Effect of Higher Order Terms on Measurement of Dynamic Stress Intensity Factor with Caustic Method

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[1] Crack tip stress fields of cracks which were being propagated at a speed of about 550m/s were measured at the time of 18 or 73 microsecons after the crack initiation, with holographic caustic method and pulsed holographic microscopy. The following results were obtained.(i) In the direction along a crack, effect of higher orber terms doesn't appear either at 18 or at 73 microseconds after the crack initiation, and the singular field is developed as far as 9mm from the crack tip. Hence, measurement of crack opening displacement always gives the true value of dynamic stress intensity factor.(ii) In the direction of 72 degrees from the crack propagation direction, effect of higher order terms appears at the time of 18 microseconds after the crack initiation. But it disappears at 73 microseconds, and the singular field is developed as far as 5mm from the tip.[2] Crack tip stress fields were measured also with a method of interferometry, and the same results as the above were obtained.[3] It can consequently be said that the higher order terms affect the measurement of dynamic stress intensity factor with the caustic method if the measurement is carried our within several ten microseconds after beginning of rapid crack propagation.