Fracture Toughness of Duplex Structures: Part I — Tough Fibers in a Brittle Matrix

Abstract

Tough maraging steel fibers were embedded in a relatively brittle maraging steel matrix by a special diffusion bonding and heat treating technique. Three indices of fracture toughness were computed. KIc as recommended by the ASTM, Komax, the fracture toughness based on the maximum load and initial crack length and Kimax, the fracture toughness based on the maximum load and instantaneous crack length. While KIc for the fibrous composite was no higher than KIc for the matrix material, both Komax and Kimax were significantly higher for the composite. Since fracture of the fibrous composites occurred in a stable manner (fast fracture was not observed) the load displacement records were converted into crack growth resistance curves. The R curves exhibited a serration at GIc, but continued to increase significantly above GIc and multiple serrations, apparently as a result of the fibers, were present. An approximate calculation shows that the increase in crack growth resistance cannot be attributed solely to plastic deformation of the fibers. Scanning electron microscopy revealed local decohesion between the fibers and the matrix and the character of the R curve was attributed to local crack front pinning by blunting or reduction in constraint. As a model of delamination in a fibrous structure, holes were drilled perpendicular to the parting plane in 7075-T6 aluminum specimens. The load versus displacement and R curves were similar to those observed in the fibrous composites. In addition, pinning of the fatigue crack was observed in the vicinity of the holes.

Impact toughness and microstructure of continuous steel wire-reinforced cast iron composite

“…A similar result was obtained for Si-Cr cast steel by Fu et al [7]. Another way to improve the mechanical properties of a brittle material is to produce its composite material by reinforcing relatively high tough material [8][9][10][11][12]. K IC and G IC of the composite were increased by adding tough reinforcement.…”

Effect of heat treatment on fracture behavior of steel-wire-reinforced gray cast iron

“…Similar results were obtained by Gerberich (1971), Antolovich et al (1972a), and Soboyejo et al (1996) for similar composite systems. Figure 4b shows the variation of fracture toughness with a/W ratio for the composite cooled in water and K IC of the composite was determined from the maximum load, P max at which the crack runs unstably to fracture.…”

Mechanical and microstructural properties of low-carbon steel-plate-reinforced gray cast iron

“…Another way to improve the mechanical properties of gray cast iron is to produce a composite material by reinforcing it with a higher-strength material as used in this study. Antolovich et al (1972) improved fracture toughness of martensitic maraging steel matrix by reinforcing austenitic maraging steel. Ozdemir et al (2003) studied the effect of graphite shape on the diffusion bonding of nodular cast iron with gray cast iron.…”