Improving fire retardancy of medium density fiberboard by nano-wollastonite

The improving effects of addition of nano-wollastonite on some fire properties of medium-density fiberboard (MDF) were studied in this work. Nano-wollastonite was added at four levels (2%, 4%, 6%, and 8%). The size range of at least 70% of nano-wollastonite particles were 30 to 110 nm. The results showed statistically significant improving effect of nano-wollastonite on time to onset of ignition. The improving effect was primarily attributed to an increase in thermal conductivity of board containing nano-wollastonite. This increase in turn resulted in better curing of resin, and a higher integrity of fibers thereof. Moreover, nano-particles provided a surface with reduced combustibility and therefore, penetration of fire to the inner layers of boards was delayed, thus improving fire properties. High and significant correlations were found between thermal conductivity coefficients of boards with different fire properties. It was concluded that for applications where fire properties are of prime importance, nano-wollastonite content of 8% can be recommended. Moreover, further studies are needed to compare and standardize the results obtained from the apparatus used here with those obtained from internationally recognized apparatuses like cone calorimeter.     

A review on powder-based additive manufacturing for tissue engineering: selective laser sintering and inkjet 3D printing

Since most starting materials for tissue engineering are in powder form, using powder-based additive manufacturing methods is attractive and practical. The principal point of employing additive manufacturing (AM) systems is to fabricate parts with arbitrary geometrical complexity with relatively minimal tooling cost and time. Selective laser sintering (SLS) and inkjet 3D printing (3DP) are two powerful and versatile AM techniques which are applicable to powder-based material systems. Hence, the latest state of knowledge available on the use of AM powder-based techniques in tissue engineering and their effect on mechanical and biological properties of fabricated tissues and scaffolds must be updated. Determining the effective setup of parameters, developing improved biocompatible/bioactive materials, and improving the mechanical/biological properties of laser sintered and 3D printed tissues are the three main concerns which have been investigated in this article.     

A multi-objective optimisation model to integrating flexible process planning and scheduling based on hybrid multi-objective simulated annealing

Process planning and production scheduling play important roles in manufacturing systems. In this paper we present a mixed integer linear programming (MILP) scheduling model, that is to say a slot-based multi-objective multi-product, that readily accounts for sequence-dependent preparation times (transition and set up times or machine changeover time). The proposed scheduling model becomes computationally expensive to solve for long time horizons. The aim is to find a set of high-quality trade-off solutions. This is a combinatorial optimisation problem with substantially large solution space, suggesting that it is highly difficult to find the best solutions with the exact search method. To account for this, the hybrid multi-objective simulated annealing algorithm (MOHSA) is proposed by fully utilising the capability of the exploration search and fast convergence. Two numerical experiments have been performed to demonstrate the effectiveness and robustness of the proposed algorithm.     

Biocompatible regenerated cellulose/halloysite nanocomposite fibers

Regenerated cellulose (RC) bio-nanocomposite fibers reinforced with halloysite nanotubes (HNT) were fabricated through wet spinning technique via ionic liquid as a green solvent. Mechanical properties, water uptake, thermal stability, and cytocompatibility of the obtained fibers were examined. FTIR spectra indicated the uniform dispersion of HNT in the cellulose network. XRD analysis, together with FE-SEM images indicated that HNT was dispersed homogenously in the polymer. Moreover, mechanical and thermal stabilities of the nanocomposite fibers were notably increased through the addition of HNT. Eventually, human skin fibroblasts proliferation on nanocomposite fibers demonstrated good cyto-compatibility. These findings highlight the potential of HNT nanocomposite fibers for biological and biomedical applications.     

Intelligent design of a dynamic machine layout in uncertain environment of flexible manufacturing systems

Since Facility Layout Problem (FLP) affects the total manufacturing cost significantly, it can be considered as a critical issue in the early stages of designing Flexible Manufacturing Systems (FMSs), particularly in volatile environments where uncertainty in product demands is inevitable. This paper proposes a new mathematical model by using the Quadratic Assignment Problem formulation for designing an optimal machine layout for each period of a dynamic machine layout problem in FMSs. The product demands are considered as independent normally distributed random variables with known Probability Density Function (PDF), which changes from period to period at random. In this model, the decision maker’s defined confidence level is also considered. The confidence level represents the decision maker’s attitude about uncertainty in product demands in such a way that it affects the results of the problem significantly. To validate the proposed model, two different size test problems are generated at random. Since the FLP, especially in multi-period case is a hard Combinatorial Optimization Problem (COP), Simulated Annealing (SA) meta-heuristic resolution approach programmed in Matlab is used to solve the mathematical model in a reasonable computational time. Finally, the computational results are evaluated statistically.     

Spritzbeton — der etwas andere Beton

Shotcrete — a special Concrete Analysis of Material Behaviour and Tests Shotcrete is one of the main support measures when doing excavational works according to the “New Austrian Tunnelling Method” (NATM). The peculiarity of a support made of shotcrete is that the young shotcrete, which runs through the hydration process, is subjected to rather large constraints. The estimation of the load bearing capability of shotcrete in comparison to the actual degree of loading needs the knowledge about its time dependent strength and the actual stress state. The problematic stress monitoring using hydraulic stress cells is replaced by the introduction of a time‐dependent stress — strain relationship and displacement resp. strain monitoring. This approach enables the calculation of the actual stresses via the strains which are derived from the monitoring data.     

A review of intelligent approaches for designing dynamic and robust layouts in flexible manufacturing systems

Facility layout problem is associated with the arrangement of facilities in a plant. It is a critical issue in the early stages of designing a manufacturing system because it affects the total manufacturing cost significantly. Dynamic and robust layouts are flexible enough to cope with fluctuations and uncertainties in product demands in volatile environment of flexible manufacturing systems. Since the facility layout is a hard combinatorial optimization problem, intelligent approaches are the most appropriate methods for solving the large size of this problem in reasonable computational time. In this paper, first of all, dynamic and robust layouts are surveyed. After a quick look of different mathematical models, including quadratic assignment, quadratic set covering, mixed integer programming, and graph theoretic models, the various solution methods especially intelligent approaches along with their advantages and disadvantages are surveyed. Finally, after review of hybrid algorithms, the conclusion of this paper is reported.