Local Material Properties Research Articles

Numerical and experimental fatigue strength evaluation of thin-walled aluminum components for aerospace application manufactured by roll forming

The design of structural components for use in commercial aircraft places high demands on the safety under static and cyclic loading conditions during the total operating time. With immerging innovative developments in the production of thin-walled sheet metal components, savings in energy consumption and material are achievable by switching from metal-cutting production to forming operations. As the forming process has an impact the local material properties due to resulting residual stress state, cold working and surface finish, the fatigue life estimation requires the consideration of the forming history.The structural component under consideration from aluminum alloy EN AW-7475 T761 is manufactured by automated, robot-assisted roll forming. Potentially existing residual stresses are determined via process simulation of the angled profile utilizing commercial finite element solver LS-Dyna®. The fatigue life assessment is carried out using the Local Strain Approach for different loading conditions.

Interfacial Structures of Heterogeneous Systems Determined by Using in-Situ XAFS

During chemical reactions and catalysis, the surface and interfacial structural properties of materials are considerably important to understand and control the reactions. However, in-situ measurements have many limits during reactions. We used in-situ X-ray absorption fine structure (XAFS) to understand the local structural properties at the surface and the interface of metal catalysts on transition−metal−oxide supports. Pt nanoparticles (NPs) with a mean size of ~1 nm on TiO2 supports are synthesized using an incipient wetness method. In-situ XAFS measurements are performed from the Pt NPs/TiO2 at Pt L3 and Ti K edges during heating from room temperature to 500 ℃ in an H2 environment. Fourier−transformed extended X-ray absorption fine structure (FT−EXAFS), which is a unique tool to quantitatively determine the local structural properties of materials around a selected species element, shows a lack of oxygen atoms as the nearest neighbors of Pt atoms at T = 250 ℃; meanwhile, the wavelet-transformed EXAFS (WT-EXAFS) with enhanced resolution shows a weak but distinguishable oxygen signal around Pt atoms. Pt−O bonds likely exist at the interface of Pt/TiO2, although oxygens on the outer surfaces of Pt NPs are mostly dissociated at T > 250 ℃ in an H2 environment. This finding strongly suggests that the combination of FT−EAXFS and WT−EXAFS can more accurately describe small amounts of light elements bonding with heavy elements than FT−EXAFS can alone. DFT calculations confirm that the presence of extra oxygen atoms at the interfaces of Pt NPs/TiO2, playing a critical role in the stability and the dispersion of Pt NPs.

RNN-based pavement moduli prediction for flexible pavement design enhancement

In order to facilitate the effective implementation of the MEPDG, researchers concentrate on quantifying local material properties, with a particular emphasis on pavement layer moduli. The layer modulus is a critical parameter necessary for calculating pavement responses (stress, strain, and deflections) resulting from traffic loading. Accurately determining the layer modulus is crucial for enhancing pavement design as it directly impacts the required pavement layer thicknesses and associated costs. Backcalculation is a commonly used method for analyzing Falling Weight Deflectometer (FWD) data to determine pavement layer moduli, with Artificial Neural Networks (ANNs) being the traditional choice. However, ANNs have limitations in terms of convergence accuracy and generalization capability. The aim of this study is to improve the backcalculation of layer moduli to enhance pavement design. By utilizing FWD data, Recurrent Neural Network (RNN) was employed to address the limitations of conventional ANN. Both ANN and RNN networks were developed and trained using identical properties. The findings demonstrate that RNN achieved faster convergence and higher convergence accuracy compared to ANN. The RNN network generated reasonable and precise layer moduli values, exhibiting a determination coefficient (R) of 0.95 in comparison to the measured values, while the ANN network had an R-value of 0.79. The results indicate that the RNN network can learn the continuity pattern between deflection basin points, thereby enhancing the accuracy of FWD backcalculation.

Super-Resolution Exciton Imaging of Nanobubbles in 2D Semiconductors with Near-Field Nanophotoluminescence Microscopy.

Two-dimensional (2D) semiconductors, such as transition metal dichalcogenides, have emerged as important candidate materials for next-generation chip-scale optoelectronic devices with the development of large-scale production techniques, such as chemical vapor deposition (CVD). However, 2D materials need to be transferred to other target substrates after growth, during which various micro- and nanoscale defects, such as nanobubbles, are inevitably generated. These nanodefects not only influence the uniformity of 2D semiconductors but also may significantly alter the local optoelectronic properties of the composed devices. Hence, super-resolution discrimination and characterization of nanodefects are highly demanded. Here, we report a near-field nanophotoluminescence (nano-PL) microscope that can quickly screen nanobubbles and investigate their impact on local excitonic properties of 2D semiconductors by directly visualize the PL emission distribution with a very high spatial resolution of ∼10 nm, far below the optical diffraction limit, and a high speed of 10 ms/point under ambient conditions. By using nano-PL microscopy to map the exciton and trion emission intensity distributions in transferred CVD-grown monolayer tungsten disulfide (1L-WS2) flakes, it is found that the PL intensity decreases by 13.4% as the height of the nanobubble increases by every nanometer, which is mainly caused by the suppression of trion emission due to the strong doping effect from the substrate. In addition to the nanobubbles, other types of nanodefects, such as cracks, stacks, and grain boundaries, can also be characterized. The nano-PL method is proven to be a powerful tool for the nondestructive quality inspection of nanodefects as well as the super-resolution exploration of local optoelectronic properties of 2D materials.

Study on correlation and scaling protocol between indentation stress-strain and uniaxial stress-strain

Most important mechanical structures produce complex local material changes during the moulding and servicing process. Obtaining the specific local mechanical properties of materials and conducting field tests are problems in structural integrity evaluation. The instrumented indentation technique (IIT) is a solution to these problems. However, the core challenge with the IIT is the quantitative correlation between indentation response and uniaxial stress-strain (USS) response. In this study, we investigate the scaling relationship between indentation stress-strain (ISS) and uniaxial stress-strain (USS). A new protocol for obtaining the mechanical properties of alloy steels using ISS curves is proposed, which can directly obtain the plastic stage of the USS curves from the ISS curves. We used a finite element inversion method based on existing theories. Models with different mechanical properties (USS curves) were established using the ABAQUS software to obtain the corresponding ISS curves. We then explored the relationship between the two; the strain-scaling factor and stress-scaling function were specifically identified. Our work proposes an ISS protocol for power-law-hardening materials. Two alloy steels (SA508 and 42CrMo) were experimentally verifieds. The predicted results are approximately consistent with the practical curves and the error was within ± 10%. Because of the universality and reliability of the protocols, it is expected to provide a theoretical reference and technical approach for the development of IITs and structural integrity evaluation of important mechanical structures.

Application of steel fibre reinforced concrete for ensuring concrete frost resistance of transport structures on regional and inter-municipal highways of Khabarovsk Krai motor roads of Khabarovsk region

In this paper the authors present the research results into the application of steel fibre reinforced concrete for ensuring frost resistance and durability of transport structures on regional and intermunicipal highways of Khabarovsk Krai. The object of the present research was concrete of reinforced concrete round culverts rings 3D 15.35 (GOST 24547-2016, OST 35-27.0-85), produced at the industrial and production enterprise CJSC «Khabarovsk Avtomost» in Khabarovsk. Pipe blocks are designed for use in the construction of culverts under motorway bankets (including industrial roads), built in areas with seismicity up to nine points in all climatic zones on periodically operating watercourses in the absence of ice. Concrete class on strength of compression is accepted by designers — B25, according to SP 35.13330.2011 (new edition of SNiP 2.05.03-84*) the grade of concrete matrix on frost resistance was assigned taking into account the average temperature of the coldest month in the area where the construction is planned. In the conditions of the region under consideration there are natural and climatic conditions for assigning the grade of frost resistance F300. One of the tasks solved by the authors was the selection of concrete composition taking into account qualitative features of initial local materials properties and the use of dispersed reinforcement, providing the concrete of transport structures with a given strength, frost resistance and water resistance. The authors have presented the strength determination results, frost resistance and waterproofing of steel fibre reinforced concrete with «PFM-NLK» and steel fibre for reinforced concrete round culverts rings 3D 15.35. The experimental studies results allowed to justify the use of steel fibre reinforced concrete for ensuring frost transport structures resistance on regional and intermunicipal highways of Khabarovsk Krai, which is a determining factor for increasing their durability. The obtained results are applied for the standard of the organisation development — CJSC «Khabarovsk Avtomost» — 002-2015 «Increase of frost resistance of concrete of transport constructions on regional and intermunicipal highways of Khabarovsk region».

Selective deuteration along a polyethylene chain: Differentiating conformation segment by segment.

To improve the circularity and performance of polyolefin materials, recent innovations have enabled the synthesis of polyolefins with new structural features such as cleavable breakpoints, functional chain ends, and unique comonomers. As new polyolefin structures become synthetically accessible, fundamental understanding of the effects of structural features on polymer (re)processing and mechanical performance is increasingly important. While bulk material properties are readily measured through conventional thermal or mechanical techniques, selective measurement of local material properties near structural defects is a major characterization challenge. Here, we synthesized a series of polyethylenes with selectively deuterated segments using a polyhomologation approach and employed vibrational spectroscopy to evaluate crystallization and melting of chain segments near features of interest (e.g., end groups, chain centers, and mid-chain structural defects). Chain-end functionality and defects were observed to strongly influence crystallinity of adjacent deuterated chain segments. Additionally, chain-end crystallinity was observed to have different molar mass dependence than mid-chain crystallinity. The synthesis and spectroscopy techniques demonstrated here can be applied to range of previously inaccessible deuterated polyethylene structures to provide direct insight into local crystallization behavior.

Numerical Modeling of Residual Stresses and Fracture Strengths of Ba0.5Sr0.5Co0.8Fe0.2O3−δ in Reactive Air Brazed Joints

Reactive Air Brazing (RAB) enables the joining of vacuum-sensitive oxide ceramics, such as Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF), to metals in a one-step process. However, damage may form in ceramic or joint during RAB. In this work, experimental microstructure characterization, measurement, and prediction of local material properties using finite element analysis were combined to enlighten these damage mechanisms, which are currently not well understood. Micromechanical simulations were performed using representative volume elements. Cooling simulations indicate that small-sized CuO precipitations are most likely to cause crack initiation in BSCF during cooling. The ball-on-three-balls experiment with porous BSCF samples was analyzed numerically to determine the values of temperature-dependent BSCF fracture stresses. The inversely calibrated fracture stresses in the bulk BSCF phase are underestimated, and true values should be quite high, according to an extreme value analysis of pore diameters.

An overview of lab-based micro computed tomography aided finite element modelling of wood and its current bottlenecks

Abstract Microscopic lab-based X-ray computed tomography (XµCT) aided finite element (FE) modelling is a popular method with increasing nature within material science to predict local material properties of heterogeneous materials, e.g. elastic, hygroexpansion and diffusion. This method is relatively new to wood and lacks a clear methodology. Research intended to optimise the XµCT aided FE process often focuses on specific aspects within this process such as the XµCT scanning, segmentation or meshing, but not the entirety of the process. The compatibility and data transfer between aspects have not been investigated to the same extent, which creates errors that propagate and negatively impact the end results. In the current study, a methodology for the XµCT aided FE process of wood is suggested and its bottlenecks are identified based on a thorough literature review. Although the complexity of wood as a material makes it difficult to automate the XµCT aided FE process, the proposed methodology can assist in a more considered design and execution of this process. The main challenges that were identified include an automatic procedure to reconstruct the fibre orientation and to perform segmentation and meshing. A combined deep-learning segmentation method with geometry-based meshing can be suggested.

Design for material properties of additively manufactured metals using topology optimization

In metal Additive Manufacturing (AM), the deposited material is subjected to a series of heating and cooling cycles. The locally occurring temperature extremes and cooling rates determine solid-state phase fractions, material microstructure, texture, and ultimately the local material properties. As the shape of a part determines the local thermal history during AM, this offers an opportunity to influence these material properties through design. In this paper, we present a way to obtain desired properties by controlling the local thermal history. This is achieved through topology optimization of the printed part while considering its entire transient thermal history. As an example of this approach, this work focuses on high strength low alloy steels, where resulting phase fractions significantly influence mechanical properties such as yield strength and ductility. These solid-state phase fractions depend on cooling rates in a particular critical temperature range. The phase composition and hence the local yield strength in target regions can be controlled by constraining the cooling time in this range. Numerical examples illustrate the capability of the proposed approach in adapting part designs to achieve various desired material properties.

An atlas of the heterogeneous viscoelastic brain with local power-law attenuation synthesised using Prony-series.

This review addresses the acute need to acknowledge the mechanical heterogeneity of brain matter and to accurately calibrate its local viscoelastic material properties accordingly. Specifically, it is important to compile the existing and disparate literature on attenuation power-laws and dispersion to make progress in wave physics of brain matter, a field of research that has the potential to explain the mechanisms at play in diffuse axonal injury and mild traumatic brain injury in general. Currently, viscous effects in the brain are modelled using Prony-series, i.e., a sum of decaying exponentials at different relaxation times. Here we collect and synthesise the Prony-series coefficients appearing in the literature for twelve regions: brainstem, basal ganglia, cerebellum, corona radiata, corpus callosum, cortex, dentate gyrus, hippocampus, thalamus, grey matter, white matter, homogeneous brain, and for eight different mammals: pig, rat, human, mouse, cow, sheep, monkey and dog. Using this data, we compute the fractional-exponent attenuation power-laws for different tissues of the brain, the corresponding dispersion laws resulting from causality, and the averaged Prony-series coefficients. STATEMENT OF SIGNIFICANCE: Traumatic brain injuries are considered a silent epidemic and finite element methods (FEMs) are used in modelling brain deformation, requiring access to viscoelastic properties of brain. To the best of our knowledge, this work presents 1) the first multi-frequency viscoelastic atlas of the heterogeneous brain, 2) the first review focusing on viscoelastic modelling in both FEMs and experimental works, 3) the first attempt to conglomerate the disparate existing literature on the viscoelastic modelling of the brain and 4) the largest collection of viscoelastic parameters for the brain (212 different Prony-series spanning 12 different tissues and 8 different animal surrogates). Furthermore, this work presents the first brain atlas of attenuation power-laws essential for modelling shear waves in brain.

Identification the Role of Grain Boundaries in Polycrystalline Photovoltaics via Advanced Atomic Force Microscope.

Atomicforce microscopy (AFM)-based scanning probing techniques, including Kelvinprobe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM), have been widely applied to investigate thelocal electromagnetic, physical, or molecular characteristics of functional materials on a microscopic scale. The microscopic inhomogeneities of the electronic properties of polycrystalline photovoltaic materials can be examined by these advanced AFM techniques, which bridge the local properties of materials to overall device performance and guide the optimization of the photovoltaic devices. In this review, the critical roles of local optoelectronic heterogeneities, especially at grain interiors (GIs) and grain boundaries (GBs) of polycrystalline photovoltaic materials, including versatile polycrystalline silicon, inorganic compound materials, and emerging halide perovskites, studied by KPFM and C-AFM, are systematically identified. How the band alignment and electrical properties of GIs and GBs affect the carrier transport behavior are discussed from the respective of photovoltaic research. Further exploiting the potential of such AFM-based techniques upon a summary of their up-to-date applications in polycrystalline photovoltaic materials is beneficial to acomprehensive understanding of the design and manipulation principles of thenovel solar cells and facilitating the development of the next-generation photovoltaics and optoelectronics.

Enrichment of meat products with natural bioprotectors and antioxidants

In the course of scientific research the chemical composition, physico-chemical and antioxidant properties of local grape and secondary raw materials of winemaking industry were studied, the technology of sausage production with the addition of grape extract of high nutritional value was substantiated and developed. Information on the antioxidant activity of grape raw materials growing in the territory of the Republic of Bashkortostan has been obtained. The presence of biologically active substances with antioxidant and antioxidant properties in the grape extract is a promising factor for the introduction of the extract in food products, including meat products, to enrich them with antioxidants. Analyzing the results of the study, we can conclude that the use of 3% grape squeeze extract will enrich meat products with a sufficient amount of antioxidants of natural plant origin. In the course of research it was found that the extract from grape squeeze has a rich dark blue color due to the high content of anthocyanins, which can affect the organoleptic characteristics of the finished meat product, in connection with that the color characteristics of the minced meat samples were analyzed. An important indicator in our scientific research was the preservation of antioxidants in the process of preparation of the extract and introduction into the minced meat. In this regard, the degree of preservation of calculated and actual total content of antioxidants in different objects was further studied. The technology of obtaining new types of food products - sausages, based on the use of grape extracts has been scientifically substantiated. It has been established that within the framework of the modern theory of positive nutrition it is more reasonable to add grape squeeze extract instead of fatty meat raw materials. This allows to enrich sausage products not only with mineral substances, organic and polyunsaturated fatty acids, vitamins, amino acids, pectin substances, but also to obtain biologically valuable meat products based on secondary grape raw materials.

Layer-Dependent Magnetism and Spin Fluctuations in Atomically Thin van der Waals Magnet CrPS4.

van der Waals (vdW) magnets, an emerging family of two-dimensional (2D) materials, have received tremendous attention due to their rich fundamental physics and significant potential for cutting-edge technological applications. In contrast to the conventional bulk counterparts, vdW magnets exhibit significant tunability of local material properties, such as stacking engineered interlayer coupling and layer-number dependent magnetic and electronic interactions, which promise to deliver previously unavailable merits to develop multifunctional microelectronic devices. As a further ingredient of this emerging topic, here we report nanoscale quantum sensing and imaging of the atomically thin vdW magnet chromium thiophosphate CrPS4, revealing its characteristic layer-dependent 2D static magnetism and dynamic spin fluctuations. We also show a large tunneling magnetoresistance in CrPS4-based spin filter vdW heterostructures. The excellent material stability and robust strategy against environmental degradation in combination with tailored magnetic properties highlight the potential of CrPS4 in developing state-of-the-art 2D spintronic devices for next-generation information technologies.

A multiscale deep learning model for elastic properties of woven composites

Time-consuming and costly computational analysis expresses the need for new methods for generalizing multiscale analysis of composite materials. Combining neural networks and multiscale modeling is favorable for bypassing expensive lower-scale material modeling, and accelerating coupled multi-scale analyses (FE2). In this work, neural networks are used to replace the time-consuming micromechanical finite element analysis of unidirectional composites, representing the local material properties of yarns in woven fabric composites in a multiscale framework. Leveraging the fast multiscale data generation procedure, we presented a second neural networks model to estimate the elastic engineering coefficients of a particular weave architecture based on a broad range of dry resin and fiber properties and yarn fiber volume fraction. As an outcome, this paper provides the user with a generalized, neural network-based approach to tackle the balance of computational efficiency and accuracy in the multiscale analysis of elastic woven composites.

Excitation of S1-ZGV Lamb wave with a compact wedged transducer and its application in local stress measurement

Residual stress and its distribution are the key indicators to ensure structural integrity. However, current ultrasonic methods are not appropriate for complex stress measurement. Considering the proximity of zero-group-velocity (ZGV) mode with the cut-off frequency and its sensitivity to local material property, this paper proposed a local stress measurement method based on S1-ZGV mode. The stress field reconstruction was demonstrated numerically with a nonuniform plate. Then, a FE model was built to investigate the excitation of S1-ZGV mode by oblique incidence approach, proving that S1-ZGV mode can be effectively excited and received with a small distance. Thus, a contact ultrasonic system along with a tailor-made compact wedged transducer was built for experimental validation. Parametric studies were performed to obtain the optimal excitation conditions for S1-ZGV mode. At last, experimental validation was carried out by standard tensile testing. The stress coefficient between the frequency shift and the applied stress was obtained with a uniform plate. The stresses of the nonuniform plate at three different positions were measured, proving that S1-ZGV method is effective for local stress measurement in thin plates.

Flexural Strengthening of Stone Masonry Walls Using Textile-Reinforced Sarooj Mortar.

The majority of historical buildings and structures in Oman were built using unreinforced stone masonry. These structures have deteriorated due to ageing of materials, environmental degradation, and lack of maintenance. This research investigates the physical, chemical, and mechanical properties of local building materials and the results of an experimental study on the out-of-plane bending effectiveness of an innovative strengthening method applied to existing masonry walls. The technique consists of the application of a basalt textile-reinforced sarooj mortar (TRM) on one face of the walls. Bending tests of masonry wall samples (1000 mm width, 2000 mm height, and 350 mm depth) were carried out on one unreinforced specimen and three different cases of reinforced specimens. The performance of unreinforced and reinforced specimens was analyzed and compared. The strengthened specimens were able to resist moments of out-of-plane bending 2.5 to 3 times greater than those of unreinforced specimen (160-233% increase). Moreover, the strengthened walls were able to sustain higher deformations (deflections) than the unreinforced specimen ranging from 20 to 130%. The results showed that using TRM was effective for the out-of-plane strengthening of stone masonry using a local material (sarooj) that is compatible with existing stone masonry building materials.

Normal and oblique ballistic impact damage behaviour of functionally graded plates: Experimental and numerical

The present study discusses experimental and numerical investigations on the dynamic response of functionally graded plates subjected to normal and oblique ballistic impact. Functionally graded plates were produced in a step-wise manner with powder metallurgy method using powder stacking-hot pressing technique. An experimental configuration was developed where projectiles impact functionally graded plates with three different compositions at impact angles of 0°, 15°, 30°, 45°, and 60°. Ballistic tests of functionally graded plates were carried out with a single-stage gas gun system using fragment simulating projectile (FSP) at velocities of approximately 610 m/s. The effect of the material composition and obliquity on damage and deformation of functionally graded plates was studied by varying the Al 6061 and SiC volumetric ratios to metal-rich (n = 0.1), linear (n = 1.0), and ceramic-rich (n = 10.0). Finite element analyses of functionally graded plates were performed with ANSYS Ls-Dyna explicit solver by employing the Mori Tanaka method to determine local material properties in the graded region and the TTO model to define elasto-plastic material behavior. The normal and oblique ballistic tests of functionally graded plates were compared with the values predicted from the finite element model in terms of damage, deformation, and fracture mechanisms. According to both numerical and experimental studies, the impact angle and material composition were found to be significant influences on damage and deformation of functionally graded plates. Given the complexity of the modeling of the ballistic impact events, the numerical models developed to predict the penetration depth and failure mechanism of plates in the ballistic impact tests showed a good agreement for n = 0.1 and n = 1.0 material compositions due to their metal-rich compositions.

Experimental Research on Natural Pozzolan as Cement Replacement

This paper presents the properties of mortar and concrete with NBRRI pozzolan as partial replacement of cement. In this research, NBRRI pozzolan from NBRRI and local cement (Dangote) are used. Firstly, chemical composition of NBRRI pozzolan and Dangote cement are analyzed. And then the physical properties of local materials used in this research are determined according to ASTM procedure. Partial replacement percentages of pozzolan are considered 10%, 20%, 30% and 40%. The strength of mortar and concrete with NBRRI pozzolan (0%, 10%, 20%, 30%, and 40%) is tested at 7 days, 14 days and 28 days. From the trial mix design, the water-cement ratio (0.555) is obtained by using the least square method. To get target strength (4000 psi), by using water-cement ratio (0.555) and 68% of maximum aggregate size (20 mm), the concrete mix proportion (1:1.9:3) is obtained. The compressive strength of concrete with various percentages of NBRRI pozzolan at 21 days and 28 days are more than 7 days and 14 days strength. Therefore, it can be concluded that NBRRI pozzolan can be used as cement replacement material when high strength performance in structures is not required.

Small-depth nanoindentation studies of an additively manufactured titanium alloy: Anisotropic nanomechanical properties and correlation with microscopic mechanical behaviour

Nanoindentation has been widely used to measure local mechanical properties of heterogeneous materials. The nanohardness (H), typically measured at indentation depths more than 200 nm, cannot be well correlated with the global mechanical behaviour of tested materials. Here, we study the H of the α phase in an additively manufactured titanium alloy using a nanoindentation mapping method with small indentation depths (< 200 nm). The results show that the α grains with various crystal orientations exhibit two groups of H values, different from a wide range of H values measured by conventional large-depth nanoindentation. The two groups of H values are attributed to a contribution of elasticity in the measurement of the H values using the small-depth nanoindentation. Furthermore, we correlate the H with the microscopic mechanical behaviour of α grains: With respect to the tensile direction, hard α grains are plastically deformed by shear banding and soft α grains are deformed by dislocation slip.