STRESSES FIELD DISTRIBUTION FOR THE R520 STEEL TO AN OSCILLATOR POSITIVE FATIGUE SOLICITATION

摘要

During the exploitation, into a piece could appear a crack because the stresses concentration into a point or certain area from material. Depending on the exterior loads, the crack could propagate and the crack surfaces will translate relatively one versus the other, determining three modes of crack growth. The most common mode in practice it is the mode I, growth trough opening, the propagation vector being perpendicularly orientated on the crack front and contained in his plane. At the tip of the crack the stresses varies during the work and depend by the solicitation state, piece or sample geometry, piece material. The paper propose an analysis of the stresses field variation from the tip of a crack for samples model CT made by general use steel R520. These were tested to axial eccentric fatigue, to the room temperature, with the asymmetry coefficients: R=0.1, R=0.3 and R=0.5. We have determined the stresses from the tip of the crack σ_x, σ_y and σ_c and we have graphical represented those variation versus the crack length variation a, durability N and stress intensity factor AK.