Purpose
Timber is one of the most of widely used traditional structural material. The properties of timber is vary according to direction of grain. Timber are subjected to axial load and bending action.
Objective
1. To understand test procedure.
2. To determine important properties.
Reference
I.S 1708
Apparatus
1. Universal testing machine in bending attachment.
2. Scale and vernier caliper.
Theory
The effect of transfer load on the beam is to cause deflection at any section of the beam. Bending moment and shear force are developed. Bending stress, shear stress can be easily calculated, when the beam is subjected to central point load. Various characterstics properties will be determined from the following equation.
1. Fiber stress at the limit of proportionality = 3wl / 2bd2
2. Modulus of elasticity = WL3/4bd3 x δ
Where,
W= Load at limit of proportionality
L = Span of test specimen
b = Breath of test specimen
d = Depth of test specimen
δ = Deflection at limit of proportionality
Diagram
Flexural Testing Machine
Procedure
Note the range of the load. Load gauge of the universal testing machine. Measure the cross sectional diameter of specimen. Adjust the required span and placed it roller supports. Fix the dial gauge below the specimen at the center of the span. Apply the load at a constant rate and required deflection. Beyond elastic limit record the deflection by scale.
Observation
1. Breadth of specimen b = 38 mm
2. Depth of specimen d = 43 mm
3. Span of the beam A = 270 mm
4. Load applied W = 1600 kg
Calculation
1. Maximum bending moment = WL / 4 = 108 x 103 N/mm2
2. Bending equation =M/I = δ/Y
3. Moment of inertia = Y = bd3/12 = 251.19 x 103
4. Y = d/2 = distance of exterim fiber from NA = 21.5 mm
Hence, the modulus of rapture of given timber specimen =
Conclusion
1. Maximum bending moment = WL / 4
= 1600 x 270 / 4
= 108000 kg/mm2
2. Moment of inertia = bd3 / 12
= 38 x (43)3/12
= 251.77 x 103 kg/mm2
3. Bearing equation = M/I = 0.428
4. Y = d/2 = 43/2 = 21.5 mm
Δ = (M/I ) x Y = 0.428 x 21.5
= 9.202 kg/mm2
Hence, modulus repreture of given timber is 9.202 kg/mm2
Conclusion
As it crack out. The crack starts from bottom and watch increasing towards support and bending was sagging. It is a brittle metal and weak in tension. It is not breaking in perpendicular to the plane.
Fibre stress = 3wl / 2bd2
= 3 x 1600 x 270 / 2 x 38 x (43)2
= 9.22 kg/mm2
Result
The fiber stress at a line of perpendicular is find out 9.22 kg/mm2
