Mechanics of Breaking

With proper training, board breaking is an excellent way to demonstrate the power of Taekwondo. A scientific understanding of the mechanics behind board breaking is helpful to all board breakers.

Board breaking is a relatively simple task, but, as with all applications of force, it can be empirically analyzed. The following is an analysis of the speed and force required to break a board.

Board breaking consists of applying a large force to a piece of wood for a short time. Since both force and instantaneous striking velocity are important, this breaking analysis was undertaken relative to breaking energy. The boards were assumed to be standard 12 in. x 12 in. x ¾ in. White Pine (P. Strobus) held tightly at both ends (so all the striking energy goes into breaking the board). Boards were assumed to be free of defects (no high local stress concentrations) and modeled according to column loading. This means that the maximum energy that the board can store before fractures begin to propagate is given by:

Umax=V*sb/2E

Where sb is the breaking stress, V is the board volume, and E is Young’s Modulus. Since the boards break mostly in tension, sb can be replaced with Mr, the modulus of rupture. The modulus of rupture is the highest tensile stress a material can undergo in bending before fracturing.