FATIGUE STRENGTH OF PLASTIC LAMINATES REINFORCED WITH UNWOVEN ''S'' GLASS FIBERS.
FOREST PRODUCTS LAB MADISON WI
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Fatigue curves are presented for plastic laminates reinforced with layers of unwoven S glass filaments in a matrix of epoxy-type resin and subjected to various alternating stress amplitudes superimposed on constant mean loads of 0 and 25,000 pounds per square inch tensile stress. The S-N curves were determined by axially loading specimens of three types of construction, namely 1 all layers of unwoven glass parallel to the principal axis, 2 alternate layers at or - 5 degrees to the principal axis, and 3 alternate layers at 0 and 90 degrees to the principal axis. All experiments were conducted on unnotched specimens, at 900 cycles per minute, in an atmosphere maintained at 73 F. and 50 percent relative humidity. Loads were applied parallel to the principal axis. The S-N curves and replication of specimens establishing the curves show that the fatigue strength of S glass laminates is significantly greater than that of similar E glass laminates. Author