Multi-scale homogenization of moving interface problems with flux jumps: application to solidification

In this paper, a multi-scale analysis scheme for solidification based on two-scale computational homogenization is discussed. Solidification problems involve evolution of surfaces coupled with flux jump boundary conditions across interfaces. We provide consistent macro-micro transition and averaging rules based on Hill’s macro- homogeneity condition. The overall macro-scale behavior is analyzed with solidification at the micro-scale modeled using an enthalpy formulation. The method is versatile in the sense that two different models can be employed at the macro- and micro-scales. The micro-scale model can incorporate all the physics associated with solidification including moving interfaces and flux discontinuities, while the macro-scale model needs to only model thermal conduction using continuous (homogenized) fields. The convergence behavior of the tightly coupled macro-micro finite element scheme with respect to decreasing element size is analyzed by comparing with a known analytical solution of the Stefan problem.     

Multi-scale structuring for thermoplastic-metal contour joints of hollow profiles

In contrast to common and classical joining technologies for composite/metal hybrid structures such as bonding and riveting, profile and contour joints offer a promising potential for novel lightweight hybrid structures. Contour joints with form locking elements on multiple scale levels enable to pass very high loads into rod- and tube-shaped fibre reinforced structures and promise high degrees of material utilization for the composite part. This paper demonstrates the advantage of multi-scale structured load introduction elements. First the intrinsic manufacturing process, whereas the thermoplastic tape braided preform is simultaneously consolidated and formed into the metallic load introduction element is shown. Numerical investigations on the macro- and generic microscale demonstrate the potential to trigger cohesive or adhesive failure by appropriate designed form locking elements. The extensive experimental investigation of meso-, macro- or combined-structured tubular specimen shows the beneficial effect of multi-scale structuring to increase the joining strength. Concluding advises for the contour joints’ design are given.     

Motivational and cognitive benefits of training in immersive virtual reality based on multiple assessments

The main objective of this study was to examine the effectiveness of immersive virtual reality (VR) as a medium for delivering laboratory safety training. We specifically compare an immersive VR simulation, a desktop VR simulation, and a conventional safety manual. The sample included 105 first year undergraduate engineering students (56 females).  We include five types of learning outcomes including post‐test enjoyment ratings; pre‐ to post‐test changes in intrinsic motivation and self‐efficacy; a post‐test multiple choice retention test; and two behavioral transfer tests. Results indicated that the groups did not differ on the immediate retention test, suggesting that all three media were equivalent in conveying the basic knowledge. However, significant differences were observed favoring the immersive VR group compared to the text group on the two transfer tests involving the solving problems in a physical lab setting (d = 0.54, d = 0.57), as well as enjoyment (d = 1.44) and increases in intrinsic motivation (d = 0.69) and self‐efficacy (d = 0.60). The desktop VR group scored significantly higher than the text group on one transfer test (d = 0.63) but not the other (d= 0.11), as well as enjoyment (d =1.11) and intrinsic motivation (d =0.83).     

Crystal growth and reflectivity studies of Zn1-xMnxTe crystals

Single crystals of Zn_1-xMn_xTe were prepared by vertical Bridgman crystal growth method for different concentrations of Mn. Chemical analysis and reflectivity studies were carried out for compositional and band structure properties. Microscopic variation in composition between starting and end compounds was observed from EDAX analysis. Linear dependence of fundamental absorption edgeE ₀as a function of Mn concentration (x) was expressed in terms of a straight line fit and a shift in E₀ towards higher energy was observed in reflectivity spectra of Zn_1-xMn_xTe.     

Crosslinkable coupling agents: Synthesis and use for modification of interfaces in polymer blends

A novel coupling agent containing 2-oxazoline and 2-oxazinone as well as hydrosilane moieties has been prepared by hydrosilylation of the corresponding allyl ether containing precursor with a methylhydrosiloxane-dimethylsiloxane copolymer. This hydrosiloxane containing coupling agent, termed as SCA, was characterized by ¹H NMR and its crosslinkability was proven by DSC. SCA was used for the modification of the interfaces in heterogeneous polymer blends. In a model blend system based on mono-carboxylic acid terminated polystyrene (PS-COOH) and mono-amino terminated poly(methyl methacrylate) (PMMA-NH₂) the 2-oxazoline and 2-oxazinone units of SCA can selectively react with the carboxylic groups or amino groups, respectively. The remaining hydrosilane units partially crosslink under the used mixing conditions.The morphology of the three-component blends prepared by melt mixing was evaluated. SCA is immiscible with the polymers and forms its own phase. The expected location of the SCA at the interface between the polymers was proven only in an annealed, strongly phase separated blend. Overall the effect of the compatibilizer on the morphology is very small. Neither the domain size nor the composition for phase inversion are significantly affected in this blend system by the presence of SCA.     

The effect of temperature on mechanical properties and failure behaviour of hybrid yarn textile-reinforced thermoplastics

Multi-axially reinforced textile composites with thermoplastic matrix are investigated under thermomechanical loading conditions. Two groups of composites made of glass fibre/polypropylene hybrid yarn are chosen as examples: a novel 3-D textile-reinforced composite with multi-layered flat bed weft-knitted reinforcement and a composite with woven reinforcement. The presented study concentrates on determining the mechanical properties depending on temperature and investigating the complex failure behaviour and its provoking phenomenological damage processes like void growth and inter fibre damage at different temperatures by the use of optical microscopy and visual observations of specimens. With the focus on automotive applications, the elasticity constants and strength values have been determined in the range from ?40 °C up to 80 °C using uniaxial tensile and compressive tests. As a result, the basic properties like stiffnesses and strengths are mathematically described depending on the temperature. Additionally, dynamic-mechanical analysis have been used to identify the glass transition range of the thermoplastic matrix system and to find correlation to the temperature-dependent mechanical properties.     

Hall effects on magnetohydrodynamic rotating flow through porous medium in a parallel plate channel with various oscillations of pressure gradient

We explored the unsteady flow of an incompressible electrically conducting viscous fluid in a gyratory porous medium with a changeable pressure gradient by taking Hall currents into account. The governing equations are then solved analytically with the help of the Laplace transforms methodology. It is regarded as three dissimilar cases, namely, an impulsive change, cosine as well as sine oscillations of the pressure gradient. The physical significances of different dimensionless parameters on velocity distributions are explored analytically and computationally. It is observed that a thin boundary layer is formed near the plate of the channel and the thicknesses of the layer increase with the increase in either the Hall parameter or Reynolds number while it decreases with an increase in Hartmann number. It is interesting to note that the rotation and Lorentz forces are having noteworthy effects on velocity profiles with pressure gradient and Hall currents.     

Viscoelastic,Mechanical and DOE-Based Study on PP-Nanocomposites

This paper deals with the quasi-static and dynamic mechanical analysis of montmorillonite filled polypropylene composites. Nanocomposites were prepared by blending montmorillonite (nanoclay) varying from 3 to 9% by weight with polypropylene. The dynamic mechanical properties such as storage modulus, loss modulus and mechanical loss factor of PP and nano-composites were investigated by varying temperature and frequencies. Results showed better mechanical and thermomechanical properties at higher concentration of nanoclay. Regression-based models through design of experiments (DOE) were developed to find the storage modulus and compared with theoretical models and DOE-based models.     

Novel Design Methods for Composite Structures under High-Strain-Rate Loading Conditions

Journal of Failure Analysis and Prevention - Fiber- and textile-reinforced composite materials are predestined for the application in high-performance lightweight constructions due to the extreme...     

Thermal desalination of ballast water using onboard waste heat in marine industry

Ballast water management is a national and international issue in the shipping industry because of potential ecological hazards caused by the release of ballast water into the marine environment. Although many international standards have been implemented in recent years, technological and practical considerations make the ballast water treatment a major challenge for many shipping companies. In this paper, a novel concept of utilizing ballast water as source water for a multieffect desalination process driven by onboard waste heat to meet the freshwater supply needs is proposed with theoretical analysis and practical considerations. A main engine with a capacity of 7500 kW in a cruise ship can serve as a potential waste heat source for water desalination of 1000 m³/d, which can provide for freshwater needs of 2000 to 4000 ship occupants. This scenario presents an attractive alternative to ballast water management and treatment as well as reducing the nonrenewable energy footprint of onboard water supplies in marine industry.