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Aviation History
1919
1919 - 0743.PDF
like to record his thanks to the various firms with whom he has been associated for their most courteous co-operation and for the ability and energy which they brought into requisition. APPENDIX I Metal Aeroplane Construction Thin strip steel of various qualities, having thicknesses ranging from .014 in. to .028 in. have been experimented Fig. 34. with by Messrs, Arthur Lee and Sons, Ltd., Sheffield, for the above. This has entailed investigations upon a matter of 135 different samples, including the following :— (1) The influence of cold work upon the physical properties of thin strip. (2) The influence of " tempering " cold worked thin strips. (3) The influence of " tempering " hardened thin strips upon the physical properties. Fig. 36. The attached graphs show the various influences. It was found that alloy steels were of no material benefit over plain carbon steels in the " as cold-worked condition " ; the alloy steels requiring to be heat treated in order to bring out their good physical properties and be of any advancement over plain carbon steels. Thin strips have been obtained and manufactured by us having yield points from 35 to 100 tons per sq. in. Not only £0 50 &A0 30 2 o 1- 20 " •• s f< t^O-" ». ^ CHART tvl? | . THE. INFLUENCE, OF COLD WORK ONTHE PHYSICAL PROPERTIES OF THIN STRIPS 300»:Tx 3' X -0I-4-" 0 5 10 15 20 2S 30 3? % RCOUCTIOW sr COLD WORK.. Fig. 37. in carrying out these experiments has this been attained, but we\have supplied on a commercial scale the Aeronautical Supplies Department and others with several tons of thin steel strips to the 60 ton yield specification in lengths of 300 to 400 ft. each. The following is a short resume of experimental work done by us:— Cold Worked Steel Strips It is found that where strips receive a greater reduction than 40 per cent, by cold work after annealing that they are made too brittle. The breaking stress of the strips are related to the cold work put upon them by the formula S = 30 + $R. S = maximum stress, JR = half the reduction and^is constant. ThiSiormula we find works out very well with strips which do not receive a greater reduction by cold work than 40 per cent., and the following table bears this out, and also that with over 40 per cent, the calculated M.S. is too high :— „ Sample Actual Breaking Stress. Calculated Breaking Stress from S = 30 + JR. ^ o 3° + 30 + 3° + 30 + 30 + 30 + 30 + ** 30.0 30 + The following table shows the influence of cold work on the physical properties :— Influence of Cold Work on the Physical Properties of Thin Strips. Length of Strip 300 ft. To. 0 I 2 3 ** 4 5 Tons per sq. 33-9 45-5 50.0 51.8 30.0 43-2 47.0 in 2 3ji 2 49J 2 60.35 2 0 2 11 2 41-75 2 0 2 - 3°-° = 45-65 - 54-62 = 61.17 = 300 = 42-5 - 50.87 = 3°-° ditio n o f strip . !d point , pe r sq . in . - « V) 8 Sg 3~i"x .022 * 27.2 3-i"x .020 t 4°-o 3-i"x .018 f 47-6 3-4"x .016 f 55-2 3~i"x .014 t 61.2 Ton s pe r sq. in . . in 45-6 50.0 54-25 .59-8 62.2 * Before cold work. jatio n pe r . o n 2 ins . G *> •2 \s W 0 11.0 10.0 3-o 2-5 2-5 The Influence of Tempering on the Worked Thin Strips. Condition of strip. As cold worked After tempering at— 2000 C 3000 C. 4000 C 5000 C 6000 C oint . sq . in . Yiel d p Ton s pe r 40-75 47-25 46.5 44.6 31.0 25.0 Ton s . in . M.S . pe r s q oscop e tes t ardness . ise n value . KE 0 $ w 1 tes t ove r a & s o f 3 tim e thickness . 5> « rad i the 220 7.00 Good 320 6.80 Good 38° 6.35 Good 42° 4.90 Good 380 5.00 Good t After cold work. Physical Properties .028-in. thick. tio n t. o n s. Elong a pe r ce n 2 i n 40.75 4-° 47.6 48.2 45-6 36.5 3i-7 See Chart No 2-5 4.0 6.0 17.0 29-5 . 2. value . Erichse n 5-6 5-36 4-23 4.72 5-12 b.o tes t rod Ben d ove r er cent , uctio n b y Id work . iM T3 0 ew None % 9.09 18.18 27.27 31-81 of Cold diam . metal . .14 0 in . wit h th e Broken Broken Broken Good Good Good Influence of Tempering Cold Worked Strips The tempering or " blueing " from o° C. to 4000 C. has increased the yield point and maximum stress over the cold worked value, a list of which is given in the preceding table and shown by Chart 2. There appears to be a critical point between 4000 C. and 5000 C, where the fall in yield and M.S. occurs, whilst the elongation is greatly increased. The M.S. and yield point does not lower again to that of the original cold worked figures until about 4250 C. is reached. This phenomena is remarkable, but there is no doubt about it, as this has been proved by us many times, it being experienced on tempering all cold worked materials. The bend tests are not improved by this tempering until over 4250 C. is reached. 743
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