Differences in Young Modulus -> Tensile/Compressive tests

In summary, the conversation discusses the different values of Young Modulus obtained through compressive and tensile tests on PDMS samples, with the compressive test resulting in a modulus twice as big as the tensile test. It is suggested that this difference may be due to elastic hysteresis and the effects of viscoelasticity at different strain rates. It is also mentioned that a higher strain rate compression test may result in a closer comparison to the Young's modulus from the tensile test. The conversation ends with a recommendation to visit a website for information on running tensile and compression tests.
  • #1
Hello everybody. I've measured the Young Modulus of PDMS samples both in compression and in tension. From compressive tests I get a Modulus twice as big as the one I get from tensile tests.

Is it normal to get two different values for Young Modulus using tensile or compressive tests? Do you think this behaviour is due to differences in molecular interactions? (eg: you need more energy to bring molecules together than to separate them (!?))

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  • #3
The Young's modulus in both compression and tension tests should be theoretically the same but only at infinitesimal strain rates. As the strain rate increases, the effects of the viscoelasticity of the material also increase. If i were to guess, I would say that your tensile test is being performed at a much higher strain rate than the compression tests.

Since you are pulling your tensile test at higher strain rates, you will get effects from the viscoelasticity of your Polydimethylsiloxane. The loss from viscoelasticity will result in a reduced Young's modulus value. The compression test is run at a much slower rate of speed, so you will not see the viscoelastic effects as much. If you were to run the compression test at the same rate of speed as say the tensile test, you would compress the material so quickly that it would squish out of the compression platens and look highly viscous. A higher strain rate compression test would result in a closer comparison to the Young's modulus from the tensile test.

If you have any questions on running tensile or compression test procedures with a universal testing machine. Check us out at www.universalgripco.com

1. What is Young's Modulus?

Young's Modulus, also known as the modulus of elasticity, is a measure of the stiffness or elasticity of a material. It is defined as the ratio of stress (force per unit area) to strain (change in length per unit length) when a material is subjected to tensile or compressive forces.

2. What is the difference between tensile and compressive tests?

Tensile tests involve pulling a material apart, while compressive tests involve pushing a material together. Both tests measure the response of a material to external forces and help determine its Young's Modulus.

3. How are Young's Modulus values affected by the type of test (tensile vs. compressive)?

The Young's Modulus values obtained from tensile and compressive tests can vary, as the material's response to these forces can differ. In general, most materials have a higher Young's Modulus in tension than in compression.

4. What factors can influence Young's Modulus during testing?

Young's Modulus can be affected by various factors such as temperature, strain rate, and the presence of defects or imperfections in the material. These factors can alter the material's response to external forces and thus affect its Young's Modulus.

5. How is Young's Modulus used in engineering and materials science?

Young's Modulus is a crucial parameter in the design and analysis of structures and materials. It helps engineers and scientists understand the behavior of materials under different loading conditions and allows for the selection of appropriate materials for specific applications.

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