Localization and localized fracture phenomena in inealastic solids under cyclic dynamic loadings

• Autorzy: Dornowski W. , Perzyna P.
• Języki publikacji: EN

Abstrakty

EN

The main objective of the paper is the investigation of localization and localized fatigue fracture phenomena in thermo-viscoplastic flow processes under cyclic dynamic loadings. Recent experimental observations for cycle fatigue damage mechanics at high temperature and dynamic loadings of metals suggest that the intrinsic microdamage process does very much dependent on the strain rate and the wave shape effects and is mostly developed in the regions where the plastic deformation is localized. The description of kinematics of finite deformations and the stress tensors is presented. The rates of the deformation tensor and the stress tensor are defined based on the Lie derivative. A general constitutive model of elasto-viscoplastic damaged polycrystalline solids is developed within the thermodynamic framework of the rate type covari-ance structure with finite set of the internal state variables. A set of the internal state variables is assumed and interpreted such that the theory developed takes account of the effects as follows: (i) plastic non-normality; (ii) plastic strain induced anisotropy (kinematic hardening); (iii) softening generated by microdamage mechanisms (nucleation, growth and coalescence of microcracks); (iv) thermomechanical coupling (thermal plastic softening and thermal expansion); (v) rate sensitivity; (vi) plastic spin. To describe suitably the time and temperature dependent effects observed experimentally and the accumulation of the plastic deformation and damage during dynamic cyclic loading process the kinetics of microdamage and the kinematic hardening law have been modified. The relaxation time is used as a regularization parameter. Fracture criterion based on the evolution of microdamage is formulated. Utilizing the finite difference method for regularized elasto-viscoplastic model, the numerical investigation of the three-dimensional dynamic adiabatic deformation in a particular body under cyclic loading condition is presented. Particular examples have been considered: (i) Dynamic, adiabatic and isothermal, cyclic loading processes for a thin steel plate with small rectangular hole located in the centre are considered. The accumulation of damage and equivalent plastic deformation on each considered cycle has been obtained. It has been found that this accumulation distinctly depends on the shape of the assumed loading cycle. (ii) A dynamic adiabatic cyclic loading process for a thin steel plate with sharp notch is investigated. The propagation of the macroscopic fatigue damage crack within the material of the plate is investigated. It has been found that the length of the macroscopic fatigue damage crack distinctly depends on the wave shape of the assumed loading cycle. The results obtained are in accord with the experimental observations performed by Sidey and Coffin [65].

Słowa kluczowe

EN

localization; crack; viscoplasticity; damage; cycle loading

PL

pęknięcie; lepkoplastyczność; awaria; obciążenia cykliczne

• Wydawca: Wydawnictwo Politechniki Poznańskiej
• Czasopismo: Foundations of Civil and Environmental Engineering
• Rocznik: 2002
• Tom: No. 1
• Strony: 41--86
• Opis fizyczny: Bibliogr. 74 poz.

Twórcy

autor

Dornowski W.

autor

Perzyna P.

• Polish Academy of Sciences. Institute of Fundamental Technological Research