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The quality of transformer insulation is related to the safe and stability operation of the power grid, and the life of the transformer oil-paper insulation system mainly depends on the state of paper insulation. With the continuous improvement of the voltage level, the requirements for insulating paper are becoming higher and higher. Based on the molecular dynamics simulation technology, the effects of carbon nanowires with three different structures on the thermodynamic properties of cellulose insulating paper were analyzed from the aspects of mechanical parameters, MSD (mean square displacement), CED (cohesive energy density) and hydrogen bond. The simulation results showed that the carbon nanowires with three different structures have improved the thermodynamic properties of cellulose. Among them, the hard chiral carbon nanowires have the most significant improvement in the thermodynamic properties of cellulose. The elastic modulus, bulk modulus, and shear modulus have been increased by 30%, 25.6%, and 32.9%, respectively. It was found that the thermal stability of cellulose insulation paper modified by three different structure carbon nanowires was improved. The increase of thermal stability was mainly due to the increase of the cohesive energy density and the number of intermolecular hydrogen bonds.

Paper-like electronics with thin multi-layer structures, which can be repeatedly bent and twisted like paper, are promising for diverse innovation application. Employing surface-mounted flexible strain sensors is a general way to monitor the bending characteristics of each layer inside paper-like electronics, however, the deviation of measured strain will reach up to 15% on account of the layer-to-layer interface sliding, neutral axes offset resulted from the extra effect of the flexible strain sensor. Here, we proposed a precise measurement method to evaluate the surface bending strain of paper-like electronics by using flexible sensors. In combination with the effects of the thickness, length, etc, a strain compensation model has been established to compensate the measurement deviation. Meanwhile, a slip failure model has been developed to guide the design of the sensitivity unit within the non-sliding area of the flexible sensor. Validated by finite element analysis and experiment, the bending strain of paper-like electronics (eg., ∼50 μm) can be evaluated much more accurate compared to the frequent access one. The newly-proposed method provides a powerful basis for further research of paper-like electronics.

The mechanical response of three different structural core sandwich panels in out-of-plane compression and shear has been analyzed. Specific core shapes examined are arc-tangent, wavy trapezoidal and hemispherical. Unit cells consisting of representative elements of the core attached to face sheets were selected for analysis. Both face sheets and core were assumed made from paper. Finite element analysis employing large deformation and rotations and orthotropic elastic–plastic behavior was used. The results show that the arc-tangent and trapezoidal cores are prone to collapse by extensive bending and buckling, whereas the hemispherical core behaved more stably in compression and shear. Core sheets with a hemispherical shape were prepared from copy paper sheets in a specially designed forming machine. Sandwich test specimens were prepared from this core and tested in out-of-plane compression, and the load-displacement response was compared to predictions from finite element simulations. The experimental and finite element results were consistent.

A finite element procedure, developed in order to account for the effect of high anisotropy at folding of coated papers, is presented. The anisotropic behaviour (with very low stiffness in the thic ...

Folding of coated paper is examined numerically using the finite element method. Particular emphasis is put on the behaviour of field variables relevant for cracking of the coating layers. In the n ...

Aramid paper honeycomb cores have been widely used in lightweight structures. However, shear properties of aramid paper can hardly be obtained accurately due to the shear buckling of the paper. Therefore, we make the paper into a laminate to prevent buckling and apply the v-notched beam test method to the laminate to obtain the in-plane shear properties of aramid paper. The shear strength and failure strain of aramid paper are characterized experimentally for the first time. The properties are then used in finite element simulations to study the shear behaviors of paper honeycombs and the good agreement with the experimental results indicates the validity of the shear properties. Furthermore, the failure mode map of the paper honeycomb subjected to combined shear and compressive loads is obtained, which presents the importance of the accurate characterization on the shear properties of the paper. This characterization method can also be applied to other types of paper.

This review paper provides a key information, allowing readers to comprehensively understand the direct tensile behavior and test methods for textile reinforced cementitious composites (TRCCs). The tensile parameters of TRCCs corresponding to bilinear or trilinear tensile stress–strain behavior were summarized and the influencing factors on the tensile parameters were discussed. Various direct tensile test methods for TRCCs were evaluated according to the geometry of specimens, load transmitting mechanism, measurement and loading methods. Conclusive requirements for a standard test method for assessing the tensile stress–strain behavior of TRCCs were proposed.

Natural fibers are gaining much interest in composite materials because of their potential to replace conventional glass fibers. In particular, unidirectional flax fiber composites have shown excellent mechanical properties with different thermoset matrices. However, few data are available when they are made with a biodegradable thermoplastic matrix. This paper compares the mechanical properties of two types of unidirectional flax composites using polylactic acid as the matrix: one made with layers of aligned flax rovings alone and the other containing an additional paper layer fabricated using paper making techniques. The results show that specific tensile properties of the flax/PLA (252 MPa·cm3·g−1) and flax-paper/PLA (217 MPa·cm3·g−1 ) composites are similar to those made using woven glass fabrics impregnated with epoxy (227–278 MPa·cm3·g−1). Very high impact strength (600 J/m) was also obtained for UD flax-paper composites compared to unreinforced resin (15 J/m). Together these mechanical properties are promising for industrial applications of this new reinforcement.

This paper presents sound absorbing structure constructed using multiple layers of fibrous papers. Sound absorbing materials converts sound wave into thermal energy due to the porosity. The proposed sound absorbing structure has helical-like shapes in layered format with cyclic winding of the mulberry papers and coconut fibers. The acoustic properties changes depending on the thickness of the air cavity between the thin layers and porosity of the layers themselves. Sound absorption coefficients were measured using two-microphone impedance tube in order to investigate the acoustic property variations with porosity. The measured results were compared to predictions utilizing wave propagations through a slit for verification of the sound absorbing mechanism. A simple method for improving the sound absorption with less material by composite structure is proposed and verified through the experiment. Dynamic stiffness and loss factor of the helical-shaped sound absorbers were measured and compared by analyzing supporting properties to the vibrating beam. Depending on the construction method, the frame dynamic properties showed variation even when the sound absorption was identical. This information is required for optimal design of absorbing layers for specific noise control applications.

The dynamic compression behaviors of aramid paper honeycombs, i.e. samples with heights 2.10 mm, 3.10 mm, 5.14 mm, and 10.11 mm, were investigated by the split Hopkinson pressure bar devices (SHPB). The results showed abnormal size effect in the peak stress for samples with height 2.10 mm. The high speed camera was used to capture the deformation process. Two deformation modes, i.e. the in-plane shear wrinkles (characterized as larger deformation and lower strength in the stress-strain curves) and the out-of-plane wall buckling (characterized as smaller deformation and higher strength in the stress-strain curves), were distinguished from the complicated deformation processes. The abnormal size effect was resulted from the dominance of in-plane shear failure for samples 2.10 mm, rather than the out-of-plane wall buckling for other samples. Further investigations were conducted in details on the effects of cell width, wall thickness, and ends constraint condition (i.e. ends bonded with face sheets) to the deformation process based on the experiments, theoretical analyses of buckling, and Finite Element method (FEM). The transition of two deformation modes was analyzed, and the abnormal size effect would disappear for samples with larger wall thickness. It might be helpful for design purpose of honeycombs to some extent.

ispartof: COMPOSITE STRUCTURES vol:226 status: published

This paper begins by briefly outlining the behaviour of paper structures under mechanical and hygrothermal loading. The results of an experimental test program are then presented and it is shown that the strain to failure is not a suitable parameter for adequately differentiating between the virgin and recycled paper structures. Indeed, the present paper postulates that the accumulated inelastic work may be a better tool for assessing the effect of furnish. The results of a creep test program are also presented and a possible extension of the master curve concept, which was developed for the visco-elastic response of amorphous polymers to the visco-plastic regime is discussed.

Paper is an orthotropic, rate sensitive material which makes modelling its stress-strain behaviour a difficult task. Classical methods are inadequate behaviour of paper and comparisons are made with previous experimental work for a particular paper. Comparisons between the two models are also made.

This work presents a complete test methodology for the testing of paper and other thin materials with the special requirements for constitutive modelling in mind. It also presents results obtained using these test regimes and speculates about what they reveal about paper. Specifically that paper seems to exhibit ‘over stress’ phenomenon.

This communication is to correct the sensitivity analysis formula of frequencies for composite structures in the paper [1]. It is further pointed out that even though the sensitivity analysis formula of frequencies has been corrected, the first derivatives of frequencies with respect to design variables cannot be achieved by direct differentiating the equations of eigenvalues and eigenvectors because the first derivatives of vibration modes with respect to design variables are still unknown. The readers are referred to the analytical solution of the sensitivity analysis of frequencies and modes for composite structures in the literature [2], which is derived using linear space theory.

A major disadvantage of polymer-based composite materials is their poor performance when exposed to relatively high heat flux. At temperatures typically above 300–400 °C, the organic matrix decomposes releasing heat, smoke, and toxic volatiles, jeopardising the composite mechanical performances. The heat flux resistance of composites can be improved by integrating protective coatings on their surface. In the present work, graphene nanoplatelet (GNP) films are employed as thermal barrier coatings (TBCs) to mitigate the thermal degradation of Carbon Fibres Reinforced Plastic (CFRP). The films were bonded onto the heat-exposed surface of CFRP laminates. Laser spot heating tests, with different laser power densities (25–150 kW/m2), were adopted to assess the effectiveness of the coating. The effect of the thickness of the protective layer has been tested too, by changing the number of layers (from 1 to 2 layers). From the results, a significant reduction in the temperatures and damages were observed. Moreover, the damage extension and residual mechanical performances of exposed samples have been assessed as a function of the power density and the protection level. A significant improvement of the post-heat flexural moduli and a significant reduction of the damaged areas have been obtained in laminates protected with high-loaded graphene nanoplatelet films.