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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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material through the thickness of this slice (See Figure 15). In general the results after the initial cuts (See Figure 16) show that residual stresses existed at the edge of the pinhole which were as high as 27,325 lbs. per square inch, with marked differences between the residual stresses at the two faces of the bar. The patterns of residual stress through the thickness were quite complex (See Figure 17) and in general the magnitudes were highest in the sections closest to the pinhole, indicating that stresses in excess of the yield strength of the material had existed at this point at some time during the life of the structure.
c. The next section discusses the investigation of the fracture toughness properties from the point of view of the modern discipline of fracture mechanics. The basic problem is to determine the parameter $ K_{Ic} $ , the "critical stress intensity factor" for the material, from which the stress level at which a given flaw size can produce a brittle fracture may be computed. Two types of specimens were employed. The first type, a notch bend specimen two inches thick, eight inches deep and thirty-six inches long, was tested as a beam at a temperature of $ 0^{\circ} \mathrm{F}. $ and at room temperature (about $ 70^{\circ} \mathrm{F}. $ ). The test arrangement for the $ 0^{\circ} \mathrm{F}. $ tests is shown in Figure 18. The specimen was wrapped with foil over layers of steel wool, through which liquid nitrogen was circulated to establish the proper test temperature. Three specimens were tested at $ 0^{\circ} \mathrm{F}. $ and two at room temperature, all of which were cut from the shank of eyebar No.330. All specimens contained chevron notches sharpened by fatigue cracking to about half the depth of the specimen.
The surface-flawed specimens were made from 1" x 2" x 24" blanks cut from eyebar No. 330, with the 2" side parallel to the thickness dimension of the bar. Tab extensions were welded to the ends for engagement of the loading grips. Each specimen was given a deliberate flaw by means of electronic discharge machining at mid length and across the center of the two-inch face. The flaw was then sharpened to a fatigue crack by fatigue loading prior to the static tension test in which fracture toughness data was obtained.
The results of these tests are summarized in Table 1. Complete data are presented in Appendix B. There is good agreement between the values of the $ K_{Ic} $ parameter obtained with the two types of specimen. All fractures were 100 percent "flat" cleavage.
A computation of stress level to produce a brittle fracture with a flaw the size of the primary pre-existent crack in eyebar No. 330 (0.12" x 0.28"), using the minimum value of stress intensity factor of 43.2 ksi $ \sqrt{\mathrm{in}} $ found for specimens at $ 32^{\circ} $ Fahrenheit, indicates that a unit stress of 88,000 psi is required. This is about 10 percent above the yield strength of the material, but since no consideration was given to the presence of the smaller secondary crack, it 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.