| Recently considerable attention has been paid to the foundation, computational capability, validity and predictive power of the endochronic theory of plasticity, proposed by K. C. Valanis in 1971. Also a lot of interest has been generated on how this revolutionary concept of plasticity without a yield surface may be used in the elastoplastic analysis of stress and strain and how the material functions of endochronic plasticity may be determined. All of these problems have been examined in this dissertation. The basic foundation of the endochronic plasticity theory was reviewed and compared with that of classical plasticity in terms of the behavior of a simple mechanical model. The comparison shows in this specific instance that classical plasticity is an idealization of the endochronic plasticity. The basic concept, intrinsic time, of endochronic plasticity was borne out by comparing the mathematical description of the above simple mechanical model with that of a dashpot.;In the case where the kernel function has a special form, an approximate method of determining material functions was found, which is very convenient for engineering applications.;Be designing a special experiment and a finite element mesh (the smallest gauge and element are equal in size and about 0.2 mm), the verification of the endochronic theory for multidimensional spatially varying plastic strain fields in the vicinity of severe geometric discontinuities (notches) in a metal plate loaded cyclically in its own plane was established. The agreement between observation and prediction is excellent despite the attendant complexities of the loading history and the geometry.;The results in this dissertation could have a wide scope of application in different branches of solid mechanics, for instance, elastoplastic structure analysis, fracture and fatigue. In this work symmetric and asymmetric loadings of a notched specimen were studied. One important result that stands out is that while the external loading conditions are symmetric and periodic, the histories of stress and strain at the notch tip are neither symmetric nor periodic in character. In cyclic tension racheting phenomena at the tip of the notches prevail and a progressive change of the residual stress field at the notch line is shown to occur.;By developing an incremental form of endochronic elastoplastic constitutive equation, an appropriate numerical algorithm was implemented in a computer program. This could be used to analyze the material response of monotonic and cyclic loading in both plane stress and plane strain. |
