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George Gall and I laid-up 21 unique lamina schedules, then did three-point bending tests to acquire flex (stiffness), failure mode, failure strength, and toughness. Then we did impact tests. The results are attached in a spreadsheet. Only 13 constructions are included because the others were tested at the beginning when we were still improving our test methods. There are some good results in the missing tests, but they are not accurate...I am afraid I would get bombarded with questions and doubts if I posted them. All the numbers listed in the spreadsheet pertain to a laminated block of eps foam that is 14”x4”x1.75”. These are representative(proportional) of how a surfboard would perform/break BUT NOT THE SAME. You have to keep in mind how things scale. Here are definitions of the parameters you see in the spreadsheet: Stiffness: The slope of the load/deflection curve in in the linear range. A larger number indicates that a surfboard with this construction is stiffer or less flexible. (I did not include units...look at the numbers in comparison to the stock glass construction listed at the bottom E+E/E). Toughness: The amount of energy that would be required to break the specimen in bending. This is more important than the amount of weight required to break the specimen in bending. Energy is calculated as the area under the load/deflection curve. Strength: The amount of weight required to break the specimen foam density: density of the foam in the specimen foam weight: weight of the foam in the specimen board density: estimated weight of a 6'0” chip without fins tough/weight ratio: structural performance index...toughest board for the weight flex/weight ratio: structural performance index...most flexible board for the weight impact rating: how well the specimens mitigated a severe impact. All impacts were identical HOW TO USE THESE NUMBERS: 1)Choose the board that flexes the way you like. Reference the layups that you know ( W+W / W or E+E / E). Do you want your board stiffer or more flexible than one of these layups? Look at the stiffness numbers, then find a few that meet your flex criteria. 2) Amongst the boards that flex properly, find the happiest medium of weight, toughness and impact resistance. Of course the constructions that I tested were engineered to be flexible, lightweight and tough. Some of you may be looking for heavy, stiff boards, so you'll have to run your own tests. **Please note that the W+W / W and E+E / E were laid up with denser foam, so they will appear to be tougher and stronger than they should be. A higher density EPS foam greatly increases the toughness and strength, but does not effect stiffness. Foam has a negligible effect on the surfboard stiffness.
https://swaylocks7stage.s3.us-east-2.amazonaws.com/s3fs-public/iteration2b_xls_4becac7903.xls