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NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. In the present work, findings of an experimental study of dynamic decohesion of bimaterial systems composed of constituents with a large material property mismatch are presented. PMMA/steel or PMMA/aluminum bimaterial fracture specimens are used. Dynamic one point bend loading is accomplished with a drop weight tower device (for low and intermediate loading rates) or a high speed gas gun (for high loading rates). High speed interferometric measurements are made using the lateral shearing interferometer of Coherent Gradient Sensing in conjunction with high speed photography. Very high crack propagation speeds (terminal crack tip speeds up to [...], where [...] is the shear wave speed of PMMA) and high accelerations ([...], where g is the acceleration of gravity) are observed and reported. Issues regarding data analysis of the high speed interferograms are discussed. The effects of near tip three dimensionality are also analyzed. In crack propagation regions governed by large crack tip accelerations it is found that for accurate analysis of the optical data use of a transient elastodynamic crack tip field is necessary. Otherwise use of a Kd-dominant analysis is sufficient. Using the dynamic complex stress factor histories obtained by fitting the experimental data, a dynamic crack growth criterion is proposed. In the subsonic regime of crack growth it is seen that the opening and shearing displacements behind the propagating crack tip remain constant, i.e., the crack retains a self-similar profile during crack growth at any speed. This forms the basis of the proposed dynamic interfacial fracture criterion. It is also found that the process of dynamic interfacial fracture is highly unstable. This is corroborated by both the very large measured values of crack tip speed and acceleration and by the observation that the energy release rate at the propagating c

The Midwest Structural Sciences Center is a collaboration between the Structural Sciences Center, Aerospace Systems Directorate of the Air Force Research Laboratory (AFRL/RQHF SSC), and a team of faculty, graduate students, and professional staff researchers of the University of Illinois at Urbana-Champaign (UI), Wright State University, University of Cincinnati, and the University of Texas at San Antonio. The team works closely to simulate, model and test structures and materials for use in future air-and space-vehicles in a risk quantified design process.

Microelectromechanical Systems (MEMS) are increasingly used in critical military applications involving high loading rate for which failure modes can develop that are not present under static loading. We focused on understanding the dynamic failure response of multilayer MEMS at the material and structural scales. Findings/significance: We have performed static and dynamic failure experiments on polysilicon, and on Au and PZT/metal MEMS (from Army Research Laboratory.) The effects of loading rate, material, and geometry were studied. Findings show that failure modes are highly dependent on loading rate and geometry, and include material failure, structural failure or delamination. In addition, MEMS response mayMicroelectromechanical Systems (MEMS) are increasingly used in critical military applications involving high loading rate for which failure modes can develop that are not present under static loading. We focused on understanding the dynamic failure response of multilayer MEMS at the material and structural scales. Findings/significance: We have performed static and dynamic failure experiments on polysilicon, and on Au and PZT/metal MEMS (from Army Research Laboratory.) The effects of loading rate, material, and geometry were studied. Findings show that failure modes are highly dependent on loading rate and geometry, and include material failure, structural failure or delamination. In addition, MEMS response may, The original document contains color images.