PSI - Issue 52

Haseung Lee et al. / Procedia Structural Integrity 52 (2024) 252–258 Haseung Lee, Hyunbum Park / Structural Integrity Procedia 00 (2019) 000 – 000

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As a result of the analysis, there is a change in the material properties as the size of the void changes when the VF is the same, but the trend is not clear. Depending on the void size, the tensile strength showed a greater change than the compressive strength. When the void is 5%, the compressive strength showed a decrease of more than 40% compared to the case without void. Stiffness tends to decrease as the void size increases, and the size is very insignificant compared to strength, and tensile stiffness is more sensitive than compression stiffness. Next, when the void size is constant, the change in properties according to the changes in void fraction was determined. For the convenience of analysis, the void size was fixed at 200, and the void location was considered in two cases, intra and inter. As in the previous analysis, after establishing the properties of the composite material with voids using the homogenization technique, a virtual experiment was conducted according to the ASTM D3039 and ASTM D6641. In the case of inter voids, there are fewer areas where they can be physically located compared to inter voids. As a result, the max void fraction that can be realized in the analysis is 2%, but in case of intra voids, max void fraction is 7%. And the analysis results are shown in the figure below.

Fig. 4. Material properties depending on intra void fraction at void diameter 200 μｍ (a) Strength.; (b) Stiffness

Fig. 5. Material properties depending on inter void fraction at void diameter 200 μｍ (a) Strength.; (b) Stiffness

As a result of the analysis, it can be confirmed that the tensile and compressive strengths decrease as the void fraction increases in both cases of intra void and inter void. The tendency of strength loss is similar in tension and compression. In the case of stiffness, it can be confirmed that the tensile stiffness is greatly affected in both intra and inter void cases. When the void fraction is 2%, comparing the change in strength properties according to intra voids and inter voids, the tensile and compression knockdown factors of intra voids are 0.612 and 0.641, and the knockdown factors of inter voids are 0.631 and 0626. It was confirmed that the compressive strength drop was higher for intra voids than for inter voids, and the drop in tensile strength was lower, but the values are expected to be at an error level.