Abstract
The effect of self-contacting surface defects generated by largely compressing metals on the ductile-to-brittle transition observed in metallic structures is investigated. In order to analyse such an effect, a finite element model of a half-space plane-strain material block with an imperfection was subjected to different levels of compression followed by reverse tensile straining. Experimentally validated associative J2 and porous plasticity models were used to describe the mechanical response of the pipeline steel employed as a baseline material for this investigation. Both models predicted onset of creasing at compressive strains of around 70%. To ascertain whether the creases created large and sharp enough defects to trigger the ductile-to-brittle transition during the tensile straining phase, a bifurcation analysis implemented within a user material subroutine was used as fracture initiation indicator. This confirmed that at compressive strains above 70% the self-contact defect acted as a crack during the tensile straining phase.
Highlights
Wrinkles can be found on the surface of largely compressed areas of metallic materials such as the compressive side of components subjected to bending actions
Unless stated otherwise, the plot with the red curves on the left (Fig. 10(a)) corresponds to the FE simulations carried out with the J2 plasticity model and the blue curves on the right (Fig. 10(b)) correspond to those performed with the porous plasticity model
The self-contacting defects may evolve into creases when the former grow very rapidly for small increments of compressive strain, this is, unsteadily
Summary
Wrinkles can be found on the surface of largely compressed areas of metallic materials such as the compressive side of components subjected to bending actions. Wrinkles are understood as undulations or surface roughness that might set in due to large straining in metallic materials They present distinct geometrical features that are periodically repeated on the surface and they are dimension-wise significantly smaller than any of the dimensions that define the rest of the solid. The formation of a crease can develop into a surface crack that might lead to catastrophic failure when unloading or further reverse straining such solid This phenomenon is important to consider in industrial applications when surface imperfections such as wrinkles are detected. Following Rice (1976), and as indicated in Morin et al (2018), the implementation has been carried out performing a bifurcation analysis and getting the strain localisation indicator from the condition of loss of ellipticity For this particular material a critical compressive engineering strain of 70% was detected. The study showed that for compressive strains above such critical strain, the lengths of the self-contacting defects generated in the compression phase were large enough to act like cracks causing the material to fracture in a brittle manner during the tensile loading
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