Mechanics and Material Aspects of Interfaces in Advanced Structures

Interfaces can be found in various kinds of modern engineering structures such as composite /sandwich structures, thin film/substrate structures, layered armor and rock. Interfaces are not only very important to material scientists, but also quite challenging to mechanics researchers. This talk will summarize some interfacial research on extremely small time scales (micro or nano-second) and length scales (micro to nanometer), which are related to homeland security and nanotechnology.

One topic will be dynamic failure mode transition at interfaces. A series of impact experiments were conducted using two high-speed optical diagnostic techniques - dynamic photoelasticity and Coherent Gradient Sensing (CGS) along with a combined mechanical, optical and electronic system. For the first time, the sequence and interaction of two major failure modes in dissimilar, layered materials- delamination and matrix cracking were revealed in real time. Moreover, enlightened by experimental observations of crack deflection/penetration at interfaces, a novel wedge-contacting-notch impact specimen was designed to explore the in-depth mechanics nature. Modeling using dynamic fracture mechanics theory made reasonable predictions. Another topic will be improving interfacial failure of dissimilar material joints using material (nanocomposite bonding) and mechanics (removing stress singularity) approaches. A novel interface/joint design, inspired from tree shape and mechanics, was developed to reduce the interfacial stress level through an integrated theoretical, numerical and experimental investigation. The new design featuring a specific pair of convex joint angles shows an effective elimination of the stress singularity at the interface/joint corners. Significant tensile loading capacity increase was observed (up to 81 %) for typical metal/polymer joints, while the material volume of the new joint decreased by at least 15 % over that of the traditional butt joint. Bulk nanofiber/epoxy composites and nanofiber-reinforced adhesives were synthesized for nanocomposite bonding.

Bio: L. R. Xu is an Assistant Professor of Civil Engineering and Materials Science at Vanderbilt University. He received his Ph.D. degree in Aeronautics and Materials Science from the California Institute of Technology in 2002. He was a winner of the Office of Naval Research Young Investigator Award in 2003 (for more information, visit his website: http://people.vanderbilt.edu/~l.roy.xu/ )

Back to Archives 2003

Back to Seminar Home Page

Last modified 24-December-2003 by website owner: NCNR (attn: )