Mohamed Rachik

MRI-based finite element modeling of facial mimics: a case study on the paired zygomaticus major muscles

Abstract Finite element simulation of facial mimics provides objective indicators about soft tissue functions for improving diagnosis, treatment and follow-up of facial disorders. There is a lack of in vivo experimental data for model development and validation. In this study, the contribution of the paired Zygomaticus Major (ZM) muscle contraction on the facial mimics was investigated using in vivo experimental data derived from MRI. Maximal relative differences of 7.7% and 37% were noted between MRI-based measurements and numerical outcomes for ZM and skin deformation behaviors respectively. This study opens a new direction to simulate facial mimics with in vivo data.

Magnetic Pulse Welding: An Innovative Joining Technology for Similar and Dissimilar Metal Pairs

Once it was widely thought to be an exceptional innovative welding solution, the magnetic pulse welding, dragged the related manufacturing industries and particular‐ ly automobile companies for its complex assembly solutions in early 2000s. Although this technique has been implemented by some giant manufacturers for various joining tasks, the process still has not been well adopted by industries. However, in recent years, many researchers turned their attention to the potential applications and insight investigations of this process due to the existence of bottlenecks and the prime novelty of this technique. This chapter clearly highlights the process, applications, require‐ ments, interfacial kinematics of the welding, numerical predictions of interfacial behaviours and multi-physics simulations. This chapter recommends that the overall outlook of the process is promising while it requires extra attention in the individual welding cases and its material combinations.

IMAGE-BASED SKELETAL MUSCLE COORDINATION: CASE STUDY ON A SUBJECT SPECIFIC FACIAL MIMIC SIMULATION

Facial muscle coordination is a fundamental mechanism for facial mimics and expressions. The understanding of this complex mechanism leads to better diagnosis and treatment of facial disorders like facial palsy or disfigurement. The objective of this work was to use magnetic resonance imaging (MRI) technique to characterize the activation behavior of facial muscles and then simulate their coordination mechanism using a subject specific finite element model. MRI data of lower head of a healthy subject were acquired in neutral and in the pronunciation of the sound [o] positions. Then, a finite element model was derived directly from acquired MRI images in neutral position. Transversely-isotropic, hyperelastic, quasi-incompressible behavior law was implemented for modeling facial muscles. The simulation to produce the pronunciation of the sound [o] was performed by the cumulative coordination between three pairs of facial mimic muscles (Zygomaticus Major (ZM), Levator Labii Superioris (LLS), Levator Anguli O...

Thermal Effect during Electromagnetic Pulse Welding Process

Magnetic pulse welding (MPW) is a solid state joining process, successfully utilized to join dissimilar metals. This advantage attracted manufacturing industries to fabricate hybrid materials to attain materials with a combination of multiple attributes. The high speed impact during the welding process causes various interfacial phenomena, which have been reported in previous research studies. Combined high speed collision, Joule heating due to eddy current and plastic heat dissipation cause noticeable heating in the workpiece. The heating from the plastic work and collision energy could particularly be significant at the vicinity of the interface compared to other regions of the workpiece. The Joule heating due to eddy current affects the entire workpiece that is prominent before the collision. There is a sharp increase of the temperature at the onset of weld formation due to dissipation of plastic work during the collision. 3D simulations of coupled electromagnetic-mechanical-thermal were carried out to investigate the heating due to the combined Joule heating and plastic dissipation. A case study of MPW, consist of a one turn coil combined with a field shaper, is used to investigate the welding process. The simulations were performed using LS-DYNA®, which has the capability of using both finite and boundary elements to solve the thermo-mechanical problem during electromagnetic forming. The predicted temperature distributions from numerical simulations show expected phenomena of Joule heating and plastic heat dissipation while the analytical approach used to estimate the localized increase in temperature due to supersonic gaseous compression. Minimizing the heating effect by identifying the influencing factors could help to optimize and control the quality of the magnetic pulse welded parts.

ARTIFICIAL MICROSTRUCTURE GENERATOR FOR DUAL-PHASE STEELS

The microstructure of low alloyed ferritic-martensitic Dual-Phase (DP) steels consists of hard coarse grained martensite islands embedded in a soft ferrite matrix. Therefore, the macroscopic mechanical properties of DP steels mostly derive from their microstructures, such as volume fractions, morphology of martensite, phase distributions and ferrite grain size. Recently, micromechanical approaches are used to predict ductility and failure mode of DP steels under varying mechanical loading scenarios. In this work, an artificial microstructure generator inspired by topology optimization was developed to construct representative volume element (RVE) with predefined design parameters within a mofidied Voronoı̈ tessellation. Micromechanical modeling of DP steel was performed on the generated artificial RVE. The plastic flow behavior of each single phase in DP steel were calculated by using a dislocation based theory. After numerical simulation, the flow curve on macro scale can be obtained from an asymptotic expansion homogenization (AEH) scheme. This approach allows studying the influence of individual microstructure features on local and global stress-strain response. To improve the robustness of this artificial microstructure generator, a proper orthogonal decomposition (POD) reduction was introduced to identify the optimal design parameters. This approach used a collection of artificial microstructures (snapshots) to find the most representative one of the real microstructure.