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(3) To investigate the mechanisms by which small initial cracks or defects could have grown to critical size.
(4) To investigate the residual stress patterns which were present in the eyebar heads due to the combination of fabricating and heat treatment processes and subsequent loading history.
The results of these investigations are presented in Reference No. 24, "Inspection and Evaluation of Two Steels from the Silver Bridge."
a. Section 1 of the Battelle report describes nondestructive test techniques applied to five eyebar heads then stored at the National Bureau of Standards and to heads of twenty eyebars from the wreckage of the Point Pleasant Bridge which were still at the reassembly site or on the Ohio shore where they fell. Dye penetrant techniques and magnetic particle techniques were used in the field investigations, with inconclusive results. Thirty eyebar heads were therefore burned off and taken to the Battelle laboratories at Columbus for examination under more favorable conditions. After cleaning and visual inspection, Zyglo dye penetrant techniques and wet magnetic particle techniques were applied. The net result of this program was that positive indications of cracks on the pinhole surface were found in five of the eyebar heads.
b. Section 2 of the Battelle report describes the experimental techniques employed to determine the residual stress that existed in typical eyebar heads of the Point Pleasant Bridge wreckage. These residual stresses arise from the differential cooling which occurs during the heat treatment process and also from the fact that some of the material around the pinhole is subjected to strains above the yield point strain when maximum dead load and live load effects occur in the structure. The residual stresses of the first kind vary sharply with the distance from the outside surfaces of the bar where cooling was most rapid. The stresses of the second kind occur with more or less uniform levels through the thickness of the bar, but vary in magnitude from the pinhole surface to the outer circumference of the eyebar head.
The laboratory used two techniques to assess the magnitude of these residual stresses. Surface residual stresses were measured by the application of strain gages to the surface and noting the changes in strain produced by removal of small amounts of material directly below the strain gage by careful work with a dental drill. The second method was also destructive in nature and involved the removal of a 2-inch wide slice of material by two parallel cuts across one limb of the eyebar head, followed by successive removal of layers of