Mariana Domnica Stanciu

The Evaluation of Rheological Properties of Composites Reinforced with Hemp, Subjected to Photo and Thermal Degradation

The cars of the future are designed so that to replace partial or total the fossil fuels. For this reason, the structural modifications of the materials used in the cars structure are researched being studied the lightweight materials, ecological and environmentally friendly, reusable and with improved performance in terms of mechanical strength (static and dynamic), thermal insulation and acoustic, with interface aesthetic. The paper aims to assess the structural modifications and visco-elastic properties of the composites reinforced with hemp mat subjected to artificial aging by exposure to UV radiation. Thus, samples having a percentage of reinforcing fiber hemp about 50% were subjected to a dynamic mechanical analysis (DMA), being determined visco-elastic behavior at different frequencies loading. Then, samples were exposed for 168 hours at the UV-A radiations, after that their rheological behavior was re-evaluated. In terms of structural and morphological changes, the samples were analyzed with the atomic force microscope (AFM) and method of contact angle both before and after accelerated aging. It was found that after UV radiation, on the surface of the composite structure reinforced with hemp mat occurred rearrangements of chemical chains and increases of the surface roughness.

Nondestructive evaluation and characterization of GFRP using non-contact ultrasound and complementary method

This paper presents two methods, non-contact low frequency ultrasound method and fiber Bragg gratings, and their application to nondestructive testing of glass fiber reinforced composites used in wind turbine blades. Theoretical models are used and experimental results are in good concordance with destructive testing results.

Mechanical and Surface Properties of Lignocellulosic Fibres Reinforced Composites

The advantages and disadvantages of natural fibers as hemp, sisal, jute, wood, and flax have been studied in terms of mechanical properties, durability, cohesion between filler and matrix. The development of natural fiber reinforced biodegradable polymer composites promotes the use of environmentally friendly materials [1]. The new materials derived from biodegradable renewable sources are considered as partial solution to environmental pollution caused by the large volume of waste [2]. Even though the fiber determines the mechanical properties like elastic modulus or strength, the matrix provides the physical and chemical durability by protecting the fiber from environmental influences [3]. The use of lignocelluloses composite with polymer matrix in the environment with UV radiation can cause photodegradation which lead to a weakening of the material and micro-cracking of the matrix [4] and [5]. Photodegradation is the main effect of UV environmental radiation on polymeric materials, which is shown by the following phenomena: breaking chemical bonds between the polymer chains, which leads to the formation of free radicals by dissociating C-H bonds from the polymer chains and to the oxidation of its surface because of peroxide radicals [6]. In addition, exposure to UV radiation can make the material more sensitive to the action of other factors (i.e. humidity) [7]. The hydrophilicity is one great drawback when using lignocelluloses fibers as reinforcement in polymer composites. Many approaches studied the tendency of interfacial strength and dimensional stability of bio-composite as results of UV action [8] and [9]. The paper is focused on the photo-degradation mechanism, which influences the surface energy of the lignocelluloses composite. The evaluation of the surface energy of the composite lignocelluloses materials was carried out by the θ contact angle method identifying the hydrophilic/hydrophobic properties of them. Because of the poor interfacial adhesion between fibers and polymers which leads to limitation of natural fibers reinforcement, Azwa et al. [10] studied the improvement of composite behavior due to addition of coupling agent. The effect of the oak particle size on the mechanical and morphological properties has been studied [6]. Mechanical properties of wood plastic composites (WPC), determined by tensile and Mechanical and Surface Properties of Lignocellulosic Fibres Reinforced Composites Stanciu, M.D. – Savin, A. – Nastac, S.M. Mariana Domnica Stanciu1,* – Adriana Savin2 – Silviu Marian Nastac3 1Transilvania University of Brasov, Department of Mechanical Engineering, Romania 2National Institute of Research and Development for Technical Physics, Nondestructive Testing Department, Romania 3‘Dunarea de Jos’ University of Galati, Engineering and Agronomy Faculty, Romania

The evaluation of the elasto-plastic behavior in case of the honed steel pipes subjected to variable internal pressure

The paper analyses the elasto-plastic behavior of ten samples of E355 steel pipe of the same inner diameter, but with wall thickness ranging between 1.100 and 2.500 mm and length about 100 mm. The samples were subjected to variable internal pressure which was increased from 0 to 600-800 bar (up to the breaking of the pipe), being used the hydraulic oil, type HM46. The outer diameter of the tested pipes was measured successive for each increase of pressure with 100 bars, thus being determined the flow curve of the pipe material characterized by the elasto-plastic behavior and a tenacious failure. It was found that thin pipes, with the ratio between the inner and outer diameter less than 1.1, shows a different flow curve compare to pipes with thick walls, having the ratio between the inner and outer diameter greater than 1.1, the deformations being about two times higher. The rheological models of each type of pipes were identified.

Theoretical Research on the Influence of the Interface Wood-Adhesive on the Stiffness of the Composite Panels Made of Wood Lamellas

The paper presents the results of the FEM (Finite Element Method) analysis applied to the anisotropic-orthotropic panels made of lamellas of hardwood (beech and maple wood) considered to be subjected to a static load. The research follows the influence of the interface wood - adhesive on the stiffness of the panels, for different lamella width.