2015 巻 (2015) 60 号 p. 51-105
In order to investigate the validity of the current JIS fatigue design diagrams for round wire helical compression springs, fatigue tests were conducted for non-shot-peened and shot-peened springs made of piano wires and valve-spring quality oil-tempered Chromium Silicon steel wires. All the spring wires supplied for the testing were commercial ones and were processed in commercial spring manufacturing lines to coil springs. Fatigue tests were conducted at room temperature until fracture or 107 cycles, under various constant stress ratios from 0.1 to 0.7. Also, load loss of each non-fractured spring at fatigue test was measured. Using each load loss thus obtained, residual shear strain γ (Shear stress relaxation divided by shear modulus) was calculated. It was found that the fatigue strengths obtained were all above the current JIS fatigue design diagrams and that the current JIS maximum design stresses were lower than those determined by the criterion that residual shear strain γ <= 0.05 % is met. Comparison of current JIS standard with the corresponding SAE and EN standards were also made.