Dynamic Loading of Plastics - What are Storage Modulus and Loss Modulus? Viscoelastic damping, DMT?
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- เผยแพร่เมื่อ 16 มี.ค. 2020
- A polymer is a visco-elastic materials. Which means, its elastic property is time dependent. Simply, the elastic modulus of a polymer will be different if the rate of loading is changed from very low to very. At high rate of loading, the elastic modulus measured will be high and vice versa. This is because a polymer always carries viscous behaviour along with the elastic nature.
Another important effect of visco-elastic behaviour can be seen when there is dynamic loading, that is, the load is continuously changing from low to high and then to low. Dynamic Loading of plastics (viscoelastic materials) gives rise to a phase lag between the stress and the strain. Therefore, the complex modulus of a viscoelastic materials is defined by two terms - Storage Modulus and Loss Modulus. Storage modulus is the modulus of the polymer that corresponds to the true elastic recovery of the materials. Loss modulus is the modulus term that is not going to be recovered and in fact lost in viscous energy dissipation.
Dynamic Mechanical Test (DMT) can be used to characterize a polymer for its many properties such as creep, stress-relaxation, glass transition temperature, dynamic stress-strain etc. Applications of viscoelastic materials include vibration control, shock absorbance, sound proofing, earthquake proofing, prevention of fatigue failure due to vibration etc.
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I'm a polymer engineering student and i want to say thank you for this video. It was great and I learned a lot from you❤️ thank you very much sir
a great way to explain the concepts of complex modulus for visco-elastic materials.
👍
Great video. Explained the concepts pretty well.
Thanks!👍
Very well explained, many thanks!
You are welcome!👍
Sir, and this I can say is very clearly explained lecture on TH-cam.
Thanks a lot!👍
Super and clear explication
Thank you so much
👍
Hello,
Thank you for the detailed video. Could you also explain how storage modulus is related to Young's modulus, if any? I have seen people using these alternatively. But these are two different properties. Isnt it?
Briefly storage modulus is actually the elastic modulus part and hence we can say Young's modulus. The word storage is used because it means the elastic energy is stored and can be recovered upon release of stress. The loss modulus is the part of energy that is lost due to viscous flow within the material. It is called loss modulus because that part of energy is lost in heat and other dissipative work.
Thanks, that's helped a lot. By the way, is that a textbook or notes in your video? Could you share this? Thanks.
A very good reference book is Plastics Engineering by R J Crawford. ✔
The thickness of silly putty will be taken into consideration...? Is the thickness of all the materials are same...?
Thanks for the thought. Yes, the thickness of the layer is important as there will be substrate effect if the thickness of silly putty is not sufficient. However, in the present case, the conclusion will not vary at all.
If we are going to determine the property of the materials (e.g. the silly putty) then the thickness should be sufficient to avoid the substrate (granite in the present case) effect. There is a test know as Rebound test to measure the resilience of rubbers. You might explore the ASTM standard for rebound type of tests.
Sir, I have doubt regarding Elastic Modulus E1 and E2. In expressions there is no time term, so is this Elastic moduli are constant for whole life(long term response)?
This data is not looked at like the creep data or stress relaxation data. Here the stress application is changing in a periodic manner. Hence the time factor is present, and the response of the material is in response to this time factor which is in the form of angular speed or frequency of the stress change. We can say that the response of the material measured here is only short-term that means how it is behaving now. If we test the same polymer after a year, for example, with the same type of stress profile and frequency, the values of E1 and E2 would be different than what they are today.
Hola muchas gracias por la explicación !!!. me podría moestrar el libro en el cual se enseña toda esta Unidad? Desde Muchas gracias,
1. Jones and Ashby, Engineering Materials 2: An introduction to Microstructure and Processing, 4th Ed., Butterworth-Heinemann, 2012.
2. Plastics Engineering by R J Crawford
In nanocomposite what we need great value of storage modules ?
Higher the storage modulus, stiffer the material and less of damping property.👍
@@engineeringmaterials-tribo5142 thanks.
i wanna ask you about a kind of smart materials known as shape memory polymers ,Shape memory polymers (SMPs) offer a unique ability to undergo a substantial shape
deformation and subsequently recover the original shape when exposed to a particular
external stimulus(like temperature ) .my question is how i can model them by FEM (abaqus) thanks in advance Sir.
Thanks for the question. I am not in the FEA field and hence I asked someone is in the field of FEA. According to him shape memory alloys can be modeled and below are the references.
www.sciencedirect.com/science/article/pii/S2590048X19300159
slidelegend.com/advanced-shape-memory-alloy-material-models-ozen-engineering_59c2b6f01723dd5342dce656.html
Modeling of SMP is possible but will require lot more work.
I hope the above helps. ✔
Sir can you please share the pdf that you used in this video...
Thanks for your interest. I wish I could but very sorry I am unable to send the pdf.✔
@@engineeringmaterials-tribo5142 can you scan it and send through Google drive