Effect of a single soft interlayer on the crack driving force

• Soft interlayers improve greatly the fracture resistance of materials.
• The basic mechanism is the strong reduction of the crack driving force.
• The parameters influencing the mechanism are worked out.
• Conditions for maximum effectiveness of a soft interlayer as crack arrester are derived.

It has recently been shown that a strong spatial variation of the Young’s modulus can improve greatly the fracture resistance and the fracture strength of an inherently brittle material. In this paper, using numerical modeling and application of the concept of the configurational forces, it is shown that spatial variations of the yield stress can also improve the fracture resistance. The reason is that, when the crack has crossed a soft interlayer, the crack driving force strongly decreases and the crack is arrested by the interlayer; this effect appears without previous delamination of the interlayer. From the numerical results, “optimum interlayer configurations” are derived, i.e. for a given matrix material and load, the magnitudes of thickness and yield stress of the soft interlayer are determined so that the crack driving force exhibits a minimum. Such optimum configurations can be used for the design especially fracture resistant materials and components.