DIC在相似材料模型中的裂隙检测

Crack detection method in similar material models based on DIC

为定量描述上覆岩层中裂隙的产生及发育,利用数字图像相关技术(DIC)在相似材料模型中进行了裂隙检测。通过定量研究散斑图案质量及DIC计算参数对检测效果的影响,针对模型局部非均匀变形,提出了子区大小选择的双参数阈值法,确定了裂隙检测所用的子区大小,并合理选择子区间距。然后使用数码相机采集1200 mm×1000 mm×50 mm(长×高×宽)的二维平面相似材料模型表面的散斑场,获取模型目标图像的应变场和位移场,得出了裂隙产生的位置、张开度和长度等定量特征,并与全站仪同步量测数据进行对照。试验表明,采用子区边长40像素和子区间距10像素的测试参数,得出了该模型3条裂隙的存在及其发育信息,验证了双参数阈值法的可靠性;随着裂隙的逐渐发育,应变局部化带由模糊到清晰,应变曲线分布特征由单峰到双峰,位移曲线逐渐呈阶梯状分布,可从应变场局部化带长度快速估计裂隙发育长度;DIC测量结果与全站仪测量结果的最大相对误差为7.73%。DIC测量系统既能有效地检测裂隙,又能达到较高测量精度。研究结果为进一步应用DIC研究相似材料模型变形提供了试验基础。

In order to quantitatively understand the generation and development of cracks in overlying strata,digital image correlation technology(DIC)was used to detect cracks in a similar material model.According to the quantitative research on the influence of speckle pattern quality and DIC calculation parameters,a two-parameter threshold method based on the selection of subset size for the local non-uniform deformation of similar material models was proposed.Meanwhile,the step size used in the test crack detection was determined,and the step size was reasonably selected.Then a digital camera was used to collect the speckle field on the surface of a two-dimensional model of similar materials of 1200 mm(L)×1000 mm(W)×50 mm(H),acquire the strain field and displacement field of the target image of the model,and obtain the quantitative characteristics such as position,opening degree and length of cracks.After the comparison with the synchronous measurement data of the total station,the test results showed that the existence and development of three cracks in the model can be obtained by using the test parameters of 40 pixels on the subset side length and 10 pixels step size,the reliability of the two-parameter threshold method was also verified.With the gradual development of cracks,the strain localization bands change from fuzzy to clear,the distribution characteristics of strain curve changed from single peak to double peak,and the displacement curve gradually presented a stepped distribution.The length of crack development can be quickly estimated according to the length of strain localization band.The maximum relative error between DIC measurement results and total station measurement results was 7.73%.DIC measurement system effectively detected cracks and achieved high measurement accuracy.The results provided an experimental basis for further applying DIC to study deformation of similar material model.