Weibull stress model for cleavage fracture under high-rate loading

This paper examines the effects of loading rate on the Weibull stress model for prediction of cleavage fracture in a low-strength, A515-70 pressure ve ssel steel. Interest focuses on low-to-moderate loading rates ((K)over dot( 1) < 2500 <root>m s(-1)). Shallow cracked SE(B) specimens were tested at fo ur different loading rates for comparison with previous quasi-static tests on shallow notch SE(B)s and standard C(T)s. To utilize these dynamic experi mental data, we assume that the Weibull modulus (m) previously calibrated u sing quasi-static data remains invariant over the loading rates of interest . The effects of dynamic loading on the Weibull stress model enter through the rate-sensitive material flow properties, the scale parameter (sigma (u) ) and the threshold Weibull stress (sigma (w-min)). Rate-sensitive flow pro perties are modelled using a viscoplastic constitutive model with uniaxial, tension stress-plastic strain curves specified at varying plastic strain r ates. The analyses examine dependencies of sigma (w-min) and sigma (u) on ( K)over dot(1). Present results indicate that sigma (w-min) and sigma (u) ar e weak functions of loading rate (K)over dot(1) for this pressure vessel st eel. However, the predicted cumulative probability for cleavage exhibits a strong sensitivity to sigma (u) and, consequently, the dependency of sigma (u) on (K)over dot(1) is sufficient to preclude use of the static sigma (u) value for high loading rates.