Explanation of the tests and values

1- Modulus of rupture, or Bend Strength

Units: lbf/in² = pounds of force per square inch. MPa = Mega Pascal Mega is one million, Pascal is a unit of force defined as one newton per square meter. A newton, in the metric system, is how much force is required to make a mass of one kilogram accelerate at a rate of one metre per second per second.

Flexural strength, also known as modulus of rupture, or bend strength, or transverse rupture strength is a material property, defined as the stress in a material just before it yields in a flexure test.

A standard size sample is placed with supports at both ends and a force is applied in the middle. The sample gradually bends (flexes) as the force is applied and eventually breaks. The force is measured at the point when the sample breaks.

It is not an absolute test because results can vary. Some woods, for example, might break later if the force was applied more gradually. The test is useful as a comparison between woods.

2- Modulus of elasticity (stiffness)

Units: lbf/in² = pounds of force per square inch. GPa = Giga Pascal Giga is billion (10⁹ or 1,000,000,000). Pascal is a unit of force defined as one newton per square meter. A newton, in the metric system, is how much force is required to make a mass of one kilogram accelerate at a rate of one metre per second squared.

Modulus of elasticity also known as Yong's Modulus measures how stiff a sample is. It is expressed as a ratio of stress over strain. In other words, how much something bends (strain) under a given load (the stress). The higher the number, the stiffer the material.

Don't worry too much about the units. They are mostly useful to compare between the different woods.

Here is my page explaining in greater detail, Yong's Modulus in relation to carbon fibre. Carbon fibre has a yong's modulus of 181 GP compared to Western red cedar which has 7.6 GP.

3- Janka Hardness

Units: lbf = pounds of force. N = Newton, A newton, in the metric system, is how much force is required to make a mass of one kilogram go faster at a rate of one metre per second squared.

The Janka Hardness Test measures the resistance of a sample of wood to denting and wear. It measures the force required to embed an 11.28 mm (.444 in) steel ball into wood to half the ball's diameter. This method leaves an indentation. Commonly used to compare woods that are suitable for use as flooring.

The higher the number, the harder the wood is to dent. BALSA requires 100 pounds of force (lbf) while SUGAR MAPLE requires 1,450 lbf to embed the steel ball halfway in the sample.

4- Average Dried Weight

units: lbs/ft³ = pounds per cubic foot. kg/m³ = kilograms per Metre cubed.

In doing the measurements for the average dried weight, the moisture content is assumed to be at 12%.

5- Shrinkage

Radial Shrinkage refers to shrinkage across the growth rings. In other words shrinkage of the radius of a log.

Tangential shrinkage is shrinkage in the direction of the growth rings.

Volumetric shrinkage is a combination of shrinkage in all directions.

longitudinal shrinkage is often not reported because it is not usually significant. Wood shrinks little in the length of a plank.

Generally, the greatest shrinkage will occur in the direction tangential to the growth rings. Wood shrinks about half of that tangentially, that is radially from the centre to the outside across the growth rings. Longitudinal shrinkage along the grain is virtually negligible in small pieces.

T/R is the ratio of Tangential over Radial shrinkage and the larger the number the less stable the wood. Less stability implies greater movement, warpage and cracking.

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