hCptl-^^^ ^ NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WARTIME REPORT ORIGINALLY ISSUED September 19^2 as Eestricted Bulletin COMPAEISCK OF TIGHTKESS OF 7^° MACHIRE-COIMTERSUNK RIYETS DEIVM IR HOLES PREP^iPED WITH 7B° AND 82° COUNTERSINKING TOOLS By Robert Gottlieb and Merven W. Mandel Langley Memorial Aeronautical Laboratory Langley Field, Va. NACA WASHINGTON NACA WARTIME REPORTS are reprints of papers originaUy issued to provide rapid distribution of advance research results to an authorized group requiring them for the war effort. They were pre- viously held under a security status but are now unclassified. Some of these reports were not tech- nically edited. All have been reproduced without change in order to expedite general distribution. L - 252 \ i /l3 ^^'3f> HATIOHAL ADVISORY COMMITTEE FOR AEROHAUTICS RESTRICTED BULLETIN ^ COMPARISON 01 TIGHTUESS OF 78° MACHIKE-COUNTEESUNK 7 RIVETS DRIVEII IN HOLES PREPARED WITH 78° AlTD 82*^ COUNTERSINKING TOOLS By Robert Gottlieb and Merven W. Mendel In the investigation of machine-countersunk rivets for aircraft reported in reference 1, it was shown that tight rivets are obtained if the rivet head projects above the skin surface before driving and that loose rivets are obtained if the rivet head lies below the skin surface before driving. In the pre-oaration of the specimens for the investigation of reference 1, 78 rivets and an 82 machine-countersinking tool were used. The present paper gives the results of a supplementary study undertaken to determine vrhether the use of a 78 countersinking tool in- stead of an 82 countersinking tool vrould substantially alter the foregoing conclusion. The specimens for this study consistod of two sheets of 34S-T aluminum alio;- riveted together in the form of a lap joint with two l/8-inch-diameter A17S-T aluminum- alloy rivets, as shown in figure 1. The nominal height of the manufactured countersunk head of the rivets was 0.046 inch. The riveting procedure used was that described in reference 1 as method C, wherein the manufactured counter- sunk head of the rivet is driven with a vibrating gun while the shank end is bucked with a bar. The height of the rivet head above or below the skin surface before driving is designated h-^, , positive when the rivet head is above the skin siirface and negative when the rivet head is below the skin surface. The testing procedure was the same as that used in the investigation of reference 1. \ RESULTS It was concluded in rcfGrcncc 1 that n comparison of the quality of Each'ine-count or sunk riveted joints on the "basis of maximum load alone is not justified; the yield load as a measure of tightness is a hcttor criterion of the strength quality of a f lush-r ivoted joint . The yield load is defined as the shear load per rivet for which the sheets are permanent ly. di splaced an amount equal to 4 percent of the rivet diameter. This definition is arhi- trary and corresponds, in a measure, to the arbitrary definition of yield point comnionly specified for aircraft materials. The effect of h-jj on yield load and maximum load is shown in figure 2 for the three sheet thicknesses used. This figure indicates that although the use of the 7B countersinking tool instead of the 82 countersinking tool increases the yield load slightly, the effect is too small to he of any practical importance. The general conclusion of reference 1, that increasing h-, in the positive direc- tion increpses the yield strength, is not altered. The hand of scatter for the test data of reference 1, ohtained with 0,040-inch sheet and rivets with head heights of 0.064 inch, is shown hy dashed lines in figure 2. The fact that the yield loads for the specimens reported herein plot within this hand indicates that the change to a head height of 0,046 inch caused no appreciahle change in the yield strength. Langley Memorial Aeronautical Lahoratory National Advisory Com.mittee for Aeronautics, Langley Field, Va. R3FBR3i;CS 1. Lundquist, Eugene E., and Gottlieh, Robert: A Study of the Tightness and Flushncss of Machine-Counter- sunk Rivets for Aircraft. ITACA E.B., Jixne 1942. ,1IACA jTlg. ''vv — 'Vn LPs I 6-') .15 32 a5 15 15 1/1/'— AA- t 3 4 3 4 3 4 ^ _ - t Figure 1.- Test specimen. \ Digitized by tlie Internet Arcliive in 2011 witli funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/comparisonoftighOOIang NACA ^ «^x -cs^ 3D- o f xr o -o f^ > ^.0 n ^ O ^ >« ir? 4x o \ o ,X. X ^. u GC i ^ o h i o 1 j I 1 'n ^ n "ikinq tool nkinq tool I \ n t \ \ \.i o ^ > ^v \ , 1 X \ o :% 1- I— r~ > V c c O O • o o o "cO cv}" 1^ oO ^^ I'd > : 1 ^" ' o ^ o i l-'V y h : : . ..Po j 1 j ■ 1 1 1 ; ; , 1 1 i 1 i 1 1 /■ )-x- ! ! y-y X- : I ' 1 ! : 1 1 r^ 1 1 U< I L3 u Ki^ c -GC -X- x_ o r ' ^r X > 1 ■ 1 o 1^ X X 1 X ! X s p 1 Fiq. 2 d) i_ a CL QJ i_ CL (/5 O > QJ > QJ C rs o I QJ -Q CZ o 8 o o tvi O O o o cr^ — (_ > o i_- =0 r< O) L_ £ OJ r) ■o loads ] tool 1 QJ J_ IS a QJ Ul "a o ly o O C O to aO O CL lO s Q) qi iSAu J3d pDO| wMjjiyoi^ [Z,\\J Jdd pDO; pi^lA \ \ UNIVERSITY OF PLOfl'D^i, 3 1262 08106 475 9 UNIVERSITY OF FLORIDA DOCUMENTS DEPARTMENT V2OMARSTON SCIENCE LIBRARY PO BOX 11 7011 ^^,,,,cA ■^SnESV1I-LE,FL 3261 1-7011 USA \