scholarly journals Variations in Orthotropic Elastic Constants of Green Chinese Larch from Pith to Sapwood

Forests ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 456 ◽  
Author(s):  
Fenglu Liu ◽  
Houjiang Zhang ◽  
Fang Jiang ◽  
Xiping Wang ◽  
Cheng Guan
Keyword(s):  
Shear Modulus ◽  
Elastic Constants ◽  
Coefficient Of Variation ◽  
Modulus Of Elasticity ◽  
Poisson’S Ratio ◽  
Poisson's Ratio ◽  
Stress Wave Propagation ◽  
Sampling Distance ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

Full sets of elastic constants of green Chinese larch (Larix principis-rupprechtii Mayr) with 95% moisture content at four different cross-section sampling positions (from pith to sapwood) were determined in this work using three-point bending and compression tests. Variations in the material constants of green Chinese larch from pith to sapwood were investigated and analyzed. The results showed that the sensitivity of each elastic constant to the sampling position was different, and the coefficient of variation ranged from 4.3% to 48.7%. The Poisson’s ratios νRT measured at four different sampling positions were similar and the differences between them were not significant. The coefficient of variation for Poisson’s ratio νRT was only 4.3%. The four sampling positions had similar Poisson’s ratios νTL, though the coefficient of variation was 11.7%. The Poisson’s ratio νLT had the greatest variation in all elastic constants with a 48.7% coefficient of variation. A good linear relationship was observed between the longitudinal modulus of elastic EL, shear modulus of elasticity GRT, Poisson’s ratio νRT, and sampling distance. EL, GRT, and νRT all increased with sampling distance R. However, a quadratic relationship existed with the tangential modulus of elasticity ET, radial modulus of elasticity ER, shear modulus of elasticity GLT, and shear modulus of elasticity GLR. A discrete relationship was found in the other five Poisson’s ratios. The results of this study provide the factual changes in the elastic constants of green wood from pith to sapwood for numerical modelling of stress wave propagation in trees or logs.

Poisson's ratio of porous and microcracked solids: Theory and application to oxide superconductors

1995 ◽  
Vol 10 (11) ◽  
pp. 2715-2722 ◽  
Author(s):  
Martin L. Dunn ◽  
Hassel Ledbetter
Keyword(s):  
Elastic Constants ◽  
Poisson’S Ratio ◽  
Mean Field ◽  
Poisson's Ratio ◽  
Oxide Superconductors ◽  
Pore Shape ◽  
Elastic Solids ◽  
Bulk Solid ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

We present a theoretical study of the effective Poisson's ratio of elastic solids weakened by porosity and microcracks. Explicit expressions of the effective Poisson's ratio are obtained using the Mori-Tanaka mean-field approach as applied to macroscopically isotropic solids containing randomly distributed and randomly oriented spheroidal pores. We focus on the influence of pore shape and concentration and devote special attention to the limiting cases of spherical, penny-shape, and needle-shape pores. A key result of this study is that the effective Poisson's ratio depends only on pore concentration, pore shape, and Poisson's ratio of the bulk solid. In other words, it is independent of any other elastic constants of the bulk solid. Also, theratioof the shear and bulk moduli behaves similarly. Unlike other elastic constants which monotonically decrease with pore concentration, Poisson's ratio may increase, decrease, or remain unchanged as a function of pore concentration, depending on the pore shape and Poisson's ratio of the bulk solid. We discuss ramifications of these findings with regard to the elastic constants of oxide superconductors, especially the bismuth cuprates, which show unusually low Poisson's ratios. We also discuss these low Poisson's ratios, including the possibility of negative Poisson's ratios.

scholarly journals Giant negative Poisson’s ratio in two-dimensional V-shaped materials

2021 ◽  
Author(s):  
Xikui Ma ◽  
Jian Liu ◽  
Yingcai Fan ◽  
Weifeng Li ◽  
Jifan Hu ◽  
...  
Keyword(s):  
Poisson’S Ratio ◽  
Poisson's Ratio ◽  
Negative Poisson’S Ratio ◽  
Two Dimensional ◽  
Auxetic Materials ◽  
Negative Poisson's Ratio ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

Two-dimensional (2D) auxetic materials with exceptional negative Poisson’s ratios (NPR) are drawing increasing interest due to the potentials in medicine, fasteners, tougher composites and many other applications. Improving the auxetic...

Multilayer Composite Materials with Non-Usual Poisson's Ratios

2007 ◽  
Vol 555 ◽  
pp. 545-552 ◽  
Author(s):  
E.H. Harkati ◽  
Z. Azari ◽  
P. Jodin ◽  
A. Bezazi
Keyword(s):  
Composite Material ◽  
Composite Materials ◽  
Poisson’S Ratio ◽  
Cellular Materials ◽  
Poisson's Ratio ◽  
Multilayer Composite ◽  
Computer Programme ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

Most of usual materials exhibit Poisson's ratio comprised between 0 and 0.5. But, for some kind of cellular materials, or for some stacking sequences of unidirectional plies, a composite material can exhibit negative or greater than 0.5 Poisson's ratios. In this paper, a study of different stacking sequences such as [±β/±θ]s plies made from highly anisotropic fibre pre-preg is presented. A special computer programme has been developed for this purpose. Eighteen stacking sequences, including the [±θ] ones, have been computed. The results show that at least one of Poisson's ratios varies between -0.8 to +0.4. Such kind of materials may find applications for particular cases, as their strength is significantly increased by this phenomenon.

The Effect of Fiber Microstructure on the Observed Poisson’s Ratio of Tendon and Ligament Tissue

2008 ◽  
Author(s):  
Shawn P. Reese ◽  
Steve A. Maas ◽  
Heath A. Henninger ◽  
Jeffrey A. Weiss
Keyword(s):  
Poisson’S Ratio ◽  
Collagen Fiber ◽  
Poisson's Ratio ◽  
Fiber Direction ◽  
Exact Nature ◽  
Tendon Tissue ◽  
Element Analysis ◽  
The Relationship ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

During tensile testing along the predominant collagen fiber direction, ligament and tendon tissue exhibit large Poisson’s ratios ranging from 1.3 in capsular ligament to 2.98 in flexor tendon [1][2]. Although the microstructure of these tissues (especially fiber crimp) has been characterized, the relationship between microstructure and Poisson’s ratio is relatively unexplored. There has been debate regarding the exact nature of the characteristic crimp within tendon fibers, however the two views most present in the literature are that of planar crimp and helical crimp. The aim of this study was to perform a finite element analysis on prototypical models of fibril bundles for both forms of crimp under tensile loading conditions. It was hypothesized that planar crimp alone would be insufficient for generating large Poisson’s ratios, and that some other microstructure (such as a helix) would be required.

Micromechanical Models of Helical Fiber Organization in Crimped Tendon and Ligament Fibers Predict Large Poisson’s Ratios

2009 ◽  
Author(s):  
S. P. Reese ◽  
S. A. Maas ◽  
J. A. Weiss
Keyword(s):  
Poisson’S Ratio ◽  
Poisson's Ratio ◽  
Uniaxial Tensile ◽  
Lateral Contraction ◽  
Tail Tendon ◽  
Poisson's Ratios ◽  
Volumetric Response ◽  
Volumetric Behavior ◽  
Poisson’S Ratios ◽  
Rat Tail

The Poisson’s ratio is a measure of how much lateral contraction occurs in response to a uniaxial tensile strain, therefore making it a metric of the volumetric behavior of a material. A Poisson’s ratio greater than 0.5 for an isotropic material subjected to uniaxial tension is indicative of volume loss, which in the scheme of biphasic theory is believed to be manifested as fluid exudation. Experimentally obtained values for the Poisson’s ratio range from 0.8 in rat tail tendon, 1.3 in capsular ligament to 3.0 in flexor tendon [1,2,3]. In spite of the important implications of this volumetric response the micromechanical origins of these large Poisson’s ratios have been largely uninvestigated.

Design Considerations for Materials with Negative Poisson’s Ratios

1993 ◽  
Vol 115 (4) ◽  
pp. 696-700 ◽  
Author(s):  
R. S. Lakes
Keyword(s):  
Stress Concentration ◽  
Poisson’S Ratio ◽  
Sandwich Panel ◽  
Poisson's Ratio ◽  
Design Considerations ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

This article presents a study of the implications of negative Poisson’s ratios in the design of components subjected to stress. When the Poisson’s ratio becomes negative, stress concentration factors are reduced in some situations and unchanged or increased in others. Stress decay according to Saint Venant’s principle can occur more or less rapidly as the Poisson’s ratio decreases. Several design examples are presented, including a core for a curved sandwich panel and a flexible impact buffer.

scholarly journals Poisson’s ratios of molded pulp materials by digital image correlation method and uniaxial tensile test

2020 ◽  
Vol 15 ◽  
pp. 155892502090827
Author(s):  
Guangjun Hua ◽  
Maoteng Yang ◽  
Weimin Fei ◽  
Fude Lu
Keyword(s):  
Poisson’S Ratio ◽  
Correlation Method ◽  
Image Correlation ◽  
Poisson's Ratio ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Corrugated Board ◽  
Bamboo Pulp ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

The mechanical properties of molded pulp materials are the basis of the structural optimum design of molded pulp products. Therefore, the correlations between Poisson’s ratio and fiber structure, molding process, and thickness were found for materials including wood pulp, bamboo pulp, sugarcane pulp, white mixed pulp, black mixed pulp, recycled corrugated board pulp, and recycled newspaper pulp by the uniaxial tensile test and digital image correlation method. The fiber structures of the selected molded pulp materials were investigated by scanning electron microscopy. The results revealed Poisson’s ratios of wood pulp, bamboo pulp, sugarcane pulp, white mixed pulp, black mixed pulp, recycled corrugated board pulp, and recycled newspaper pulp to be 0.169, 0.108, 0.202, 0.120, 0.166, 0.098, and 0.044, respectively. Microstructural investigation further revealed that Poisson’s ratios of molded pulp materials were related to the fiber structure and drying method. The pulp material dried outside mold under lower pressure and temperature had a smaller Poisson’s ratio, while that dried inside mold under higher pressure and temperature had a larger Poisson’s ratio. The layered phenomenon of the molded pulp materials was also found by scanning electron microscopy images: the outer layer was denser than the inner layer. These results can provide guidance for the numerical simulation analysis and optimal design of molded pulp products.

scholarly journals Regularly configured structures with polygonal prisms for three-dimensional auxetic behaviour

2017 ◽  
Vol 473 (2202) ◽  
pp. 20160926 ◽  
Author(s):  
Junhyun Kim ◽  
Dongheok Shin ◽  
Do-Sik Yoo ◽  
Kyoungsik Kim
Keyword(s):  
Poisson’S Ratio ◽  
Three Dimensional ◽  
Unit Cell ◽  
Poisson's Ratio ◽  
Numerical Verification ◽  
Geometric Conditions ◽  
Unit Cells ◽  
Negative Poisson's Ratio ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

We report here structures, constructed with regular polygonal prisms, that exhibit negative Poisson’s ratios. In particular, we show how we can construct such a structure with regular n -gonal prism-shaped unit cells that are again built with regular n -gonal component prisms. First, we show that the only three possible values for n are 3, 4 and 6 and then discuss how we construct the unit cell again with regular n -gonal component prisms. Then, we derive Poisson’s ratio formula for each of the three structures and show, by analysis and numerical verification, that the structures possess negative Poisson’s ratio under certain geometric conditions.

Compliant Cellular Materials With Elliptical Holes for Extremely High Positive and Negative Poisson's Ratios

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Jaehong Lee ◽  
Kwangwon Kim ◽  
Jaehyung Ju ◽  
Doo-Man Kim
Keyword(s):  
Poisson’S Ratio ◽  
Longitudinal Direction ◽  
Materials Design ◽  
Cellular Materials ◽  
Poisson's Ratio ◽  
Yield Strain ◽  
Large Rotation ◽  
Elliptical Holes ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

Cellular materials' two important properties—structure and mechanism—can be selectively used for materials design; in particular, they are used to determine the modulus and yield strain. The objective of this study is to gain a better understanding of these two properties and to explore the synthesis of compliant cellular materials (CCMs) with compliant porous structures (CPSs) generated from modified hexagonal honeycombs. An in-plane constitutive CCM model with CPSs of elliptical holes is constructed using the strain energy method, which uses the deformation of hinges around holes and the rotation of links. A finite element (FE) based simulation is conducted to validate the analytical model. The moduli and yield strains of the CCMs with an aluminum alloy are about 4.42 GPa and 0.57% in one direction and about 2.14 MPa and 20.9% in the other direction. CCMs have extremely high positive and negative Poisson's ratios (NPRs) (νxy* ∼ ±40) due to the large rotation of the link member in the transverse direction caused by an input displacement in the longitudinal direction. A parametric study of CCMs with varying flexure hinge geometries using different porous shapes shows that the hinge shape can control the yield strength and strain but does not affect Poisson's ratio which is mainly influenced by rotation of the link members. The synthesized CPSs can also be used to design a new CCM with a Poisson's ratio of zero using a puzzle-piece CPS assembly. This paper demonstrates that compliant mesostructures can be used for next generation materials design in tailoring mechanical properties such as moduli, strength, strain, and Poisson's ratios.

Plane‐wave reflection coefficients for gas sands at nonnormal angles of incidence

Geophysics ◽  
1984 ◽  
Vol 49 (10) ◽  
pp. 1637-1648 ◽  
Author(s):  
W. J. Ostrander
Keyword(s):  
Reflection Coefficient ◽  
Poisson’S Ratio ◽  
Wave Reflection ◽  
P Wave ◽  
Poisson's Ratio ◽  
Angle Of Incidence ◽  
High Porosity ◽  
Low Velocity ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

The P-wave reflection coefficient at an interface separating two media is known to vary with angle of incidence. The manner in which it varies is strongly affected by the relative values of Poisson’s ratio in the two media. For moderate angles of incidence, the relative change in reflection coefficient is particularly significant when Poisson’s ratio differs greatly between the two media. Theory and laboratory measurements indicate that high‐porosity gas sands tend to exhibit abnormally low Poisson’s ratios. Embedding these low‐velocity gas sands into sediments having “normal” Poisson’s ratios should result in an increase in reflected P-wave energy with angle of incidence. This phenomenon has been observed on conventional seismic data recorded over known gas sands.

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