Laser Shearography method (LSM) has shown a great potential for application in nondestructive testing (NDT) especially in the early detection of cracks in concrete. It is based on a refinement of electronic speckle pattern interferometry (ESPI) that records a sheared image of the speckle interferogram. The speckle interferograms are recorded before and after stressing and then compared to find the defects on the surface of tested object based on localized fringe irregularity.; In this research project, LSM was employed on 3" x 3" x 11.25" concrete prisms subjected to Duggan heat or freeze-thaw treatment prior to storage in limewater. Lasershearography images were taken at distinct intervals to detect the onset of cracking and to measure its subsequent propagation. Data analysis of the results after treatment revealed fine cracks at early ages in the concrete, with resolution better than 10 microns. The freeze-thaw treated concrete specimens exhibited more cracks over time compared to those subjected to the Duggan heat cycle.
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机译：激光剪切成像法（LSM）在无损检测（NDT）中尤其是在混凝土裂缝的早期检测中显示出了巨大的潜力。它基于电子散斑干涉图（ESPI）的改进，该技术记录了散斑干涉图的剪切图像。在施加应力之前和之后记录斑点干涉图，然后根据局部条纹不规则进行比较以发现被测物体表面的缺陷。在该研究项目中，将LSM用于3“ x 3” x 11.25“混凝土棱柱上，先进行Duggan加热或冻融处理，然后再储存在石灰水中。在不同间隔拍摄激光剪切图像以检测裂纹的发生并进行测量处理后结果的数据分析显示，混凝土早期出现细小裂纹，分辨率优于10微米；与经过Duggan热循环的样品相比，经冻融处理的混凝土样品随时间推移出现更多的裂纹。
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