Study On A Fuzzy Set Plasticity Cyclic Constitutive Model Of Noncohesive Material

Constitutive models for engineering materials have been the key content in (?)(?) calculation for geotechnical engineering. Recent decades have seen extensive developments of constitutive models for a wide range of engineering materials, including soils. The past decade has also seen a rapid expansion in the study of cyclic constitutive models for engineering materials in the world. Hence, it is of great necessary to understand the cyclic stress-strain behavior of soil.Recently, cyclic behavior of pavement materials under traffic loading is another challenging task for geotechnical engineers. A typical example is railroad ballast. The ballast is used to fill in irregular surface topology, distribute and transfer loads from a surface structure or system to the subgrades or subsoils as uniformly and widely as possible in order to provide stable and stiff long-term embankment support for railways. The performance of modern high-speed trains relies heavily on the dynamics interaction behavior of the vehicle-support system. Thus, it is of a special key point to develop the cyclic constitutive model of unbound granular materials to determine the over characteristics and constitutive properties of the ballast and to ensure stable and long-lasting properties for such a material that is not homogeneous.The research focuses on the development of cyclic constitutive model based on fuzzy set plasticity theory, its numerical intergration, and finite element implementation as well. Unlike conventional elasto-plastic hardening models, with the aid of membership function, the fuzzy set model provides analytical and simple crpometrical interpretation to formulate hardening, hysteresis features, material (?)nory, non-proportional loading, drained and undrained behavior, and features concerning long-term cyclic effects (shakedown). The cyclic constitutive model developed in this study is a rate independent elasto-plastic model capable of account for:realistic stress-strain behavior under complex stress paths, repeated load cycles, and accurate reverse loading features. Based on test datas, the presented fuzzy set plasticity model can well predict the stress-strain behavior of granular materials under complex stress paths and the long-term behavior of unbound granular material under repeated loads. Calculated resilient modulus from the complete stress-strain curve is also discussed.Finally, the implicit integration scheme for the fuzzy set plasticity model is also described and implemented in a finite element analysis computer code. A mixed control strain-based fully implicit intergration scheme is developed for the fuzzy set model. And it is use to compare with explicit intergration scheme. Meantime, a modified random search method provides a straightforward method to calibrate constitutive model parameters.