RANDOM LOAD FATIGUE TESTING: A STATE OF THE ART SURVEY

NEW TECHNIQUES FOR THE EVALUATION OF FATIGUE LIFE FOR METAL STRUCTURES ARE ANALYZED. THE TECHNIQUE FOR CONTINUOUS LOAD ANALYSIS, REFERRED TO AS PSD ANALYSIS (AFTER THE POWER SPECTRAL DENSITY PLOT WHICH RESULTS) IS BECOMING RECOGNIZED AS A VALID APPROACH TO THE DELINEATION OF FATIGUE LOADS. THE PSD PROFILE IS THE RESPONSE IN STRESS OF A STUCTURE TO UNIT ENERGY SINEWAVE EXCITATION AT EACH FREQUENCY, OVER THE FREQUENCY RANGE OF INTEREST IN SERVICE LOADING. ONCE THE SERVICE LOADS HAVE BEEN ANALYZED, THE FATIGUE ENGINEER USES ONE OF THE FOLLOWING FOUR DIFFERENT METHODS TO FIND A STATISTICALLY-DEFINED LOAD SPECTRUM FOR THE VEHICLE IN QUESTION: (1) CUMULATIVE DAMAGE THEORY WITH CONSTANT AMPLITUDE S/N CURVES FROM TESTS, OR FROM THE LITERATURE, (2) REPEATED BLOCKS OF A PROGRAM OF CONSTANT AMPLITUDE CYCLES AT STRATIFIED STRESS LEVELS IN ARBITRARY SEQUENCE IN APPROXIMATE CONFORMITY TO THE RELATIVE FREQUENCY OF SERVICE LOADS FROM THE LOAD SPECTRUM, (3) A TEST LOADING INVOLVING GROUPS OF CONSTANT AMPLITUDE CYCLES OR INDIVIDUAL CYCLES USUALLY CALLED UP IN A COMPUTER-RANDOMIZED SEQUENCE OF VARYING LOAD LEVEL, BUT WHOSE NUMBERS AT A GIVEN LOAD LEVEL ARE PRESELECTED TO RESULT IN THE FINAL RELATVIE FREQUENCY DICTATED BY THE SERVICE LOAD SPECTRUM, AND (4) USING EITHER THE ACTUAL RANDOM PROCESS, AS WITH ACOUSTIC FATIGUE, OR WITH SAMPLES FROM SERVICE, OR AN ANALOGOUS RANDOM PROCESS WITH SIMILAR GENERAL CYCLE CORRELATION CHARACTERISTICS TO THE PROCESS IN SERVICE, EITHER AS A STATIONARY PROCESS, OR WITH THE RMS PROGRAMMED TO RESULT IN THE SAME LOAD FREQUENCY AS GIVEN BY THE LOAD SPECTRUM. THE GROWTH OF TEST DATA IN THE LAST TWO CATEGORIES IS SPECIFICALLY DESCRIBED. LITERATURE AVAILABLE IN TWO OTHER RANDOM LOAD TEST AREAS ARE DESCRIBED: ACOUSTIC FATIGUE AND RANDOM LOAD CRACK PROPAGATION. A FEW EXAMPLES ARE PRESENTED OF TESTING PRACTICAL STRUCTURES WITH BOTH STATIONARY AND PROGRAMMED RMS STRESS LEVELS. THE UNIVERSALITY OF ENDURANCES OBTAINED FOR A GIVEN MATERIAL TESTED WITH A STANDARD FREQUENCY DENSITY PROFILE (PRESENTED IN THE FORM OF AN RMS-STRESS LIFE CURVE) IS NO LESS THAN THE CORRESPONDING S-N DATA FOR THE SAME CONDITIONS. TABLES ARE INCLUDED CONCISELY, LISTING MUCH OF THE AVAILABLE RANDOM FATIGUE ENDURANCE DATA, WITH SOURCES, FOR SIMPLE SPECIMENS. NINETY PAPERS WERE FOUND TO CONTAIN RELEVANT TEST DATA, AND THE RESULTS OF APPROXIMATELY 3,000 TESTS OF VARIOUS TYPES ARE TABULATED WITH CROSS REFERENCES.

• Supplemental Notes:
  • Vol 8, No 4, PP 11-45, 10 FIG, 4 TAB, 6 PHOT, 9 REF
• Authors:
  • Swanson, S R
• Publication Date: 1968-4

Media Info

• Serial:
  • Materials Research and Standards
  • Publisher: American Society for Testing and Materials (ASTM)

Subject/Index Terms

• TRT Terms: Accelerated tests; Acoustics; Cracking; Distributions (Statistics); Fatigue (Mechanics); Fatigue tests; Load tests; Loads; Loss and damage; Metals; Power spectra; Repeated loads; Sampling; State of the art studies; Static loads; Statistical analysis; Stochastic processes; Stresses; Structures
• Uncontrolled Terms: Crack propagation; Fatigue life; Loading
• Old TRIS Terms: Continuous sampling; Cumulative distributions; Spectral lines; Test results
• Subject Areas: Bridges and other structures; Data and Information Technology; Geotechnology; Highways; Materials;

Filing Info

• Accession Number: 00216651
• Record Type: Publication
• Files: TRIS
• Created Date: Aug 19 1994 12:00AM