Determination of Paris law constants with a reverse engineering technique

Abstract

Paris law constants are commonly obtained with a well established procedure based on standard specimens, notched and pre-cracked. Pre-cracking produces through cracks with stable shapes, nearly straight, similar during all propagation. However, in several situations specimens with corner and surface cracks are recommended. In these cases cracks having significant propagation will continuously modify their shape, beginning with corner or surface geometries and subsequently transforming into through cracks, resulting into a transition region with significant crack shape modification. The aim of this paper is to determine Paris law constants from the analysis of crack shapes on the surface of fracture, in regions of intense shape modification. A double-U specimen of a new generation nickel base superalloy was used to obtain experimental crack shapes within transitory region as well as the number of load cycles between them. An automatic crack growth technique based on the finite element method (FEM) was employed to obtain fatigue constants from crack propagation data.

Influence of Micro-Structure on the Fatigue Crack Propagation in Bridge Steel

“…Values of the exponent m can range from 2.0 to 7.0 with most values being between 3.0 and 4.0 [7]. The measured material constant m shows good agreement with data from literature S355 J0 steel grade, comparison of the experimental data are stated in the Table 2.…”

Optimization and Analysis of Processes with Moving Materials Subjected to Fatigue Fracture and Instability

“…Paris' constants have been measured for many materials, e.g. for nickel based superalloys by Bazant and Xu (1991), for concrete by Branco et al (2009), and for epoxy by Brown et al (2009), and the constants vary a lot for different materials. Parameter k is approximately 3 for many materials (Farahmand and Nikbin, 2008) but it may also be larger (for epoxy, k = 9.7, see Brown et al, 2009) or smaller (for rubber, k = 0.211, see Schubel et al, 2003).…”

Lynx: A user‐friendly computer application for simulating fatigue growth of planar cracks using FEM

“…One of the most efficient ways, widely used in literature, consists of an automatic procedure based on the finite element method. The numerical model is usually generated using commercial finite element packages . However, it is a relatively complex and time‐consuming task since these programs have been developed for general purposes and not for such specific situations.…”