Fatigue Damage Mechanics Under Impact Load And Analysis Of Fatigue Damage For Hammer-Foundation

Fatigue failure is an important phenomenon in many engineering projects. The study of the impact fatigue damage process in structures of geotechnical engineering has advanced function for development either in continuum damage mechanics or in geotechnical engineering applications. Because of the structural behavior in soils, many national and international scholars have introduced "damage" conception into constitutive models of soils. However, the papers deal with the point of view on the soil failure under cyclic loading as the fatigue damage of soils failure still not been seen widely.Based on the characteres of the bearing capacity of the hammer foundation system and the response near the soil ground under long time repeated impact loadings, the theory of continuum damage mechanics has been applied to study the fatigue damage in the hammer foundation system, and the concept of impact fatigue damage has been taken into account of the theory continnum damage mechanics. The mechanism modeling of coupling between the micro-damage accumulation under once time impact loading and the macro-damage development due to long time repeated impact loadings has been carried out for estimation of the life period of impact fataigue damage under critical fataigue damage conditions. The principal results obtained in this thesis are listed bellows:1) A model of total dissipation potential of the elasto-plastic damage has been theoreticaly presented for the the modified Cam Clay criterion failure model by combination of the damage strain energy release rate based on thermodynamics of continuum damage mechanics and the damage energy norm Ï„ proposed by Zhao Xihong professor, as well as the kinetic equation of damage develop and the elasto-plastic damage constitutive equation have been achieved both in strain space and stress space respectively.2) The "memory parameter" of soil medium defined by M.van Eekelen under cyclic loadings has been developed as the definition of "fatigue parameter" of soil medium in order to represent the degeneration behavior in fatigue damage process for soil structures, consequently, different types of fatigue damage growth equations and life equations of fatigue damage process have been expressed based on this advanced definition. A material property of "anti-fatigue damage parameter" has been defined in order to express the capability of soil property to against the fatigue damage process. The degeneration characters of fatigue damage process and fatigue damage constitutive behavior have been analyzed for three typical soils by theoretical models developed in this study using experimental data collected from deferent articles. The results show that the fatigue damage life of soil body under shear cyclic loadings increases exponentially with increasing of capability of anti-fatigue damage parameter for soil medium. The estimation of fatigue damage life under shear cyclic loadings has been carried out as an essential modeling analysis for icy soil.3) The developed program in analysis for impact fatigue damage process under long time repeated impact loadings has been applied into a hybrid model consists of the two degree of freedom dynamic model of a hammer-foundation system and two dimensional finite element model for the soil ground near the hammer-foundation in order to present a method to analyze the fatigue damage growth and to estimate the fatigue damage life of the hammer-foundation system. A fatigue life...