Research

Our group performs mechanical response-based residual stress measurements, as shown here via the contour method on additive manufactured Ti-6Al-4V fatigue specimens.

Application of nano-second YAG laser pulses under confinement induces a compressive surface stress state, improving fatigue performance.

Lattice structures enabled by AM allow for lightweight components. However, lattice structure failure modes often differ from bulk specimen behavior due to pronounced surface roughness and porosity infuences.

Due to the layered build process and laser scan strategy, AM components demonstrate an orienation dependency in their thermal expansion response. We have quantified these effects for multiple thermal cycles using digital image correlation.

This information is important for accurate predictions of thermally-driven residual stress accumulation during deposition. Unchecked, these stresses can crack AM components before they are even finished being made.

Material extrusion additive manufacturing (MEAM) of the piezoelectric polymer PVDF is quite challenging due to the high coefficient of thermal expansion and difficulting in controlling microstructure. Our group has refined printing parameters and explored in situ electrical fields as means for enhancing PVDF printability and properties.

Optimizing PVDF deposition parameters and wiring with electrodes enables custom parts to be printed with piezoelectric sensing or actuation capabilities for “smart structure” applications.

Structures with multiple stable buckled states offer potential advantages for vibration-based energy harvesting devices. The nonlinear behavior of these buckled structures broadens the bandwidth of viable energy harvesting vibration frequencies and produces large strains/energy production outputs associated with transitioning between buckled states.

By prescribing the power level duty cycle during plasma-enhanced chemical vapor deposition of silicon nitride, a tightly controlled compressive residual stress state can be engineered. These residual stresses can be used to make buckled MEMS devices with nonlinear dynamic behavior, offering larger deflections and lower natural frequencies than their linear behavior counterparts.

Extremely thin films (100s of nm in thickness) are susceptible to periodic cracking when drying, especially if deposited on a mediated film layer that prevents bonding. Such cracking, when controlled, can be used as a template for further film patterning, similar to conventional microfabrication techniques, though without the equipment.

Laser spallation is a non-contact method for quantifying adhesion strength between a film and substrate. A nano-second laser pulse induces a rapidly expanding plasma to generate a shock wave that propogates through the specimen, ultimately loading the film-substrate interface in tension.