Properties Of Constituent Materials Research Articles

Spectral Radiative Properties of Ceramic Particles for Concentrated Solar Thermal Energy Storage Applications

This work investigates the spectral radiative properties of ceramic particles using a monochromator and a Fourier-transform infrared spectrometer (FTIR) with integrating spheres at wavelengths from 0.38 μm to 15 μm. Particles are encased between two transparent windows to obtain the directional-hemispherical reflectance of the particle bed. Two types of commercially available particles with three different sizes are examined. Integration over the solar spectrum reveals that the solar absorptance of the particle beds is between 0.940 and 0.957. The total emittance at 1000 K is also estimated by assuming the spectral emittance is independent of temperature. The optical constants of particles are modeled with effective medium approaches, considering the optical properties of individual constituent materials. The absorptance of the particle is estimated using the effective optical constants and compared with that of the particle bed from the measurement. This work facilitates the characterization of radiative properties of particles with a windowed method and provides a modeling scheme for approximating the radiative properties of composite ceramic materials.

Decrease in the camber degree of Au/ceramic co-fired structure for LTCC technology

To relieve the camber of Au/ceramic co-fired structure, investigation on the sintering of gold paste with different constituent material properties was performed in this study. The sintering initial temperature of gold paste was correlated with the gold particle size, the glass softening point and the glass content closely. By adjusted the gold paste sintering shrinkage behaviour the camber evolutions were obviously changed, including the camber direction and the camber degree. When glass content in gold paste was 3 wt% and the softening point was 730 °C, the Au/ceramic co-fired structure exhibited the minimum camber, of which the ht/ho value was 0.96. The results of this work have shown the relationship between the camber evolution of Au/ceramic structure and the sintering shrinkage behaviour of gold paste, which would give an avenue to solve camber in the LTCC application.

Fatigue behavior assessment for steel fiber reinforced concrete beams through experiment and Fatigue Prediction Model

The fatigue flexural behavior of steel-fiber-reinforced concrete (SFRC) beams was assessed through the experiment on SFRC beams subjected to fatigue loading and the analysis of Fatigue Prediction Model (FPM). The stress level, tensile reinforcement strength, and steel fiber volume fraction were considered in the program. Test results indicated that steel fibers can improve the fatigue performance of the beams. The fatigue life of the beams increased significantly with the increase of steel fiber volume fractions from 0 to 1.0%, and slightly decreased for 1.5% steel fiber volume fraction because of the fiber cluster. A FPM of SFRC beam was proposed based on the fatigue properties of constituent materials and cross-section analytical method. This model can simulate the development of strains in concrete and steel bars of beams under fatigue loading, and can also be extended to assess the effects of reinforcement ratio upon the fatigue life and failure mode of SFRC beams.

Effect of Bimodal-Sized Hybrid TiC–CNT Reinforcement on the Mechanical Properties and Coefficient of Thermal Expansion of Aluminium Matrix Composites

Aluminium (Al) matrix reinforced with carbon nanotubes (CNT), micron-sized titanium carbide (TiC) particles, and bimodal (nano + micron) hybrid TiC–CNT is fabricated by solution ball milling, followed by cold compaction and vacuum sintering to improve the mechanical properties and reduce thermal expansion. The hardness, wear resistance, compressive strength and CTE of pure Al, 0.6 wt% CNT/Al, 10 wt% TiC/Al, and hybrid 10–0.6 wt% TiC–CNT/Al composites have been investigated in this work. Analysis of strengthening mechanisms based on theoretical models, microstructure, and properties of constituent materials is performed. Microstructure analysis reveals an excellent distribution of the reinforcement phase and no new phase formation in sintered composites. The hardness value of bimodal TiC–CNT reinforced Al composite is significantly higher than monomodal TiC reinforced composite, reaching 2.3 times the hardness value of pure Al. Similarly, the wear resistance improved, and CTE reduced with CNT and TiC addition but is even significantly better in the hybrid reinforced composite. Experimental values of CTE show good agreement with the theoretical model. The strength and ductility of materials are mutually exclusive, but the compressive strength of pure Al has been doubled without significant loss in ductility through the use of bimodal-sized hybrid TiC–CNT reinforcement in this work.

Failure modeling and analysis of composite laminates: Interval-based approaches

Composite materials inherently exhibit scatter in their basic characteristics such as the mechanical properties of constituent materials, fibers orientations, ply thicknesses, and applied loads. The uncertainties present in the basic parameters are available, in most cases, in the form of ranges or intervals. The use of the existing deterministic failure theories, which do not consider the observed variabilities in the input parameters, leads to poor failure assessment of composite materials. Several probabilistic failure models have been proposed in the past few decades. However, the probabilistic methods require a knowledge of the probability distributions of the basic variables which are not available in most practical systems. This work, for the first time, presents an interval-based failure analysis of composite materials using the truncation-based interval analysis and the universal gray system theory. These methods require only the lower and upper bounds of the uncertain parameters which are available in most practical systems. The application of the proposed interval-based failure models is demonstrated by considering two types of graphite/epoxy laminates: [0/±45/90] S and [0/90]2. This work shows that more realistic and meaningful failure assessment can be made using the universal gray system theory and the truncation-based interval analysis compared to the deterministic failure analysis.

Role of fiber arrangement in the thermal expanding behavior of unidirectional metal matrix composites

The influence of fiber arrangement on thermal expanding behavior of unidirectional fiber-reinforced metal matrix composites (MMCs) is evaluated using a unit cell micromechanical approach. Both regular and random fiber arrangements are considered in the MMC simulation by extending the number of sub-cells of the representative volume element (RVE). Moreover, the unit cell micromechanical model is used to investigate the role of fiber cross-section on the coefficients of thermal expansion (CTEs) of unidirectional MMCs. The validity of the model is verified by comparing the predictions and those available experimental measurements. The effective axial CTEs are not dependent on the MMC microstructure with different types of fiber arrays and cross-sections. However, the results show that besides the volume fraction, shape and the arrangement type of fibers plays a significant role in the effective transverse CTEs of MMCs. The discrepancy between the transverse predictions of the model with a random fiber arrangement and those of the model with a regular fiber arrangement increases with the rise of difference between the constituent material properties. Also, the effects of different statistical distributions of the random fiber arrangement, the number of RVE sub-cells and fiber orientation on the MMC thermal expanding response are examined.

A microscopic elasto-plastic damage model for characterizing transverse responses of unidirectional fiber-reinforced polymer composites

Abstract A phenomenological-based micromechanical method, comprising the coupling of the matrix constitutive model and the cohesive zone (CZM) model at fiber-matrix interfaces, is presented to investigate the mechanical behaviors of unidirectional (UD) fiber-reinforced polymer (FRP) composites subjected to transverse tension and compression. The key point of this method is the establishment of a novel elasto-plastic damage constitutive model using a fracture plane based yield criterion. Both plastic deformation and progressive failure procedure is incorporated in the implicit simulation. Special focus is given to the determination of the input values of constituent material properties, suggesting that directly using the macroscopic matrix properties to characterize the mechanical responses at the microscale level may bring large discrepancies in homogenized stress-strain responses of UD composites. A parametrical study is also carried out to calibrate cohesive parameters. The numerical results, in good agreement with experimental measurements, clearly reveal the damage scenarios and the dominant failure mechanisms. It can be concluded that the debonding of the fiber-matrix interfaces is responsible for the ultimate transverse tensile strength, while compression failure is governed by two possible modes, i.e. matrix compressive failure if matrix failure firstly occurs, and matrix tensile and interface debonding failure when debonding initiates first. Besides, the distribution of fracture plane angles in matrix is examined to further validate the predictive capacity of the proposed model.

Seismic response analysis of a hydraulic fill dam

The seismic response of a highly heterogeneous hydraulic fill dam was evaluated by studying the natural frequencies of the first and second modes of vibration and analyzing the crest accelerations of different two-dimensional or 2D sections of the dam when subjected to two different earthquake excitations. The existing methods for determination of the natural frequency of earthen embankment structures can only be used to analyze the structural response at small strain levels. However, during seismic events, the natural frequency of an earthen dam is significantly affected by the nonlinear material behavior exhibited by the geomaterials at high strain levels. Hence, a novel method was devised to evaluate the strain-dependent natural frequency for plane strain 2D dam sections, using a synthesized multi-sine base excitation. The degradation of first and second natural frequencies of transverse vibration for all the 2D sections followed a linear trend when plotted against the respective crest’s root mean square strain on a logarithmic scale. The slope of the degradation curve was found to depend on the constituent material properties prevalent in the individual sections. The observed variations in natural frequencies and crest accelerations of the 2D dam sections were also used to assess the suitability of using two-dimensional plane strain analyses for studying the response of a long earthen dam having variability in material properties. Results indicate that there is a considerable chance of erroneous estimation of the seismic response of such highly heterogeneous earthen dams that are conventionally analyzed using plane strain models. A 2D analysis was found to merely capture the seismic response of the individual sections of the dam as independent entities while ignoring the stiffening or weakening effect of the adjacent neighboring segments that may have different material properties.

Uncertainty in Fibre Strength Characterisation Due to Uncertainty in Measurement and Sampling Randomness

Carbon fibres have exceptional mechanical properties and are used for critical structural applications such as composite pressure vessels and aerospace components. For such high performance applications, reliability-based designs and lifetime assessments require very accurate strength models. Accuracy of the predictions made by composite strength models depend on realistic material properties of constituents, which are used as input. In practice however, fibre strength properties reported by different sources show significant variations. The work described here aims at understanding the influence of measurement uncertainty and sampling randomness on the uncertainty in calculated tensile strength distribution parameters. Tensile strength data for T700 carbon fibres obtained from single fibre testing process has been analysed for uncertainties. A parametric bootstrap method has been used for the evaluation. It has been shown that although both the causes studied of uncertainty are critical, the sampling randomness has a larger influence on the uncertainty of fibre strength, as compared to the uncertainty due to measurement. Choosing an insufficient sample size for analysis can thus result in uncertain or even inaccurate fibre strength properties, which would limit the reliability of composite strength models. The knowledge of the causes and effects of these uncertainties can help in taking appropriate measures for improving the accuracy of results. This would thereby enhance the capability of composite strength models to estimate the behaviour of different composite structures more accurately.

(Invited) Radiation Effects on the Self-Heating of AlGaN/GaN High Electron Mobility Transistors

Gallium nitride (GaN) has emerged as one of the most attractive wide bandgap materials for near-future electronics technology, specifically for applications that require high-power and high-frequency devices. The spontaneous and piezoelectric polarization of GaN utilized in AlGaN/GaN high electron mobility transistors (HEMT), provides significantly low ON-resistance due to the formation of a two-dimensional electron gas (2-DEG) channel at the AlGaN/GaN heterointerface without any intentional doping. The fact that these devices do not rely upon dopants to carry the current, in conjunction with superior material property of GaN, makes AlGaN/GaN HEMTs perfect candidates for deep space applications. However, the high voltage operation and the inherently low ON-resistance in AlGaN/GaN HEMTs result in extremely high power densities. Consequently, intense self-heating deteriorates device performance and more importantly, reliability.In order to counter the potential thermal problems associated with these device technologies for deep space applications, it is necessary to advance the knowledge of device irradiation and its effect on self-heating, material interfaces, and properties of constituent materials. To achieve this goal, a set of AlGaN/GaN HEMTs were irradiated with a proton flux at an energy level of 1 MeV at a fluence of 2x1015/cm2. Diverse optical thermography techniques including infrared thermography, thermoreflectance thermal imaging, and micro-Raman spectroscopy were used to quantify the effect of radiation on the device temperature distribution. It was observed that, as compared to pre-irradiated devices, irradiated devices show a 40% higher device peak temperature under identical power dissipation (5 W/mm). To understand the contributing factors behind the observations (and the resulting deterioration of device mean-time-to-failure), the device material stack and transmission line measurement (TLM) structures were analyzed further. Steady-state thermoreflectance (SSTR) measurement, standard electrical characterization, and 3D coupled electro-thermal modeling were performed to capture changes in the thermal conductivity, interfacial thermal boundary resistance, ohmic contact resistance, and sheet resistivity of the devices. This comprehensive study will support the exploitation of the full potential of GaN electronics for deep space and other applications that require radiation hardness.

Retraction Note: Repair of Buckled Concrete Filled Steel Tube Columns Subjected to Axial Compression

Concrete filled steel tube (CFST) columns are the main loaded elements in the structures as they provoke the superior mechanical properties of constituent materials. However, concrete filled double steel tube (CFDST) columns refer to a new type of composite elements which have very high level of fire resistance and the potential to be implemented in high-rise structures. Columns are exposed to high stresses due to the increasing loads of daily life. Therefore, unpredictable deformations may occur and affect the performance and safety of structures. This article first studies the effectiveness of a concrete filled circular steel tube (CFCST)-based technique for repairing buckled and stressed CFST columns, then it studies the advantages of CFDST columns in improving the capability of composite members. The CFCST-based repairing system is to place the deformed CFST column in a larger diameter steel tube, and then the concrete is poured in the gap between the deformed column and the larger tube. Buckled CFST specimens with different tube tkicknesses were repaired and tested to failure under axial compression. The performance of repaired CFST columns was compared with that of undamaged counterpart columns. Based on findings, it can be concluded that the repair technique restored the capacity of the deformed columns from 97% to 100% of the capacity of the undamaged counterpart columns which confirm the effectiveness of repairing using CFCST-based technique. Results of the study provide significant information to the available test data concerning repairing of CFST members.

Large amplitude vibration of sandwich plates with functionally graded auxetic 3D lattice core

Full-scale modeling and nonlinear FEA are presented for large amplitude vibration of sandwich plates with functionally graded (FG) auxetic 3D lattice core. For the first time, auxetic 3D lattice metamaterials with FG configurations along the out-of-plane direction are designed, of which the fundamental vibration frequencies are analyzed and verified by experiments using 3D printed specimens. Both results suggested that the effects of FG configurations and strut incline angles are significant, and the FG-X specimen possesses the highest fundamental frequency. Subsequently, by means of full-scale nonlinear FE simulations, the large amplitude vibration characteristics are investigated for the sandwich plates, in which the novel construction of auxetic 3D lattice core with three FG configurations along the thickness direction is proposed. And the constituent material properties are taken to be temperature-dependent. Results revealed that FG configurations have distinct effect on the natural frequencies, nonlinear-to-linear frequency ratios of sandwich plates, along with EPR-amplitude curves, which will become stable when the vibration amplitude is sufficiently large.

Impact resistance of nacre-like composites diversely patterned by 3D printing

Multi-layered composites structured by replicating biological creatures are very promising protective material applicable in various industries for the outstanding mechanical characteristics. Particularly, nacre is the most sought-after creature for biomimicry due to the exceptional impact resistance, secured by hierarchically patterned architecture. Therefore, numerous efforts have been devoted aiming to develop high functional composites by mimicking the nacre. However, optimization of dimensions and material properties for the nacre-like geometry has not been fully investigated thus far. In this study, we utilize a combination of fabrication, testing, and simulation to explore an optimal design of the nacre-like composite. Various types of 3D nacre-like architecture are designed, and corresponding specimens are fabricated using a dual-extruder 3D printer. Under drop weight impact loading, impact performances of each specimen are demonstrated. The test is simulated with finite element models of the nacre-like composite, and the experiment and numerical results are in good agreement. Both results reveal that the nacre-like composite outperforms the monolithic stiff material upon impact. Furthermore, adequate dimensions of each constituent and desirable material properties are determined. This insight on the nacre-like design can be employed as a guideline toward further optimization for a new generation of high-performance material systems.

RETRACTED ARTICLE: Repair of Buckled Concrete Filled Steel Tube Columns Subjected to Axial Compression

Concrete filled steel tube (CFST) columns are the main loaded elements in the structures as they provoke the superior mechanical properties of constituent materials. However, concrete filled double steel tube (CFDST) columns refer to a new type of composite elements which have very high level of fire resistance and the potential to be implemented in high-rise structures. Columns are exposed to high stresses due to the increasing loads of daily life. Therefore, unpredictable deformations may occur and affect the performance and safety of structures. This article first studies the effectiveness of a concrete filled circular steel tube (CFCST)-based technique for repairing buckled and stressed CFST columns, then it studies the advantages of CFDST columns in improving the capability of composite members. The CFCST-based repairing system is to place the deformed CFST column in a larger diameter steel tube, and then the concrete is poured in the gap between the deformed column and the larger tube. Buckled CFST specimens with different tube tkicknesses were repaired and tested to failure under axial compression. The performance of repaired CFST columns was compared with that of undamaged counterpart columns. Based on findings, it can be concluded that the repair technique restored the capacity of the deformed columns from 97% to 100% of the capacity of the undamaged counterpart columns which confirm the effectiveness of repairing using CFCST-based technique. Results of the study provide significant information to the available test data concerning repairing of CFST members.

Investigation of the effect of shape of inclusions on homogenized properties by using peridynamics

Fiber-reinforced composite materials are widely used in many different industries due to their superior properties with respect to traditional metals including their light weight, corrosion resistance, high strength, impact resistance, etc. Fiber-reinforced composite materials are composed of a strong fiber material, which mainly carries the applied load, and soft matrix material, which transfers the load to the fiber material and keep the fibers together. Macroscopic analysis of fiber-reinforced composite materials is done by utilising the homogenised material properties which mainly depends on individual material properties of fiber and matrix. In this study, in addition to the effect of individual material properties of constituents, the effect of the shape of fibers (inclusions) on homogenised properties is investigated by using a new methodology called peridynamics.

Testing and Finite Element Modelling of Concrete Block Masonry Walls under Axial and Out-of-Plane Loading

The current Canadian masonry design standard, CSA S304-14 (2014), appears to underestimate the capacity of loadbearing masonry walls for some loading combinations and wall sizes. This is compounded by the fact that most testing has been completed on walls with pinned base supports, a condition that is not representative of practice. To understand the structural response of concrete block walls under eccentric axial and combined axial and out-of-plane loads better, walls with height to thickness ratio of 12.6 were tested. The displacement profiles under pinned-fixed and pinned-pinned boundary conditions were obtained for both load combinations and were used with the constituent material properties to calibrate finite element models. Models were developed using micro-modelling approaches, modelling units, mortar and grout as merged parts, or individually with friction contact interfaces, having rebar embedded in the grouted cells. The contact modelling approach showed broad agreement with the test results. Both the test results and the modelling showed a clear reduction in out-of-plane displacements, and change in the displaced profile, when a pinned connection was not forced at the wall base.

Optimization of tunable guided-mode resonance filter based on refractive index modulation of graphene

To fabricate a tunable optical filter with a fast response in the near infrared region, a tunable guided-mode resonance (GMR) filter using graphene was proposed and its performance was optimized. In this study, a rigorous coupled wave analysis method was employed to systematically investigate the effects of geometrical configuration of graphene-integrated GMR filters and the optical properties of constituent materials including graphene on their spectral response in terms of tunability and extinction ratio. It was found that as the graphene is located close to the waveguide and the evanescent-field strength at the interface increases, the GMR filter exhibits better tunability. The bandwidth of the filter could be drastically reduced by adopting a low-index contrast grating layer, so that the extinction ratio of an optical signal could be greatly improved from 0.91 dB to 27.99 dB as the index contrast decreased from 0.99 to 0.47, respectively. Furthermore, new practical device designs, that is easy to fabricate and effectively implement the electric-field doping of graphene at low gate voltage, were also suggested and theoretically validated. These results demonstrate not only the excellent potential of a graphene-based tunable GMR filter but also provide practical design guidelines for optimizing the device performance.

Test methods for characterizing concrete properties at elevated temperature

SummaryFire resistance of structural members is dependent on the thermal and mechanical properties of constituent materials and these properties vary as a function of temperature. Currently, there are limited standardized test procedures for evaluating thermal and mechanical properties of construction materials at elevated temperatures. This paper provides a review and assessment of test methods and procedures for evaluating high temperature thermal and mechanical properties of concrete. The drawbacks and variations in currently available test procedures and methods in standards are discussed. Recommendations on the most suitable methods and procedures for measuring thermal and mechanical properties at elevated temperature is presented. In addition, applicability of the proposed high temperature test methods and procedures is illustrated through a case study on conventional concrete specimens. Further, the need for developing standards by organizations such as American Society for Testing and Materials (ASTM), with standardized specifications and test procedures for measuring high temperature properties of construction materials, is laid out.

Effect of pressure on temperature measurements using WRe thermocouple and its geophysical impact

Our understanding of the Earth's interior strongly depends on the physical and chemical properties of the Earth's constituent materials, which have been determined using high-pressure/high-temperature experiments involving thermocouples. Thus, knowledge of the pressure effect on the thermocouple electromotive force (EMF) is indispensable for an accurate understanding of the Earth's interior. We have determined the effect of pressure on a W3Re-W25Re thermocouple up to 16 GPa and 1173 K by the single-wire method using a multi-anvil apparatus in conjunction with synchrotron radiation. The difference between the nominal temperature and the real temperature was determined to be −29 K at 16 GPa and 1173 K when using this thermocouple. There have been many debates addressing the discrepancy between the depth of the 660-km seismic discontinuity in the Earth's mantle and the pressure–temperature conditions of the postspinel phase boundary in Mg2SiO4. This discrepancy disappears when the temperature value is corrected. The transport properties (e.g. rheology, element diffusion, electrical conductivity) in the Earth appear to slow down with depth more rapidly than was previously estimated because of the effect of pressure on the thermocouple.

A multiscale approach for virtual testing of highly aligned short carbon fiber composites

This paper presents an efficient multiscale approach for high fidelity virtual testing of highly aligned short fiber reinforced composites (SFRCs), based solely on constituent material and interface properties with no need of calibration data. The method is based on a hierarchical, bottom-up characterization of SFRCs and the link of mechanical behaviors of materials and microstructures from a lower scale to a higher scale. It starts with a microscopic unit cell model to estimate the transverse and shear properties of the aligned short fiber composites. Next, two types of mesoscale models with explicit consideration of fiber discontinuity and possible local fiber misalignments are employed to obtain effective properties of material domains with such morphologies. Such obtained meso-scale mechanical properties and damage behaviors are then integrated into the macroscale virtual laminar via the stochastically integrating of possible material defects. Results indicate that for perfectly aligned SFRCs the strength reduction is about 25% as compared to that of the continuously reinforced composites. However, misalignment of short fibers can cause a further strength reduction of 20–35% with the volume fraction of the misalign regions varying from 1% to 10%.