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Acoustic Emission, Fatigue, and Crack Propagationj KYP·72-33; HPR·PL·L(L2), Part Lii·B

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Acoustic Emission, Fatigue, and Crack Propagationj KYP·72-33; HPR·PL·L(L2), Part Lii·B 457 October 197 6 ma0aL4Jmcsoo ma!P@mu DEP.A.R'I"NIEN'I" OIF 'I"R.A.NSPOR'I".A.'I"ION ACOUSTIC EMISSION, FATIGUE, A..l\!D CRACK PROPAGATION Theodore Hopwood II 111VIIIflll fJI RIIIARtll I.IXIIItiTflll JULIAN CARROLL JOHN C. ROBERTS GOVERNOR SECRETARY OF TRANSPORTATION COMMONWEALTH OF KENTUCKY DEPARTMENT OF TRANSPORTATION BUREAU OF H/GHWA YS DIVISION OF RESEARCH 5.33 SOUTH LIMESTONE LEXINGTON, KENTUCKY 40508 COMMONWEALTH OF KENTUCKY DEPARTMENT OF TRANSPORTATION JULIAN M. CARROLL JOHN C. ROBERTS BUREAU OF HIGHWAYS GovERNOR SECRETARY JOHN C. ROBERTS COMMISSIONER Division of Resea.rch 533 South Limestone - Lexington, KY 40508 November 5, 1976 H.3.33 MEMO TO: G. F. Kemper State Highway Engineer Chairman, Research Committee 11 SUBJECT: Research Report No. 457; "Acoustic Emission, Fatigue, and Crack Propagationj KYP·72-33; HPR·PL·l(l2), Part lii·B The state of knowledge pertaining to fatigue and the nucleation and growth of cracks in new steels is given in design textbooks and treatises. The state of knowledge pertaining to the detection or discovery of flaws, defects, cracks, or Lnsidious, fatigue damage Ln aged, steel bridges remaLns more formative and less practicable. It would be desirable to have tell·tale lights or alarms on bridges to forewarn of weakening 11 in any part. Presently, the closest approach to a warning system is acoustical monitoring. Steels do cry out in pain 11 when over~stressed; they do not cry very loudly. listening is done through contacting wJcrophones and amplifiers. A crack grows because of high stress at the apex. Isolating a noise artd locating the point of origin is much more complicated. Apparently, fatigue damage remaiilS insidious and not measurable until a crack develops. This is our conclusion from our investigations thus far. We have reported previously on acoustic monitoring following welding (Report 393; June 1974) and on fatigue analyses (Reports 251,275, 318, 323, and 411). An additional report will cover acoustic monitorLng of constrained, welded joints. Respectfully~ o_:_ ,.e; .d!! /"7:~. Havens Director of Research. sh Enclosure cc 1s: Research Committee Technical Report Documentation Page No. 1. Report No. 2. Government Accession No. 3. Recipient's Cotalog 4. I itle and Subtitle 5. Report Date October 1976 6. Performing Organization Code Acoustic Emission, Fatigue, and Crack Propagation 8. Performing Organiz:ation Report No. 7. Authorl s) Theodore Hopwood II 457 10. (TRAIS) 9. Performing Orgonizotion Nome and Address Work Unit No. Division of Research No. Kentucky Bureau of Highways 11. Contract or Grant KYP-72-33 533 South Limestone I.e xington Kentucky 40508 13. Type of Report and Period Covered 12. Sponsoring Agency Nome end Address lr'tterim 14. Sponsoring Agency Code 1s. Supplementary Note$ Study Title: Evaluation of the Fatigue Life of Critical Members of Major Bridges 16. Abstract I Acoustic emlSSlOTI was used in conjunction with tensile tests to evaluate the condition of structural steel specimens subject to various tensile fatigue lives. The results indicate that the acoustic emissions detected were the result of plastic deformation. There was no apparent relationship between fatigue history of the steel specimens and the amount of plastic deformation they can accommodate. Further tests revealed that acoustic emission has the physical capability of detecting cracks on large structural steel members. This may prove beneficial for the comprehensive testing of steel bridges. 17. Key Words 18. Distribution Stctemenf acoustic emission pearlitic steels brittle fracture stress·corrosion cracking fatigue s.tress·intensity martensitic steels nondestructive evaluation 21. No, of P cges 22. Price 19. Security C!ossif. (of this report) 20. Security Clcssif. (of this pcge) Form DOT F 1700.7 18-721 Reproduction of completed page authorized Research Report 457 ACOUSTIC EMISSION, FATIGUE, AND CRACK PROPAGATION Interim Report KYP-72-33, HPR-PL-1(12), Part Ili-B By Theodore Hopwood II Research Engineer Division of Research Bureau of Highways DEPARTMENT OF TRANSPORTATION Commonwealth of Kentucky The contents of this report reflect the views of the author who is responsible for the facts and the accuracy of the dat-a presented herein, The contents do not necessarilY reflect the official views or po-licies of the Kentucky Bureau of Highways, This report does not constitute a standard, specification, or regulation. October 197 6 INTRODUCTION 25, 1940. It had been in service for 5 years. The temperature was about 7 F (-14 C). The bridge did not In the past 30 years, at least 26 major steel bridges collapse upon cracking. throughout the world have suffered insidious fractures While the trusses were being fabricated, distortion resulting in their partial or complete collapse. When this occurred due to weld contraction. The welders corrected study was initiated in 1972, five years had passed since the alignment as the truss progressed across the canal. the Silver Bridge collapse at Point Pleasa.L1.t, West The distortion was probably caused by poor weld Virginia. During the course of this study, the Osage detailing. The steel used in several of the bridges was River Bridge at Warsaw, Missouri, collapsed June 9, found to have high sulphur and phosphorous contents. !975; and the US 75 bridge over the South Canadian Notched impact tests revealed that the steel had low River in Oklahoma collapsed May 22, 1976. impact toughness at the temperatures at which the The first wrought-iron bridge was built in England bridges failed. Cleavage cracks were not restricted to over 200 years ago and is still in use. Wrought iron was points through or adjacent to welds. The failures were used predoiTlinently in early metal bridges and continued not attributable to poor steel weldability. to be widely used for this purpose through the end of The Duplessis Bridge (see Figure 2) at Quebec, the 19th century. The Roebling Suspension Bridge over Canada, was completed in 1947. The bridge was of the Ohio River at Covington, constructed of wrought welded plate-girder construction with plate thicknesses iron, masonry, and timber, has served since 1865. to 2 1/2 inches (64 mm). The bridge had six, 180-foot Pneumatic steelmaking, jointly discovered in the (59-m) and two, !50-foot (49-m) spans. Wilen the bridge mid-19th century by Henry Bessemer in England and was 27 months old, two cracks were found on flange William Kelly at Eddyville, Kentucky, led to the use plates near butt welds, traveling toward the web. of steel in long bridge spans .. However, steel was not Inspection revealed the cracks had probably been in the used in an American bridge until 1880. At the turn of girders prior to erection. Repairs were made by riveting, the century, open-hearth steelmaking began to supplant and all tension joints were reinforced with riveted plates. the Bessemer-Kelly process. Now, the open-hearth A year after repairs, traffic was suspended, and a l 0-day process is gradually being replaced by the basic oxygen inspection was performed on the bridge. The repairs process. were reported to be satisfactory. However, the west - Most metal bridges in service today are made of portion of the bridge collapsed under its own weig..ht steeL \Vh.ile most of these bridges have performed 2 weeks later. The temperature at the time of failure satisfactorily, a few recent failures are worthy of was -30 F (-37 C). Investigation after the accident discussion. Prior to World War II, some 50 Vierendeel revealed that improper material selection was responsible truss bridges were built over the Albert Canal i11. for the failure. The thick sections (ordered to ASTM Belgium. The Vierendeel truss is a welded, through-type A 7) were found to be of rimming quality, unsuitable truss, without diagonals; stiff posts and knees connect for welding, and showed extensive segregation of carbon the lower and upper chords. Structural members and sulphur. Charpy tests revealed low impact toughness consisted of !-beams, plates, or mixed !-beams and plates (3-6 ft-lb (4-8 J) at 100 F (37 C)) (1). of a Belgium, standard Bessemer steeL Plate thicknesses The Kings Bridge at Melbourne, Australia, was built varied up to 2 1/2 inches (64 mrn). The first failure in 1961. The structure consisted of four lanes of occurred at Hassell, March 14, 1938 (see Figure 1). The plate-web girders 100 feet (30.5 m) long and 5 feet (1.5 bridge had been in service 14 months. It had a span m) deep and a reinforced concrete deck. In July 1962, of 244 feet (74.5 m). The bridge collapsed under the one span of the bridge collapsed under the weight of load of a tramcar and some pedestrians about 6 minutes a 45-ton (41-Mg) truck. The bridge sagged 1 foot (0.3 after ·a loud report of the first crack. Witnesses said the m); further collapse was prevented by the concrete deck. failure occurre-d in the lower chord, causing the arch Inspection revealed that all girders had brittle fractures to absorb the load and eventually collapse. The in nearly identical locations. The cracks ran from the temperature at the time of the fracture was -4 F (-20 heat-affected zone of the weld at the upper flange and C). A second truss, at Herenthals-Oolen, failed on March traversed through the parent metal to the lower flange. 19, 1940, after 3 years of .service. Cracking was It was also evident that failures had occurred accompanied by three loud reports. Five hours later, a sequentially over the 15-month period since the bridge train passed over the bridge without causin_g it to opened. The final fracture caused the bridge to collapse. collapse. One crack was found to be 7 feet (2.1 m) long This failure was the result of improper material and open l·inch (25·mm).
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