PSI - Issue 77

P. Santos et al. / Procedia Structural Integrity 77 (2026) 339–347 P. Santos et al. / Structural Integrity Procedia 00 (2025) 000 – 000

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b)

Fig. 4. a) Load - CMOD curves; b) J-integral – CMOD of the SENT specimen according to the cohesive model. The asymptotic maximum of the curves illustrating the load-CMOD corresponds to A = W condition, and means that the physical crack as well as the cohesive zone fully occupy the entire SENT cross-section. The notable feature of the J-integral is its tendency to linearly increase once the parabolic growth in the SSY regime is surpassed. According to Eq. (8), the remote stress limit  ∞ Y is: A=W ⇒σ ∞Y =Y ( 1 − W a ) 2 [12] Thus, the dependence between the relative crack size and the slope of the J-integral straight part may be fitted by the linear equation: dω dJ M = ( 1.00 − 1.03 W a ) Y [13] 4. Agreement between experimental and cohesive model results The similarity of shapes observed when comparing the J-integral - CMOD curves based on the cohesive model (Fig. 4) with that resulting from the experiments (Fig. 2c) is the first indication that the steel behaviour responds to the cohesive model. The identification of the constant slope that the two types of curves, both theoretical and experimental, exhibit when the SSY regime is overcome allows the cohesive resistance value Y of the undamaged steel to be obtained from Eq. (12). The value Y J thus obtained must be a material constant regardless of the crack size. Furthermore, the experimental observation that the crack growth and the load drop begin almost simultaneously suggest that both processes are activated as the extension of the cohesive zone becomes unstable because the applied remote stress approaches the asymptotic limit  ∞Y given by Eq. (13). Thus, this limit would provide a second value Y  for the cohesive strength of the steel if identified with the experimental maximum value  m . However, this second value would be a less sound estimate than the value Y J resulting from the slopes dJ/d ω M because the onset and development of extended yielding to which Y J is linked can be better defined from the tests than the instability condition associated to Y  . Table 3 shows the cohesive strength values Y J and Y  respectively found by each procedure. - Mechanics of Materials IV - Lecture 1