Computational Physics GroupKarel Matous |
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Design of Prestressed Skin/Flange AssemblyK. Matous and George J. Dvorak Department of Mechanical Engineering, Aeronautical Engineering and Mechanics Rensselaer Polytechnic Institute 110 8th Street, Troy, NY 12180 AbstractA prestressing procedure
for reduction of adhesive peel and shear stresses at the
leading edge of a skin/flange assemble is analyzed for
tensile and bending loads applied to the skin. Both an
analytical solution based on the Green's functions and
finite element solution are presented for specific
examples, together with design diagrams. Substantial shear
stress reduction is obtained with the proposed procedure.
ConclusionThe results suggest a relatively simple method
of adhesive stresses reduction in a skin/flange assembly
loaded either by skin tension and/or bending, acting
transverse to the longitudinal axis of the flange. While
certain special fixtures would be required for
prestressing, the expected enhancement of load bearing
capacity and/or endurance may well be worth the extra
cost. Since the adhesive stress distributions depend
both on adhesive and adherend elastic moduli, details of
the joint geometry, and the GFA cannot account correctly
for peel stress in the adhesive and is inaccurate in
evaluating the shear stress, therein a finite element
method is strongly preferred. The proposed design
diagrams based on elastic stress analysis should suffice
and lead to conservative designs in most applications.
Finite element evaluation of the stress distributions is
used for construction of the design diagrams. Scaling of
solutions obtained for a single load magnitude is
indicated in the elastic case. In an actual composite
structure, both flange and skin are made of a laminate
consisting of several fibrous layers. Layup details may
influence the adhesive stresses at the leading edge of
the bondline, and also the interlaminar stresses at the
free edges of the laminated flange. Indeed, failure of
the joint often originates in the flange end and extends
along ply interfaces before reaching the adhesive layer.
Since the laminates were homogenized in our analysis,
the results do not reflect that level of detail.
However, inasmuch as the goal was to minimize the stress
concentrations at the bondline leading edge by
superposition of the prestress and applied loading
stress distributions, the differences between the
layered and homogenized solutions should not have a
large effect on the loading combinations found to
generate the minimized stress distributions.
AcknowledgmentThe authors appreciate
financial support of this work by the Ship Structures and
Systems S&T Division of the Office of Naval Research.
Dr. Yapa D.S. Rajapakse served as program monitor.
Download the paper here © 2009 Notre Dame and Dr.
Karel Matous
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