Microscopic mechanisms and mechanics of craze growth and fracture

Abstract

Abstract Isolated air crazes have been produced in thin films of polystyrene (PS) bonded to copper grids by straining these in tension. The craze thickness profile, r(x), was directly determined from a series of transmission electron micrographs taken along the craze. Local values of the craze fibril volume fraction v 1 and fibril extension ratio λ were established at frequent intervals along the craze by optical densitometry of the micrographs. The craze surface displacement profile w(x), craze surface stress profile S(x) and the true stress a t in the craze fibrils are computed from these parameters. The λ(x) profile provides conclusive evidence that the craze increases in thickness as it grows in length by drawing new polymer from the craze surface into the fibrils rather than by creep of the existing fibrils. The S profile exhibits a modest maximum at the craze tip but falls slowly over a distance of about 15 μm behind the craze tip to a value about 10% below the applied tensile stress. The λ of the d...