As a first step toward formulating guidelines for the design of dynamically reliable MEMS, we analyze the mechanical response of, and formulate failure criteria for, a large class of shock loaded microsystems. MEMS are modeled as microstructures attached to elastic substrates, and the shocks are modeled as pulses of acceleration applied to the substrate over a finite time duration. The relevant time scales in the analysis are the acoustic transit time, the time period of vibrations, and the duration of the applied shock load. For many MEMS structures and shock loads (with durations in the range 50-5000 /spl mu/s), the substrates respond as rigid bodies and are expected to be immune to stress-wave-induced damage. Time-domain criteria, obtained to distinguish between the impulse, resonant, and quasistatic responses of the microstructures, correlate well with the experimentally observed responses of different MEMS devices. The formulation of displacement-based and stress-based failure criteria is discussed, along with their sensitivity to the applied strain rate. A case study, in which these results are applied to evaluate the reliability of a packaged surface-micromachined device, is presented.

The reliability of microelectromechanical systems (MEMS) in shock environments

Stiff string approximations in Rayleigh-Ritz method for rotating beams

The impact properties of composites of glass fibre or carbon fibre in polyester or epoxy resin were studied Impact was by high-velocity water jets ( approximately 700 ms-1), which previous work has shown successfully simulate rain erosion damage and other impact situations involving high-stress (of the order of 1 GPa) and short-duration (few mu s) loading The failure of the composites is analysed and the damage mechanisms are identified An assessment is made of the effect of such variables as reinforcement geometry, volume fraction of fibres, matrix toughness, void content and surface condition

http://iopscience.iop.org/article/10.1088/0022-3727/9/10/018/pdf

The failure of composite materials under high-velocity liquid impact

Dynamic photoelasticity using TDI imaging

A photoelastic study of the elastodynamic-stress fields around a circular, elastic inclusion (Solithane 113) embedded in an elastic plate (Hysol 4485) is presented. The edge of the plate was loaded by an explosive charge, which produced a plane, compressional stress wave of triangular shape. Isochromatic-fringe patterns were obtained, which give the maximum shear stresses, both inside the inclusion and in the surrounding medium. The principal stresses on the axis of symmetry were determined through the use of the oblique-incidence method. It was found that small tensile stresses are generated at the interface on the shadow side of the inclusion. The focusing effect inside the inclusion predicted by ray theory was not observed. Finally, the shape of the wavefront as the wave passes the inclusion was determined.

A dynamic photoelastic study of stress-wave propagation through an inclusion: A dynamic photoelastic study of stress-wave propagation through an inclusion showing the effects of the reflections and refractions at the interface

J. H. Hemann

Papers

Tensile failure of interface bonds in a composite body subjected to compressive loads.

Experimental and Analytical Investigation of Dynamic Stress Concentrations at a Circular Hole

Dynamic Scattered Light Photoelasticity in Two-Dimensional Problems