Abstract
Material damage caused by complicated prestrain like cyclic prestrain and various direction prestrain. It is so important to understand the mechanism of material damage for high-precision lifetime evaluation of steel structure. Material damage depends on not only equivalent plastic strain but the order of pestrain loaded. Also, material damage can be expressed by effective damage strain from back stress uploading and total dislocation density calculated from conventional mechanism based on strain gradient plasticity (CMSGP). These ideas can be extended to multiaxial problems and material damage can be estimated by these parameters as well as uniaxial problems.
Highlights
Brittle fracture of steel is suggested to occur because microcrack appearing in brittle layer at the grain boundary propagates into the matrix as being driven by a lot of piled-up dislocation [1]
Though deterioration of fracture toughness derived from single prestrain has been investigated very well, there are not enough data about deterioration from complicated prestrain, for example cyclic prestrain and various direction prestrain, and mechanism of deterioration have not been discovered
From subsection 3.1 and 3.2, it is suggested that material damage of uniaxial cyclic prestrain problem can be expressed by effective damage strain from back stress updating and dislocation density calculated from conventional mechanism based on strain gradient plasticity (CMSGP)
Summary
Brittle fracture of steel is suggested to occur because microcrack appearing in brittle layer at the grain boundary propagates into the matrix as being driven by a lot of piled-up dislocation [1]. Loading plastic deformation, equivalent to dislocation’s increase, is directly connected to the increase of danger of brittle fracture Because of these mechanisms, loading prestrain to material means getting close to material limit conditions and leads to deterioration of fracture toughness. In the beginning, as an easy case material toughness change when tensile and compression prestrain are loaded in the same direction of cleavages is investigated and material damage rule is discussed using Finite Element Method (FEM). Based on these results, FEM analysis is extended to multiaxial stress filed and material damage in the case that prestrain is given in two directions is investigated
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