Micro-scale finite element analysis of stress concentrations in steel fiber composites under transverse loading

Abstract

Steel fibers, with their high stiffness and high ductility, have a potential to provide a new range of properties in polymer composites, in comparison with carbon and glass fiber composites. However, the high stiffness contrast between the steel fiber and the polymer matrix plus the fiber’s non-circular cross-section are likely to generate high stress concentrations in a composite under transverse loading. In the present study, these stress concentrations are analyzed using finite element modeling and compared with the case of carbon and glass fiber composites. The study is performed for an isolated fiber and multiple fibers in hexagonal and random packings with 40% and 60% of fiber volume fractions. According to the results, in spite of a high contrast between the stiffness values of steel and glass fibers, no significant difference between the transverse stress concentrations was observed for steel and glass fibers in the hexagonal packing due to the difference in material properties. Differences in stress concentrations were noted for the case of randomly packed fibers. The polygonal cross-section of steel fibers was found to introduce extreme stress concentrations.

On the high stress concentrations in steel fiber composites under transverse loading

“…2 One of the challenges of using steel fibers in composites is the stiffness contrast between the fibers and polymeric matrix which can lead to high stress concentrations generated at the fiber/matrix interface. In our previous studies, 3 it was shown that the stress concentrations in steel fiber composites are close to the glass fiber ones although they are approximately 2.6 times stiffer. This statement is correct in case the steel fibers have circular cross sections.…”

“…These stress components are considered in the assessment of the structural integrity of fiber/matrix interface. 3 As mentioned, the results are compared with glass and steel fibers with circular cross sections. The normal and shear stress components for these circular cross sections are shown in Figure 4(c) and (d).…”

“…12,13 The micro-CT images show that their original circular cross section can change to an irregular pentagon or hexagon unlike the conventional carbon and glass fibers. It was shown in Sabuncuoglu et al 3 that these cross sections generate significant stress concentrations near the corners of polygons. However, according to the SEM images of fibers, it was realized that the actual cross section of fibers have some rounded fillets at the corner of fibers ( Figure 2).…”

Molecular dynamics study of toughening mechanisms in nano-composites as a function of structural arrangement of reinforcements

“…This stress concentration may increase with volume fraction [43], though at a higher rate for higher volume fractions. These results are in conformity with the predictions that the strain to failure may decrease with increase in volume fraction [44].…”

“…In the case of hexagonal arrangements, finite element simulations predicted that the stress concentration for normal stresses is higher for stiffer reinforcements [43]. This stress concentration may increase with volume fraction [43], though at a higher rate for higher volume fractions.…”