Experimental J estimation equations for single-edge-cracked bars in four-point bend: Homogeneous and bi-material specimens

The present paper provides the plastic n factor solutions for J testing of single-edge-cracked specimens in four-point bend (SE(PB)), based on limit (slip line field) and detailed finite element limit analyses. Both homogeneous specimens and bi-material specimens with interface cracks are considered. Moreover, two different n factor solutions are developed, one for J (or C^* in creep crack growth testing) estimation based on the load-load line displacement (LLD) records, n_P^VLL, and the other J estimation based on the load-crack mouth opening displacement (CMOD) records, η_P^CMOD. It is found that the use of load-LLD records can be recommended only for testing deeply cracked SE(PB) specimens. Moreover, depending on how the LLD is measured, a different value of η_P^VLL should be used. On the other hand, the use of load-CMOD records is recommended for all possible crack lengths. Moreover, the proposed η_P^CMOD solution can be used not only for a homogeneous specimen but also for any bi-material specimen with an interface crack.