Related Material Parameters Research Articles

Sound absorption characteristics of nanocomposite polyurethane foams infused with carbon nanotubes

Flexible, open-cell polymeric foams are among the most commonly used and effective materials for passively dissipating noise and vibration. Their unique cellular structure results in materials which are lightweight but still highly absorptive, making them particularly useful for weight-sensitive applications, such as aircraft cabin noise reduction. “Nanocomposite” polymeric foams, which are synthesized from polymeric materials containing nanoscale fillers (e.g. carbon nanotubes and silicate nanoclays), have altered morphological and mechanical properties in comparison to conventional counterparts. Many of these same properties intrinsically control the sound absorption characteristics of polymeric foams. Thus, by utilizing nanoscale fillers to control relevant morphological and mechanical properties, polymeric foams with enhanced sound absorption properties could potentially be created. In this study, various composites of polyurethane foam and multi-walled carbon nanotubes were synthesized and then experimentally characterized to observe the effects of the nanofiller infusion on sound absorption in terms of the normal incidence sound absorption coefficient. Additionally, a number of related material parameters were measured including porosity, flow resistivity, elastic modulus, loss factor, and density, and connections were made between the effects of the carbon nanotubes on these properties and the observed changes to sound absorption. Results indicated that polymeric foams infused with multi-walled carbon nanotubes exhibited an increased ratio of sound absorption to density, depending on the weight fraction of carbon

Numerical modelling of tyre–pavement-interaction phenomena: constitutive description of asphalt behaviour based on triaxial material tests

As basis for the subsequent numerical modelling of tyre–pavement-interaction phenomena, an adequate representation of asphalt material behaviour is required. Therefore, in the present publication, experimental investigations by the repeated load triaxial test and a new approach of the interpretation of the test results are presented. Based on these results, an appropriate asphalt material model that considers elastic, viscous as well as plastic properties and that allows for large strain theory is selected for the numerical modelling by finite element method. The related material parameters are identified based on the experimental data by an optimisation procedure. Exemplarily, the numerical simulation of data points of the Cole–Cole-plot and the computation of an asphalt test sample in triaxial stress state are conducted. The comparison of experimental and numerical results shows good agreement. Therefore, the material model and the parameters may be used subsequently for structural pavement computations.

Multi-scale identification of concrete material parameters

A multiscale method for determining fracture related material parameters in concrete is presented. A homogenized constitutive law is used in the coarse-scale while the fine-scale accounts for the meso-scopic features of concrete, i.e. the cement matrix, micro-cracks and aggregates. The fine-scale and the coarse-scale is coupled by the Lagrange multiplier method. A meshless method is applied where material failure is modeled by the extended element free Galerkin method. The well-posedness of the boundary value problem is restored by means of cohesive zone approach. The interface between the cement matrix and the aggregates are also modeled through the cohesive zone approach. The validity of the method is shown for two benchmark problems with available experimental results.

Electro- and thermomigration induced Cu3Sn and Cu6Sn5 formation in SnAg3.0Cu0.5 bumps

Two important trends in the microelectronics business are the development of three dimensional packaging solutions which increase the number electronics components on the same area, and the application of VLSI electronics under harsh environment conditions. Both trends lead to a growing importance of intermetallic compound (IMC) formation in Sn based solder joints. Due to miniaturization a growing part of the solder joint volume is transformed into IMCs and finally the reflow process becomes a transient liquid phase soldering (TLPS) process. For harsh environment applications TLPS enables the transformation of low melting Sn contacts into high melting IMC joints. In both cases a model for the prediction of migration-induced IMC formation is required for the fabrication of IMC joints.For the general prediction of the migration induced IMC formation the related material parameters are needed. Against this background the Cu3Sn and Cu6Sn5 formation was observed during temperature storage tests on Amkor® Package-on-Package packages (12×12mm) with SnAg3.0Cu0.5 ball grid arrays. A mathematical model was developed to calculate the average mass flux of Sn and Cu during the stress tests. Based on the mass flux values the activation energies and diffusion constants for Cu and Sn in Cu3Sn and Cu6Sn5 were determined. Afterwards the temperature storage was combined with an AC and a DC current load to investigate thermo- and electromigration-related phenomena. Based on the IMC formation speed during the AC and the DC tests the heat of transport Q* and the effective charge of the moving ion Z* were calculated. An interpretation of the material parameters is given in consideration of the high defect density in Cu3Sn and Cu6Sn5.

Descriptor-based methodology for statistical characterization and 3D reconstruction of microstructural materials

3D reconstructions of heterogeneous microstructures are important for assessing material properties using advanced simulation techniques such as finite element analysis (FEA). Nevertheless, for many materials systems like polymer nanocomposites, only 2D microstructural images are available even with the state-of-the-art imaging techniques. This paper proposes a new descriptor-based methodology for reconstructing 3D particle-based heterogeneous microstructures based on 2D images. The proposed methodology characterizes a 2D microstructural morphology using a small set of microstructure descriptors covering features including material composition, dispersion status, and phase geometry, and then reconstructs statistically equivalent microstructures in a 3D space based on the 3D descriptors derived from 2D characterization and a few reasonable assumptions. Our approach is the most useful when the direct 3D microstructure analysis, such as 3D tomography, is not available due to either high cost or difficulties in sample preparations. Other practical features of descriptor-based characterization include low dimensionality, which enables optimal parametric design of microstructures, as well as physically meaningful mapping of processing related material parameters. In reconstruction, the proposed algorithm is capable to generate large size 3D structures at a low computational cost. Furthermore, since the algorithm is stochastic, it can be used to construct both Representative Volume Element (RVE) and Statistical Volume Element (SVE) for FEA studies. We demonstrate the proposed methodology by characterizing and reconstructing polymer nanocomposites.

Low cycle fatigue behaviour of a Cr–Mo–V matrix-type high-speed steel used for cold forging

The low cycle fatigue (LCF) behaviour of a Cr–Mo–V matrix-type high-speed steel (matrix-type HSS), which was used as cold forging tool material, was investigated. Fatigue tests were conducted under strain-controlled cyclic loading conditions with different axial strain amplitude levels at room temperature. The tests indicated that hysteresis loops formed when the total strain amplitude was 1.5%, 1.0% and 0.75%. At total strain amplitudes that were less than 0.7%, there was no cyclic plastic deformation or hysteresis loop observed. The material fatigue behaviour was analysed specifically at the above three strain levels to investigate the cyclic plastic deformation of the material because the low cycle fatigue behaviour was of principal interest in this study. At all selected total strain amplitudes, the cyclic stress responses showed cyclic softening, and reached a “quasi-stabilised” softening state before the material finally ruptured from fatigue. The cyclic strain–stress relationship and the strain–life relationship were obtained through the test results, and related material parameters were calculated. Fractographic and metallographic analyses were also conducted in this study. The metallographic structure of the steel before and after heat treatment was examined. Two types of carbide phases were found in the steel. The fatigue damage process through the crack initiation and propagation was explained by observing the features of the fractures.

An experimental characterization of the acoustically dissipative properties of light-weight nanocomposite polyurethane foams augmented with carbon nanotubes

Flexible, open-cell polymer foams are among the most commonly used and effective materials for passively dissipating noise and vibration. Their unique microcellular structure results in materials which are light weight but still highly absorptive, as well as relatively strong and stiff, making them particularly useful for weight-sensitive applications, such as aircraft cabin noise reduction. "Nanocomposite" polymer foams, which are synthesized from polymer materials containing reinforcing nano-scale fillers, have been shown to have altered morphological and mechanical properties in comparison to conventional counterparts. These same morphological and mechanical properties fundamentally control the acoustic absorption and vibration damping provided by polymer foams. Thus the alteration of these properties by nano-scale reinforcing materials can potentially be exploited to enhance the dissipative properties of these materials. In this study, various composites of polyurethane foam and multi-walled carbon nanotubes were synthesized and then experimentally characterized to observe the effect on noise and vibration dissipation. Sound absorption coefficient and loss factor were measured, along with a number of related material parameters. Results indicate inclusion of carbon nanotubes can increase the ratio of the sound absorption coefficient to weight for polymer foam treatments, dependent on both the carbon nanotube particle size and weight fraction.

Characterization of PWR vessel steel tearing under severe accident condition temperatures

Abstract In the event of a severe core meltdown accident in a pressurised water reactor (PWR), core material can relocate into the lower head of the vessel resulting in significant thermal and pressure loads being imposed on the vessel. In the event of reactor pressure vessel (RPV) failure there is the possibility of core material being released towards the containment. On the basis of the loading conditions and the temperature distribution, the determination of the mode, timing, and size of lower head failure is of prime importance in the assessment of core melt accidents. This is because they define the initial conditions for ex-vessel events such as core/basemat interactions, fuel/coolant interactions, and direct containment heating. When lower head failure occurs (i) the understanding of the mechanism of lower head creep deformation; (ii) breach stability and its kinetic of propagation leading to the failure; (iii) and developing predictive modelling capabilities to better assess the consequences of ex-vessel processes, are of equal importance. The objective of this paper is to present an original characterization programme of vessel steel tearing properties by carrying out high temperature tearing tests on Compact Tension (CT) specimens. The influence of metallurgical composition on the kinetics of tearing is investigated as previous work on different RPV steels has shown a possible loss of ductility at high temperatures depending on the initial chemical composition of the vessel material. Small changes in the composition can lead to different types of rupture behaviour at high temperatures. The experimental programme has been conducted on various French RPV 16MND5 steels for temperatures ranging from 900 °C to 1100 °C. Comparisons between the tests performed on these various 16MND5 steels show that this approach is appropriate to characterize the difference in ductility observed at high temperatures. The aim of this experimental study is also to contribute to the definition of a tearing criterion by identifying, on the basis of CT results, the related material parameters at temperatures representative of the real severe accident conditions. This experimental campaign has been carried out in partnership with IRSN in the framework of a research programme whose purpose is to complete the mechanical properties database of 16MND5 steel and to model tearing failure in French RPV lower head vessels under severe conditions ( Koundy et al., 2008 ).

Simulation of pressure distribution in a pyrophyllite high-pressure cell by finite-element analysis

The pressure-transmitting behavior and pressure distribution of a pyrophyllite cell in a cubic-anvil large volume high-pressure apparatus is investigated by finite-element analysis (FEA). The mechanical equations describing pyrophyllite under high pressure are given, which are composed of the Drucker–Prager criterion and a linear equation of state. The related material parameters such as cohesive strength, angle of internal friction etc. are experimentally measured. The FEA simulation includes the non-uniformity deviatoric stress caused by plastic deformation and the isotropy hydrostatic pressure of the pyrophyllite cell caused by volume compression. The results demonstrate that, in such a pyrophyllite cell, almost 90{%} of the pressure is isotropy hydrostatic pressure, and the pressure gradient mainly arise from non-uniform deviatoric stresses. Simulated data are displayed using the contour and the path plots.

Loading of a Gravel-Buried Steel Pipe Subjected to Rockfall

Increasing rockfall activity in the European Alps has raised the need for designing protection systems for Alpine infrastructure. This paper is concerned with protection of steel pipelines by a gravel overburden of height H. Rockfall-induced loading of such pipes is estimated by means of a three-dimensional, quasi-static, elasto-plastic finite-element (FE) model. Maximum impact forces F and corresponding penetration depths w are estimated based on dimensionless formulas, related to real scale impact tests onto gravel layers. The forces F are applied as surface loads onto the FE model, at a distance (H−w) from the pipe. Material behavior of gravel is represented by a cap model, which is based on pressure-independent linear elasticity and associated plasticity. Related material parameters are identified from acoustic and static material tests. The structural FE model is validated by comparing FE-predicted stresses in the pipe with stresses determined in a real-scale structural experiment. This is reasonable only because the real-scale test is independent of the experiments used for identification of the material parameters used as input for the structural FE model. Satisfactory FE predictions motivate use of the FE model for estimating the loading of the steel pipe in untested scenarios, concerning, e.g., different heights of overburden, or different impact intensities. These estimates show some efficiency of gravel protection systems for modest rockfall, with impact energies well below 3,500kJ.

Response Times and Their Temperature Dependence Measured for a Series of Liquid Crystals Using Gain Spectra of Stimulated Light Scattering

In the present work we have shown the opportunity of using the process of stimulated light scattering due to recording of dynamic orientation gratings for directly measuring the characteristic orientation relaxation time of liquid crystals (LCs) and related material parameters, the elastic constants and the coefficients of orientational viscosity. The measurement consists in obtaining the gain spectra of LCs and determining the magnitude of the gain coefficient and the optimum frequency shift between interfering laser beams. We have designed a setup where the gain spectra of stimulated light scattering process in LCs are obtained within seconds. These spectra are highly specific to LCs serving as a precise and fast tool for studying LC materials and their mixtures with the purpose of optimizing their linear and nonlinear optical properties. Using this technique we have found that certain azo LC materials are faster compared to several well-known Merck's formulations for LC displays.

An experimental study on the effect of chloride penetration on moisture diffusion in concrete

Chloride penetration and moisture diffusion are two important transport processes for studying the long-term durability of concrete. The chloride penetration and moisture transfer in concrete are considered as two coupled transport processes. An experimental study was conducted for determining the related material parameters in the coupled transport processes. For the coupled moisture diffusion, we consider that the total moisture fluxJ H t is resulted from two driving forces: the gradient of moistureH, and the gradient of free chlorideC f , that is,J H t =−D H-H grad(H)−D H-Cl grad(C f′ ). In this formulation, two transport parameters are involved: the moisture diffusion coefficientD H-H and the coupled moisture diffusion coefficient due to chloride diffusionD H-Cl . A seepage test was designed specifically for determining the two transport parameters. The test data showed that the chloride penetration accelerates the moisture diffusion significantly. The two transport parameters were determined using the present test data. The result showed thatD H-Cl is not a constant, but depends linearly on the free chloride concentration.

Analysis of transport critical current density in a bent BiPbSrCaCuO silver-sheathed tape

The experimental results on the magnetic behavior of the transport critical current density in a bent Bi based superconducting tape have shown that the irreversible strain limit ε irrev for the onset of permanent strain damage to Ag sheathed superconductors is not dependent on the magnetic field, nor does the normalized I c (H, ε) I c (0, ε) current depend on the strain at least up to 0.5 T at 77 K. Such a behavior has been attributed to two reasons: (1) The intrinsic pinning properties are unchanged in a bent tape; (2) The strain effect is extrinsic and arises from superconductor cracks. Thus, based on these arguments a Josephson junction tunneling model with cracks in between the grain boundaries is proposed to explain the J c behavior quite well for a bent granular high- T c superconducting tape. Our model calculation shows that the critical current density of high- T c superconductor may be enhanced by increasing the strain tolerance ε irrev and the ε irrev is determined by the properties of Ag sheathed tape and its related material parameters, which are dependent on the connectivity of the grain boundaries.

Conventional and torque magnetometry on disc-shaped high-T c superconductor samples : I. A steady-state dynamical theory

A nonlinear, macroscopic electrodynamic theory is given to explain the irreversible part of the magnetic momentum m irr and the torque momentum Γ irr observed in conventional (CM) and torque magnetometry (TM) on HTSC discs and thin films with oblique external time-dependent magnetic field H 0( t) and off-plane rotation of H 0( t), respectively. This theory relates m irr and Γ irr with the nonlinear conductivity tensor σ of the mixed state, and with microstructure-dependent material parameters entering σ, which govern the thermally activated vortex motion under anisotropic pinning. In the steady state, m irr and Γ irr is understood to result from a current j excited by an “applied” electrical field E 0 induced by the external inductance B 0 ( t) = H 0( t). The limiting case of discs with large aspect ratio and thickness much smaller than the nonlinear skin depth is studied in detail. It is shown that, except of some singular cases, j and m irr becomes strictly azimuthal and axial, respectively, while | δB| ⪡ | B 0| where B = B o + δB is the total inductance. The boundary value problem is solved in a self-consistent approximation making use of the strong sublinear characteristic of j versus the total electrical field E under CM and TM conditions, which allows to replace σ by an effective pseudo-linear quantity ḡs governed by the dominating azimuthal E -mode. Formulae or m irr and Γ irr are given, showing, in spite of the simple configuration of E and B , a complicated nonlinear dependence upon the components of σ. To interpret CM and TM experiments, a phenomenological description of σ( E, B ) is presented based upon symmetry arguments, as well as theoretical and experimental facts, which is valid for anistropic and layered HTSC, including the isotropic, and the anisotropic intrinsic and twin-boundary pinning. The possibility to determine σ and related material parameters from CM and TM results is discussed in detail.

Effect of uniaxial stress on the electron spin resonance in zinc-blende semiconductors.

We present a study of the effect of uniaxial stress on the electric-dipole spin resonance absorption in zinc-blende semiconductors. We show that previous work in this field omits an important contribution to the transition amplitude, leading to an underestimate of the strength ${C}_{2}$ of the stress-induced spin-orbit coupling in InSb. The necessary correction factor is between 3 and 4. We suggest experimental configurations that would permit an accurate measurement of this and other related material parameters. One of these exploits the possibility of an interference between stress-induced and stress-free spin-flip transition amplitudes. In this way, not only the magnitude of ${C}_{2}$, but also its sign, could be determined.