Three Point Test

The three point test method test the bending strength and elasticity of lumber and other wood based material.  The ASTM standard says this is accomplished by:

"The test specimen is simply supported and loaded on the wide face by two equal, concentrated forces spaced equidistant between the supports.  The specimen is loaded at a prescribed rate and, as applicable, observation of load or deflection, or both, is made until failure occurs or a preselected load or deflection is reached."

The standard also has three properties for the testing machine:

1. A reaction frame to support the test specimen.
2. A loading mechanism for applying load at a specified rate or prescribed load interval.
3. A force-measuring apparatus that can be calibrated to provide an a percent error smaller than ±1 percent for loads over 4450 N.

The machine's bearing plates need to be as wide as the specimen and eased edges to avoid a crushing failure at the load and support points.  The apparatus shall also include appropriated mechanisms such as rollers or pivots to minimize the axial forces in the specimen.

The test specimen's length should be between 17 to 20 times the depth.  For a 2"x4" piece of wood, this between 34 and 40 inches.