Recently, I have read a book and I have found these two terms: modulus of elasticity in tension and Young's modulus. For example, for a gasket material, the modulus of elasticity in tension is 2 MPa while the Young's modulus is 100 MPa. So, now I am confused because in the past I thought that there is no difference between these two moduli. I thought that they are two terms for the same property.
This recent information generated a big question in my mind: how can we measure these two moduli?
Hi Aimen,
Yes, there is no difference between them, but...
The Young modulus (Y) is the relationship between stress (s) and strain (e) at very low deformations and in a static experimental condition (after relaxation).
The modulus of elasticity (E) is basically the same but it can be determined in a dynamic way (without time enough to let relax the sample).
So, the Young modulus should be equal to the elastic modulus at strain rates equal to zero [Y = E(de/dt = 0)]. That means that at high strain rates (de/dt >> 0), the elastic modulus is bigger than the Young modulus because the former incorporates viscosity factors (E’’ > 0) which increase the value.
Thus, the Young modulus is lower than the elastic modulus in tension when the sample doesn't relax. E^2 = (E')^2 + (E'')^2. The Young modulus is related to the storage elastic modulus of the sample Y = E', but many people assume Y = E which is wrong.
SALUT!
Tony
There are no differences in therminological sence. Young modulus (by tension, compression, bending) is modulus of elasticity corresponding these stress states.
Hi Aimen,
Yes, there is no difference between them, but...
The Young modulus (Y) is the relationship between stress (s) and strain (e) at very low deformations and in a static experimental condition (after relaxation).
The modulus of elasticity (E) is basically the same but it can be determined in a dynamic way (without time enough to let relax the sample).
So, the Young modulus should be equal to the elastic modulus at strain rates equal to zero [Y = E(de/dt = 0)]. That means that at high strain rates (de/dt >> 0), the elastic modulus is bigger than the Young modulus because the former incorporates viscosity factors (E’’ > 0) which increase the value.
Thus, the Young modulus is lower than the elastic modulus in tension when the sample doesn't relax. E^2 = (E')^2 + (E'')^2. The Young modulus is related to the storage elastic modulus of the sample Y = E', but many people assume Y = E which is wrong.
SALUT!
Tony
Hi,
I am confirming the explanations by Antoni Sanchez-Ferrer . Cyclic loadings which are applied on natural materials (wood) seriesly is an effecting factor.
Thank you very much for all who participated in answering my question.
So, does the method of measuring the modulus of elasticity in tension differ than the method of measuring Young's modulus? How can we measure the modulus of elasticity in tension and the Young's modulus?
Note: As I mentioned in my first question, the Young's modulus of a gasket material is 100 MPa and the modulus of elasticity in tension is 2 MPa. The surprise is that the Young's modulus is greater than the modulus of elasticity in tension which is in contrast to what mentioned in the answer of Tony!
Dear Tony
There are a tensile testing machine and a hardness measuring device for soft materials in our lab. Do you prefer a certain technique which you think is better than the others?
Aimen
Hi Aimen,
You have to perform uniaxial stretching on the sample.
1) do small deformations
2) let relax the sample and the value coming from the plateau is the value to be considered (see the attached figure)
3) repeat the process several times until getting enough points for fitting a straight line
For the evaluation of E = E' + iE", you might need a DMA equipment and work out the elastic components at different frequencies.
SALUT!
Tony
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