Materials Science Plays a Role
To continue with the FEA stress analysis of sports equipment series, this week’s blog will look at the engineering of snowboards, skis and the mechanical strength properties that affect them. Material science plays a large role in finding the perfect mix of materials to create the ultimate equipment. Snowboards are assembled in a series of layers. First the core, which can be made of carbon fiber, Kevlar, aluminum honeycomb or wood, is laminated together in a series of vertical strips. The material used in the core has a large impact on the eventual properties of the finished board. Next, fiberglass is bonded to the core with epoxy. More fiberglass material is layered next along with any dampening material that will help the core absorb the stress of the rider. The top layer is merely for appearance and does not have much impact on the structural integrity of the board.
Engineering Starts in the Middle
There are four main materials that can be used to make the core of a snowboard, each with different benefits and detriments. Again, the most common material is wood. A single piece of wood can contain knots and irregularities, but by using several pieces bonded together, the likelihood of those imperfections affecting the board is decreased. Often, hardwood and softwood will be combined to trade some of the strength for a lighter overall weight. By using a lot of narrow laminates instead of one large piece of wood the board is able to handle about 20% more torsional force. A board with a higher torsional flexibility is able to make a sharper turn while a more rigid board would require more force to accomplish the same task.
[i] Another type of material used in the core process is carbon fiber which is lighter, stronger and more responsive than wood but is much more expensive. Carbon fiber can support a stress of up to 500 ksi while the strongest woods can only support up to 1400 psi. For the average rider a carbon fiber core may be well above and beyond what their skill level demands, but for Olympic riders who put their board’s maximum strength to the test, carbon fiberis a must. The next type of core is Kevlar which is strong and fairly light, but unlike carbon fiber which performs extremely well under compression stresses, Kevlar performs very well under tension stresses. The difference is that a Kevlar board does not bend as much, so it is better for staying on the snow and going fast while a carbon fiber core is designed to lessen the impacts from jumps and rails. The final core is an aluminum honeycomb which is lighter than carbon fiber and just as strong with a compressive strength between 2.1 and 3.5 MPa compared to the 3.0 to 3.5 MPa of carbon fiber. [ii]
While the top layer may only serve as a visual stimulus, the other two or sometimes three fiberglass layers serve an important function to the integrity of the board. Their first purpose is to insulate the core of the board from the elements, especially water. Wood is especially susceptible to deformation when wet while carbon fiber and Kevlar will not perform as well in conditions of extreme cold, so the fiberglass layers act as a barrier to these potential threats. There are two main types of wraps that the fiberglass can be laid in, these are bi-axial and tri-axial. A bi-axial wrap has fiberglass strands weaved at 90o angles to each other and create a dependable and lightweight layer that is able to handle many cycles of stress. A tri-axial wrap has fiberglass strands wrapped at 45o, 0o and -45o and has similar properties to the triaxial wrap but can handle much more torsional stress than a bi-axial wrap. [iii]
By understanding the engineering and materials information that goes into the production of these types of equipment, designers are constantly able to create the lightest, strongest and most durable boards and skis for any skill set. As with other equipment we have discussed in this series, the ability for engineers to utilize CAD and FEA in the design process allows for quicker production at substantially lower costs which allows for more consumers to enjoy their favorite sports.
[i] Kornexl, E. et. al. , Science and Skiing , Taylor & Francis, 2013, pgs. 634
[ii] Honeycomb Aluminum-Material Information www.goodfellowusa.com
[iii] Snowboard Construction www.mechanicsofsport.com