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<p>Digital Image Correlation (DIC) is a widely adopted non-contact optical technique for full-field deformation and strain measurement in engineering structures, where measurement accuracy is strongly governed by the quality and stability of the applied surface speckle pattern. Conventional random speckle patterns, although effective, function solely as passive optical textures and do not support information integration or traceability, thereby limiting their applicability in long-term structural health monitoring (SHM). This study investigates a QR-code-derived speckle pattern fabricated using a spray-painting technique as a multifunctional alternative for DIC-based structural monitoring. The proposed pattern is evaluated using established speckle quality metrics, including entropy, gradient-based parameters, and higher-order intensity descriptors, and is compared with a manually generated random speckle pattern. Numerical rigid-body translation simulations employing FFT-based sub-pixel shifting are conducted to quantify systematic (bias) and random displacement errors under controlled conditions. Experimental validation is performed through three-point bending tests on reinforced concrete beams of varying strength grades, where DIC-derived load–displacement responses are independently verified using dial gauge and machine crosshead measurements. Emerging research also demonstrates that advanced sub-pixel estimation techniques and hybrid optimization frameworks can further enhance displacement accuracy beyond conventional interpolation approaches.</p><p>The results demonstrate that the QR-code-derived speckle pattern exhibits stable correlation behaviour and displacement accuracy comparable to benchmark reference datasets, showing moderately lower systematic and random displacement errors than the manually generated baseline speckle pattern under the investigated conditions. In addition, the pattern retains its information readability under deformation and cracking conditions, confirming its dual-function capability. QR-code readability was maintained throughout the elastic and early post-cracking stages, with successful decoding achieved up to the onset of major crack localization. Thus, the proposed approach introduces a functionally integrated speckle design that enables simultaneous deformation measurement and data encoding without compromising DIC performance, offering significant potential for data-linked, non-contact SHM applications. However, the comparison presented in this study is limited to a practical manually generated baseline speckle pattern and does not include optimized industrial fabrication techniques such as air-sprayed or water-transfer speckles, which require further investigation.</p>

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Feasibility investigation of QR-code-derived speckle patterns for DIC-based structural health monitoring

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月5日

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  • B. Murali Krishna,
  • Hanuma Kasagani,
  • Vinay Kumar Gaddam,
  • V. Ramya Krishna,
  • Teja S R R Parthipati,
  • M. Charanlal,
  • Shankar Karuppannan

摘要

Digital Image Correlation (DIC) is a widely adopted non-contact optical technique for full-field deformation and strain measurement in engineering structures, where measurement accuracy is strongly governed by the quality and stability of the applied surface speckle pattern. Conventional random speckle patterns, although effective, function solely as passive optical textures and do not support information integration or traceability, thereby limiting their applicability in long-term structural health monitoring (SHM). This study investigates a QR-code-derived speckle pattern fabricated using a spray-painting technique as a multifunctional alternative for DIC-based structural monitoring. The proposed pattern is evaluated using established speckle quality metrics, including entropy, gradient-based parameters, and higher-order intensity descriptors, and is compared with a manually generated random speckle pattern. Numerical rigid-body translation simulations employing FFT-based sub-pixel shifting are conducted to quantify systematic (bias) and random displacement errors under controlled conditions. Experimental validation is performed through three-point bending tests on reinforced concrete beams of varying strength grades, where DIC-derived load–displacement responses are independently verified using dial gauge and machine crosshead measurements. Emerging research also demonstrates that advanced sub-pixel estimation techniques and hybrid optimization frameworks can further enhance displacement accuracy beyond conventional interpolation approaches.

The results demonstrate that the QR-code-derived speckle pattern exhibits stable correlation behaviour and displacement accuracy comparable to benchmark reference datasets, showing moderately lower systematic and random displacement errors than the manually generated baseline speckle pattern under the investigated conditions. In addition, the pattern retains its information readability under deformation and cracking conditions, confirming its dual-function capability. QR-code readability was maintained throughout the elastic and early post-cracking stages, with successful decoding achieved up to the onset of major crack localization. Thus, the proposed approach introduces a functionally integrated speckle design that enables simultaneous deformation measurement and data encoding without compromising DIC performance, offering significant potential for data-linked, non-contact SHM applications. However, the comparison presented in this study is limited to a practical manually generated baseline speckle pattern and does not include optimized industrial fabrication techniques such as air-sprayed or water-transfer speckles, which require further investigation.