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The description of monotonic and cyclic behavior of material is possible by generalizing the internal stress concept by means of a set of internal variables. In this paper the classical isotropic and kinematic hardening rules are briefly discussed, using present plastic strain tensor and cumulated plastic strain as hardening variables. Some additional internal variables are then proposed, giving rise to many possibilities. What is called the “nonlinear kinematic hardening” leads to a natural description of the nonlinear plastic behavior under cyclic loading, but is connected to other concepts such as the Mroz’s model, limited to only two surfaces, and similarities with other approaches are pointed out in the context of a generalization of this rule to viscoplasticity.

The constitutive equations developed in Part I with a combination of isotropic and nonlinear kinematic hardening rules can describe the usual monotonic and cyclic behavior of metals and alloys. Some materials, especially type 316 stainless steels, show interaction of many complex phenomena such as viscoplasticity, cyclic hardening, time softening and aging effects. . . On the basis of experimental results obtained in Electricite de France or taken from the literature the descriptive ability of the developed constitutive equations is discussed and a new methodology is proposed which treats instantaneous plasticity and creep by using a viscoplastic strain component alone.

Major solutions needed in frlcture analysis are (d) simple and accurate matedal characterization and (ô) easy transferring of malerial data lo cracked structures. ln !h€ proposed methodology. constitutive relationships. including cavity growth and coalescence, are used. Material characterization is based on the simple notched tension lest. Several structural steels have been characterized. especially 4508 steel. and the direct transferring of material data hâs been demonstrated wilh tests on circumf€rentially cracked tension specimens.In addition. the extrapolation of material data io different inclusion conl€nls and temperatures was attempted, with favorabl€ rcsults for the first factor through a specific parameter of the model. Th€ temperature dcpendence of 4508 steel ductiliiy is related to an inverle strain rale effect on the flow curv€: the modeling of this effect gives encoùraging results, but it must be refined to producc an effeclive prediction. KEY WORDSI ductile fracture. damâge mechanics. local approach to fracture, crack iniriation, slable crack growth, 4508 steel. inclusion contenls, notched tension test. fracture mechanics. nonlinear fracture mcchanics Some of the major problems engineers have to cope with in fracture analysis are the following:(a) material characterization, that is. the generation of adequate data from specimen testing, and(ô) the transferring of fracture mechanics data (o the struclural analysis of components.As a mattcr of fact, the generation of matedal data can be money and time consuming: for example, the determination ofJ-Ad resistance curves is still a toilsome task, though some progress was gained with partial unloading cornpliance methods. Frequently, existing material data do not correspond to the specific application (in reference to temperature, strain rate, irradiation. aging, and so forth), and hazardous extrapolations are necessary.

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