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Ace 402 lec 5 effective

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Dr Mohamed Elfarran

This document discusses effective sheet width and inter-rivet buckling in aerospace structures. It explains that stringers stiffen wing and fuselage skins, and skins provide stiffness to stringers even when buckling. An effective width calculation accounts for this effect. The document also describes how inter-rivet buckling can occur if rivet spacing is too long, and provides equations to calculate the effective rivet spacing to prevent this issue.

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Ace 402 lec 5 effective
Effective sheet width  In aerospace structures, Wing and fuselage skins are stiffened by stringers.  The stringers are usually connected to skins using rivets.  Therefore the skins add stiffness to the stringers even in buckling.  This effect can be represented using what we call Effective Width. ACE 402- Dr Mohamed Elfarran
Effective sheet width Before skin buckling both the skin and stringers carry the same compressive loads as in Fig. a. As the load increase, the skin buckles and cannot carries more than the buckling load, as in Fig. c. But at the skin-stinger connection, the skin stiffened by the stringers that help carry higher loads. ACE 402- Dr Mohamed Elfarran
Effective sheet width Assume skins are simply supported to the stringers, then the effective width takes the form, For light stringers the factor 1.9 is replaced by 1.7. If a clamped connection is assumed between skins and stringers ACE 402- Dr Mohamed Elfarran
Effective sheet width When calculating the effective sheet at the end of the skin (free skin edge), we use the equation Then, the total effective width for this particular stringer takes the form ACE 402- Dr Mohamed Elfarran
Effective sheet width If the stringers and skins have different material properties. We multiply the effective width equation by a correction factor . Notice that the symbol F used by Bruhn refers to stress which we usually refers to it by the symbol sigma ACE 402- Dr Mohamed Elfarran
Inter-Rivet Buckling ACE 402- Dr Mohamed Elfarran
Inter-Rivet Buckling • If the distance between the skin rivets are too long, this can leads to inter-rivet buckling. • Therefore, the rivet spacing is designed such that to prevent the inter- rivet buckling. • To do so, we assume the sheets between rivets act as a column with restrained ends. ACE 402- Dr Mohamed Elfarran
Inter-rivet buckling of sheets under compression is the rivet spacing These charts are for clamped end conditions, i.e. flat- head rivets ACE 402- Dr Mohamed Elfarran
Inter-rivet buckling of sheets under compression For other end conditions we use equivalent rivet spacing = 4 where C: rivets fixity coefficient P: rivet spacing And get Fir form figure C7.14 The rivets fixity coefficient For flat head 4 For spot welds 3.5 Brazier 3 counter-sunk 1 ACE 402- Dr Mohamed Elfarran
Inter-rivet buckling correction  If > then no inter-rivet correction and = +  If < then = , = + ACE 402- Dr Mohamed Elfarran

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Ace 402 lec 5 effective

  • 2. Effective sheet width  In aerospace structures, Wing and fuselage skins are stiffened by stringers.  The stringers are usually connected to skins using rivets.  Therefore the skins add stiffness to the stringers even in buckling.  This effect can be represented using what we call Effective Width. ACE 402- Dr Mohamed Elfarran
  • 3. Effective sheet width Before skin buckling both the skin and stringers carry the same compressive loads as in Fig. a. As the load increase, the skin buckles and cannot carries more than the buckling load, as in Fig. c. But at the skin-stinger connection, the skin stiffened by the stringers that help carry higher loads. ACE 402- Dr Mohamed Elfarran
  • 4. Effective sheet width Assume skins are simply supported to the stringers, then the effective width takes the form, For light stringers the factor 1.9 is replaced by 1.7. If a clamped connection is assumed between skins and stringers ACE 402- Dr Mohamed Elfarran
  • 5. Effective sheet width When calculating the effective sheet at the end of the skin (free skin edge), we use the equation Then, the total effective width for this particular stringer takes the form ACE 402- Dr Mohamed Elfarran
  • 6. Effective sheet width If the stringers and skins have different material properties. We multiply the effective width equation by a correction factor . Notice that the symbol F used by Bruhn refers to stress which we usually refers to it by the symbol sigma ACE 402- Dr Mohamed Elfarran
  • 7. Inter-Rivet Buckling ACE 402- Dr Mohamed Elfarran
  • 8. Inter-Rivet Buckling • If the distance between the skin rivets are too long, this can leads to inter-rivet buckling. • Therefore, the rivet spacing is designed such that to prevent the inter- rivet buckling. • To do so, we assume the sheets between rivets act as a column with restrained ends. ACE 402- Dr Mohamed Elfarran
  • 9. Inter-rivet buckling of sheets under compression is the rivet spacing These charts are for clamped end conditions, i.e. flat- head rivets ACE 402- Dr Mohamed Elfarran
  • 10. Inter-rivet buckling of sheets under compression For other end conditions we use equivalent rivet spacing = 4 where C: rivets fixity coefficient P: rivet spacing And get Fir form figure C7.14 The rivets fixity coefficient For flat head 4 For spot welds 3.5 Brazier 3 counter-sunk 1 ACE 402- Dr Mohamed Elfarran
  • 11. Inter-rivet buckling correction  If > then no inter-rivet correction and = +  If < then = , = + ACE 402- Dr Mohamed Elfarran