Issue 38

T. Sawada et alii, Frattura ed Integrità Strutturale, 38 (2016) 92-98; DOI: 10.3221/IGF-ESIS.38.12 95 (a) 0.0 V f (b) 0.2 V f (c) 0.5 V f Figure 2 : Multiaxial static strength evaluation with Tsai-Hill failure rule. Fatigue strength properties Fatigue strength in uni-axial loading is generally evaluated by using the S-N diagram. S-N diagrams are associated with the relationships among the number of cycles to failure and stress range, stress amplitude, or maximum stress in uni-axial loading. However, we have to deal with stress states of combined axial stress and torsion stress in this paper. Therefore, S- N diagrams are organized by using principal stress applied on specimen surfaces σ p1 , and the number of cycles to fracture N f . σ p1 was calculated as follows: 2 2 1 1 p1 12 2 2              (5) where σ 1 and τ 12 are the axial stress and shear stress applied. Figs 3 and 4 show the relationships between σ p1,max as cyclic maximum principal stress and N f as fracture cyclic numbers on a double logarithmic chart obtained as S-N diagrams. Arrows in the diagrams show that the fatigue tests were terminated after reaching 1×10 6 cycles. Figure 3 : Relationships between σ p1, max and N f with various α in C-SGP. Since the value of the fatigue life in C-SGP are scattered widely, fatigue life in C-SGP can no longer be expected to sort in V f and α by using the S-N diagram. Meanwhile, S-N diagram in I-SGP indicates the characteristic to decrease σ p1, max with increasing N f without dependence on fatigue test conditions. Comparing the fatigue properties in molding processes, they 0 25 50 75 100 125 0 25 50 75 100 Torsion strength τ S [MPa] Axial strength σ L [MPa] 0 25 50 75 100 125 0 25 50 75 100 Torsion strength τ S [MPa] Axial strength σ L [MPa] 0 25 50 75 100 125 0 25 50 75 100 125 Torsion strength τ S [MPa] Axial strength σ L [MPa] α = 2/1 α = 1/1 α = 1/2 α = 0/1 α = 1/0 α = 2/1 α = 1/1 α = 1/2 α = 0/1 α = 1/0 α = 2/1 α = 1/1 α = 1/2 α = 0/1 α = 1/0 10 100 0 1 10 100 1000 10000 100000 1000000 Peak stress σ p1, max [MPa] Fracture cycles N f [cycles] 0.5Vf, α=1/0 0.5Vf, α=2/1 0.5Vf, α=1/1 0.5Vf, α=0/1 0.2Vf, α=1/0 0.2Vf, α=2/1 0.2Vf, α=1/1 0.2Vf, α=0/1 0.0Vf, α=1/0 0.0Vf, α=2/1 0.0Vf, α=1/1 0.0Vf, α=0/1 10 1 10 2 10 0 1 3 1 4 1 5 1 6 10 -1 Static strength