Todd L. Jessen

Effect of composite layering on the fracture toughness of brittle matrix/particulate composites

Abstract Glass matrix/Ni particulate composites, ranging from 0 to 25% particulate phase, were prepared both as single-volume-fraction composites and as multi-volume-fraction layered composites. Fracture toughness (K c ) measurements were made on all composites using the applied moment double cantilever beam technique. The measured toughness values for the layered composites were found to be equivalent to those of the single-volume-fraction composites. The fracture toughness measured for the layered composites was found to be dependent on the volume of composite phase tested and ultimately on the number of crack-particle interactions which occurred. R-curve like behaviour was observed in the layered composites.

Effects of processing on mechanical properties and microstructure of a ceramic composite

Abstract The effects of processing on the microstructure and mechanical behaviour of a Tyranno SiC fibre-reinforced zirconia titanate composite were evaluated. The microstructure was analysed using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Mechanical behaviour was characterized by strength and toughness measurements, which were correlated with the microstructure of the composite and its fibre/matrix interface. BN-coated fibres modified the interfacial microstructure by allowing debonding and fibre pull-out to occur. Incorporating CO-treated fibres and hot-pressing in an atmosphere of CO at an overpressure of 111.5 kPa limited fibre degradation during consolidation and resulted in improved in situ fibre strength. As a result, a strong (705 MPa) and tough ( 17.1 MPa m 1 2 ) Tyranno SiC fibre-reinforced composite was fabricated via hot-pressing at 1270°C at an applied pressure of 17.25 MPa.

PiezogranTM: High sensitivity/low‐cost composites for wide aperture arrays

A shift in US Navy emphasis from blue water to littoral regions has resultled in a need for improved acoustic devices. Wide aperture arrays will be hull‐mounted, thereby making device weight critical. The Naval Research Laboratory has developed a unique, low‐weight composite, transducer design, PiezogranTM, to address this need. Piezograns consist of discrete, polycrystalline piezoelectric‐ceramic elements dispersed in an epoxy matrix between two pressure plates. These plates make a direct mechanical as well as electrical contact to the piezoelectric elements. This design approach uses a 1‐3 composite structure for high‐gain operation with the flexibility of variable element spacing and ceramic volume fraction while achieving both low tooling and fabrication costs. Independent tests of 3.8‐cm diameter PiezogranTM prototypes have yielded high hydrostatic response (dh>150 pC/N) and capacitance of 1.18 nF. Ten‐centimeter‐square array panels have also been assembled and are currently undergoing testing. This ...