The Effect of Load and Crack Misalignment on Stress Intensity Factors for Bend-Type Fracture Toughness Specimens

Abstract

Mode I and Mode II stress intensity factors (SIF) are presented for three-point bend specimens with misaligned locations of loadings and cracks. Such stress intensity factors were obtained through the application of the weight function technique and the particular stress distribution applicable to a three-point eccentrically loaded beam. Mode I and Mode II stress intensity factors for an eccentrically loaded four-point beam having a misaligned crack were obtained by superposing the data applicable to the load and crack on a misaligned three-point loaded beam. The results of these analyses were then employed to evaluate the effect of load and crack misalignment on Mode I and Mode II stress intensities of specimen configurations included in ASTM E 399 for Plane-Strain Fracture Toughness of Metallic Materials and in ASTM C 1421-99 for the Determination of Fracture Toughness of Advanced Ceramics at Ambient Temperature. The SIF ratios for Mode II-to-Mode I were also determined for both the eccentrically loaded three-point beam and the four-point beam having misaligned cracks. Differences in the Mode I stress intensities were determined for the cases where the load and crack misalignments are taken into account and those idealized cases where they are not. Finally, recommendations are presented to reduce, where necessary, these differences to an acceptable degree.