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.

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.

Model‐based inversion of amplitude‐variations‐with‐offset data using a genetic algorithm

Geophysics ◽  
1995 ◽  
Vol 60 (4) ◽  
pp. 939-954 ◽  
Author(s):  
Subhashis Mallick
Keyword(s):  
Reflection Coefficient ◽  
Acoustic Impedance ◽  
Poisson’S Ratio ◽  
Input Data ◽  
Synthetic Data ◽  
Single Layer ◽  
P Wave ◽  
Poisson's Ratio ◽  
Reasonable Accuracy ◽  
Avo Inversion

I cast the inversion of amplitude‐variation‐with‐offset (AVO) data into the framework of Bayesian statistics. Under such a framework, the model parameters and the physics of the forward problem are used to generate synthetic data. These synthetic data are then matched with the observed data to obtain an a‐posteriori probability density (PPD) function in the model space. The genetic algorithm (GA) uses a directed random search technique to estimate the shape of the PPD. Unlike the classical inversion methods, GA does not depend upon the choice of an initial model and is well suited for the AVO inversion. For the single‐layer AVO inversion where the amplitudes from a single reflection event are inverted, GA estimates the normal incidence reflection coefficient [Formula: see text] and the contrast of the Poisson’s ratio (Δσ) to reasonable accuracy, even when the signal‐to‐noise ratio is poor. Comparisons of single‐layer amplitude inversion using synthetic data demonstrate that GA inversion obtains more accurate results than does the least‐squares fit to the approximate reflection coefficients as is usually practiced in the industry. In the multilayer AVO waveform inversion, all or a part of the prestack data are inverted. Inversion of this type is nonunique for the estimation of the absolute values of velocities, Poisson’s ratios, and densities. However, by applying simplified approximations to the P‐wave reflection coefficient, I verify that [Formula: see text], the contrast in the acoustic impedance (ΔA), and the gradient in the reflection coefficient (G), can be estimated from such an inversion. From the GA estimated values of [Formula: see text], ΔA, and G, and from reliable estimates of velocity and Poisson’s ratio at the start time of the input data, an inverted model can be generated. I apply this procedure to marine data and demonstrate that the the synthetics computed from such an inverted model match the input data to reasonable accuracy. Comparison of the log data from a nearby well shows that the GA inversion obtains both the low‐ and the high‐frequency trends (within the bandwidth of seismic resolution) of the P‐wave acoustic impedance. In addition to P‐wave acoustic impedance, GA also obtains an estimate of the Poisson’s ratio, an extremely important parameter for the direct detection of hydrocarbons from seismic data.

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.

scholarly journals PETAL AUXETICS WITH TARGETED POISSON’S RATIO USING ISOGEOMETRIC SHAPE OPTIMIZATION

2021 ◽  
Author(s):  
Deepak Kumar Pokkalla
Keyword(s):  
Shape Optimization ◽  
Poisson’S Ratio ◽  
Poisson's Ratio ◽  
Stress Concentrations ◽  
Optimization Framework ◽  
Optimization Stage ◽  
Auxetic Materials ◽  
Potential Applications ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

Auxetic materials with negative Poisson’s ratio have potential applications across a broad range of engineering fields. Several design techniques have been developed to obtain auxetics with targeted mechanical properties. However, many of these finite element based techniques are difficult to use directly for auxetics, particularly during the design optimization stage which involves evolving boundary parts with large curvatures. This paper focusses on a series of smoothed petal auxetics, with lower stress concentrations at connecting parts, compared to the reference star shaped structures. An isogeometric shape optimization framework to achieve target Poisson’s ratios at large deformation is presented. Several smoothed petal auxetic designs with target constant Poisson’s ratios up to an effective tensile strain of 30% are shown to demonstrate the capability of the optimization framework.

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