Tests on Wood

Compression Test

1. Obtain nominal 3-1/2" compression cube specimens of three different woods (Southern pine, spruce, and oak for example). The cubes can be cut from a 4x4 section but should be clear wood. Ensure that the surfaces are to be parallel to one another. One set of specimens should be tested with the load applied parallel to the grain, and the other set of specimens should be tested with the load applied perpendicular to the grain. The number of test repetitions within a set depends on the desired confidence limits. Only one test per set will be run as part of this laboratory, as its objectives are to demonstrate the techniques and not to develop large robust data sets for engineering design.
2. Measure the cross-sectional dimensions (width and thickness) of each test specimen to the nearest 0.002 in. using a caliper. Measure the total length (in the direction of loading) for the compression specimens. As the specimens may vary slightly in dimensions throughout their length, take several measurements, and record the approximate average for each measured dimension.
3. After setting up the universal testing machine (see first manuscript on this series: Materials Constants), carefully center the specimen on the compression platen and lower the crosshead until a slight load is applied. Use the fine controls to back the load off to as close to zero as possible.
4. Apply the compressive load slowly with a loading rate between 20 psi to 50 psi per second.
5. The compression test may continue for several minutes with the load continually increasing and with significant strain seen in the specimen. Continue the test until a maximum load is obviously reached.
6. Record the maximum load from the screen.
7. Repeat for all specimens, both with specimens parallel and perpendicular to the grain.

Tension Test

1. Obtain dog-bone specimens of three different woods (Southern pine, spruce, and oak for example). One set of specimens should be tested with the load applied parallel to the grain, and the other set of specimens should be tested with the load applied perpendicular to the grain. Note that these are not the specimen type required for ASTM tests on wood, as the intent is to demonstrate tensile behavior and not to develop a database for design.
2. Proceed as normal with the usual tension test machine (see second manuscript on this series: Tensile Tests on Steel).

Bending Test

1. Obtain a 2x4 about 24 in. long of dense Southern pine.
2. Install a four-point bending test apparatus on the universal testing machine (Fig. 1).

Figure 1: Four-point bending apparatus.

3. Start the testing machine and associated software. Make sure the software is set to capture the maximum load and record the loads and crosshead values.
4. Install the 2x4 into the apparatus and lower the upper crosshead until the apparatus just begins to make contact with the wood beam.
5. Apply the load slowly (around 2000 lbs per minute) until the beam fractures (Fig. 2).

Figure 2: Wood beam flexural failure.

6. Record the failure load.