Optimum notch configurations for the chevron-notched four-point bend specimens

Abstract

The failure sequence following crack formation in a chevron-notched four-point bend specimen is examined in a parametric study using the Bluhm slice synthesis model. Premature failure resulting from crack formation forces which exceed those required to propagate a crack beyond α is examined together with the critical crack length and critical crack front length. An energy based approach is used to establish factors which forecast the tendency of such premature failure due to crack formation for any selected chevron-notched geometry. A comparative study reveals that, for constant values of α1 and α0, the dimensionless beam compliance and stress intensity factor are essentially independent of specimen width and thickness. The chevron tip position α0 has its primary effect on the force required to initiate a sharp crack. Small values for α0 maximize the stable region length, however, the premature failure tendency is also high for smaller α0 values. Improvements in premature failure resistance can be realized for larger values of α0 with only a minor reduction in the stable region length. The stable region length is also maximized for larger chevron base positions, α1, but the chance for premature failure is also raised. Smaller base positions improve the premature failure resistance with only minor decreases in the stable region length. Chevron geometries having a good balance of premature failure resistance, stable region length, and crack front length are 0.20⩽ α0⩽0.03 and 0.70⩽α1⩽0.80