Strength Of Such Materials Research Articles

Estimating compressive strength of concrete containing rice husk ash using interpretable machine learning-based models

The construction sector is a major contributor to global greenhouse gas emissions. Using recycled and waste materials in concrete is a practical solution to address environmental challenges. Currently, agricultural waste is widely used as a substitute for cement in the production of eco-friendly concrete. However, traditional methods for assessing the strength of such materials are both expensive and time-consuming. Therefore, this study uses machine learning techniques to develop prediction models for the compressive strength (CS) of rice husk ash (RHA) concrete. The ML techniques used in the present study include random forest (RF), light gradient boosting machine (LightGBM), ridge regression, and extreme gradient boosting (XGBoost). A total of 348 values of CS were collected from the experimental studies, and five characteristics of RHA concrete were taken as input variables. For the performance assessment of the models, multiple statistical metrics were used. During the training phase, the correlation coefficients (R) obtained for ridge regression, RF, XGBoost, and LightGBM were 0.943, 0.981, 0.985, and 0.996, respectively. In the testing set, the developed models demonstrated even higher performance, with correlation coefficients of 0.971, 0.993, 0.992, and 0.998 for ridge regression, RF, XGBoost, and LightGBM, respectively. The statistical analysis revealed that the LightGBM model outperformed other models, whereas the ridge regression model exhibited comparatively lower accuracy. SHapley Additive exPlanation (SHAP) method was employed for the interpretability of the developed model. The SHAP analysis revealed that water-to-cement is a controlling parameter in estimating the CS of RHA concrete. In conclusion, this study provides valuable guidance for builders and researchers to estimate the CS of RHA concrete. However, it is suggested that more input variables be incorporated and hybrid models utilized to further enhance the reliability and precision of the models.

Fabrication of mullite micro/nano fiber-based porous ceramic with excellent mechanical and thermal insulation properties

Mullite fiber-based porous ceramics is one of the most commonly used high-temperature insulation materials. However, how to further reduce the thermal conductivity and improve the strength of such materials has been a challenge in the field of high-temperature insulation. In this paper, mullite micro/nano fiber-based porous ceramic was prepared by introducing mullite nanofibers into mullite microfiber-based porous ceramics and the effect of microfiber/nanofiber weight ratio on the samples properties were characterized and analyzed. Results showed that the compressive strength and high-temperature thermal insulation properties of the porous ceramics increased significantly with an increase in the nanofiber content. For the porous ceramics with similar density (about 0.50 g/cm3), the compressive strength of the sample with a microfibers/nanofibers weight ratio of 1:2 was 1.43 MPa, which was much higher than that of the porous ceramics prepared with only microfibers (0.26 MPa). Meanwhile, the backside thermal equilibrium temperature of the sample with a microfiber/nanofiber weight ratio of 1:2 at 900 °C environment was 355.8 °C, which was much lower than that of the porous ceramic prepared with only microfibers (476.5 °C). In addition, in order to investigate the temperature resistance of mullite micro/nano fiber-based porous ceramics, the sintering temperatures was increased from 1400 °C to 1500 °C. Results shows that the high-temperature thermal insulation performance of mullite micro/nano fiber-based porous ceramics with high mullite nanofiber content decays more seriously. The back-temperature test showed that the thermal equilibrium temperature of the samples with a mullite micron/nanofiber weight ratio of 1:1 in 900 °C environment increased rapidly from 386.3 °C to 454.2 °C when the sintering temperature was increased from 1400 °C to 1500 °C. The preparation of mullite micro/nanofiber-based porous ceramics provides a new strategy to improve the performance of fiber-based porous ceramics.

Role of particle size on the cohesive strength of non-sintered (green) ceramics

Preparation of particle-loaded foams, followed by drying, sintering and/or cross-linking are widely explored routes for developing lightweight ceramics with high mechanical strength. The non-sintered dry ceramic foams are less studied due to their intricate production and the assumed poor mechanical strength of the obtained "green" materials. Here we produce lightweight ceramics from foamed particle suspensions containing spherical silica particles with radii varied between 4.5 nm and 7 µm. The wet foams are prepared in the presence of cationic surfactant and were dried at ambient conditions to obtain porous materials with mass densities between 100 and 700 kg/m3. The materials containing smaller particles exhibited much higher strength (by up to 2000 times), approaching that of the sintered materials. A new theoretical expression for predicting the mechanical strength of such materials is derived and is used to explain the measured strengths of the produced materials through the van der Waals attraction between the particles in the final dry materials.

Effect of biomineralization on the early mechanical properties and microstructure of fly-ash cement-based materials

The lower early strength of fly ash (FA) as the partial replacement of cement has always been an inherent question, biomineralization furnishes a developing technology for promoting hydration and improving early compressive strength of FA cement-based materials (FACM). In this paper, the effects on the properties of FACM of biomineralization were investigated by two treatment methods, direct mixed bacteria (BDM) and drying-soaking (BDS). The properties, including microscopic performance and the mineral fraction of the paste were explored by using hydration heat, X-ray diffraction (XRD), thermogravimetric differential heat analysis (TG-DTG), pore structure tests, and scanning electron microscopy (SEM). The experimental results revealed that the early strength performance of the biomineralization treated FACM was significantly improved and achieved a maximum when the FA content was 10 %. With curing ages of 3 days, 7 days, and 14 days, the strength improvement in BDM was 33.01 %, 10.54 %, and 16.24 %, and that of BDS was 25.65 %, 8.68 %, and 3.54 %, respectively. XRD and TG-DTG analysis demonstrated that there were no new hydration products in the FACM specimens after biomineralization treatments. However, the hydration of FACM was promoted and more AFt and CSH gels being facilitated by biomineralization. The microstructure results also showed that the increase in the amount of hydration products changed the micropore structure distribution by refining the porosity, resulting in a more compact structure. The BDM approach more effectively promotes the formation of hydration products than the BDS method. The ability of these bacteria to facilitate the generation of hydration products of FACM can be applied to solve issues with the early strength of such materials.

Analytical Model for the Load-Bearing Capacity Analysis of Winter Forest Roads: Experiment and Estimation

In northern forests, winter is the preferred time for logging operations, since, when wet soils freeze, their strength increases, which ensures a high load-bearing capacity of winter forest roads and reduces the cost of forestry work by increasing the load on forestry equipment, including when driving through frozen lowlands. The present article analyzes frozen loamy–sandy soil, which, at subzero temperatures, behaves like a brittle material with a sufficiently high, but limited, strength. Well-known models commonly use empirical parameters, correlations, and numerical methods to estimate the strength of such materials. An analytical model of the full load–displacement curve would reduce the number of necessary calculations and increase the ability to predict the bearing capacity of winter forest roads. However, there are few of these models. Such models were developed, as a rule, to study stress–strain in concrete and rocks, meaning that researchers have to recalculate the load into stress and displacement into deformation, which is not always simple. This work aimed at theoretically justifying a new analytical model for quantifying the bearing capacity of winter forest roads and assessing the adequacy of the model by comparing it with experimental data. To achieve this purpose, the concepts of fracture mechanics and methods of mathematical modeling were used. The model was verified using experimental data, and model examples for determining the peak load were provided. Prospects for development of the research topic were also considered, taking into account new developments in forest road monitoring for logging management.

Effects of breccia and water contents on the mechanical properties of fault-core-zone materials

Determining the mechanical properties of fault-core-zone materials is challenging because of the low strength of such materials, which affects field sampling, specimen preparation, and laboratory testing. We overcame this problem by preparing and testing mechanical properties of 132 artificial fault-core-zone specimens consisting of mixtures of breccia, sand, clay, and water. The unconfined compressive strength (UCS), elastic modulus (E), and penetration resistance value (PRV) of these fault-core-zone materials were measured, and the effects of breccia content and water content on mechanical properties were assessed. Results show that UCS is inversely proportional to breccia content and water content, and that E is inversely proportional to water content. Furthermore, the inverse relationship of UCS with water content varies with breccia content. UCS is proportional to both PRV and E, and the relationship for each varies with breccia content. High coefficients of determination (R2 = 0.62–0.88) between the parameters suggest that breccia content, water content, and PRV are potentially useful parameters for estimating the mechanical properties of fault core zones.

Влияние предварительной химической обработки на качество твердофазных сварных соединений проволок при изготовлении пористых сетчатых материалов

Porous mesh materials with an organized structure, stable and reproducible properties are used in the manufacture of filter elements, thermal protection systems, rocket and turbojet engines, and other products with a given set of properties. The interlayer strength of such materials is significantly affected both by the modes of plastic deformation and welding and by the technology of preliminary chemical cleaning of the wire mesh surface. Etching work-pieces in a mixture of inorganic acids and organophosphorus complexones reduces the thickness of oxide films and additionally activates the contact surfaces in the welded joint. The study introduces the etchant solutions for treating VT1-0 titanium and corrosion-resistant 12Kh18N10T steel wires. The solutions increase the strength of the welded joints made by vacuum rolling welding and diffusion welding, compared with similar processes without pretreatment. The study also specifies the modes of technological processes of chemical etching and diffusion welding of 12Kh18N10T steel meshes, which provide maximum interlayer strength.

Effect of sintering temperature and calcium amount on compressive strength of brushite-metakaolin polymer materials

The effect of Ca2+ amount and sintering temperature on mechanical properties of geopolymer-brushite (GPB) binders was investigated. Brushite and raw abandoned kaolinite clay thermally transformed into metakaolin were used for GPB synthesis. The complete phase and structural analyses were performed by X-ray powder diffraction, and Fourier transforms infrared spectroscopy (FT-IR). The pore-filling effect as a consequence of Ca2+ ions incorporation into the hybrid geopolymer networks improved the compressive strength. On the other hand, the chosen biscuit sintering at 800 and 900oC caused the phase transformation of brushite into calcium pyrophosphate, which negatively affected the compressive strength of such materials. The obtained results indicate that the usage of relatively high sintering temperatures is not always the necessary step for producing geopolymer-based types of cement with prominent mechanical properties.

The Research of Physical and Mechanical, Thermophysical Properties of Epoxy-Polyester Composite Materials Filled with Discrete Fibers to Increase the Reliability of Vehicles

In the article the polymeric materials based on epoxy-polyester binder with addition of dispersed fibers were developed. The mechanical and thermophysical methods were used. The influence of carbon fibers (0.01–0.30 pts.wt.) and cotton (0.01–0.30 pts.wt.) on the physical and mechanical, thermophysical properties of epoxy-polyester composites was investigated. The results of the experiment showed that the introduction of carbon fibers leads to an increase in the fracture stresses, the flexural modulus; the maximum increase was observed for the carbon fiber content q = 0.01 pts.wt. (fl = 71.0 MPa, E = 3.8 GPa, W = 7.8 kJ/m2 ). The heat resistance of composite materials at this content of carbon fibers is maximal (T = 337 K), and the coefficient of linear thermal expansion (CLTE) is minimal and decreases in all temperature ranges (compared to the matrix). It was found, that the introduction of cotton fibers at a content q = 0.02 pts.wt. into the composition leads to an increase of the flexural modulus from E = 3.6 GPa (matrix) to E = 3.8 GPa and flexural stresses from fl = 50.4 MPa to fl = 55.2 MPa. The impact strength of such materials decreases from W = 8.3 kJ/m2 to W = 4.9 kJ/m2 . The results of the study of physical and mechanical properties of composite materials with the addition of cotton fibers were confirmed by thermophysical properties. It was found, that the heat resistance of materials increases from T = 335 K to T = 338 K at this content. The developed composite materials filled can be used to protect equipment, which are exposed to high temperatures or dynamic loads at moderate temperatures

In situ-grown carbon nanotubes enhanced cement-based materials with multifunctionality

Smart cementitious materials integrated with carbon nanotubes (CNTs) have potential applications as sensors in structural health monitoring (SHM). The sensitivity to strain (gauge factor) and strength of such materials are limited by the difficulty in dispersing CNTs. Here we synthesized CNTs in situ on the surface of fly ash (FA) to significantly improve the CNT dispersibility and enable the cement mortar to exhibit an outstanding strain-sensing capability. The mortar with CNT-coated FA (CNT@FA) at 2.0 wt% CNT concentration had a gauge factor of 6544, about one order of magnitude higher than that of mortar with commercial CNTs under the same condition. Its electrical resistivity can reversely vary as high as 69% upon cyclic compressive loading. The great self-sensing ability of cement mortars reinforced with in situ-grown CNTs was explained by two mechanisms: 1) the high possibility of the breakup/formation of CNT conductive paths provided by the unique morphology of CNT@FA; 2) high ratio of tunneling resistance with respect to the total resistance caused by the good dispersion of CNTs, which is demonstrated by optical microscopy measurements. The compressive and flexural strength values of the mortars with CNT@FA are also higher than those of the plain mortar at an age of 28 days. The CNT@FA mortars with enhanced electrical and mechanical properties have potential applications in assessing the conditions of civil engineering structures.

Stochastic Constitutive Model of Isotropic Thin Fiber Networks Based on Stochastic Volume Elements.

Thin fiber networks are widely represented in nature and can be found in man-made materials such as paper and packaging. The strength of such materials is an intricate subject due to inherited randomness and size-dependencies. Direct fiber-level numerical simulations can provide insights into the role of the constitutive components of such networks, their morphology, and arrangements on the strength of the products made of them. However, direct mechanical simulation of randomly generated large and thin fiber networks is characterized by overwhelming computational costs. Herein, a stochastic constitutive model for predicting the random mechanical response of isotropic thin fiber networks of arbitrary size is presented. The model is based on stochastic volume elements (SVEs) with SVE size-specific deterministic and stochastic constitutive law parameters. The randomness in the network is described by the spatial fields of the uniaxial strain and strength to failure, formulated using multivariate kernel functions and approximate univariate probability density functions. The proposed stochastic continuum approach shows good agreement when compared to direct numerical simulation with respect to mechanical response. Furthermore, strain localization patterns matched the one observed in direct simulations, which suggests an accurate prediction of the failure location. This work demonstrates that the proposed stochastic constitutive model can be used to predict the response of random isotropic fiber networks of arbitrary size.

Measurement of tensile strength of nuclear graphite based on ring compression test

Nuclear graphite is a type of quasi-brittle material, in which the ratio of the tensile strength to the compressive strength is higher than that of ceramic and hard rock materials. In this case, it is difficult to achieve a perfect splitting mode when the Brazilian splitting test is used to measure the tensile strength of such materials, leading to significant measurement errors. In this study, a ring compression test for measuring the tensile strength of the nuclear graphite material was proposed, and related principles and experimental verification were presented. The results showed that a regular tensile failure mode can be achieved using ring compression tests, and the tensile strength of nuclear graphite can be accurately measured. Furthermore, it was found that the accuracy obtained from ring compression tests was much higher than that from Brazilian splitting tests.

Hardening in the Transition to Nanocrystalline State in Pure Metals and Solid Solutions (Ultimate Hardening)

The state of the grain boundaries and the solid solution is analyzed for influence on the yield stress over a wide range of grain sizes for pure metals, low-doped alloys, and multicomponent solid solutions, including high-entropy alloys. A generalized equation is derived using the averaging integrals to describe the yield stress and hardness normalized to Young’s modulus versus the grain size. The potential to reach the maximum hardening for nanostructured materials through the use of grain-boundary engineering is considered. The concept of ‘useful’ impurities intended to bring the strength of such materials to the level comparable with the maximum (theoretically) possible one (E/2π–E/30) is proposed.

Characterisation of time-dependent, statistical failure of cellulose fibre networks

Cellulosic materials have special advantages for transport packaging, because of their light-weight and recyclable natures and also relatively high specific strength. The strength of such materials is normally evaluated by applying monotonically increasing, quasi-static displacement (or load). However, in real circumstances, the material is subjected to far more complex loading histories, such as creep, fatigue, and random loading. Failures under such circumstances are, not only time-dependent, but also notoriously variable. For example, the coefficient of variation for creep lifetime reaches or even exceeds 100%. The objective of this study is to develop a method to characterise both time-dependent and statistical natures of failures of cellulosic materials. We have used a general formulation of time-dependent, statistical failure, originally proposed by Coleman (J Appl Phys 29(6):968–983, 1958). We have identified three material parameters: (1) characteristic strength, representing short term strength, (2) brittleness parameter (or durability), and (3) Weibull shape parameter related to long-term reliability. These parameters were determined by special protocols of creep and constant loading-rate (CLR) tests for a series of containerboards. Results have shown that these two test methods yield comparable values for the materials parameters. This implies the possibility of replacing extremely time-consuming creep tests with the more time-efficient CLR tests. Comparing the cellulose fibre networks with fibres and composites used for advanced structural applications, we have found that they are very competitive in both reliability and durability aspects with Kevlar and glass-fibre composites.Graphical abstract

Strength of Low-Dimensional Objects

Filaments, films, tubes, membranes, and shells are considered as a general class of low-dimensional objects, the thickness of which is much smaller than their length and possible displacements. The strength of such materials almost achieved the theoretical limit, and their bearing capacity is restricted by macroscopic elastic (or viscoelastic) loss of stability rather than fracture. The generality of the phenomena of the loss of bearing capacity in low-dimensional objects and elastic (or viscoelastic) instability and its modes (wrinkles and focuses in twisting of a wire and a ribbon and in buckling, corrugation, curvature condensation of tubes and shells and plastic folds in flicking) is analyzed.

骨部分置換用ポーラスチタン–ポリグリコール酸–炭酸カルシウム複合体の開発

Porous materials show low Young’s moduli and excellent bonding to living bone. However, the strength of such materials is often insufficient in the initial stage of implantation. Thus, the objective of this study was to increase strength and Young’s modulus of porous titanium by filling the pores with a biodegradable mixture of polyglycolide (PGA) and calcium carbonate (CaCO3). The mixture was introduced into porous Ti (porosity: 60%) using a heat injection technique. When the pores were filled with PGA-CaCO3, compressive strength and Young’s moduli were drastically increased and influenced by the content of CaCO3. In an animal test, unfavourable autopsy findings could not be confirmed in rats and no bone was observed in the pores of the Ti-PGA composite. Decomposition of PGA lowered the surrounding pH, it was found to inhibit bone formation in the pores. Addition of CaCO3 to PGA could suppress the decrease in pH.

A novel, hydroxyapatite-based screw-like device for anterior cruciate ligament (ACL) reconstructions

BackgroundRupture of the anterior cruciate ligament (ACL) is one of the most common injuries of the knee. Common techniques for ACL reconstruction require a graft fixation using interference screws. Nowadays, these interference screws are normally made of titanium or polymer/ceramic composites. The main challenge of application of a fixation device made entirely of bioactive ceramic is in relation to the low strength of such materials. The purpose of this study was to evaluate a novel geometry for a fixation device made of pure hydroxyapatite for ACL reconstructions that can overcome some problems of the titanium and the polymer/ceramic screws. MethodsFinite Element Analysis was used for optimization of the stress distribution in conventional interference screw geometry. For experimental evaluation of the new fixation device, ex vivo tests were performed. ResultsThe innovative screw-like fixation device is characterized by multiple threads with a large thread pitch. The novel design enabled the insertion of the screw into the bone without the application of an external torque or a screwdriver. In turn, it also allowed for the use of low-strength and high-bioactivity materials, like hydroxyapatite. Ex vivo tests showed that the novel screw can sustain pull-out forces up to 476 N, which is comparable to that of the commercially available BioComposite™ interference screws (Arthrex Inc., Germany), as a reference. ConclusionsIn summary, the novel screw design is a promising strategy to develop all-ceramic fixation devices for ACL reconstructions, which may eliminate some drawbacks of the current interference screws.

Strength and Deformability of Brittle Polycrystalline Materials in Triaxial Stress-State State

The strength and deformability of brittle polycristalline materials (rock, cement, gypsum) in triaxial stress-strain state are analyzed. It is shown that the strength of such materials increases. The subcritical and postcritical stress-strain curves for polycristalline materials are presented.

Разработка метода оптического анализа изображения поверхности образца древесно-цементного композита

Barking waste at a pulp and paper mill can be used for construction materials fabrication. The paper presents principles of an estimation technique based on image analysis of the surface for assessing wood-cement composites properties. Images of side faces of wood-cement composites samples obtained under certain lighting parameters are characterized by optical density anisotropy. Analysis of fractal dimensions of images of top, bottom, and side faces surfaces shows that their structure depends on the molding process of a wood-cement composite. The results obtained allow us to hope that a method of nondestructive testing the sample strength of such materials could be developed in future.

High-performance biosourced poly(lactic acid)/polyamide 11 blends with controlled salami structure

High-performance biosourced poly(l-lactide) (PLLA)/polyamide 11 (PA11) (55/45) blends with small amounts of rubber, ethylene glycidyl methacrylate-graft-styrene-co-acrylonitrile (EGMA-g-AS), were fabricated by simple melt compounding. Epoxide groups in EGMA-g-AS are ready to react with both PA11 and PLLA, and thus EGMA-g-AS could be manipulated to locate mainly in either PA11 phase or PLLA phase by variation of the blending sequence. It was found that the blend with salami structure in which EGMA-g-AS is predominantly dispersed in the PLLA phase provides not only significantly improved tensile ductility, but also excellent film impact strength, while keeping relatively high modulus. The elongation at break and the film impact strength of such materials with 6 phr EGMA-g-AS are 322% and 361 kJ m−2, which are 78 and 5.2 times those of unmodified PLLA, respectively. In contrast, the blends with EGMA-g-AS mainly in the PA11 phase fracture in a brittle mode with low toughness. The toughening mechanism of the PLLA/PA11 blends with the sub-inclusion salami structure was investigated using a double-notch technique. The brittle-to-tough transition was observed on increasing the rubber sub-inclusion concentration in the PLLA phase. © 2013 Society of Chemical Industry