Chapter 22
Axioms of the Inelastic Body Model
22.1 Deformational Softening
We have already said that (p. 317) the yield stress of materials studied here
substantially depends on the loading rate and it goes down when the rate decreases.
The lowest value of the yield stress is called the yield stress (τ y ). It is believed that
the elastic limit is defined only by the type of the stressed state and, unlike the stress
yield stress, does not depend on the loading rate.
22.2 Initial Shear Resistance
According to Cottrell’s [1] representations of the picking up of dislocations from
blocking atmospheres, we can suggest the following mechanism of deformational
softening. In case stress exceeds the elastic limit, some dislocations are liberated from Cottrell clouds. Other dislocations can be displaced together with the
surrounding atmosphere. Successive liberation of dislocations from atmospheres
leads to changes in the structure and, consequently, mechanical properties of the
material. When the yield stress occurs, liberated dislocations start moving. Since
displacements of free dislocations require much lower stress than for smoothening
of dislocations from blocking atmospheres, the start of plastic yield is accompanied
by the drop of material resistance to deformation. This results in the following.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
V. Molotnikov, A. Molotnikova, Theory of Elasticity and Plasticity,
https://doi.org/10.1007/978-3-030-66622-4_22
321
Axioms of the Inelastic Body Model
22.1 Deformational Softening
We have already said that (p. 317) the yield stress of materials studied here
substantially depends on the loading rate and it goes down when the rate decreases.
The lowest value of the yield stress is called the yield stress (τ y ). It is believed that
the elastic limit is defined only by the type of the stressed state and, unlike the stress
yield stress, does not depend on the loading rate.
22.2 Initial Shear Resistance
According to Cottrell’s [1] representations of the picking up of dislocations from
blocking atmospheres, we can suggest the following mechanism of deformational
softening. In case stress exceeds the elastic limit, some dislocations are liberated from Cottrell clouds. Other dislocations can be displaced together with the
surrounding atmosphere. Successive liberation of dislocations from atmospheres
leads to changes in the structure and, consequently, mechanical properties of the
material. When the yield stress occurs, liberated dislocations start moving. Since
displacements of free dislocations require much lower stress than for smoothening
of dislocations from blocking atmospheres, the start of plastic yield is accompanied
by the drop of material resistance to deformation. This results in the following.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
V. Molotnikov, A. Molotnikova, Theory of Elasticity and Plasticity,
https://doi.org/10.1007/978-3-030-66622-4_22
321