INFLUENCE OF ASYMMETRY COEFFICIENT VARIATION UPON THE STRESSES FROM THE CRACK TIP TO AN AXIAL ECCENTRIC FATIGUE SOLICITATION

摘要

The stresses field from the tip of a crack by axial eccentric fatigue fracture depends upon the way of solicitation, pieces or sample material, degree of load, sample geometry. Attaching an axis system (xyz) on the crack front, and respecting the conditions of a plane stress state, the stress field is expressed by the components σ_x σ_y and τ_(xy), (σ_z=0). The tests program was realised on 10TiNiCr175 alloy steel samples, CT model. These was tested until fracture, to fatigue, with the asymmetry coefficients R=0.1, R=0.3 and R=0.5. During the realised tests on ambient temperature, we have noted the crack length a, and the corresponding number of cycles N. At any moment of the tests, we have calculated the stress intensity factor AK, and the stresses on the crack front σ_x σ_y and τ_(xy), respectively the normal principal stresses σ_1,σ_2 and the stress σ_c to the composed solicitation by traction and bending of the sample. We have represented the graphics of variation of all stresses, versus the variation of the crack length a, durability Nandversus the stress intensity factor AK, for those three loads coefficients.