Dependence on strain rate of the nucleation of cracks in polystyrene at 293°K

Abstract

The processes associated with the deformation and fracture of polystyrene tested in uniaxial tension have been studied over a range of strain rates from 1.4 × 10−2 to 4.3 × 10−7 sec−1 and at constant stresses between 4.1 and 2.9 kg/mm2. The effect of strain rate on the surface craze distribution prior to fracture, the fracture stress, the mechanism of nucleation of cracks, and the nature of fracture surfaces associated with slow and fast crack propagation have been determined. The changes in fracture surface appearance have been studied using optical and stereoscan microscopy. The observations are consistent with the model presented in a previous paper. Fracture is preceded by craze formation, cavitation in the craze, coalescence of cavities to form large planar cavities which propagate slowly until a critical stage is reached at which fast crack propagation occurs. The effect of changes of strain rate and material variables on these processes is discussed.

Analysis of the internal crazes in notched SAN

“…These markings are referred to as mackerel or patch pat-terns depending on whether they are regular or irregular. 38 The solid dark bands through the mirror region suggested that occasionally the crack also jumped from one craze to another as it propagated. The hackle pattern was observed when the crack passed beyond the tip of the damage zone and propagated through initially uncrazed material.…”

Electron microscopic investigations of the structure of crazes in polystyrene

“…Figure 7 shows a fracture surface with small hillocks with diameters of about 100 to 200 nm, which are the remains of ruptured, relaxed and fused fibrils. The problem of visibil- ity of crazes on fracture surfaces in general has been discussed in many papers [8,9,[22][23][24][25]. The crack propagation through the crazes occurs without any essential plastic deformation.…”

Microscale digital image correlation study of irradiation induced ductile-to-brittle transition in polyethylene

“…In this process voids form between the fibrils because of the relatively weaker van der Waals forces that occur between the fibrils. Numerous studies have concluded that brittle fracture in polymers is the result of craze formation followed by fibril breakdown [12][13][14][15][16][17][18][19][20][21][22]. In addition to crazing other deformation mechanisms are possible, such as shear yielding similar to that observed in metals, especially for polymers that exhibit bulk plasticity.…”