A method of elastic-plastic stress and strain calculation at a notch root

Fatigue limit evaluation of metals using an infrared thermographic technique

— The problem associated with short crack growth, defined as situations in which the intensity of the crack tip field is underestimated by linear elastic fracture mechanics analyses, is briefly reviewed.



Two cases are identified, cracks growing in plastically strained materials, such as occurs in high strain fatigue studies and at notch roots, and small cracks growing in single grains as occurs close to the fatigue limit in plain specimens.



Important mechanical and metallurgical features of short cracks are discussed with particular reference to the upper and lower bound definition of a short crack.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1460-2695.1982.tb01250.x

The short crack problem

— The growth of ‘small’, half-penny shaped surface fatigue cracks in a precipitation hardened aluminum alloy is compared with the growth of ‘large’cracks in fracture mechanics type specimens. It is found that the small cracks grow much faster than LEFM equivalent large ones, and also experience growth rate perturbations. It is suggested that localized microplasticity in nominally elastic specimens is responsible for the rapid growth of small cracks and that grain size limitations on the microplastic regions cause transient decelerations and sometimes permanent arrest, in crack growth.

The growth of small fatigue cracks in 7075–t6 aluminum

Fracture testing of a soft rock with semi-circular specimens under three-point bending. Part 2—mixed-mode

The tensile strength, fatigue crack propagation behaviour, and fracture toughness of a low-alloy sin tered steel were determined for the porosity range 11–17%. Static and cyclic strength were found to increase with density in a non-linear fashion. The pores both exerted a stress-concentrating influence and reduced the load-bearing section. The micromechanism of failure was always ductile fracture in the necks between sintered steel particles. It was concluded that the stress state at the tips of cracks subjected to static or cyclic loading was closer to plane stress than to plane strain. Retardation of fatigue crack propagation appeared to occur due to the blunting action of the pores. The presence of a wear mechanism had little influence upon fatigue crack growth rates. A companion paper (following) attempts to model the static and cyclic behaviour of the steel, based on the known micromechanisms of failure. PM/0172

Effect of Density on Tensile Strength, Fracture Toughness, and Fatigue Crack Propagation Behaviour of Sintered Steel

Fatigue crack growth under compressive loading

Initiation and propagation are considered to be controlled by the extent of total plastic shear deformation φ. Crack initiation and crack propagation occur when φ, exceeds a critical threshold value which can be equated to threshold conditions determined from linear elastic fracture mechanics analyses. When a crack is in a plastically deformed zone φt=φp+φe. where φp is the component of φt due to notch bulk plasticity and φe, is the component of φt due to a linear elastic fracture mechanics (LEFM) analysis of the crack tip plasticity field.



When cracks initiate at notch roots φt > φth. As the crack propagates in the notch plastic zone the rate of decrease of vp will be different from the rate of increase of φe and it is possible for φt to decrease to a level below φth thereby creating a non-propagating crack.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1460-2695.1979.tb01350.x

Elastic-plastic fracture mechanics for initiation and propagation of notch fatigue cracks

— This paper reports the results of an experimental and numerical investigation of the interaction and coalescence of two coplanar semi-elliptical cracks. Fatigue crack growth data were obtained from a four-point bend specimen using the direct current potential difference method and a beachmarking technique. A finite element simulation of the experimental conditions was also performed. Crack advance was computed from the Paris equation on a step by step basis. Good agreement between experimental fatigue crack growth data and the finite element predictions is demonstrated.

R.A. Smith

Papers

Effect of Density on Tensile Strength, Fracture Toughness, and Fatigue Crack Propagation Behaviour of Sintered Steel

Fatigue crack growth under compressive loading

Elastic-plastic fracture mechanics for initiation and propagation of notch fatigue cracks

A study of the interaction and coalescence of two coplanar fatigue cracks in bending

Fatigue crack growth at stress concentrations—the role of notch plasticity and crack closure