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From the viewpoint of continuum mechanics, cohesive and adhesive fracture have been shown to be similar. The energy approach to adhesive fracture has provided a method of interpreting the results from a convenient “blister” test that may be used quantitatively to evaluate bond strengths for particular bi-material bond systems. Inquiring further into adhesive fracture, the effect of including an elastic adhesive interlayer between the two other materials is investigated analytically and experimentally. The experimental system is typical of the propellant-liner-steel combination frequently encountered in a solid rocket motor.

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A testing method using the Rheometrics Mechanical Spectrometer as the loading instrument to measure the fracture toughness Ku, which is related to a specific sample geometry and dimensions (half-inch compact tension) is reported. The small sample size requirement makes it attractive to do fracture toughness testing on newly synthesized material for preliminary material study and comparison purposes. Commercially available epoxy resins were used to check the procedure at different temperatures (-150" to 250OC). An empirical crack length averaging method was used that appears to give constant Ku values independent of the a/W ratio values. The fracture surfaces were studied using scanning electron micros-COPY,