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The multispecimen J-integral technique ASTM Test Method for JIc, a Measure of Fracture Toughness (E 813-87) has been applied to a series of rubber-toughened polymers to determine the generality of the method for polymeric materials. The experimental procedures produce results that are similar in form with those found in the metals and ceramics literature. However, many of the procedures involving data analysis require reexamination.
In this study, the effects of side grooves, ligament depths, and the relationship between critical initiation J and G values are examined. The use of side-grooved specimens for J testing is a viable way of experimentally verifying plane strain conditions. The ASTM E 813-87 recommendation for the allowable range of ligament depths appears to be inappropriate for toughened polymers. However, the recommendation of W/B = 2 as an experimental starting point is sensible. Finally, the JIc to Gc relationship was explored. In separate, nonstandard K tests involving large specimens, the initiation point, Gc, was defined at 2.5% crack growth. JIc, as calculated by the ASTM E 813-87 construction, was as much as 50% lower than this Gc value. However, when comparing critical J and G values for specific crack growths, good agreement between the two tests was obtained, provided the crack growth was small. Although the current JIc construction provides a conservative estimate of the Gc value, it is an open question whether the JIc value is appropriate for polymer design.
multiple specimens, J, -integral, toughened polymers, ligament depth, elastic-plastic fracture, test methods
Group leader, E. I. du Pont de Nemours, Inc., Wilmington, DE