Finite element analysis of an axi-symmetric forward spiral extrusion of Mg-1.75Mn alloy

A potential severe plastic deformation process known as axi-symmetrical forward spiral extrusion (AFSE) has been studied numerically and experimentally. The process is based on the extrusion of cylindrical samples through a die with engraved spiral grooves in a near zero shape change manner. The process was simulated using a three dimensional finite element (FE) model that has been developed using commercial software, ABAQUS. In order to verify the finite element results, hot rolled and annealed samples of the alloy were experimentally processed by AFSE. The required extrusion forces during the process were estimated using the FE model and compared with the experimental values. The reasonable agreement between the FE results and experimental data verified the accuracy of the FE model. The numerical results indicate the linear strain distribution in the AFSE sample is only valid for a core concentric while the strain distribution in the vicinity of the grooves is non axi-symmetric. The FE simulation results from this research allows a better understanding of AFSE kinematics especially near the grooves, the required extrusion force and the resultant induced strain distribution in the sample. To compare the mechanical properties of the Mg-1.75Mn alloy before and after the process, a micro shear punch test was used. The tests were performed on samples undergoing one and four passes of AFSE. After four passes of AFSE, it was observed that the average shear strength of the alloy has improved by about 21%. The developedfinite element model enables tool design and material flow simulation during the process.

Finite element analysis of plastic deformation in variable lead axisymmetric forward spiral extrusion

A modified axisymmetric forward spiral extrusion (AFSE) has been proposed recently to enhance the strain accumulation during the process. The new technique is called variable lead axisymmetric forward spiral extrusion (VLAFSE) that features a variable lead along the extrusion direction. To assess the effect of design modification on plastic deformation, a comprehensive study has been performed here using a 3D transient finite element (FE) model. The FE results established the shear deformation as the dominant mode of deformation which has been confirmed experimentally. The variable lead die extends strain accumulation in the radial and longitudinal directions over the entire grooved section of the die and eliminates the rigid body rotation which occurs in the case of a constant lead die, AFSE. A comparison of forming loads for VLAFSE and AFSE proved the advantages of the former design in the reduction of the forming load which is more pronounced under higher frictional coefficients. This finding proves that the efficiency of VLAFSE is higher than that of AFSE. Besides, the significant amount of accumulated shear strain in VLAFSE along with non-axisymmetric distribution of friction creates a surface feature in the processed sample called zipper effect that has been investigated. © 2012 Springer Science+Business Media New York.

Finite element model updating using estimation of distribution algorithm

Finite Element (FE) model updating has been attracting research attentions in structural engineering fields for over 20 years. Its immense importance to the design, construction and maintenance of civil and mechanical structures has been highly recognised. However, many sources of uncertainties may affect the updating results. These uncertainties may be caused by FE modelling errors, measurement noises, signal processing techniques, and so on. Therefore, research efforts on model updating have been focusing on tackling with uncertainties for a long time. Recently, a new type of evolutionary algorithms has been developed to address uncertainty problems, known as Estimation of Distribution Algorithms (EDAs). EDAs are evolutionary algorithms based on estimation and sampling from probabilistic models and able to overcome some of the drawbacks exhibited by traditional genetic algorithms (GAs). In this paper, a numerical steel simple beam is constructed in commercial software ANSYS. The various damage scenarios are simulated and EDAs are employed to identify damages via FE model updating process. The results show that the performances of EDAs for model updating are efficient and reliable.

Nonlinear dynamic modeling of ionic polymer conductive network composite actuators using rigid finite element method

Ionic polymer conductive network composite (IPCNC) actuators are a class of electroactive polymer composites that exhibit some interesting electromechanical characteristics such as low voltage actuation, large displacements, and benefit from low density and elastic modulus. Thus, these emerging materials have potential applications in biomimetic and biomedical devices. Whereas significant efforts have been directed toward the development of IPMC actuators, the establishment of a proper mathematical model that could effectively predict the actuators' dynamic behavior is still a key challenge. This paper presents development of an effective modeling strategy for dynamic analysis of IPCNC actuators undergoing large bending deformations. The proposed model is composed of two parts, namely electrical and mechanical dynamic models. The electrical model describes the actuator as a resistive-capacitive (RC) transmission line, whereas the mechanical model describes the actuator as a system of rigid links connected by spring-damping elements. The proposed modeling approach is validated by experimental data, and the results are discussed. © 2014 Elsevier B.V. All rights reserved.

Variation of yield loci in finite element analysis by considering texture evolution for AA5042 aluminum sheets

 Yield function has various material parameters that describe how materials respond plastically in given conditions. However, a significant number of mechanical tests are required to identify the many material parameters for yield function. In this study, an effective method using crystal plasticity through a virtual experiment is introduced to develop the anisotropic yield function for AA5042. The crystal plasticity approach was used to predict the anisotropic response of the material in order to consider a number of stress or strain modes that would not otherwise be evident through mechanical testing. A rate-independent crystal plasticity model based on a smooth single crystal yield surface, which removes the innate ambiguity problem within the rate-independent model and Taylor model for polycrystalline deformation behavior were employed to predict the material’s response in the balanced biaxial stress, pure shear, and plane strain states to identify the parameters for the anisotropic yield function of AA5042.

Slope stability analysis for filled slopes using finite element limit analysis method

This paper uses the finite element upper and lower bound limit analysis to assess the stability of slopes mostly found in embankment cases where frictional materials are filled on purely cohesive undrained clay. For comparison purposes, the commonly used stability assessment method, limit equilibrium method (LEM) is also employed. The final results for both methods are then presented in the form of comprehensive chart solutions for the convenience of practicing engineers during preliminary slope designs. The failure mechanism will also be discussed in this paper. Ultimately, it should be noted that finite element limit analysis method holds the upper hand as its prior assumptions are not required. Thus, the obtained failure mechanism from the slope stability analysis will be more realistic. Hence, it will provide a better understanding for the slope failure surface. Therefore, engineers should design more carefully when the LEM is applied to the slopes with frictional materials filled on purely cohesive undrained clay. © 2014 American Society of Civil Engineers.