considered. The material for the research was the
picabur body, which is produced by extrusion
stamping from St3 steel at Geoburtechnica.
3 RESULTS AND DISCUSSION
The method is based on the theory of plastic flow,
since it allows one to determine the kinematic, stress
and deformation states at any point in the zone of
plastic deformation, and take into account anisotropy,
non-stationarity and the history of deformation. The
following basic assumptions are used: the material is
considered rigid-plastic, and strain or rate hardening
is taken into account by the average value of the yield
stress over the deformation zone; Contact friction
forces during ordinary extrusion obey Siebel's law,
and when extruding with active friction forces, they
obey Amonton's law.
Theoretical analysis is carried out in the following
sequence:
1. The source of plastic deformation of the
workpiece is divided into areas convenient for setting
the field of suitable flow velocities in them. The
specified expressions for flow rates can include both
specific dependences, justified experimentally, and
functions of a general form
v
x
= v
x
(x, y, z, t),
v
y
= v
y
(x, y, z, t),
v
z
= v
z
(x, y, z, t), (1)
At the boundaries between regions, the continuity
condition can be observed in a relaxed form,
satisfying the condition of constant flow in integral
form.
2. Based on the flow rates (1), the components of the
strain rate are found:
ξy =
(
+
). (2)
3. Each region contains the intensity of strain rates.
ξ
1
=
𝜉
𝜉
(3)
If it is necessary to simplify the solution, the value
of the strain rate intensity is averaged over one or
several coordinates and in the process of further
analysis is considered independent of these
coordinates.
4. Expressions (2) and (3) are substituted into the
equations for the relationship between stresses and
strain rates
σ
y
=𝜕
𝜎+
𝜉
(4)
Where 𝜕𝑦 - Kronecker symbol.
5. From the joint solution of the system of equilibrium
equations
= 0,
(5)
taking into account expressions (4), the stresses
are found. Arbitrary integration constants are found
from the boundary conditions. If necessary, to
simplify the solution of the system, the Huber-Mises
energy plasticity condition is used in the form
σ
ii (max)
– σ
jj (min)
= βσ
3
(6)
where β is the Lode coefficient, which for an
isotropic material is taken equal to its average value β
= 1, 1.
The use of a simplified plasticity condition that
does not take into account the tangential stresses
instead of the flow law associated with the exact
energy condition is not a disadvantage, since, on the
one hand, it allows one to avoid a decrease in
accuracy using approximate integration methods, and
on the other hand, the analysis showed that all the
main terms obtained from the proposed method, the
stress formulas coincide with those obtained on the
basis of the associated flow law, and the minor terms
give a slight overestimation of the result, which,
firstly, is consistent with the upper estimate method,
and secondly, makes it possible to compensate for the
mismatch of tangents that is always present in the
boundary conditions for non-zero friction stresses,
which cannot be taken into account in existing
momentless theories of plasticity.
6. Based on the found stresses, based on the
coupling equations (4) and kinematic boundary
conditions, the specific form of the velocity functions
specified at the beginning of the solution in general
form is determined.
7. If it is necessary to take into account the
anisotropy of the properties of the initial workpiece,
the plasticity condition and the relationship between
stresses and strain rates from the theory of plasticity
of anisotropic Mises -Hill bodies are used. The
analysis of this theory made it possible to introduce
an indicator of the form k = σ
sp
/ σ
sz
(where σ
sz
is the
yield stress along the axis of the workpiece, σ
sp
is the
yield stress in the radial direction), and obtain the
plasticity conditions of an anisotropic body in the
form