An experimental study of impact-induced failure events in homogeneous layered materials using dynamic photoelasticity and high-speed photography |
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Authors: | L Roy Xu Ares J Rosakis |
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Institution: | a Department of Civil and Environmental Engineering, Station B351831, Vanderbilt University, Nashville, TN 37235, USA;b Graduate Institute of Technology, California Aeronautical Laboratories, Pasadena, CA 91125, USA |
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Abstract: | The generation and the subsequent evolution of dynamic failure events in homogeneous layered materials that occur within microseconds after impact were investigated experimentally. Tested configurations include three-layer and two-layer, bonded Homalite specimens featuring different bonding strengths. High-speed photography and dynamic photoelasticity were utilized to study the nature, sequence and interaction of failure modes. A series of complex failure modes was observed. In most cases, and at the early stages of the impact event, intra-layer failure (or bulk matrix failure) appeared in the form of cracks radiating from the impact point. These cracks were opening-dominated and their speeds were less than the crack branching speed of the Homalite. Subsequent crack branching in several forms was also observed. Mixed-mode inter-layer cracking (or interfacial debonding) was initiated when the intra-layer cracks approached the interface with a large incident angle. The dynamic interaction between inter-layer crack formation and intra-layer crack growth (or the so-called “Cook–Gordon Mechanism”) was visualized for the first time. Interfacial bonding played a significant role in impact damage spreading. Cracks arrested at weak bonds and the stress wave intensity was reduced dramatically by the use of a thin but ductile adhesive layer. |
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Keywords: | Impact failure Layered materials Interfacial bonding Dynamic photoelasticity High-speed photography |
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