Failure in laminates in tension under increasing stress,constant stress,and cyclic stress

Both monotonic and cyclic tension experiments have been carried out to fracture on transparent laminates made from flat ribbon glass and polyethylene sheets by heat bonding in a vacuum. The distribution of the measured tensile fracture stresses in monotonic loading correlates very well with the distribution of fracture stresses calculated from the measured distribution of element fracture stresses and the yield strength in shear of the polyethylene, according to a detailed statistical theory worked out earlier by Scop and Argon. Although the expected mode of fatigue damage by propagation of delamination cracks emanating from isolated stable fractures in reinforcing elements was observed, actual fatigue failure was a result of a more rapid mechanism of continued fracturing in reinforcing elements by a humidity-induced time-integrated static fatigue process. While laminates subjected to static stresses of the same magnitude as those in the dynamic experiments failed by the development of an identical form of damage during the same length of time under stress in laboratory air, other laminates tested in the same manner in dry air had 5 to 10 fold increased lives. In addition re-testing of individual elements of delaminated composites showed that elements can often be damaged during lamination, which must be taken into account in any quantitative study.