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MEMS technologies create complex devices with critical dimensions on the order of 1–100μm from alimited, but expanding materials base. Two standard MEMS technologies of interest to Sandia National Laboratories are surface micromachining (SMM) and LIGA-based high aspect ratio microfabrication. SMM techniques produce complex devices on the surface of a silicon wafer with critical dimensions of about 2μm using a patterned multilayer film deposition process. LIGA (Lithographie, Galvanoformung, Abformung) is a process in which structural material is electrodeposited into a polymethyl-methacrylate (PMMA) mold realized by deep x-ray photolithography. The resolution of the LIGA process can be as precise as 1μm, but typical component sizes range in the 100’s of microns. In both technologies, material microstructural features, e.g. grains and defects, scale with component sizes. Consequently, issues surrounding the mechanical response of components fabricated from these technologies are often caused by this microstructure-component size scale equivalence. The objective of this paper is to present an overview of select mechanical properties results and associated microstructure evaluations expected to be useful for developing damage mechanics models that accurately predict the lifetime of MEMS devices. A companion paper (IMECE2002-32393) discusses experimental results and observations from micromechanical evaluation studies of SMM-MEMS. This paper discusses experimental results and observations on LIGA fabricated materials and some complementary, straightforward polycrystal elastic deformation simulations of SMM polysilicon.

Sandia National Laboratories has the need to predict the behavior of structures after the occurrence of an initial failure. In some cases determining the extent of failure, beyond initiation, is required, while in a few cases the initial failure is a design feature used to tailor the subsequent load paths. In either case, the ability to numerically simulate the initiation and propagation of failures is a highly desired capability. This document describes one approach to the simulation of failure initiation and propagation.

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Characterization of the damage state of a thermally degraded energetic material (EM) is a critical first step in understanding and predicting cookoff behavior. Unfortunately, the chemical and mechanical responses of heated EMS are closely coupled, especially if the EM is confined. We have examined several EMS in small-scale experiments (typically 200 mg) heated in both constant-volume and constant-load configurations. Fixtures were designed to minimize free volume and to contain gas pressures to several thousand psi. We measured mechanical forces or displacements that correlated to thermal expansion, phase transitions, material creep and gas pressurization as functions of temperature and soak time. In addition to these real-time measurements, samples were recovered for postmortem examination, usually with scanning electron microscopy (SEM) and chemical analysis. We present results on EMS (HMX and TATB), with binders (e.g., PBX 9501, PBX 9502, LX-14) and propellants (AVAP/HTPB). DISCLAIMERThis rcporr was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof. nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any spccific commercial product, process, or senice by trade name, trademark, manufacturer, or otheiwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States G o m m e n t or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.