| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1988: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1987: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
In ductile fracture, voids near a crack tip play an important role. From this point of view, a large deformation finite element analysis has been made to study the deformation of the crack tip, the stress and strain field and the distribution of void volume ratio near the crack tip under mixed mode deformation, employing Gurson's constitutive equation which has taken into account the effects of voids nucleation and growth. The result shows that one corner of the crack tip sharpens while the other corner blunts, the field near a crack tip can be divided into four characteristic fields (K field, HRR field, Blunted crack-tip field, and Damaged region), and the strain and void volume fraction become concentrated in the sharpened part of a crack tip with increasing Mode II component. The minimum specimen size limitation for J-characterization in large scale yielding under mixed mode deformation is invesigated using the elastic/plastic finite element results.
Fracture toughness tests on compact tension-shear specmens, three-point and four-point mixed mode (Mode I + Mode II ) bend specimens of an aluminium alloy A5083-0 are conducted. The fractured surface and the cross section of the crack tip are observed by a scanning electron microscope. For the four-point bendspecimen, one corner of the crack tip is blunted and the other sharpenedas predicted by the finite element analysis. The critical stretched zonewidth (SZWc) is dependent on a mixed mode ratio ( ratio of Mode I to II component ) while the critical stretched zone length along the deformed tip (SZLc) is almost same. The critical value of the J-integral under the mixed mode condition increases with increasing Mode II component. This dependence is explained referring to the relation between J-integral and SZL by the finite element analysis.
The analysis for the growth of a relatively large hole near a crack tip accounts for different morphology of fractured surfaces which vary depending on a mixed mode ratio.
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