Lugs and pins:

1. 530.418 Aerospace Structures and MaterialsLecture 16: Joining: lug analysis (9.8)Lecture 17: joining:fasteners (9.2-9.3)

2. Lugs and pins: • Typical applications require rotation movement and the transfer of very highly concentrated loads, e.g. • Trunnion joints of landing gear • Engine pylon mount pin • Horizontal tail pivot joints • Removable joints for fighter wing root mounts • Door hinges • Lugs should be sized conservatively because their weight is small relative to their importance.

3. Bushing Pin Types of applied loading for lugs: • Loading is that of a bolt in shear P P P Axial Transverse Oblique

4. Types of lug failures: • Shear out and bearing failure • Tension failure • Hoop tension failure of lug tip • Same as shear and bearing – no additional calc needed • Pin shear off • Pin bending • Bushing yielding

5. Female Male Design considerations • Most designs use symmetric double shear lugs • Fitting factor (l =1.15) used for both suts and sy • MS > 20% unless tested • t/D = lug thickness/hole diameter > 0.3 • Watch grain orientation • Page 323 ; figure 9.8.3 • Forged materials better than cast • Use bushings as needed

6. Case I: axial load (a=0) Shear-bearing failure Projected bearing area Dt Efficiency factorf(geo, mat) Fig. 9.8.5 suts along x

7. Case I: axial load (a=0) Tensile failure Minmum net section area (W-D)t Efficiency factorf(geo, mat) Fig. 9.8.6 suts along x

8. Case I: axial load (a=0) c) Yield failure - lug Minimum of Pbru and Ptu Yield factor Fig. 9.8.7

9. Case I: axial load (a=0) d) Yield failure - bushing Smaller of bushing on pin or bushing on lug(watch thickness)

10. Case I: axial load (a=0) e) Pin shear-off failure Shear UTS

11. Case I: axial load (a=0) • Pin bending (if pin is too small) • -> causes failure in lug due to moments and uneven loading • See pp 327-329

12. Which failure mode dominates ? Must check allfailure modes !!

13. Example of lug analysis … (p 329)

14. Example of lug analysis … (p 329)

15. Example of lug analysis … (p 329)

16. Case II: Transverse Load (a=90)

17. Case II: Transverse Load (a=90)

18. Case II: transverse load (a=90) Yield load is … Projected bearing area Dt Efficiency factorfor transverse load ktru and ktry = f(Aav/Abr) Fig. 9.8.12 sys along y

19. Case III: Oblique Load (a=0-90) Axial component of P smaller of Pbru or Ptu Transverse component of P Ptru

20. Case III: Oblique Load (a=0-90) Axial component of P Py , lug Transverse component of P Py , transverse

21. Fasteners • Permanent • rivets • Removable • Screws, bolts • Nuts • Washers

22. Fastened joint failure modes

23. Fastener strength allowables: • Fastener shear off Allowable ultimate shear strength of fastener material See Fig. 9.2.5, 9.2.6

24. Fastener strength allowables: • Sheet bearing load (protruding head only) Allowable ultimate bearing strength of sheet material

25. Fastener strength allowables: • Counter sunk fasteners – allowable ultimate and yield loads See Figs. 9.2.8, 9.2.9

26. Fastener strength allowables: • Tension allowable in a joint; lowest of: • Rivet tension allowable • See Figs. 9.2.10 ,12,13 • Tensile allowable for threaded steel fastener • Ft,all = Ftu Am Where Am = max. minor area of 1st thread • Countersunk fastener and sheet combinations • See Figs. 9.2.10,11

27. + + + + Splices • Necessary because of: • Manufacturing limitations on sheet width and length • To obtain desired spanwise taper of section area – a cost consideration • For fail-safe design • Design of splices (how many rivets?) • Want required strength at lowest weight and cost • Good idea to ‘balance’ the design • Example • Page 289-91