PSI - Issue 37

Dániel Antók et al. / Procedia Structural Integrity 37 (2022) 796–803 Dániel Antók, Tamás Fekete et. al.: Evaluation Framework … / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 3. The image of a specimen near its final failure, compared to the simulated geometry, using full 3D geometry model

The adequacy of the developed DTs for the problem in hand is illustrated by two examples. On Figure 3., the image of a specimen near to its final failure is compared to the simulated geometry on a full model: the two results show good qualitative agreement; however, a more accurate tracking of the asymmetry detectable on the image requires further refinement of the full model – in such a case, a simple model is inadequate to precise tracking of geometry – . The second example describes our approach to the problem of determining an appropriate flow curve for a given structural material. The simple geometric model is used here. The model with the mesh can be seen on Figure 4. (a). Two flow curves are shown in equation (3). Case (a) is an analytical form of the flow curve by fitting a power law to measured stress-strain data – see e.g., Ludwik (1909), Ramberg and Osgood (1943) and Hollomon (1945) – . ( ) ( ) 0 0 1 (a) ˆ ˆ ˆ (b) with n p i i i i i i K K          + = +  = +    = −  (3) where  is true stress, σ 0 is the flow stress,  is the true equivalent plastic strain, K is the strength coefficient, and n is the strain-hardening exponent. The predictions based on case (a) show that a finer flow curve is needed. When using flow curve in case (b), constructed as a sequence of linear functions per interval over enough intervals – see e.g., Ruggieri (2020) – simulations clearly provide much better results, in terms of Force and  ; see Figure 4. (b). The result clearly shows that the system's validity limits can go far beyond the limits of standard based evaluation methods.

Fig. 4. (a) The meshed simple model; (b) Predictions based on two – case (a): standard, case (b): improved – flow curves