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This is the final highway accident report (NTSB-HAR-71-1) from the National Transportation Safety Board, adopted in December 1970. It covers the collapse of the U.S. 35 bridge between Point Pleasant, West Virginia, and Kanauga, Ohio, on December 15, 1967, which killed 46 people. The Board found that the cause was a cleavage fracture in eyebar 330 at joint C13N. That fracture grew from a flaw produced over 40 years by stress corrosion and corrosion fatigue, in a spot that could not be seen or found by inspection.
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eyebar also showed results similar to those obtained by NBS. There was a layer approximately 0.10 inches thick on each face in which the Rockwell C hardness (obtained by conversion from Vickers diamond point hardness, DPH) averaged about 24, then a layer extending to a depth of about 0.40 inches in which the hardness was between 25 and 30, and followed by a gradual decrease of hardness toward the core material at the center of the thickness, where the hardness averaged about 21. This is a result of the slack quench obtained in the heat treatment and the decarburization of the outer surface. The profiles beginning at the pinhole surface show similar effects, but the layer of apparently decarburized steel was either thin or absent.
The results on the A7-24 steel also corroborated the work at other laboratories, indicating that its chemical composition and mechanical properties were within the limits of the specifications for the material. The 15 ft. 1b. transition temperature, based on results of Charpy impact tests, was between 50 and 70 degrees Fahrenheit.
b. A single slow bend test of a notch beam specimen was performed at $ 32^{\circ} \mathrm{F} $ to check the fracture mechanics parameters developed at Battelle. The specimen of eyebar material used was somewhat smaller than those tested at Battelle, being 1.82 inches thick, 5.80 inches deep and about 28 inches long. It was tested in three point loading on a span of 24 inches and fractured at a load of 21,100 pounds. The depth of the notch and fatigue crack totaled 2.29 inches. The value of the critical stress intensity factor computed from these results is 39.3 ksi. Vin., about nine percent below the minimum obtained by Battelle, which was 43.2 ksi. Vin. The indicated failure stress for the critical flaw in eyebar No. 330 based on this lower value of the critical stress intensity factor is 75,000 psi.
c. A careful examination of the depth of pitting on various surfaces of the C13 head of eyebar No. 33 was conducted, in which the pit depths were measured by noting the change of focusing adjustment necessary for the microscope between the surface near the pit and the bottom of the pit. The results of this examination are summarized as follows: Document, cited by the archive. The PDF is mirrored here; the original link is above. The text was read from the page images by GLM-OCR; expect the odd misread word. 202 pages are in the text index: search them above, or from the library's search.