Lower Tensile Stiffness Research Articles

Modeling and simulation of anisotropic cross-linked cellulose fiber networks with an out-of-plane topography

Non-woven cellulose fiber networks of low areal density are widely used in many industrial applications and consumer products. A discrete element method (DEM) modeling framework is advanced to simulate the formation of strongly anisotropic cellulose fiber network sheets in the dilute limit with simplified hydrodynamic and hydroelastic interactions. Our modeling accounts for in-plane fiber orientation and viscous drag indirectly by using theories developed by Niskanen (2018 Fundamentals of Papermaking, Trans. 9th Pulp and Paper Fundamental Research Symp. Cambridge, 1989 (FRC) pp 275–308) and Cox (1970 J. Fluid Mech. 44 791–810) respectively. Networks formed on a patterned and flat substrate are simulated for different fiber types, and their tensile response is used to assess the influence of the out-of-plane topographical pattern, specifically, on their stiffness and strength. Sheets with the same grammage and thickness, but composed with a higher fraction of softwood fiber (longer fibers with large diameter), have higher strength and higher strain to failure compared to sheets made from hardwood fibers (short fibers with small diameter). However, varying the fiber fraction produces only an insignificant variation in the initial sheet stiffness. The above simulation predictions are confirmed experimentally for sheets comprised of fibers with different ratios of Eucalyptus kraft and Northern Bleached Softwood Kraft fibers. Sheets with out-of-plane topography show an unsymmetric mass distribution, lower tensile stiffness, and lower tensile strength compared to those formed on a flat substrate. The additional fiber deformation modes activated by the out-of-plane topography, such as bending and twisting, explain these differences in the sheet mechanical characteristics.

Working mechanism evaluations and simplified models of corner bracket type inter‐module connections

SummaryIn modular steel buildings, the corner bracket type inter‐module connection is a commonly used way of connecting adjacent modules together. However, the detailed working mechanisms of this connection are still not well known. In this study, the mechanical properties of two corner bracket type inter‐module connections were identified based on reported tests and refined finite element simulations. A simplified multi‐spring model of the corner bracket type inter‐module connections was proposed and was then incorporated into the two‐dimensional analysis of a framed modular building and a braced modular building to investigate the effect of connection properties on lateral sway performance of modular structures. Results indicated that the corner bracket type inter‐module connection had a lower tensile stiffness and resistance than compressive ones. Tensile and bending resistances of the connection were correlated with each other and were determined by the out‐of‐plane prying deformation of bracket endplates. The inter‐module connection possessed the extrusion‐resisting and separation‐permitting behavior between assembled brackets. The lateral sway performance of the pure framed modular building was closely related to the vertical shear stiffness of inter‐module connections. However, in the braced modular building, the tension and horizontal shear stiffnesses of inter‐module connections were the critical aspects.

Mechanical properties of low-density paper

Abstract For the mechanical properties of paper, tensile testing has been widely used. Among the tensile properties, the tensile stiffness has been used to determine the softness of low-density paper. The lower tensile stiffness, the greater softness of paper. Because the elastic region may not be clearly defined in a load-elongation curve, it is suggested to use the tensile modulus which is defined as the slope between the two points in the curve. The two points which provide the best correlation with subjective softness evaluation should be selected. Low-density paper has a much lower tensile strength, but much larger elongation at the break. It undergoes a continuous structural change during mechanical testing. The degree of the structural change should depend on tensile conditions such as the sample size, the gauge length, and the rate of elongation. For low-density paper, the tensile modulus and the tensile strength should be independent of each other. The structure efficiency factor (SEF) is defined as a ratio of the tensile strength to the tensile modulus and it may be used a guideline in developing superior low-density paper products.

Tunable tensile response of honeycomb plates with nanoscale thickness: Testing and modeling

Plate mechanical metamaterials with nanoscale thickness demonstrate significantly enhanced mechanical properties compared to solid plates that lack micropatterning. We have previously reported how the honeycomb corrugation greatly increases the bending stiffness, but any functional applications also require a full understanding of the tensile properties. Here we report that, surprisingly, the tensile properties of alumina plates with nanoscale thickness can be measured using conventional materials testing tools and that the tensile stiffness of honeycomb corrugated plates is greatly reduced, providing an unusual combination of high bending stiffness and low tensile stiffness that cannot be achieved with unpatterned plates. These measurements, along with finite-element (FE) simulations, provide validation for our analytical model that fully characterizes the tensile response of the corrugated nanoplates, thus enabling predictable tuning of their mechanical properties by changing the corrugation geometry. Plates optimized for high bending stiffness and low tensile stiffness can find applications as wings of microflyers or deployable aerospace components.

Thin-Shell Thickness of Two-Dimensional Materials

In applying the elastic shell models to monolayer or few-layer two-dimensional (2D) materials, an effective thickness has to be defined to capture their tensile and out-of-plane mechanical behaviors. This thin-shell thickness differs from the interlayer distance of their layer-by-layer assembly in the bulk and is directly related to the Föppl–von Karman number that characterizes the mechanism of nonlinear structural deformation. In this work, we assess such a definition for a wide spectrum of 2D crystals of current interest. Based on first-principles calculations, we report that the discrepancy between the thin-shell thickness and interlayer distance is weakened for 2D materials with lower tensile stiffness, higher bending stiffness, or more number of atomic layers. For multilayer assembly of 2D materials, the tensile and bending stiffness have different scaling relations with the number of layers, and the thin-shell thickness per layer approaches the interlayer distance as the number of layers increases. These findings lay the ground for constructing continuum models of 2D materials with both tensile and bending deformation.

Mechanical Property Characterization of Aligned Plant Yarn Reinforced Thermoset Matrix Composites Manufactured via Vacuum Infusion

This article evaluates the mechanical properties of vacuum-infused unidirectional plant fiber composites (PFRPs), composing of bast fiber yarns and thermoset matrices. PFRPs are found to have lower fiber volume fractions than E-glass composites (GFRPs). Apart from the expected (30–40%) lower density of PFRPs, they have 60–80% lower tensile strength, 30–60% lower tensile stiffness, 5–10 times lower impact strength, and 20–30% lower interlaminar shear strength than GFRPs. Importantly, critical fiber lengths are of the same order (0.2–0.5 mm). Composites reinforced with flax rovings exhibit exceptional fiber tensile modulus of 65–75 GPa and fiber tensile strength of about 800 MPa.

Seismic stability of reinforced slopes: failure mechanisms and displacements

Failure mechanisms of reinforced slopes with different seismic resistance capacities were examined, based on the results of tilting table tests previously reported by the authors. Three seismic resistance levels for slopes reinforced using various reinforcement materials and facing rigidities were identified, based on various ultimate tilting angles and modes of wall deformation. It was found that a high reinforcement interface friction angle (δr = 30°) is a prerequisite for attaining the highest level of seismic resistance with an ultimate tilting angle, θf ≥ 20° (or a critical seismic coefficient, [Formula: see text]). Reinforcement length and reinforcement stiffness play secondary roles, in the sense that these two factors are optional in attaining the highest level of seismic resistance. When a high tensile stiffness reinforcement was used, base sliding failure associated with maximum slope face deformation over the lower third of the slope occurred for slopes with a medium or a low seismic resistance level. Therefore, for a slope reinforced using a high tensile stiffness reinforcement, a maximum slope deformation in the lower third portion of the slope face may be used to identify a ‘less robust’ slope with a relatively low seismic resistance capacity. For slopes reinforced with a low tensile stiffness reinforcement, maximum deformation in the lower third of the facing is the dominant mode of deformation, regardless of the seismic resistance level. The bending rigidity of the facing may moderately influence the seismic resistance level when using a reinforcement sheet with a high interface friction angle (δr = 30°), but it has no influence on the seismic resistance level when using reinforcement sheets with relatively low surface friction angles of δr = 20° and 15°.

Calculation of errors in strain-gauge measurements

In many instances when measuring strains in components with a low tensile stiffness (plastics, reinforced rubber, etc.), it becomes necessary to take into account the possible errors due to the stiffening effect of strain gauges over their glued area. This error can be accounted for by applying the deformation distortion coefficient whose value can be determined from (11). For the practical application of this formula it is necessary to know the stiffness W of strain gauges as well as the elasticity constants of the component. The stiffness of strain gauges can be determined by a simple method, described in the article.