Showing papers on "Vibration fatigue published in 1971"

On cumulative fatigue damage in seismic structures

Abstract: THE VIABILITY OF CUMULATIVE FATIGUE DAMAGE AS A DESIGN CRITERION FOR SINGLE DEGREE-OF-FREEDOM STEEL SEISMIC STRUCTURES IS INVESTIGATED. TWO ENSEMBLES OF EARTHQUAKE ACCELERATION RECORDS ARE GENERATED AND USED AS EXCITATION INPUT IN SIMULATIONS INVOLVING STRUCTURES HAVING VARIED STRENGTH FACTORS AND PERIODS OF VIBRATION STRAIN AND STRESS HISTORIES ARE OBTAINED FOR THE EXTREME FIBERS OF CRITICAL SECTIONS OF THE STRUCTURES. THESE ARE EVALUATED FOR CUMULATIVE FATIGUE DAMAGE BY A MODEL WHICH INCORPORATES THE RAIN FLOW CYCLE COUNTING METHOD, A FACTOR TO ACCOUNT FOR THE MEAN STRESS OF EACH STRAIN REVERSAL AND AN EMPIRICAL ADJUSTMENT TO THE STRAIN-FATIGUE LIFE FUNCTION TO ACCOUNT FOR THE SEQUENCE EFFECT OF THE STRAIN HISTORIES. FATIGUE DAMAGE IS FOUND TO BE SIGNIFICANT IN STRUCTURES HAVING PERIODS OF VIBRATION AT THE LOWER END OF THE MEDIUM PERIOD RANGE OF THE DESIGN EARTHQUAKE SPECTRA. THE DAMAGE MAY BE ESTIMATED FROM A HYSTERETIC ENERGY PARAMETER PERTAINING TO THE CRITICAL SECTION OF THE FRAME. /ASCE/

A Reliability Approach to the Fatigue of Structures

Abstract: ANALYZING THE FATIGUE DAMAGE OF A NOTCHED SPECIMEN SUBJECTED TO A RANDOM-STRESS HISTORY OF NARROW-BAND CHARACTERISTICS, THE CRACK PROPAGATION FACTOR IS TREATED AS A HOMOGENEOUS RANDOM PROCESS REFLECTING STATISTICAL VARIATIONS OF MATERIAL PROPERTY WITHIN THE SPECIMEN. ON THE BASIS OF THE PROPOSED STATISTICAL-MECHANICAL MODEL OF FATIGUE FAILURE, INTO WHICH A CRACK PROPAGATION MODEL AND A FRACTURE CRITERION ARE INCORPORATED, STATISTICAL DISTRIBUTION OF FATIGUE LIFE IS PREDICTED WITH THE AID OF THE MONTE CARLO TECHNIQUE BY DIGITALLY SIMULATING THE STRESS HISTORY AND THE CRACK PROPAGATION FACTOR AS RANDOM PROCESSES. THE RESULTS INDICATE THAT THE SPACIAL RANDOMNESS IN MATERIAL PROPERTY CAN, AND IN FACT SHOULD BE CONSIDERED IN ORDER TO ACCOUNT FOR THE LARGER SCATTER OF FATIGUE LIFE OBSERVED IN THE EXPERIMENT PERFORMED UNDER THE CONDITIONS COMPATIBLE WITH THE ASSUMPTIONS USED IN THE ANALYSIS. /ASTM/

The Effect of Load Interaction and Sequence on the Fatigue Behavior of Notched Coupons

Abstract: CONSTANT AMPLITUDE FATIGUE TESTS WITH VARIOUS CONDITIONS OF OVERLOADS WERE CONDUCTED TO UNDERSTAND THE EFFECTS OF LOAD INTERACTION AND SEQUENCE IN NOTCHED COUPONS. THE RESULTS WERE ANALYZED WITH PARTICULAR EMPHASIS ON THE LOCAL RESIDUAL STRESSES AT NOTCHES. FATIGUE LIFE RESULTS FROM THE TESTS HAVING A VARIATION IN THE NUMBER OF CYCLES BETWEEN THE PERIODIC OVERLOADS WHICH REINFORCE THE CONCEPT OF A FADING RESIDUAL STRESS. OTHER FATIGUE LIFE TRENDS COULD BE PREDICTED BY ASSUMING A STABLE RESIDUAL STRESS. CONDITIONS WHICH COULD CAUSE CYCLE-DEPENDENT OVERLOAD RESIDUAL STRESSES ARE DISCUSSED. AN EXPONENTIAL ANALYSIS FORM IS SUGGESTED FOR CALCULATING THE CYCLE-DEPENDENT LOCAL STRESSES FOR APPLICATION TO CUMULATIVE DAMAGE PREDICTIONS. /ASTM/

On the Probabilistic Determination of Scatter Factors using Miner's Rule in Fatigue Life Studies

Abstract: A PARTICULAR TWO-PARAMETER FAMILY OF LIFE-LENGTH DISTRIBUTIONS FOR FATIGUE LIFE IS ASSUMED. THIS FAMILY, FIRST FORMULATED BY FREUDENTHAL AND SHINOZUKA IN 1961, WAS SYSTEMATICALLY EXAMINED BY BIRNBAUM AND SAUNDERS IN 1968 WHERE IT WAS DERIVED, USING CONSIDERATIONS FROM RENEWAL THEORY, FOR THE NUMBER OF CYCLES NEEDED TO FORCE A FATIGUE-CRACK EXTENSION TO EXCEED A CRITICAL VALUE. BY EMPLOYING THIS NEW FAMILY, TOLERANCE BOUNDS ARE OBTAINED FOR THE POPULATION OF LIFE TIMES UNTIL FATIGUE FAILURE UNDER A PROGRAMMED LOAD. THIS IS ACCOMPLISHED BY UTILIZING A GENERALIZATION OF MINER'S RULE WHICH COMPUTES THE MEAN LIFE UNDER THE PROGRAMMED LOAD IN TERMS OF THE MEAN LIVES UNDER SIMPLER PROGRAMMED LOADS AT STRESS LEVELS FOR WHICH DATA ARE AVAILABLE. SUCH BOUNDS HAVE NEVER BEEN OBTAINED PREVIOUSLY FOR ANY OTHER LIFE-LENGTH DISTRIBUTION AND THE CONFIDENCE LEVEL EXACTLY DETERMINED. THIS PAPER CONCLUDES WITH AN APPLICATION OF THESE RESULTS TO A SET OF REAL FATIGUE DATA. /ASTM/

Product Reliability and Random Fatigue

Abstract: The fatigue life of a mechanical component in a conventional ional test situation depends upon the stress amplitude. A change in the stress amplitude during a laboratory test-program involves a consideration of the damage produced by each stress cycle imposed upon the test specimen. A direct extension of this elementary concept to irregular stress waveforms provides a logical basis for a statistical analysis of product reliability due to random fatigue. The statistical behavior of the fatigue life is related to the probability distribution of the maxima and minima in a random stress waveform. The fundamental relation between the probability of survival and the maxima-minima is derived in this presentation, which contains a theoretical application to a simple random stress oscillation. The same expression may be used in the development of a computer program to evaluate product reliability from a numerical analysis of experimental data.

Direct measurement of fatigue damage in aircraft

Abstract: A fatigue life gauge, mounted on a mechanical amplifier and bonded to a structure, will integrate the load/frequency pattern to which it is exposed. Subject to static calibration establishing the strain/load relationship registered by the device, gauge manufacturers data will closely predict the output for programmed loading within the range of 0–2 to 40 ohms. The purpose of the device is to compare the rate of loading, accumulated by a test structure, with the rate accruing to similar structures undergoing variable service loading. Inasmuch as this loading affects the fatigue life of a component, the device will monitor fatigue damage. Some agreement is shown between laboratory test of an aircraft fin and measurements taken during routine flying. The device is sensitive to change in aircraft utilisation. In the case of fin structure, no correlation exists between the measured damage factor and the damage assessed by the standard aircraft fatigue meter.