Fatigue investigations of two 4XXX0-series aluminum alloys (acc. PN-EN 1706) within a range of fewer than 104 cycles at a coefficient of cycle asymmetry of R = –1 were performed in the current paper. The so-called modified low-cycle test, which provided additional information concerning the fatigue life and strength of the tested alloys, was also performed. The obtained results were presented in the form of diagrams: stress amplitude σa – number of cycles before damage N. On the basis of the microscopic images of sample fractures, the influence of the observed casting defects on the decrease of cycle numbers at a given level of stress amplitude were analyzed. Based on the images and dimensions of the observed defects, stress intensity factor KI was analytically determined for each. Their numerical models were also made, and stress intensity factor KI was calculated by the finite element method (FEM).

Brittle fracture of the reinforced composite element has been a matter of considerable concern to engineers for many years. It is now generally accepted that the mode of failure is the centerpiece of the problem. The publication presents the experimental and numerical procedure used to determine the state of' the stress in the photoelastic model of reinforced beams. The fracture process of fiber reinforced composite materials is very complicated, and the fracture strength is affected by: matrix cracking, fiber breakage and interfacial debonding between matrix and fibers. The criterion used to calculate the maximum load was derived based on two processes only: matrix cracking and deformation of the rei nforcerncnt. The theoretical ultimate bending moment was calculated using the strain energy release rate Ge and the stress intensity factors (K11 and K1) corresponding to the crack propagation of the matrix and the elastic-plastic deformation or the yield limit of the reinforcement.

The paper presents the results of experimental investigations into variations of the stress tensor components due to both the interaction between subsurface fatigue crack faces and rolling contact. The load assumed represents real interaction between the railway wheel and rail. The Grating Holographic Interferometry (GHI) method was employed. The results obtained were compared with those resulting from numerical simulations performed using FEM. The results reveal a strong influence exerted by shape, crack thickness distribution and roughness of the crack faces, respectively, on the distribution of displacement and stress tensor component fields. A new concept consisting in application of the effective crack thickness was proposed. The best agreement between experimental and numerical results was achieved in the case when the real crack shape, effective crack thickness and the friction coefficient of 0.3 were assumed.