Fatigue Strength and Life Estimation Methods Using Critical Distance Stress Theory

Generally, the critical distance stress theory was applied for the fatigue limit estimation of general structures. In this method, it needs only two parameters, fatigue limit of smooth specimen (σ_w0), and threshold stress intensity factor range (ΔK_th). In this paper we extended this method for the estimation of low cycle fatigue life too. In this improvement we define the critical distance (r_c’) on static strength conditions, which is calculated using ultimate tensile strength (σ_B) and fracture toughness (K_IC), in addition to the critical distance on fatigue limit condition (r_c). Then the critical distances of any low cycle fatigue conditions can be calculated by interpolation of critical distance on fatigue limit (r_c) with critical distance on static strength (r_c’). By unifying these low cycle fatigue life estimation methods with high cycle fatigue limit estimation method, we can estimate the full range fatigue life easily. And to confirm the availability of this estimation method we perform the fatigue test for circle hole specimens, sharp V notch specimens and fretting fatigue specimens.

Keywords:High cycle fatigue; Low cycle fatigue; Fatigue life; Critical distance stress theory; Threshold of stress intensity factor range; Fracture toughness