27.

TABLE VI. STRENGTH OF RIVETED PLATES.-YORKSHIRE IRON.*

Remarks. Exp. 24.

sequence.

Rivet-heads broke off, and the plate torn across them in con

Exp. 25. Rivet-heads cracked across and rivet-holes torn out.

Remarks. Here the rivets were the same length as the machine rivets, experiments

1, 2, 3, and were worked with great care on both sides.

Exp. 26. Both rivet-heads broken, and the plate torn across them.

Exp. 27. Torn across at rivet-holes, and one livet-head split.

*The nature and appearance of the fractures of all the irons and their riveted joints are shown in Plate IV.

Remarks.-Exp. 28. Both rivets cracked across, metal torn across the rivet-holes. Exp. 29. Torn across at the rivet-holes, both rivets slightly cracked near the head.

The plates used in the foregoing experiments are of Yorkshire iron, the same as those employed in Tables I. and II. The specimens were prepared in the same manner and of the same thickness, but 1 inch wider at the joint. This was done in order to retain sufficient metal round the rivet-holes, making the breadth of the plate the same after the rivet-holes were punched out as that of the plates torn asunder in the preceding experiments. In all these experiments, only two half-inch rivets were used in the breadth of the plate. The lap was, however, increased, after the three first experiments, from 1 to 2 inches, to give greater strength in the longitudinal line of the plate, and to prevent the metal tearing in that direction. This precaution was found necessary as the metal gave indications of weakness, in consequence of the lap being rather narrow. Another reason for enlarging the lap was a desire at the commencement to begin with the least possible quantity, and by direct experiment to ascertain the maximum distance which the plates should overlap each other in the joints, and to determine the strongest and best form of uniting them. To these points every attention was given, for the purpose of collecting the facts on which are founded the tabulated results on that part of the subject which treats of the comparative dimensions of rivets and extent of the lap in reference to the thickness of the plates. In this department of the inquiry will be found the depth of lap, diameter and length of rivets, and the distances

of holes for nearly every description of joint; also the thickness of the plate, with a column of strengths as deduced from the experiments.

If we examine the nature of the fracture in the foregoing experiments, it will be found that the machine-riveting is superior to that done by the hammer; the mean of the three first experiments being to the mean of the fourth and fifth as 54. In the eighth and ninth the strengths are nearly the

same.

On comparing the strength of plates with their riveted joints, it will be necessary to examine the sectional areas taken in a line through the rivet-holes with a section of the plates themselves. It is perfectly obvious that, in perforating a line of holes along the edge of a plate, we must reduce its strength; and it is also clear, that the plate so perforated, will be to the plate itself nearly, as the areas of their respective sections, with a small deduction for the irregularities of the pressure of the rivets upon the plate; or, in other words, the joint will be reduced in strength somewhat more than the ratio of its section through that line to the solid section of the plate. For example, suppose two plates, each 2 feet wide and three-eighths of an inch thick to be riveted together with ten 2-inch rivets. It is evident that out of 2 feet, the length of the joint, the strength of the plates is reduced by perforation to the extent of 7 inches; and here the strength of the plates will be to that of the joint as 9:6-187,* which is nearly the same as the respective areas of the solid plate, and that through the rivet-holes, namely, as 24:16.5.† From these facts it is evident that the rivets cannot add to the strength of the plates, their object being to keep the two surfaces of the lap in contact; and being headed on both sides, the plates are brought into very close union by the contraction or cooling of the rivets after they are closed. It may be said that the pressure or adhesion of the two surfaces of the plates would add to the strength: but this is not found to be the case, to any great extent, as in almost every instance the experiments indicate the resistance to be in the ratio of their sectional area, or nearly so.

If we take the ultimate strength of the Yorkshire plates in * The ratio of the areas. †The ratio of the breadth of metal.

Tables I. and II., it will be found that the mean breaking weight of eight specimens, each with a sectional area of 46 inch, is 26,168, and the strength of the single joint*, of the same description of plates with an area of 44 inch, is 18,591; this reduced, gives the ratio of the strength as 25,030: 18,591, or as 1:742, the comparative strength of a single riveted plate of equal area through the line of the rivets. It will be observed that in this comparison the areas of the sections are nearly equal, and consequently there is a difference in strength between the solid part of the plate and that part where the perforations have been made of 32 per cent. The difference is considerable, but it probably arises from the narrowness of the specimen, and the lateral strain induced by the position of the rivet, and the bending upwards of the end of the plates. From these facts I would infer that single riveting is weaker, and probably the loss of strength in this description of joint, including loss caused by the rivet holes, is not less, under ordinary circumstances, than 50 per cent.

* I use the term single joint to distinguish it from the double-riveted joint, which will be treated of hereafter.

Remarks.-Exp. 31. With the first weight the plates became bent, so as to be in a direct line with the straining force.

Exp. 32. Tore across the two rivet-holes, in the direction AB.

With 22,027 lbs. the single rivet seemed somewhat opened, but the other two seemed quite close.

Plate tore across at the single rivet and one of the double ones.

Rivets sound in this and the preceding experiment.

In the first experiment, the rivets (two in number) were evidently too weak, which caused them to shear directly across as if cut by a pair of scissors. In the next experiment the rivets were increased in number and size, which gave an excess of strength to the retaining power of the rivets, and caused the plate to tear. If we take the mean of the experiments as respects the area of the rivets to that of the plates, we find two half-inch rivets about the proportion, or the area of the rivets in the last experiments should have been 4 inch, which is nearly equal to the area of the plate through the rivet-holes.*

* Subsequent experiments made for ascertaining the strength of rivets (vide experiments on the strength of rivets for the Britannia and Conway Tubular Brdges) fully corroborate these views, namely, that riveted joints exposed to a tensile strain are directly, or nearly so, as their respective areas; or, in other words, the collective areas of the rivets are equal to the sectional area of the plate taken through the line of the rivets.