脆性材料在雷射衝擊強化（Laser Shock Peening, LSP）作用下的裂紋起始與擴展，會高度受雷射誘發應力場的各向異性影響。尤其在無塗層雷射衝擊強化（LSPwC）條件下，因雷射與材料直接交互作用，容易產生拉伸釋放波，進而導致裂紋分支與不穩定破壞。本研究證實，以橢圓光斑取代傳統圓形光斑，可透過幾何載入本身的方向性偏置，明顯提升裂紋導引能力，並有效抑制側向分支裂紋，進一步提升破壞路徑的可控性與重現性。

本研究建立一套實驗與數值整合之分析架構，結合光斑足跡重建、有限元素應力分析與 XFEM 裂紋模擬，以連結能量沉積、應力演化與裂紋路徑預測，並以奈秒 Nd:YAG 雷射（1064 nm）進行驗證。在單晶矽實驗中，橢圓光斑沿目標切割方向配置，可在 0.7 mm 間距下形成更筆直的主裂紋並降低側向分支；相較之下，0.5 mm 間距因應力場重疊干擾而較不穩定。此外，橢圓光斑在無 pre-crack 的條件下，仍可獲得與有 pre-crack 相近，甚至更佳的導引效果，顯示光斑幾何設計可降低對機械式預裂紋的依賴。

在 Corning® EXG 玻璃方面，橢圓載入於未改質玻璃即可在較低能量下促發明顯剪應力主導的裂紋行為；並在內部改質玻璃（50 mJ、間距 0.7 mm）中，產生更平順且一致的缺口與分離前緣。整體而言，橢圓光斑 LSP 能有效抑制分支裂紋，強化裂紋線性與加工可預測性，提供一條應用於半導體與先進玻璃材料之精密分離與切割的可行策略。

Crack initiation and propagation in brittle substrates are highly sensitive to the anisotropy of laser-induced stress fields during laser shock peening (LSP), particularly under laser shock peening without coating (LSPwC), where direct laser–material interaction can generate tensile release waves and trigger unstable branching. In this study, we demonstrate that elliptical-spot LSP provides a notably improved crack-guidance capability compared with conventional circular spots by introducing a built-in directional bias in the loading geometry. An integrated experimental–numerical framework was established, combining optical footprint reconstruction, finite element stress analysis, and XFEM-based fracture modeling, to link laser energy deposition to stress evolution and crack-path prediction under nanosecond LSP (Nd:YAG, 1064 nm).
Experiments on single-crystal silicon show that elliptical focusing aligned with the target cutting direction produces straighter main cracks and fewer lateral branches, while maintaining stable crack transmission at a pulse spacing of 0.7 mm (more stable than 0.5 mm due to reduced stress-field overlap). Notably, the elliptical spot can achieve crack guidance comparable to, and in some cases better than, pre-cracked cases, indicating that geometric beam shaping can reduce reliance on mechanically introduced starter flaws. For Corning® EXG glass, elliptical loading promotes clear shear-dominated cracking at relatively low energy in pristine glass and improves the notch uniformity and separation-front smoothness in internally modified glass at 50 mJ with 0.7 mm spacing. Overall, the results confirm that elliptical-beam LSP effectively suppresses branching, enhances fracture linearity, and improves process predictability in brittle materials, providing a practical route toward controlled separation and precision dicing in semiconductor and advanced glass manufacturing.

[1] J.-M. Li, "Research on laser shock peening of the crack growth behaviour for brittle material," Master, National Cheng Kung University, 2025.
[2] K. Chen et al., "Research on the temperature and stress fields of elliptical laser irradiated sandstone, and drilling with the elliptical laser-assisted mechanical bit," Journal of Petroleum Science and Engineering, vol. 211, p. 110147, 2022.
[3] J. Dudutis, R. Stonys, G. Račiukaitis, and P. Gečys, "Glass dicing with elliptical Bessel beam," Optics & Laser Technology, vol. 111, pp. 331–337, 2019.
[4] U. J. Gutiérrez‐Hernández, H. Reese, F. Reuter, C. D. Ohl, and P. A. Quinto‐Su, "Nano‐Cracks and Glass Carving from Non‐Symmetrically Converging Shocks," Advanced Physics Research, vol. 2, no. 10, p. 2300030, 2023.
[5] C. Yang, Z. Ye, J. Lu, and Y. Jiang, "Laser shock forming of SUS304 stainless steel sheet with elliptical spot," The International Journal of Advanced Manufacturing Technology, vol. 56, no. 9, pp. 987–993, 2011.
[6] S. Zhou, Y. Huang, and X. Zeng, "A study of Ni-based WC composite coatings by laser induction hybrid rapid cladding with elliptical spot," Applied Surface Science, vol. 254, no. 10, pp. 3110–3119, 2008.
[7] K. Ding and L. Ye, Laser shock peening: performance and process simulation. Woodhead Publishing, 2006.
[8] J. Lu, L. Zhang, A. Feng, Y. Jiang, and G. Cheng, "Effects of laser shock processing on mechanical properties of Fe–Ni alloy," Materials & Design, vol. 30, no. 9, pp. 3673–3678, 2009.
[9] C. S. Montross, T. Wei, L. Ye, G. Clark, and Y.-W. Mai, "Laser shock processing and its effects on microstructure and properties of metal alloys: a review," International journal of fatigue, vol. 24, no. 10, pp. 1021–1036, 2002.
[10] M. S. Schneider et al., "Laser shock compression of copper and copper–aluminum alloys," International journal of impact engineering, vol. 32, no. 1-4, pp. 473–507, 2005.
[11] C. Ye and G. J. Cheng, "Effects of temperature on laser shock induced plastic deformation: the case of copper," 2010.
[12] T. Fras, L. Colard, E. Lach, A. Rusinek, and B. Reck, "Thick AA7020-T651 plates under ballistic impact of fragment-simulating projectiles," International Journal of Impact Engineering, vol. 86, pp. 336–353, 2015.
[13] E.-H. Kim, M.-S. Rim, I. Lee, and T.-K. Hwang, "Composite damage model based on continuum damage mechanics and low velocity impact analysis of composite plates," Composite Structures, vol. 95, pp. 123–134, 2013.
[14] A. Rajendran and J. Kroupa, "Impact damage model for ceramic materials," Journal of Applied Physics, vol. 66, no. 8, pp. 3560–3565, 1989.
[15] C. Yao, Q. Jiang, J. Shao, and C. Zhou, "A discrete approach for modeling damage and failure in anisotropic cohesive brittle materials," Engineering Fracture Mechanics, vol. 155, pp. 102–118, 2016.
[16] S. Hirobe, K. Imakita, H. Aizawa, Y. Kato, S. Urata, and K. Oguni, "Mathematical model and numerical analysis method for dynamic fracture in a residual stress field," Physical Review E, vol. 104, no. 2, p. 025001, 2021.
[17] C. Samuel et al., "Effect of Laser Shock Peening without Coating on Grain Size and Residual Stress Distribution in a Microalloyed Steel Grade," Crystals, vol. 13, no. 2, p. 212, 2023. [Online]. Available: https://www.mdpi.com/2073-4352/13/2/212.
[18] X.-Z. Li, M. Nakano, Y. Yamauchi, K. Kishida, and K. A. Tanaka, "Microcracks, spall and fracture in glass: A study using short pulsed laser shock waves," Journal of Applied Physics, vol. 83, no. 7, pp. 3583–3594, 1998, doi: 10.1063/1.366575.
[19] Y. Zhang, C. Yang, H. Qiang, and P. Zhong, "Nanosecond shock wave-induced surface acoustic waves and dynamic fracture at fluid-solid boundaries," Physical Review Research, vol. 1, no. 3, p. 033068, 11/01/ 2019, doi: 10.1103/PhysRevResearch.1.033068.
[20] C. Zhang, Y. Dong, and C. Ye, "Recent developments and novel applications of laser shock peening: a review," Advanced Engineering Materials, vol. 23, no. 7, p. 2001216, 2021.
[21] T. Nam, Finite element analysis of residual stress field induced by laser shock peening. The Ohio State University, 2002.
[22] Z. Zhou et al., "Thermal relaxation of residual stress in laser shock peened Ti–6Al–4V alloy," Surface and Coatings Technology, vol. 206, no. 22, pp. 4619–4627, 2012.
[23] H. Amarchinta, R. Grandhi, K. Langer, and D. Stargel, "Material model validation for laser shock peening process simulation," Modelling and simulation in materials science and engineering, vol. 17, no. 1, p. 015010, 2008.
[24] G. Cheng and M. Shehadeh, "Multiscale dislocation dynamics analyses of laser shock peening in silicon single crystals," International journal of plasticity, vol. 22, no. 12, pp. 2171–2194, 2006.
[25] F. Wang et al., "Localized plasticity in silicon carbide ceramics induced by laser shock processing," Materialia, vol. 6, p. 100265, 2019.
[26] L. F. Zhang, Y. K. Zhang, and A. X. Feng, "The fracture microphology of the ceramics by strong laser shock processing," in Materials Science Forum, 2006, vol. 532: Trans Tech Publ, pp. 137–140.
[27] R. A. Brockman et al., "Prediction and characterization of residual stresses from laser shock peening," International Journal of Fatigue, vol. 36, no. 1, pp. 96–108, 2012.
[28] B. Liu, S. Li, R. Li, C. Chen, and L. Liang, "Finite element simulation and experimental research on microcutting mechanism of single crystal silicon," The International Journal of Advanced Manufacturing Technology, vol. 110, pp. 909–918, 2020.
[29] X. Cheng, L. Yang, M. Wang, Y. Cai, Y. Wang, and Z. Ren, "The unbiased propagation mechanism in laser cutting silicon wafer with laser induced thermal-crack propagation," Applied Physics A, vol. 125, pp. 1–11, 2019.
[30] P. Peyre and R. Fabbro, "Laser shock processing: a review of the physics and applications," Optical and quantum electronics, vol. 27, pp. 1213–1229, 1995.
[31] W. Zhou, X. Ren, Y. Yang, Z. Tong, and E. A. Larson, "Finite element analysis of laser shock peening induced near-surface deformation in engineering metals," Optics & Laser Technology, vol. 119, p. 105608, 2019.
[32] R. Fabbro, J. Fournier, P. Ballard, D. Devaux, and J. Virmont, "Physical study of laser‐produced plasma in confined geometry," Journal of applied physics, vol. 68, no. 2, pp. 775–784, 1990.
[33] C. Ye, S. Suslov, B. J. Kim, E. A. Stach, and G. J. Cheng, "Fatigue performance improvement in AISI 4140 steel by dynamic strain aging and dynamic precipitation during warm laser shock peening," Acta materialia, vol. 59, no. 3, pp. 1014–1025, 2011.
[34] T. Belytschko and T. Black, "Elastic crack growth in finite elements with minimal remeshing," International journal for numerical methods in engineering, vol. 45, no. 5, pp. 601–620, 1999.
[35] M. Benzeggagh and M. Kenane, "Measurement of mixed-mode delamination fracture toughness of unidirectional glass/epoxy composites with mixed-mode bending apparatus," Composites science and technology, vol. 56, no. 4, pp. 439–449, 1996.
[36] Hibbitt, Karlsson, and Sorensen, ABAQUS/Standard: User's manual. Hibbitt, Karlsson & Sorensen, 1997.