A survey of failure criteria and parameters in mixed-mode fatigue crack growth
- PDF / 381,410 Bytes
- 21 Pages / 595.276 x 793.701 pts Page_size
- 70 Downloads / 148 Views
A SURVEY OF FAILURE CRITERIA AND PARAMETERS IN MIXED-MODE FATIGUE CRACK GROWTH D. Rozumek 1, 2 and E. Macha1 From the present survey of the mixed-mode crack growth criteria based on the fracture toughness K Ic (critical J-integral), it follows that this concept is very extensively and variously used by different authors. The criteria discussed in the work are based on the parameters K, δ, W, and J. The most extensively applied models include the mixed mode I + II described by the stress intensity factor K. The criteria presented in the work are based on the factors affecting the fatigue crack growth during testing, namely stress, crack-tip displacement, or energy dissipation. In the case of mixed-mode cracking, special attention should be paid to the energy approach (application of the J-integral and strain energy density), which seems to be very promising for elastoplastic materials. Under mixed-mode cracking, two things should be taken into account: the rate and direction of fatigue-crack growth. Moreover, the nonproportional loading, crack closure, or overloads strongly affect the process of fatigue crack growth in the case of mixed-mode cracking. Keywords: mixed-mode fatigue, crack-growth criteria, threshold value, critical value, biaxial loading.
The mixed-mode fatigue crack-growth criteria can be split into three groups according to the applied parameters, namely, stress, displacement, and energy-based criteria. The stress criteria presented by Suresh [1], Kocańda [2], and Richard et al. [3] are widely known and often used. They describe the stress state near the crack tip in brittle materials with an error of 5–20% in the elastoplastic materials for stresses 0.4 σy < σ < 0.7 σy [2]. In fracture mechanics, the displacement criteria are described by using the parameter of crack-tip opening displacement δ [since the crack tip opening displacement (CTOD) is a certain measure of strains in the area near the tip, they are also called “strain criteria”). These criteria are applied for elastoplastic materials up to the yield point σ y and are not valid above this point. The energy-based criteria use the strain-energy density [4] and the J-integral [5]. They include both stress and strain states near the crack tip. In the literature we usually encounter fatigue crack growth for simple modes of displacements given by Irwin [6] in 1957 [tensile (mode I), sliding (mode II), and tearing (mode III)]. In practice, we observe mixed-mode displacements. They are connected with given loads (obtained by the superposition of crack modes I, II, and III), i.e., tension with torsion (mode I + III), bending with torsion (mode I + III), tension with shear (mode I + II), shear with torsion (mode II + III), etc. The description of the mixed modes of fatigue crack growth should include two components: the increment of crack length and the direction of crack growth. There are various criteria aimed at the determination of this direction under multiaxial loading, some of them are discussed in the present work. The tests of crack growth u
Data Loading...
