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Nowadays, Machine Learning (ML) model of the structure-property relation based on large data from reliable physical models becomes a new and promising approach for material design. The present work demonstrates such approach to examine the variation in microstructure features on mechanical properties of paper materials. After the generation of a “big” dataset of fiber network samples, morphological feature data, including interfiber contact properties were extracted and statistically evaluated. By performing cohesive finite element simulations, the mechanical properties including failure strain, effective stiffness, and maximal stress of fiber networks under tensile test were determined and served along with structural feature data for the ML analysis. Gradient Boosting method achieved a performance score of approx. 0.9 for all mechanical properties of such complex fibrous structure. It was found that “disorderness” represented by the variation of fiber network orientation and the mean contact area size to be the most influential factors to the failure strain and effective stiffness. Whereas the failure strength was driven by the homogeneous distribution of the contact areas. The results validated the strong orientation dependence of fibrous materials in experimental observations and enlighten the importance of sensitivity as feature parameters and the striking potential of ML for material optimization.

In present investigation, an attempt was made to optimise the peak stress for paper laminate composite using FRANC2D software. It was observed that the laminate having the triangular geometry supposed to be most appropriate as it has the lowest value of peak stress contour compared to other models like parallel strip, up-down tapered and down-up tapered. The minimum peak stress was observed for the samples having triangular geometry while the maximum was observed for down-up tapered samples. Therefore, the hypothesis adopted to use in-built materials with variables reinforcement area and strip geometry and length in the FRANC2D software to optimize the sample geometry and then apply it to the paper laminate by considering its mechanical properties might be use to optimize the peak stress of paper laminate composite in tensile loading conditions. It was also observed a length of one-quarter of the length of the plane strip, might be the optimum length of the paper laminate samples. However, it feels that, the above model can be further modified considering a more significant mechanical properties as well as different sample geometries.

The heat dissipation factor of conventional epoxy impregnated paper bushings is a subject of concern due to the large quantities of power in a High Voltage Direct Current (HVDC) system. The present work deals with the selection of better insulation as a replacement to the conventional resin impregnated material employing nano-hexagonal-Boron Nitride and nano-hexagonal-Boron Nitride added with nano-cellulose-fiber. The bushing of the converter transformer is designed using the Finite Element Method (FEM), and the electrothermal analysis is performed at the loaded working condition. Besides, numerous optimization schemes are also presented for adapting the structure of the thermal conductor enclosed in the inner conductor. The electrothermal performances of the above materials with the optimized structure are compared and an advanced scheme is proposed. Further, the results obtained from the designed system are employed in the form of an Artificial Neural Network to simplify the process of thermal computation characterized by the selected scheme. The internal parameters of the neural network are tuned implementing a hybrid amalgamation of Particle Swarm optimization - Grey Wolf Optimiser and the performance is compared against the actual values. The supremacy of the implemented algorithm is justified by a comparative analysis with other well-established algorithms using various statistical parameters.

The thermal response in paper has been studied by thermography. It was observed that an inhomogeneous deformation pattern arose in the paper samples during tensile testing. In the plastic regime a pattern of warmer streaks could be observed in the samples. On the same samples digital image correlation (DIC) was used to study local strain fields. It was concluded that the heat patterns observed by thermography coincided with the deformation patterns observed by DIC. Because of its fibrous network structure, paper has an inhomogeneous micro-structure, which is called formation. It could be shown that the formation was the cause of the inhomogeneous deformations in paper. Finite element simulations was used to show how papers with different degrees of heterogeneity would deform. Creped papers, where the strain at break has been increased, were analysed. For these paper it was seen that an overlaid compaction of the paper was created during the creping process. During tensile testing this was recovered as the paper network structure was strained.

The moisture transport at the fuser nip of printers is postulated to be the main reason for paper curls. However, the fundamental mechanisms of paper curling remain unclear. Observing the moisture transport inside a sheet of paper through experiments is difficult because moisture transport rapidly occurs in a micro-scale thickness. Therefore, developing a theoretical model is crucial to understand the mechanisms of paper curling and to control the curls. In this study, we proposed a multiphysics model that includes the moisture and heat transport and mechanical deformation. The elasticity, plasticity, viscosity, and expansion caused by moisture were considered in the mechanical model to describe the complex material characteristics of paper. The curvature of curls was calculated using an effective two-spring model. The mechanisms of curling in printers and the direction of curls were understood through finite element simulations. The proposed model can qualitatively predict the paper curls observed in experiments. The temperature- and moisture-dependent material properties of paper will be studied in the future to improve the proposed model.

Paper is a complex material consisting of a network of cellulose fibres at the micro-level. During manufacturing, the network is dried under restraint conditions due to tension in the paper web in machine direction. This gives rise to internal strains that are stored in the produced sheet. Upon exposure to a moisture cycle, these strains may be released. This results in permanent shrinkage that may cause instabilities such as curl or waviness of the sheet. The prime objective of this paper is to model this irreversible shrinkage and to link its magnitude to the properties of the fibres and of the network. For this purpose, randomly generated fibrous networks of different coverages (i.e. ratio of the area occupied by fibres and that of the sheet) are modeled by means of a periodic representative volume element (RVE). Within such RVEs, a finite element method combined with a kinematic hardening plasticity model at the scale of the fibres is used to capture the irreversible response. The computational results obtained demonstrate that the magnitude of the irreversible strains increases with coverage until a certain coverage and beyond that coverage decreases in magnitude. This phenomenon is explained by considering the area fraction of free-standing fibre segments relative to bonded fibre segments in the network. A structure–property dependency of irreversible strains at the sheet-level on the micro-structural parameters of the network is thereby established., SCOPUS: ar.j, info:eu-repo/semantics/published

The Electric Field and Voltage Distribution (EFVD) are an important parameter for assessing high voltage bushing transformer performance. However, conducting laboratories experiment is dangerous, difficult and expensive due to several aspects. Therefore, Finite Element Method (FEM) software is the best option used as a tool for the assessment of bushing transformer's performance in terms of EFVD. But, before an assessment of analysis could be carried out, an accurate model of bushing transformer must first to be designed. In this research, Computer Aided Design (CAD) software has been employed to design the 145kV bushing transformer based on actual dimension. Upon completion, the design has been exported to FEM software for further analysis. In FEM software, measurement and analysis of electric field and voltage distribution (EFVD) have been carried out. The measurements are performed at various locations of bushing transformer such as of the porcelain surface (both air and oil side), along with aluminum foils, and at oil-impregnated paper (OIP). The results obtained have been compared with other researchers and it is found very satisfactory.

The aim of this research is to develop a physical model useful for measuring the influence of ageing, temperature and water content on the high voltage behavior of oil-paper insulation. The insulation model, made in accordance with the instrument transformer design practice, is placed in a specifically designed capsule in which those parameters can be controlled. All the parts of the capsule were electrically optimized using finite element method-based software. A procedure for insulation preparation that quantifies the water content has been developed. The partial discharge tests verify the applicability of the designed capsule. Thermal testing verifies the model’s useful temperature range up to 120 °C.

Understanding heat transfer in corrugated fibreboard is important to the design of more effective packaging for industries which involve the freezing and chilling of food. In this work the thermal conductivity of papers which compose corrugated fibreboard were measured and used to validate finite element models of heat transfer in fibreboard. The results showed paper to be highly anisotropic, with thermal conductivity in the machine and cross machine directions being almost an order of magnitude larger than in the thickness direction. The finite element models showed good agreement with experimental results and demonstrated that the majority of heat transfer in corrugated fibreboard is though the fluted medium. Based on the finite element models, simple models for the prediction of the thermal performance of corrugated board were evaluated and shown to be very effective in reproducing the results of the more complex finite element methods. These simple methods can be used to perform corrugated fibreboard design calculations, and the models with and without radiation can be used to provide estimates of the lower and upper bounds of the thermal resistance for a given board design.

The finite element model for paper honeycomb was constructed, and the finite element method of out-of-plane compression for the paper honeycomb was studied. Then four kinds of paper honeycomb with different structural parameters were simulated and analyzed using finite element software ABAQUS. Moreover, the results obtained from finite element method were verified based on the existing theoretical research results and experimental results, respectively. The results show that stress–strain curves obtained from finite element method clearly show the four deformation stages of the paper honeycomb under out-of-plane compression, which is basically consistent with the trend of the typical curve. The values of initial peak stress, plateau stress and densification strain are close to the theoretical results. The stress–strain curves and deformation contours coincide with experiments well. The differences of initial peak stress σpk, plateau stress σpl and densification strain εD between theoretical, finite element method and experimental results are less than 15%. Therefore, the finite element method can be used to analyze the stress–strain curves and deformation characteristics of paper honeycomb. In addition, the results also show that the thickness of specimen has little effect on the stress and strain. However, people often prefer to use the thicker paper honeycomb to get better cushioning effect in practical applications, which was explained.

Bushing is the most important part of transformer to connect external component. Bushing fault is one of the prime reasons causing transformer faults. Moisture is an important factor leading to aging of bushing insulation, so it is necessary to evaluate the moisture content of bushing. In the current research, it can confirm whether the oil-paper insulation bushing is uniform damp. But there is no research related to the moisture location of oil-paper insulation bushing. We use Comsol software to carry out a simulation study of the finite element analysis method for nonuniform damp bushing. And the distribution characteristics of hydronium ions and hydroxide ions under electrode polarization can be obtained from the simulation analysis. In this paper, the polarization and depolarization current (PDC) experimental platform was set up and models of nonuniform damp bushings were made. The position information of the high-moisture capacitive screen can be obtained through two different wiring methods. The validity of the method can be verified by the distribution law of hydrolysis ions in this simulation.

In order to satisfy the demands for both safety and global warming reduction, a high-strength seismic reinforced steel bar is required in the structural steel market. Recent developments in computational thermodynamics and related application software have made it possible to design a suitable material as well as support engineers of steel manufacturing companies in the production of the designed material with minimum benchmarks in practical operations. This paper reports our recent success in developing grade 600 MPa reinforced steel bars for seismic safety in South Korea. First, conventional alloy design based on CALPHAD-type computational thermodynamics was carried out. For this purpose, a typical alloy system of Fe-0.30C-0.23Si-1.37Mn-0.14V-0.22Cu (in wt%) was selected, and thermodynamic and kinetic calculations were carried out using MatCalc and JMatPro software. Second, in order to reduce V content in the steel for economic reasons, a cooling process designed using finite element (FE) simulation based on the thermodynamic database was performed. For this application, Fe-0.34C-0.22Si-1.34Mn-0.04 V (in wt%) alloy was chosen, and the FE software ABAQUS was applied for modeling the TempCore process. The mechanical properties of the steel products with a diameter of 32 mm produced based on the simulated results satisfy the required properties for grade 600 MPa seismic reinforced steel bars.

Uniform standard in the structural design for insulated tubular bus is not available both at China and abroad, and there are few reports about insulated tubular bus, which causes a waste of resources and even leads to grid failure. In this paper, epoxy/paper composites insulated tubular bus was investigated and a two-dimensional model was preferred in the simulation due to the axial symmetry of insulated tubular bus. The distribution of electric field and temperature in composite insulated materials were studied with the changes of the diameter/thickness of copper pipe and the thickness of insulation materials. According to the results simulation results, the structure of insulated tubular bus was optimized, the thickness of copper pipe conductor and insulation had been greatly reduced. Compared to the non-optimized initial structure, the amount of copper pipe conductor used for the optimized insulated tubular bus was reduced by 48%, the amount of insulation materials were reduced by 52.5%, and the current density of copper pipe conductor increased by 92.2%.

The moisture-induced degradations during the use of paper are of growing concern for the existing paper materials stored in libraries, archives and museums. Knowing the moisture profiles is therefore a primary step in order to understand paper deterioration and give an assessment of degradation rate of library collections in their preservation. In this paper, the theoretical models based on 2-D scanning electron microscope real image microstructure were established for describing moisture transport in paper sheet in response with external humidity and the moisture diffusion profiles. The acid-catalyzed hydrolysis kinetic in combination with moisture diffusion theory gave the complementary explanation for the time-dependent natural aging process of a paper sheet and book stacks. The differential equations were solved by a numerical approach based on the finite element method implemented in commercial COMSOL Multiphysics. The 2-D simulation results, with a mesh based directly on SEM characterization of microstructure, could show the equilibrium moisture contents and the degradation rates as a function of relative humidity in cellulose pores and cellulose fibers across the transverse section of paper. For the stacks composed of books, the air gaps between the books provided convenient channels for diffusion and transport, accelerating the moisture transport process in the book stacks.

Damage detection and localization in civil engineering constructions using dynamic analysis has become an important topic in recent years. This paper presents a methodology based on non-destructive detection, localization and quantification of multiple damages in simple and continuous beams, and a more complex structure, namely two-dimensional frame structure. The proposed methodology makes used of Firefly Algorithm and Genetic Algorithm as optimization tools and the Coordinate Modal Assurance Criterion as an objective function. The results show that the proposed combination of Coordinate Modal Assurance Criterion and Firefly Algorithm or Genetic Algorithm can be easily used to identify multiple local structural damages in complex structures. However, the convergence rate becomes slower for the case of multiple damages compared to the case of single damage. The effect of noise on the algorithm is further investigated. It is found that the proposed technique is able to detect the damage location and its severity with high accuracy in the presence of noise, although the convergence rate became slower than in the case when no noise is present. It is also found that the convergence rate of Firefly Algorithm is much faster than that of Genetic Algorithm.

Paper forming is the first step in the paper machine where a fiber suspension leaves the headbox and flows through a forming fabric. Complex physical phenomena occur during paper forming due to the interaction between fibers, fillers and fines as well as chemicals added to the suspension. Understanding this process is important for the development of improved paper products because the configuration of the fibers during this step has a large influence on the final paper quality. Since the effective paper properties depend on the micro-structure of the fiber web, a continuum model is inadequate and the properties of each fiber need to be accounted for in the simulations. In the present work, a framework for microstructure simulation of early paper forming has been developed. The simulation framework includes a Navier-Stokes solver and immersed boundary methods are used to resolve the flow around the fibers. The fibers are modeled with a finite element discretization of the Euler-Bernoulli beam equation in a co-rotational formulation. The contact model is based on a penalty method and includes friction as well as elastic and inelastic collisions. The fiber model and the contact model are validated against demanding test cases from the literature with excellent results. The fluid-structure interaction in the model is examined by simulating an elastic beam oscillating in a cross flow. Finally, a simulation of early paper forming is performed to demonstrate the potential of the proposed framework. The unique modeling approach can be used to increase the fundamental understanding of paper forming and support process optimization.

Many failures had occurred in operation of insulated tubular bus because of the poor product quality, and its primary reason was that some defects were led into the insulation system in the production, then the local electric field would increase and then result in partial discharge, which could accelerate the aging and even breakdown of the materials. In this research, a 1/4 three-dimensional model was established according to the actual structure of insulated tubular bus, and the simulation results obtained from static electric field and quasi-static electric field were compared. Besides, the electric field distribution of insulated tubular bus with typical defects was simulated based on ANSYS software. These three defects were air void, moisture and damage of semi-conducting layer. The simulation results showed that the electric field distribution of insulated tubular bus with typical defects was more suitable with quasi-static electric field simulating. The maximum electric field value was different with different defects, and dependent on the location and size of defects.

Cockling of paper is a common problem occurring in the production, storage and end-use of paper. It is usually induced by a moisture content change. In many cases, cockling is an irreversible phenomenon; i.e. the initial shape is not obtained although the initial moisture content is restored. This kind of moisture content change occurs in copying machines and in the printing process, for example. In this paper, we present a continuum mechanical model, which is used to study the irreversible cockling of paper. In the model, paper is treated as an orthotropic elasto-plastic material and the model takes into account the small-scale variation of fibre orientation. The model is used to show the importance of the through-thickness moisture gradient on the cockling phenomenon during a cyclic moisture content change. The results suggest that the moisture gradient is a crucial factor for the irreversible cockling.

The overlap separation mechanism is widely used to separate paper sheets from each other in automatic teller machines. In this study, we first derived a formula used for expressing the normal separation condition of paper sheets. Then we analyzed the deformation force acting on the paper sheet surfaces by treating the paper sheet as an elastic beam and using Clapeyron's theorem of three moments. Furthermore, by using the finite element analysis software LS-DYNA, we developed a three-dimensional simulation method that can accurately reproduce normal separation, misfeeding, and double feeding behaviors. Finally, the effects of the main parameters on deformation force will be discussed. The results show that the deformation force is proportional to the overlap; the bigger the width of gate-roller or the distance of roller edges, the bigger the deformation force. Moreover, the width of the feed-roller has hardly any effect on deformation force. It is shown that separation defects obtained by the elastic beam model agree well with those obtained by the FE model.

This paper presents a method to predict the through-thickness moisture content distribution and associated induced deformations of paper and cardboard sheets as they are subjected to relative humidity changes. The transient moisture diffusion problem is solved using a “natural” analytic approach that has previously been applied for solving transient heat conduction in multi-layer solids. The deformation behaviour of the sheet during the moisture diffusion process is predicted using a semi-analytical approach based on a Rayleigh–Ritz minimization of the total potential energy. Geometrically nonlinear effects are taken into account. Curvatures of the originally flat sheet are predicted as a function of time, as are the shapes of the sheet for steady-state condition. As multiple solutions exist, stability is studied. The developed model was used to study the deformation behaviour of one paper and two cardboard sheets. Comparisons with finite-element results demonstrate that the developed model provides accurate results. The displacements obtained for steady-state conditions are within +6%. Comparisons with previous steady-state analyses reveal important differences in the shape of one cardboard sheet. This suggests that the moisture diffusion process may influence the configuration assumed by the sheet at steady-state equilibrium. Hence, it may be necessary to take the moisture diffusion into account in the analysis to accurately predict the hygro-mechanical behaviour of paper or cardboard sheets.

In this research work, a coupled-field finite element model of electro-active paper energy harvester is presented, and the results are verified experimentally. Electro-active paper is a smart form of cellulose coated with electrodes on both sides. A finite element model was developed, and harmonic and transient analyses were performed using a commercial finite element analysis package. Two 80 mm × 50 mm and 100 mm × 50 mm aluminum cantilever benders bonded with electro-active paper were tested to validate the finite element model results. Displacement and voltage generated by the energy harvester at the electrode surfaces were measured. The electro-active paper energy harvesters were excited at their fundamental resonance frequencies by a sinusoidal force located 18 mm from the free end. The voltage obtained from the 80 mm × 50 mm and 100 mm × 50 mm electro-active paper energy harvester finite element model was 3.7 and 7 mV, respectively. Experimental results have shown good agreement with the finite element model. The direct piezoelectric effect of electro-active paper shows potential for a cellulose-based eco-friendly energy harvester.

Paper insulated cables were the first commercially used cables and they continue to be in service even today owing to their long history of reliability. Under repeated load cycling and varying electric stress and temperature, however, the dielectric properties of the cable undergo changes. In this work, the relative permittivity of paper insulation from a used and aged oil impregnated paper cable has been measured at different electric fields and temperatures using dielectric spectroscopy. Electric field along the radius of the cable has been obtained using a software based on finite element method. The results obtained through dielectric spectroscopy have been used to input the properties of the cable paper insulation in the software. A comparison of the radial electric field distribution inside the paper cable has been made for two cases; one where the relative permittivity of insulation is dependent on temperature and electric field and the other where it is independent. The results of this work may prove to be useful for monitoring of ageing cables and for cable joints involving paper cables.

An anisotropic elasto-plastic constitutive model of paper material is presented. It is formulated in a spatial setting in which anisotropic properties are accounted for by use of structural variables. A multiplicative split of the deformation gradient is employed to introduce plasticity. A similar approach is used to model the plastic deformation of the substructure. The yield surface adopted is based on the Tsai–Wu failure criterion, used previously to model failure of paper material. A non-associated plasticity theory is employed to calibrate the model to experimental data. It turns out that a multi-axial loading situation is needed to calibrate the model and here a biaxial tension test is audited. The model was implemented into a finite element environment and the creasing process of a corrugated board panel is investigated.