Abstract
Studies have suggested that brittle fractures occur in steel because microcracks in the brittle layer at grain boundaries propagate as a result of the increase in piled-up dislocations. Therefore, prestraining can approach the limits of a material, which could lead to a decrease in fracture toughness. However, strains are tensors comprising multiple components, so the effect of prestrain on fracture toughness is not simple. Additionally, the mechanism of change in critical stress due to prestrain has not been thoroughly investigated. For the lifetime evaluation of steel structures with a complicated load history, it is important to generalize the effect of complicated prestrain on the decrease in fracture toughness. In this paper, a single prestrain was applied in a direction different from the crack opening direction. A general three-point bending test was employed for fracture evaluation. Numerical analyses using the strain gradient plasticity (SGP) theory, which is a method based on the finite element method (FEM) are carried out; conventional macroscopic material damage rules are considered as well. Using these FEM analyses, the critical stress is calculated. Finally, the change in critical stress can be expressed by the yield point increase and dislocation density and formulated based on the identified micromechanisms.
Highlights
Iron is the most abundant element on earth and is used in many applications, including high-rise buildings, large structures, infrastructure, and ships
finite element method (FEM) analysis based on crystal plasticity was conducted to examine the mechanism in more detail and to formulate the generalized effect of prestrain on critical stress
V is the plastic displacement of the clip gage, and δ is the plastic displacement of the clip gage, and δquasi.cr is the “quasi-crack tip opening displacement (CTOD)”
Summary
Iron is the most abundant element on earth and is used in many applications, including high-rise buildings, large structures, infrastructure (e.g., pipelines for transporting natural gas and storage tanks for natural gas), and ships. Shear dstress, is thediameter, grain diameter, t is the thickness of the carbide layer, and is the frictional This equation is based on experimental results, which showed that brittle cracks always initiated by stress. There are some mandatory parameters that are difficult to determine in which makes it difficult to apply this itmodel in actual engineering this improved model, which makes difficult to apply this modelapplications In addition to these approaches purely regarding the critical stress condition of the material itself, a number of studies of critical stress after prestraining have been investigated. It is clear that, regarding toughness degradation under plastic prestrains, the number of piled-up dislocations is the main factor that controls brittle fracture performance This relationship is effective only for one fracture toughness specimen configuration, so generalization to actual steel structures is necessary. FEM analysis based on crystal plasticity was conducted to examine the mechanism in more detail and to formulate the generalized effect of prestrain on critical stress
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