Experimental Results Of Fatigue Tests Research Articles

セラミックスの強度信頼性評価（第５報） 加工損傷を有するセラミックスの強度信頼性評価法の提案

This paper describes the method for strength reliability evaluation of ceramics with machining damages and the prediction of the life of PSZ ceramics with thermal cracks caused by laser heating. The stress intensity factor of a four point bending model with machining damages is analyzed concerning with the number of cracks and crack density using finite element method. It is necessary to know the interactive interference of cracks within ten times area of each crack length in order to obtain the stress intensity factor of the crack tips which lead to failure. Also the crack growth parameter m and C of PSZ ceramics with the thermal crack damages are calculated from approximate equation of stress intensity factor in the machining damage model. As the result, it is found that the experimental results of fatigue test of the specimen with crack damages caused by laser heating agrees with the life predicted from analysis

Finite element analysis of crack growth life prediction under complex load history

This paper presents an innovative methodology for predicting the remaining crack growth life. To simulate the true load history effect, the present paper investigates the effect of various load sequences and the crack closure model is used to consider the residual stress effect during fatigue crack growth. The stress intensity factor, which is computed by a comprehensive finite element computer code, ABAQUS, is corrected to an effective stress intensity factor when the crack closure model is considered. Using the Paris equation, the fatigue crack growth rate under different load sequences can be calculated. The crack growth coefficient in the Paris equation, C, obtained from usually constant amplitude fatigue tests in which residual stress effects are not included, has to be modified to C 0 with the crack closure model using the present method. Also, the predicted results are compared with the experimental fatigue test results. The methodology has been proven to be very efficient and accurate.

A geometrical assessment of machined ceramic surface for estimating fatigue strength

Effects of surface micro-geometry on fatigue strength of silicon nitride(Si 3N 4) were discussed and the data-processing techniques for a geometrical assessment of its surface finish were developed. Taking no account of conventional roughness standards, new topographical parameters based on profile valleys were proposed to correlate with the fatigue strength of test specimens. The sampling conditions and the calculation method were examined in detail. Judging from the experimental results of fatigue tests, it was made clear that the fatigue strength of Si 3N 4 can be estimated to some extent with the statistical values on the micro-geometry at the bottom of valleys. The metrological discussion on the correlation was also made.

A New Approach to the Evaluation of Fatigue Under Multiaxial Loadings

A critical review of the methods for evaluating fatigue of metals under simple (proportional) and complex (nonproportional) loadings indicates that most of the criteria are expressed in terms of either stresses or strains. In this paper a new approach to the evaluation of fatigue under these loadings is proposed. This approach is based upon the idea of relating fatigue life to the plastic work during a cycle of the loading. A procedure is outlined for the calculation of plastic work which involves explicit considerations of the material constitutive relations. It is based on the structure of modern plasticity theories and a new “hardening rule.” Validity of the constitutive relations to predict the cyclic stress-strain response is demonstrated for out-of-phase multiaxial loadings. Available experimental results of fatigue tests under out-of-phase loadings are shown to be in good agreement with the predictions using the new approach.

Fatigue Strength of Butt Welded Joints Having Angular Distortion

In structures subjected to cyclic loading, fatigue damage is usually concentrated at location with geometric discontinuity such as butt welded joints, where stress and strain concentrations are present.In this paper, experimental results of fatigue tests on butt welded specimen are discussed and also a method to estimate the fatigue strength of butt welded joints with arbitrary amount of angular distortion is proposed, which showed a good agreement with the test results.The tests were performed on butt welded joint specimens prepared from two types of high tensile strength steels, namely WES HW 50 and HW 70. Butt welded joints with various amount of angular distortion were prepared to investigate its effect on fatigue strength. Effects of span and overstressing prior to fatigue were also studied. From these investigations it was found that, regardless of the amount of angular distortion, span or overstressing, the strain range measured at a point 5 mm from the toe of the weld, denoted εR has a good correlation with the failure life Nf.Stress and strain relation at a joint with angular distortion was previously proposed by Yada et al. This method was modified here to obtain strain behavior for repeated loading. The calculated strain range and the experimentally obtained strain range εR were in good agreement for any of the test conditions in specimens with angular distortion.It was concluded that, knowing the εR-Nf curve for butt weld joints of a given steel, fatigue life for joints with arbitrary amount of angular distortion can be obtained through calculation.Overstressing was effective in increasing the fatigue strength of butt welded joints with angular distortion above a certain stress level, but no apparent difference was seen for all stress levels in practically straight butt welded joints. The effect of overstressing was quantitatively explained, which is in accordance with the experimental results.It is pointed out a typical expression in present standards for allowable amount of angular distortion which is in terms of “initial amount of distortion over a certain span” may require reconsideration.

The Study on the Fatigue Strength by Varying the Stress-Amplitude withd the Superposed Mini-Sinusoidal Stress Wave on the Based Sinusoidal Stress Wave : Report 1, Some Experimental Results of Fatigue Test by New Simple Device for Superimposing Secondary Mini-Stress Wave

The Study on the Fatigue Strength by Varying the Stress-Amplitude withd the Superposed Mini-Sinusoidal Stress Wave on the Based Sinusoidal Stress Wave : Report 1, Some Experimental Results of Fatigue Test by New Simple Device for Superimposing Secondary Mini-Stress Wave