Slaviša S. Putić

Delamination Detection in Woven Composite Laminates with Embedded Optical Fibers

Woven glass fiber reinforced plastics (GRP) are being widely applied to advanced structures in aerospace, automobile, and marine industries. Optical fibers, originally developed for telecommunications, can be used as sensors that can monitor the state of damage and strain in advanced composite materials. In intensity-based sensors a parameter, such as strain, produces a change in the power of the light propagating in the fiber. The present study aimed to assess the effectiveness of using an optical fiber, stripped of the buffer and acrylate coated, for delamination detection in woven GRP three-point bend specimens.

In vitro biocompatibility assessment of Co-Cr-Mo dental cast alloy

Metallic materials, such as Co-Cr-Mo alloys, are exposed to aggres- sive conditions in the oral cavity that represents an ideal environment for metallic ion release and biodegradation. The metallic ions released from dental materials can cause local and/or systemic adverse effects in the human body. Therefore, dental materials are required to possess appropriate mechanical, physical, chemical and biological properties. The biocompatibility of metallic materials is very important for dental applications. Accordingly, the aim of this study was to examine metallic ion release and cytotoxicity of Co-30Cr-5Mo cast alloy as the initial phase of biocompatibility evaluation. Determination of the viability of human (MRC-5) and animal (L929) fibroblast cells were conducted using three in vitro test methods: the colorimetric methyl-thiazol- tetrazolium (MTT) test, the dye exclusion test (DET) and the agar diffusion test (ADT). Furthermore, the morphology and growth of the cells were analyzed using scanning electron microscopy (SEM). The obtained results indicated that Co-30Cr-5Mo alloy did not release harmful elements in concentrations high enough to have detrimental effects on human and animal fibroblasts under the given experimental conditions. Moreover, the fibroblast cells showed good adhesion on the surface of the Co-30Cr-5Mo alloy. Therefore, it could be con- cluded that Co-30Cr-5Mo alloy is a biocompatible material that could be safely used in dentistry.

Numerical and Analytical Modelling of Elastic-Plastic Fracture Mechanics Parameters

Structural integrity and service reliability depend on the fracture resistance of a material. Cracks in the material are the locations of stress concentration, and elastic-plastic deformation can occur causing the development of mixed-mode type of fracture ahead the crack tip. Crack behavior in the elastic-plastic region is analyzed applying numerical and analytical simulation based on fracture mechanics parameters, characterizing the response of the material at the crack tip. Numerical and analytical results are compared with the corresponding experimental results obtained in previously performed fracture mechanics tests with standard single-edge notch bending – SEN(B) specimens. The comparison shows an acceptable level of agreement, enabling application of the proposed numerical model of crack growth in the mixed-mode fracture analysis for structural integrity assessment.

Stress Field Analysis in Composite Laminates with Embedded Optical Fiber

A typical intensity-modulated optical fiber sensor system consists of a light source, a sensing device, within which the intensity of light is altered by the measurand in some way, a detector to measure the intensity of the transmitted signal and optical fibers to carry light between these components. The optical fiber coating interaction with the host material plays a major role in determining the proper transfer of load from the structure to the optical fiber. Three-dimensional (3D) finite element (FE) model of the structure was performed to study and predict the behaviour of the stress/strain fields in and around acrylate coated embedded optical fibers in flexural test coupons of carbon fiber composite. The modeling results and the fracture surface scanning electron micrographs suggest that the soft acrylate coating is debonding.

Organoclay-polymer nanocomposites

The properties of polymer nanocomposites exceed the properties of common composite materials due to the nanoscale size and morphology of the fillers used. Particulate fillersare commonly used in polymers forimproved mechanical and thermal properties, as well as modified electrical properties and cost reduction. Organically modified layered clays, such asmontmorillonite, are among the most widely used fillers for the improvement of polymer matrices. Presented in this review are some of the most studied clay nanocomposites including clay-polyolefin, clay-polyester and clay-thermoplastic polyurethanenanocomposites. Additionally, the properties of clay-biopolymers nanocomposites will also be discussed.

EFFECT OF ALKALINE SOLUTIONS ON THE TENSILE PROPERTIES OF GLASS-POLYESTER PIPES

Construction materials, traditionally used in process equipment, are today successfully replaced by composite materials. Hence, many pipes are made of these materials. The subject of this study was the influence of liquids on the state of stresses and tensile strengths in the longitudinal and circumferential direction of glass-polyester pipes of a definite structure and known fabrication process. These analyses are of great importance for the use of glass-polyester pipes in the chemical industry. The tensile properties (the ultimate tensile strength and the modulus of elasticity) were tested and determined for specimens cut out of the pipes; flat specimens for the tensile properties in the longitudinal direction and ring specimens for the tensile properties in the circumferential direction. First, the tension test was performed on virgin samples (without the influence of any liquid), to obtain knowledge about the original tensile properties of the material composite studied. Subsequently, the specimens were soaked in alkaline solutions: sodium hydroxide (strong alkali) and ammonium hydroxide (weak alkali). These solutions were selected because of their considerable difference in pH values. The specimens and rings were left for 3, 10, 30 and 60 days in each liquid at room temperature. Then, the samples were tested on tension by the standard testing procedure. A comparison of the obtained results was made based on the pH values of the aggressive media in which the examined material had been soaked, as well as based on the original tensile properties and the number of days of treatment. Micromechanical analyses of sample breakage helped in the elucidation of the influence of the liquids on the structure of the composite pipe and enabled models and mechanisms that produced the change of strength to be proposed.