Experimental Mechanics

, Volume 22, Issue 1, pp 8–15 | Cite as

Photoelastic studies on progress of separation in interference fits

A photoelastic method is presented for studying the progress of separation in interference fits by identifying the break in electric circuit between metallic pin and a series of wires laid on CR-39 sheet
  • S. P. Ghosh
  • B. Dattaguru
  • A. K. Rao
Article
  • 48 Downloads

Abstract

Interference fits are used extensively in aircraft structural joints because of their improved fatigue performance. Recent advances in analysis of these joints have increased understanding of the nonlinear load-contact and load-interfacial slip variations in these joints. Experimental work in these problems is lacking due to difficulties in determining partial contact and partial slip along the pin-hole interface. In this paper, an experimental procedure is enumerated for determining load-contact relations in interference/clearance fits, using photoelastic models and applying a technique for detecting progress of separation/contact up to predetermined locations. The study incorporates a detailed procedure for model making, controlling interference, locating break of contact up to known locations around the interface, estimating optically the degree of interference, determining interfacial friction and evaluating stresses in the sheet. Experiments, simulating joints in large sheets, were carried out under both pin and plate loads. The present studies provide load-separation behavior in interference joint with finite interfacial friction.

Notations

2 a

diameter of hole

E, G, v

elastic constants; Young's modulus, rigidity modulus and Poisson's ratio

e

Ep/Es

f

material fringe constant in tension

h

thickness of model

P

pin load per unit thickness

r, θ;X,Y

polar and Cartesian coordinates relative to hole center

S

applied far-field stresses

So

applied stress-level parameter

\(2\theta _s ,2\theta _c \)

arcs of separation or contact

λ

proportional interference between pin and hole=(pin diameter-hole diameter)/hole diameter

μ

friction coefficient

σ, τ

direct and shear stresses with appropriate subscripts

\(\tau _{max} \)

maximum shear stress at a point

Subscripts

cr

threshold for initiation of separation

s, p

refers to sheet and pin

x, y, r, π

directions, associated with load and stress level

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References

  1. 1.
    Frocht, M.M. andHill, H.N., “Stress Concentration Factors around a Central Circular Hole in a Plate Loaded through Pin in a Hole,”Trans. ASME, J. Appl. Mech.,62,A5-A9 (March 1940).Google Scholar
  2. 2.
    Jessop, H.T., Snell, C. andHollister, G.S., “Photoelastic Investigation on Plates with Single Interference Fit Pins with Load Applied to Plate Only,”Aeronaut. Quart.,7,297–315 (1956).Google Scholar
  3. 3.
    Jessop, H.T., Snell, C. andHollister, G.S., “Photoelastic Investigations on Plates with Single Interference Fit Pins with Load Applied to (a) Pin Only and (b) Pin and Plate Simultaneously,”Aeronaut. Quart.,9,147–163 (1958).Google Scholar
  4. 4.
    Lambert, T.H. andBrailey, R.J., “The Influence of the Coefficient of Friction on the Elastic Stress Concentration Factor for a Pin Jointed Connection,”Aeronaut. Quart.,13,17–29 (1962).Google Scholar
  5. 5.
    Cox, H.L. andBrown, A.F.C., “Stresses Round Pins in Holes,”Aeronaut. Quart.,15,357–372 (1964).Google Scholar
  6. 6.
    ESDU Engineering Science Data Unit, 251–259, Regent Street, London, WIR 7AD, England.Google Scholar
  7. 7.
    Rao, A.K., “Accurate Determination of Interference in Pin Joints,“Experimental Mechanics,9 (2),45–48 (1969).Google Scholar
  8. 8.
    Venkataraman, N.S., “A Study into the Analysis of Interference Fits and Related Problems,”PhD Thesis, Indian Institute of Science, Bangalore, India (1966).Google Scholar
  9. 9.
    Eshwar, V.A., “Partial Contact and Friction in Pin Joints,”PhD Thesis, Indian Institute of Science, Bangalore, India (Dec. 1977).Google Scholar
  10. 10.
    Ghosh, S.P., “Analysis of Joints with Elastic Pins,”PhD Thesis, Indian Institute of Science, Bangalore, India (Nov. 1978).Google Scholar
  11. 11.
    Rao, A.K., “Elastic Analysis of Pin Joints,” Invited Paper in Int. Jour. of Comp. and Strucs, Special issue commemorating the 65th birthday of Prof. J.H. Argyris of the Univ. of Stuttgart and the Imperial College of Sci. and Tech; Published in 9 (2) (1978).Google Scholar
  12. 12.
    Durelli, A.J. and Riley, R.J., “Introduction of Photomechanics,” Prentice-Hall (1965).Google Scholar

Copyright information

© Society for Experimental Mechanics, Inc. 1982

Authors and Affiliations

  • S. P. Ghosh
    • 1
  • B. Dattaguru
    • 2
  • A. K. Rao
    • 2
  1. 1.Ministry of EducationGovernment of IndiaIndia
  2. 2.Department of Aeronautical EngineeringIndian Institute of ScienceBangaloreIndia

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