Issue 68

B. Spisák et alii, Frattura ed Integrità Strutturale, 68 (2024) 296-309; DOI: 10.3221/IGF-ESIS.68.20

 Evaluation of test results for mini and normal SENB specimens.  2D load simulation, using a modified VCCT method, from which the fracture toughness value is determined according to ASTM E1820-20.  Unloaded 2D simulation using a modified VCCT method, from which the fracture toughness value is determined directly from the simulation. An important applicability criterion of the standard is that a minimum of 8 points or a correlation factor of at least 3 points between 0.4J Q and J Q or a correlation factor of more than 0.96 is required to determine the initial predicted crack size (a 0q ). In addition, if the optically measured crack size, a 0 , differs from a 0q by more than 0.01W or 0.5 mm, the data set is not satisfactory according to this test method. Fig. 15 shows the evaluation results of the measured normal SENB specimen according to ASTM E1820-20. The number of validated points exceeded 8 and at least one measurement result fell between the 1.5 mm and 2.0 mm construction lines. In this case, the value of J Q was found to be 446.70 kJ/m 2 . Note that the relative standard deviation of the material properties related to the crack propagation resistance of the materials (K IC , J IC ) is a "coefficient of variance" (standard deviation/expected value×100) of 10% or more. However, the experimental work is based on the intersection of these values with different curves, so two-tenths order of magnitude was used in order to make more accurate comparisons. Fig. 16 shows the evaluation results of 2D normal SENB specimen simulations according to ASTM E1820-20. In this case, the value of J Q was found to be 443.12 kJ/m 2 .

Figure 15: Evaluation of standard SENB measurement results according to ASTM E1820-20.

Figure 16: Evaluation of standard SENB 2D simulation results according to ASTM E1820-20.

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