Crack initiation and growth under fretting-fatigue and fretting-wear contact conditions have been investigated using model epoxy materials which allowed an in situ visualization of damage processes within the contact zone. A fretting-fatigue predictive model has been used to analyze these experiments on the basis of an accurate determination of the contact conditions and knowledge of the bulk fatigue properties of the epoxy materials. A special emphasis has been directed towards crack nucleation and early growth during Stage I and Stage I-to-Stage II transition, Stage II crack growth. Photoelastic experiments especially showed that crack propagation under fretting-fatigue loading was strongly dependent upon the complex cyclic micro-sliding behaviour of the crack faces. Under a fretting-wear condition, the constancy of the local contact conditions within the gross slip regime allowed the derivation of realistic estimates of the crack initiation times from the theoretical model.
Hard coatings are more and more used to improve the mechanical and tribological behavior of surfaces. Thermomechanical cracking can occur in these coatings when they slide under heavy loads. We present a two-dimensional model of a finite thickness layered medium submitted to a moving heat source. The analytical solution of the temperature and thermoelastic stress fields is obtained using Fourier transforms. The behavior of each layer is described by transfer-matrices and a relation between the displacement- and stress-vectors is given. The originality of the study is the use of a Fast Fourier Transform algorithm. With this method, calculation time is reduced, no singularity problems are met in the inverse transform and each parameter (especially the thickness of the layers) can be studied over a wide range.
This paper analyzes the effects of multiple cracks situated in the contact zone vicinity of an elastic isotropic component, modeled as a half-plane. Friction between the crack faces is taken into account using Coulomb’s law. Straight arbitrarily oriented cracks are considered. Any contact condition can be modeled between the crack faces as well as any loading condition over the half-plane surface, including complete loading cycles. The method has been tested for up to 5 cracks and shows no limitation in crack number. Further, the method is general as no prior assumptions concerning the state of the crack, i.e., the slip-stick-open configurations along the crack are required. The stress intensity factors (SIFs) calculated for two crack configuration are compared with those obtained for single cracks.
A semianalytical model of multiple fatigue crack analysis in sliding contact is developed. Linear elastic fracture mechanics is applied. Frictional resistance between crack faces is taken into account. Five crack interaction mechanisms have been identified. Load transfer between cracks can cause both significant increases and drops in stress intensity factors both in mode I and II. The interaction depends on the distance between cracks, their relative position with respect to the loading zone, and the interfacial crack coefficient of friction.
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