抄録
We investigated on the forming pressure effects on the fatigue strength and on the other mechanical properties. Test pieces of the forming pressures 160, 80, and 50kg/cm2 were prepared. Fatigue characteristics were tested on the rotating bending fatigue test machine, whose number of revolution per minute were either 1900 or 1000. The thermo-paint was coated on the surface of the piece for fatigue test so that its temperature might be known, and the colour changing might show the aspect of internal heat producing.
Main test results obtained were as follows:
1) The forming pressure has a remarkable effect on the mechanical properties in the case of loading parallel to the laminates, but the effect in the case of loading perpendicular to the laminates was not clearly detected. In the case of loading parallel to the laminates, fatigue strength, bending stiffness, tensile strength and tensile stiffness decrease, and impact strength increases as the forming pressure is lowered, but compressive strength has maximum values at a forming pressure of 80kg/cm2.
2) The apparent S-N diagram of cotton cloth laminates consist of three curves for the higher, middle and lower stresses. The true fatigue strength at a curve of higher stress must be larger than that given by the curve, because points on the curve show the numbers of revolution at which certain deflections are given by the stresses. The points on the curve of middle stress show the numbers of revolution at which the test pieces are fractured mainly due to the effect of internal heat producing. In this case the temperatures of the surface of the test pieces are about 110-150°C. The points on the curve of lower stress show the numbers of revolution at which the test pieces are fractured mainly by the effect of stress. In this case the temperatures of the surface of the test pieces are about 70-110°C. At a fatigue limit (N=107), the temperatures of the test pieces are below 50°C.
3) As the number of revolution per minute decreases, the fatigue strength slightly increases. As the effect of the number of revolution per minute are not extinguished in curves of middle and lower stresses, the effect of internal heat producing has to be taken into consideration at lower stress at which test pieces are fractured mainly through the effect of stress.
