Issue 1

JTAM, Sofia, vol. 35 Issue 1 (2005)

Numerical Investigation on a Standrtd Rubber Vibration Mount Subjected to Large Static and Dynamic Deformations

Al. B. Kazakoff
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgari

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.

JTAM, Sofia, vol. 35 Issue 1 pp. 01 (2005)

Simulation of Microdeformation Processes and Study of Stress-Strain State of Composites Based on a Metal Matrix with Polymer Fillers

V. A. Kovtun1, T. V. Semenova1, M. Mihovski2
1V. A. Belyi Metal-Polymer Research Institute of NASB, 32a, Kirov Str., 246050 Gomel, Belarus
2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl.4, Sofia 1113, Bulgaria

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.

JTAM, Sofia, vol. 35 Issue 1 pp. 02 (2005)

Static Indentation Response of Sandwich Composite Beams

V. Rizov, A. Mladensky
University of Architecture, Civil Engineering and Geodesy, 1, Chr. Smirnensky Blvd., 1046 Sofia, Bulgaria

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.

JTAM, Sofia, vol. 35 Issue 1 pp. 03 (2005)

Implantation of Reconstitution Technology

G. Kortenski
Institute of Metal Science, Bulgarian Academy of Sciences, 67, Shipchensky Prohod Str., 1574 Sofia, Bulgaria

Implantation of new reconstitution technology. Evaluation of temperature and hardness distribution in the insert part after two welding processes.

JTAM, Sofia, vol. 35 Issue 1 pp. 04 (2005)

Low-Cycle Fatigue as Damping in 304 Stainless Steel

Mehmet Colakoglu
Faculty of Technical Education, Afyon Kocatepe University, A N Sezer, Campus, 03300 Afyon, Turkey

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.

JTAM, Sofia, vol. 35 Issue 1 pp. 05 (2005)

Polypropylene Reinforced with Short Glass Fibers – Fiber Orientation and Mechanical Properties

D. S. Popov, Ch. D. Betchev
University of Chemical Technology and Metallurgy, 8, St. Kl. Ohridski Blvd., 1756 Sofia, Bulgaria

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.

JTAM, Sofia, vol. 35 Issue 1 pp. 06 (2005)

Wave Transmission Behind a Submerged Breakwater

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

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.

JTAM, Sofia, vol. 35 Issue 1 pp. 07 (2005)