Estimation Procedures for J and CTOD Fracture Parameters Using Three-Point Bend Specimens

This work presents the development of J and CTOD estimation procedures for deep and shallow cracked bend specimens based upon plastic eta factors and rotational factors. The techniques considered include: i) estimating J and CTOD from plastic work and ii) estimating CTOD from the plastic rotational factor. The primary objective is to derive estimation techniques which are applicable to determine J and CTOD fracture parameters for a wide range of a/W-ratios and material flow properties. Very detailed non-linear finite element analyses for plane-strain models provide the evolution of load with increased load-line displacement and crack mouth opening displacement which are required for the estimation procedure. Laboratory testing of a structural steel using shallow and deep crack bend specimens provide the data needed to determine the CTOD-values for the material based upon the proposed methodology. These fracture toughness values are compared against the results obtained based upon the estimation equations given by BS 7448. The present analyses, when taken together with previous studies, provide a fairly extensive body of results which serve to determine parameters J and CTOD using bend specimens with varying geometries.