Fatigue Crack Initiation and Growth in a High-Strength Ductile Steel Subject to In-Plane Biaxial Loading

Experimental studies aimed at understanding the fatigue process in metals and polymers have usually been performed under uniaxial stress. Only in the last two decades or so has much experimentation been carried out on fatigue crack propagation under biaxial stress. This paper reviews the available published data. Crack propagation behaviour under biaxial stress is dictated by 3 parameters: stress biaxiality itself, which is defined here as the ratio of the in-plane principal stresses, crack angle with respect to the applied principal stress directions and stress intensity factor range. Depending on the first two parameters. cracks may grow in Mode I, Mode 11 or Mixed-Mode. Crack growth data have been presented using these three divisions. Two short sections have been included on initiation and cyclic stress/strain behaviour under biaxial stress to emphasise the fact that crack growth cannot be fully understood without knowing something of them. The accumulated data do not lead to adequate conclusions on either the qualitative or quantitative behaviour of cracks subject to cyclic in-plane biaxial stress. Reasons for the confusion and even contradiction of independent results are put forward and some discussion given to the possible directions of future experimental work.

Section: Presentation and Consideration Of Resultssupporting

confidence: 59%

The Behaviour of Fatigue Cracks Subject to Applied Biaxial Stress: A Review of Experimental Evidence

Smith

Pascoe

1983

“…Smith and Pascoe [22] suggested from biaxial fatigue tests on a HYlOO steel that the tensile stress component parallel to the crack surface decreased the mode I crack growth rate and the compressive component increased the fatigue crack growth rate. Moreover, the three stages of crack growth which could be observed in the behaviour of mode I crack growth seemed to vanish in mode I1 or mixed-mode crack growth.…”

Section: A Brief Historical Reviewmentioning

confidence: 99%

Fatigue Crack Growth Behaviour of Sm45c Steel Under Cyclic Mode I With Superimposed Static Mode Ii Loadings

You

Lee

1997

The practical applications of studies related to constant amplitude mode I loading are somewhat limited, since mode I crack growth is often influenced by mode I1 (sliding mode) or mode I11 (tearing mode) in industrial situations. For these cases, criteria, rules, and laws have to be worked out and verified by experiments. However, it is very difficult to evaluate mixed-mode fatigue cracking due to crack surface interference, crack closure, crack branching, etc. This paper, which defines the length of a branched crack as an effective slant crack with a length equal to the distance between the two crack tips, explains the influences of crack surface interference by introducing concepts of adhesive wear and scrutinizes some related researches on mixed-mode crack growth behaviour. Additionally an effective stress intensity factor range is described which considers crack closure and crack surface interference and is verified with crack growth tests under mode I fatigue loading and cyclic mode I with a superimposed static mode I1 loading. NOMENCLATURE 2a,,, 2a, = effective crack length and precrack length AK,, K,, = mode I SIF range and static mode I1 SIF, respectively A,,, = contact area under cyclic mode I with superimposed static mode I1 loading AK,,, AKeff = equivalent and effective stress intensity factor ranges, respectively K,,,,, Kll,lock = crack opening and crack locking stress intensity factors, respectively U = mode I crack opening ratio oad = adhesion strength

“…Smith (E.W.) and Pascoe [26,27] used a cruciform specimen to produce fully reversed mode I1 loading with a static mode I load, on HYlOO steel, a high yield, ductile, weldable steel. This static mode I load was different from the mode I load used by Smith (M.C.…”

Section: Experimental Workmentioning

confidence: 99%

A Review of Fatigue Crack Growth in Steels Under Mixed Mode I and Ii Loading

Bold¹,

Brown²,

Allen³

1992

The majority of methods for predicting the direction of propagation of mixed mode cracks have assumed that they branch to grow as mode I cracks. However, under some circumstances mode I1 crack growth occurs. Rolling contact fatigue cracks are one example of an industrial problem where cracks appear to grow under predominantly mode I1 loading without branching. This paper reviews the available models and the experimental studies in the literature on mixed mode I and I1 loading, and discusses the parameters that affect the mode of crack growth.