13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- V V pl pl pl P dJ dV J da Bb b η γ = − (15) where Vγ is the geometry factor of front face compact tension specimen. The Vγ as follows ' ' 1 V V V b W η λ γ λη λ η Δ ⎛ ⎞ = − − ⎜ + ⎟ ⎝ ⎠ (16) Substituting Eq 14 into Eq 16, it is interesting to find that Vγ γ Δ = . Integrating Eq 15 gives the plastic component of J in reference to the CMOD-based plastic factor and geometry factor 0 0 pl V a V V pl pl pl a P J dV J da Bb b η γ = − ∫ ∫ (17) As similar to the load line compact tension specimen, we obtain the following CMOD-based J estimation equation for a growing crack ( ) ( 1) 1, ( ) 1 1 pl i i i i i V V pl i Vpl i i i i J J A a a Bb b η γ + + + ⎛ ⎞⎛ ⎞ = + − − ⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠ (18) The CMOD-based J formulation is the other way to determine J resistance curves for 1/2FFCT specimens. Based on the detailed FEA, the plastic factor of front face compact tension specimen is investigated. The function, λ(a/W) , is obtained by linear fitting of the least squares method, considering the difference strain hardening of material mechanical behavior. The λ(a/W) is expressed as (be shown as in Fig. 2) ( ) ( / ) 0.3412 / 1.5356 a W a W λ =− + (19) 0.000 0.500 1.000 1.500 2.000 0.40 0.50 0.60 0.70 0.80 a/W λ function λ(a/W) function Figure 2. The function λ versus a/W curve From Eqs 12, 14, the plastic factor of front face compact tension specimen is fitted by the following curve
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