Topic 4- Mechanical properties of materials
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What are the British/European standards for test methods?
ISO
What American group set standard test methods?
American Society for Testing and Materials (ASTM)
How can we measure strain and deformation as a material is stretched?
Using a strain gauge and clamps.
Why is it important to use a strain gauge when testing materials?
Without the strain gauge we would end up measuring the displacement of everything, not just the sample, e.g. grips.
How do we measure stress?
Most commonly using a tensile test with a uniform static load applied.
What are the units for stress?
N/m^2 or N/mm^2
What is the equation for stress? What do each of the symbols stand for?
Ft/Ao. Ft = tensile force. Ao = original area before loading.
What is the difference between tensile strain and lateral strain?
Tensile strain is applied, lateral strain is resulting.
What is the equation for tensile strain?
Extension / original length
What is the equation for lateral strain?
• extension x original length / original width
What is the gauge length?
The length of the material that will be subject to stretching.
Is elastic deformation reversible or non-reversible?
Reversible
What type of materials have a high E (Young’s Modulus)?
Ceramics
Which materials have a low E?
Polymers
How does Young’s Modulus relate to stiffness?
Higher E = more stiff.
What does the slope of a stress-strain graph depend on? (Slope proportional to elastic modulus)
Bond strength of material.
What is E for Aluminium (Al)?
70 GPa
What is E for steel?
210 GPa
What is E for aluminium oxide (Al2O3)? (alumina ceramic)
380 GPa
What is E for Red Oak wood (anisotropic) along the grain and across the grain?
Along the grain: 12 GPa. Across the grain: 0.6 GPa.
What is Poisson’s ratio, v?
The ratio of lateral to axial strains.
What is Poisson’s ratio for metal?
0.33
What is Poisson’s ratio for ceramics?
0.25
What is Poisson’s ratio for polymers?
0.4