Kichiro Endo

Torsional Creep Tests of a Mild Steel under Varying Stresses

Torsional creep tests of a mild steel were carried out under varying stress levels at 500°C by using thin walled tubular test pieces. In the present test conditions under constant stress, buckling occurs within the range of primary creep, where the relation between strain γ and time t is expressed by Andrades equation, γ=γ0+βtn, like as in tensile creep tests. For varying stress tests, stress level is varied to the lower stress of τu=-12.8, -6.4, 0kg/mm2 and is maintained for 60min after the upper stress τ0=12.8kg/mm2 for 60min, and the cycle is repeated. The instantaneous strain, creep rate, and total creep are greater when the previous stresses are higher in the reverse direction. Accordingly, the creep resistance is increasing with test time, and yet the increase is smaller when the stress returns to the constant τ0 from higher τu. The instantaneous recovery of strain in releasing of stresses is constant if the stresses were in the same height, and is not varied by the number of cycles. The rate of recovery strain under τu=0, i.e. during the rest of load, is in linear relation with time when the both are shown by logarithmic coordinate, and is not affected by the number of cycles.

Experimental Studies on Temperature Rise of Specimens during Fatigue Test

Tests were carried out to measure temperature rise of specimens together with damping constant due to the internal friction of materials, during the fatigue test. Temperature rise is a function of the magnitude of cyclic stresses, and a relationship between temperature rise and life of the specimen is found. Damping constant c is influenced by temperature of specimens, and has no relation to the magnitude and the cycle number of stresses after considerable repetitions. When plotted c under fatigue tests and damping constant measured by torsion pendulum against temperature, the curves thus obtained have shapes similar to each other, having the same temperature for extreme point. And the fatigue strength vs. temperature has an inverse shape of the former. Further, scatters of fatigue lives are found to be influenced by the differences of damping constant, that is, temperature rise of specimens.

The Corrosion Fatigue Strength of High Strength Steel Wire

The corrosion fatigue strength of wires of 0.75% C-steel is presented, relating to the residual stresses. Steel wires as drawn which have high tensile residual stress, wires annealed at 250°C after cold drawing to decrease the residual stress, wires annealed at 630°C after drawing to vanish the residual stress, and wires surface rolled after annealed at 630°C which have high compressive residual stress were tested under rotating bending in stream of city water. The corrosion fatigue strength is lowered by tensile residual stresses and is improved considerably by compressive residual stress. The influence of residual stress on fatigue strength is more remarkable under corrosive circumferences than in air. The corrosion fatigue tests of wire strands are also made.

Further Report on Pitting

We made experiments on the limit value pgs of pitting strength under various stress conditions in rolling contact of rollers with sliding motions. The endurance tests using various lubricants and with and without sliding motion, confirmed the question about the influence of lubricants on pitting strength. Moreover, we made tests on the influence of the methods of finishing roller surfaces on pitting strength.

The limiting Strongth for rolling Contact

アムスラー磨耗試驗機にて摩擦モーメントの測定により轉り接觸の斑磨耗耐久限度を求め,滑りを伴なうとき耐久限度は潤滑油の摩擦係數すなわち油性に影響されることを知つた。また滑りを伴なう接觸應力を破損の定理に適用してみると主歪または剪斷歪エネルギのある深さまでの平均値を許容應力とするとき比較的によく適合すると考えられる。