Analysis the growth of crack in ductile material by stereo

• Main Authors: Wang, Jau Shyong, 王昭雄
• Other Authors: Luo P.F.
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/58749516360756882033

碩士 === 中華工學院 === 航空太空工程研究所 === 85 === The growing Crack-tip behavior was studied by using a stereo vision to measurethe three-dimensional deformation field around the crack tip of fracturespecimens made from ductile material. In the experiment the compact tension(CT) specimen was used as the fracture specimen which was made of 304L stainless steel. The ratio of crack length to specimen width, a/w, is 0.45. Adisplacement-controlled loading was applied to the specimen with a MTS machineuntil a crack extension of delta a=4mm was reached. Usingthe out-of-planedisplacement field around the crack tip of the CT specimen measured by thestereo vision and the mapping equation of reflected caustics, the caustic wasgenerated on the virtual screen placed behind the specimen. No ray will reachthe screen at points inside the caustic and a dark region, a shadow spot, willbe created. The J integral was then computed by using the maximum transversediameter of the shadow spot. Results indicate that prior to crack initiation,the J-integral value obtained by using the out-of-plane displacement field isin a good agreement with the far field J-integral obtained by using thein-plane displacement field or the Merkle-Corten formulae. After the crackinitiaion, the J-integral obtained by using the out-of-plane displacementfield deviates from the far field J-integral gradually as the crack grows. Theout-of-plane displacement along a radial direction for a specific radial anglewas measured by the stereo vision and compared to the HRR field. Experimentalresultsindicate that prior to the initiation, the w displacement has a goodtrend following the HRR field for radial lines between 0 degree and 60 degree.As the crack grows up to delta a=3.956 mm, the w displacement still has a goodtrend following the HRR field for radial lines from 0 degree to 90 degree.