seminar today by Prof Mary Boyce from MIT

Beth Pruitt pruitt at stanford.edu
Thu Apr 24 14:50:28 PDT 2008


periodic elastomeric structures and their acoustic structural models, 
i.e. "phononic crystals"
>
>
>Mechanics of Deformation-Triggered
>Pattern Transformations and Superelastic Behavior
>in Periodic Elastomeric Structures
>
>Presented by
>
>Mary C. Boyce
>Department of Mechanical Engineering
>Massachusetts Institute of Technology
>Thursday, April 24, 2008
>4:15 PM in Building 300, Room 300
>
>Periodic microstructures abound in nature and provide numerous 
>interesting and unique mechanical, photonic, phononic and 
>hydrophobic properties. Here, novel and uniform deformation-induced 
>pattern transformations have been found in periodic elastomeric 
>cellular solids upon reaching a critical level of mechanical load. 
>This behavior is accompanied by a superelastic stress-strain 
>behavior where, after reaching the critical load, the material 
>deforms elastically to large deformations at nearly constant stress. 
>Numerical simulations utilizing Bloch wave analysis clearly show the 
>mechanism of the pattern switch to be a form of local 
>microstructural elastic instability, giving reversible and 
>repeatable transformation events as confirmed by experiments. The 
>nature of the instability and accompanying pattern transformation 
>depend on the initial periodic pattern. The deformation-triggered 
>transformations have been physically realized for several periodic 
>elastomeric structures including square and oblique arrays of 
>circular holes as well as rectangular arrays of elliptical holes, 
>each subjected to axial compression. A ligament buckling instability 
>was found to trigger the transformations in the square and 
>rectangular lattices and a shear instability triggered the 
>transformation in the oblique lattice. Post-deformation 
>transformation is observed to accentuate the new pattern and is 
>found to be elastic and to occur at nearly constant stress, 
>resulting in superelastic behavior.
>Furthermore, periodic microstructures are a known method to control 
>wave propagation and create materials with tailored band gap 
>structures. Here, we calculate the acoustic band structures of 
>different periodic elastomers at different levels of deformation. We 
>demonstrate the ability to use deformation to transform phononic 
>band gaps. The elastomeric nature of the material makes the 
>transformation in both structural pattern and phononic band gap a 
>reversible and repeatable process, creating a phononic band gap 
>switch.
>
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