Yj. Kim et Kh. Schwalbe, On the sensitivity of J estimation to materials' stress-strain curves in fracture toughness testing using the finite element method, J TEST EVAL, 29(1), 2001, pp. 18-30
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.