Poisson’s ratio is one of the material properties describing ability of the material to accommodate deformations. Thus, when a material is squeezed in one direction it will try to expand in other direction when unconstrained. Equally when the material is stretched it will contract in other directions. Poisson’s ratio relates various moduli of materials. Thus, Young’s modulus or elastic modulus, E is related to shear modulus G through a relationship E=2G (1+Γ), where n is Poisson’s ratio. Equally bulk modulus, B is related to Elastic or Young’s modulus through a relationship B=E / 3(1-2Γ). Poisson’s ratio varies from 0 to 0.5 with most metals and alloys around 0.33. Materials with some very low passion’s ratio are concretes, cork, wood etc. Generally, Poisson’s ratio is measured in the elastic range of a simple tensile test.
Application and Influence
Just like several mechanical properties like Yield, ultimate strength, etc., Poisson ratio helps in the design of structures. It helps to understand secondary stresses that will develop during service. Thus, for example in high pressure fluid transport through pipes, when pressure pulses arise the hoop stress that develops will induce secondary stresses in longitudinal direction which will force the pipes to contract. If these pipes have welded sections, sometimes the weldment may fail due to this contraction. Another situation where Poisson’s effect may impact is in Geological deformations like earthquakes, etc. Materials with high Poisson’s ratio will contract a lot compare to materials with low Poisson’s ratio.
Capability – At Touchstone Testing Laboratory, we have capability to measure Poisson’s ratio. Typically, we measure Poisson’s ratio in tension mode. We use biaxial strain gage or dual extensometer to measure the deformation. Generally, we measure Poisson’s ratio at ambient conditions like room temperature air. If the customer requires we can measure Poison’s ratio in non-ambient conditions like low temperatures or high temperatures.
Tensile testing helps to determine basic load bearing capabilities of materials under tension. These properties are used in engineering and design of components and structures. Typical examples where these properties are used are design of guy cables that support bridge structure, wind turbines, aircraft wings and fuselage structures, etc. One can get several material parameters… Continue Reading
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