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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1. Introduction A long-term durability of carbon fiber reinforced plastic (CFRP) is one of the most important issues for composite materials fields. Damage accumulation subjected to cyclic loadings has to be quantified to predict residual strength and residual lifetime of CFRP. In the present study, the damage accumulation of CFRP laminate is modeled for all range of life, i.e. from intact, before transverse crack occurring, increase of transverse cracks, delamination, until ultimate failure, considering entropy value. When a polymer material is subjected to some load, material entropy increases with deformation even at the stage where void nucleation is not found yet. This can be verified by molecular dynamics simulation. Subsequently, a void of a few angstrom size appears with increase of loadings, and some void are united and becomes larger void, consequently, the polymer results in ultimate failure. Using molecular simulation, damage (void content) and entropy is linked. Let us go up to next step which is microscale analysis. By representative volume element (RVE) and some of micromechanical models, the ply property including time- and load-dependent degradation is determined for each direction. At this stage, both interface failure and matrix failure are considered. The determined ply properties are utilized in meso scale analysis, which is ply level homogenization, i.e. CFRP laminate analysis. For this stage, the degradation of ply properties is quantified by load history. Thus, we can predict the residual strength and lifetime based on nanoscopic phenomena for CFRP laminates without any experimental results, through entropy value. This homogenizing method is schematically shown in below figure.

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Fig. 1 Overview for multiscale analysis regarding durability of CFRP based on entropy based damage. For above calculations, entropy value is dealt with as a damage index. This scheme is originally based on the thermodynamic theory. On the other hand, the entropy is mechanical value and also be thermodynamic value. So if we can identify the value of entropy, we can know the damage state of CFRP, postulating that we complete above calculation. So we have two objectives for this study. One is establishment of above multiscale numerical simulation, and another is establishment of measurement method for entropy. After those, we can acquire the system of identifying internal damage state, residual strength, remaining lifetime, and degradation of CFRP. In this paper, we introduce our current studies to our goal. For the meantime, numerical simulations are proceeded very well but establishment of entropy measurements is still under examination and any significant results are not obtained yet. 3UHGLFWLRQV RI UHVLGXDO VWUHQJWK DQG OLIHWLPH GHSHQGLQJ RQ ORDGLQJ KLVWRU\ 8VLQJ HQWURS\ YDOXH DV GHWHULRUDWLRQ LQGH[ UHVLGXDO VWUHQJWK DQG OLIHWLPH RI &)53 ODPLQDWH LV TXDQWLILHG EDVHG RQ QDQR VFRSLFDO SKHQRPHQD 1XFOHDWLRQ RI YRLGV GDPDJH HQKDQFHPHQW RI HQWURS\ 'HWHUPLQDWLRQ RI TXDQWLWDWLYH GHWHULRUDWLRQ DV SO\ SURSHUW\