吳宛錚 數位影像相關係數法於微觀鑽孔法應用之研究
Application of the digital image correlation method to the micro Hole-Drilling method 摘要 結構物或是機械零件在製作加工時，常因高溫鍛造等行為而造成殘餘應力。殘餘 應力會影響構件原本可承受之強度或是使用年限，因此量測殘餘應力對結構物與 機械的使用安全性是相當重要的。ASTM-E837-01 規範中所述之鑽孔法為一半破 壞性檢測技術，其方法為在鑽孔周圍貼上應變計來量取鑽至不同深度之表面應 變。隨著鑽孔直徑的減小，試體受到的破壞會也跟著減少，使得此方法愈來愈接 近非破壞性檢測。但是當鑽孔尺寸過小時，應變計無法遵守ASTM 規範貼在鑽孔 周圍的規定，故無法使用應變計進行應變的量測。數位影像相關係數法(DIC)為一 非接觸式且多尺度的量測技術，其原理為比對試體變形前後之影像灰階關係來得 到位移及應變場。因此本研究將不同鑽孔階段的影像拍攝下來，利用DIC 法與未 鑽孔前之試體影像做比對，以探討在DIC 輔助下以鑽孔法進行非破壞檢測之可行 性。實驗結果顯示，量測所得之應變值與ASTM 規範中之經驗值在數值大小與 趨勢上均吻合，反算所得之應力與所施加之應力大小及方向亦相當接近，表示 DIC 能夠成功的應用在微觀的鑽孔法中，以進行非破壞檢測來求得試體之殘餘應 力。
After the components of structure or machinery are processed, the proceeding such as high-temperature forging might generate the residual stress. Residual stress will reduce the strength or service life of component; hence, the measurement of residual stress is important to ensure the safety of structure and machinery. The Hole-Drilling method described in ASTM-E837-01 is a semi-destructive
measurement method, strain gauges are attached around the hole to measure the surface strain in various drilling depth. With the decreasing of diameter, the destruction degree is reduced; smaller hole makes the method more like non-destructive testing.
However, if the drilling hole is too small, the strain gauge can not be attached around the hole to comply with ASTM standard, therefore the strain can not be measured by strain gauge. DIC is a non-contact and multi-scale measurement method, it compares the gray-scale of image before and after deformation to obtain the displacement and strain field.
Hence, to assess the feasibility of hole-drilling for implementing the non-destructive testing assisted by DIC method, the images of specimen in different drilling states are taken, and applied DIC method to compare the these images with the image
captured before drilling.
The result shows that the trend and value of measured strain is fit with the theory value given in ASTM and the determined residual stresses and direction are close to the theory value, it means that the DIC method can be applied in the micro-scale hole-drilling method to determine the residual stresses of specimen.
