Occurrence and morphology of bead-on-string structures in centrifugal forcespun PA6 fibers

This research aimed at investigating the morphology and frequency of bead-on-string occurrences on forcespun nano- and sub-micron fibers. The formation of bead-on-string structures was observed on a range of fiber samples forcespun in varied conditions from PA6 solutions of different concentrations. Bead-on-string structures were characterized for morphology using SEM micrographs, and were counted on all samples. Two major factors appeared to affect both the morphology and the bead count, namely spinning solution concentration, i.e. viscosity, and spinning needle gage or diameter. Low viscosity solutions resulted in large numbers of mostly spherical beads. Solutions with higher viscosity appeared to suppress the fluid jet instability thus resulting in significantly fewer beads with exclusively elongated spindle-like shapes. Spinning needle diameter also had a significant impact on beading behavior, with the larger diameter exhibiting higher bead counts. A significant interaction between the two factors was detected and its impact on the competition between the fluid jet visco-elastic relaxation and the Rayleigh instability is discussed.     

Resistance factors for blind bolts in direct tension

Blind bolts are developed to be used in applications where access for installation is from one side of the connection only, as in the case of connecting the end-plate of a beam to a hollow column. Blind fasteners offer many advantages including strengths and sizes comparable to A325 fasteners, potential use in tension applications as well as in moment-resisting connections and ease of installation. In this study, reliability analyses are conducted in order to develop resistance factors for blind bolts designed following the AISC's LRFD specification. The limit state that is considered is the direct tension only. The applied loading consists of dead load, live load and wind. Probabilistic resistance models are developed for blind fasteners based on experimental test results. The statistics of load models on building structures are compiled from the available literature. The study considers a wide range of live-to-dead load ratios and several wind load intensities. The results of the reliability analysis indicate that a resistance factor in the order of 0.65 is adequate.     

Adaptive sliding mode control for fuzzy singular systems with time delay and input nonlinearity

This paper addresses the sliding mode control problem for a class of uncertain Takagi‐Sugeno fuzzy singular systems with state delay and subject to input nonlinearity. Our purpose is focused on designing an adaptive sliding mode controller for such a complex system. First, a new fuzzy integral‐type sliding function is designed. Then, an adaptive sliding mode control scheme is established such that the resulting closed‐loop system is insensitive to all admissible uncertainties and satisfies the reaching condition. Moreover, delay‐dependent sufficient conditions are derived such that the admissibility and the L₂‐L_∞ performance requirement of the sliding mode dynamics can be guaranteed in the presence of time delays, external disturbances, and sector nonlinearity input. Finally, the validity and applicability of the proposed theory are illustrated by a numerical example.     

FE simulation of repaired timber beams under tensile load using CFRP patches

Timber is a highly orthotropic material with highest strength presented in tension along the grain direction. Repaired timber structural elements in pure tension using carbon fibre–epoxy patches provide new opportunities as it is well adapted to the nature of wood. Such repairing process is very interesting as it is easy to use for assembling two damaged parts of timber and has a low environmental impact. Before this process can become widespread in the industry, it is necessary to develop numerical tools for predicting the behaviour of such assemblies under tensile loads. Only a few experimental tests have been offered in the literature, and even fewer numerical studies have been carried out to analyse the complex mechanical behaviour of timber. The present paper describes the use of carbon fibre–epoxy patches for repairing timber beams under tensile stress along the grain direction. The repaired beams with CFRP patches using varying repair lengths were examined. The load-carrying capacity increased by about 47%, passing from a repair length of 5 mm (F = 3.8 kN) to a repair length of 10 mm (F = 6.6 kN) at a displacement u = 0.3 mm. A three-dimensional (3-D) numerical methodology for virtual loading process under pure tension, including the interaction between two adherent surfaces and taking the presence of an adhesive layer into account, is presented from both theoretical and numerical point of views. Predicted and measured load–displacement responses and failure modes are compared. The predicted results are in good agreement with the experimentally measured test data.     

Activated Carbon from Some Agricultural Wastes Under Action of One-Step Steam Pyrolysis

A one-step steam pyrolysis scheme was applied, in the range 600–700°C, for the production of activated carbons from five lignocellulosic materials. The products were characterized by N₂/77 K adsorption for evaluating their surface area and pore volume. Simple carbonization at 700 C resulted in poor adsorbing carbons whereas porosity was remarkably enhanced under action of steam. Carbon precursors derived from date palm wastes (branches, leaves and date pits) proved feasible raw materials that produced good adsorbing carbons. Rice husks and barbecue charcoal developed porosity to a lower extent, due to the inherent ash content. All obtained carbons were essentially microporous due to the limited gasification. Steam is suggested to play a double role: it promotes both the release of volatiles with partial devolatalization, and enhances carbon formation.     

Modelling of a hybrid photovoltaic thermal collector based on CdTe

A few years ago, silicon photovoltaic panels had yields of 10 to 18%, which made them interesting because is not profitable enough (too expensive to energy conversion yield too low).But recently, thin film technology appears to increase the efficiency and reduce the cost. For application in hybrid collectors, various types of solar photovoltaic hybrid collectors (PVT) based on new materials for solar cells have been developed as the binary semiconductor, ternary and quaternary materials and organic. CdTe is a the most appropriate binary materials for use in photovoltaic structures in thin layers, this material can produce a high yield of about 15% and is also known by a direct band structure gap of a value of 1.45 eV and a very high absorption coefficient (>105 cm^–1 in the visible). In this work we present the modeling of a hybrid photovoltaic thermal collector based on the thin films solar cells of CdTe, and then we made the determination of the temperature levels of the various layers through the development of the energy balance sheet involves heat exchange between the different components of the collector and to study its electrical and thermal performance, and finally compare their efficiency with it of the PVT collector based on monocrystalline silicon.     

Determination of ball mill residence time distributions form tracer data taken in closed-circuit operation

Based on a method which searches on the parameter values for models, the possible one- and two-detection system tracer methods for the determination of ball mill residence time distributions from data taken on closed-circuit recycle systems are treated. Mathematical relationships for the most promising approaches are developed for both methods. This includes deriving, demonstrating, and verifying (with existing simple analytical models of closed-circuit mills) analytical models of tracer input and output based on the use of tanks-in-series and finite stage models with the convolution integral principle. Simulated results for typical processes are given and non-linear search methods are described and demonstrated for determining mill residence time distribution model parameters.