Keizo Fujitani

A statistical aspect on fatigue behavior of alumina ceramics in rotating bending

Abstract Statistical fatigue tests in rotating bending were carried out by using round bar specimens of alumina ceramics, in which fatigue life distributions were examined at five stress levels by assigning 20 specimens to each level. Based on these results, the probabilistic fatigue property of this material was given as the quantitative P-S-N characteristics in wide range of fatigue life 1 8 . Furthermore, SEM observations were made on the fracture surfaces, and the effect of material defects on the fatigue life was also discussed.

Statistical analysis of fatigue behaviour of spot-welded joints in tension-shear-type loading

Abstract When an external force is applied to a spot-welded structure, the load at each spot is not uniform. Fatigue life of the welded spot cannot be accurately predicted even if the load is known. In this study, distribution characteristics of the load at each spot of a welded joint were examined experimentally, and fatigue life distributions were investigated for both single-spot and multi-spot joints. By combining the life distributions of single-spot joints and the distribution properties of the loads assigned to the respective spots, fatigue life distributions of multi-spot joints were theoretically derived. It was found that the theoretical fatigue life distributions were in good agreement with experimental ones.

Low-Cycle Torsional Fatigue of High Carbon Steel under Multiple Repeated Loads

The fracture criterion of low-cycle fatigue based on variable strains, which is represented as1/C0∫N0γpadn=1 for the varying plastic strain amplitude, has been verified experimentally by carrying out the low-cycle fatigue tests under the tension-compression and rotating bending conditions. The low-cycle torsional fatigue tests under multiple repeated loads were made on the 0.84% C piano wires and the applicability of the above mentioned criterion was examined.The main results obtained are as follows:(1) The experimental values of the cumulative damage obtained from the above criterion are larger than the values calculated from the linear damage criterion, and they scatter around in the vicinity of unity.(2) The test results indicate the existence of an exponential relationship between the equivalent stress amplitude τeq and the equivalent plastic strain amplitude γp.eq.

Application of an Improved Low-Cycle Torsional Fatigue Testing Machine to Test under Manifold Repeated Load on Two Stress Levels

There has been but little study so far made on the low-cycle torsional fatigue on cold drawn wires of small diameters under actual loads. In order to pursue studies on this problem, therefore, we designed and manufactured a low-cycle torsional fatigue testing machine suitable for the test of these wires. There are many types of torsional fatigue testing machines, but the one designed by the authors has a merit in that by using a photo cell the change of the load can be conducted easily and exactly.By using this testing machine we carried out the low-cycle torsional fatigue tests of piano wires under manifold repeated load on two stress levels at room temperature.The main results obtained are as follows:(1) The cumulative cycle ratio Σn/N obtained from the test results were not in agreement with the unit, giving values greater than unity for large stress ratio of τA/τw and those less than the unit for small stress ratio.(2) The time strength at 103 cycles for piano wiresrises whenever it is subjected to multiple repeated loads.(3) The test results show that the plots of total plastic strain versus the number of stress cycles to failure deviate from the linear relation between them which holds under a constant stress amplitude.