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Interfacial crack analysis in layered media using couple-stress elasticity and the displacement discontinuity method |
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| รหัสดีโอไอ | |
| Title | Interfacial crack analysis in layered media using couple-stress elasticity and the displacement discontinuity method |
| Creator | Sok An Yin |
| Contributor | Jintara Lawongkerd, Advisor |
| Publisher | Thammasat University |
| Publication Year | 2568 |
| Keyword | Interfacial crack, Couple-stress elasticity, Displacement discontinuity method, Multilayered media, Size-dependent behavior |
| Abstract | This thesis develops a displacement-controlled formulation for analyzing a pre-existing interfacial crack in multilayered elastic media using couple-stress elasticity and the displacement discontinuity method. The pre-existing crack represents an initial microdefect that may arise from weak interfacial bonding, small voids, incomplete curing, poor surface preparation, residual thermal or shrinkage stresses, fatigue, impact, moisture, corrosion, or material degradation. The crack is modeled as a prescribed normal displacement discontinuity, and the corresponding reaction stress, displacement, rotation, and couple-stress fields are obtained using Fourier integral transforms, layer flexibility matrices, and Gauss–Legendre quadrature. The formulation agrees well with published benchmark results, with maximum and mean relative errors of approximately 1% and 0.5%, respectively. The results show that increasing the normalized material length-scale parameter increases the near-tip reaction stress while reducing displacement and rotation, confirming the stiffening effect of couple-stress elasticity. Material mismatch strongly influences the response, with the near-tip reaction stress following the order SHS > HHS > HSS. Size-dependent effects are strongest for short cracks, while the predicted response gradually approaches the classical elastic solution as the crack length increases. In multilayered systems, soft-to-hard interfaces generally produce higher reaction stresses than hard-to-soft interfaces. Therefore, the intrinsic material length scale, crack size, stiffness mismatch, stacking sequence, and crack position are key factors governing interfacial cracking and delamination in layered media. |
