Crack closure

About: Crack closure is a research topic. Over the lifetime, 28157 publications have been published within this topic receiving 588158 citations.

Molecular dynamics simulation of crack tip processes in alpha‐iron and copper

Abstract: The intrinsic crack tip processes of either propagation by cleavage or blunting by the nucleation of dislocations from the nonlinearly stressed region at the crack tip have been simulated by a molecular dynamics approach in alpha‐iron and in copper, utilizing the Johnson and Morse potentials, respectively, and a new fixed stress boundary condition at the border between the inner discrete region and the outer anisotropic linear continuum. The simulations showed that alpha‐iron is inherently brittle, and fails by cleavage along a cube plane when the stress intensity factor reaches the critical Griffith value. No dislocations are nucleated in iron and even the development of restricted crack tip twinning in special orientations does not alter this intrinsic brittleness. In copper crack tip blunting at a level somewhat less than the Griffith stress intensity factor always prevented brittle crack growth by cleavage. Thus, copper is inherently ductile. Because it permitted the unhindered development of substantial nonlinear crack tip displacements, and did not prevent dislocations from penetrating through the border between the inner nonlinear material and the outer linear continuum, the new stress boundary condition was found to be far superior to the fixed or flexible boundary conditions used at this border by previous investigators. This is reflected in the observed critical stress intensity factors for brittle cleavage that were found to be nearly equal to the expected Griffith value for the stress boundary condition while the displacement boundary conditions gave results nearly three times higher.

Effect of Electrolyte pH on Crack Propagation in Glass

Abstract: : Crack velocity studies were conducted in various acids, bases and neutral solutions using the double cantilever beam techniques. Results are explained in terms of crack tip pH, which is controlled by the electrolyte at low crack velocities and by the glass composition at high crack velocities. The crack velocity data are consistent with the known dependence of strength on pH for soda-lime silicate glass. Results also suggest that the slope of the universal fatigue curve should depend on surface pH. (Author)

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.