Sandwich to Single Skin Laminate : A study of tapered transitions subjected to shear load

Abstract:

Any geometrical change and material transition renders a weak point accumulating stress concentrations in structural members. This research focuses on the transition between a sandwich panel and a single skin laminate, a setup commonly seen in yachts today. The need for different material layouts over a yacht’s complete structure leaves theses transitions inevitable. While the sandwich provides a strong and stiff, yet lightweight solution, the single skin is far more compliant and stronger when subjected to localised loads. The project included applying both finite element modelling and practical testing of the studied transition. Combining a computer based evaluation method with physical testing shortened production time and helped to focus the research on problematic areas of the design. Part of the project was also to highlight differences with these methods, their shortcomings and benefits, as well as how they can be used together as an effective way of research. The studied setups combined of three tapers including one to one, three to one, four and a half to one ratios and two different core thickness of the sandwich panel. Theses where partly modelled and tested in four point bending in a series of three load cases. Ranging from a shear load dominated to a much more mixed loading case including bending moment, the shear strength of the core could be seen as a reoccurring weak point of the structure. Results from modelling support earlier research on the benefits of a longer taper, lowering the stress concentrations at the tip of the transition, thus lowering the risk of further delamination. The practical testing indicated how the compression of the taper increased the shear strength of the core, making the taper far stronger than anticipated, leaving the uncompressed core material as the weakest point and the majority of times the source of failure. Successful in locating the critical element in the construction new difficulties with theconstruction could also be detected. The influence of the asymmetric laminate used, could be shown to affect the stress distributions but leaves more to be researched on how the laminates and core work together over the taper. The results and conclusions show that more work on this subject is needed, the complexity of the problem still needs tackled by decreasing the numbers of variables to reach a more general how tapers behave depending on the materials in use.