Fatigue crack propagaion under mixed mode loading

Mixed model fatigue crack propagation is analyzed in this paper, using a centre cracked plate geometry, loaded under uniaxial cyclic tension. Based on maximum principal stress criterion, a modified Paris expression of fatigue crack growth rate is derived in terms of K and crack angle ₀ for an inclined crack. It is also shown that it is more convenient to express the Paris equation by means of crack lengthprojected on the x—axis, a_x rather than the actual length, a itself. The crack trajectory due to cyclic loading is predicted. ₀ is varied from 29° to 90°. Experimental data on Type L3 aluminium agree fairly well with predicted values when ₀ exceeds 30°.Notation a Half-length of inclined crack - a_x Length of the half length of inclined crack when jected on the x-axis - a Crack growth increment - da/dN Rate of fatigue crack propagation - da _x /dN Rate of fatigue crack propagation when projected along the x-axis - a_ij Variables in Sih's strain energy density factor equation - C, m Coefficient and exponent in Paris equation respectively - K _I K _II K _III Opening, sliding and tearing mode stress intensity factors factors respectively - K Stress intensity factor range - k Stress intensity factor range in Sih's equation - K _x Stress intensity factor range when crack length is projected on the x-axis - K _th Threshold stress intensity factor range - S Strain energy density factor range - Crack angle, which is the angle made by crack plane with the loading axis - ₀ Value of of the original inclined crack - f(₀) Function of ₀ - Angle between the direction of a certain point on the crack trajectory and the horizontal axis - ₀ Direction of crack growth with respect to crack plane - Shear modulus - v Poisson's ratio - Stress range