Weibull stress model for cleavage fracture under high‐rate loading

Abstract

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 vessel steel. Interest focuses on low‐to‐moderate loading rates ( K˙ I < 2500 MPa √m s −1 ). Shallow cracked SE(B) specimens were tested at four 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 experimental data, we assume that the Weibull modulus ( m ) previously calibrated using 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 ( σ u ) and the threshold Weibull stress ( σ w‐min ). Rate‐sensitive flow properties are modelled using a viscoplastic constitutive model with uniaxial, tension stress–plastic strain curves specified at varying plastic strain rates. The analyses examine dependencies of σ w‐min and σ u on K˙ I . Present results indicate that σ w‐min and σ u are weak functions of loading rate K˙ I for this pressure vessel steel. However, the predicted cumulative probability for cleavage exhibits a strong sensitivity to σ u and, consequently, the dependency of σ u on K˙ I is sufficient to preclude use of the static σ u value for high loading rates.