Accounting For Effects Of Constraint On Propagation Of A Fatigue Crack

Abstract

The paper describes the application of two parameter constraint-based fracture mechanics to the behavior of fatigue cracks. The different levels of constraint in the vicinity of the tip of a fatigue crack are quantified by means of the T-stress. The paper seeks to quanti~ the experimentally observed effect of the specimen geometry on the rate of propagation of a fatigue crack. To this aim a modified Paris law that takes the different values of the corresponding constraint parameter T into account is then suggested. It is shown that, depending upon the material properties, the geome~, and the loading of the specimen, a constraint may cause a difference of as much as 100°/0 in the rate of propagation of a fatigue crack for extreme values of the T-stress, The problem is solved numerically by means of the finite element method, and results are compared with data obtained experimentally using two specimens with different values of the T-stress (a center cracked and a compact tension test specimen).