Terms Of Material Properties Research Articles

Microstructure models of cement: their importance, utility, and current limitations

Microstructure models seek to explain or predict various material properties in terms of the structure or chemical composition at scales of several hundred nanometres to several hundred micrometres. Such models therefore bridge the scaling gap between atomistic models and continuum methods, and consequently can help establish and validate scaling relations across those scales. Microstructure models have been applied to cementitious materials for at least four decades to help understand setting, strength development, rheological properties, mechanical behavior, and transport properties. This letter describes the current state of cement microstructure modelling in several areas that are important for engineering. It is not meant to be an exhaustive review, instead highlighting the kinds of models that can now be applied to different aspects of cement binder behaviour. Special attention is paid to challenges or limitations of each kind of model. This is done to promote the judicious use and interpretation of models and especially to indicate where future research could make inroads on problems that are currently inaccessible to microstructure models.

4D structures for the short-time building of emergency shelters

The increasing number of internal displaced people due to conflicts or natural disasters over the years represents the need to create structural solutions for first emergency shelter, which are currently supplied in tarpaulin and structures improvised by the locals. Innovative technologies like 4D printing could present an alternative, being possible to develop 3D structures with smart materials that react with environmental stimulus, such as water, light, heat and others. Unlike 3D printing, which is static, the factor ‘time’ adds a dimension to the 4D, making the structures self-assembling, multifunctional or self-repairing. Given this, the aim of this paper is to present research for the application of 4D-printed structures, for crises, to speed up and ease the assembly process, replacing the structures currently used with one that integrates the emergency kit. It also presents a review on emergency shelters, as well as on 3D and 4D printing processes, clarifying its definition and introducing a case study demonstrative of the process, by printing with shape memory filaments, specifically poly lactic acid and shape memory polymers. A concept was developed and validated, evaluating the possibility of applying 4D printing process in the development of structures that are easy to transport and assemble in emergencies, using the beneficial characteristics of shape memory polymer material. Therefore, the simulation of the concept and the improvement of material properties in terms of specific strength and toughness, which can be achieved using composite materials, are indicated as future recommendations. Moreover, the concept must be evaluated from a structural point of view.

Further development in modeling fatigue failure in metals with a multi-spring non-linear mechanical system

This paper presents further development of a spring mechanical system, proposed by Guranlick et al, in (1) deriving equations for the determination of the mechanical system parameters in terms of material properties; (2) developing applications for deriving fatigue life relations with consideration for the ratio of the minimum to maximum stress; and (3) extending the model to incorporate the hysteresis behavior of steel under cycling loading. These applications are demonstrated in this paper with numerical illustrations.

Cellulose nanostructures obtained using enzymatic cocktails with different compositions

Cellulose nanostructures obtained from lignocellulosic biomass by the enzymatic route can offer advantages in terms of material properties and processing sustainability. However, most of the enzymatic cocktails commonly used in the saccharification of biomass are designed to promote the complete depolymerization of the cellulose structure into soluble sugars. Here, investigation was made of the way that the action of different commercially available cellulase enzyme cocktails can affect the production of nanocellulose. For this, enzymatic cocktails designed for complete or partial saccharification were compared, using eucalyptus cellulose pulp as a model feedstock. The results showed that all the enzymatic cocktails were effective in the formation of nanocellulose structures, with the complete saccharification enzymes being more efficient in promoting the coproduction of glucose (36.5 g/L, 87% cellulose conversion). The presence of auxiliary enzymes, especially xylanases, acted cooperatively to favor the production of nanostructures with higher crystallinity (up to 79%), higher surface charge (zeta potential up to −30.9 mV), and more uniform dimensions within the size range of cellulose nanocrystals (80 to 350 nm). Interestingly, for the enzymatic cocktails designed for partial saccharification, the xylanase activity was more important than the endoglucanase activity in the production of nanocellulose with improved properties. The findings showed that the composition of the enzymatic cocktails already used for complete biomass saccharification can be suitable for obtaining nanocellulose, together with the release of a glucose stream, in a format compatible with the biorefinery concept.

Characterization of a Radiofluorogenic Polymer for Low-Energy Electron Beam Penetration Depth Visualization.

Low-energy (80–300 keV) electron beam accelerators are gaining in importance in the radiation processing industry due to their ease of use and wide range of applications (e.g. product surface sterilizations or polymer curing and cross-linking). Due to their very low penetration depth (tens to hundreds of microns), currently used film dosimeters exhibit dose gradients over their thickness and do not resolve the dose response in the first microns of the irradiated material. Hence, the surface dose, defined as the dose in the first micron Dµ, cannot be measured directly. This study presents a polymer material as a dosimeter candidate for high-dose low-energy electron beam irradiations. The readout of the dose-dependent fluorescence intensity, originating from a pararosaniline dye reaction when irradiated, is measured using fluorescence microscopy. So far, no in-depth characterization of the material has been performed, leaving the stability and fluorescence properties of the material not fully optimized. We describe the improvements in polymer composition and the fabrication method, and characterize the material properties in terms of the thermal stability, glass transition temperature, refractive index, hardness, rheological behavior, and water affinity. All of these create a complex set of requirements a polymer needs to fulfill to become an effective dosimeter when measuring using confocal microscopy. The fluorescence readout procedure will be addressed in further studies.

Effects of laser and electron beam welding on the mechanical properties of bake hardening sheets

Abstract Bake hardening sheets are frequently used materials in the automotive industry. The unique feature of these materials like hardening with the paint baking process is convenient for the manufacturer. Also, the bonding technique is a common issue for assembly lines. With new technologies regarding the welding process after the 1990s, the concept of welding has changed. In this study, the electron beam and laser beam sources, which are still considered new, are used for welding 260 BH bake hardening sheets used in the automotive industry as galvanized and non-galvanized. The characterization analysis of the mechanical behavior of the bonded materials was conducted. The macroscopic and microscopic structural modifications, as well as residual stresses, were measured, and they were compared with each other. From the experiments, very effective results have been found. The results were analyzed in detail from different perspectives in terms of material properties and types of weldment processes.

Bending Strength and Fracture Behaviour of Metal-Ceramic Interpenetrating Phase Composites Manufactured by Using Semi-Solid Forming Technology

Interpenetrating Phase Composites (IPC) belong to a special category of composite materials, offering great potential in terms of material properties due to the continuous volume structure of both composite components. While manufacturing of metal-ceramic IPC via existing casting and infiltration processes leads to structural deficits, semi-solid forming represents a promising technology for producing IPC components without such defects. Thereby, a solid open pore body made of ceramic is infiltrated with a metallic material in the semi-solid state. Good structural characteristics of the microstructure as the integrity of the open-pore bodies after infiltration and an almost none residual porosity within the composites have already been proven for this manufacturing route within a certain process window. On this basis, the following paper focuses on the mechanical properties such as bending strength of metal-ceramic IPC produced by using semi-solid forming technology. Thereby, the impact of the significant process parameters on these properties is analysed within a suitable process window. Furthermore, a fractographic analysis is carried out by observing and interpreting the fracture behaviour during these tests and the fracture surface thereafter.

AN ANALYSIS OF IN-SITU SYNTHESIZED AL 6061 ALLOY METAL MATRIX COMPOSITES: REVIEW

Many alloys and aluminum composites have been produced in recent years for improved material performance. Al 6061 is now an aluminum alloy with a wide range of uses owing to its excellent microstructure. For the manufacture of aluminum matrix composites (AMC), it is a wise option for the matrix. The in-situ process produces Al 6061 aluminum alloy matrix composites, according to this research. It investigates the mechanical properties of Al 6061 composites, modern in-situ fabrication, processing conditions, and multiple reinforcements employed. Numerous researches have shown that the latest in-situ process is commonly used and ideal for designing Al-6061 Alloy composites reinforcing TiC, TiB2, Al2O3, SiC, and other inorganic, biological elements, hybrid, and nanomaterials. A variety of researchers indicated that higher reinforcement material increased the composites' mechanical and tribological properties. Moreover, hybrid composites outperformed single-reinforcement composites in terms of material properties. Industrial and agricultural residues are also recorded to be used in hybrid composites. Scientific investigations should concentrate on in-situ processing and material characterization of Al 6061 nanocomposites, which have a lot of promise as exotic technologies.

Assessing the Economic Viability of the Plastic Biorefinery Concept and Its Contribution to a More Circular Plastic Sector.

It is widely accepted that plastic waste is one of the most urgent environmental concerns the world is currently facing. The emergence of bio-based plastics provides an opportunity to reduce dependency on fossil fuels and transition to a more circular plastics economy. For polyethylene terephthalate (PET), one of the most prevalent plastics in packaging and textiles, two bio-based alternatives exist that are similar or superior in terms of material properties and recyclability. These are polyethylene furanoate (PEF) and polytrimethylene terephthalate (PTT). The overarching aim of this study was to examine the transition from fossil-based to renewable plastics, through the lens of PET upcycling into PEF and PTT. The process for the production of PEF and PTT from three waste feed streams was developed in the SuperPro Designer software and the economic viability assessed via a discounted cumulative cash flow (DCCF) analysis. A techno-economic analysis of the designed process revealed that the minimum selling price (MSP) of second generation-derived PEF and PTT is 3.13 USD/kg, and that utilities and the feedstock used for the production of 2,5-furandicarboxylic acid (FDCA) needed in PEF synthesis contributed the most to the process operating costs. The effect of recycling PEF and PTT through the process at three recycling rates (42%, 50% and 55%) was investigated and it was revealed that increased recycling could reduce the MSP of the 2G bio-plastics (by 48.5%) to 1.61 USD/kg. This demonstrates that the plastic biorefinery, together with increasing recycling rates, would have a beneficial effect on the economic viability of upcycled plastics.

Electronic structure and stability of Cs2TiX6 and Cs2ZrX6 (X = Br, I) vacancy ordered double perovskites

Vacancy ordered halide perovskites have been extensively investigated as promising lead-free alternatives to halide perovskites for various opto-electronic applications. Among these, Cs2TiBr6 has been reported as a stable absorber with interesting electronic and optical properties, such as a bandgap in the visible, and long carrier diffusion lengths. Yet, a thorough theoretical analysis of the exhibited properties is still missing in order to further assess its application potential from a material's design point of view. In this Letter, we perform a detailed analysis for the established Ti-based compounds and investigate the less-known materials based on Zr. We discuss in detail their electronic properties and band symmetries, highlight the similarity between the materials in terms of properties, and reveal limits for tuning electronic and optical properties within this family of vacancy ordered double perovskites that share the same electron configuration. We also show the challenges to compute accurate and meaningful quasi-particle corrections at the GW level. Furthermore, we address their chemical stability against different decomposition reaction pathways, identifying stable regions for the formation of all materials, while probing their mechanical stability employing phonon calculations. We predict that Cs2ZrI6, a material practically unexplored to date, shall exhibit a quasi-direct electronic bandgap well within the visible range, the smallest charge carrier effective masses within the Cs2BX6 (B = Ti, Zr; X = Br, I) compounds, and a good chemical stability.

Study on mechanical properties and microstructure for three compounds of Al-Sn-Mg ternary alloys

ABSTRACT In the present study, the microstructure and mechanical properties of Al-Sn-Mg ternary alloy were investigated depending on the composition. When the microstructures of the compositions of the alloy are examined, it was observed that Mg2Sn, Mg3Sn1,67 intermetallic phases were formed at the grain boundaries. However, the grain size of each phase changed depending on the composition. It has been observed that such changes in the microstructure affect the mechanical properties of the material. The 94 at. % Al-2.5 at. % Sn-3.5at. % Mg has been found to have the most suitable material properties in terms of ductility and strength. The hardness of [96.5-x] at. % Al-[x] at. % Sn-3.5 at. % Mg (x = 2.5, 8.5 (eutectic composition), 14.5) compounds was measured 52 HV 0.1, 47 HV 0.1, 40 HV 0.1 for bulk samples and 72 HV 0.1, 56 HV0.1, 51 HV 0.1 for rod-shaped samples, respectively.

A thermomechanical and photochemical description of the phase change process in roll-to-roll nanoimprinting lithography

In this paper, a model for the phase change process due to irradiation with an Ultraviolet (UV) light in a mold filled with a viscoelastic fluid in roll-to-roll nanoimprinting lithography is developed. Employing a thermomechanical approach, constitutive equations for the phase change of a mixture of viscoelastic fluid and solid constituents of the polymer are derived. A general model describing phase change that relates both thermomechanics and photochemistry is presented. A function defining the mass fractions of fluid and solid in the mixture is utilized in the thermomechanical description, and the governing equations for the evolution of the fluid and solid mixtures are obtained based on photochemical reactions under UV light. General properties and kinematic equations that impact phase change in terms of material properties and process parameters are obtained. A simplification of the model without sacrificing the underlying physics to make the problem amenable to analysis is put into place. The general model of phase transition is simplified by assuming that the gradient of the displacement, the strain and its time rate, are small; this results in an integro-differential quasilinear system of equations. A numerical scheme is proposed to solve the problem and results from the numerical simulations are presented and discussed.

Free-edge crack onset induced by thermal loading

In composite laminates the layer-wise material mismatch induces highly localized stress concentrations at the free edges. This is referred to as free-edge effect. As a consequence interlaminar crack initiation may occur in addition to the typically considered intralaminar failure modes. The stresses do not necessarily have to be caused by mechanical loads. Also temperature differences may induce significant interlaminar stresses. In the present study, delamination onset in symmetric angle-ply laminates caused by thermal stresses is investigated by means of the coupled stress and energy criterion within the framework of finite fracture mechanics on the basis of the well-known generalized plane strain state. Using this relatively young criterion, both failure load and the length of the initiated crack can be predicted. Besides the intrinsic material properties in terms of strength and fracture toughness, only the interlaminar stresses as well as the released energy during crack initiation are required for the evaluation of the coupled criterion. Since no analytical closed-form solution of the free-edge effect is known, the required field quantities are obtained by employing a finite element model. Effects as the influence of the thickness and the orientation of the individual layers on the failure temperature are studied. For that purpose, a dimensional analysis is performed allowing to scale the results of a certain boundary value problem to self-similar configurations yielding a significant reduction of the numerical effort. It is revealed that especially for thick angle-ply laminates with large fiber orientation angles and temperature differences as they may occur in aeronautical applications interlaminar crack initiation can be the predominant failure mode. For validation purposes the results obtained by the coupled criterion are compared to the widely-used cohesive zone model.

Experimental validation of the applicability of effective spring boundary conditions for modelling damaged interfaces in laminate structures

The paper presents the experimental validation of the applicability of the effective spring boundary conditions (ESBC), where spring stiffness is expressed in terms of material properties and damage characteristics, for modelling the dynamic behaviour of laminates with damaged interfaces. For this purpose, several intact and defected multi-layered samples manufactured from aluminium plates adhesively bonded with two-sided epoxy tape have been considered. To simulate imperfect interfaces, either a particular surface of one of the adherents or of the adhesive has been mechanically damaged with varying severity before the bonding. Elastodynamic motion excited in the samples by thin surface-mounted piezoelectric transducers has been acquired with laser Doppler vibrometer in the form of B-scans of the specimen’s top surface. The wavenumber-frequency analysis of the measured data is performed to extract information on dispersion curves of guided waves propagating in the investigated laminates. It is demonstrated that changes in the properties of guided waves caused due to damaged interfaces are adequately described by the ESBC, and spring stiffness expressed via material and damage characteristics in ESBC allows to characterize properly the severity of the interface degradation in multi-layered structures.

Multiscale analysis of elastic waves in soft materials: From molecular chain networks to fiber composites

We provide a multiscale analysis of elastic waves in soft microstructured materials including the underlying molecular chain network mechanisms and micromechanics of hyperelastic fiber composites. First, we examine the interplay between the crosslinked and entangled polymer chains and elastic wave characteristics in finitely deformed materials. Next, we study the shear wave propagation in a class of heterogeneous hyperelastic composites. In particular, we consider the transversely isotropic fiber composites with phases characterized by the stiffening behavior stemming from the non-Gaussian statistics of polymer chains. By employing a micromechanics-based approach, we derive explicit expressions for phase velocities in terms of material properties and volume fraction of the phases. Our results indicate the significant influence of the variety of length-scales mechanisms on the elastic wave characteristics. We provide examples to illustrate the influence of the mechanisms under different loading conditions, wave propagation directionality, and material microstructure parameters.

Computational modeling and simulation of gas focused liquid micro-sheets

The purpose of this work is to numerically evaluate the behavior of microscopic gas-focused liquid sheets in terms of material properties, nozzle structure and operating conditions used for experiments in spectroscopy and scattering where a short optical path is required. The numerical simulations are presented of a gas flow focusing nozzle, capable of producing a stream consisting of a sequence of perpendicular micrometre thin liquid sheets. The nozzle structure consists of a central circular capillary for delivery of the liquid and two circular capillaries that provide the focusing gas flow in a converging direction from opposite directions. High velocity impinging gas jets accelerate and form a thin elliptically shaped liquid sheet which contracts downstream and eventually forms a similar shaped sheet in the plane perpendicular to the primary sheet. The process repeats further downstream with another contraction, forming the tertiary sheet, existing now in the same plane as the primary sheet. This produces a liquid jet in form of a series of perpendicular micrometre thin liquid sheets. Three dimensional conservation equations of mass, energy and momentum for a compressible two-phase system are solved with a finite volume approach and an algebraic volume of fluid method. The influence of liquid viscosity, density, surface tension, nozzle layout variation as well as gas and liquid operating parameters on the evolution of the primary liquid sheet is elaborated. The parameter space of six flow characterizing dimensionless numbers is explored in the following ranges: Reynolds gas number 64–130, Reynolds liquid number 122–620, Weber number 23–803, ratio of liquid to gas mass flow rate 16–58, viscosity ratio 26–79, and density ratio 4807–7221. The layout of the primary sheet is given in terms of sheet thickness, width and length. The results show minor effect of dynamic viscosity, a moderate effect of density and a dominant role of the surface tension. The liquid sheet shape is sensitive to the variation of gas and liquid flow rates as well as the nozzle's structure width and the angle between the liquid delivery and the focusing gas capillaries.

Experimentally-validated orthotropic elastic model for Wire-and-Arc Additively Manufactured stainless steel

Abstract Wire-and-Arc Additively Manufactured (WAAM) alloys are characterized by specific mechanical properties which can largely differ from the conventionally-manufactured alloys. In detail, the printing process results in a peculiar microstructure, characterized by preferential crystallographic orientation with reference to the printing direction, that leads to an anisotropic mechanical behavior of the printed part. Previous experimental tests on WAAM-produced stainless steel plates showed in particular a strong anisotropic elastic behavior. Based on the above, the present work formulates a specific anisotropic elastic model for a WAAM-processed austenitic stainless steel, considering an orthogonally anisotropic (or orthotropic) constitutive law and a procedure to calibrate the elastic parameters based on the experimental results. In detail, the procedure is applied to calibrate the numerical values of the elastic parameters of a specific WAAM 304L austenitic stainless steel. For this aim, specific investigations on both the mechanical and microstructural features were carried out. Experimental tensile tests were performed on specimens with different orientations with reference to the printing direction. In detail, Young’s modulus and Poisson’s ratios were evaluated for samples oriented along three different orientations with regard to the printing deposition layers: longitudinally (L), transversally (T) and diagonally (D) to them. Digital Image Correlation (DIC) optical measuring system was used to acquire the full strain fields during the test. Microstructural analysis was also carried out to study the inherent microstructure, characterized by a distinctive grain growth direction, and to assess the preferred crystallographic orientations of specimens extracted along the three considered directions. The experimental results are used to calibrate the orthotropic elastic model. From the calibrated model additional material properties in terms of Young’s and shear modulus for any printing direction are derived. The resulting values exhibit very large variations with the printing angle, with ratios between minimum to maximum values around 2 for the Young’s modulus and 3.5 for the shear modulus. This marked orthotropic behavior could open unexplored design possibilities based on deformability issues. Additionally, the calibrated orthotropic model can also be used for future experimental explorations of the mechanical properties of WAAM alloys and for stiffness-based structural design optimizations.

Experimental Procedures & First Results of an Innovative Solid Oxide Fuel Cell Test Rig: Parametric Analysis and Stability Test

Solid Oxide Fuel Cells are a promising technology for Solid Oxide Fuel Cells (SOFC) are a promising technology For high-efficiency electrochemical conversion of a vast range of fuel gas mixtures, thigh operating temperature conditions (650–900 °C) represent a challenge both at system level and at laboratory testing level, in terms of material properties and performance dynamics. In this work a detailed procedural analysis is presented for an innovative all-ceramic compact SOFC test rig and first experimental testing results are reported in terms of polarization curves obtained under parametric variation of operating conditions (H2 content, air ratio λ and temperature) and short-term voltage stability test under load (140 h at 0.3 A/cm2). The electrochemical characterization results confirm the validity of the used all-ceramic cell holder, showing excellent cell performances in terms of polarization. H2 content has the most impact on SOFC performance, followed by temperature and finally air ratio, whose impact in the analyzed range is hardly seen. From the short-term stability test, the test bench setup reliability is demonstrated, showing no significant performance degradation after 140 continuous hours under load, which confirms the high quality and reproducibility of the results.

Nonlinear static characterisation of masonry-infilled RC building portfolios accounting for variability of infill properties

The seismic assessment of existing masonry infilled reinforced concrete (RC) building portfolios is a highly relevant issue in Italy and other Mediterranean countries, particularly in regions where a large part of the built environment was not designed according to modern seismic codes. In the past, masonry infills were generally considered as non-structural elements and were not accounted for in the design process. However, the results of experimental tests and past earthquake evidence demonstrated the influence of masonry infills on the global and local behaviour of RC buildings. Furthermore, the acknowledgment of different construction practices points out the significant variability affecting the masonry infills in terms of material properties, thickness, presence of openings and manufacturing techniques. This paper deals with the large-scale performance analysis of existing masonry infilled RC building portfolios accounting for the uncertainty related to the variability in the mechanical properties and the modelling of masonry infills. To accomplish this goal, a fully integrated building stock, representative of masonry infilled RC buildings designed according to the Italian codes in force between 1960 and 1980, was developed, using a simulated design approach. Statistical data and results of experimental tests were used to identify the main masonry infill typologies adopted in the Italian context. Detailed numerical models, whose prediction capability was appraised through the results of cyclic quasi-static tests, were developed to estimate the lateral response of the analysed RC buildings. Different response parameters, which can be easily implemented in seismic risk assessment frameworks, were considered and quantified, at the portfolio level, to understand the uncertainty propagation and impact of the masonry infills’ variability on the expected performance of existing RC buildings. The results demonstrated that the variability related to the definition and modelling of the masonry infills induces significant dispersion, with respect to the mean, on the lateral response of different classes of buildings within a given portfolio. Moreover, the provided parameters for multi-linear idealised capacity curves can be used in simplified seismic fragility and risk models for existing buildings, including a proper estimate of the associated uncertainty, leading to a more accurate quantification of economic losses.

A finite element approach for the prediction of the mechanical behaviour of layered composites produced by Continuous Filament Fabrication (CFF)

Continuous Filament Fabrication (CFF) is the additive manufacturing process for producing material reinforced with long fibres. Differently from other processes, CFF allows producing components in composite materials without using tools, moulds or post-processing operations and with a strengthened area only where it is strictly required. This innovative way of producing composites makes a new design approach necessary for better exploitation of the material. This work presents a preliminary study based on 3D Finite Element (FE) method to predict the mechanical behaviour of composite materials fabricated by CFF. With this aim, a FE model is developed to determine the actual material properties in terms of longitudinal, transverse and shear modulus. Comparisons between experimental and numerical tensile results at different fibre orientations validate the model. The robustness of the proposed approach is confirmed by the comparison with the experimental characterisation of composites produced with two different fibre reinforcements, Carbon and Kevlar®.