Abstract: A three-dimensional finite element analysis was conducted to simulate the effects of the varying material parameters on the contraction behaviors of a muscle-tendon complex using an active finite element method. The material behavior of the skeletal muscle was assumed to be orthotropic and the muscle model consists of two parts: the active and the passive parts. An active finite element method was then used for accommodating both the active and passive behaviors of the muscle into the muscle model. In this active-passive muscle model, the active component is governed by an activation level, a time period, a muscle sensitivity parameter and a strain rate. The material property of the passive component was assumed to be viscoelastic and the tendon is assumed to be linear elastic. The effects of activation amplitude and viscoelastic material parameters on the active, passive and total force-length relationship of the cat muscle under isometric contraction were predicted. The predicted results were found to be close to the experimental data reported in the available literature. Hence, the active-passive muscle model was extended to simulate the stress distribution of the cat muscle subject to shortening contraction and different activation amplitude. By varying the magnitude of the material parameters, different muscle behaviors could be generated. The proposed active finite element method lays a good foundation for simulation of human musculoskeletal motion.
Abstract: The uniform nickel coatings on substrate of low carbon steel were prepared by an electrodeposition method. The residual stress in the electrodeposited nickel coating was measured by X-ray diffraction (XRD). It was tensile when the coating was not treated. Laser beam thermal shock was used to modify the mechanical properties of the nickel coating. Laser beam thermal shock could redistribute the residual stress in the nickel coating. The residual stress could be converted from tensile to compressive. A tensile method to determine the stress-strain curve of the coating is proposed where the stress-strain relationship of the substrate without coating was determined for the specimen loaded by an applied tensile force.
Abstract: The intent of this article was to study the failure mechanism of thermal barrier coatings (TBCs) induced by buckling. The main content included the following two parts. The first part investigated the thermal residual stresses fields in TBCs with thermal cycles, which induced by the non-linear coupled effect of temperature gradient, thermal fatigue and creep strain of TBCs. One found that the residual stresses in ceramic coating were compressive and accumulated with thermal cycles, which may be high enough to induce the buckling failure of ceramic coating. The second part studied the critical buckling failure loading of the ceramic coating in TBCs under the condition of the compressive loading by use a theoretical model. Finally, a buckling plane, i.e. s T n − plane, was obtained by combined the above sections and applied to predict the buckling failure of the TBCs system. In this plane, it was divided into the two parts, i.e., non-buckling region and buckling region.
Abstract: A micromechanical model based on continuum analysis has been investigated by using finite element analysis (FEA) in discontinuous metal matrix composites (DMMC). To assess the tensile and compressive constitutive responses, a cyclic stress-strain behavior has been performed. For analysis procedure, the elastoplastic FEA and the regularly aligned axisymmetric single fiber model have been implemented to evaluate the internal field quantities. Accordingly, the fiber and matrix internal stresses were investigated for the constrained representative volume element (RVE). Further, the local plasticity in the matrix were described during loading and unloading precesses, which can predict the damage mechanisms as well as strengthening mechanisms. On the other hand, a thermoelasto- plastic analysis has been performed using FEA for the application to the continuum behavior in a discontinuous metal matrix composite. The internal field quantities of composite as well as overall composite behavior and an experiment was demonstrated to compare with the numerical simulation. As the procedure, the reasonably optimized FE mesh generations, the appropriate imposition of boundary conditions, and the relevant postprocessing such as elasto-plastic thermo-mechanical analysis were taken into account. For micromechanical model, the temperature dependent material properties and precipitation hardening effects have been employed to investigate field quantities. It was found that the residual stresses are induced substantially by the temperature drop during heat treatment and that the FEA results give a good agreement with experimental data.
Abstract: The effect of the surface properties on the microtribological characteristics of AlN-based electrostatic chuck (EC) for silicon plasma etching was investigated using automatic microscratch testing technique in combination with SEM examination of the scratch track. The scratch testing was performed by applying a progressive indenter load. The scratch failure model varied systematically with the surface properties of AlN. The data of the onset of brittle fracture were used as characteristic features of the AlN failure. It was found that the critical load, Lc, the smallest applied normal load leading to unacceptable damage such as chipping and cracking, increases with decreasing the average grain size, density and fracture toughness of AlN and decreases with increasing the surface roughness and area density of pre-existing polishing damages. The resistance to cohesion and adhesion failure of AlN with 0.1 µm Al2O3 oxide layer on top was stronger than that of the AlN bulk material. The fracture initiation and ductile to brittle transition in AlNAl2O3( 0.1µm) was in form of discontinuous chipping. The results infer the potential of the combination of the scratch data with the material properties for the understanding of the effect of the surface topography on the mechanical properties and chucking performance of AlN-based EC.
Abstract: Thermal shock and thermal fatigue of ferroelectric (FE) thin films were investigated by the pulsed laser tests. The power density was gradually increasing in the single pulsed laser heating test which simulated a thermal shock, the part melting threshold of Pb(Zr0.52Ti0.48)O3 (PZT) thin films was found by scanning electron microscopy (SEM). After thermal shock resulted the highest temperature below Curie point at the surface of PZT thin film, X-ray diffraction (XRD), SEM and RT66A standard ferroelectrics analyzer were used to study the microstructure, crystal grain sizes, and ferroelectric failure behavior. It was found that XRD peak of PZT thin film after laser beam heating was stronger than that before laser beam heating, crystal grain sizes decreased, and the ferroelectric properties were degraded. However there was no crack observed by SEM, until PZT thin films were melted. The fined grain effects on ferroelectric properties and XRD patterns of PZT thin film, depolarization due to the single pulsed laser heating were discussed respectively. The pulsed cycles with a certain power density were gradually increasing in the repetition pulsed laser heating test. It was interesting to find that the cracks will initiate and propagate due to the thermal fatigue induced by the repetition pulsed laser. The possible origins of the thermal fatigue cracks were also discussed.