Compression Test
Compression testing is one method used to evaluate the strength of bamboo, particularly its resistance to crushing forces. This test involves applying a compressive force to a sample of bamboo until it reaches its maximum stress, and then measuring the resulting deformation. By analyzing the data collected from compression tests, engineers and researchers can gain insights into the structural behavior of bamboo and make informed decisions about its use in various applications.
Aim:
This test is performed to find the maximum compressive stresses, compression modulus of elasticity and stress-strain curve in the bamboo test specimen.
Dimensions:
ISO 22157 (2019) specifies the dimensions for a compression specimen as < outer diameter (D) or < 10 times outer thickness (10δ). Placement of the strain gauges should be parallel to the loading axis placed diametrically opposite to one another at mid-height of the specimen.
Key:
δ culm wall thickness
D outer diameter of bamboo culm
F load
L length of specimen (L is the lesser of D or 10δ. If D<20 mm, L = 2D)
1 upper loading plate
2 intermediate layer
3 bamboo specimen
4 intermediate layer
5 lower loading platen
Loading Rate:
The tests were done on Bambusa Tulda and Psudoxytenanthera (Madhavi) . It was found that both these species of bamboos are structurally very similar. The time for these tests is to be 300 +/- 120 seconds. Having found the strength of Bambusa Tulda to be ~ 68 MPa from ISO 22175 (2019), and checking the c/s of the gauge of specimens, a speed on 0.002 mm/s was set for the test.
σ_ult = 68 MPa
c/s = π/4 × (outer diamter²-inner diameter²) = 1289.48 mm²
force = 68 × 1289.48 = 87.7 kN
E = 10000 MPa
From that, ε=0.0068 mm/mm
For a 90 mm long specimen, elongation would be=0.6 mm
For 300 seconds, test speed=0.002 mm/sec
These calculations can be used to find the test speed for different species of bamboo.
Number of Tests :
Code specifies to try at least 3 samples with node at the centre and 3 without node, we plan to do total 6 tests.
Expression of results:
The modulus of elasticity in tension parallel to the fibres Ec,0 shall be calculated as the secant between the stress and strain pairs at 20% and 60% of Ultimate load, F_ult.
The tensile strength of the specimen will be averaged for the total number of tests and noted down in N/mm² or MPa.
The stress-strain curve will be plot and noted. The strain will be on x-axis while stress will be on y-axis.
