On the sensitivity of J estimation to materials' stress-strain curves in fracture toughness testing using the finite element method

The present paper reports the accuracy of the J estimation equations for th ree typical homogeneous fracture toughness testing specimens: M(T), C(T), a nd SE(B) specimens, based on systematic 2D FE analyses. A wide range of cra ck lengths is considered, except for C(T) specimens where only deep cracks are considered, a/W = 0.45 to 0.7. By carefully selecting the properties of the materials in the analysis, particular emphasis is placed on the sensit ivity of such equations to the strain hardening as well as the type of stre ss strain curve, such as continuously hardening materials or materials with Luders strain. Two different J estimation schemes are considered, one base d on load-load line displacement records and the other on load-crack mouth opening displacement (CMOD) records. For all cases considered, the J estimation based on load-CMOD records gives more accurate results, compared to those based on load-load line displacem ent records. Moreover, the J estimation is not sensitive to the material's strain hardening and to the type of the stress-strain curve, except for sha llow-cracked M(T) specimens with a/W < 0.2. For shallow-cracked M(T) specim ens with a/W < 0.2, the J estimation equation is not sensitive to the mater ial, for materials with Luders strain, but is sensitive for continuously ha rdening materials. The error increases with the hardening, i.e., a higher h ardening material gives a larger error in J.