PSI - Issue 52

Jun Koyanagi et al. / Procedia Structural Integrity 52 (2024) 187–194 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 3 Results obtained from MD simulations: the fracture entropy is close even when stress state varies. (a) triaxial, (b) biaxial, (c) uniaxial, and (d) shear stress states.

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Fig. 4 Void nucleation and growth with deformation under uniaxial tensile which is equivalent to triaxial tensile.

2.3. Possibility for quantitative detection of mechanically induced invisible damage by thermal property measurement via entropy generation for a polymer material (Sakai et al. 2022) The values of entropy estimated from the heat capacity measured by DSC, entropy calculated from the dissipated energy during mechanical testing, and the entropy obtained from MD simulations were compared for PA6 subjected to a tensile load of 25%. Qualitatively, the numerical magnitudes were as expected, but only the entropy value measured by DSC was significantly larger. Since DSC is a destructive test, it is believed that the entropy increased during sample preparation. Based on this, a non-destructive method for measuring specific heat is currently being developed. 3. Studies for Micro-Scale Simulations 3.1 Residual strength prediction for unidirectional CFRP considering entropy damage (Sato et al. 2021) Sato et. al. 2021 introduced a non-linear viscoelastic constitutive equation considering entropy damage into finite element analysis and conducted micro-scale analysis. We developed a finite element that associates dissipated energy with damage, counting it in real-time depending on the stress-strain-time history. We used this method to predict residual strength after stress relaxation (constant strain) and obtained good agreement with experimental results as shown in Fig. 5. The model for predicting strength reduction during constant strain is unprecedented worldwide.