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The article analyses the effects of paper moisture content on energy absorbed during its tensile testing in the range of moisture equilibrium obtained during paper air conditioning at a temperature of 23 °C. To predict changes in breaking energy caused by changes in moisture content, two calculation methods were proposed. The methods were verified on the basis of laboratory tests and calculation results, and their practical usefulness was confirmed. [ABSTRACT FROM AUTHOR]

Buckypaper (BP) is a planar film that consists of random network of multiwall carbon nanotubes (MWCNTs) held together by weak van der Waals interactions at tube-tube junctions. Although individual carbon nanotubes (CNTs) possess remarkable electrical properties, the electrical resistance of pristine BP is usually too high for practical applications. However, the electrical resistivity of BP can be attenuated by applying modest compressive stresses. Herein, we report an analytical model for predicting the electrical resistivity of BP under defined level of compressive strain. The predictive piezoresistive model of BP was developed by formulating a direct relationship with the structural parameters, physical and electrical properties of CNTs. The basis of the piezoresistive model relied upon the geometrical probability approach in combination with classical Hertzian contact mechanics and constriction resistance techniques. A comparison has been made between the theoretical and experimental results of electrical resistivity of BPs with varying densities. A reasonably good quantitative agreement was obtained between the theory and experiments. The main source of error was caused by the uncertainty in the measurement of the initial BP thickness. Through theoretical modeling, the initial volume fraction of CNTs was found to be one of the key parameters that modulated the piezoresistive behavior of BP. [ABSTRACT FROM AUTHOR]

An in-plane elasto-plastic material model and a hygroexpansivity-shrinkage model for paper and board are introduced in this paper. The input parameters for both models are fiber orientation anisotropy and dry solids content. These two models, based on experimental results, could be used in an analytical approach to estimate, for example, plastic strain and shrinkage in simple one-dimensional cases, but for studies of the combined and more complicated effects of hygro-elasto-plastic behavior, a numerical finite element model was constructed. The finite element approach also offered possibilities for studying different structural variations of an orthotropic sheet as well as buckling behavior and internal stress situations under local strain differences. A few examples are presented of the effect of the anisotropy and moisture streaks under stretching and drying conditions on strain differences and buckling. The internal stresses were studied through a case in which the drying of different layers occurred at different stages. Both the anisotropy and moisture streaks were capable of rendering the buckling of the sample visible. The permanency of these defects highly depends on several process stages and tension conditions of the sheet, as demonstrated in this paper. The application possibilities of the hygro-elasto-plastic model are diverse, including investigation into several phenomena and defects appearing in drying, converting and printing process conditions. [ABSTRACT FROM AUTHOR]

The in-plane shear strengths (IPSS) of copy paper, filter paper, and sack paper were obtained from an asymmetric four-point bending (AFPB) test. Rectangular tabs of medium-density fibreboard (MDF) were bonded to the paper specimen. The length of the clearance between the tabs was varied, and the influence of the clearance on the IPSS value was investigated. The IPSS obtained from the AFPB test was compared with that obtained from a 35° off-axis tension (OAT) test, which was proposed in a previous study. The IPSS values obtained from the AFPB tests on the copy paper and sack paper were significantly lower than those obtained from the 35° OAT tests because of the localised buckling caused by the negative principal stress. In contrast, the IPSS values obtained from the AFPB and OAT tests on the filter paper were in agreement when the clearance length was >5 mm because the buckling effect was excluded. [ABSTRACT FROM AUTHOR]

To model advanced 3-D forming strategies for paper materials, the effects of environmental conditions on the mechanical behavior must be quantitatively and qualitatively understood. A tensile test method has been created, verified, and implemented to test paper at various moisture content and temperature levels. Testing results for one type of paper for moisture contents from 6.9 to 13.8 percent and temperatures from 23 to 168 degrees Celsius are presented and discussed. Coupled moisture and temperature effects have been discovered for maximum stress. Uncoupled effects have been discovered for elastic modulus, tangent modulus, hardening modulus, strain at break, tensile energy absorption (TEA), and approximate plastic strain. A hyperbolic tangent function is also utilized which captures the entire one-dimensional stress-strain response of paper. The effects of moisture and temperature on the three coefficients in the hyperbolic tangent function may be assumed to be uncoupled, which may simplify the development of moisture- and temperature-dependent constitutive models. All parameters were affected by both moisture and temperature with the exception of TEA, which was found to only be significantly dependent on temperature. [ABSTRACT FROM AUTHOR]

Highlights: [•] Modeling of cutting forces while applying a slicing motion to the push-cutting process. [•] Analysis of state of stress at the cutting edge. [•] Stress Intensity Factors for cutting with a symmetrical and asymmetrical cutting knife. [•] Fracture toughness of the paper sheet material is determined through DENT test. [•] The new model is verified by sideways push-slice cutting stacked thin paper material. [Copyright &y& Elsevier]

Abstract: The rheological nature of paper or board is usually treated either as elasto-plastic or as viscoelastic depending on the studied paper making process or behavior in converting and end use. In this paper we study several stress–strain curve models and the determination of material parameters from an elasto-plastic point of view. Finally, a suitable approach for all stress–strain curves measured from 180 strips is constructed using a linear function for an elastic region and a nonlinear function for a strain hardening region. This model determines a proportional limit (elastic limit) and gives fairly elegant dependencies between material/fitting parameters and two important factors of mechanical properties of paper: dry solids content and anisotropy. In this paper the dependency of a plastic strain on dry solids content and anisotropy is estimated using the introduced stress–strain curve model. Correspondingly, the model can be used to estimate many other mechanical behaviors, for example, the tension differences arising from non-uniform moisture content of the paper web profile. However, the main target of this study is to produce competent parameters based on modeled stress–strain curves for further construction of a material model. This elasto-plastic material model will be utilized in out-of-plane deformation and fracture models. [Copyright &y& Elsevier]

Abstract: In certain conditions, iron gall inks induce substantial damages on cellulosic supports. Existing curative treatments necessitate the immersion of the documents in aqueous solutions. This implies several undesirable side effects: mechanical stress of the most damaged papers, substantial colour changes, and a drastic modification of the paper/ink composition. This work investigated an alternative treatment that consists in compressing the document between two interleaves that are charged with active compounds. When this operation is operated in moist conditions, active compounds may migrate from the interleaves to the document, and thus achieve the treatment of the paper. As high humidity conditions may additionally induce some migration of iron and acidic compounds out of the ink line, it first appeared necessary to research humidity conditions which minimize these undesirable migrations. This investigation was performed on a set of 53 original manuscripts and led us to consider that a relative humidity of 80% was quite reasonable. The second part of the paper deals with the evaluation of interleaving treatment efficiency. It was performed on laboratory samples, using several types of antioxidant halide salts (NaCl, NaBr, CaBr2) (halides are known to act as radical scavengers). These compounds were tested separately or in combination with calcium carbonate as an alkaline buffer. The samples were made of Whatman paper that was preliminary impregnated with iron gall ink. It has shown that a charge of 2% calcium carbonate in the interleaves has no impact on the treatment efficiency, which mainly depends upon the concentration of salts, the contact pressure and the duration of the treatment. Elemental measurements show that the mobility of the salts is much higher than that of iron, suggesting the possibility to find optimum treatment conditions that minimize the iron migration risk while achieving an effective migration of halides. [Copyright &y& Elsevier]

Abstract: The growth of molds on paper containing cellulose is a frequent occurrence when the level of relative air humidity is high or when books become wet due to water leaks in libraries. The aim of this study is to differentiate the bioreceptivity of different types of book paper for different fungi. Laboratory tests were performed with strains of Aspergillus niger, Cladosporium sp., Chaetomium globosum and Trichoderma harzianum isolated from books. Four paper types were evaluated: couché, Pólen (offset), recycled and a reference paper containing only cellulose. The tests were carried out in chambers with relative air humidity of 95% and 100%. Mold growth was greatest in the tests at 100% relative humidity. Results of stereoscopic microscopy observation showed that Cladosporium sp. grew in 74% of these samples, A. niger in 75%, T. harzianum in 72% and C. globosum in 60%. In the chambers with 95% air humidity Cladosporium sp. grew in only 9% of the samples, A. niger in 1%, T. harzianum in 3% and C. globosum did not grow in any sample. The most bioreceptive paper was couché and the least receptive was recycled paper. The composition of the recycled paper, however, varies depending on the types of waste materials used to make it. [Copyright &y& Elsevier]

Impact of maintenance conditions upon the paper resistance was investigated. Dependencies of tensile strength and resistance to bending of different paper type on paper fibers direction and humidity were presented. [ABSTRACT FROM AUTHOR]

Abstract: A new two-dimensional network model is proposed as a micromechanics model to simulate paper’s failure process due to sequentially breakages of fibers and/or bonds. Paper is approximated as a network composed of fibers any two of which link to each other by their intersecting point, namely so-called bond. Fibers distribute along three particular directions, leading to network’s macro-level isotropy. In the framework of finite element method, nodes correspond to fiber-to-fiber bonds, while elements are fiber segments between every two neighboring nodes and described by Timoshenko beam theory. Element breaks when its equivalent internal tensile stress reaches the tensile strength of fiber. Strength of nodes, i.e. fiber-to-fiber bonds is assumed to be dependant on shearing interaction between fibers, considering the dominant interaction is shearing in a plane problem. Numerical examples show the model’s capacity of reflecting basic failure characteristic in paper. Influences of fiber length and the ratio of fiber strength to bond strength are analyzed in detail. [ABSTRACT FROM AUTHOR]

This research work presents a method for the determination of the limit of elasticity of paper considered as a variable dependent on stress and the time of its duration. For plane stress it was found that in the case of a low share of permanent strain in the total strain, we can assume that the highest value of its share appears on one of the principal axes of stress. Such an assumption allowed to use a one-dimensional rheological model to define the permanent range in a two dimensional state of stresses for paper. [ABSTRACT FROM AUTHOR]

Abstract  From the non-Gaussian model that has very recently been developed in the paper [I], new stress-strain equations have been derived. They have been examined in comparison with mechanical data taken from the literature for unswollen and swollen rubbers. It is found that the model can well explain the literature data. [ABSTRACT FROM AUTHOR]

The stress strain law on the basis of the model of a visco-elastic body is proposed. Procedure for numerical integration of equations of motion is developed. Results of numerical calculations of vibrations of a visco-elastic structure are presented. It is assumed that a paper in a printing device is loaded in its plane and thus a problem of plane stress is analyzed. The principal stresses are calculated and represented at the centers of finite elements. They substantially determine the vibration behavior and stability of the polymeric film. The first eigenmodes are presented for a paper performing transverse vibrations as a plate having additional stiffness due to static tension in its plane. Stresses in the polymeric film in the transverse and longitudinal direction of transportation of the tape were determined by using experimental methods for the symmetric and non-symmetric loads. For the investigation of the eigenmodes a special experimental setup was used in which the eigenmodes of the paper tape were determined by using the method of projection moire under the action of vibrations to the tape of paper for the symmetric load. Comparison of the experimental and numerical results of investigation was performed. [ABSTRACT FROM AUTHOR]

Abstract: Results reported in Part 1 of this series showed that paper strength improvements could be optimized by varying pH and the overall content of ionic groups in random terpolymers containing a fixed molar ratio of acidic and basic monomeric groups. Further treatment of kraft fiber slurries with polyaluminum chloride (PAC), after polyampholyte addition, yielded significant strength benefits. The present paper shows how these results can be explained in terms of the streaming potential (SP) of glass fibers, which were used as a model substrate. The data suggest that aluminum ions interact both with the anionic carboxyl groups of the polyampholytes and with anionic silanol groups at fiber surfaces. The streaming potential of the treated surfaces could be changed by varying the pH, the overall density of charged groups of the polyampholytes, the ratio of cationic to anionic groups on the polymer and by post-treatment with polyaluminum chloride. [Copyright &y& Elsevier]

Interaction between screw dislocations and a partially debonded interface in cylindrically anisotropic composites subjected to uniform stress at infinity is investigated in this paper. Using Muskhelishvili’s complex variable method, the closed forms of complex potentials are obtained for a screw dislocation and a screw dislocation dipole located inside either matrix or inhomogeneity. Explicit expressions of stress intensity factors at the crack tips, image forces and image torques acting on dislocation or the center of dipole are provided. The results show that the crack and dislocation geometry combination plays an important role in the interaction between screw dislocations and interface crack. Furthermore, it is found that the anisotropy of solids may change the shielding and anti-shielding effects arising from screw dislocations and the equilibrium position of screw dislocations. The presented solutions are valid for anisotropic, orthotropic or isotropic composites and can be reduced to some novel or previously known results. [ABSTRACT FROM AUTHOR]

Abstract?? In order to investigate the way in which fibre properties affect the mechano-sorptive creep phenomenon in paper, single wood fibres were exposed to tensile stresses at a constant humidity of 80% relative humidity (RH) and in a cyclic humidity environment varying between 80 and 30% RH. Contrary to earlier claims, it was demonstrated that single wood fibres exposed to a cyclic RH show a considerably higher creep than that corresponding to the highest RH experienced in the cycle, i.e., a mechano-sorptive behaviour. The creep strain rate at cyclic humidity was shown to be a function of the creep rate at constant climate, and to be an apparent linear function of the applied stress. [ABSTRACT FROM AUTHOR]

The article discusses that the mathematical expressions of plate instability could be applied to thin webs such as paper that have small but finite plate bending stiffness. It recalls the subject of plate instability and expand the theory to broaden the orthotropic properties of many webs. It examines the effects of web shear stiffness, web tension, and the traction between webs and rollers on troughs and wrinkles. It determines what levels of misalignment are acceptable in each span of a process machine for a given web material.

Abstract: For spatial stability analysis of shear deformable thin-walled curved beams with non-symmetric cross-sections, an improved analytical formulation is proposed. Firstly the displacement field is introduced considering the second order terms of semi-tangential rotations. Next an elastic strain energy is derived by using transformation equations of displacement parameters and stress resultants and considering shear deformation effects due to shear forces and restrained warping torsion. And then the potential energy due to initial stress resultants is consistently derived with accurate calculation of Wagner effect. In addition, closed-form solutions for in-plane and lateral-torsional buckling loads of curved beams subjected to uniform compression and pure bending are newly derived. In the companion paper, FE procedures are developed by using curved and straight beam elements with arbitrary thin-walled sections. In numerical examples, to illustrate accuracy and validity of this study, closed-form solutions for in-plane and out-of-plane buckling loads are presented and compared with those obtained from analytical solutions by other researchers. [Copyright &y& Elsevier]

Abstract: The creep of paper is accelerated by moisture cycling. This effect is known as mechano-sorptive creep. It is assumed that this is an effect of transient stresses produced during moisture content changes in combination with non-linear creep behaviour of the fibres. The stresses produced by the moisture content changes are often much larger than the applied mechanical loads. If this is the case, the mechanical loads are only a perturbation to the internal stress state, and it will appear as if the mechano-sorptive creep is linear in stress. It is possible to take advantage of this feature. In the present report the pure moisture problem is first solved. The mechanical load is then treated as a perturbation of the solution to the moisture problem. Using this strategy, it is possible to linearize a non-linear network model for mechano-sorptive creep and to formulate a continuum model. As a result, the number of variables in the model is reduced. This is a significant improvement as it will be possible to use the linearized model to describe the material in a finite element program and solve problems with complicated geometries. [Copyright &y& Elsevier]

Microindentation as a method for determining important material properties of paper coating materials is studied experimentally and numerically. The bulk of the investigation is concentrated upon the short-lived elastic part of a spherical indentation test, but determination of the failure stress of the coating is also discussed. The results indicate that microindentation can be a powerful tool for material characterization of these materials, but only if careful efforts are made to account for the influence from plasticity as well as from boundary effects. [ABSTRACT FROM AUTHOR]

Nowadays our society demands the reuse of industrial products. Then we should not only re-investigate the materials of products but also originate a new design method of industrial products. We have investigated the cellular structure by using abandoned paper, because the cell''s shape can be proposed arbitrarily by folding a paper. As examples, we have proposed the structure constructed by connecting many folded cells formed in a hexagonal cross area. This structure will have characteristics such as almost high rigidity, high stiffness, crushing stress, relative insensitivity to the overall loss of stability. To estimate the characteristics of these structures, we must analyze the deformation in loading. When the structure with thin walls formed by paper is loaded, the shape of deformation is different from that of the metal, wall swells and does not maintain its flatness. Therefore, we cannot apply the traditional theory of elasticity for the analysis. In this paper, we propose a new estimation method by analyzing the swelling. [Copyright &y& Elsevier]

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An elastic–plastic material model for the out-of-plane mechanical behaviour of paper is presented. This model enables simulation the elastic–plastic behaviour under high compressive loads in the through-thickness direction (ZD). Paper does not exhibit a sharp transition from elastic to elastic–plastic behaviour. This makes it advantageous to define critical stress states based on failure stresses rather than yield stresses. Moreover, the failure stress in out-of-plane shear is strongly affected by previous plastic through-thickness compression. To cover these two features, a model based on the idea of a bounding surface that grows in size with plastic compression is proposed. Here, both the bounding and the yield surfaces are suggested as parabolas in stress space. While the bounding surface is open for compressive loads, the yield surface is bordered by the maximum applied through-thickness compression. [Copyright &y& Elsevier]

Rolls of films and paper are routinely stored under varying conditions before being unwound into downstream operations. During storage, interlayer pressures can change relative to the pressures generated during winding. These changes can lead to problems such as film/paper blocking (increased interlayer pressure) and roll shifting/cinching (decreased interlayer pressure). To study the storage effect, a nonlinear wound roll stress model including air entrainment is first developed and applied to predict the in-roll stresses during film/paper winding. Thereafter, a thermal stress model is used to study the temperature effect on wound roll stresses. Key inputs to the models are the stack modulus, contact clearance, and air film reference clearance. A method is developed to measure these key model inputs. Results of a parametric study show that among the processing conditions, storage temperature and thermal expansion coefficients of the core and the film/paper are key factors that affect in-roll stresses during storage. Limitations of the models will also be discussed along with recommendations for future modeling development. [ABSTRACT FROM AUTHOR]

Stochastic two-dimensional elastic–plastic network models are used to represent the inelastic deformation behavior of well-bonded paper. Linear kinematic hardening is employed with an initial non-zero back stress to represent anisotropic fiber yield. Network models are used to simulate simple monotonic tension and simple cyclic tension of paper materials. The performance of the models is compared to experimental results and found to perform reasonably well. The results suggest that interfiber bonding must be explicitly accounted for to adequately describe the material. Some discrepancy between the model and experimental cyclic tension results is believed to be due to time-dependent strain recovery in the material which is not represented in the network models. Experimental results are also presented which show that simple tension failure in these materials occurs along a line of localized deformation in a majority of the samples. This line is generally observed to form immediately prior to failure and is oriented at a well-defined angle with respect to the loading direction. [Copyright &y& Elsevier]

Summary The quality of a wound roll is highly dependent upon the in-roll stress distribution, which is controlled by the operating parameters of the center-wind torque, nip and tension. With increasing demands for higher performance of paper winding systems in terms of higher winding speeds, wider web widths and larger wound roll diameters, it becomes of vital importance to determine and understand the optimum operating conditions of these machines. In this paper, a numerical formulation for estimating the in-roll stress of a wound roll is proposed with taking account of the effect of nonlinearity in web compressibility, air-entrainment and permeance. The in-roll stress is calculated as the superposition of the stress increments caused by each winding. The theory of elasto-hydrodynamic lubrication with the compressibility of air is introduced to evaluate the effect of air-entrainment at the roll-inlet. Permeance of air is newly incorporated into the winding model, which is expressed under the assumption that permeance is proportional to the pressure difference of both sides of a web. In order to assure the applicability of the proposed theory, winding tests were conducted using the dry-end section of the paper-making pilot machine. The numerical analysis and experimental observation show the significant effect of the air-entrainment and permeance upon the in-roll stress. [ABSTRACT FROM AUTHOR]

Certain aspects of the handle of fabric laminates are related to properties of the component fabrics. Particular attention is paid to a theoretical prediction of the bending stiffness of a laminate from the bending and tensile properties of its components. This theoretical stiffness is a minimum value; if, in practice, the observed stiffness is much greater than this, it may generally be assumed that excess of adhesive or of melted foam is the cause. The paper also reports work on other features of the bending behaviour, such as the degree of recovery from bending, and on the shearing behaviour. The work is concluded by a brief study of some faulty laminates. [ABSTRACT FROM AUTHOR]