Experimental Research On Influence Of Voids On Main Crack And Its Time-effects Of Polypropylene Materials

In the studies on rupture theories of materials, the interaction between defects and their effects on properties of materials have received much attention and research. But most of those papers were about elastic materials, yet few about visco-elastic ones. In this paper, under the theoretical framework of rheology of bodies with defects, series of experiments on influence of voids on a main crack of polypropylene plane were made by using Moire technique, and analogous calculations were made by using Algor Finite Element Analysis. At the same time, the time-effect of influence of voids on the main crack was investigated. Much attention was paid to strain fields, G1 and COD, which can properly identify the character of the main crack. Experimental results and theoretic analyses in this paper show that: (1)Using Algor Finite Element Analysis, the influence law of voids with varying angles and distances on the main crack were reached in elastic materials. The relation between the stress on the extensional line of crack-tip and the location of voids was also obtained. The influence of voids on the main crack grows when the distance increases. As the angle of voids increases, the influence on the main crack grows at first, but when the angle reaches 450 and continues to increase, the influence changes to decrease. (2)The results which is similar to that of elastic materials was reached in polypropylene plane when the load was applied in a short time and the revised term was obtained. At the same time, the relation between the strain on the extensional line of crack-tip in visco-elastic materials and the location of the voids was obtained. (3)Voids have influence on energy release rate of crack body, and energy release rate is closely concerned with voids'location and time. In the polypropylene plane with voids, the relation between strain field before the crack-tip and the location of voids was discussed (4) The energy dissipation of crack in the polypropylene plane increases in each type of specimen as the time grows. But the growth value relevant to each type was different which will be dilated.