Determination of fibre-matrix interfacial properties in ceramic-matrix composites by a fibre push-out technique

A simple concentric cylinder model is developed for the fibre push-out test in order to interpret the experimentally observed indenter load-displacement curves in ceramic-matrix composites. The fibre-matrix interface is assumed to be partially bonded and partially frictionally coupled. It is shown that a slope change in the loading curve corresponds to bonding at the fibre-matrix interface. In contrast an insignificant change in the slope is predicted for composites in which the fibre-matrix interface is frictionally coupled. This model also provides a framework for determining the interfacial debond energy and the interfacial shear strength in ceramic composites using the fibre push-out tests. The predictions of this model are compared with the push-out test results performed on zircon-SiC composites uniaxially reinforced with either uncoated or BN-coated SiC monofilaments, which suggested that the fibre-matrix interfaces in both of these composites are frictionally coupled.     

Pyrolysis of peat: Product yield and characterization

Pyrolysis of peat obtained from Yeniça?a, Bolu, Turkey was conducted in a fixed-bed tube furnace under various conditions, and variations in the structure of the char, tar and gas products were examined. The chars produced were studied by proximate and ultimate analyses. The maximum tar yield of 20.41% was obtained at a heating rate of 20 °C/min, a temperature of 450 °C, a sweeping gas flow rate of 100 ml/min and a 0.5–2.0 mm size range. The chemical composition of the tar was examined by elemental analysis, FTIR spectroscopy, ¹H-NMR spectroscopy and column chromatography. The chemical composition of the tar with dense aliphatic structure was established to be CH_1.22O_0.25N_0.02. The composition of the gases obtained at a heating rate of 20 °C/min for the 0.5–2.0 mm size range was examined by gas chromatography.     

Modelling of evaporation from the reservoir of Yuvacik dam using adaptive neuro-fuzzy inference systems

Adaptive neuro-fuzzy inference system (ANFIS) models are proposed as an alternative approach of evaporation estimation for Yuvacik Dam. This study has three objectives: (1) to develop ANFIS models to estimate daily pan evaporation from measured meteorological data; (2) to compare the ANFIS model to the multiple linear regression (MLR) model; and (3) to evaluate the potential of ANFIS model. Various combinations of daily meteorological data, namely air temperature, relative humidity, solar radiation and wind speed, are used as inputs to the ANFIS so as to evaluate the degree of effect of each of these variables on daily pan evaporation. The results of the ANFIS model are compared with MLR model. Mean square error, average absolute relative error and coefficient of determination statistics are used as comparison criteria for the evaluation of the model performances. The ANFIS technique whose inputs are solar radiation, air temperature, relative humidity and wind speed, gives mean square errors of 0.181 mm, average absolute relative errors of 9.590% mm, and determination coefficient of 0.958 for Yuvacik Dam station, respectively. Based on the comparisons, it was found that the ANFIS technique could be employed successfully in modelling evaporation process from the available climatic data.     

Statistical fibre failure and single crack behaviour in uniaxially reinforced ceramic composites

A lower bound to the work of pull-out is estimated for a ceramic composite under uniaxial loading assuming that matrix crumbling does not occur. Fibre failure is assumed to be governed by Weibull distribution. In order to compute a lower bound to the energy dissipation it is assumed that the failure occurs by a single matrix crack. The fibre/matrix interface is assumed to be constrained by friction only. The work of pull-out estimated from the present model is compared to the energy dissipation before fibre failure which was computed by Aveston, Cooper and Kelly (ACK) in 1971. Comparisons are made with the surface energy of monolithic materials.     

Production of anorthite refractory insulating firebrick from mixtures of clay and recycled paper waste with sawdust addition

Production of porous anorthite refractory insulating firebricks from mixtures of two different clays (K244 clay and fireclay), recycled paper processing waste and sawdust addition are investigated. Suitability of alkali-containing-clay, low-alkali fireclay, pore-making paper waste and sawdust in the products was evaluated. Prepared slurry mixtures were shaped, dried and fired. Highly porous anorthite ceramics from the mixtures with up to 30% sawdust addition were successfully produced. Physical properties such as bulk density, apparent porosity, percent linear change were investigated as well as the mechanical strengths and thermal conductivity values of the samples. Thermal conductivities of the samples produced from fireclay and recycled paper waste decreased from 0.25 W/mK (1.12 g/cm³) to 0.13 W/mK (0.64 g/cm³) with decreasing density. Samples were stable at high temperatures up to 1100 °C, and their cold strength was sufficiently high. The porous anorthite ceramics produced in this study can be used for insulation in high temperature applications.     

Fabrication of Gentamicin Sulfate-Loaded 3D-Printed Polyvinyl Alcohol/Sodium Alginate/Gelatin-Methacryloyl Hybrid Scaffolds for Skin Tissue Replacement

3D-printed scaffolds can better mimic the function of human skin, both biologically and mechanically. Within the scope of this study, the effect of the addition of different amounts (10, 15, 20 mg) of gentamicin sulfate (GS) to a 10 mL solution of natural and synthetic polymers is investigated. Sodium alginate (SA), gelatin-methacryloyl (GelMA), and polyvinyl alcohol (PVA) are chosen as bioactive materials. The surface morphology and pore structures are visualized by scanning electron microscopy (SEM). According to the results, it is observed that the pore sizes of all scaffolds are smaller than 270 µm, the lowest value (130 µm) is obtained in the scaffold loaded with 15 mg GS, and it also has the highest tensile strength value (12.5 ± 7.6 MPa). Similarly, it is observed that the tensile strength (9.7 ± 4.5 MPa) is high in scaffold loaded with 20 mg GS. The biocompatibility test is performed with fibroblast cells, and the results show that the scaffolds are biocompatible with cells. The antibacterial test is carried out against the S.aureous and E. coli and the results indicate that all GS-loaded scaffolds demonstrate antibacterial activity.     

Effects of expanded vermiculite on the properties of fired bricks from water treatment sludge

In the present study, the suitability of using water treatment sludge (WTS) as the main raw material and expanded vermiculite (EV) as aggregate in the production of fired bricks was investigated. Mixtures containing between 75%–100% WTS by weight (wt.) and 5%–25% EV by wt. were prepared at various proportions. The mixtures were compressed under 40 MPa pressure and fired at 1000°C. It was found the incorporation of EV in fired bricks resulted in a decrease in thermal conductivity, compressive strength, and bulk density and an increase in apparent porosity and water absorption. For the addition of 5%–25% EV by wt., bulk density ranged between 2.01 and 1.69 kg/m³, compressive strength 19.3 and 8.3 MPa, water absorption 21.1% and 10.1%, and thermal conductivity 0.678 and 0.374 W/m-K, respectively. Based on the promising physical and mechanical properties, fired bricks incorporating WTS and EV can potentially offer an alternative to the traditional production of clay bricks while adhering to the principle of a circular economy.     

Combinatorial Benders cuts for decomposing IMRT fluence maps using rectangular apertures

We consider the problem of decomposing Intensity Modulated Radiation Therapy (IMRT) fluence maps using rectangular apertures. A fluence map can be represented as an integer matrix, which denotes the intensity profile to be delivered to a patient through a given beam angle. We consider IMRT treatment machinery that can form rectangular apertures using conventional jaws, and hence, do not need sophisticated multi-leaf collimator (MLC) devices. The number of apertures used to deliver the fluence map needs to be minimized in order to treat the patient efficiently. From a mathematical point of view, the problem is equivalent to a minimum cardinality matrix decomposition problem. We propose a combinatorial Benders decomposition approach to solve this problem to optimality. We demonstrate the efficacy of our approach on a set of test instances derived from actual clinical data. We also compare our results with the literature and solutions obtained by solving a mixed-integer programming formulation of the problem.