TESTS FOR STRENGTH PROPERTIES

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