SECOND ANNUAL PROJECT REVIEW AND TECHNICAL REPORT 1 MAY 1966-30 APRIL 1967

The finite-element method was used to calculate the longitudinal stiffness of short fiber composites; the instability of parallel edge cracks determined from the energy concept and the strength and inherent crack size obtained from the stability calculations; Young's modulus calculated for randomly oriented fibrous composites; a mathematical approach proposed for calculating stress fields around interior cracks; and invariant properties of a laminated composite derived from the transformation equations of the anisotropic moduli. The electron scanning microscope provided insight into fracture mechanics; composites were improved by incorporating a flexible layer around the fiber; polyacrylic acid reacted with ZnO to produce a high modulus, temperature- resistant matrix; data obtained indicating silane couplers decrease water diffusion at the interface; a decrease in fracture toughness associated with a change in crack propagation mechanism; and the viscosity of aggregate suspensions described by the Mooney equation. Techniques were developed for whisker fiber classification; strands of well-oriented whisker fibers made and fabricated into high performance composites; x-ray diffraction techniques applied to measuring fiber orientation, property maps developed for short fiber composites; short boron fibers encapsulated to make a pre-preg molding compound in bead form; fiber-matrix dry mix molding explored; and data obtained relating matrix properties to fatigue characteristics. Report on Monsanta/Washington Univ., ARPA Association Project Development of High Performance Composites. See also AD-487 208.