2013) is chosen. In this paper, the Tippman model is presented with its solving using the SPH. A parametric study is proposed in order to catch the relevant parts of this model. A simple experimental procedure is then proposed to feed the model and the results of impact simulations at different velocities are compared to experimental measurements realized in the laboratory

Modeling the powder compaction process using the finite element method and inverse optimization

This paper focuses on studying and adapting modeling techniques using the finite element method to simulate the rigid die compaction of metal powders. First, it presents the implementation of the cap constitutive model into ABAQUS FE software using the closest point projection algorithm. Then, an inverse modeling procedure was proposed to alleviate the problems raised by the interpretation of the experimental tests and to more accurately determine the material parameters. The objective function is formed, based on the discrepancy in density data between the numerical model prediction and the experiment. Minimization of the objective function with respect to the material parameters was performed using an in-house optimization software shell built on a modified Levenberg–Marquardt method. Thus, an integrated simulation module consisting of an inverse optimization method and a finite element method was developed for modeling the powder compaction process as a whole. The simulation and identification module developed was applied to simulate the compaction of some industrial parts. The results reveal that the maximum absolute error between densities is 2.3%. It corresponds to the precision of the experimental method

Prediction procedure for hail impact

The constant increase of composite materials’ performances makes them more and more used in recent aircrafts. Structures, as the wings or the fuselage, may suffer from hail impacts that can make critical damages or even perforate them. In order to guaranty the safety of passengers, aircrafts have to be certified and simulations have to demonstrate good agreements with real behaviour of the structures and the hail projectile. The aim of this work is to propose a procedure to analyse the home made manufacturing of the ice generally performed in laboratories, its mechanical characterization and a mechanical model that can predict the time-space profile of the impact force on a rigid structure. Because of the high strain level of the hail during the impact, the Smooth Particle Hydrodynamics (SPH) method will be used. Indeed, the finite elements method needs heavy remeshing that are time consuming to avoid mesh distortion. The SPH is a numerical meshless method that calculates interactions between particles at every time increment. Models available in the literature have been studied and the model of J.D. Tippmann (Tippmann, Kim, et Jennifer D. Rhymer 2013) is chosen. In this paper, the Tippman model is presented with its solving using the SPH. A parametric study is proposed in order to catch the relevant parts of this model. A simple experimental procedure is then proposed to feed the model and the results of impact simulations at different velocities are compared to experimental measurements realized in the laboratory

FEA-Based Comparative Investigation on High Speed Machining of Aluminum Alloys AA6061-T6 and AA7075-T651

Independent research studies have shown notable dissimilarity in the machining behaviour of aluminum alloys AA6061−T6 and AA7075−T651 commonly used in automotive and aeronautical applications. The present work attempts to investigate this dissimilarity based on experimental and numerical data with a focus on chip formation and generated residual stresses under similar high−speed machining (HSM) conditions. The numerical data were calculated by a finite element modeling (FEM) developed using DeformTM 2D software. The results showed that both studied alloys exhibit different chip formation mechanisms and residual stress states at the machined surfaces. On one hand, the AA6061−T6 alloy generates continuous chips and tensile residual stresses whereas the AA7075−T651 alloy produces segmented chips and compressive residual stresses. FEM results showed that the AA6061−T6 alloy generates lower cutting temperature at the tool−chip interface along with higher equivalent total strains at the machined surface as compared to the AA7075−T651 alloy. Based on the experimental and numerical results, it was pointed out that the differences in terms of thermal conductivity and initial yield stress are the main reasons explaining the dissimilarity observed.</jats:p

Robust methodology to simulate real shot peening process using discrete-continuum coupling method

Shot peening is widely used in automotive and aeronautic industries to improve fatigue life of metallic components. Its beneficial effects are mainly due to the residual stress field caused by the plastic deformation of the near-surface region resulting from multiple shot impacts. It is therefore important to know the values of the induced residual stresses in order to predict the mechanical strength of the peened component, and to know how these stresses vary by changing the shot peening parameters. The problem is that experimental measurement of residual stress is costly and time-consuming, and generally involves semi-destructive techniques. These difficulties make assessment of compressive residual stresses in real (industrial) peened components very challenging. On the contrary, numerical simulation can provide an alternative way to deal with this task. Consequently, several shot peening models have been developed in the literature. Although these models were successfully applied to investigate important physical phenomena encountered in shot peening, their application to assess residual stresses resulting from a real shot peening test is still not within reach. Indeed, due to computation costs and the complexity of the process, they cannot be directly applied to simulate a complete shot peening experiment. Development of a robust methodology allowing these models to properly simulate such an experiment at minimal cost (i.e. using simplifying assumptions) is thus needed. The present paper aims to meet this need. First, a new discrete-continuum coupling model combining the strengths of the existing shot peening models was developed. To avoid expensive computation times, only major shot peening features are included in this model. Then, a comprehensive methodology explaining how this model can be applied to simulate a real shot peening experiment was proposed. To validate the developed model as well as the associated methodology, they were applied to simulate a real shot peening experiment from the literature. Relatively good results were obtained compared to experimental ones, with relatively little computation effort

Engineering Investigations on the Potentiality of the Thermoformability of HDPE Charged by Wood Flours in the Thermoforming Part

International audienceA dynamic finite element method is used to analyze the thermoformability of composites containing wood and a thermoplastic matrix for five different proportions of wood flour. Linear viscoelastic properties can be obtained by small amplitude oscillatory shear tests and the viscoelastic behavior is characterized using the Lodge model. To account for enclosed gas volume, which inflates the thermoplastic composite membrane, a thermodynamic approach is used to express the external work in terms of a closed volume. Pressure load is deduced by thermodynamic law using the Redlich-Kwong gas equation. The Lagrangian method together with the assumption of membrane theory is used in the finite element implementation. In addition, the influence of air flow on thickness and stress and the energy required to form a thin polymeric part in the thermoforming process are analyzed for five different proportions of wood flour in the HDPE material. POLYM. ENG. SCI., 49:1594-1602, 2009. (C) 2009 Society of Plastics Engineer