Large Variation In Properties Research Articles

Temperature stability and enhanced transport properties by surface modifications of silica nanoparticle tracers for geo-reservoir exploration

Tracer tests are an important tool for characterizing and monitoring subsurface reservoir properties. However, they are limited both because of the tracer molecules constraining factors such as irreversible adsorption, retention, and degradations, i.e. interaction processes of fluorophore molecule with surrounding media resulting in a large variation in transport properties. Elaborate tests utilizing more than one tracer to distinguish time or location of injection are complex and interpretation is ambiguous because each tracer interacts differently. In this study, we present an approach to increase tracer stability and enhance the transport uniformity of different tracers, thus making tests utilizing multiple tracers simpler and more feasible. We present this concept of tracer multiplicity by encapsulating an anionic, cationic or amphoteric fluorophore inside mesoporous silica nanoparticle carriers coated with a protective titania layer. Upon encapsulation, increased thermal resistance and drastically lowered sorption affinity towards quartz sand was detected in batch and flow-through experiments. An additional advantage of the presented nanoparticle tracers over molecular tracers is their modularity, which is demonstrated by surface modifications and application of additives that greatly reduce sorption and increase recovery rates in the flow experiments. With the here presented concept of tracer multiplicity, we introduce a new approach for colloidal tracer design that has the potential to expand and enhance measurable parameters, measurement accuracy and simplicity of analysis.

Investigating strengthening and softening mechanisms in Al/Ni multilayers via molecular dynamics simulations of uniaxial compression

Due to their nanoscale features, nanometric multilayers can have a large variation in properties for varying bilayer heights. While the hardening at small feature sizes and the consequent softening at even smaller feature sizes have been observed for decades, the underlying mechanisms are still under debate. In this study, molecular dynamics uniaxial compression simulations are employed to study the mechanical properties of Al/Ni multilayers for bilayer heights h from 100 nm down to 5 nm. The effect of the microstructure on Young’s modulus and the yield strength was investigated. Furthermore, the mechanical properties of equiatomic and equivolumetric multilayers were compared. A comparison with experimental results from the literature showed good agreement. Both the hardening at intermediate bilayer heights as well as the softening at very small bilayer heights were observed. The results are discussed in the context of possible hardening and softening mechanisms. While the Hall–Petch effect with a h−1/2 scaling is not contradicted, it is shown that, although the underlying mechanisms are different, both the hardening as well as the softening are based on a general size effect with a scaling of ln(h)/h.

Numerical and experimental investigation on the heat transfer and mass transport in LPBF in-situ alloying of Al/Cu alloy

PurposeLaser powder bed fusion (LPBF) in-situ alloying is a recently developed technology that provides a facile approach to optimizing the microstructural and compositional characteristics of the components for high performance goals. However, the complex mass and heat transfer behavior of the molten pool results in an inhomogeneous composition distribution within the samples fabricated by LPBF in-situ alloying. The study aims to investigate the heat and mass transfer behavior of an in-situ alloyed molten pool by developing a three-dimensional transient thermal-flow model that couples the metallurgical behavior of the alloy, thereby revealing the formation mechanism of composition inhomogeneity.Design/methodology/approachA multispecies multiphase computational fluid dynamic model was developed with thermodynamic factors derived from the phase diagram of the selected alloy system. The characteristics of the Al/Cu powder bed in-situ alloying process were investigated as a benchmark. The metallurgical behaviors including powder melting, thermal-flow, element transfer and solidification were investigated.FindingsThe Peclet number indicates that the mass transfer in the molten pool is dominated by convection. The large variation in material properties and temperature results in the presence of partially melted Cu-powder and pre-solidified particles in the molten pool, which further hinder the convection mixing. The study of simulation and experiment indicates that optimizing the laser energy input is beneficial for element homogenization. The effective time and driving force of the convection stirring can be improved by increasing the volume energy density.Originality/valueThis study provides an in-depth understanding of the formation mechanism of composition inhomogeneity in alloy fabricated by LPBF in-situ alloying.

Modeling of frontal polymerization of carbon fiber and dicyclopentadiene woven composites with stochastic material uncertainty

A novel finite element modeling framework is proposed for simulating dicyclopentadiene (DCPD) frontal polymerization in carbon fiber (CF) woven composites. A mesoscale CF/DCPD representative volume element (RVE) model was developed with two triggering directions, resulting in out-of-plane and in-plane DCPD polymerization. The Arrhenius equation coupled with a modified Prout-Tompkins autocatalytic model was used to evaluate the dynamic DCPD polymerization process. The rate and degree of DCPD cure were calculated by the material property uncertainties of DCPD with and without random void inclusions (3 % used as a reference in this work). The DCPD frontal polymerization in CF/DCPD composite was strongly influenced by the triggering direction. In the RVE model considered in this work, DCPD frontal polymerization was slightly faster in the in-plane (warp/weft yarn) directions than the out-of-plane (thickness) direction; polymerization occurs first in DCPD resin and is followed by CF/DCPD interface. Material property uncertainty and void inclusion had significant effects on both out-of-plane and in-plane DCPD polymerization. A large variation in DCPD material properties and the presence of void inclusions significantly delayed the rate and degree of DCPD frontal polymerization. This work provides the preliminary estimation of the frontal polymerization of DCPD-based composites and guides the structural applications of these materials.

Charpy absorbed energy in simulated heat-affected zone of laser-arc hybrid welded joints by high-strength steel for bridge structures

The application of laser-arc hybrid welding (so-called, hybrid welding) to the fabrication of steel bridge members has recently been investigated. One-pass full-penetration butt joints of steels for bridge high-performance structure (SBHS400 and SBHS500) with a thickness of 15 mm were performed by hybrid welding. The sound butt joints by hybrid welding were confirmed by a series of tests. The Charpy impact test was performed on the test pieces extracted from the hybrid welded butt joints with specified test temperatures. A phenomenon known as fracture path deviation (FPD) occurred in most test pieces, due to a large variation in material properties of the heat-affected zone (HAZ), resulting in the difficulty of estimating the toughness of HAZ in hybrid welded joints. Therefore, the Charpy impact test was conducted on the test pieces subjected to the welding thermal cycle tests of hybrid welding, which can exclude the heterogeneity of material properties and obtain the Charpy absorbed energy of the HAZ with high accuracy. The test results indicated that FPD was not observed in all thermal cycle simulated test pieces because the uniform metallographic structures in the vicinity of the notch were formed by the simulated thermal cycle tests, and all thermal cycle simulated test pieces satisfied 47 J at the specified test temperatures, a value that prevents brittle fracture for SBHS. Besides, for investigating the effect of the high Charpy absorbed energy guaranteed by SBHS on the toughness of hybrid welded joints, the Charpy absorbed energy of the thermal cycle simulated test pieces of SBHS and those of conventional steel (SM400B) were compared. The results showed that some of the thermal cycle simulated test pieces of SM400B failed to satisfy 27 J, suggesting that SBHS may ensure a Charpy absorbed energy of 47 J or more in the HAZ of hybrid welded joints.

Large Degree of Variation in Sorption Properties within a System of Isoreticular, Mixed-Ligand Ni- and Co-Based 2-Periodic Metal–Organic Frameworks

Two Ni-based and two Co-based mixed-ligand metal–organic frameworks (MOFs), which are all isoreticular with each other, are shown to have a large variation in nitrogen, carbon dioxide, hydrogen, and water vapor sorption properties, despite their similar structures. The MOFs have 1,2-bis(4-pyridyl)ethane (bpe) as the common ligand with the second ligand being either 2-nitroterephthalate (2-nta) or 2-bromoterephthalate (2-bta) for the Ni-based MOFs or 2-nta or 2-aminoterephthalate (2-ata) for the Co-based MOFs. The four MOFs have the formula [Ni(2-nta)(bpe)(H2O)2]n·2(DMA)n (1), [Ni(2-bta)(bpe)(H2O)2]n·2.8(DMF)n (2), [Co(2-nta)(bpe)(H2O)2]n·2(DMA)n (3), and [Co(2-ata)(bpe)(H2O)2]n·3(DMA)n·(H2O)n (4), respectively, where DMA = N,N′-dimethylacetamide and DMF = N,N′-dimethylformamide. Variable-temperature powder X-ray diffraction (VT-PXRD) studies indicate that the activated MOF structures are different from those of the as-synthesized MOFs, showing that the 2-periodic layers are dynamic upon desolvation. For the same metal ion, the MOF involving the 2-nta ligand has higher sorption, while sorption for the Ni-based MOFs is higher than for the Co-based MOFs. MOF 1 has the highest sorption within the isoreticular series and also has the highest sorption (the highest for water vapor) compared to other MOFs with the same or related ligands.

Dynamic response and breakage of trees subject to a landslide-induced air blast

Abstract. Landslides have been known to generate powerful air blasts capable of causing destruction and casualties far beyond the runout of sliding mass. The extent of tree damage provides valuable information on air blast intensity and impact region. However, little attention has been paid to the air blast–tree interaction. In this study, we proposed a framework to assess the tree destruction caused by powerful air blasts, including the eigenfrequency prediction method, tree motion equations and the breakage conditions. The tree is modeled as a flexible beam with variable cross-sections, and the anchorage stiffness is introduced to describe the tilt of the tree base. Large tree deflection is regarded when calculating the air blast loading, and two failure modes (bending and overturning) and the associated failure criteria are defined. Modeling results indicate that although the anchorage properties are of importance to the tree eigenfrequency, tree eigenfrequency is always close to the air blast frequency, causing a dynamic magnification effect for the tree deformation. This magnification effect is significant in cases with a low air blast velocity, while the large tree deflection caused by strong air blast loading would weaken this effect. Furthermore, failure modes of a specific forest subject to a powerful air blast depend heavily on the trunk bending strength and anchorage characteristics. The large variation in biometric and mechanical properties of trees necessitates the establishment of a regional database of tree parameters. Our work and the proposed method are expected to provide a better understanding of air blast power and to be of great use for air blast risk assessment in mountainous regions worldwide.

Stacking domain morphology in epitaxial graphene on silicon carbide

Terrace-sized, single-orientation graphene can be grown on top of a carbon buffer layer on silicon carbide by thermal decomposition. Despite its homogeneous appearance, a surprisingly large variation in electron transport properties is observed. Here, we employ Aberration-Corrected Low-Energy Electron Microscopy (AC-LEEM) to study a possible cause of this variability. We characterize the morphology of stacking domains between the graphene and the buffer layer of high-quality samples. Similar to the case of twisted bilayer graphene, the lattice mismatch between the graphene layer and the buffer layer at the growth temperature causes a moir\'e pattern with domain boundaries between AB and BA stackings. We analyze this moir\'e pattern to characterize the relative strain and to count the number of edge dislocations. Furthermore, we show that epitaxial graphene on silicon carbide is close to a phase transition, causing intrinsic disorder in the form of co-existence of anisotropic stripe domains and isotropic trigonal domains. Using adaptive geometric phase analysis, we determine the precise relative strain variation caused by these domains. We observe that the step edges of the SiC substrate influence the orientation of the domains and we discuss which aspects of the growth process influence these effects by comparing samples from different sources.

Comparison of rehabilitation treatments on mechanically reconstructed soils following strip coal mining activities: effects on soil properties

A rainfed rehabilitation trial on mechanically reconstructed soil, following strip coal mining, was laid out in the Mpumalanga Province of South Africa. It was used to evaluate seven rehabilitation treatments with four different depths of topsoil on coal spoil over three experimental seasons. A strip plot design was used to apply the treatments. The test crop was a grass mixture comprising of annual and perennial species. Trial measurements included soil physical, chemical and microbiological measurements, as well as growth and composition of the grass stand. Monthly rainfall was very variable with annual totals below the long-term values. Statistical significance was proved for most measurements. Relatively high soil bulk densities, stratified with depth, were measured, indicating undesirable soil compaction. Infiltration rates increased while soil strength decreased dramatically with increased topsoil thickness. A reciprocal interaction of profile water content and biomass yield was observed with water content decreasing as biomass yield increased. A large variation in soil chemical properties was observed as a function of the treatments. This study highlights the fact that the monitoring of soil and plant properties should be a prerequisite in any rehabilitation study. Similar trials on different soils and in different rainfall regions should be considered to expand our knowledge of the impacts of different soil treatments in a range of ecosystems.

Settlement characteristics of immersed tunnel of Hong Kong–Zhuhai–Macau Bridge project

The settlement performance of an immersed tunnel in the Hong Kong–Zhuhai–Macau Bridge (HZMB) transportation project is described. The geological profile underlying the immersed tunnel is presented and the corresponding field monitoring system is introduced. The function of semi-rigid elements is analysed. The observed results related to longitudinal deformation patterns during construction (e.g. long-term settlement, differential settlement and structural behaviour) are described and analysed. Differential settlement occurred when there was a large variation in soil properties, at the joints of two adjacent elements and in different segments of the same element. Differential settlement occurred in both the longitudinal and transverse direction. During the operational period, permanent settlement was strongly related to back-silting. Tide loading and the immersion of adjacent elements may have caused transient settlement related to elastic deformation, but tide loading had less influence on the permanent settlement.

Improving Quantum Well Tube Homogeneity Using Strained Nanowire Heterostructures.

Bottom-up grown nanostructures often suffer from significant dimensional inhomogeneity, and for quantum confined heterostructures, this can lead to a corresponding large variation in electronic properties. A high-throughput characterization methodology is applied to >15,000 nanoskived sections of highly strained GaAsP/GaAs radial core/shell quantum well heterostructures revealing high emission uniformity. While scanning electron microscopy shows a wide nanowire diameter spread of 540-60+60 nm, photoluminescence reveals a tightly bounded band-to-band transition energy of 1546-3+4 meV. A highly strained core/shell nanowire design is shown to reduce the dependence of emission on the quantum well width variation significantly more than in the unstrained case.

Fluorescence profile of a nitrogen-vacancy center in a nanodiamond

Nanodiamonds containing luminescent point defects are widely explored for applications in quantum biosensing such as nanoscale magnetometry, thermometry, and electrometry. A key challenge in the development of such applications is the large variation in fluorescence properties observed between particles, even when obtained from the same batch or nominally identical fabrication processes. By theoretically modeling the emission of nitrogen-vacancy color centers in spherical nanoparticles, we are able to show that the fluorescence spectrum varies with the exact position of the emitter within the nanoparticle, with noticeable effects seen when the diamond radius, $a$, is larger than around 100 nm, and significantly modified fluorescence profiles found for larger particles when $a=200$ and 300 nm, with negligible effects below $a=100$ nm. These results show that the reproducible geometry of point defect position within a narrowly sized batch of diamond crystals is necessary for controlling the emission properties. Our results are useful for understanding the extent to which nanodiamonds can be optimized for biosensing applications.

Effect of spatial variation of spoil material properties on slope displacements under rapid drawndown of pit lakes

In many European countries, lignite or brown coal is used as a fuel source in steam-electric power generation. Upon completion of mining activities, a reclamation plan is imperative to ensure environmental and social prosperity of local areas. Abandoned mine pits are often reclaimed by creating a pit lake. Reclamation of large lignite open pit mine sites may use large amounts of previous overburden materials or “spoils” to create the slopes of the pit lake. Spoils are anthropogenic materials with large spatial variation in properties, hence, considering mean values of shear strength and hydraulic parameters to assess stability and seasonal displacements will not fully simulate actual field conditions. This paper considers the effect of spatial variation on slope stability and ground movements during rapid drawdown events (a critical case) using coupled flow-deformation 2D finite element analyses, incorporating unsaturated soil suctions above the phreatic surface. Effects of heterogeneity and randomness of spoils on the response of the slope are considered through random field modelling and the Monte-Carlo simulation technique. Four lognormally distributed random variables (spoil cohesion, friction angle, void ratio, and permeability coefficient) are examined. The effect of spatial variability of spoils is shown to be important; a significant number of the random field analyses resulted in larger displacements compared to a benchmark deterministic analysis adopting uniform mean parameter values.

Growth rules for irregular architected materials with programmable properties.

Biomaterials display microstructures that are geometrically irregular and functionally efficient. Understanding the role of irregularity in determining material properties offers a new path to engineer materials with superior functionalities, such as imperfection insensitivity, enhanced impact absorption, and stress redirection. We uncover fundamental, probabilistic structure-property relationships using a growth-inspired program that evokes the formation of stochastic architectures in natural systems. This virtual growth program imposes a set of local rules on a limited number of basic elements. It generates materials that exhibit a large variation in functional properties starting from very limited initial resources, which echoes the diversity of biological systems. We identify basic rules to control mechanical properties by independently varying the microstructure's topology and geometry in a general, graph-based representation of irregular materials.

Data-driven approach to characterize and optimize properties of carbon fiber non-woven composite materials

Carbon fiber non-woven composite (CFNWC) is a novel and cost-effective material. However, since the large variation in mechanical properties of CFNWC under the same micro‐parameter, it is difficult to predict its performance accurately. In this work, a data-driven method that combines principal component analysis (PCA) and Bayesian neural networks (BNNs) is proposed to predict the stress-strain curve of CFNWC. Specifically, PCA is applied to reduce the dimension of the stress-strain curve, while BNNs are formulated for predicting both the strain-stress curves and the uncertainty of the predictions. The predictions and the uncertainty interval of BNNs are in very good agreement with the actual stress-strain curves. In this work, it is also found that the performance of artificial neural networks (ANNs) as a popular predictive tool to predict the mechanical properties of composites is worse than the BNNs, which is due to the uncertainty quantification ability of BNNs. Finally, BNNs are used to optimize the volume fraction of carbon fiber to obtain the best performance of CFNWC, which aims to design a stiff and lightweight automobile door. The results have strongly demonstrated the feasibility and effectiveness of BNNs to characterize and optimize the properties of CFNWC.

Microstructure evolution and tensile property of TiAl alloy using continuous direct energy deposition technique

Attributing to the fast solidification and thermal cycling during additive manufacturing process, massive phase transformation could take place thus leading to the formation of unpredictable microstructures with large variation in mechanical properties. In this paper, a continuous direct energy deposition technique (CDED) is adopted to prepare TiAl alloy seceding from the thermal cycling, and the evolution of microstructure, microhardness and tensile properties of alloy are investigated. Results indicate that the microstructure of alloy composes of columnar grains with very fine (α2 +γ) lamellae, and no heat-affect band is observed. A heat transfer model is established to assist in explaining the solid-phase transformation and microstructure formation mechanism of TiAl alloy. Furthermore, a special duplex γ microstructure (DP γ) forms which composes of massive γ phase surrounded by feathery-like γ phase. By dissecting crystallographic orientation from EBSD results, the formation mechanism of DP γ is clarified as the result of sequential solid-state phase transition in (α + γ) phase region, in which the feathery-like microstructure forms firstly followed by the massive γ phases nucleating at the inter-phase boundaries of feathery-like γ. Tensile property of as-deposited alloy reveals of 535 MPa with 1% elongation, and the highest hardness of around 320HV is detected at the top region of alloy with the finest interlamellar spacing.

Large short-range variation in soil properties in a natural grassland indicates non-tree related catena disruption

Landscape position co-determines soil formation, and hence soil properties are related to landscape position. In many landscapes, the importance of landscape position is large, and thus relations between soil properties and landscape position are strong. This is particularly true for agricultural landscapes, where tillage has smoothed over local variation in soils. It is less true for some forested landscapes, where local impacts of trees on soil formation have increased local variation. This raises the question whether soil-landscape relations are strong in natural grassland, with neither trees nor plowing. We answer this question for hillslopes in a natural grassland in the American Great Plains by quantifying soil-landscape relations and soil spatial autocorrelation based on a dataset of 100 soil observations. We find that soil-landscape relations are weak, even when accounting for topographic features specific for the study site, and that short-range variation in soil properties is about as large as long-range variation. We conclude that non-tree related natural processes disrupt the formation of clear catenas, and hypothesize that these include small burrowing mammals and infilling of parent-material fractures with finer material.

Comparison of Machine Learning Methods towards Developing Interpretable Polyamide Property Prediction.

Polyamides are often used for their superior thermal, mechanical, and chemical properties. They form a diverse set of materials that have a large variation in properties between linear to aromatic compounds, which renders the traditional quantitative structure–property relationship (QSPR) challenging. We use extended connectivity fingerprints (ECFP) and traditional QSPR fingerprints to develop machine learning models to perform high fidelity prediction of glass transition temperature (), melting temperature (), density (), and tensile modulus (). The non-linear model using random forest is in general found to be more accurate than linear regression; however, using feature selection or regularization, the accuracy of linear models is shown to be improved significantly to become comparable to the more complex nonlinear algorithm. We find that none of the models or fingerprints were able to accurately predict the tensile modulus , which we hypothesize is due to heterogeneity in data and data sources, as well as inherent challenges in measuring it. Finally, QSPR models revealed that the fraction of rotatable bonds, and the rotational degree of freedom affects polyamide properties most profoundly and can be used for back of the envelope calculations for a quick estimate of the polymer attributes (glass transition temperature, melting temperature, and density). These QSPR models, although having slightly lower prediction accuracy, show the most promise for the polymer chemist seeking to develop an intuition of ways to modify the chemistry to enhance specific attributes.

Extraction and Effects of Mechanical Characterization and Thermal Attributes of Jute, Prosopis Juliflora Bark and Kenaf Fibers Reinforced Bio Composites Used for Engineering Applications

In the present work tensile, flexural, impact and hardness properties of Prosopis juliflora bark (PJb), jute fiber (JF) and kenaf fiber (KF) reinforced polyester composites are expressed for the first time. The challenge in working with natural fiber composites (NFC) is the large variation in properties and characteristics. The properties of NFC to an enormous degree are impacted by the sort of fibers, a natural condition where the plant fibers are sourced and the kind of fiber treatments. In this experimental investigation JF as a base material, PJb and KF are filler materials. The weight percentage of JF has been maintained as constant and the remaining two fiber fillers were varied. To investigate the mechanical characteristics of tensile, flexural, impact and hardness tests were performed as per ASTM standard. The mechanical test outcomes exposed a reliable propensity of an expansion in the above mechanical credits to including natural fiber fillers. Fourier transform infrared spectroscopy (FTIR) is utilized to identify the chemical composition of NF and SEM analysis utilized for interfacial adhesion between the NF and polyester matrix. Thermal consistency/degradation of NF was identified through Thermogravimetric analysis (TGA).

Determination of Mechanical Properties and Characterization of Alkali Treated Sugarcane Bagasse, Pine Apple Leaf and Sisal Fibers Reinforced Hybrid Polyester Composites for Various Applications

In this work tensile, flexural, compression, impact and hardness properties of alkaline treated sugarcane bagasse (SB), pine apple leaf (PALF) and sisal fiber (SF) reinforced with polyester composites are expressed for the first time. This effort to develop hybrid composite materials with improved execution for worldwide applications is a progressing procedure. Be that as it may, with their remarkable and wide scope of inconstancy, common fiber composites could rise as another elective designing material which can substitute the utilization of manufactured fiber composites. The challenge in working with natural fiber composites (NFC) is the large variation in properties and characteristics. In this experimental investigation SF as a base material, PALF and SB are filler materials. The weight percentage of SF has been maintained as constant and the remaining two fiber fillers were varied. The NFC are prepared by hand layup method and mechanical characteristics of tensile, flexural, compression, impact and hardness tests were performed as per ASTM standard. The experiment results revealed a consistent tendency of an increase in the above mechanical attributes to adding natural fibers/fillers. Better interlinking capability between the NFC and polyester matrix is also responsible for the effective resistance capability. This type of composite materials can be useful for various engineering fields.