OK here comes another techno rant. Following on from my post on board weight and volume comes my next installment on measuring what we all speculate on. This time my target is flex. It seems flex is a big negative when people talk about epoxy boards, but has anyone set out to measure it properly? We may have already found the best flex for a surfboard in old style pupe boards. But if we can measure it, we can reproduce it. My snowboarding jaunts have taught me much about the power of flex. Like to get air through the transition between turns on a surfboard? Probably not really practically possible, but the theory behind the possibility is powerful.
Elasticity of a material (or object) can be measured using a machine that applies stress (load) while measuring the deflection (movement) of the objet being placed under load. The load can take many forms such as bending, squashing, stretching or shearing. In fact the bending characteristics can be worked out if you know how the material(s) squashes and stretches under load. The classic “Stress/Strain” graph gives an insight into how materials flex under load and their ability to spring back. Materials and objects have what is known as a modulus of elasticity (or elastic modulus) which generally speaking measures the flex characteristics. This technique of measuring materials as they are placed under load is a foundation tool of materials scientists and is very useful. The testing can be non-destructive or destructive, depending on your budget. Generally, testing done within a material’s elastic limit will not harm it. Beyond this limit, you move from the elastic range into the plastic and the material is cooked. You could test the individual materials used in a sandwich construction and apply maths to determine what various sandwich recipes will do, or just grab a complete board and start bending it within the special apparatus.
Basically you are trying to work out how much force is required to bend the board. The board will snap back with equal force when the load is removed IF the material is within its elastic limit. Rubber and steel are both elastic materials, but have very diffent elastic moduluseseses.
We talk about the impact of board weight yet nobody knows what they weigh. We talk about how volume affects performace yet nobody knows the volume of their board. We talk about flex and “this one feels stiff” is the best we have.
Some stress/strain testing of various boards and/or construction materials would give a good basis for working out the most desirable flex characteristics and reproducing them. It would be intersting to see how various construction systems stack up in the flex dept. I would love to see more science applied to the surfboard, again the artist can get the same results through trial, error and “feel”. What can I say, I’m a left brained operator!
PS - its been more than a few years since I had to know this stuff and my memory may be a little cloudy, feel free to correct any errors I have made.