the spool in an almost static position. He described the casting as "tremendously strong." (N.T. 450.) He made rough calculations of the margin of safety and found that a casting meeting the requirements specified would be twenty-five times the required strength to carry the weight of the 1500 lb. reel. From his observation of: (1) the x-rays showing certain voids, (2) the sample P-15(b) of the fractured surfaces indicated on Exhibit P-56, and (3) microscopic examination and micro-hardness tests of samples from 15(a) and 15(b) shown on the same Exhibit P-56, he testified that it was his opinion that the tensile strength of the casting which fractured, without regard to the weakness caused by the welding, but judging from the porosity alone, was not reduced by more than thirty percent. He went on to say that even if the porosity of this casting had reduced its tensile strength by fifty percent (which he did not concede), the casting still would never have broken from the foundry defects when loaded from above with the weight of the bobbin.
Dr. Grosvenor testified that the Brinell hardness had gone up to about 400 (from the normal of 170) at the closest point he could measure, with even harder regions close to the surface where he could not measure it precisely but could get an indication of the hardness through microscopic examination. He said that it had gone way over "file hardness", i.e., the degree of hardness at which it could scarcely be scratched with a file, and that this hardness had embrittled the structure. Dr. Grosvenor said that hardening causes expansion -- sizable expansion, tugging on adjacent areas, setting up residual stresses of considerable magnitude. He testified that the fracture as shown in the photograph P-39 was in the heat-affected zone, an area of high stress, quite close to the weld, and that the heat affected zone spread out for perhaps 3/8". According to Dr. Grosvenor, the significance of the fracture adjacent to the weld, rather than in some other porous area, was that: (1) the casting originally had a reinforcing rib in the form of a three-sided square, and the weld left a valley between the weld and the rib -- a thinner area surrounded by two thick areas -- which created a structural notch; and (2) the residual stresses set up in this valley (between the balancing weight and the rib) resulted in triaxial stresses which created a more dangerous concentration than would prevail if there were a simple tension or biaxial stress. In Dr. Grosvenor's opinion, the crack started and ran up that valley, then branched out, crossed the rib, and went up another weld heat-affected zone on the outside, on the other side where there was still a chance for triaxial stress.
Addressing the matter of Dr. Talbot's tests, Dr. Grosvenor said that they did not compare with the ASTM test requirements, which prescribe machining the dross off the test bar before testing for ductility. He would not accept the tension test made on an original cast surface. And he said that Dr. Talbot "did not" reproduce in his tests the stress pattern which took place when the accident occurred. (N.T. 472.) It was Dr. Grosvenor's opinion that there was no evidence of fatigue failure indicated in the photographs or in his examination of the two pieces of the casting placed in evidence and shown on the photograph P-56. He testified that this appeared to be an overload fracture rather than a fatigue fracture which would show progressive small steps with markings similar to beach marks or clam shell marks. Furthermore, Dr. Grosvenor noted that a fatigue fracture surface is usually quite smooth, but no smoothness was indicated in the photographs. (See N.T. 52 through 55.) On the other hand, the surface produced by an instantaneous break was rougher and more jagged.
Dr. Grosvenor testified that the load alone -- the weight of the loaded spool -- was so small that barring some untoward incident, such as an impact, they may go on forever, but that if they lasted for 60 weeks and didn't break, they didn't fail by fatigue. He stated that "the welding very seriously damaged the strength of the cradle casting that broke." (N.T. 448.) In his opinion, the casting failed because of the high stresses and the embrittling from the welding combined. He demonstrated the high stress pattern. He examined the sample 15(b) by microscope and did a micro-hardness test. It had a hardened zone and therefore a volume change which had to produce stresses, and the line of crack ran along the side of the weld bead, crossed over and ran up along the side of another weld bead. As he said, "There is evidence aplenty of a high stress pattern because this is a part that is lightly loaded in ordinary service." (N.T. 473.) Dr. Grosvenor gave the opinion that the stress pattern of the weld, per se, caused the rupture, and he testified that he believed that the bending started on the outside of the surface shown on P-39, not on the inside surface shown on P-56. Dr. Grosvenor also pointed out that Dr. Talbot had testified that in cutting the samples it was found that they were hard in the heat-affected zone next to the weld; that he (Talbot) said that he might have made micro-hardness tests, but did not; and that Talbot did not find the striations or beach marks usually found in a fatigue failure.
We asked Dr. Grosvenor whether, if Dr. Talbot's tests were proper by ASTM standards, and his tensile strength yield strength and elongation figures were accurate, he (Dr. Grosvenor) would then agree that the cause of the fracture was fatigue and a poor casting as opposed to the effect of the welding. He replied:
No, not at all. Because even with his test method, with which I disagree completely, he has with the exception of two bars, he has strengths which run up to at least two thirds the required specified strength. He has two that are low. And if I were to take these as indicative of the character of the material, then the strength of the material is reduced, let's say, to not more than half of 60,000 is 30,000. . . The thing is twenty-five times or more, twenty-five or more times as strong as it need be, and to take half of it would make it twelve or thirteen times as high. It still has a safety factor of twelve or thirteen if we base it on his tests. (N.T. 497-98.)
We then observed that Dr. Talbot's tensile and yield strength figures were far better than the elongation figures. Dr. Grosvenor replied:
A. In the normal use and the stresses to which this is subjected, his percent of elongation has no effect because in the normal operation of this that saddle is never deformed by 1/10 of 1 percent.