Although composite materials are widely used, many problems remain to be solved. This study derives the in-plane and transverse strength and shear stiffness of unidirectional fiber-reinforced composites from torsion experiments on rectangular cross section bars, using Lekhnitskii's equations. An equation is derived, to obtain the transverse stiffness and shear strength as a function of the fiber angle. The non-linear behavior and fracture strength in torsion of rectangular, antisymmetric angle-ply laminate bars were predicted. The predictions agree relatively well with experimental results.
A 2024 aluminum alloy matrix composite reinforced with potassium titanate fibers having a crystallite size of 76 nm was fabricated by squeeze casting. The effect of heat treatment and the bending strength were examined for the composites with Si contents of 0.15 wt% and 1.00 wt%, respectively. The differences of the hardness and Mg and Cu contents between interior and exterior of the specimen were found for the composite with the Si content of 0.15 wt%. On the other hand, the hardness and contents of the alloying elements mentioned above of the composite with the Si content of 1.00 wt% were uniform at all locations. The potassium hexatitanate fibers/2024 base alloy composite with solution treatment at 555°C for 4 hours and aging at 205°C for 16 hours showed the highest hardness and bending strength values.
Effect of water soluble potassium content of potassium hexatitanate fibers on the mechanical properties of polyamide 66 reinforced with potassium hexatitanate fibers were investigated. Two types of fibers with the water soluble potassium contents of 4 ppm and 127 ppm were used for the reinforcement. Some mechanical properties of the composites were investigated using dry test pieces and moisture absorbed test pieces having water content of 2.5 wt%. The mechanical properties of polyamide 66 reinforced with fibers with 4 ppm of water soluble potassium were higher than those of with fibers of 127 ppm of water soluble potassium. In particular, it was found that on moisture absorbed condition, the composites reinforced with low-potassium-leaching potassium hexatitanate fibers showed higher mechanical properties. The potassium hexatitanate fibers with negligible amount of leachability were found to be useful as a reinforcing material for polyamide 66.