抄録
The relation between some mechanical properties and mechanism of the fracture of polystyrene has been studied by the morphological observation of the fracture surface when molecular weight, temperature and strain rate have been changed.
The morphology of fracture surface varies with the molecular weight, temperature and strain rate. The area of mirror region becomes larger as the temperature becomes higher and has a maximum value at certain temperature, covering all the fracture surface. The temperature, at which this maximum is observed, is shifted to higher one with the molecular weight of polystyrene and is depressed with lowering the strain rate. The maximum becomes distinct with the molecular weight.
The depression of the tensile strength with the temperature becomes more pronounced with the molecular weight and the strain rate. These tensile strength behaviors are well explained on the basis of the morphological observation on the fracture surface.
The elongation of polystyrene is found to be more closely related with the morphological observation. With the occurrence of crazes, the elongation goes down until it reaches a minimum value, where all the fracture surface becomes the mirror region, i.e., covered with crazes. The effects of temperature, the molecular weight and the strain rate on the elongational behavior are also discussed in terms of the morphological observations.
Summarizing these results, it is found that the tensile strength and the elongation of polystyrene are reasonably correlated with detailed morphological observations on the fracture.
