Edge crack test-piece

Fig. 5.59 Trouser and edge-crack test pieces used in the study of the tearing of elastomers. Expressions for -d ldA are given in each case. (After Andrewsy Chapter 9 in Polymer Science ed. Jenkinsy North-Hollandy 1972.)...

The areas where a test piece is attached to clamps and cut edges are preferential sites for cracking. It is generally good practice to coat clamped areas with an ozone resistant paint (which does not affect the rubber in any way) but cut edges are best left. For most purposes a Hypalon-based paint is satisfactory. Clamps, even when made of material such as aluminium, should be soaked in ozone prior to use. Any pattern or flaws on the test piece surface will also tend to act as stress raisers and show preferential cracking. 

FIGURE 10.30 Growth of an edge crack in a test piece of a natural rubber vulcanizate stretched repeatedly to 46% extension. (From Greensmith et al. (1963).)... 

Tensile strip test piece with an edge crack of length c. 

In treating adhesives as polymeric materials, it is possible to use Fracture-mechanics test specimens to determine material properties independent of geometry. A typical sample would be the compact tension test-piece, where a sheet of material, typically 6-mm thick and 100-mm square, has a sharp crack inserted in one edge. The sample is then loaded perpendicular to the plane of the crack and the load at which crack propagation... 

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