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本文引用粘性物体(viscous material)断裂的能量条件,来决定金属在恒温状态(isothermal condition)下的断裂力学条件。根据分析结果,金属在平均张力与平均压力(average tension and average compression)下,应服从不同的力学条件;在平均张力下,这条件是平均张力与八面切应力(octahedral shear stress)间的椭圆关系;在平均压力下,是平均压力与八面切应力间的双曲线关系。这两个条件的数值,靠金属的体积弹性系数、切弹性系数、固态表面能与其中微小裂口的半径而定。和实验事实比较,在平均压力下,理论与实验结果很接近;在平均张力下,两者间有些差别,但变化趋势,仍然一致。由这两条件在应力空间中的表示,证明了最大畸变能(maximum distorsion energy)不可能用作金属断裂条件。再引用连续体的普遍应变硬化(strain hardening)函数与上述结果,得到两个延度(ductility)的表示,和实验事实在质上一致,没有作量的比较。The theoretical conditions for brittle rupture were found with one single normal stress as the only mechanical variable. But, for the conditions of ductile rupture, experi-mental facts demand the specification of some stress states instead of a single stress and certain arbitrary stress functions were taken for this purpose. A theoretical formulation of the conditions for ductile rupture has not been made up to this date. Fundamentally, such problem would be approached from the dislocation theory, but quantitative treatment is difficult in the present state of this theory. Alternatively it may be possible to approach this problem from the view point of relaxation, should the basic phenomenon of strain hardening associated with ductile fracturing be well interrepted from this view point. It is believed that future studies along such lines will throw more light on the understanding of this problem. Yet, it was thought that if one considers the thermodynamic relation among various types of energy involved in ductile fracture instead of simply taking some arbitrary stress functions as criterion, the conclusions thus obtained would be helpful in understanding this problem, Thus this paper was written.
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