Paris' law

About: Paris' law is a research topic. Over the lifetime, 13815 publications have been published within this topic receiving 224818 citations. The topic is also known as: Paris-Erdogan law.

Roughness-Induced Crack Closure: An Explanation for Microstructurally Sensitive Fatigue Crack Growth

Abstract: The concept of roughness-induced crack closure is utilized to explain the role of prior austenite grain size and pearlite interlamellar spacing on near-threshold fatigue crack propagation in fully pearlitic eutectoid steel tested at low and high stress ratio in lab air and purified helium. It is shown that at low load ratios, near-threshold growth rates are significantly reduced for coarse-grained microstructures, compared to fine-grained at constant yield strength, due to roughness-induced crack closure. Using roughness-profile microscopy, it was found that fracture surface roughness near threshold scaled with grain size and inversely with yield strength, macroscopic roughnesses at threshold being considerably larger than the conventionally calculated cyclic crack tip opening displacement. Auger analysis of near-threshold corrosion products showed it to be iron oxide; the oxide thickness was seen to be decreased by increased stress ratio. The significance of this model to near-threshold fatigue crack growth behavior, in terms of load ratio, microstructure, and environment is discussed.

Local Yielding Attending Fatigue Crack Growth.

Abstract: Fatigue crack growth rate measurements were performed at 100°C on an Fe-3Si steel in three thickness conditions and at different ΔK-levels. The test pieces were subsequently sectioned and etched to reveal the plastic deformation attending crack growth both on the surface and in the interior. Unlike preceding studies, the Fe-3Si steel displayed classical cyclic crack growth: well-defined fatigue striations with a spacing close to the per-cycle growth rate, and essentially the same growth rates that have been reported for low and medium strength steels. A highly strained region, approximately one-fifth the size of the monotonie plastic zone, is identified as the cyclic plastic zone. On this basis three regions with distinct cyclic strain histories that precede the crack are identified: a microstrain region wherein the material receives ∼103 to 104 strain cycles in the range 0 < Δe P ≲ 10-3; a cyclic plastic zone corresponding to ∼200 cycles in the range 10-3 < Δ∈ P ≲ 10-1, and a COD-affected zone that receives ∼10 strain cycles in the range 10-1 ≲ Δ∈ P ≲ 1. It is suggested that the damage associated with the instabilities in the fatigue substructure to overstrain contribute to the growth mechanism.