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plates , }, and inch thick being a loss by annealing of 5.6 per cent. lengthways, and 5•2 per cent. crossways. With Lowmoor iron, the loss was 4.8 and 1.8 per cent., and with Bowling, 8.0 and 9.1 per cent. respectively.
It would appear from this that steel plates, even in the solid or unpunched form should always be annealed With annealed plates, those strained lengthways of the grain are 10 per cent. stronger than those strained crossways, and with those not annealed, 4.2
per cent. (40.) “Effect of Punching and Drilling.”—Mr. Sharp made experiments on steel plates by punching and drilling rivet-holes of the diameter and pitch commonly used for riveted joints, the results of which are given by Table 10, which shows that by punching cold in the usual way, the metal left between the holes is damaged from 24.1 to 38 per cent., the mean being 33 per cent., which is very great as compared with wrought iron. Mr. Kirkaldy's experiments on Yorkshire iron in Table 4 gives the loss due to punching from 6.7 to 21.2 per cent., the mean of the whole being 15 per cent. only ; Mr. Fairbairn's experiments on Lowmoor iron in single-riveted joints gave 1.0_676 = • 24, or 24 per cent. loss, by col. 4 of Table 5.
After the punched plates were annealed, the tensile strength was restored to 35.86 tons per square inch, or nearly to that of the solid plate, which in this case was 36•22 tons, and this again is the strength of the metal in a drilled plate which by Table 10 = 36.3 tons per square inch. From this we find when the holes are drilled the metal left between holes is uninjured, its strength per square inch being equal to that in a solid plate.
It is not very clear how these experiments were made, but it would appear that the plates in Table 10 were all annealed to begin with ; then after the holes were punched the strength was reduced from 36.22 to 24.333 tons per square inch, which by annealing a second time was restored nearly to its normal value, or to 35.86 tons. The drilled and annealed plates gave 36.3 tons, or practically the same strength as the annealed solid plate, which was 36.22 tons.
(41.) “ Riveted Joints in Steel Plates.”—Steel plates Pinch
STEEL RIVETED-JOINTS : EFFECT OF PUNCHING RIVET-HOLES.
Table 10.-Of the EFFECT of Punching and DRILLING RIVET-HOLES
in STEEL PLATES.
thick, were riveted together with it rivets, 13 pitch; the joints being in the six different forms given in Table 5. Unfortunately the results were vitiated by the weakness of the rivets. Of course when a joint fails by the rivets shearing it is no test of the strength of the plate: the only fair way is to take those cases where the rivets failed as giving the strength of the rivets, and vice-versa.
Taking from Table 11 the plates which failed, we have three with punched holes giving 40.98, 43.63, and 39.11 tons, the
= 41.24 tons per square inch. Then two plates with drilled holes failed with 39.25 and 42.93 tons respectively, the mean
41.09 tons per square inch of metal between holes, which shows that with riveted joints, as with unriveted plates (40), the strength of annealed steel plates is the same whether the holes are punched or drilled. The mean of the five experiments on punched or drilled plates is 41.2, say 41 tons or 91,840 lbs. per square inch, which may be taken as the breaking weight of metal between rivet-holes in ordinary double-riveted steel joints. It will be observed that in some of the experiments from which that datum was derived, the joint had a back and front plate, the rivets being therefore subjected to a double-shear, but that fact seems to have made no difference to the results.
(42.) “ Strength of Steel Rivets.”—The resistance of mild steel rivets to a shearing strain may be obtained from Table 11:
TABLE 11.–Of Experiments on the STRENGTH of RIVETED JOINTS,
in STEEL PLATES.
in seven cases the rivets were sheared with strains varying from 25.95 to 18.75 tons, the mean of the whole being 23.77 tons or 53,245 lbs. per square inch, which is remarkably low. It is generally admitted that the shearing and tensile strains are equal to one another, and (123) shows that this is correct so far as wrought iron is concerned. But the mean tensile strength of bar steel is 47.84 tons per square inch, this being the mean of sixty-six experiments in Table 1, so that it would appear that the fibres of steel are very seriously damaged in the act of riveting, the shearing strength being reduced to half the normal tensile strength.
This is the more remarkable because it is really lower than the shearing strength of wrought iron : the direct experiments of Mr. E. Clark in (123) give 24. 14 tons per square inch as the mean of four experiments with single-shear, which is 13
per cent. greater than 23.77 tons the shearing strength of steel.
Moreover it should be observed that the strength of steel rivets was obtained from joints in steel plates, where the friction due to the grip of the rivets (20) must have contributed to the apparent strength, so that the resistance of the rivets alone must have been considerably less than 23.77 tons per square inch, which however must be accepted as the apparent shearing strength of steel rivets in double-riveted joints of steel plates.
(43.) “ Proportions of Steel Joints.”—The pitch and other proportions of riveted joints with steel plates may be determined on the same principles as those of wrought-iron plates, but the relative weakness of steel rivets will affect the pitch very considerably.
We shall take the tensile strength of the metal between rivetholes in steel joints of all kinds at 41 tons, or 91,840 lbs. (41), and the apparent shearing strain of steel rivets in joints at 53,245 lbs. per square inch (42): hence the rivets are 58 per cent. only of the strength of the plates.
Say we take for illustration 3-inch plates, double-riveted: by col. 3 of Table 14 the rivets should be 1 inch diameter; then the area of the rivets must be 91840 = 53215 1.725, that of the plate between holes being 1.0, hence for two it rivets to each space as with double-riveted joints, whose area = •3712 X 2 = •7424 square inch, we require •7424 ; 1.725 = .43 square inch of plate. The distance between holes will therefore be .43 = 3=1.146, or 1 inch; the pitch 1} + 11 = 113; the ratio of metal left between holes, to the solid plate = 1} 113, or 18 -- 29 = · 621; and the strain on the solid part of the plate when the metal between holes is breaking becomes 91840 X •621 = 57033 lbs. per square inch. Table 12 has been calculated in this way throughout.
Comparing steel joints with double-riveted wrought-iron ones in Table 8, col. 9 gives for -inch plate 34,177 lbs. per square inch: hence we obtain 57033 = 34177 1.67, or 67 per cent. in favour of steel for Girder-work: for Boilers see (65), (74).
TABLE 12.-OF DOUBLE-RIVETED JOINTS in STEEL PLATES: for
(44.) In riveting plates for girder-work, we have only to consider the proper proportions of area of rivets to area of plate between rivet-holes, but for steam-boiler joints we have further to consider the space, or distance between rivet-holes with reference to the pressure of steam, otherwise the joint may not be steam-tight. A riveted joint may be abundantly strong enough to resist the strain, but if the pitch of the rivets is too great, it will give trouble by leaking.
(45.) “ Space between Rivets."-An ordinary lap-joint, Fig. 16, is made steam-tight by caulking at C, and although the contraction of the rivet in cooling will draw the two plates together, still there will be a small space at D, sufficient to allow the steam to enter, being stopped in its passage by the caulking at C. The plate at E, between two rivets may therefore be regarded as a beam loaded all over by the pressure of the steam, and if that pressure exceeds a certain amount, the effect will be to cause the beam to spring or deflect slightly and thereby to leak at C.
We have now to consider the relations between the thickness of plate, distance between the insides of the rivet-holes, and the pressure of steam.