I was going through this website :https://www.tf.uni-kiel.de/matwis/amat/iss/index.html where it answered a question: Why is the maximum of the (nominal) stress-strain curve and the beginning of necking related? So for explaining the relation it stated that curves taken at different strain rates may not be very different, you always need somewhat larger stresses at higher strain rates to achieve the same strain. Why do you need somewhat larger stresses at higher strain rates to achieve the same strain achieved in lower strain rate?. Can someone give an explanation for such behaviour?
Dislocations have limited velocities. At slow rates of strain, materials can flow and creep and achieve large deformations without great force. Think of geology, glaciers, salt crystals, etcetera.
And it may be better to think of the forces and stresses as the independent variable, as the cause of the deformation. The convention of putting the strain on the horizontal axis may cause misunderstandings.