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<p>Conventional drilling of bolt holes in textile composites severs reinforcing fibers and degrades structural performance; therefore, integrally formed composite specimens with preformed bolt holes are essential for strength optimization. In this study, we propose a 3-D braided-in-hole process and investigate the mechanical properties and failure mechanisms of the resulting composite–aluminum alloy bolted joints under quasi-static tension. Through tensile experiments combined with digital image correlation techniques, the spatiotemporal evolution of the full-field strain around the hole and the macroscopic progressive damage characteristics are systematically quantified. To address the challenges of damage recognition against complex backgrounds, an automated crack extraction algorithm combining the local standard deviation and the Hough circle transform is proposed. Precise tracking of the in-situ crack evolution using this algorithm confirms that the three-dimensional braided structure substantially delays the initiation of micro-cracks. Compared with the drilling process, the integrated braided structure significantly enhances the ultimate bearing strength, increasing the average value from 391.33 MPa to 535.61 MPa, with a single-specimen peak of 606.84 MPa indicating its upper-limit potential. Furthermore, this structural advantage effectively suppresses stress localization and reduces the maximum out-of-plane secondary bending angle from 6.275<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(^{\circ }\)</EquationSource> </InlineEquation> to 3.572<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(^{\circ }\)</EquationSource> </InlineEquation>.</p>

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Damage Mechanism of Braid Hole Composite Bolt Joints Under Quasi–Static Tension

  • 期刊论文

  • 发表日期：

    2026年7月21日

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  • Huajun Ding,
  • Ming Cai,
  • Bohong Gu,
  • Baozhong Sun,
  • Ruiyun Zhang

摘要

Conventional drilling of bolt holes in textile composites severs reinforcing fibers and degrades structural performance; therefore, integrally formed composite specimens with preformed bolt holes are essential for strength optimization. In this study, we propose a 3-D braided-in-hole process and investigate the mechanical properties and failure mechanisms of the resulting composite–aluminum alloy bolted joints under quasi-static tension. Through tensile experiments combined with digital image correlation techniques, the spatiotemporal evolution of the full-field strain around the hole and the macroscopic progressive damage characteristics are systematically quantified. To address the challenges of damage recognition against complex backgrounds, an automated crack extraction algorithm combining the local standard deviation and the Hough circle transform is proposed. Precise tracking of the in-situ crack evolution using this algorithm confirms that the three-dimensional braided structure substantially delays the initiation of micro-cracks. Compared with the drilling process, the integrated braided structure significantly enhances the ultimate bearing strength, increasing the average value from 391.33 MPa to 535.61 MPa, with a single-specimen peak of 606.84 MPa indicating its upper-limit potential. Furthermore, this structural advantage effectively suppresses stress localization and reduces the maximum out-of-plane secondary bending angle from 6.275 \(^{\circ }\) to 3.572 \(^{\circ }\) .