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144 AIRCRAFT ENGINEERING May, 1943 Th e Damping Capacity of Engineering in reaction at the increase of temperature, are Some facts concerning these tests are referred Materials . By W. H. Hatfield, G. Stan- rathe r surprising. t o in the text, amongst which are tha t the cast field an d L. Rotherham . [E. & F . N. Spon.] Figures 4 and 5 show in graphical forms the iron persists in showing higher damping damping percentages together with the usual capacities tha n steel, also tha t cast iron appears This is a paper read before the North East properties of elongation and stress against a t o show a marked increase in capacity when the Coast Institution of Engineers and Shipbuilders base of temperature from 0 to 500 deg. C , and linearity of Hookes Law is exceeded. o n May 15, 1942, and is reprinted from its for the 0·1 per cent and 0·36 per cent carbon Furthe r observations arc given for a nickel- Transactions. steels. Most certainly these tables, and par" chrome-molybdenum steel which had been ticularly the graphs, illustrate interesting fea The earlier part of the introduction makes it oil hardened and tempered, after which a tures about the tendency of damping against quit e clear just how a free vibration would be vibration phase of 6,480 cycles was applied ; heat rise ; the rapid increase of damping up affected without damping in some form. as is "remarked in the text, after a preliminary Furthe r paragraphs continue to develop the t o 100 deg. C , with an equally rapid decrease drop in damping capacity the material shows various types of vibration, forced and natural, to 140 deg. C , is remarkable in the lower carbon a decided tendency to remain at a constant and the damping forces that may affect them; steel as against the almost steady increase with value of these conditions. th e terms " hysteresis and damping capacity " less general variation in the damping capacity A discussion follows comparing the results ar e discussed in brief. A point is made here of the 0·36 per cent carbon material obtained in these experiments with those of pre which is sometimes not fully appreciated by Table B is devoted to cast-irons and cutting vious investigators, th e possibility being pointed man y Engineers ; that " hysteresis "i s the steels. I t is surprising to note that the cast-iron, out of the use of relatively simple experimental result of certain inelastic properties existing of which four samples have been examined, apparatu s to obtain data such as the authors in all engineering materials, and that therefore have given ; further lines of development are have damping capacities up to nearly 20 per there is no truly clastic material. It is also suggested. cent at such relatively low loads as 3 tons per pointed out how the "damping capacity" of square inch. In the conclusions the similarity of results a material is directly related to energy loss. A further series of test on specimens in cast in sintered carbides and cobalts are observed ; Following the introductory paragraphs we iron are recorded in Table H, and attention is in the case of mixtures containing cobalt it is find a brief section on methods of expressing drawn to the fact that four of these samples inferred that this material may be responsible Damping Capacities with references to previ for damping, while on the other hand it is are from adjacent blades of a marine screw ; ously published work. suggested that in carbon and alloy steels the th e results are not exactly the same but very comparable, and we suppose within the prac cementite appears to contribute little to the Some paragraphs are devoted to the influ tical limitation of the experiments. Three capacity. The results obtained appear to bear ences of Speed and Temperature on damping forces; the effects of temperature are of other samples, showing respectively an increase out such observations. Further comments are particular importance and too often the tem in graphite, also similarly show increases in mad e on the importance of strain and the dis perature conditions of a vibrating system are damping capacity. The point it would appear tribution of constituents ; also that magnetic ignored when assessing the probable results— is of some significance. influences in certain of the alloys may affect indeed most mathematical equations ignore the th e results obtained. Continued in Table B are two samples of fact completely. It is somewhat surprising to tool steel of the tungsten-cobalt mixture and As a brief Appendix, of some interest, results find that the realization of this goes back as Table J continues the details of these two steels are published on the well-known 28/32 tons far as 1865, which would give all the more with data concerning Shear Modulus and per square inch steel much used in crankshafts cause for regret a t its non-appearance in modern Damping at loads u p to 8 tons per square inch. and the like ; the results compared with the equations. nearest carbon steel show an increase in damp Almost pure nickel and cobalt have both ing capacity over the latter. After referring to five familiar methods of been recorded and this table is completed with determinatio n of damping capacity we complete nickel-copper and nickel-iron alloys and further For those who may wish to pursue further th e preliminaries and arrive at a description of details of these metals are given at various work on this very absorbing subject, there are th e early work with which this paper is con loads and many temperatures in Table K. some 17½ pages of bibliography which should cerned. One curious feature is apparent in this latter satisfy the greatest of appetites. table concerning the nickel-iron alloy which, The approximation of damping capacity as There is no doubt that while several earlier found in this early experimental work, for as opposed to all other materials so far exam publications have referred to some particular dampin g not exceeding 20 per cent, is noted ined, shows a decrease of capacity the higher the aspect of this problem, they have been of a with some interest, as is also the fact that those temperature . much narrower character than the paper now early experiments were made on an existing presented, and it is this wide vision which gives The earlier parts of Table C are devoted to standar d machine. it its special value. th e light-alloys, care being taken to test these A clear description of a machine specially within their low value of limit of propor Several suggestions are made in the paper for developed and used by the authors in their tionality ; the remainder of this table giving future work, and here it is felt should be late r work follows ; noteworthy points being results of copper-zinc alloys. mentioned the great possibilities and important th e thoroughness which required a specially aspect of dealing with rubber in its natural Table D is of great interest in view of modern built camera and also the particular care taken and synthetic forms. In post-war days there tendencies to seek for uses of new materials. t o ensure that uniform temperature was ob Details arc given for lead, solder, glass, ivory, is no doubt of the uses to which this material taine d and recorded over the test specimen. ivorine, and seven specimens of bakelite ; with will be put in engineering construction, and The considered accuracy, within 2½ per cent, is th e exception of glass an d ivory, which as might some knowledge of damping capacities similar certainly excellent. be expected are low, the remainder at 200 lb. t o those published for other materials would be Following this we come to the actual investi per square inch show a capacity in the 20-30 invaluable. gation; steels are dealt with first of all, and per cent range. The record of damping capaci I t was suggested in the discussion that a Table A is devoted to a complete list of the ties for these miscellaneous substances from possible use to which the machine referred to physical analyses and mechanical properties loads of 25 t o 3,500 lb. per square inch is given in the paper could be put was in the testing of together with percentage damping values, the in Table O. materials for their damping capacity and list including steels of ordinary low carbon comparing such results, instead of using the I t is of interest to note tha t lead, solder, glass content, stainless, and several of the nickel- and ivory show increases in capacity with the present method of destruction testing. This is chrome family. In addition, Table E gives a higher loads, while ivorine and five of the bake- very interesting, but it can be pointed out more detailed account of four of- the carbon lites show decreases of capacity; of the tha t rubber has been tested in a not dissimilar steels ; the first, of 0·09 per cent Carbon, has remaining two plastics one shows a curious manner for some time now. been checked for percentage damping at tem tendency to give a constant value of damping One final point, this time of slight criticism, peratures from 20 deg. C. t o 600 deg. C , rising for varying loads. One important omission is tha t the layout of the paper might have been in 20 degree steps, at each of which the con from this table, or perhaps a further similar improved if all the tables had been arranged ditions have been noted at stress values of table could with advantage have been devoted together. With the present arrangement the 2, 3, 4 and 5 tons per square inch involving to it, is rubbe r ; particularly with the increasing written matter is rendered somewhat disjointed 120 values of damping percentage for this use and knowledge of the many natural and and some slight and perhaps unnecessary con particular steel. synthetic mixes. fusion could have been avoided. Table E, in addition to the very complete An exceedingly interesting record is included To anyone having even a passing interest an d satisfying picture of the 0·09 per cent of the damping capacities from a 0·26 per cent in materials and their damping capacities, and carbon steel, also has some 24 values of damping carbon steel and a cast iron specimen taken in vibration problems, the data published here percentage for each of three steels of 0·1 , 0·26, under vibration amplitudes from about 2 centi cannot be ignored and indeed is well worth an d 0·36 per cent carbon content; for such metres downwards and, conversely, increased every moment of the time occupied in study ligh t differences in mixture the variations in cycles up to 1,750 for the steel specimen and ing it, C. W. percentage damping, and indeed the difference 270 cycles for the cast iron.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: May 1, 1943
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