Correlation between ultrasonic shear wave velocity and Poisson’s ratio for isotropic porous materials

A new correlation between ultrasonic shear wave velocity and Poisson’s ratio has been established for isotropic porous material based on physical acoustic theory. Poisson’s ratio may decrease, increase or remain unchanged with decrease in shear wave velocity depending on pore-shape and Poisson’s ratio of the bulk solid. In case of decreasing Poisson’s ratio with decreasing shear wave velocity, it passes through a minimum and then increases again to reach a limiting value of 0.5. It has been further demonstrated that the Poisson’s ratio versus porosity relation deduced from the proposed correlation agrees with the experimental data extremely well.

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Combining Maxwell’s methodology with the BEM for evaluating the two-dimensional effective properties of composite and micro-cracked materials

Maxwell’s methodology is combined with the boundary element method (BEM) for evaluating the two-dimensional effective elastic properties of composite, porous, and microcracked isotropic materials with periodic or random structure. The approach is based on the idea that the effective properties of the material can be deduced from the effects that a cluster of fibers, pores, or cracks embedded in an infinite matrix has on the far-fields. The fibers, pores, or cracks can have arbitrary shapes, sizes, and elastic properties, provided that the overall behavior is isotropic, and their effects are assumed to be the same as those of an equivalent circular inhomogeneity. The key aspect of the approach is to precisely account for the interactions between all the constituents in the cluster that represent the material in question. This is done by using the complex-variables version of the BEM to solve the problem of a finite cluster of fibers, pores or cracks embedded an infinite isotropic, linearly elastic matrix. The effective properties of the material are evaluated by comparing the far-field solutions for the cluster with that of the equivalent inhomogeneity. It is shown that the model adequately captures the influence of the micro-structure of the material on its overall properties.     

Young’s modulus and Poisson’s ratio of concrete at high temperatures: Experimental investigations

When exposed to fire, Young’s modulus of concrete degrades. Thus, exact knowledge of temperature-dependent reduction is important to determine the fire-resistance of concrete or composite members. Nevertheless, existing material properties for the Young’s and shear modulus of concrete are linked with some incertitudes.In addition, normative regulations lack information on the temperature-dependent Poisson’s ratio. In an attempt to overcome some of the existing uncertainties, experimental work was conducted to investigate elastic material properties of fire-exposed concrete. For this purpose, the Impulse Excitation Technique was used as an innovative testing technique. Based on experimental results, the authors propose new elastic material formulations for fire-exposed concrete.     

Scaling of conductivity and Young’s modulus in replicated microcellular materials

Scaling exponents for the conductivity and stiffness of replicated microcellular materials exceed commonly predicted values of 1 and 2. We show here that this is caused by the fact that, in replicated microcellular materials, the solid architecture varies with the relative density: a simple derivation based on the physics of powder consolidation returns and explains the observed scaling behaviour. The same derivation also gives an explanation for Archie’s law, known to describe the conductivity of wet soils.     

Mandel and Cryer problems of fluid-saturated foams with negative Poisson’s ratio

Summary. Professor Lakes created foams with negative Poissons ratios in 1987. Since then he has examined interesting and fantastic characteristics of such foams and proposed their realistic and future possible applications. The present study was motivated by our interest in how such a foam behaves for a sudden loading if it is saturated with fluid. To highlight mechanical interactions between elastic deformation of such a foam and diffusion of the saturating fluid, we solved four problems in a unified manner: 2D and 3D, Cryer and Mandel problems. It is found that for all these problems the pore fluid pressure near the sample center climbs up from its initial pressure and then declines and vanishes; its peak is much higher for negative Poissons ratios, that is, much more remarkable Mandel-Cryer effect. Stress components such as tangential stress also show similar behavior, and the tangential stress has tension near the sample surface in spite of compressive loading. It is also found that for the step-like axial compression the Mandel cylinder sample laterally expands immediately after the loading, then shrinks and finally becomes thinner than its original thickness; a possible application is proposed.     

Development of an image analysis technique for measurement of Poisson’s ratio for viscoelastic materials: application to leather

The application of a computerised image analysis system to simultaneously measure longitudinal and axial strain in naturally available anisotropic-viscoelastic material like leather is described. The results are used to calculate Poisson’s ratio and indicate that this parameter varies with position and orientation on the hide and depends on the degree of pre-existing fibre orientation. The origins of this dependency can be explained by a simple microstructural model. The practical implication of the findings for detecting lines of tightness (maximum fibre’s orientation) is discussed.     

Health monitoring of aerospace composite structures – Active and passive approach

Impact damage is one of the major concerns in maintenance of aircraft structures built from composite materials. Damage detection in composite materials can be divided into active and passive approaches. The active approach is usually based on various non-destructive techniques utilizing actuators and/or receivers. In contrast passive approaches do not involve any actuators; receivers are used to “sense and/or hear” any perturbations caused by possible hidden damage. Often strain data are used to localize impacts and estimate their energy. The assumption is that damage occurs above well-defined energy of impacts. The paper illustrates one active and one passive method recently developed for impact damage detection. The first method, based on guided ultrasonic waves, utilises 3-D laser vibrometry and does not require any signal processing. Simple laser scans, revealing the change in Lamb wave response amplitudes, have been used to locate delamination and estimate its severity in a composite plate. In contrast, the second method does not require any sophisticated instrumentation but relies on advanced signal processing. An array of piezoceramic sensors has been to detect strain waves transmitted from an impact applied to the composite aircraft structure. The modified multilateration procedure with Genetic Algorithms has been used to locate impact position.     

Definition of diagonal Poisson’s ratio and elastic modulus for infill masonry walls

The prediction of the response of infilled frames through the simplified approach of substituting the infill with an equivalent pin-jointed strut is treated. In this framework the results of an experimental study for the mechanical characterization of different types of masonry infills having the aim of estimating strength, Young modulus and Poisson’s ratio are presented. Four types of masonry were investigated and subjected to ordinary compressive tests orthogonally to the mortar beds and along the directions of the mortar beds. The experimental campaign confirmed the possibility of using an orthotropic plate model for prediction of the Poisson’s ratio and Young modulus along the diagonal direction of infills (these parameters are requested by a model already known in the literature for the identification of struts equivalent to masonry infills). The experimental campaign made it possible to recognise a correlation between the Poisson’s ratios and the strengths of masonries investigated along the orthotropic axes and to obtain the diagonal Poisson’s ratio without specific experimental tests. Finally, the experimental responses of some infilled frames were used to test the reliability of the model proposed here.     

Tensile fatigue of conventional and negative Poisson’s ratio open cell PU foams

In this paper, we present a comparative analysis between the cyclic loading tensile behaviour of conventional and auxetic thermoplastic PU foams. While the two types of foam share the same base material (open cell PU–PE), one batch is transformed into an auxetic one (i.e., negative Poisson’s ratio) using a special manufacturing process involving moulding and exposure to particular temperature profiles to stabilise the transformation of the microstructure. The effect of the stiffness degradation and accumulation of energy dissipation versus the number of cycles are discussed for different loading levels r. The results show that the fatigue behaviour until failure, subjected to cyclic loading depends on the loading levels and occur in three stages. The results obtained shows also that the auxetic foam have enhanced characteristics under static loading and tensile fatigue compared to the conventional parent phase form.     

Quantification and integration of Kano’s model into QFD for optimising product design

With increasing concerns on customer needs in today’s competitive market, the issue of incorporating customer requirements into product design arises the interest of both researchers and practitioners. Quality Function Deployment (QFD) is a well-known methodology for customer-driven product design. However, conventionally, QFD analysis has a major challenge in understanding customer needs accurately. Kano’s model, which studies the nature of customer needs, provides a way for a better classification of customer needs. However, seldom research contributions are found in terms of integrating Kano’s model with QFD quantitatively. In this research, a novel integration approach is proposed. At first, Kano’s model is quantified by identifying relationship between customer needs and customer satisfaction (CS). Next, both qualitative and quantitative results from Kano’s model are integrated into QFD. Finally, a mixed non-linear integer programming model is formulated to maximise CS under cost and technical constraints. In this research, an illustrative example associated with the design of notebook computers is also presented to demonstrate the availability of the proposed approach.     

Prediction of Young’s modulus and Poisson ratio for foamed metals using octahedron model

Abstract

The present paper deals with the mathematical–physical expression of Young’s modulus and Poisson ratio of foamed metals. As it is known that, Young’s modulus and Poisson ratio are two basic mechanical parameters of engineering materials. Foamed metal is a class of excellent engineering materials with dual attributes of structural and functional characteristics; therefore, these two parameters are investigated for these materials, and the relevant mathematical–physical expressions are derived from the ‘octahedron model’ of porous materials in the present paper. The results show that the apparent Young’s modulus displays a quite complicated mathematical relationship to porosity of the porous body, and the apparent Poisson ratio is just a characteristic of the material constant almost not relative to porosity of the foamed metal.     

A composite material with Poisson’s ratio tunable from positive to negative values: an experimental and numerical study

The Poisson’s ratio describes an extent of transverse deformation of a material when an axial strain is applied. A change of the Poisson’s ratio from positive to negative can equip a material with a set of specific properties. In this paper, a study of a composite material with a tunable Poisson’s ratio is presented. Samples of such a composite were first fabricated with two different polymers based on a composite structure proposed in our previous work using a multi-material additive-manufacturing system. Using both experimental and numerical methods, deformation mechanisms and mechanical properties of this composite material were analyzed. The obtained results demonstrate that its Poisson’s ratio can be reduced by increasing the difference in stiffness of constituent materials and turned from positive to negative when this difference is sufficiently high. Additionally, the study also validates a possible method to fabricate composites with designed structures and multi-constituent materials using additive-manufacturing techniques.     

A mixed integer programming approach to designing periodic frame structures with negative Poisson’s ratio

Materials and microstructures with specific configurations are able to have negative Poisson’s ratio. This paper proposes a topology optimization methodology of frame structures to design a planar periodic structure that exhibits negative Poisson’s ratio. Provided that beam section of each existing member is chosen from a set of some given candidates, we can reduce the topology optimization problem to a mixed-integer linear programming problem. Since the proposed approach treats frame structures and stress constraints are rigorously addressed, the optimal solution contains no hinge region. A heuristic method with local search is used to solve large-scale problems. Numerical examples and fabrication test demonstrate that planar periodic frame structures exhibiting negative Poisson’s ratio can be successfully obtained by the proposed method.     

Sensitivity of flexible pavement design to Michigan’s climatic inputs using pavement ME design

Climate condition is an important factor that affects the performance of pavements and distress predictions using mechanistic-empirical analyses. This study aims to analyse the sensitivity of flexible pavement distress predictions to climatic inputs using the AASHTOWare Pavement ME Design software in the state of Michigan. Typical traffic parameters, pavement structures and material properties for the state of Michigan were used as inputs for the analysis of flexible pavement performance. Six representative sites geographically distributed throughout Michigan and two typical traffic levels (high and medium) were incorporated in a comprehensive analysis of the effects of climate on flexible pavement performance predictions. A normalised sensitivity index was adopted to quantitatively evaluate the sensitivity of distress predictions to the five individual climatic variables: temperature, wind speed, precipitation, percent sunshine and relative humidity. The results of this study showed that the prediction of flexible pavement performance in Michigan is most sensitive to changes in temperature with other climatic factors such as wind speed, percent sunshine, precipitation and relative humidity impacting predictions to a lesser extent. Higher temperature and percent sunshine at a given location increased rutting and International Roughness Index (IRI) predictions, but reduced the likelihood of fatigue cracking. An increase in wind speed or precipitation reduced rutting and IRI predictions, but increased fatigue cracking predictions. Ambient relative humidity had a negligible effect on all flexible pavement distress predictions. These findings provide insights into the sensitivity of flexible pavement designs under different climate conditions. The sensitivity results are also beneficial for the Michigan Department of Transportation as they seek to improve the existing climatic files in PMED through evaluation of new climatic data sources.