Journal of
Theoretical and Applied Mechanics
Volume
36, Number 2, 2006
Contents
A.
Nedev
Acad. G. Bonchev Str., Bl. 4, 1113
e-mail: anedev2005@yahoo.com
ANALYSIS
OF THE BLANK-HOLDER PRESSURE FOR DIFFERENT BLANK THICKNESSES AND MATERIALS
DURING DEEP DRAWING PROCESS
Abstract. This paper is devoted to the numerical investigation of
the influence of the stamp specific
Blank-Holder Pressure (BHP) on the Drawing Force (DF) upon four different metal
structures Steel 08, Copper, Aluminum and Brass 63 during deep drawing process.
The analysis is done for three blank thicknesses depending on different values
of BHP. The numerical results for the DF at several values of the strain
hardening material exponent are also given. The deep
drawing process producing a cylindrical cup with inside diameter 50 mm from
blank of diameter 105 mm and thicknesses 0.5, 1.5 and 3 mm is considered. In
the case of thickness 1.5 mm, which is taken as a basic one, the obtained
results for materials Steel 08, Aluminum and Brass 63 are compared with the
experimental ones.
The deep drawing
process is simulated by using FEM-ANSYS code. The results are presented by
“Drawing Force-P – Punch Travel-S” diagrams. On the basis of the differences in
the “P-S” diagrams a conclusion is drawn about the reasonable
range of BHP in every considered case.
Key words: deep drawing process, finite element method,
blank-holding pressure.
V. A. Kovtun, T. V. Semenova, Yu. M.
Pleskachevsky
V.
A. Belyi Metal-Polymer Research Institute of NASB,
32a,
e-mail: vadimkov@yandex.ru
M. Mihovski
Acad.
G. Bonchev Str., Bl. 4,
e-mail: nntdd@imbm.bas.bg
STRAIN STATE OF METAL-POLYMER POWDER MATERIAL UNDER
COMPRESSIVE LOADS DURING ELECTROCONTACT SINTERING
Abstract. Strain-strength properties of structurally
inhomogeneous metal-polymer powder materials formed by electrocontact sintering
were studied by using computer simulation. Displacements of the nodal contact
points and distribution fields of equivalent stresses were calculated in
various cross-sections of the copper-PolyTetraFluoroEthylene (PTFE) composite
under the action of distributed compressive loads. The mesoscopic structural
level effect on the defect formation processes and regularities of plastic
deformation in a group of metal-polymer powder particles have been studied.
Key words: strain-strength
properties, Stress-Strain State (SSS), composite powder metal-polymer
materials.
N.
Nikolov
Acad.
G. Bonchev Str., Bl. 4, 1113
e-mail: n.nikolov@imbm.bas.bg
LOSS OF STABILITY OF THE DEFORMATION PROCESS DURING DEEP DRAWING TECHNOLOGICAL PROCESS
Abstract. This paper
considers the loss of stability of the plastic forming process during deep
drawing process of circular blank having diameter 105 mm and thickness 1.5 mm.
The Steel 08kp, Steel 10, Aluminum, Copper, and Brass 63 represent different
blank material structures. The coefficient of deep drawing is 0.476 close
to the limiting one.
Comparisons
between numerically obtained effective and critical strains are given at the
end of second geometrical stage and under maximal drawing force for the blank
area covering the punch roundness and supporting two-dimensional tension.
Localization of plastic strains could be expected in these areas. On this
basis, the forming limits are predicted.
Key
words: deep drawing, numerical experiments,
limiting strains, localization of plastic strain.
Nikolay
K. Vitanov
Akad. G. Bonchev Str., Bl. 4, 1113
e-mail: vitanov@imbm.bas.bg
Khristo Tarnev
8,
Holger Kantz
Max Planck Institute for the
Physics of Complex Systems,
38, 
Str., 01187
Abstract. We discuss the
problem for detecting long-range correlations in sequences of values obtained
by generators of pseudorandom numbers. The 
exponent for a
sufficiently long sequence of uncorrelated random numbers has the fixed value 
. The presence of long-range correlations leads to deviation
from this value. We calculate 
by the method of
MultiFractal Detrended Fluctuation Analysis (MFDFA). We discuss frequently used
tests for randomness, finite sample properties of the MFDFA, and the conditions
for the correct application of the method. The fluctuation function 
used in the MFDFA
reacts to trends caused by low periodicity presented in the pseudo-random
number generator. In order to select appropriate generators from the numerous
possibilities we propose a test for the ensemble properties of the generated
pseudo-random sequences with respect to their robustness against presence of
long-range correlations, and a selection rule which orders the generators that
pass the test. In addition for each selected generator we choose pseudo-random
sequences with appropriate length on the basis of the closeness of the exponent of the
generated sequence to its value 1/2 characteristic for the case of absence of
correlations.
Key words: multifractal
detrended fluctuation analysis, -exponent, random number generators, long-range correlations.
Petia
Dineva
Acad. G. Bonchev Str., Bl. 4, 1113
e-mail: petia@imbm.bas.bg
Dietmar Gross
64289
e-mail: gross@mechanik.tu-darmstadt.de
Tsviatko
Rangelov
Institute of Mathematics and
Informatics,
Acad. G. bonchev Str., Bl. 8, 1113
e-mail: rangelov@math.bas.bg
Wave scattering in cracked piezoelectric materials -
a BIEM approach
Abstract.
A
non-hypersingular traction Boundary Integral Equation Method (BIEM) is
developed for the solution of Boundary Value Problems (BVP) describing wave
scattering by cracks in an infinite plane region. The numerical solution is
based on a frequency dependent fundamental solution obtained by Radon
transform. The proposed method is an efficient and flexible approach without
limitations concerning the type of the material, the crack geometry, the type
of the incident wave and the wave parameters.
The accuracy and convergence of the method is validated
by comparing the calculated Stress Intensity Factors (SIF) with existing results
obtained with other methods. In this context the dependence of the SIFs on the
frequency, the incidence angle and the wave type is discussed. For the
considered cases of a cracked piezoelectric, elastic-anisotropic and
elastic-isotropic continuum the method ensures a good accuracy and high
efficiency.
Key
words:
piezoelectric material, wave scattering by cracks, non-hypersingular traction
BIEM, stress intensity factors.