Shoulder fillet effects in strength distributions of microelectromechanical system components

Abstract

The failure forces and fracture strengths of polysilicon microelectromechanical system (MEMS) components in the form of stepped tensile bars with shoulder fillets were measured using a sequential failure chain methodology. Approximately 150 specimens for each of four fillet geometries with different stress concentration factors were tested. The resulting failure force and strength distributions of the four geometries were related by a common sidewall flaw population existing within different effective stressed lengths. The failure forces, strengths, and flaw population were well described by a weakest-link based analytical framework. Finite element analysis was used to verify body-force based expressions for the stress concentration factors and to provide insight into the variation of specimen effective length with fillet geometry. Monte Carlo simulations of flaw size and location, based on the strength measurements, were also used to provide insight into fillet shape and size effects. The successful description of the shoulder fillet specimen strengths provides further empirical support for application of the strength and flaw framework in MEMS fabrication and design optimization.

Sensitivity of void mediated failure to geometric design features of porous metals

“…Furthermore, depending on the scale of a part relative to the particles comprising the granular feedstock, adherence to the designed geometry can be poor [2,3]. For example, surface roughness can be comparable to small, high curvature geometric features that result from sophisticated topology optimization and more mundane corners and fillets [4,5,6,7,5,8], preventing the precise manufacture of some designs.…”

“…There is a large body of literature on the probabilistic failure of brittle materials [11,12,13,14,15], in large part focused on the applicability of the Weibull and related distributions. This is a mature field of study that has recently been applied to advanced materials, such as silicon based micro-electro-mechanical systems (MEMS) [16,17,18,8]. There has also been focus on the uncertainty due to the ductility and porosity of metals, AM or otherwise.…”