TESTING OF WOOD
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Standard tests are conducted on timber specimens to reliably compare different timber species. Tests are done using small, standardized samples that are collected from various locations and tested under both green and dry conditions. Mechanical and physical properties are then evaluated, including strength in compression, tension, and shear. The results show strength levels for various species, with some being exceptionally or extremely strong, while others are somewhat weak or very weak. Important tests to determine strength include tension, bending, compression, indentation, shear, and nail and screw pulling tests.
TESTING OF WOOD
- 1. STANDARD TESTS ON TIMBER SPECIMENS
- 2. Testing small clear specimens, also known as standard specimens: Most reliable comparison of different species Expenses involved in collection of material, preparation of specimens and testing should be as low as possible without prejudice.
- 3. Internationally recognized standard size of specimens cross section INDIA: 5 cm × 5 cm EUROPE: 2 cm × 2 cm In India, 11 mechanical tests and 6 physical tests are carried out as a routine on all species of timber using samples from different localities.
- 4. Various species of timber or timber of same species are collected from as many localities as possible When logs are received in the laboratory, their condition is recorded; photographs are taken and the logs are marked in the cross section to convert the scantlings or stricks for obtaining specimens for the various tests in green and dry conditions.
- 6. All the even numbered stricks from the upper half of the log and the odd numbered stricks from the lower half of the log are sorted out for testing in green condition; the rest will be tested in the air dry or kiln dry condition as the case may be. All the stricks to be tested under one required condition bundled together are called composite bolts.
- 7. STRENGTH The strength of wood is its ability to resist external forces tending to alter its shape. These forces depending on the direction of application, may be compressive, tensile or shearing, hence there is the necessity of qualifying the strength- in compression, tension or shear. A timber specimen strong in one respect may not be equally strong in another, other things being equal, strength varies with density, conditions of seasoning, soundness and absence or presence of defects.
- 8. The results of laboratory tests have shown the strength properties of some of the timbers as under: Exceptionally strong: Mesua ferrea, Schleichera trijuga, Shorea robusta, Xylia dolabriformis. Extremely strong: Anogeissus acuminata, Acacia nilotica, Grewia tiliaefolia, Terminalia alata. Very strong: Tectona gradis, Anogeissus latifolia, Termnalia belerica. Strong: Dalbergia latifolia and D.sissoo, Syzygium cuminii, Albizia lebbeck and A.procera. Moderately strong: Adina cordifolia, Cedrus deodara, Cederla serrata, Chukrasia tabularis, Mangifera indica. Somewhat weak: Abies pindrow, Bischofia javanica, Pinus roxburgii, Holoptelia integrifolia. Weak: Picea smithiana, Cedrela toona, Pinus wallichiana, Lannea cormandelica, Boswellia serrata. Very weak: Hymenodictyon excelsum, Bombax ceiba, Cryptomeria japonica.
- 9. IMPORTANT TESTS TO DETERMINE THE STRENGTH OF WOOD Tension STATICBENDING COMPRESSION INDENTATIONTEST Shear Brittleness test Nailand screwpulling test
- 12. Tensile modulus of elasticity (kN/mm2) Modulus of elasticity = Where, P = Load at limit of proportionality in Newton (N) L = Gauge length of the specimen in mm ∆ = Displacement at limit of proportionality in mm A = Cross- sectional area in mm2
- 13. a): Sample before testing b) Sample after testing Tensile Strength Testing Load direction
- 15. Bending modulus of elasticity (kN/mm2) Modulus of elasticity = Where, P = Load at limit of proportionality in Newton (N) L = Gauge length of the specimen in mm ∆ = Displacement at limit of proportionality in mm b = breadth of the specimen in mm h = height/depth of the specimen in mm
- 16. Bending modulus of rupture (kN/mm2) MOR= Where, P = Maximum load (kN) L = Length of test piece (mm) b = Breadth of test piece (mm) h = Thickness of test piece (mm)
- 17. a) Sample before testing b) Sample after testing Bending Strength Testing Load direction
- 19. Compression Modulus of elasticity (kN/mm2) Modulus of elasticity = Where, P = Load at limit of proportionality in Newton (N) L = Gauge length of the specimen in mm ∆ = Displacement at limit of proportionality in mm A = Cross- sectional area in mm2
- 20. Grain direction Load directio n • (a)Sample before testing compression parallel to grain strength (b) Sample after testing compression parallel to grain strength • (c) Sample before testing compression perpendicular to grain strength (d) Sample after testing compression perpendicular to grain strength a c b d