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Many plant materials in nature have the ability to change their shape to respond to external stimuli, such as humidity or moisture, to ensure their survival or safe seed release. A well-known example for this phenomenon is the pinecone, which is able to open its scales at low humidity due to the specific bilayer structures of the scale. Inspired by this, we developed a novel humidity-driven actuator based on paper. This was realized by the lamination of untreated paper made from eucalyptus fibers to a paper–carboxymethyl cellulose (CMC) composite. As observed, the hygroexpansion of the composite can be easily controlled by the amount of CMC in the impregnated paper sheet, which, thus, controls the morphologic deformation of the paper bilayer. For a more detailed understanding of these novel paper soft robots, we also studied the dynamic water vapor adsorption, polymer distribution and hygroexpansion of the paper–polymer composites. Finally, we applied a geometrically nonlinear finite element model to predict the bending behavior of paper bilayers and compared the results to experimental data. From this, we conclude that due to the complexity of structure of the paper composite, a universal prediction of the hygromorphic behavior is not a trivial matter. [ABSTRACT FROM AUTHOR]

The Proton Exchange Membrane Fuel Cell (PEMFC) performances are strongly impacted by the compression of the Gas Diffusion Layer (GDL). Despite its fibrous microstructure, this material is usually considered as a continuous medium and characterized with uniform loading. However, the GDL is subjected to a heterogeneous compression onto rib/channel patterns in the fuel cell assembly. In the present study, a complex behavior of the GDL response is experimentally revealed when the material is loaded with a rib/channel pattern, compared to uniform compression. The tests are simulated by finite element modeling using a classical strain-dependent elastic law, using parameters fitted from uniform compression experiments. It is shown that the numerical results do not reproduce the effect of pattern observed experimentally. Hypotheses to interpret these results involve mechanisms at the fiber microscale including fiber fracture, cross-link breakage and fiber rearrangement, which are exacerbated by larger material deformation caused by the heterogeneous loading. • Unexpected impact of rib/channel patterns on GDL compression. • Experimental investigation of the effect of rib/channel width on GDL deformation. • Numerical study with classical model unable to reproduce experimental results. • Interpretations based on mechanisms at the fiber microscale. [ABSTRACT FROM AUTHOR]

The potential of paper and paperboard as fiber-based materials capable of replacing conventional polymer-based materials has been widely investigated and evaluated. Due to paper's limited extensibility and inherent heterogeneity, local structural variations lead to unpredictable local mechanical behavior and instability during processing, such as mechanical forming. To gain a deeper understanding of the impact of mechanical behavior and heterogeneity on the paper forming process, the Finite Element Method (FEM) coupled with continuum modeling is being explored as a potential approach to enhance comprehension. To achieve this goal, utilizing experimentally derived material parameters alongside stochastic finite element methods allows for more precise modeling of material behavior, considering the local material properties. This work first introduces the approach of modeling heterogeneity or local material structure within continuum models, such as the Stochastic Finite Element Method (SFEM). A fundamental challenge lies in accurately measuring these local material properties. Experimental investigations are being conducted to numerically simulate mechanical behavior. An overview is provided of experimental methods for material characterization, as found in literature, with a specific focus on measuring local mechanical material structure. By doing so, it enables the characterization of the global material structure and mechanical behavior of paper and paperboard. [ABSTRACT FROM AUTHOR]

The present article provides a comprehensive analysis of the aging phenomenon of transformer insulation and the corresponding changes in insulation performance that occur over time. The present manuscript outlines diverse insulating materials that are employed in transformers, the fundamental aging mechanism of the insulation, the function of space charges in the aging of the insulation, and various simulation methodologies utilized for diagnosing the insulation status of the transformer. The primary focus of this paper is to examine the various numerical techniques employed in modeling and analyzing the aging characteristics of transformer insulation. The mechanisms underlying the accumulation of charge and distortion of electric fields in insulation are explained through the utilization of numerical modeling techniques. This paper focuses on understanding the mechanism of insulation aging, thereby facilitating the optimization and maintenance of insulation performance throughout its operational lifespan. [ABSTRACT FROM AUTHOR]

The study aims to present the results of paper compression under an axial load. Different heights of samples subjected to compression were taken into account. The main goal of the analysis was to determine experimentally the maximum compression load. In addition, numerical models based on the finite element method (FEM) were validated to refer to empirical results. The performed numerical simulations were founded on Green–Lagrangian nonlinear equations for large displacements and strains. The progressive failure of the compressed orthotropic material after exceeding maximum stresses was based on Hill’s anisotropy theory. Nonlinear calculations were conducted by using a typical Newton–Raphson algorithm for achieving a sequence convergence. The accuracy of the developed model was confirmed experimentally in compression tests. The technique of analysing the shape of the compressed paper sample on the basis of images recorded during the measurement was used. The obtained test results are directly applicable in practice, especially in the calculation of the mechanical properties of corrugated cardboard and in determining the load capacity of cardboard packaging. Knowing the maximum compressive stress that packaging paper can withstand allows packaging to be properly designed and its strength assessed in the context of the transport and storage of goods.

Alumina-based multilayer laminates with layers of varied porosities and ceramic fiber reinforcements, which can be achieved by including paper-derived ceramic layers, are interesting candidates for chemically stable and thermal shock resistant materials. In order to investigate the complex sintering behavior of these laminates, the sintering of each alumina layer contained within a laminate, each one with its individual sintering anisotropy and sintering shrinkage, has to be considered separately. For this purpose, sintering curves are determined by dilatometry measurements, serving a consecutive examination by an analytical model. Modeling parameters specific to each layer, are applied in finite-element-type sintering simulations for symmetrical multilayer laminates. Differences in the sintering shrinkages may cause internal stresses at layer interfaces and, in turn, may influence the thermal and mechanical properties of multilayer laminates after sintering. Accordingly, the prediction of developing internal stresses within alumina-based multilayer laminates by the presented sintering simulations is a key aspect of this study. [Display omitted] • Individual laminates sintering dilatometry. • Anisotropic sintering assessment by analytic modeling. • Finite element simulation of multilayer laminates sintering. [ABSTRACT FROM AUTHOR]

The dynamic mechanical behavior and cushioning performance of honeycomb sandwich panels, which are extensively employed in product cushioning packaging due to their exceptional energy absorption capabilities, were examined using a combination of experimental and numerical methods. Several factors, such as maximum acceleration–static stress, cushioning coefficient–static stress, and other curves, were analyzed under various impact conditions. The simulated stress–strain, deformation modes, cushioning coefficients, and other parameters demonstrate consistency with the experimental results. The acceleration, maximum compression, and cushioning coefficient obtained from the experiment and simulation calculation were 30.68 g, 15.44 mm, and 2.65, and 31.96 g, 14.91 mm, and 2.79, respectively. The results indicate that all error values were less than 5%, confirming the precision and reliability of the model. Furthermore, the model was utilized to simulate and predict the cushioning performance of honeycomb sandwich panels with different cell structures and paper thicknesses. These results provide a solid basis for enhancing the design of subsequent honeycomb element structures.

Femoral deformities are highly prevalent in children with cerebral palsy (CP) and can have a severe impact on patients' gait abilities. While the mechanical stress regime within the distal femoral growth plate remains underexplored, understanding it is crucial given bone's adaptive response to mechanical stimuli. We quantified stresses at the distal femoral growth plate to deepen our understanding of the relationship between healthy and pathological gait patterns, internal loading, and femoral growth patterns. This study included three-dimensional motion capture data and magnetic resonance images of 13 typically developing children and twelve participants with cerebral palsy. Employing a multi-scale mechanobiological approach, integrating musculoskeletal simulations and subject-specific finite element analysis, we investigated the orientation of the distal femoral growth plate and the stresses within it. Limbs of participants with CP were grouped depending on their knee flexion kinematics during stance phase as this potentially changes the stresses induced by knee and patellofemoral joint contact forces. Despite similar growth plate orientation across groups, significant differences were observed in the shape and distribution of growth values. Higher growth rates were noted in the anterior compartment in CP limbs with high knee flexion while CP limbs with normal knee flexion showed high similarity to the group of healthy participants. Results indicate that the knee flexion angle during the stance phase is of high relevance for typical bone growth at the distal femur. The evaluated growth rates reveal plausible results, as long-term promoted growth in the anterior compartment leads to anterior bending of the femur which was confirmed for the group with high knee flexion through analyses of the femoral geometry. The framework for these multi-scale simulations has been made accessible on GitHub, empowering peers to conduct similar mechanobiological studies. Advancing our understanding of femoral bone development could ultimately support clinical decision-making. • Distal femoral growth plate stresses quantified with subject-specific simulations. • Large dataset of 50 femurs – 26 healthy, 24 femurs of participants with cerebral palsy. • Knee flexion angle is of high relevance for typical bone growth at the distal femur. • Workflow reveals plausible growth results supported by geometrical analysis. • Multi-scale workflow based on free software published on GitHub. [ABSTRACT FROM AUTHOR]

Ultrathin devices are rapidly developing for skin‐compatible medical applications and wearable electronics. Powering skin‐interfaced electronics requires thin and lightweight energy storage devices, where solution‐processing enables scalable fabrication. To attain such devices, a sequential deposition is employed to achieve all spray‐coated symmetric microsupercapacitors (μSCs) on ultrathin parylene C substrates, where both electrode and gel electrolyte are based on the cheap and abundant biopolymer, cellulose. The optimized spraying procedure allows an overall device thickness of ≈11 µm to be obtained with a 40% active material volume fraction and a resulting volumetric capacitance of 7 F cm−3. Long‐term operation capability (90% of capacitance retention after 104 cycles) and mechanical robustness are achieved (1000 cycles, capacitance retention of 98%) under extreme bending (rolling) conditions. Finite element analysis is utilized to simulate stresses and strains in real‐sized μSCs under different bending conditions. Moreover, an organic electrochromic display is printed and powered with two serially connected μ‐SCs as an example of a wearable, skin‐integrated, fully organic electronic application. [ABSTRACT FROM AUTHOR]

Today, the toilet paper market offers product types with varying number of plies, providing better mechanical strength and liquid absorption. Several tissue paper perforation systems exist, and the best commonly applied is a top-cutting mechanism that includes an oblique blade, a combined oblique blade, or a simple spiral blade. The perforation efficiency must be high to have an easy sheet separation from the roll of the toilet paper, which does not always occur. Hence, consumer satisfaction can depend on the perforation performance. To study this, a laboratory perforation system was used to perforate different commercial toilet papers (in brands and number of plies) and evaluate their perforation efficiency. A finite element method (FEM) was used to simulate the curve of the progression of perforation efficiency as a function of the cut distance. The main findings were a stabilization of the perforation efficiency from a cut distance of 6 mm and a 15% increase in the cut distance for the laboratory blade to match the industrial perforation efficiency. The FEM analysis confirmed the behavior of the evolution of perforation efficiency with the increase of the cut distance. [ABSTRACT FROM AUTHOR]

The dynamic mechanical behavior and cushioning performance of honeycomb sandwich panels, which are extensively employed in product cushioning packaging due to their exceptional energy absorption capabilities, were examined using a combination of experimental and numerical methods. Several factors, such as maximum acceleration–static stress, cushioning coefficient–static stress, and other curves, were analyzed under various impact conditions. The simulated stress–strain, deformation modes, cushioning coefficients, and other parameters demonstrate consistency with the experimental results. The acceleration, maximum compression, and cushioning coefficient obtained from the experiment and simulation calculation were 30.68 g, 15.44 mm, and 2.65, and 31.96 g, 14.91 mm, and 2.79, respectively. The results indicate that all error values were less than 5%, confirming the precision and reliability of the model. Furthermore, the model was utilized to simulate and predict the cushioning performance of honeycomb sandwich panels with different cell structures and paper thicknesses. These results provide a solid basis for enhancing the design of subsequent honeycomb element structures. [ABSTRACT FROM AUTHOR]

Purpose. To substantiate the breakdown mechanism of capacitor paper on the basis of numerical-field models with segmented cross-sections of cylindrical volumes of air and water, and also use the proposed models to determine the breakdown strength of air in micron-sized gaps under normal conditions. Methodology. The model bases on a finite element solution to an electrostatic problem in a volume of capacitor paper consisting of cellulose and pores with air and water. First, the possible scenarios for the growth of breakdown in capacitor paper are analyzed and to the conclusion is made, that complete breakdown developed from a partial breakdown in the air cavity. A brand of capacitor paper is chosen in such a way that when its thickness changed, the breakdown strength of the electric field changed over a wide range. Then, for the paper with the lowest average electric field intensity the possibility of explaining the complete breakdown by the breakdown of air segments on the basis of the Paschen dependence is checked. Further points of the obtained dependence by constructing models of papers of the same brand and a different thickness under the assumption of the similarity of electrostatic fields are determined. As such a criterion, the constancy of the equivalent effective permittivity are taken. Results. The dependence of the breakdown strength of the air in the range of 1.36...5.54 μm under normal conditions is determined. The obtained relationship is between the Peschot and Taev curves. Originality. For the first time, the possibility of indirectly estimation the breakdown strength of an insulating material using an electrostatic field model is indicated. Practical value. The proposed method for the numerical calculation of the breakdown voltage of air inclusions in the presence of water inclusions in the thickness of solid insulation can be applied to other types of solid thin-layer insulation.

The study aims to present the results of paper compression under an axial load. Different heights of samples subjected to compression were taken into account. The main goal of the analysis was to determine experimentally the maximum compression load. In addition, numerical models based on the finite element method (FEM) were validated to refer to empirical results. The performed numerical simulations were founded on Green–Lagrangian nonlinear equations for large displacements and strains. The progressive failure of the compressed orthotropic material after exceeding maximum stresses was based on Hill's anisotropy theory. Nonlinear calculations were conducted by using a typical Newton–Raphson algorithm for achieving a sequence convergence. The accuracy of the developed model was confirmed experimentally in compression tests. The technique of analysing the shape of the compressed paper sample on the basis of images recorded during the measurement was used. The obtained test results are directly applicable in practice, especially in the calculation of the mechanical properties of corrugated cardboard and in determining the load capacity of cardboard packaging. Knowing the maximum compressive stress that packaging paper can withstand allows packaging to be properly designed and its strength assessed in the context of the transport and storage of goods. [ABSTRACT FROM AUTHOR]

Flexible sensors have versatile applications in a home environment to create better ambient intelligence, which still have high fabrication costs and disposable value. As a proof‐of‐concept example to resolve these problems, the graphite‐based sensors on a disposable paper cup by laser patterning to measure the water level and temperature are proposed. The optimal process parameters of graphitic film, sensing mechanisms, and the sensor performance are investigated in the experiments. Moreover, the paper cup with graphitic sensors is simulated by the finite element method to analyze the experimental results. This fast and low‐cost manufacturing method may open up avenues for the development of disposable flexible electronics in smart home necessities. [ABSTRACT FROM AUTHOR]

The aim of this discussion is to establish a connection between the model for sandwich beams presented in Schöftner (Acta Mech 234:2543–2560, 2023) and the so-called Krajcinovic model. Although the two models turn out to be quite similar, Krajcinovic model displays a richer kinematics and has been developed in the literature by following slightly different methodologies with respect to that adopted by Schöftner, the latter having the merit of providing equilibrium equations that allow the computation of the interfacial stresses. We also offer some remarks on the capabilities and accuracies of the models discussed. [ABSTRACT FROM AUTHOR]

This work deals with fracture mechanisms in quasi-brittle materials, focusing on the characterization of the Fracture Process Zone (FPZ) of specimens under tensile load. Particularly, paper was used as model material. Experiments were conducted on notched and unnotched specimens. Based on an image analysis of these observations, a stochastic finite element model was developed, using both a nonlocal stress-based approach and a discretized random field modeling of the Young's modulus. The proposed methodology allowed characterizing the damage zone and the size of the FPZ, analyzing the influence of the mesostructure, composed of flocs (fiber aggregates where the basis weight is larger than the average one) and antiflocs (complement of flocs). The area of the active FPZ and the normalized stress drop were linked using a surface energy dissipated in the active FPZ. The stress drop, until limiting value, increased with the width of the active FPZ. Finally, a relationship between the surface energy and the nonlocal internal length was established. [ABSTRACT FROM AUTHOR]