LAB 6 COMPRESSION TESTING OF WOOD The goal of this lab is to help provide better understanding of the properties of wood. Four samples will be tested; two for compressive strength with the load parallel to the grains and two with the load perpendicular to the grains. This will enable the calculations of the modulus of elasticity and the maximum strength under compression for both loading parallel and perpendicular to the grain. The influence of grain direction and wood type, as well as failure mechanism can be identified.
1.0 Introduction Introduce the subject in the report and state briefly the purpose and usefulness of the study. Briefly introduce the type of wood (i.e. Oak is a kind of hard wood, pine is a kind of soft wood), the type of tests
2.0 Testing Procedure 2.1 2.1
Details Details of the samples
Briefly introduce the type of wood (i.e. Oak is a kind of hard wood, pine is a kind of soft wood).
Mention briefly what differences can be seen between the
properties of the hard and soft woods (density, surface hardness, etc.).
2.2
Specimen geometry Table 1: Specimen Dimensions
Wood Name
Test Type
Thickness (mm)
Width (mm)
Length (mm)
Compression Parallel to Grain Oak
Compression Perpendicular to Grain Compression Parallel to Grain Pine
Compression Perpendicular to Grain
2.3
Detail of testing equipm ent
Briefly describe the testing equipment & procedure. Photographs or a schematic of the test equipment may aid your description.
3.0 Measured data Describe what constitutes failure for wood under compressive testing. What is the nature of the failure? Mention briefly what differences can be seen between the mechanical properties of the hard and soft woods.
Table 2: Failure Loads
Wood Name
Test Type
Failure Load (kN)
Compression Parallel to Grains Oak
Compression Perpendicular to Grains Compression Parallel to Grains Pine
Compression Perpendicular to Grains
4.0 Discussion Strength is the defined as: σ
max
=
P A
(Equation 1)
Where P is the peak load and A is the cross sectional area of the block. Strain is defined as: ε
c
=
ΔL
L
(Equation 2)
Were ∆L is the change in length of the specimen and L is the length (or height). 4.1
Variability of Material
Plot the a histogram of compressive strength for all the four loading cases. Discuss the variability in the mechanical strength of wood. The tested samples were clear timber. What would happen to the variability if defects such as knots were included? How do Civil engineers deal with this variability? Table 3 describes the variability in strength of the wood.
Table 3: Variability in Wood
Wood
Oak
Pine
4.2
Test
Average Strength
Standard Deviation
Compression Parallel to Grains Compression Perpendicular to Grains Compression Parallel to Grains Compression Perpendicular to Grains
Stress vs. Strain
Individual engineering stress-strain curves are required for each specimen. In addition one stress strain plot off all the samples is required to clearly show the difference between their mechanical properties. Discuss any significant points / behaviour observed in the loading of the samples. 4.3
Mechanic al pro perties
Describe the calculation of mechanical properties (For more details refer to mechanical properties section of Tensile Testing of Metals Lab)
Table 4: Mechanical Properties
Wood Name
Test Type
Specimen No.
Compression Parallel to Grains
Oak 1
Compression Perpendicular to Grains
Oak 2
Compression Parallel to Grains
Pine 1
Compression Perpendicular to Grains
Pine 2
Strength (MPa)
Failure ε
E (GPa)
Oak
Pine
4.4
Descr ipti on of Specimen Failur e
Include a sketch or picture that shows the observed failure in the lab. Why type of failures were witnessed?
Describe the mechanics of the failures, highlighting
the differences between the parallel and perpendicular tests. 4.5
Sources of Error
Define the sources of Error this testing procedure
5.0 Concluding Remarks Summarize the findings. Note that the conclusions should satisfy each objective, stated or implicit, in the Introduction. There must not be any new material.
6.0 References Document the references considered in preparing the report.
