Dl 14 ~ wey Ss a QQ 250 ea se 1 av t Be TN „le 2z 3! go ee Ố o Fig DL 22 é ¿ ` sie bo th — —— 4 ve 21000 ya 1 ¢G,000 x TT i Siow “ mộ N a 82 £ a fad em Boas ™ 150 Fig D1 21 ear Ae 2 2 ma and M, = +200 x 1.75 - 1000 x 25 = -600 in.1lb and Py act through the 3olt will be reacted equally by each load on each bolt due to Py = 1b.; H load on each dolt due to 250 1b 4 woo Ore Qs Mề ) w Oct a a
The load produced on saca bolt due to the moment load My = -6C0 in.1b will vary directly as the distance of the bolt from the canter of
resistance which coincides with the bolt group cantroid,
the Let rg equal the distance from bolt group centroid to bolt (a) Then the resisting acaeant developed dy bolt (a) equals rarg, where Fe equals the load on bolt (a) Since the bolt
ads are proportional to their distance from 1 QO, the resisting moment My developed by bolt ( 5) will equal similarly for bolt (e) reso re equals, a FITTINGS AND CONNECTIONS BOLTED AND RIVETED For the bolt group of Fig 01.22 rg = rp = Tạ = Tq = 1.25"
Hence, I = Ir? = 4x 1.257 = 6.25 in
Therefore the moment load Fy on gach bolt W111 equal
eM :
Fo eps = 120 lb
Fig C4.31 shows the resulting H, V and moment loads applied to each bolt The resultant
load can be found graphically by drawing the force polygons as showm in Fig Cl.23 The resultant bolt loads can likewise be determined analytically For example consider bolt (c)
TH = 250 + 120 x 1.25 ke + 0 = 3546 1b iV = ~50 - 120 x + 0 5 ~122 1b,
1.25
Hence R = VSH? + iv? = faas* + 122? 3
Case where Bolts or Rivets are of Different Diameters
367 1b
when the joint bolts or rivets are not all the same size, the moment load on each bolt is proportional to the bolt area times its distance
to the bolt group centroid Thus the bolt areas must enter equation (15) hence, Mag Ta Py = nA, ryt tn Ast * tN AA Ty 7 7 ¬_ wr rte (16)
n = number of bolts of each size
Since theory of loads on 2 multiple bolt
group is only approximate, reascnable margins of safety should be maintained
RIVETED CONNECTICNS
D1.18 Types of Rivets
From an aercspace structural standpoint rivets may ce placed into two zeneral classizi- cations, namely:-
The Protruding Head type of rivet
(2) The Flush tyve rivet
Fig D1.24 illustrates the protruding head type of rivet ig 01.25
illustrates a number of modifications of the pro-
truding head type of rivet chat nave been used in ths past
=
Trang 2ANALYSIS AND DESIGN OF FLIGHT VEHICLE STRUCTURES | ' : ' TA AR HAS HAm TA “8, Fig D1.25 QD Ì : No.| Rivet Types m 1 |Roưnd Head ©! | m LÍ 4 razier —A—
For many years the round head rivet was used for all interior work and before the era of nign speeds it was used as 2 surface rivet as well when wind tunnel experiments showed that such rivets gave appreciable drag, designers turned to rivets with less head protrusion, thus the development of the 3razier and modified Brazier type of rivet head Then as the age of relatively high airplene speeds
rrived a flush surface was needed, particularl on certain sensitive portions of the airplane surface, thus various modifications of the countersunk head involving press and machine countersinking of the sheets wers developed Pig D1.26 tliustrates the flush type of rivet As fllustrated in Fig Dl.26, this flush type rivet can be used in several differ- ent ways, thus the method shown in Fig Bl.26a is referred to as the machine countersunk type;
that in Fig Dl.26b as the oress countersunk double dimpled type; and that in Fig Dl.26c as the combined press and machine countersunk type or the dimpled machine countersunk type
Se Machine Countersunk Type Fig a Countersunk - Double a Type Fig b Combined S and Machine Sa Tountersunk; or Jimpled Macnine Countersunk Type Fig ¢ Fig, D1 26 DL 15 Fig D1L.27 illustrates the approximate sheet thickness limitations for the three metnods of flusn riveting
Approx Shset Limitations For countersunk Rivets (AN-426)
fame 1/8 Dia Rivet
— 5/32 Dia Rivet
eo van
Poss, 3/16 Dia Rivet
Approx Limitations For Press Countersunk or Double Dimpled Rivets (AN-d26)
awe sae ¬1
= + 1/8 Dia Rivet
aay 5/32 Dia Rivet
= et 3/16 Dia Rivet Approx Limitations For Pres
Trang 3
DI, 16
DI.19 Rivet Materlal
Since aluminum alloy ts by far the most widely used matertal in the aircraft industry, it follows that aluminum alloy is the material most Widely used for rivets Table D1.5
{column 1) lists the 5 aluminum alloys used for rivets and the ultimate shearing stress Fsy for each material Rivets made from 2017-13 (Foy “ 34000) and 2024-7381 (Fgy = 41000) are rivets that must be driven soon after heat treatment or before age hardening takes place The aging or hardening is slowed oy Keeping rivets in refrigeration after heat treatment The other rivet material 1s less hard or less brittle in the aged state and thus can be stored in air and driven anytime These so-called softer rivets have less shear
strength, but since a great deal of aircraft construction involves thin sheet, bearing is often critical and thus rivet shear is not critical Most surface or skin riveting involves the softer rivet, usually 2117-T3
(Fey = 30,000)
D1 20 Strength of Rivets Protruding Head Type
Rivets are widely used in airplane structures to fasten or tle together two or more structural units Standard methods of stress analyses of riveted joints consider two primary types of failure, namely, the shear of the shank of the rivet and the bearing or compressive failure of the metal at the point where the rivet bears against the connecting
Sheet or plate
Fig 01.28 illustrates the main forces on a rivet in transferring a load from one plate to another The load is transferred to the rivet from the plate by bearing of the plate on the rivet The load 18 then transferred along the rivet and resisted by bearing action
on the other plate Since the plate bearing forces on the rivet are not in the same line, the forces tend to shear and bend the rivet Bending of the rivet is usually neglected if there are no intermediate filler plates In Fig (a) o? D1.28, the rivet is in single shear, whereas in Fig (b) the rivet is in double shear ¥P Cp nỦ + ae TS Fig D1 28
The ultimate shear strength of a rivet is Ziven by the following equation:- (by FITTINGS AND CONNECTIONS
BOLTED AND RIVETED
ultimate shear strength of rivets
(ios )
Fsụ = ultimate allowable shear stress for rivet (pst}
area of rivet cross-section = np*/4, where D equals the nominal rivet hole diameter
nm = number of shear areas per rivet Reference (17) shows that the shear strength of protruding head aluminum alloy rivets is affected by increasing D/t (Diameter of rivet over sheet thickness) ratios The conclusions in Reference (17) are as follows:- Rivets in Single Shear:- For values of D/t up ta 3:- Single shear strength = basic allowable single Shear strength
For values of D/t greater than 3:-
Single shear strength = basic allowable Single shear strength times [1-0.04 (D/t -3)] For Rivets in Double Shear:~- For values of D/t up to 1.5:- Double shear strength = basic allowable double shear strength
Por values of B/t greater than 1.5:- Double shear strength = basic allowable double
shear strength tines
[1-0.13 (B/t-1.5)]
Table DL.S (from Ref 2) gives the shear strength of protruding and flush head aluminum alloy rivets and the corrections to take care of the D/t influence on the rivet shear strength Table D1.8 gives the allowable bearing strengths between the protruding head rivet and the various aluminum alloy sheet and Plate material The bearing values are given for two e/D ratios, namely 1.5 and 2.0, where 9 1S the edge distance measured from che center of the hols to the edge of the plate Any reduction in edge distance may cause bulging
or the edge of the sheet due to driving energy
Edge distance should not be less than e/D = 1.5
D1,21 Strength of Rivets, Flush Type -
Since flush rivets on the flush end of the flush riveting involves
or press countersinking or both, the strength of
the flush type rivet is different than the
common protruding head type
Trang 4ANALYSIS AND DESIGN OF FLIGHT VEHICLE STRUCTURES Fig D1.29 illustrates a machine counter-
sunk rivet Due to the 2ull P on the two sheets ahich are held together by the rivet and
induced force Py 13 produced on the sloping Side of the nead of the rivet This induced force tends to shear and bend the portion 1-1 of the rivet head The sharp edge of the countersunk Sheet at point (a) tends to cut
into the rivet These combined influences tend
to cause excessive deflections and finally fatlure as roughly illustrated in Fig D1.30 i £ a ma kL Fig D1 29 = É 3 7 7 II AE Ttg DI.30
In the press countersunk or dimpled type of flush rivet connection, see Fig D1.26b and %, because of the interlocking of the sheets due to the dimple, the joint could transmit a load without a rivet if the sheets were held together Since there is no clearly defined bearing or shear surface in this type of joint, the manner in which the loads are transferred is quite complex As a result resort must be made to tests to establish design allowables Tables D1.?, D1.11 and D1.12 give the ultimate
and yield strength of flush type rivets (Ref 2)
D1 22 Blind Rivets,
The name "Blind" rivet is given to that type of rivet which can be completely installed from one side of the joint, and is therefore
almost exclusively used where it 1s impossibla
or impractical to drive the normal rivet, which requires access to both sides of the joint, There are two general types of blind rivets, namely where the inside or blind head is formed mechanically or where it is formed by an
explosive force
fig D1.21 111ustrates the Dupont explosive type and Figs 32 to 34a inclusive
{llustrate the mechanically formed head type Inserted Installed Fig D1.31 Dupont Explosive D117 Hex Head | a {1 AK | SEK Ww Inserted Tnstalled Fig D1 32 Jo Bolt OC * PR Ụ INSERTED Fig D1.33 Cherry Type INSTALLED ARAZIER HEAD (6951) INSERTED WSTALLED Fig D1.34 Deutch Type WSSSy INSTALLED
Fig D1.34a Huck Lock Bolt
D1, 23 Riveted Sheet Splice Information
In splicing or connecting two sheets to- gether by means of rivets or bolts, the joint
or connection may fail in the various ways as explained in detail for single and muitiple bolt fitting units Thus one must check the shear strength of the rivets; bearing of rivets on the sheets; tear out of the sheet edges and tension on sections through the rivet holes
Types of Sheet Splices or Connections
Fig D1.35 tllustrates the various types of sheet splices In the offset lap splice between two sheets of different gauges, the of2set should be 1n the heavier matertal a single shear butt splice, the butt splice plate should be equal to the thinnest of the two sheets being spliced and Likewise in the
For
Trang 5FITTINGS AND CONNECTIONS DI.35 Rivet Size to Use No exact rul optimum rive number o2 pract enter into the 4 rivets, nanel7 tạ Tang le and ar rivets The com
5/32, 3/16 and i/ meters
sizes Snould not be used Sheet sclices unless there Dacking uD structure as buckls under the driving of the a structural desisn s sint is one in whict given the a ms heat splice if, the optimum be rivet he 2 the
gest oractical size
Spacing Shest Sdge Distances
The allowadls given in (Rez 1)
of two diameters Therefore in general cistance in a joint should be less thân 2 diameters for protruding aead rivets, and diameters 2lush rivets rivet-shee are 5ased on diameters are as structural ivets are 1/8, The larger 1 Strength ind Dearing sheets are practically relative to ven splice, because derations usually Small hard the and- he rivet for press and machine countersunk wy BOLTED AND RIVETED sine rivet should not be nat given in Tables 4 and 8, Table A
PROTRUDING HEAD RIVET i
NORMAL MINIMUM SPACING | Rivet Diameter 1⁄8 5/39 3/16 1/4! Normal Minimum I Spacing 1/2 9/16 11/16 7/8 Table B
NORMAL MINIMUM SPACING
PRESS AND MACHINE COUNTERSUNK FLUSH RIVETS 1/8 3/16 Rivet Diameter 5/32 1⁄4 Normal Minimum Spacing 11/16 | 27/32 121/32 1-1/4
In gener ral the minima rivet row spacing should be such as co made the distance detveen any two rivets in the two rows not less than the minimun rivet spac the rivet size being used
Splice Sheet Tension =Erfi
wnen a sheet is spliced by mean:
or volts it means of rivets
the sheet is weakened since the rivet holes cut away a part of the sheet malerial Tne ratio of the tension strength of the spliced sheet to the unspliced sheet ts called the sheet tension efficlency of the joint [If the minimum rivet spacing is used ani only one row of rivets the sheet efficiency will be around 70 to 75 sercent The designer should strive for a higher efficiancy
Trang 6ANALYSIS AND DESIGN OF FLIGHT VEHICLE
fr 1.15 The rivet a uminum alloy The horn aluminum alioy The margin vetad connection will be
mital cable pull of 400 1b, can
an equivalant force system at @ 0i aterline o? the tubs, consisting of a rsional moment of 400 x 5 = 2000 in.1lb., and a horizontal 400 lb farce eplaced jonsider attachment of collars to norn:- ater ri daoutle snear
Load per rivet due to
(Rivet arn is 1 tarque = inch) 2000/5 x 1 = 3Z4 12, Load per rivet due 29 herizontal force 400/€ = 67 lb Resultant load on most cribical rivet is S++ $7 = 401 lb DL.5 the singls shear strength 222 r rivet of 2117-T3 material is 388 1b, @ the rivets are in double shear the shear strength of one rivet would 5e 2 x s88 = 778 15 Referring to the table at the bottom of Table DL.5, we find a rivet factor a2 935 to apply for a 1/é rivet on 963 sheet th TheraZore rivet strength ts 935 x 786 718 15, M.S in rivet shear = (718/401) ~1 = 79 aars on twe collars ckness, toon 063 2024 8 Aberial 1s obtained from Tables D1.9 and 31.2 The dearing str ing strength of 1/8 eet based on an SS Fpr = 100,000 is 310 to Table DL.A for 2024-T3 1.5, we find 2 correct 2n is on two rivet = x the bearing 26 = 1388 Lb MAS = 1588/401 = 2.96 STRUCTURES D119
The rivets gre in singla shear
shear strength 2f 2 5/32 rivet from Table 91, 5 = 596 x ,99S = 594 12 (The value of the correction from middls M.S = (594/334) -2 = 179 Bearing strength on 96) Table D1.S for 050 thickne: ts 795 1D correcting to 043
730 For £2024-T3 tubs mater
we obtain a material factor of 1 Ther3 fore Dear strangth of one rivet on Subs wall is 1.24 X 780 = 967 1b, M.S = (967/334) -l1 = 1.9 PhosLz
Fig D1.37 shows a plate fittt
to a double channel section by 6 -
rivets The design fitting loads are show in the figure The rivetsd connection will be checked for strength under tha given design fitting loads
Solutton:-
The given force system will be replaced by an equivalent force system acting at the center
of gravity of the rivet group This force
Trang 7
DL 20 FITTINGS AND CONNECTIONS,
Table D1.5 Shear Strengths of Protruding and Flush-
BOLTED AND RIVETED Head Aluminum-Alloy Rivets Diameter of rivet,in % 3 1 l$ % % % % Shear strength, Ib: 3058, Fi =28 kei 99 208 368 336 | 802 | 1⁄40 | 2/290 | 3,280 211723, Fy = 80 ksi 106 217 388 398 sez | 1350 | 2460 | 3/510 2017-T31s, Fy =34 bat 3017-T3, Pye 38 kei 2024-T31*, Z„=41 ket 120 135 143 296 275 347 | ge 531 494 675 812 | LI80 | 2120 | 3360 | 4800 735 | 1,000 | 1970 | 3110 | 4/450 97 | 1,760 | 2790 | 3/870 Singie-shear rivet strength factors Sheet thickness, in.: 0.016 0.018 0.020 0.025 0.032 2 9.086 0.040 Double-shear rivet strength factors Sheet thickness, in.: 0.016 bene eee 0.688 0.018 9.020 seca "¬ 9.025 vàn "¬ cae ` 870 00382 935 0.036 : | 974 9.040 - .887 0.045 1.000 0.050 0.063 0.071 0.080 0.000 0.100 0.125 0.160 0.190 0.250 0.688 740 792 919 948, 474 1.000 0888 | T40 792 331 870 935 987 1.000 192 0.714 883 818 985 883 874 8đ85 1.000 1.000
NơtE: Values of shear strength should be multiplied by the factors given herein whenever the D/¢ ratio is large enough
to require such s correction
Shear values are based on sress corresponding to the
nominal hole diameters specified in table 8.1.1.11(đ), note «
* The -T31 designation refers to rivets that hava been heat-treated and then maintained in the heat-treated condition until driving,
Shear stresses in table 8.1.1.11(đ} corresponding ta 90
Trang 8ANALYSIS AND DESIGN OF FLIGHT VEHICLE STRUCTURES
Table D1 Standard Rivet-Hole Drill Sizes and Nominal Hole Diameters D1 21 Rivet size, in " | Mạ 1% 1 % 1% 4 ws % Drill No ne 51 41 30 21 n F P w
Nominal hole diameter, (in.) ) 0.067 | 0.096 | 0.1285 | 0.159 | 0.191 | 0.257 | 0.323 | 0.386 Table D1.7 Ultimate and Yield Strengths of Sotid 100° Machine-Countersunk Rivets Strength, Ib Rivet material 2117-T3 2017-T3 | 2024-T31 Clad sheet material ¬ 2024-T3, 2024-T4, 2024-Té, 2024-T81, 2024-T86, snd 7075~T6 Rivet diameter,in l4 | wx | % % % % | X % | % Sheet thicknesa, in.: ** 0.190 "¬= 324 “476 Thu kg va °355 *580 *728 | 758 “6ã7 *859 | “1,200 886 690 O17 7 °1,338 942 720 “Q69 ¡ “1,452 992 746 1,015 { °1,452 1,038 1,054 | °1,640 1,090 1,773 ¬" 1,881 "xa (VÀ 755 1,090 1,970 1,180 2,120 Yield strength : 204 370 | 362 eee 345 419 ae 538 594 401 515 610 614 811 481 557 a 669 902 562 623 788 761L 982 638 746 861 842 1,053 854 1,017 913 1,115 1,018 1,313 1,021 1,357 ¬ 1,574 " 1,694 17583 | 1,925
Nore: The values in thia table are based on “good” manu- facturing practice, and any deviation from this will produce significantly reduced values
ở Sheet gage is that of the countersunk sheet In cases
where the lower sheet is thinner than the upper, the sbear- bearing allowable for the lower sheet-rivet combination shouid
be computed
2 Increased attention should be psid to detail design in cases
where D/t>>4.0 becnuse of possibly greater incidence of dif-
fieulty in ‘service
Trang 9
D1 22
FITTINGS ann CON Table DI.8 Alưmin
(K = ratio o
NECTIONS, lum-Alloy Sheet ang
Trang 10
ANALYSIS AND DESIGN OF FLIGHT VEHICLE STRUCTURES Table D1.9 Unit Bearing Strength of Sheet on Rivets, For 2 100 ksi Sheet thickness in Unit bearing strength for rivet diameter indicated, ib? 5 in x 4% in 0.125 0.180 0.200 0.250 1028 1137 1285 1606 2036 2570 3210 872 636 716 795 1002 1129 1272 1481 1390 1988 2544 3180 3970 8070
a Bearing values are besed on areas computed using the
Table D1.10 Unit Bearing Strengths for Pin Size Indicated; 1b *
Trang 11
D1, 24
Since rivets are same size, all rivets are
assumed to share equally in resisting H and V Loads = 3000/6 = 1335 direction and to the right Load t due to Vg,g, = 3000/6 = 500 lb Load on each rivet due to He,g, acting in on each rt actiag down
From equesion (15), the load on a rivet due to Họ on rivet group 2quals F = Mr/I
Ls ir? = 1.6257 x4+9.625"x2 = 11.4 Consider rivet marked c;
r= 1.625 = arm to c.g of bolt group Po = Mr/I (3000 x 1,625)11.4 = 1280 1b, Since rivets b, 4d and e are the same
distance as rivet c from the c.g., the moment load on these bolts will also equal 1280 Fig
1.38 shows the H, V, and M loads on the rivets Bb, c, dands Since the arm r to the rivets
f and g is only 0.425, the load due to moment Will be constderably smaller and thus these rivets will not be critical Observation of Fig 51.58 shows rivet c is the rivet with the largest resultant load = vary* + BFy* a¥y = 1333+ 1280x121 .5/1,625 = 25135 1b, mM kJ < a -500 - 1280 x 0.625/1.625 = - 992 2513" + 9927 denca, A = 2700 15 fhe rivets are in double shear material is 2117-T31 Rivet
From Table D1.5, Single shear value = 1760 lb or double shear strengta = 3520 lb
Bearing strength of 1/4 rivet on the.071 4-73 clad channel section from Tables D1.9 1.4 ts 1325 x 1.20 = 2190 Since rivet
on two channels, dearing strength of lyet = 2x 2190 = 4380 lb Rivet shear rog py " eo @ Ễ tao MOS = (3520/2700) -1 = 30
a problem for the reader, change rivets diameter and cetermine whether ng still shows a positive margin
Fig 01.39 shows a lap joint involving ‘wo rows of rivets as shown Sheet material is
2024-73 clad, and rivets are 3/22 diameter and
FITTINGS AND CONNECTIONS
BOLTED AND REIVETED
2117-13 material and of the protruding head type
The ultimate design tension load in the sheet including a 1.15 fitting factor of safety 1S 1000 1b./inch, The limit fitting load is 2/3 x 1000 = 667 1b./in The margin of safety of the sheet splice will be determined ahr « ~ - — ~ ~ + —- 1000#/in, “*— /* 1000#/in - ~ ~ ~ + — - a 8/16 a = 04 04 Fig D1.39 Solution:-
AS an analysis unit, a width of sheet equal
to the rivet pitch of 1 tnen will be used Thus load on 1 inch unit = 1000 lb
Check Tension in Sheet at Section Through Holes Đ = m Pt(ailow) = A Feu A = net area = (1- 159).04 = 0336 (,159 = drill diameter for 5/22 Table D1.6) rivet, Pry for 2024-TS clad = 60,000 psi Pe lariow) 7 (0886 x 90000 = 2016 1b M.S = (2016/1000) -1 = 1.01
Cneck Shear of Rivets
Rivets are in single shear and two rivets act in the 1l inch unit which was assumed From Table D1.5, single shear strength for 5/32, 21018 et is 596 1b The strength factor middle tadle of Tatle D1.5 for 04 sheet thickness 13 hinh Thus for two rivets the shear strength is 2x 96é¢4 x 596 = 1150 1b M.S ® (1150/1000) - 1 = 15 Check Bear Rivets on 04 Sheet 18 From Taols D1.9, th strength 52ased on For of rivet on O4 sheet = 9356
a ultimate bearine 100,000 psi for 5/32
Trang 12ANALYSIS AND DESIGN OF FLIGHT VEHICLE STRUCTURES Table O1.8 for 2024-TS clad material and an
D ratio of 2.0, we find correction factor K = 1.14 Ther re rivet bearing strength is 1.14 x 636 x 2 = 1450 1b
M.S = (1450/1000) -1 2 45 Check Rivet Shear Out
distance is 5/16 in or e/D = out strength is satisfactory Since dg2
2.0, shear 2OBLEM 4
Assume rivets are changed to the solid 100° dimpled type What would be the M.S for the rivets Referring to Pig DlL.27, we find the sheet thicknesses are such as to prevent double dimpling From Table D1.11 and 51.12, we obtain the ultimate and yleld strength of a
5/32 rivet on 04 sheet as 635 and 506 lbs respectively yhence, Ultimate M.S = (2635/1000) ~1 Yield M.S = (2x 506/667) - 1 227 49 "
NOTE: In checking tensile strength of sheet tnrough nole section, the drill size for dimpled rivets is slightly larger than for protruding head type
PROBLEM 5
This 1s a typical problem involving the rivet loads in 4 sheet-stringer type of gonstruction as {llustrated in Fig D1l.40 Before the rivet size and spacing at the points
(1) to (10) can be determined, the rivet loads at these points must be known The shear flow in direction and magnitude on the webs and skin are shown on the figure and are in lbs per
inch, These values represent the results in one of the flight conditions The structural
designer must look at all the shear flows in the vartous flight and landing conditions in order to obtain the critical rivet leads It is assumed the shear flows as shown include
any diagonal tension effect in the various
sheet panels
The rivet loads in lbs./in i to 10 witli be as follows:-
ae line Since 0S vertical web ands
+ point dene shear flow of 1075 lbs./in
Cl Lys
in the vertical web must obviously be reacted by the rivets in rivet line (1), thus load on rivet line (1) 1s 1075 158./1n
Rivet line (2) By the same reasoning since S4ia ands at soint (2), the load on rivet line
(2) equals shear flow in panel 2-3 or 575 los./in Rivet line (3) Rivet line (6) Rivet line (7) D1 25 STs 7425 ts 150 point 3 150 1 Point 7 Sketch b
The skin is continuous over stringer at point (3) Sketch (a} shows a free body of the skin and stringer at point (3) Since the summation of the forces parallel to
the stringer must equal zero, it is observed
that the load transferred to the stringer 18 150 1bs./⁄1n
ivet lines (4) and (5) Since the sheets end over the stringer, th load in rivet lines (4) and (5) are 425 and 275 lbs./in respectively
Rivet lead = 275-125 = 180 los./in
The skin is lap spliced over the stringer 2t point 7 Sketch (>) shows a free body The load produced on the stringer is 150 from equilibrium Thus the worst shear load on the rivet is 150 lps./in which is greater then the shear on another cross-section of the rivet which equals 125 lbs./in as the shear flow in panel 6-7 Rivet Load at (3) Rivet Load at (9) Rivet Load at (10 175 - 25 = 150 lbs./in 175 lps./in ) = $75 los./in „u DI.35 Rivets in Tension
Great judgnent should be used in using rivets in tension There is a general saying,
"Never use 2 rivet in tension." If this re- quirenent was strictly followed, it would be difficult to design 2 conventional airplane
For example, the skin on the upper surface of
the wing, due to the upward suction af places the rivets shat hold the skin to stringers and ribs in tension, however these tension loads in most cases are relitively small
Trang 13
9z'10 Table D1 14 Ultimate Strength of Solid 100° Dimpled Rivets Ultimate strength, Ib a mm Hn 3 Rivet aterial 207 83 2017 “T4 2024 ‘TSI z _—— a 90246, |2021 | 2021-13, | X21-T6, 2021-13, 20240 P86 |2021-73 | 2024 Tú, | 2021 1, 2021 "Tú, 2023 5
aod 4, | TRủ and 2014 THỊ, | 2021 and and 3024 THỊ, and “THỊ, 2024 ‘THE, 2
Clad gheet nuướrbl, |{ 2021 7P, 2024-74 | 2024-7H0, | 2024716, 7075-'Eư 9024-74 | 2021-1786, | 20214 and a and 7075 T6 and and 7075 “FS 9 2021 PSL 2024 “DMI 70/ã-'T6 z ————k——— —— ee cre ween ——_ l8 oO Rivet dianveter ¢in,) te | oi 1% |%6| 14 | ?ế 3á t4 3 | ta | 7% Má 1 16 % ‘6 Mi 5 —— Su in me - fe - wef ee | fee wee ef eee foe ee - s a Sheet thickness, in 00160 wo 0.020 302 + So 04 a8 |1 419 : 5 0.082 41S | 456 [ote 72 725 | 600 0HI | 072 vu + + 74 m oom 451} 505 |035 | H39 ROL | 728 | 905 | 775 845 1,108 | 941 1,300 9 0 0ã0 ARE ADS pits ĐH) 1086 | 810 10897 | 861 1,432 1,508 1,110 1,705 > 0003 asi | 4,012 1,142 | 922 | 1,240 | 930 1,095 1,08 | 1,236 2,010 2 0071 ins) 1,018 1,190 | 95% | 1,301 | 957 1,853 1,930 | 1,291 2,150 k 0.081 1,071 1230 1,357 1,995 2AH1 | 1,340 2,260 2 0.090 1,008 1,267 1,408 2,115 2,145 | 1,882 2,305 < 0.100 AM 2,220 2,282 : 2,255 3,155 5 .-_! m 8
Nore: The values fn this table ace bayed on “good” manufacturing practice and for double dimpled joints and of the upper dimple wheet for dimpled, machine-counter- any deviation from this will produce significantly reduced values gunk joints, The thickness of the machine-countersunk sheet must be
at least } tabulated gwưe thicker than the upper sheet In no case shall allowailes be obtained a These allowables apply to double dimpled shects and to the upper sheet dimpled by extrapolation for skin gages other than those shown
Trang 14Table D1, 12 Yield Strength of Solid 100° Dimpled Rivets Chad sheet usa terial Rivet dianeter tu.) (016 0020 g2 0010) 0.056 0.081 tui 0.080 (1.090 0.100 Yield strength, tb 2117- tả 2017-Tả 2024-131 2021 PA, |9021-T3, | 2021-T3, | 2024 ‘rsd | 2024-3, 2024-4, | 2024-TH6 2024-83, 2024-1 2021 "PHÚ 21111, | 202104, | 2021204, and 2024-16, and and and and and 2034 te, | 2021 T6, | 2024-16, | 7075-06 | 2021-31 7075-'E6 3034 T4 2024 “TRL 7075 Tủ and 2024-P6L, | aad 3034 "PHI nil 2021-TBI -E8Ú ` Ta Ma te | Me | oe Me ?á | ti “4 tis M ? M HK ” 3à tí a " tI 257 us 3đ | 41 t0 450 - vod `
x 467 | ase | 512 |a25 | G40 fad 5u | 705 | 582 619 } 7N -
zú 404) 506 | Gut |o06 | 782 [san 75 | 867] 978] Goo] 879] ste} a2] 0832| 978
ang | 571 | 757 [677 | 905 Jost 76 | 1,007 | 4,508 | 738 | 1,308 | 9ổi | 1/308 | 1,152 [1548
019 | B11 729 | 995 |r4x sie Ƒ 11A | 1/803 | 925 | 1,561 | 1,068 | E564 | 1277 | 1,058 wil | 878 1752 | 1,004 |778 812 | 1,156 b | 15 | b1 | 3,106 | 1711 | 12382 | 3,40 ne 1,070 1,196 | 2,014 | 1,152 | 1,928 | 1,177 | 1,938 930 1,100 1,231 5 | 12406 | 2,121 | 1,824 | 2,120 2,255 2,268 2455
Nore: ‘The values in this table are based on “good” any devi lon from this will produce significantly reduced a These sllowables apply to double dimpled sheela and inte a machine-countersunk lower sheet Sheet gaxe is
manufacturing practice and values
to the upper sheet dimpled
that of the thinnest sheet
Trang 15
D1 28
Tension on rivets shall oe restricted to conditions in which tension load is ineiiental to the major shear carrying purcose of the rivet When it is
fficult to determine if the tension component is incidental or major, a bolt shall be used
The followiag are examples of joints where rivets are considered to de satisfactory tenslon carrying mediums
(a) Skin attachment to rios and frames
(p>) Attachment of sheet panels to beam flanges and stringers, where inter- rivet buckling or diagonal sheet wrinkling produce tension loads on rivets
Skin attachment on 4 pressurized nacelle or body
Do not usa rivets to fasten control vrackets to a supporting structure If there is no load reversal on the
assembly, the tenston allowablzs given in the following tables can be used
ere ts load reversal on the assembly, 9 nm load on the rivet should not
*
Rivets loaded in both shear and tension should be checked for combined stresses, using the tateraction equation,
(6)
Re? + Rgt = 1
A sufficiant number of rivets shall be used to insures that failure of any one rivet due to improper installation, eracked head, etc., shall not resuit in the failure of the structure that is being neld together by the o & rivets
D1 26 Rtvet Tension Strengths
Reference to the structures design manuals
ous alreraft companies shows that rivet
@ not the same or, in other ‘dized as in the case of shear las 4, B& 0 have deen taken
The values given are ives to values found in other FITTINGS AND CONNECTIONS BOLTED AND RIVETED Table A
PROTRUDING HEAD RIVETS (AN470, 4N442) ULTIMATE TENSILE STRENGTH Se =f Use this table for 24ST Alclad sheet and harder Allowable Rivet Load, Lbs Per Rivet Sheet Gauge | 3/32 | 1/8 | 5/32 | 3/16 1/4 5/16 | 3/8 016 a +020 120 142 „025 159 197 223 O32 214 269 v1 354 - 040 277 353 420 474 588 „051 277 471 561 649 799 929 064 495 736 854 | LƠIT | 1262 012 485 T158 961 | 1245 | 1482 | 1669 „081 758 | 1094 | 1440 | 1721 | 1952 „091 T094 | {651 | 1982 | 2265 102 1883 | 2274 | 2622 „125 1982 | 2890 | 3353 „ 198 1882 | 3130 | 4336 188 3130 | 4470 „250 | 4470 Table B
1002 FLUSH HEAD RIVET (AN428) MACHINE COUNTERSUNK JOINT ULTIMATE TENSILE STRENGTH — Use this table for 24ST Alclad sheet and harder Allowable Rivet Load, Lbs Per Rivet Sheet Gauge | 3/32 | 1/8 | 5/32 | 3/16 | 1⁄4 8/16 | 3/8 040 191 O81 249 319 „064 249 438 501 072 446 592 653 081 446 633 T13 ,09L 683 912 102 985 † 1275 ,125 985 | 1698 | 1841 „156 1783 | 2660 | 2950 188 1783 | 2817 | 3827 „350 2817 | 4023 (tain | 040 | 051 | 064] 072 ] 102 | 125 | 156 Table C
Trang 16(2) (3) (4) ANALYSIS AND DESIGN OF FLIGHT VEHICLE STRUCTURES D129
streamline strut The tube is flattened slightly at the end to fit a simple bu 4 fitting Loads shown are design strut loads Using a fitting factor of 1.20, check the strength of the entire fitting unit Assume no shock or vibration Fig 3 illustrates a fitting unit on the
end of an extruded (1) section The web on the (1) section extends cut to form PROBLEMS: 2014-16
The single bolt fitting unit as shown in
Fig 1 1s subjected to a design fitting GR
load of 12000 lbs in axial tension The 17000"
pin is an AN Steel bolt 3/8 inch diameter “1
Bushing {1s 1/16 wall and steel Fry =
125000 Lug material is 2014-T6 bar, \ fora AW, BOLT
Feu 2 $8000 The fitting is not subjected hy * STEEL
to shock or vibration, Strength check the hen)
colt and lug (A) and give all margins of 4 °
safety
Same fitting as in Problem 1 but design fitting load is a transverse load of
10,900 lb Strength check and give all Fig 2
margins of safety
Same fitting as in Problem 1 out lug (A) ase aS
is subjected to a design fitting load — 7
acting at 452 with a value of 11000 lb Strength check for this loading —_— —>p 1⁄4 — — )—~w⁄ p^- Lugs B Ce c—=_- j9? 1 Fig 3
A 1/2 inch diameter AN steel bolt is part of the fitting lug, which is reinforced subjected to a combined shear and tension by steel fitting plates Strength check the load The shear load on the bolt is fitting for a design load of 45000 lb Use 10,000 lbs and the tension load 1s fitting factor of 1.15
12,000 lbs Find margin of safety under
this combined loading (8) Fig 4 shows a typical beam end-single pin fitting uit The fitting plate is attached Design a hings pin using a standard AN to beam section by the rivet pattern as steel bolt and a male lug to carrying an shown The loads shown on figure are axial tensile load of 25,000 lps Use applied loads Using a factor of safety
fitting factor of 1.15 Use steel bushing,| on applied loads of 1.5 and a fitting No shock or vibration Assume lugs of factor of 1.2, determine the margin of
female part of fitting 1/2 as thick as safety of the rivet attachment of fittiag male lug Design the male lug from two plate to veam section
materials (1) 2024-T4 aluminum alloy cá (2024-13 ANCLES) fora 217-73 and (2) AISI steel, Fyy * 180000
Pig 2 tllustrates an end fitting for a
(2024-74
Trang 17
FITTINGS AND CONNECTIONS BOLTED AND RIVETED ›
nine “the “Pesultant iva AN steel bolts in Ot lps, load accing as Or Hobe bp ed Pare Marr
« 8 find the size 22 2017-3 rivets
y to carry the ultima design load 92 3000 ibs
tting clate is steel COO, and the 2024-T5 O81 inca thick “F£axecuAuaae 922 ee | pote | Fig &
Design the lightest overlap sheet solice for 051 clad 2024-T6 and protruding head type rivet Design tension load on sheet = 2350 lb./in Give all details of jotnt Rework design in Proolam 13 to uss doubls
dimpled rivets
1 Airerart Sle
Military Handbook MIL-HDBK-5 August, 1962 Metallic Materials and Elements for Flight Venicle Structures,
Cozgzone, Melson, and Hoblit: Analysis of
Lugs and Shear Pins Made of Aluminum and
Trang 18
CHAPTER D2
WELDED CONNECTIONS
D2.1 Introduction
Since the overall structure of an airplane, misstle or space vehicle cannot se fabricated as a single continuous unit, such structures
involve many structural parts which must be
fastened together For certain materials and types of structural units, welding plays an important role in Joining or connecting structural units Research 1s constantly going on to devslop better welding machines and welding techniques and also to devalop new
materials that can be welded witheut producing
a detrimental strengtn influence on the base or unwelded material A fair size book could os written on the subject of welding and design for welding This brief chapter can only be a bria? introduction to the subject
D2.2 Gas Welding
There are two types of gas welding, namely, oxyacetylene and oxyhydrogen Practically all gas welding in aircraft work 1S oxyacetylene Some welders prefer the oxydrogen flame in
welding aluminium alloys because the flame is
not so hot The major aircraft structural units in which gas welding plays an important part are welded steel tubular fuselages, engine mounts, and landing gears and the attachment of plate and machined fittings to such structure
D2.3 General Notes on the Practical Design of Welded Joints
The designer of welded can greatly help the welder or connections by adherring general rules structures in steel obtain zood joints to the following
Li 1E is muc easier to obtain a good weld when the parts being welced together are of equal thickness It is general design practice to try and keep thickness ratio detween the two welded parts less than %
to 1 Seme destgnars try to keep within a 2to 1 ratio im order to eliminate possibilities of welders ourning the thinner sheet
tị Designers usually consider 0@5 as the minimum thickness to be welded in general practical structural joints as there ts considerable danger that the average
welder might burn a thinner gauge, D2 1 (3) (4) (7) (8) (19)
In general avoid welds in tension since they produc? a weakening effect In some connections it ts difficuit to avoid all tension loads on welds, thus weld stresses should be kept low and if possible
incorporate a fishmouth joint or ÿinger patch to put part of weld in shear A weld should not encircle a tube in 2 plane perpendicular to the tube Length Standard splices or joints for overlapping tubes, and end socket fittings in tubes
have been developed, which require no strength check These are the diagonal weld and the fishmouth welds as illustrated
in Fig D2.1
Tapered gusset plates should be incorporated in all important welded joints to insure gradual change in stress intensity in
members These gussets lessen the danger
of fatigue failure by reducing stress intensity
BUTT WELD FISHMOUTH WELD
Fig D2.1
A weld over a weld should not be made
To prevent burning of sheet welds should not be made on doth sides of 2 thin sheet
If two welds are placed close together
of shrinkage space may cause cracking lack
Cracks usually develop if welding {s dene on bends
Ahen tubes are spliced by welding locate splice near one end of the tube, to avoid effecting column properties In general it is not good practice to weld brackets
to the middle of column members Clamps are preferable
In welding members together local internal
Trang 19
D2.2
(12) Standard aircraft bolts should not be welded in place since they are made of nickel steel and therefore cannot be satisfactorily welded Since standard aircraft nuts are made of 1025 steel they can be welded in place if desired
D2.4 General Types of Welded Steel Fitting Units
Pig D2.2 taken from aircraft tubing hand- book of the Summerill Tubing Company summarizes the common types of tube terminals and dis- cusses their structural merit Fig 02.3 fllustrates the conventional concentric butt welded fuselage Joint which tests show is
satistactory where vibration is not present
Tests have shown that the fatigue strength of a welded joint as illustrated in Fig 02.5 when the members are subjected to reverse bending is reduced considerably, thus it is common practice to add additional Joint re- inforcement such as finger plates or insert gussets as illustrated in Figs 02.4 and 02.5 to joints subjected to vibration
Figs D2.6 to D2.8 illustrate methods of splicing a longeron at a truss joint The vertical and diagonal members strengthen the putt weld on the spliced member
Figs D2.9 and D2.10 illustrate fitting plate attachments to tubes Except for Light
Titting loads, the fitting plate should extend through to both sides of tube or to the adjoin- ing members, The fitting type illustrated in Fig D2.11 1s only used for secondary conditions where loads or plate are relatively light
Since eccentricity of member forces on a joint produce bending in the connecting aembers which may Lower the fatigue strength of the
joint, such cases of joint eccentricity as {llustrated in Figs D2.12 to D2.i4 snould be eliminated in Joint design
D2.5 Electric Are Welding
This method of welding ts based upon the neat generated in an electric arc Arc welding
to a limited extent has been used for many years in aircraft fabrication No doubt the flexibility and general all around good results gbtained with gas welding retarded its
extensive use, nowever in recent years its use is increasing rapidly as its economies and ad-
vantages become apparent to the designer In are welding the applied heat 1s more concen- trated and quicker welding results with less expansion and warning 45 compared to gas
welding In the design 97 tubular joints, care should be taken to make all welds as accessibdle as possible To secure proper stress distri- putton in arc welded Joints the designer should follow the recommendations as illustrated tn Figs D2.15 to D2.18 WELDED CONNECTIONS pm OR OPE Angie "A" to be not less than 30° Fig D2 17 30° or more Fig D2 18
The fact that less expansion and warring takes place since the heat is concentrated makes it possible to nold to closer tolerances
on parts requiring machining after welding an allowance of 1/16 inch ts generall sufficiant on most assemblies Slectric welding cermit welding of thin sheets as low as 016 inch thickness
D2.6 Effect of Weiding on Base Metal
Trang 20ANALYSIS AND DESIGN OF FLIGHT VEHICLE STRUCTURES D2 3 Fig, D2.2 } i TYPICAL WELDED STEEL TUBE TERMINALS 7 Fig D2.9
Hetge a boss oot trong TP ng teh
Tay no/0 704 Eccemtiry wath respecr The aot 2 Tu ‘nd nape Satisfactory up 10 30" angle of banal Avid “ymingting welding at apoasire ws OF cially arwvented for wie ranges OF & TH same becrion OF the Tube
po %
@ M7
i |
ferry wre 9 wee ere Angie A of ninge axis witn respect "a Pope Sor charges oF css section Shacid sig 0 gest et aa!
‘aus may vary over wie Penge arene ty Mersin fake tod Dit Di Fig D2 10
INCORRECT
q -
+77: 1.5 ———i
i | eastern ga mane SH ae on cd eth fia Fig D2 11
Reproduced by permission from Summeriil "Aircraft Tubing Data" Fig D2, 12 Fig D2.6 —¬ AM Fig, D2.7 Fig D2.5 Fig D2.8
Trang 21
D2.4
ue to cold working is lost in the material ad- acent to the weld which lowers strength to a
i degree welding, however, does produce 2 brittle material which nas lower resist- WELDED CONNECTIONS the respective minimum tensile ultimate values test
to shock, vibration and reversal of stress, Table D2.2 (Ref 1) Strength of Welded Joints it is customary to assume an efficiency of
soints less than 100 percent Material Heat trearment |Fsu, | Few
“ subsequent to welding| ksi | ksi
table DZ.1 gives the allowable ultimate Carbon and alloy steeis.|None - ++ +| 32 sy tensile stress for alloy steels ror material ; 32 | 51 adjacent to weld when structure 1s welded after H neat treatment Alloy steels - - v2 | NON ve nh h| 43 12
Table D2 1 (Ref 1) Alloy steels - - | Stress relieved | 50 85
Allowable Ultimate Tensile Stresses Near Fusion -
Welds in 4130, 4140, 4340, or 8630 Steels? Alloy steels | Stress relieved
./ 60 | 100 t
L (Section thickness 1/4 inch or less) Steels + | Quench and temper | |
j Ultimate tensile 4130 125 kai 63 | 105
e of joint : nae see
Type of | stress, ksi 4140 - “| 180kgi .| TẾ |125
| Tapered joints of 30° or less? ‹ 90 4340 + * 18Ú kmi .| 90 | 150 |
| AH othera - * 80 ]
3 Welded after heat treatment or normalized after weld
b Gussets or plate inserts considered 0° taper with center line
For welding members the allowable modulus of steels when welded after
not axceed the following (Ref 1) subjected to bending, rupture for alloy neat-treatment snould as specified in
Por tapered joints of 30° or less, use modulus of rupture Fy equivalent to that for
steel naving Fry = g0000 osi
For all other types of welds, use Fp equal to 9 of that for steel having Fry = 90000 pst
“napter C4 gives chart for determining the moduius of rupture Fp for alloy steel tubes and Chapter CZ gives a procedure of determining Fp for other shapes subjected to bending Strength of Base Material when Structure is
@t-Treaced After Welding
Reference (1) says that for materials neat-treated after welding, the allowatle
stresses in the parent material near 2 welded Soint may equal the allowacls stress for the heat-treated material, in other words, 10
eduction for welding However, it is good sign practice to be conservative on welded ints, thus 4 reduction of 10 to 20 percent
* the neat-treated properties is tn saleulating the tensile or vend in the member adjacent to the well
often used ing strengtn
D2.6 Weld-Metai Allowable Stress
able D2.2 (from Ret 1) gives the allow- able weld-metal strengths Zor the various
steels These design allowable stresses for the eld matertal are dased on 385 percent of A
D2.7 Allowable Load for Welded Seams
The allowable load on a welded seam can be caloulated by the following equation:-
Pa * Fay oF Pep (Lt) - - 7 77777 Beh
where,
Pg = allowable load in lbs Fsụ and Fop trom Table 02.2
length of welded seams in inches
thickness of thinnest material joined by the weld in the case of lap welds between two steel plates or between plates and tuoes (inches)
+ = average thickness in inches of the weld metal in the case of tube assembiies, but not to be greater than 1.25 times the thickness of the welded stock D2.8 Brazing Brazing as appli process of uniting st copper-zine mixture, with an air-gas 2lame molten mixtur depends on tn elearance a ee ẻ Detwe many factors, @ norkman, 2?Tects 1 cach oP sy buy
The requirements of the procuring or
goverment agencies shoult ba noted before using
Trang 22
ANALYSIS AND DESIGN OF FLIGHT VEHICLE STRUCTURES D2.5 D2.9 Welding of Aluminum Alloys This 1s conservative since weld does not
extend across the plate, thus any decrease of The neat-treatable alloys, commonly tensile strength oropertiss should be less than
to as the strength alloys, such as
21, 7975, not be waldad with the
torch without destroying their 1 properties, wnizh are not restored eat-treated after welding These lays are generally classed as umweldable
tant research is soing on to develop aminum alloys that have relatively high
gta which can be welded without aporeclaplel se of the strength properties A recent
ký lopment Đy the Aluminum Company of America new alloy designated x7005, which develops strength after welding ene Teo ew pow v0 0 0 gi bị on tư g
The strain-hardened alloys, namely, 1100 and 3003, are readily joined by gas welding either aa oxyacetylene, or an oxyhydrogen flame is used and sheet thicknesses as low as 020 are successfully welded It 1s common practice
use these materials in welded fuel or oil tank for aireraft
D2 10 Dlustrative Problems Involving Welding
Fig D2.19 shows two plates welded usr to *orm a lap joint The material is alloy steel Fhy = 95000 psi Find the margin o? safety of the welded seams under the load of 5200 lbs acting as shown —.065 Flg D2.19 From squavion D2.1, Pa = Fsy Lt Fg, trom Table D2.2 = 43000 total weld seam length = 2x12 2 in, = 065 43000 x 2x 065 = + = (5850/5000) - 1 = 5580 «il
Tensile strength of 065 plate using a
reduced allowable stress due to welding of 30000 as per Table D2.1, gives ạ = 1x 065 x 80000 = 5200 1D S assumed ahove PROBLEM 2 OES GUSSET A—— án Hien WASHCG “3m OF GUSSET oner} 2100" ÄTIE 0D) | TUậC THICKNESš 049 ‘WELD ONE SIDE ONLY Fig D2 20 Pig
between the ands of
gusset is used as a fitting to take from a 3/16 diameter steel tie rod
D2.20 shows @ gusset plate inserted two tubes of a truss The
the pull Determine the margin of safety of connection of gusset to tubes All material steel, Fy = 95000
Resolving the wire pull into components parallel to the tubes, we obtain P = 2100 x sin 45° = 1480 x 1.2 (fitting factor) = 1780 lb The allowable weld load is zoverned by thinnest material or 049 of the vertical tubs
Pạ = Fay Lt
= 43000 x 1,125 x ,049 3 2370 1b M.S = (2370/1780) - 1 = 33
PROBLEM 3
In general welded fittings involving slates and tubes present conditions for xhien it is difficult to determine the actual stress flow through the joint, thus the general procedure is to make conservative assumptions regarding the stress flow distribution and check the fitting units for these conservative assumptions The following example illustrates this asproximate procedure o2 strength checking a welded fitting Joint
In Fig DZ.21 the ?Pitting plate which welded te tne three stzel tubes f
Trang 23
32.6 ie If 058 TUE Tait WASHERS F Sẽ TUAä€E _!5 _—UAE 3 CONTINUOUS THRU “FITTING PLATE —_ aut 1,058 3 HH 7 rễ 8 8 vất ( \ TT { i { ‘DIA BUSHING 081-c£0 F08 ~ 12065 TU eee ay Fig D2.21 Solution Shear Strength of Clevis Pin: Load on pin # 14000 1b Double shear strength of 1/2 diameter AN clevis polt = 2 x 14722 = 29444 M.S =(294444/14000) -~leil.l
Bearing of Clevis Bolt on Bushing:
Bearing stress fp = ese = 59500 pst Ultimate bearing stress = 175000 psi Thus a large margin of safety is available to take care of wear due to slight rotation or shock
Bearing Stress Bushing on Lug: + 2 24000 fo * S625 X 375 = 59500 psi Allowable bearing stress For = 140,000 psi (See Chanter B2) The result shows that bearing on lug 1s not at all critical Shear Out Strength of Fitting Plate: «1875 x 2 = 164 washers = (.625 ~ 3125) 1875 x 2 = .118 Total shear out area = 282 sq.in Shear area main plate = (.75 - 3125) fg = 14000/0.282 = 49700 psi Fsu for steel when Fru = 95000 1s 55000 See Chapter Bz WELDED CONNECTIONS
This value will be decreased to 50000 because of welding effect on material
properties
M.S = (50000/49700) - 1 # „01
This margin of safety is conservative since shear out area is conservative
Tension Stress on Section Through Bolt Hole: Area of Section Through Hole:
Main plate = (1.5 - 625) 1875 = - Washers = (1.25 - 675) 1875
Total net area = fy = 14000/.282 = 49700 pst Ftu from Table D2.1, allowing full correction for welding effect, equals g0000 psi
M.S = (80000/49700) - 1 = „81
Tension stress on gitting plate at Section 1-1 (See Fig 02.21)
Net area = (2.5 - 1.25) 1875 = 235 sq.in The entire load of 14000 will be assumed to pass this section, khích {Ss no doubt con- servative ty = 14000/.235 = 59500, Fy = 80000 pai O.K Check of Connection Between Fitting Plate and Tubes
It will be assumed that the horizontal component of the wire pull will be transferred to tube (4) by the weld between the tube and the fitting place This is 4 conservative assumption
Horizontal load component = 14000 x 2/5 = 12600 1b
The weld length between tube {A) and the fitting plate is 1.5 inches on tne upper tube surface and 2 inches on the lower surface TO oe conservative, a total weld length of 2x 1.5 = 3 tnches will be assumed acting
Te fitting plate is welded to the tube on both sides and since twice 065, the tube thick~ ness is less than the plate thickness, 2 total weld length based on cube strength is 2 x 326
inches
Fey Lt = 50000 x 8 x 065 = 19500 1b MS = (19500 /12500) - 12 56
It will be assumed that the vertical com- ponent of the wire pull will be taken into tuba (B) by the weld along each side of the
tube
Trang 24ANALYSIS AND DESIGN OF FLIGHT VEHICLE STRUCTURES The weld length on one side of tube is
9.625 inches long and 1 inch on the other total weld length of only 2 x 0.625 = 1.25 inches will be assumed which is conservative
A
Pa = 50000 x 1.25 x 2x 058 = 7250 Thus even under the assumed conservative assumption, the weld attachment for transferring} vertical component to tube (B) is more than adequate
SPOT WELDING D2 11 Spot Welding
After many years of research and testing, spot welding of aluminum alloys, magneslum alloys and corrosion resistant steels has become a reliable established practice of joining many parts or units of flight vehicle structures
The spot welding process 1s accomplished by clamping two or more sheets of metal between capner or copper alloy electrodes, under
comparatively high pressure and causing an electric current of low voltage to flow between the electrodes for a predetermined interval
The current creates an intense heat at point "A" (See Fig a) which melts the metal locally due to the resistance set up by the sheets AS soon as the metal is molten to the extent shown at "B", the predetermined time of current flow is completed and the sheets are forged together by the pressure on the electrodes "P" This pressure depends on the thickness of the sheet Lae SSS Flush surface Fig a
D2.12 Spot Welding of Aluminum Alloys
In general, aluminim alloy spot welded joints should not be used in primary or critical| structures without the specific approval of the military or civil aeronautic authorities The
following are a few types of structural con- nections in aerospace structures where spot welding should not be used
(1) Attachment of flanges to shear webs in stiffened cellular construction in wings (2) Attachment of shear web flanges to wing sheet covering (3) Attachment of wing ribs to beam shear webs D2.7 (4) Attachment of hinges, brackets and fittings to supporting structure
(5) At joints in trussed structures
(6) At juncture points of stringers with ribs unless a stop rivet is used
(7) At ends of stiffeners or stringers unless a stop rivet is used
(8) On each side of a joggle, or wherever there is a possibility of tension load component, unless stop rivets are used
(9) In general most aluminum and aluminum alloy material combinations can be spot welded Table D2.3 gives information on this subject
Table D2.3 Acceptable Material Combinations for Spot Welding = s|#|#|=* siA = Đ E|E|ã|S|S œ| si la |9ứ|e|e|s|?|đ#|xs|iđ 2| wa|é |@ z|â|Sâ! s|È|B|5|B5 Material ]øä|8|S|S|Đ|=|=jO|lã|A|DjS Clad 70759 , Bare 7075 Bare 20240 , Clad 2014 Bare 20140 , , (*) (*) }|~ (*) @ The various aluminum and aluminum-alloy materials re-
ferred to in this table may be spot welded in any combi- nations except the combinations indicated by the asterisk {*) in the table The combinations indicated by the asterisk (*) may be spot weided only with the specific approval of the procuring or certificating agency
5 This table applies to construction of land- and carrier- based aircraft only The welding of bare, high-strength
alloys in construction of seapianes and amphibians is
prohibited unless specifically authorized by the procuring or certificating agency
¢ Clad heat-treated and aged 7075 material in thicknesses less than 0.020 inch shall not be welded without specific approval of the procuring or certificating agency
D2 13 Spot Strengths
Trang 25D2 8
Dé.4, for magnesium alloys in Table 02.5, and for steels in Table D2.6 The minimum edge distances from snot welds is also given in the tables
Fig D2.22 gives the maximum static strength of spot welded joints having the same pitch in all rows in aluminum alloys together with the maximum pitches with which these values can be obtained For joints having
larger pitches, use Table D2.4
Fig D2.23 gives the tensile strength single spot welds in 7075-T6 clad material D2 14 Reduction of Tensile Strength of Parent Metal Due
to Spot Welding
Spot welding decreases the ultimate tensile strength of the sheet material being spot welded Fig 02.24 gives the efficiency in tension for spot welding of aluminum alloy sheets
Table D2 4 (Ref 1)
Shear Strengths and Minimum Edge Distances for Bare and Clad Aluminum Alloys Nominal Materials & Tensile Strength, ksi Mint | + Minimum or tniee| above 9 Sheet eve $6128 to $6|20 to 27 51295224) Edge +9) below Distance, 7 inches Inches | shear Strength of Sheet, Pounds 0.012 60 52 14 18 | 3/16 0.018 96 T8 56 40 | 3/18 0.020 112 | 106 90 62 | (3/16 9.028 148 | 140 | 118 88 | 1⁄32 0.032 208 | 188 | 188 132 | 1⁄4 0.040 276 | 249 ] 240 180 | 9/32 0.081 384 | 354 | 339 240 | 5/16 0.064 552 | 500 | 451 320 | 11/32 0.072 878 | 589 524 384 | 3⁄8 0.081 842 | 691 | 620 424 | 13/32 0.091 1020 | 810 | 703 484 | 7/18 9,102 1230 | 960 | 780 548 | 7/16 0.114 | 1465 | 1085 | 803 591 | 7/16 0.125 1898 | 1300 | 840 629 | 9/16 0/186 | 2400 | | 5/8 Tabie D2.5 (Ref 1) Shear Strengths for Magnesium Alloys T -
Nominal Thickness Mages Minimum Edge of Thinner Sheet, Inches eet Shear Strength Distance, Inches of Sheet, Lbs 9, 020 51L | 98 3/16 0 025 cĩ TL] 87 1/32 0 032 ¡ 108 | 139 1⁄4 0.040 137 | 189 ¡ 9⁄38 0,051 i 186 | 281 j 5/18 0.064 | 242 | 388 | 11⁄32 0.072 179 | 318 Ị 3/8 0.081 ¡ $20 Ì 4P cị 13/32 0.091 | 388 Ì 498 1⁄18 0 102 i 488 | 586 1/18 0.114 : 488 | 688 1/16 0.125 | 544 | T35 9/16 WELDED CONNECTIONS
Table D2.6 Spot-Weld Maximum Design Shear Strengths for Uncoated Steels# and
Nickel Alloys (Ref 1)
Material Ultimate Tensile Nominal Thickness Strength, 1b
of Thinner
sheet, in 150 ksi and | 90 ksi to | Below 90 above 180 ksi ksi 0 006 70 ST tae 0, 008 120 85 70 0.010 165 127 92 9.012 220 185 120 0.014 270 198 142 0,016 320 235 170 0.018 390 270 198 9.020 425 310 225 9.025 580 425 320 9.030 750 585 403 0.032 835 623 453 9.040 1,168 850 850 0 042 1, 275 920 712 0, 050 1, 700 1, 205 955 0.086 3, 038 1, 388 1, 166 0.080 2, 265 1, 558 1,310 0 063 2, 479 1, 888 1, 405 9.071 3, 012 2, 024 1, 656 0.080 3, 540 2,405 1, 980 0.090 4, 100 2, 810 2, 290 0.095 4, 336 3,012 2,476 9.100 4,575 3, 200 2,645 9.112 5, 088 3, 633 3, 026 0.125 5, 665 4, 052 3, 440
@ Refers to plain carbon steels containing not more than 0.20 percent carbon and to austenitic steels The reduction in strength of spotweids due to the cumulative effects of time- temperature-stress factors is not greater than the reduction in strength of the parent metal, 5 —— 7078-76 CLAD rom 6061 -T6 2 —— m rst MIN “ # 3 a 5 8 2 3 3 @ 3 1 'Đ 1a 9 + 2đ 2 wad = gages š
fig D2.22 (Ref 1) Maximum Static Strength of Spot Weided Joints in Aluminum Alloys and Corresponding Maximum Spot