Issue 2

JTAM, Sofia, vol. 42 Issue 2 (2012)

Fracture in Composites – an Overview (Part I)

V. I. Rizov
Department of Technical Mechanics,, University of Architecture, Civil Engineering and Geodesy, 1, Chr. Smyrnensky Blvd, 1046 Sofia, Bulgaria

An overview of the literature for the last twenty years on the fracture mechanics of unidirectional fibre reinforced polymer composites is presented. Pure mode (I, II, and III) as well as mixed mode longitudinal cracks (i.e., cracks that prolongate along the fibres) are considered mainly. It is shown that the strain energy released rate is the most widely used parameter for fracture toughness characterization. Various solutions for determination of the strain energy release rate in composites using linear-elastic fracture mechanics are presented. Studies on fracture in composite sandwich structures are reviewed, too. Some analyses of damages and their influence on fracture behaviour also are considered. Topical problems of composite fracture mechanics are formulated.

JTAM, Sofia, vol. 42 Issue 2 pp. 03-42 (2012), [Full Article]

Stress and Strain Definition of an Open Profile Thin-Walled Beam at Constrained Torsion by Boundary Element Method

Zlatko Tcvetanov Zlatanov
TU – Sofia, Plovdiv branch, 25, Canko Djustabanov Str., 4000 Plovdiv, Bulgaria

Thin-walled beams with open profile at constrained torsion are investigated in this paper. A thin-walled beam loaded by an external bi-moment at constrained torsion is investigated in this paper. An analytical variant of the boundary element method (BEM) is presented, which is based on a new scheme of the integral ratios transformation of the initial parameters method in a system of linear algebraic equations. Only one dimensional integrals are used defining the one dimensional continuum.

JTAM, Sofia, vol. 42 Issue 2 pp. 43-54 (2012), [Full Article]

A Comparative Study of Random Patterns for Digital Image Correlation

G. Stoilov, V. Kavardzhikov, D. Pashkouleva
Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia, Bulgaria

Digital Image Correlation (DIC) is a computer based image analysis technique utilizing random patterns, which finds applications in experimental mechanics of solids and structures. In this paper a comparative study of three simulated random patterns is done. One of them is generated according to a new algorithm, introduced by the authors. A criterion for quantitative evaluation of random patterns after the calculation of their autocorrelation functions is introduced. The patterns’ deformations are simulated numerically and realized experimentally. The displacements are measured by using the DIC method. Tensile tests are performed after printing the generated random patterns on surfaces of standard iron sheet specimens. It is found that the new designed random pattern keeps relatively good quality until reaching 20% deformation.

JTAM, Sofia, vol. 42 Issue 2 pp. 55-66 (2012), [Full Article]

Analysis of Mode II Crack in Bilayered Composite Beam

Victor I. Rizov, Angel S. Mladensky
University of Architecture, Civil Engineering and Geodesy, 1, Chr. Smirnensky Blvd, 1046 Sofia, Bulgaria

Mode II crack problem in cantilever bilayered composite beams is considered. Two configurations are analyzed. In the first configuration the crack arms have equal heights while in the second one the arms have different heights. The modulus of elasticity and the shear mod- ulus of the beam un-cracked part in the former case and the moment of inertia in the latter are derived as functions of the two layers characteristics. The expressions for the strain energy release rate, G are obtained on the basis of the simple beam theory according to the hypotheses of linear elastic fracture mechanics. The validity of these expressions is established by comparison with a known solution. Parametrical investigations for the influence of the moduli of elasticity ratio as well as the moments of inertia ratio on the strain energy release rate are also performed. The present article is a part of comprehensive investigation in Fracture mechanics of composite beams.

JTAM, Sofia, vol. 42 Issue 2 pp. 67-78 (2012), [Full Article]

Simulation of Water-Entry and Water-Exit Problems Using a Moving Mesh Algorithm

Roozbeh Panahi
Marine Transportation and Tehcnology Department, Transportation Research Institute, No. 65, Hekmat St., Noori Highway, Tehran, Iran, Post Code: 14639-17151

Simulation of the water-entry and water-exit particularly, at the interface of two phases i.e. water and air due to the effect of flow-induced loads, gravity force and trapped air cushion presence is very complicated. This paper attempts to introduce a finite volume-based moving mesh algorithm in order to simulate such problems in a viscous incompressible two-phase medium. The algorithm employs a fractional step method to deal with the coupling between pressure and velocity fields. Interface is also captured by solving a volume fraction transport equation. A boundary-fitted body-attached mesh of quadrilateral Control Volumes (CVs) is implemented to record hydrodynamic time histories of loads, motions and interfacial flow changes around the structure. Forced water-exit of a cylinder is simulated based on the introduced algorithm, together with free symmetric and asymmetric water-entry of wedges. Results show that the presented algorithm is favorably capable of assessing such complexities when comparing to experimental data.

JTAM, Sofia, vol. 42 Issue 2 pp. 79-92 (2012), [Full Article]


Michail Todorov

JTAM, Sofia, vol. 42 Issue 2 pp. 93-98 (2012), [Full Article]