PSI - Issue 48

Bernadett Spisák et al. / Procedia Structural Integrity 48 (2023) 326–333 Spisák et al / Structural Integrity Procedia 00 (2019) 000 – 000

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In the following, the applicability of this new method is presented, in which a 2D plane strain model was developed for both normal and miniaturized CT specimens. The VCCT method requires a predefined crack path, which is limited to the element boundaries. In general, the smaller the distance between the neighboring nodes, the more accurate the prediction of the J-integral value. Due to this a denser mesh was generated for this simulation and instead of the previously showed mesh, where at the crack tip the mesh size was 100  m, here the size of the elements were chosen for 25  m, however the boundary conditions were the same. The mesh for both the normal and miniaturized specimen is shown on Fig. 7.

(a) (b) Fig. 7. Finite element mesh for the modified VCCT simulation (a) normal CT (b) miniaturized CT.

Table 2 summarizes the results. The measurements were evaluated based on ASTM E1820-20. For the evaluation our improved version of the elastic compliance E1820 test analysis software made by NISTIR (Lucon (2022)) was used. Also, in case of the normal CT specimen a simulation with the inclusion of GTN parameters with unloading was generated so the evaluation method described in ASTM E1820-20 could be applied. Similarly, two simulations were done with the VCCT model. In the first case the simulation was done with unloading and the fracture toughness was determined the same way as in case of the measurement, while in the second version no unloading was done and the fracture toughness was taken directly from the simulation. Here it should be noted that the simulations with GTN parameters and unloading is a more time-consuming solution than the VCCT method. In case of the miniaturized CT specimen the evaluation was done on the measured values, but the simulation was only carried out without unloading, and the fracture toughness was determined directly from the simulation. From the results it can be seen, that with every type of simulation methods the fracture toughness values are in good agreement with the measured ones. From this it can be concluded that the modified VCCT method is a well usable for the determination of the fracture toughness, as it is also working well in case of the miniaturized CT specimen.

Table 2. Fracture toughness results.

Fracture toughness (kJ/m 2 )

Difference

Type of specimen

Origin of data

Analyzing method

Measurement

338.18 325.77 345.73 346.32 347.40 317.80

-

Simulation with GTN parameters

ASTM E1820-20

-3.7% +2.2% +2.4% +2.7% -6.02%

Normal CT

Simulation with VCCT Simulation with VCCT

Simulation

Measurement

ASTM E1820-20

Miniaturized CT

Simulation with VCCT

Simulation

6. Conclusions and summary In the first part of the paper, the determination of GTN parameters using the ANN method on small flat specimens as opposed to the commonly used small cylindrical specimens was presented. As shown in the article, an ideal set of parameters can be determined with this specimen, which has been verified with different side notch specimens and with standard and miniaturized CT specimens. In case of the miniaturized CT specimen the effect of the geometry