Band 20, Heft 1

In this study, the effect of nanoparticle on hygroscopic thickness swelling rate of composites from hemp fiber and recycled plastic was investigated. To meet this objective, hemp fiber was mixed with either virgin or recycled polypropylene (PP) at 50% by weight fiber loading. The samples were made by melt compounding and then injection molding. The concentration was varied as 0, 1, and 3 per hundred compounds (phc) for nanoclay. The amount of coupling agent was fixed at 2 phc for all formulations. The long-term thickness swelling rate of samples was evaluated by immersing them in water at room temperature for several weeks (up to 3000 h). The results indicated that whether or not virgin plastic is used has a significant effect on the thickness swelling of composites. The thickness swelling of the hemp fiber/recycled plastic composites was higher than those of virgin plastics. Furthermore, with the addition of nanoclay content in composites, thickness swelling decreased. The swelling rate parameter ( K SR ) of the composites was influenced by plastics virginity and nanoclay. The minimum K SR values were observed in composites made of 50VPP/50F/2C/3N. Morphological findings showed that samples containing 1 phc of nanoclay had higher order of intercalation and better dispersion.

This composite has been developed by solidification processing by the addition of 0.5–3. 5 wt% powders of oxide TiO 2 to molten Al-Cu alloy. The dry sliding wear behavior of pins of cast composite, fabricated by the solidification of the melt-particle slurry in mold, has been determined by pin-on-disc wear tests carried out conventionally and while removing wear debris by camel brush. The accumulated volume loss in composites increases linearly with increasing the sliding distance, and the wear rate increases more or less linearly with increasing load. The increasing particle content decreases the wear rate at a given load. The accumulated volume loss is considerably higher when the wear debris is removed by a camel brush during dry sliding wear. The relatively brighter compacted oxide transfer layer could be observed in the SEM micrograph of worn pin surfaces of the composites developed by the addition of TiO 2 . At higher loads, the oxide debris are expected to get better compacted to form the transfer layer, spread over a larger area of the sliding surface, and thus, their removal causes a larger wear compared to that without the removal of wear debris.

Silver loaded montmorillonite (Ag-MMT) was prepared by ion exchange reaction under microwave irradiation. The effects of microwave irradiation time, AgNO 3 concentration, and microwave power on the silver content of Ag-MMT were investigated using the Volhard method. The time of ion exchange reaction was found to be greatly shortened under microwave irradiation. The most suitable reaction condition was in 0.2 m AgNO 3 under 100% microwave power irradiation for 4 min, and the silver content was determined and was found to be 1.23 wt%. The results of the Fourier transform infrared spectrum (FT-IR) and Ag + release tests confirmed the successful loading of silver and its good slow-release property. The X-ray diffraction (XRD) patterns and ultraviolet-visible (UV-vis) spectra proved the existence of metallic Ag nanoparticles. The Ag-MMT showing a large inhibition zone, high inhibition ratio, and low minimum inhibitory concentration (MIC) value against Staphylococcus aureus ATCC6535 presented a very good antibacterial property.

Xanthan-gum-facilitated aspirin-loaded ethyl cellulose microparticles were prepared by multiple-emulsion solvent evaporation technology and the impact on variation in process parameters was investigated systematically. Scanning electron microscopy was performed to determine the surface morphology of the microparticles before and after dissolution study. X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) analysis were performed, and yield value, swelling study, encapsulation efficiency, flow properties and dissolution profiles of the prepared formulations were evaluated. The size of microparticles varied between 247 and 410 μm, and 58.34% drug entrapment efficiency was achieved depending on the variation in process parameters. The drug release in acid solutions was slower than in alkaline solution. The microparticles provided extended drug release in alkaline dissolution medium, and the drug release was found to be controlled by Fickian diffusion mechanism. XRD and DSC analyses revealed the amorphous nature of drug in the microparticles. FTIR data indicated the stable character of the encapsulated drug in the microparticles. Thus, variation in process parameters showed a slow and prolonged release of aspirin in simulated intestinal fluid.

Widespread applications and advantages of different types of composite materials have drawn researchers’ attention toward the science and technology of composites. Among these materials, cementitious composites have a special place, as they have many applications in various fields of structural and civil engineering. Due to the importance of cementitious composites and their behavior, investigation of their properties is of great importance. Thus in the present study, thermal and mechanical properties of the self-compacting cementitious composites containing different fractions of nano TiO 2 have been investigated. Mechanical properties were assessed through compressive, split tensile and flexural tests. The thermal properties were assessed through thermogravimetric analysis (TGA) and conduction calorimetry tests. Accelerated peak appearance in conduction calorimetry tests and more weight loss in thermogravimetric analysis could indicate that TiO 2 nanoparticles could lead to strength development at earlier ages and improve the properties of the self-compacting cementitious composites.

This paper investigates the influence of class F fly ash and silica nano-micro powder on water permeability and thermal properties of high performance concrete (HPC) as one of the most important cementitious composites. For this purpose, a fraction of Portland cement was replaced by silica fume, silica nanoparticles, blend of silica fume and silica nanoparticles and three percentages of fly ash as 10%, 2%, 10+2% and 5%, 10%, 15%, respectively. Specimens were prepared with two binder contents as 400 and 500 kg/m 3 . Thermal properties were investigated via thermogravimetric analysis (TGA). Capillary water absorption tests of the specimens were carried out at the age of 90 days. The results showed that the pozzolanic admixtures especially blend of silica fume and SiO 2 nanoparticles have a significant effect on thermal properties and particularly capillary water absorption.

Marble dust and fly ash are waste materials and used in various area and industries as an additive material. However, there are still significant amounts of marble dust and fly ash left as waste. Therefore, the reuse of these wastes provides benefits to reduce construction costs and increase sustainability. In this study, a laboratory testing program was conducted on granular soil specimens amended with marble dust and fly ash. The specimens were prepared with granular soil and marble dust-fly ash at different mixing ratios. They were compacted with standard and modified Proctor energies. The specimens were subjected to unconfined compression, California bearing ratio, and freezing-thawing tests. The results of the study show that the strength of a specimen is dependent on the additive ratio, the curing period, compaction energy, and the number of freeze-thaw (F-T) cycles. Generally, unconfined compressive strength (q u ) and California bearing ratio (CBR) increased with additive materials, curing times, and high compaction energy. q u decreased and weight loss increased with increasing additives and increasing F-T cycles.

In this paper, the effect of silica fume on the workability and durability of concrete composites containing fly ash, including water impermeability, dry shrinkage property, carbonation resistance and freeze-thaw resistance, are presented. Four different silica fume contents (3%, 6%, 9% and 12%) were used. The results indicate that the addition of silica fume has greatly improved the durability of water impermeability, the carbonation resistance and the freeze-thaw resistance of the concrete composites containing fly ash. With the increase in silica fume content, the length of water permeability and the carbonation depth of the specimens decrease gradually, and the relative dynamic elastic modulus of the specimens has a tendency to increase. However, the addition of silica fume has a little adverse effect on the workability and dry shrinkage property of concrete composites containing fly ash. With the increase in silica fume content, both the slump and the slump flow decrease gradually, and the dry shrinkage strain increases gradually.

In this study, composites of knitted fabric made from side-by-side multiple glass and polypropylene yarns have been investigated. These composites have been produced by a new manufacturing method – the hot press method. By using various knitted fabrics made from different components of glass and polypropylene yarns, several types of knitted structures and yarn components were investigated: rib 1-1, full Milano and full cardigan. The mechanical properties of composites were measured in three directions. The results showed that hot-pressed knitted composites of glass and polypropylene yarns have high strength, impact resistance, work-to-break and elongation, simultaneously. The highest bending resistance and maximum stiffness are achieved for rib-knitted composites consisting of 8 wt% glass and 92 wt% polypropylene yarns. The highest impact energy absorption was obtained with 18 wt% glass content and 82 wt% polypropylene matrix.

This paper presents an efficient and accurate numerical method based on the three-dimensional (3-D) elasticity theory for the transient analysis of functionally graded (FG) hollow cylindrical shells subjected to asymmetric dynamic pressure. The Fourier expansion is employed to describe the displacement components and dynamic pressure in the tangential direction. In addition, the layerwise theory is used to accurately account for the displacement components in the radial direction. The equations of motion and the related boundary conditions are derived using Hamilton’s principle. Then, differential quadrature method (DQM) is implemented to discretize the resulting equations in the both spatial and time domains. The convergence, accuracy and performance of the present method are established through the convergence study and comparison with available results in the literature. Also, the effects of different parameters such as thickness-to-inner radius ratio and boundary conditions on the dynamic behavior of hollow FG cylinders are investigated. The present method can accurately predict transient displacement and stress with less computational efforts.

This paper deals with thermal buckling load optimization of symmetrically laminated angle-ply general quadrilateral and trapezoidal thin plates. The objective function is to maximize the critical temperature capacity of the quadrilateral and trapezoidal laminated plates and the fiber orientation is considered as a design variable. The mathematical formulation is based on the classical laminated plate theory for the frequency analysis. The modified feasible direction method is used as the optimization routine. Therefore, a program based on FORTRAN is used. Finally, the significant effects of aspect ratios, boundary conditions, taper ratios and unsymmetric trapezoidal plates on the optimal results are investigated and the results are compared.

Adhesive anchors are widely used in seismic strengthening applications to add new structural members or sections to existing concrete members due to their high tensile and compressive strengths, low cost, and easy and fast installation. To safely design such anchors, it is very important to know their pullout capacity under axial tensile forces. This paper explores the pullout capacity of both single and groups of adhesive anchors loaded in tension in uncracked concrete. Quadruple anchor groups were considered for group effect. To this end, 142 single anchor tests including edge effect (located near a concrete edge) and 175 quadruple group anchor tests (totally 317 tests) were obtained from literature. The formulated three-layered artificial neural network method (ANN) was trained using 75% of the data set by using different learning algorithms. The methods were tested with the remaining 25%. The variables taken into account in this study are anchor diameter, embedment length, concrete compressive strength, concrete body height, edge distance (for single anchors), and anchor spacing (for group anchors). It was determined that experimental data can be estimated to a notably close extent via the ANN model.