Computational analysis of the thermal conductivity of the carbon–carbon composite materials

Experimental data for carbon–carbon constituent materials are combined with a three-dimensional stationary heat-transfer finite element analysis to compute the average transverse and longitudinal thermal conductivities in carbon–carbon composites. Particular attention is given in elucidating the roles of various micro-structural defects such as de-bonded fiber/matrix interfaces, cracks and voids on thermal conductivity in these materials. In addition, the effect of the fiber precursor material is explored by analyzing PAN-based and pitch-based carbon fibers, both in the same type pitch-based carbon matrix. The finite element analysis is carried out at two distinct length scales: (a) a micro scale comparable with the diameter of carbon fibers and (b) a macro scale comparable with the thickness of carbon–carbon composite structures used in the thermal protection systems for space vehicles. The results obtain at room temperature are quite consistent with their experimental counterparts. At high temperatures, the model predicts that the contributions of gas-phase conduction and radiation within the micro-structural defects can significantly increase the transverse thermal conductivity of the carbon–carbon composites.     

A robust numerical approach for the simulation of skin–stringer debonding growth in stiffened composite panels under compression

In this paper, a numerical study on skin–stringer debonding growth in stiffened composite panels has been carried out. A novel numerical methodology is proposed here to investigate the compressive behaviour of a stiffened composite panel in the presence of skin–stringer partial separation. The novel numerical methodology, able to overcome the mesh size and time increment dependency of the standard Virtual Crack Closure Technique (VCCT), is an evolution of a previously developed and tested numerical approach for the circular delaminations growth. The enhancements, with respect to the previously developed approach, rely mainly in the capability to deal with the different defect shapes characterising a skin–stringer debonding. The proposed novel methodology has been implemented in a commercial finite element platform and tested over single stiffener composite panels. The effectiveness of the suggested numerical methodology, in predicting the compressive behaviour of stiffened panels with skin stringer debondings, has been preliminary confirmed by comparisons, in terms of load versus applied displacement and debonding size at failure, with literature experimental data and numerical results obtained with the standard VCCT approach.     

Disassembly methodology for conducting failure analysis on lithium–ion batteries

To facilitate construction analysis, failure analysis, and research in lithium–ion battery technology, a high quality methodology for battery disassembly is needed. This paper presents a methodology for battery disassembly that considers key factors based on the nature and purpose of post-disassembly analysis. The methodology involves upfront consideration of analysis paths that will be conducted on the exposed internal components to preserve the state (operational or failed) of the battery. The disassembly processes and exposures must not alter the battery materials once they are removed from their hermetically sealed containers. Because the process of battery disassembly can involve exposure to potentially hazardous compounds or lead to thermal run-away, a brief review concerning the safety hazards of disassembly is also given.     

3D Stochastic Modeling of Grain Structure for Aluminum Alloy Casting

A 3D stochastic modeling was carried out to simulate the dendritic grains during solidification of aluminum alloys,including time-dependent calculations for temperature field, solute redistribution in liquid, curvature of the dendritic tip, and growth anisotropy. The nucleation process was treated by continuous nucleation. A 3D simplified grain shape model was established to represent the equiaxed dendritic grain. Based on the Cellular Automaton method,a grain growth model was proposed to capture the neighbor cells of the nucleated cell. During growing, each grainc ontinues to capture the nearest neighbor cells to form the final shape. When a neighbor cell was captured by other grains, the grain growth along this direction would be stopped. Three-dimensional calculations were performed to simulate the evolution of dendritic grain. In order to verify the modeling results, the predictions were compared with the observation on samples cast in the sand mold and the metal mold.     

A model for a long-term diffusion of multispecies in concrete based on ion–cement-hydrate interaction

A model for simulating a long-term diffusion in concrete under submerged conditions has been developed. The model focuses on the interaction between cement hydrates and electrolyte solution adopting the physical properties of concrete as alternative parameters for estimating long-term diffusion. The model was verified by the large variety of long-term experimental data involving verification of cement hydrates, porosity properties, pH value, element distribution, and chloride penetration for sulphate-resistant Portland cement (SRPC) concretes. Evaluating impacts of hundreds of years’ exposure on concrete durability, a simulation was also performed for an exposure time of 500 years. The results confirmed the importance of ion–cement-hydrate interaction in the evaluation of a long-term diffusion of harmful substances such as chlorides into concrete. The simulation results show also that the solid phases of the SRPC concrete mix that was used are stable in the long-term. The threshold concentration of chlorides which may initiate reinforcement corrosion defined as Cl^?/OH^? ratio could be exceeded in concrete after moderate exposure period under the conditions investigated with typical protective concrete layers. Using of case-specific values for a threshold chloride content and evaluating the method used for estimating the initiation time of reinforcement corrosion are recommended in the structures with a long-design service life.     

A simulation model of the Triple Helix of university–industry–government relations and the decomposition of the redundancy

A Triple Helix (TH) network of bi- and trilateral relations among universities, industries, and governments can be considered as an ecosystem in which uncertainty can be reduced when functions become synergetic. The functions are based on correlations among distributions of relations, and therefore latent. The correlations span a vector space in which two vectors (P and Q) can be used to represent forward “sending” and reflexive “receiving,” respectively. These two vectors can also be understood in terms of the generation versus reduction of uncertainty in the communication field that results from interactions among the three bi-lateral channels of communication. We specify a system of Lotka–Volterra equations between the vectors that can be solved. Redundancy generation can then be simulated and the results can be decomposed in terms of the TH components. Furthermore, we show that the strength and frequency of the relations are independent parameters in the model. Redundancy generation in TH arrangements can be decomposed using Fourier analysis of the time-series of empirical studies. As an example, the case of co-authorship relations in Japan is re-analyzed. The model allows us to interpret the sinusoidal functions of the Fourier analysis as representing redundancies.     

Tailoring the Spatial Distribution and Content of Inorganic Nitrides in Solid–Electrolyte Interphases for the Stable Li Anode in Li–S Batteries

Among the alternatives to lithium-ion batteries, lithium–sulfur(Li–S)batteries are considered as an attractive option because of their high theoretical energy density of 2570 Wh kg^-1. However, the application of the Li–S battery has been plagued by the rapid failure of the Li anode due to the Li dendrite growth and severe parasitic reactions between Li and lithium polysulfides. The physicochemical properties of the solid–electrolyte interphase have a profound impact on the performance...     

Finite element analysis of 3D elastic–plastic frictional contact problem for Cosserat materials

The objective of this paper is to develop a finite element model for 3D elastic–plastic frictional contact problem of Cosserat materials. Because 3D elastic–plastic frictional contact problems belong to the unspecified boundary problems with nonlinearities in both material and geometric forms, a large number of calculations are needed to obtain numerical results with high accuracy. Based on the parametric variational principle and the corresponding quadratic programming method for numerical simulation of frictional contact problems, a finite element model is developed for 3D elastic–plastic frictional contact analysis of Cosserat materials. The problems are finally reduced to linear complementarity problems (LCP). Numerical examples show the feasibility and importance of the developed model for analyzing the contact problems of structures with materials which have micro-polar characteristics.     

Permeability prediction for the meso–macro coupling in the simulation of the impregnation stage of Resin Transfer Moulding

The impregnation stage of the Resin Transfer Moulding process can be simulated by solving the Darcy equations on a mould model, with a ‘macro-scale’ finite element method. For every element, a local ‘meso-scale’ permeability must be determined, taking into account the local deformation of the textile reinforcement. This paper demonstrates that the meso-scale permeability can be computed efficiently and accurately by using meso-scale simulation tools. We discuss the speed and accuracy requirements dictated by the macro-scale simulations. We show that these requirements can be achieved for two meso-scale simulators, coupled with a geometrical textile reinforcement modeller. The first solver is based on a finite difference discretisation of the Stokes equations, the second uses an approximate model, based on a 2D simulation of the flow.     

Considerations for the industrial application of structural adhesive joints in the aluminium–composite material bonding

The composite materials of the polymeric matrix reinforced with carbon fibre have an extensive industrial application as they provide light and resistant structures. However, in many products (automobiles, aircraft, etc.) the structural adhesive parts must be joined to other components manufactured with aluminium alloys. The use of structural adhesive to carry out these bonds may be a good alternative if a specific design of the adhesive joint is carried out maximising its performance and reducing its limitations. In this respect, one of the most relevant aspects of the design of the joint consists of the selection of the structural adhesive and the most appropriate surface treatment for the substratum. The present paper describes a procedure to optimise this decision by means of the combination of experimental techniques with multi-criteria decision tools. This methodology allows selecting, amongst the various alternatives, the adhesive and surface treatment better combining mechanical performance and adaptation to the manufacturing process. Thus, it has been concluded that polyurethane adhesive with a peel ply surface treatment for carbon fibre, and sandpapered for aluminium, are the best alternatives.     

Quartz–titania composites for the photocatalytical modification of construction materials

In this paper the synthesis of photocatalytically modified core–shell composites is reported. The synthesis was realized by hydrolysis and condensation of tetrapropylorthotitanate on ground quartz, which is used as an additive in mortar and concrete. This allowed a controlled growth of titania layers on the particles with different thicknesses. The efficiency of the coating process was studied by interpretation of XRF results. The morphology of the composites was analyzed via SEM. Photoactivity of the particles was studied by analyzing the titania crystal phases of the shell (XRD) and calculating the photonic efficiency of NO-degradation measurements. Moreover methylene blue degradation was performed to reflect the self cleaning properties of the composite materials.     

An elastic–plastic constitutive model for ceramic composite laminates

Existing phenomenological constitutive models are unable to capture the full range of behaviors of ceramic composite laminates. To ameliorate this deficiency, we propose a new model based on the deformation theory of plasticity. The predictive capabilities of the model are assessed through comparisons of computed and measured strain and displacement fields in open-hole tension tests. The agreements in the magnitude of strains and in the size and shape of shear bands that develop around a hole are very good over most of the loading history. Some discrepancies are obtained at high stresses. These are tentatively attributed to non-proportional stressing of some material elements: a feature not captured by the present model.     

A Monte Carlo simulation for the study of the influence of the thickness of the source in 3H β-ray spectroscopy

A Monte Carlo simulation for the study of the influence of the thickness of the radioactive source in β-ray spectroscopy is presented in this paper. We make use of the Bethe-Bloch formula for ionization loss and Rutherford scattering cross section to trace the tracks of the β particles from a randomly sampled point source of given energy, which has been implanted in an aluminum coating with copper backing. We have studied seven groups of β rays with momenta from 119.14262 to 139.12328 keV/c. There are the peak shift, the broadening of the line width and the low energy tail. Their momentum dependences have been found. The program can be applied to similar cases with minor modification.     

Amorphous SnO–Sb2O3–SiO2 glassy anode: high-performance electrode materials for Na-ion batteries

Journal of Materials Science: Materials in Electronics - Amorphous SnO–Sb2O3–SiO2 glass anode prepared by simple mechanical ball milling method. Physical and electrochemical properties...     

Molecular dynamics simulation of the nonlinear behavior of the CNT-reinforced calcium silicate hydrate (C–S–H) composite

Calcium–Silicate–Hydrate (C–S–H), which is the major constituent of the cement at the nanoscale, is responsible for the strength and fracture properties of concrete. This research is dedicated to the numerical study of enhanced mechanical properties of C–S–H reinforced by embedding carbon nanotube (CNT) in its molecular structure. Series of molecular dynamics (MD) simulations indicate that the tensile strength of CNT-reinforced C–S–H is substantially enhanced along the direction of CNT as compared to the pure C–S–H. The results of tensile loading reveal that CNT can efficiently bridge the two sides of cracked C–S–H. In addition, CNTs can severely intensify the “transversely isotropic” response of the CNT-reinforced C–S–H. Furthermore, the pull-out behavior of CNT reveals that the force-displacement response can be estimated by a bilinear model, which can later be used for simulation of cohesive crack propagation and multiscale simulation of crack bridging at macro scale specimen of CNT-reinforced cement.