This preliminary study examined the relationship of interfacial shear strength (IFSS) to modulus of rupture (MOR) for several different wood–plastic composites (WPCs). Plastics utilized were high-density polyethylene (HDPE) and polypropylene (PP). Pine and oak were used as the wood species. Compatibilizers used included maleic-anhydride-grafted polyethylene (MAPE) and maleic-anhydride-grafted polypropylene (MAPP). A strong correlation between IFSS and MOR was observed in a limited composition region. PP/oak WPCs showed poor correlation between MOR and IFSS, probably due to the roughness of the oak surface. Compatibilizer systems incorporating liquid components did not give good results and appeared to be inappropriate for this test method.

This article reports a two-dimensional, finite-difference heat transfer model for calculating the transient temperature distribution in a polycrystalline silicon cantilever during and after irradiation by a Nd:YAG laser. Results include the peak surface temperature after irradiation and the uniform temperature increase in the microcantilever following subsequent heat conduction through the thickness. The calculations reveal that the time scale after which the temperature is uniform through the thickness is on the order of hundreds of nanoseconds and that the microcantilever cools in the order of tens of milliseconds. The effects of energy transfer to the environment by convection and radiation on the cooling time are also investigated. The accuracy of the model predictions are shown through highspeed temperature measurements using a novel MEMS temperature sensor.

To characterize microelectromechanical systems (MEMS) during laser processing, imaging and metrology techniques need to be developed that are capable of visualizing the dynamics of MEMS structures and that are compatible with high power lasers. This study describes a high-speed, interferometric imaging system for measuring out-of-plane deflections of polycrystalline silicon (polysilicon) MEMS structures. A HeNe laser with a wavelength of 632.8 nm illuminates the structures. Since polysilicon is semitransparent at 632.8 nm interference occurs between light waves reflected from the top of the microstructure and light waves transmitting through the structure and reflecting off the substrate. The interference produces fringes along microstructures that correspond to changes in height. Using a high-speed CCD camera, transient interferometric images of the dynamic motion of MEMS devices are captured The imaging technique is demonstrated by obtaining the first transient images of the repair of adhered polysilicon microcantilevers, due to Nd:YAG pulsed laser heating. The experimental results clearly show failed structures peeling from the substrate as they are repaired.

We present a model for reducing adhesion in MEMS structures using laser heating and compare the model to experimental results. Using a fracture mechanics model, the interface between the stiction-failed microcantilever and the substrate is treated as a crack, and the energy release rate is calculated using elastic theory. In order to include the effect of laser irradiation of the microcantilevers, an associated thermal strain energy is included in the fracture model. As the beam peels, the free length reaches a critical value where the beam buckles, decreasing the energy of the system. The results of the model predict a temperature difference of 100 K is able to repair microcantilevers as long as 600 μm. Experiments are performed that demonstrate the peeling of stiction-failed beams from the substrate after laser irradiation as predicted by the thermomechanical model.