Investigation into cylinder-on-flat adhesion elastic–plastic micro-contact under repeated loading and unloading condition

The evolution of microcontact induced deformation and stress states under repeated loading and unloading condition is of great interest for the scientific understanding as well as from the engineering design considerations of microelectromechanical systems (MEMS) based switches and similar other devices since they operate under cyclic condition. This study, therefore, investigated the microcontact interaction between deformable smooth cylindrical segment and deformable smooth flat using the finite element analysis. Elastic and elastic–plastic material behaviors and adhesion interaction are considered. The detailed information about contact area, displacement and stress state in the contact region under cycling condition are presented. Contact area varies nonlinearly even when the applied load is varying linearly in a cycle. Additionally, contact areas during loading and unloading portions of a cycle are not equal at the same load level. The deformation and contact area increases in the presence of adhesion force and also with elastic–plastic material behavior. However, the adhesion force is reduced while the contact area is increased during the microcontact between elastic–plastic bodies in comparison to those between elastic bodies. The maximum increase in stress and deformation states occurs during the first cycle, and then slowly with increasing number of cycles. Further, the maximum stress state is not at the contact surface and also not at instant of the maximum applied external force. Finally, adhesion force during microcontact interaction can be of the same order as the applied external force. Therefore, design and analysis of microcontacts in micromechanical switches and similar other devices should include the effects of adhesion force and cyclic effects. The views expressed in this article are those of the authors and do not reflect the official policy or position of the United State Air Force, Department of Defense, or the U.S. Government.     

On the coupling between fluid flow and mesh motion in the modelling of fluid–structure interaction

Partitioned Newton type solution strategies for the strongly coupled system of equations arising in the computational modelling of fluid–solid interaction require the evaluation of various coupling terms. An essential part of all ALE type solution strategies is the fluid mesh motion. In this paper, we investigate the effect of the terms which couple the fluid flow with the fluid mesh motion on the convergence behaviour of the overall solution procedure. We show that the computational efficiency of the simulation of many fluid–solid interaction processes, including fluid flow through flexible pipes, can be increased significantly if some of these coupling terms are calculated exactly.     

Relationships between the local characteristics of the force and strain criteria during propagation of a long fatigue through crack

Based on the analysis of the fracture mechanical concepts of evaluating the kinetics of a long fatigue crack and the mechanical situation at its tip, a reliable relationship between the local characteristics of the force and strain criteria is established. __________ Translated from Problemy Prochnosti, No. 6, pp. 113–121, November–December, 2007.