Journal of
Theoretical and Applied Mechanics
Volume 35, Number 1, 2005
Institute of Mechanics, Bulgarian Academy of Sciences,
Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria,
e-mail: alex_kazakoff@yahoo.co.uk
NUMERICAL INVESTIGATION ON A STANDRTD RUBBER VIBRATION
MOUNT SUBJECTED TO LARGE STATIC AND DYNAMIC DEFORMATIONS
Abstract. Shock protection
mounts comprising viscoelastic elements, are widely used in modern warship
design to reduce the high accelerations imposed by non-contact underwater
explosions. The objective of this work is to investigate the static and dynamic
behaviour of viscoelastic materials subjected to large deformations and to give
some quidelines for Finite Element (FE) modelling. The standard vibration mount
L68 kg, subjected to defined shock input loading was used in the analysis. Both
ELASTIC and HYPERELASTIC options within the ABAQUS computer code were used in
the Finite Element (FE) analysis to cover the full range of deformation
magnitudes. An ELASTIC analysis suffices up to a nominal 50% strain level, above
this an HYPERELASTIC analysis is needed to reproduce good correlation with
experimental data. Dynamic transient responses of half-sine shock impact in
vertical direction are measured and compared with the FE optimal mesh
prediction.
Key
words:
shock and vibration protection, Finite Element (FE) analysis, viscoelastic
mounts, dynamic transient responses, and half-sine shock impact.
V. A. Belyi Metal-Polymer Research Institute of NASB,
32a, Kirov Str., 246050 Gomel, Belarus,
e-mail: vadimkov@yandex.ru
Institute of Mechanics, Bulgarian Academy of Sciences,
Acad. G. Bonchev Str., Bl.4, Sofia 1113, Bulgaria,
e-mail: nntdd@imbm.bas.bg
SIMULATION OF MICRODEFORMATION
PROCESSES AND STUDY OF STRESS-STRAIN STATE OF COMPOSITES BASED ON A METAL
MATRIX WITH POLYMER FILLERS
Abstract. The Stress-Strain
State (SSS) of composite metal-polymer materials consisting of a copper matrix
and polymer filler particles of spherical, square, rectangular and elliptical
shapes has been simulated and analyzed in order to describe mechanical
properties and behaviour of heterogeneous media. It has been attempted to
predict deformation and strength characteristics of composite materials in
response to compressive loads. The calculations have visualized essential
inhomogeneity of the stress-strain state of the structures under study
indicating that stress concentrations emerge just as on the surface as in the
material bulk, where structural defects may appear leading to failure.
Key words: Stress-Strain State (SSS),
composite, metal-polymer materials.
V. Rizov, A.
Mladensky
University of
Architecture, Civil Engineering and Geodesy,
1, Chr.
Smirnensky Blvd., 1046 Sofia, Bulgaria,
e-mail: V_RIZOV_FHE@AUCG.BG
Abstract. The paper addresses the elastic-plastic
response of sandwich composite beams with a foam core to local static loading.
The study deals with a 2D configuration, where a sandwich beam is indented by a
steel cylinder across the whole width of the specimen. The ABAQUS finite
element package is used to model the indentation response of the beams. The
purpose of the numerical modelling is to develop correct 2D simulations of the
non-linear response in order to further understand the failure modes caused by
static indentation. The numerical results show good agreement with performed
experiments.
Key words: sandwich
composite material, static indentation, elastic-plastic behaviour.
Institute of
Metal Science,
Bulgarian Academy of Sciences,
67, Shipchensky
Prohod Str., 1574
Sofia, Bulgaria,
e-mail: kortenski@ims.bas.bg
Abstract. Implantation of new reconstitution
technology. Evaluation of temperature and hardness distribution in the insert
part after two welding processes.
Key words: fracture toughness, reconstitution
technology, master curve approach, Precracked Charpy V-notch Specimen (PCCv), Reactor Pressure
Vessel Steel (RPVS), 20MnMoNi55.
Faculty of
Technical Education, Afyon Kocatepe University, A N Sezer,
Campus, 03300
Afyon, Turkey,
e-mail: colakoglu@aku.edu.tr
Abstract. Fatigue damage is one of the major
factors to failure in engineering materials. Energy absorption, called damping,
occurs in engineering metals as a function of the cyclic loading history. The
damping behaviour of materials has been estimated by using many different
methods and parameters, such as the loss factor versus strain amplitude,
frequency range, porosity, etc. The damping values of engineering materials and
structures are usually determined experimentally because of forming a part of
design process. A damping monitoring method, which measures the damping factor
by vibration excitation, was used in this study to investigate energy
dissipation for low cycle fatigue. The effects of the number of fatigue cycles
on the damping factor and frequency were studied in 304 stainless steel under a
constant cyclic load.
Key words: damping,
fatigue, vibration, frequency, stainless steel.
University of
Chemical Technology and Metallurgy,
8, St. Kl.
Ohridski Blvd., 1756 Sofia, Bulgaria,
e-mail: polylab@uctm.edu
POLYPROPYLENE REINFORCED WITH SHORT GLASS FIBERS –
FIBER ORIENTATION AND MECHANICAL PROPERTIES
Abstract. Although mechanical testing can give
useful information for the reinforcing effect of fiber-like filler implemented
in polymer matrix, further investigations are required, in order to study the
influence of the fiber filler on the properties of the composite. Specimens in
two directions were taken for this purpose: along and across the direction of
the melt flow being injected into the rectangular matrix. The
fiber orientation investigation showed that the increasing of the fiber
fraction causes better alignment along the flow. At the same time, the
orientation along the flow is higher in the end of
the molded plate than in its beginning. The tensile tests performed
showed that the yield strength is higher for
the specimens taken along the length than for those,
taken transversally. The composite becomes brittle with increasing of the glass
fiber content, which is influenced by the fiber orientation. The results
obtained by DMTA testing confirmed these observations and showed that the
values of the storage modulus respond to the change of the fiber orientation.
Key words:
polypropylene, reinforcing, glass fibers, fiber orientation.
Dorina
Dragancheva, Valeri Penchev
Department on
Coastal Hydraulics and Environment Protection,Bulgarian Ship Hydrodynamics
Centre-Varna, Bulgarian Academy of Sciences,
P.O.Box 58,
Varna 9003, Bulgaria,
e-mails: d.dragancheva@bshc.bg, v.penchev@bshc.bg
Abstract. The main problem in coastal protection
engineering is to sustain the coast as a natural ecosystem and to maintain also
the coastal regions and beaches for balanced using for recreational purposes.
From environmental point of view development and evolution of coastal regions
affected by wave erosion, artificial reefs (= submerged breakwaters with broad
crest) are a new class of innovative shoreline erosion control structures.
Wave transmission measurements over rubble
mound trapezoidal submerged breakwater with broad crest on a wide range of
irregular and regular incident wave conditions and crest submergence change are
analyzed and discussed in this paper. Test results are compared to the
calculated ones by known design formulae of Ahrens, d'Angremond, Van der Meer
& de Jong, Seabrook & Hall, Friebel & Harris, as well as to other
recently published experimental tests of submerged breakwaters.
Two-dimensional tests of the submerged
breakwater presented in the paper have been carried out in the wave flume (WKS)
of the Franzius Institute, Hanover University under a joint research project
supported by 5-th Framework Program of the European Community.
The experimental study has been carried out
for wave conditions of the Bulgarian Black Sea coast.
Key words:
artificial coastal reef, experimental modelling, wave breaking, wave
transmission.