Experimental investigation on the ball burnishing of carbon fiber reinforced polymer

The polymer-based materials are generally used in all industrial applications. Even if polymer bars can be machined easily, they need surface finishing treatment after the machining process. The ductile properties make coarse roughness on the surface that causes the elastic structure of polymer materials. The carbon fiber reinforced composite materials differ from polymer-based materials by high strength and stiffness. Its structure exhibits similar performances such as metallic materials. The effect of ball burnishing on the surface quality of rod workpiece was investigated in this study. To enhance the surface quality of high strength carbon fiber reinforced polymer rod workpiece, burnishing process was performed in three different parameters (force, feed rate, number of passes) and under four different mediums (dry, wet, boron oil, and mineral oil) conditions. The results of the experiments were analyzed, and optimum burnishing parameters were determined and discussed in detail. The best surface roughness value of the CFRP material used in the experiments was obtained as burnishing force: 250 N, feed rate: 0.05 mm/rev, four passes and wet medium. According to the results of variance analysis, it was found that the CFRP workpiece is the important leading factor for surface roughness with a contribution ratio of 62.47%.     

Effect of Untreated Surface Disbonds on Performance of FRP-Retrofitted Concrete Beams

Retrofitting concrete structures with externally bonded fiber-reinforced polymer (FRP) laminates has become an increasingly common practice. Disbonds at the concrete-FRP interface, if left untreated, may adversely affect the performance of the retrofitted system. Disbonds in the form of surface voids and cracks are the subject of this paper. Voids may occur due to poor compaction or defective formwork, or in the form of air entrapment between resin and FRP laminate during application. Cracks, on the other hand, generally result from loading. This study is comprised of a detailed experimental program and a nonlinear finite-element analysis. In the experiments, surface cracks were simulated by cutting slits in concrete, herein termed as surface cuts. The study shows that leaving surface disbonds untreated, within the considered range of disbond variables, does not have a significant impact on the overall structural performance. A threshold of 12.7 mm for void diameter was deemed conservative for structural performance. On the other hand, 38 mm spacing was considered an appropriate threshold for epoxy injection in crack widths between 0.25 and 0.8 mm. Hence, conservative thresholds in current practice may be revised accordingly, unless considered necessary to avoid environmental effects.     

All‐Stabilizing Proportional Controllers for First‐Order Bi‐Proper Systems with Time Delay: An Analytical Derivation

In this paper, a simple derivation for an all‐stabilizing proportional controller set for first‐order bi‐proper systems with time delay is proposed. In contrast to proper systems, an extremely limited number of studies are available in the literature for such bi‐proper systems. To fill this gap in the literature, broader aspects of the stabilizing set are taken into consideration. The effect of zero on the stabilizing set is clearly discussed and we also prove that, when their zeros are placed symmetrically to the origin, the stabilizing set of non‐minimum phase plant is always smaller than that of the minimum phase one. Moreover, for an open‐loop unstable plant, maximum allowable time delay (MATD) is explicitly expressed as a function of the locations of the pole and zero. From that function, it is shown that for a minimum phase plant, the supremum of the MATD is two times that of the time constant of the plant and the infimum of the MATD is the time constant of the plant. We also prove that the supremum is the time constant and the infimum is zero for a non‐minimum phase plant.     

Learning the stress function pattern of ordered weighted average aggregation using DBSCAN clustering

Ordered weighted average (OWA) operator provides a parameterized class of mean type operators between the minimum and the maximum. It is an important tool that can reflect the strategy of a decision maker for decision-making problems. In this study, the idea of obtaining the stress function from OWA weights has been put forward to generalize and characterize OWA weights. The main idea in this paper is mainly constructed on the basis that, generally, stress functions can be constructed using a mixture of constant and linear components. So, we can consider the stress function as a piecewise linear function. For obtaining stress functions as piecewise linear functions, we present a clustering-based approach for OWA weight generalization. This generalization is made using the DBSCAN algorithm as the learning method of a stress function associated with known OWA weights. In the learning process, the whole data set is divided into clusters, and then linear functions are obtained via a least squares estimator.     

The effects of middle infrared radiation intensity on the quality of dried tomato products

The effects of air temperature (T) (unheated and 35 °C), infrared radiation intensity (IP) (894, 1004, 1190, 1314 and 1410 Wm^?2) and air velocity (Av) (1.0, 1.5 and 2.0 ms^?1) on drying characteristics of tomatoes, drying time (DT), specific energy consumption (SEC) and quality parameters were investigated. DT and SEC varied between 114 and 249 min, 10.04 and 18.22 MJ kg^?1 water, respectively, and were significantly affected by process variables. Shrinkage ratio (S) and rehydration ratio (R_r) were varied between 0.129 and 0.214, 2.11 and 2.86 for all the drying conditions, respectively. Total colour change (ΔE) varied from 5.30 to 13.19. Vitamin C content decreased, while lycopene content increased with infrared drying. For optimum points, desirability of functions of all targets had satisfactory, very good and excellent desirability values and ranged between 0.54 and 0.99.     

Iterative skew minimization for low swing clocks

This paper presents a new methodology that implements a low swing clock tree. For low power IC design, low swing clock trees are one of the known techniques to lower the overall power dissipation through decreasing the power consumption of the clock network, while trading off the clock skew, local timing (slack) and the variation-tolerance (due to decreased noise margin). In this paper, an iterative skew minimization scheme for low swing clock trees is proposed via in-place buffer sizing considering multiple process corners. The proposed approach can preserve the power savings of the low swing clock tree implementation across multiple process corners. The effect of the decreased clock swing on the local timing is analyzed: The degradation in the timing slack is shown to be insignificant due to bounded clock slew eliminating most of the timing degradation on the clock network or the logic paths induced by decreased clock swing. The experimental results show that the proposed methodology can achieve an average of up to 11% power savings, with a skew degradation of less than 5% compared to the original full-swing clock tree, satisfying a practical skew budget. The proposed scheme is highly practical as it only performs in-place buffer sizing on the original clock tree.     

Synthesis and characterization of pyrrole and thiophene functional polystyrenes via “click chemistry”

Novel side-chain pyrrole or thiophene functional polystyrenes (PS-Py and PS-Th) were synthesized by using ‘‘click chemistry’’ strategy. First, approximately 40% of chloro groups of poly(styrene-co-chloromethylstyrene) P(S-co-CMS), prepared by nitroxide mediated radical polymerization (NMRP), were converted to azido groups by using NaN₃ in N,N-dimethylformamide. Propargyl pyrrole was prepared by etherification of 4-(1H-pyrrol-1-yl)phenol prepared by Clauson-Kaas reaction using propargylbromide. Propargyl thiophene was synthesized by heterogeneous esterification reaction between 3-thiophenecarboxylic acid and propargylbromide. Finally, azido-functionalized polystyrene was coupled to these propargyl functional heterocyclics with high efficiency by click chemistry. The intermediates at various stages and final polymers were characterized by spectral analysis and cyclic voltammetry.     

Effects of microwave and conventional baking on the oxidative stability and fatty acid composition of puff pastry

The effects of microwave and conventional baking on the fatty acid and trans fatty acid compositions of puff pastries, which contain high amounts of hydrogenated fat, were investigated. In addition, free fatty acids, peroxide value, and induction time for oxidative stability by the Rancimat method have been compared for microwave- and conventionally baked puff pastries. The data indicate there were considerable changes in acidity, peroxide value, and Rancimat induction time in both microwave- and conventionally baked samples. Although the content of saturated fatty acid such as palmitic and stearic and the ratio of saturated to unsaturated fatty acids did not change significantly, an apparent increase was determined in trans oleic acid levels by both baking methods. In addition, a significant decrease in linoleic acid content of the samples was found by microwave baking.