The Janka hardness test (; ), created by Austrian-born American researcher Gabriel Janka (1864–1932), measures the resistance of a sample of wood to denting and wear. It measures the force required to embed an steel ball halfway into a sample of wood. (The diameter was chosen to produce a circle with an area of 100 square millimeters ne square centimeter) A common use of Janka hardness ratings is to determine whether a species is suitable for use as

flooring Flooring is the general term for a permanent covering of a floor, or for the work of installing such a floor covering. Floor covering is a term to generically describe any finish material applied over a floor structure to provide a walking surface ...

. For hardwood flooring, the test usually requires a sample with a thickness of at least 6–8 mm, and the most commonly used test is the ASTM D1037. When testing wood in lumber form, the Janka test is always carried out on wood from the tree trunk (known as the heartwood), and the standard sample (according to ASTM D143) is at 12% moisture content and clear of knots. The hardness of wood varies with the direction of the

wood grain Wood grain is the longitudinal arrangement of wood fibers or the pattern resulting from such an arrangement. Definition and meanings R. Bruce Hoadley wrote that ''grain'' is a "confusingly versatile term" with numerous different uses, includin ...

. Testing on the surface of a plank, perpendicular to the grain, is said to be of "side hardness". Testing the cut surface of a stump is called a test of "end hardness". Side hardness may be further divided into "radial hardness" and "tangential hardness", although the differences are minor and often neglected. The results are stated in various ways, leading to confusion, especially when the actual units employed are often not attached. The resulting measure is always one of

force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a ...

. In the United States, the measurement is in pounds-force (lbf). In Sweden it is in

kilograms-force The kilogram-force (kgf or kgF), or kilopond (kp, from la, pondus, lit=weight), is a non-standard gravitational metric unit of force. It does not comply with the International System of Units (SI) and is deprecated for most uses. The kilogram-f ...

(kgf), and in Australia, either in newtons (N) or kilonewtons (kN). This confusion is greatest when the results are treated as units, for example "660 Janka". The Janka hardness test results tabulated below followed

ASTM ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...

D 1037-12 testing methods. Lumber stocks tested range from 1" to 2" thick. The tabulated Janka hardness numbers are an average. There is a standard deviation associated with each species, but these values are not given. No testing was done on actual flooring. Other factors affect how flooring performs: the type of core for engineered floorings, such as pine, HDF, poplar, oak, or birch; grain direction and thickness; floor or top wear surface, etc. The chart is not to be considered an absolute; it is meant to help people understand which woods are harder than others.

Typical Janka hardness values

References

External links

Janka Hardness Scale For Wood – Side Hardness Chart of Some Woods

USDA – Wood Handbook – Wood as an Engineering Material

USDA – Janka Hardness Using Nonstandard Specimens
{{DEFAULTSORT:Janka Hardness Test Woodworking Woodcarving Wood Hardness tests