Are Composites of Wood Stronger than Solid Wood?
To determine if a wood composite, which is made of a combination of materials that have been saturated with a resin or glue, has greater torsional resistance (twisting) and drop resistance (bending) than a compa
- 2½-by-2-feet (76-by-61-cm) panel of wood (for test platform)
- metal workshop vise with clamps (to support test bars)
- assorted screws nuts, and bolts (to fasten the metal workshop horse to the test platform)
- round disk (calibrated in degrees) with attached 4-inch (7.6-cm) arm
- wire fishing line
- spring scale
- several ¼-pound (112-g) lead fishing weights
- 10 composite bars (1 foot (30 cm) long by 3/8 inch (1 cm) square)
- 10 solid wood bars (1 foot (30 cm) long by 3/8 inch (1 cm) square)
Experiment 1: Torsional Resistance (Twisting)
Weight will be applied to the wire fishing line from the 4-inch arm at a setting of 4 pounds (1.8 kg) on the attached spring scale. This will move the arrow on the 4-inch arm to measure the degree of twist on the round disk through which the test sample passes (see diagram). This will be done to both the composite and solid test bars.
- Set up the test platform as shown in the diagram for the torsional resistance test. In general, this means that a test bar will be held between two clamps supported by a metal workshop vise. One end of the test bar will pass through a rotating round disk that will measure the arc of twist (in degrees) on the test bar. Attached to the side of the round disk is a 4-inch arm with a hooked wire line that will suspend a spring scale. Various lead fishing weights will be hooked onto the spring scale which will cause the 4-inch arm to move downward while rotating the round disk. This will cause the test bar to twist.
- Place the composite bar in the holding apparatus
- Attach the spring scale to the 4-inch arm. This will automatically place a factor of 4:1 on the scale
- Apply force to the wire line by adding weights to the spring scale at a predetermined weight of 4 pounds (1.8 kg). Now, measure the arc of twist on the scaled round disk
- Continue to increase the weight at increments of 1 pound (0.45 kg), and measure the arc of twist until the composite wood bar snaps.
- Remove the composite bar, and repeat steps 2 through 5 with four of the composite bars and five of the solid wood bars
Experiment 2: Drop Resistance (Bending)
The test bar will be held at one end, and a predetermined amount of weight will be applied at the opposite end, by means of an attached spring scale. The amount of drop resistance will be measured in thousandths of an inch or millimeters.
- Set up the test platform for the drop resistance test This can be done by removing the side of the vise with the attached round disk and 4-inch arm.
- Place a composite bar in the remaining holding apparatus and attach the wire line to the opposite end of the bar.
- Hook the spring scale to the wire line.
- Apply weight through the spring scale at a predetermined weight setting, and measure the drop of the bar with a ruler.
- Continue to increase the weight by ¼-pound (112-g) increments, and measure how far the bar drops until it snaps.
- Remove the composite bar, and repeat steps 2 through 5 with the remaining composite bars and the remaining solid wood bars.
- Compare the amounts of weight that were needed to move each bar one degree mark when torsional resistance was tested. Which bar proved to be more resistant?
- Compare the amounts of weight that were needed to snap each bar when drop resistance was tested. Which bar proved to be more resistant?
- Which type of bar continued to show resistance even after the others had reached their peak resistance?
- From your experimental results, which bar do you conclude is better at resisting force?
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