Reasonable Knock-Down Factors for Sandwich Face Wrinkling
2008 (English)Conference paper (Other academic)
Design rules and formulas used to predict wrinkling failure of sandwich structures ofteninclude a knockdown factor to compensate for "imperfections" in the sandwich structure. The knockdown is usually based on experience and empirically derived from compression testing. It can be substantially large and clearly affect the design. For example the most widely used Hoff's formula suggests a reduction of 45%, from 0.91 to 0.5, due to the effect of imperfections. The wrinkling formulae are also often simplified, thus neglecting the effect of the stacking sequence of the face sheet laminate. These types of rough “rule of thumb” design constraints must be re-evaluated and questioned.Today’s modern design methods and highly optimised structures seek a weigh treduction of the few last percent. This demands a higher level of accuracy in the designprocess and yesterday’s methods must be improved to meet the demand. In this paper an alternative method to derive a reasonable knockdown factor is presented and it is shown that this factor can also be predicted based on constituent material properties and assumed amplitude of initial imperfections. The design method previously published by the authors in  is extended to fully anisotropic materials anda first ply failure criterion. The results have thus far been confirmed by tests and good agreement has been achieved.
Place, publisher, year, edition, pages
wrinkling, buckling, imperfections, compression strength, stability, sandwich
IdentifiersURN: urn:nbn:se:kth:diva-57921OAI: oai:DiVA.org:kth-57921DiVA: diva2:472680
European Conference on Composite Materials 13
QC 201201182012-01-182012-01-042012-01-18Bibliographically approved