Hi, experts.
My understanding is that a plastic strain increment (△ε_p) can never be negative (it can be either positive or zero), as long as the material conforms to the consistency condition.
That is to say, ε_p for t(timestep)=n+1 is always larger than that for timestep=n.
This is because the plastic deformation is permanent; the plastic strain is accumulated as the deformation proceeds and not recovered after unloading.
Then I am wondering if this is the case for an elastic strain increment (△ε_e) as well.
My question is,
Is an elastic strain increment always non-negative? or can it be negative?
As of now, I assume that if the total strain(ε = ε_e + ε_p) for t=n+1 is smaller than that for t=n, the negative elastic strain increment is possible. Am I right?
Please leave comments if anyone knows the answer.
Thank you in advance!
Your understanding regarding plastic strain increment (Δε_p) is correct. In the context of plastic deformation, the plastic strain increment is always non-negative (Δε_p ≥ 0) because plastic deformation is permanent, and the material undergoes irreversible changes during plastic flow. Plastic strain accumulates over time and is not recovered after unloading.
Regarding the elastic strain increment (Δε_e), it is important to understand the difference between elastic and plastic deformation. Elastic deformation is reversible, and the material returns to its original shape when the load is removed. In an elastic material, the strain is directly proportional to the stress applied, following Hooke's law.
For an elastic material, the elastic strain increment can indeed be negative (Δε_e < 0) under certain conditions. It implies that the material is experiencing compressive strain, and when the load is removed, it will spring back to its original shape. In other words, during unloading, the material is undergoing elastic recovery and reducing the strain.
In summary, for an elastic material, the elastic strain increment can be positive or negative depending on the loading conditions. On the other hand, for a plastic material, the plastic strain increment is always non-negative, and it accumulates over time as plastic deformation is irreversible.
Kristaq Hazizi
Thank you for your detailed answers. It really helped me grasp the concept of elastic and plastic deformation.
Yet I have a new question I came up with reading your answer: what exactly is a 'plastic material'? Can't any material undergo purely plastic deformation only, without elastic deformation? Plastic deformation commences when elastic deformation passes the threshold(=yield point) and yielding occurs, which means plastic deformation is always preceded by elastic deformation. In this sense, I think 'elasto-plastic' material is a more accurate term. I am curious what is meant by 'plastic material'. I googled it but failed to find a satisfactory answer. I hope you give one.
Thank you in advance! I appreciated your earlier answer again.
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