Videos

Bending of a Notched Specimen of Strombus gigas

This movie shows the cracking that develops from a notch that was machined into a four-point bend specimen of the shell of Strombus gigas. The crack, visible as a light thin line, grows along a direction 45 degrees with respect to the horizontal axis under increasing load. What is remarkable is that there is not any discernible crack opening displacement. Crack opening is resisted by the lamellae that are aligned in the direction perpendicular to the direction of propagation. Structural Basis for the Fracture Toughness of the Shell of the Conch Strombus Gigas, Nature, Vol. 405, June 29, pp. 1036-1040, 2000.

MEMS Silicon Fatigue Experiment

This movie shows a notched polycrystalline beam that is brought to resonance by the electrostatic forces developed in a comb drive. The etch holes fabricated into the specimen that enable complete release become blurry as the amplitude of vibration increases because the specimen is vibrating at approximately 15 kHZ. S-N curves for the silicon have been constructed by loading numerous specimens to different levels of maximum displacement (a finite element model is used to determine the associated maximum stress at the notch-root) and recording the number of cycles to failure. Fatigue Failure in Polysilicon Not Due to Simple Stress Corrosion, Science, Vol. 298, pp. 1215-1219, Nov. 8, 2002.

Collagen Fibril Pulled Using a MEMS Device

This movie shows a single collagen fibril attached at both ends to a polycrystalline silicon MEMS device and loaded in tension. The device contains a movable pad actuated by an electrostatic comb-drive that allows constant, monotonically increasing, or cyclic loading (up to ~10 kHz) depending on whether dc or ac voltages are applied. Using tungsten probes, one anchor is electrically grounded, and a voltage is applied to the fixed fingers. The resulting electrostatic attraction between the fixed fingers and movable fingers pulls the device to the left. Stress-strain Experiments on Individual Collagen Fibrils, Biophysical Journal, Vol. 95, pp. 3956-3963, 2008.

Tension Test on Carbon Nanotube

This movie shows the tension test performed on a carbon nanotube using a MEMS platform. The force-displacement curve provided the effective elastic modulus and the tensile strength of the tube. Development and Application of a Novel Micro-fabricated Device for In-Situ Testing of 1-D Nanomaterials, Journal of MEMS, Vol. 19, No. 3, pp. 675-682, 2010.

Pull-out Test of a Carbon Nanotube Embedded in an Epoxy Matrix

This movie shows a carbon nanotube being pulled out of an epoxy matrix. The experiment provided the fracture energy of the interface between the tube and the matrix. The first portion of the force-displacement trace is linear. At some point it bends over, indicating a reduction in stiffness produced by the initiation and extension of a crack at the interface between the tube and the matrix. At some point the tube is completely debonded from the matrix, and starts sliding out of the substrate. The latter portion of the load-displacement curve reflects the stiffness of the machine. Interface Toughness of Multi-wall Carbon Nanotube Reinforced Epoxy Composites, ACS Applied Materials and Interfaces, Vol.3, Issue 2, pp. 129-134, 2011.