ASTM D198 is an umbrella spec for a multitude of assorted lumber tests including compression, flexure, shear, tension, and torsion. Each test requires slightly different fixturing and therefore all recommendations will be based on the type of test method.
The cut and direction of the grain is extremely important for almost every mechanical test covered under D198. Therefore, it is vitally critical that tests such as compression and tension are listed as parallel or perpendicular-to-grain.
Summary of Tests:
Compression Testing requires the use of compression platens that exceed the area of the wood sample. One of the platens must be spherically seated to properly align the compression test.
Flexure Testing uses a relatively wide bend fixture to ensure that the test can achieve a full bend rupture.
Shear Testing by means of a torsion test is the most common method of determining shear strength Four point bending methods are also specified in D198. Oregon State has performed extensive experiments on wood shear testing which also involved both a 4 and 5 point bend fixture.
Tension Testing is performed parallel-to-grain. Scissor grips and pneumatic grips work best for tensile wood testing.
Torsion Testing is used for determining shear strength. Torsion machines are different from static Universal Testing Machines (UTMs) and are used to twist the sample.
Calculations for ASTM D198 include Modulus of Rupture (MOR), and Modulus of Elasticity (MOE). Other, more simple figures such as the Ultimate Tensile Strength (UTS) and Elongation can also be studied.
ASTM D143 - Small Clear Specimens of Timber
ASTM D1037 - Wood-Base Fiber and Particle Panel testing
ASTM D2555 - Clear Wood Strength Values