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Fine-grained nuclear graphite is one of the key structural materials for high temperature gas-cooled reactors as well as several Generation IV nuclear fission reactor designs. However, its deformation and fracture behaviours at elevated temperatures are not well understood. In light of this, the current study focused on investigating the flexural strength and fracture toughness of two fine-grained graphite (SNG623 and T220) using real-time X-ray computed micro-tomography imaging at room temperature, 750 °C and 1100 °C. Specifically, nonlinear-elastic fracture mechanics-based JR(Δa) R-curves at these temperatures were presented with evolution of damage and failure micro-mechanisms, local strain distributions and J-integral fracture analysis, purveying notable findings. Compared to the coarser-grained Gilsocarbon nuclear graphites used in the current UK Advanced Gas-cooled Reactors (AGRs), these modern fine-grained graphites display deficient fracture resistance in the form of far less stable crack growth prior to catastrophic fracture and reduced failure strain at 1100 °C. Moreover, their elevation in strength and toughness at high temperatures is remarkably lower than that of Gilsocarbon graphite. Based on in situ high-temperature Raman spectroscopy mapping, we believe that one of the major causes of this behaviour can be attributed to the smaller magnitude of ‘frozen-in’ residual stress relaxed at elevated temperatures compared with Gilsocarbon graphite.

The paper provides new experimental evidence for vulnerable artifacts on the dependence of failure strain on the loading rate corresponding to typical environmental loads lasting between hours and months. Animal glue-based ground was chosen for this study as an easily available, hygroscopic and brittle material as well as due to its abundance in collections and its relevance when discussing the risk of mechanical damage to objects. Gesso specimens were tested using dynamic mechanical analysis and tensile testing at different frequencies, under a variety of loading rates and temperatures. The time-temperature superposition principle was used to predict the material response to slow deformations (lasting hours to months) that are otherwise inaccessible on laboratory timescales. The results demonstrate that brittle materials such as animal glue-based grounds do not benefit from longer cycles of applied loads as failure strain is not time-dependent within the investigated timescale. [ABSTRACT FROM AUTHOR]

The complex modeling and computational cost are unavoidable in analysis of finite element models (FEMs) when mechanical properties of woven composite materials are predicted. To overcome the drawbacks of FEMs, two different artificial neural network models (ANNMs) based on quasi-static axial compression experimental data of 2.5D woven composite plates (2.5DWCPs) are constructed: (1) The direct strength prediction model (DSPM) is a non-destructive way to predict strength, which is meaningful in engineering; (2) The indirect strength prediction model (ISPM) is based on stress–strain curves, which firstly proposes a simplified data processing method including the state variables (SVs). The SVs are introduced to modify the experimental stress–strain curves, which not only reduces training data size but also significantly improves prediction accuracy. Then, the performance of the DSPM and the ISPM has been evaluated by numerical examples. The results indicate that the DSPM has simple and direct expressions of input parameters (IPs) and output parameters (OPs), which makes it easier to construct and train ANNMs. The ISPM not only utilizes sufficient training data from experiments but also performs well in predicting stress–strain curve and failure strain. In short, two proposed ANNMs have ability to fast and accurately predict compression strength, which are more suitable for engineering than FEMs. To reduce experimental costs, the DSPM is proposed to produce reasonable results. If a lot of experimental data are prepared, the ISPM can produce more accurate results. [ABSTRACT FROM AUTHOR]

The failure strain of a tube is a function of the biaxial strain ratio (axial strain/hoop strain) to which it is subjected. The relationship between failure strain and the strain ratio can be determined experimentally using expansion due to compression tests with a tensile load (EDCT), in which a ductile pellet placed inside the tube is compressed axially so it expands in diameter and imposes a hoop strain on the tube. At the same time, a tensile load on the ends of the tube creates an axial strain. This study investigates the capabilities and limitations of EDCT tests using two devices that allow experiments to be performed on a standard tensile testing machine. The first device applies an axial force on the ends of the sample, and the second device applies an axial displacement. Tests on zirconium alloy tubes confirmed that the failure strain is dependent on the strain ratio and the metallurgical state of the material. EDCT tests can produce a range of strain ratios, but there is an upper limit on the strain ratio that can be obtained, and it is dependent on the plastic behaviour of the sample and the friction conditions between the components. [ABSTRACT FROM AUTHOR]

Abstract Determination of failure strains is a topic of great interest for the design of composite structures. To evaluate the ultimate strains of a composite, tensile tests have been carried out on specimens with a range of fiber orientations between 0° and 90°. Ultimate tensile strengths obtained present low or moderate dispersion, the average values constituting a good estimation of the failure stress. Values of failure strains obtained present high dispersion for almost all orientations, so it is proposed to take as failure strain threshold the minimum value for each orientation. Finally, the shear behavior of the material has been evaluated. [ABSTRACT FROM AUTHOR]

ObjectivesIn order to solve the problem of numerical simulation of flat-nosed projectile penetration into metal plates, the influence of mesh size on element failure strain value and residual velocity of projectiles was studied. MethodsThe finite element software LS-DYNA was used to simulate the process of uniaxial tensile test of Q235 steel sample, and the failure strain of the element under the grid density is obtained by the elongation of the tensile sample during fracture. In the meantime, the correction curve of the failure strain with the grid density was plotted and dynamically corrected. Then, the numerical simulation of flat-nosed projectile penetrating Q235 steel plate was carried out with the target plate meshed with different sizes. The failure strain of Q235 steel material was selected according to the correction curve. Finally, the residual velocity of the projectile is compared with the experimental results to analyze the influence of mesh size on the simulation results of the penetration resistance problem of the metal plate in the numerical simulation.ResultsThe results show that the element failure strain selected in the numerical simulation should increase with the increase in grid density, and in the case of the metal plate anti-penetration problem, it should increase with the increase of the grid density. In the problem of penetration resistance of metal plates, the simulation results of residual velocity prediction gradually converge with the experimental results. With the increase of mesh density, when the grid size is 0.5 mm, the average relative error of the numerical simulation and the test fitting curve in the velocity section is 5.13%, and the error between the numerical simulation and the test is larger in the low-speed section. Moreover, the residual velocity of the projectile body is more sensitive to mesh density in the low velocity range.ConclusionsThe related calculation methods and research results have a certain reference value for the selection of mesh size and material failure strain in the projectile penetration problem.

The purpose of this study was to develop injury risk functions (IRFs) for the anterior and posterior cruciate ligaments (ACL and PCL, respectively) and the medial and lateral collateral ligaments (MCL and LCL, respectively) in the knee joint. The IRFs were based on post-mortem human subjects (PMHSs). Available specimen-specific failure strains were supplemented with statistically generated failure strains (virtual values) to accommodate for unprovided detailed experimental data in the literature. The virtual values were derived from the reported mean and standard deviation in the experimental studies. All virtual and specimen-specific values were thereafter categorized into groups of static and dynamic rates, respectively, and tested for the best fitting theoretical distribution to derive a ligament-specific IRF. A total of 10 IRFs were derived (three for ACL, two for PCL, two for MCL, and three for LCL). ACL, MCL, and LCL received IRFs in both dynamic and static tensile rates, while a sufficient dataset was achieved only for dynamic rates of the PCL. The log-logistic and Weibull distributions had the best fit (p-values: >0.9, RMSE: 2.3%–4.7%) to the empirical datasets for all the ligaments. These IRFs are, to the best of the authors’ knowledge, the first attempt to generate injury prediction tools based on PMHS data for the four knee ligaments. The study has summarized all the relevant literature on PHMS experimental tensile tests on the knee ligaments and utilized the available empirical data to create the IRFs. Future improvements require upcoming experiments to provide comparable testing and strain measurements. Furthermore, emphasis on a clear definition of failure and transparent reporting of each specimen-specific result is necessary.

In this study, two types of cemented tailings backfill (CTB) were prepared by breaking up the waste clay bricks (WCB) from dismantled buildings and replacing part of the cement with brick powder and part of the tailings with brick aggregate. The mechanical properties of the modified CTB were investigated. The results showed that the strength of CTB with 10% brick powder content increased by 16.24% at the curing age of 28 days, while the content of 20% brick powder only decreased by 0.11%. The strength of the brick aggregate with less than 20% content can be increased at each curing age, and the strength of the 15% brick aggregate at the curing age of 7 d and 28 d is increased by 65.54 and 58.8%. The failure strain of the CTB-containing brick powder decreases with the extension of the curing time, and the failure strain of the CTB-containing brick aggregate decreases significantly at the curing age of 7 days. In addition, a three-stage damage constitutive model was established based on the results obtained in the present study, and the laboratory test results of CTB under uniaxial compression were effectively described with high confidence. [ABSTRACT FROM AUTHOR]

This article presents data from the investigation of the thermal characteristics and mechanical behaviors of twelve different compositions of a polyurethane shape memory polymer (SMP). Each of the SMP compositions has a unique molar ratio of three monomers: (i) hexamethylene diisocyanate (HDI), (ii) N,N,N,N-Tetrakis(2-Hydroxypropyl)ethylenediamine (HPED), and (iii) Triethanolamine (TEA). The thermal characteristic datasets for each composition include the glass transition temperatures, as obtained from differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), and the thermal degradation thresholds, as found from thermogravimetric analysis (TGA). The mechanical behaviors of the SMPs are represented by the failure stresses and strains, as obtained by cyclic tensile testing and failure testing, respectively. The interpretation of these measurements as well as a discussion of the potential usage of candidate SMP compositions for medical devices can be found in the companion article by Kunkel et al. (2018) [1], Synthesis and characterization of bio-compatible shape memory polymers with potential applications to endovascular embolization of intracranial aneurysms.

Copyright of Journal of Zhengzhou University: Engineering Science is the property of Editorial Office of Journal of Zhengzhou University: Engineering Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil stabilization using cement is regarded as one of the conventional methods to improve the engineering properties of soil used in infrastructure and road bodies. Considering the environmental problems caused by the production and consumption of cement, finding a suitable replacement for cement is necessary. The present study aims to experimentally evaluate the effect of using zeolite instead of cement in the stabilization of pavement layers. In this research, only 5% of cement was used in the control sample, while zeolite was used instead of cement in other samples by 20, 30, 40, and 60 wt.% of cement. According to the analysis, the highest unconfined compressive strength was obtained in the sample containing 30% (wt.% of cement) of zeolite instead of cement (equivalent to 1.5% of the total stabilizing materials) after 28 days of treatment, which was 29% more than that of the sample without zeolite. Evaluating the fracture strains reveals that using zeolite instead of cement increases the fracture strain by 33%, and in other words, changes the behavior of the sample from brittle mode to soft mode. [ABSTRACT FROM AUTHOR]

Environmental temperature is usually variable in the field and can significantly affect the mechanical behavior of cemented soil. However, how the initially low-temperature curing affects the strength behavior of cemented lean clay is still pending. To identify the influence of changing temperature on the strength behavior of cemented lean clay, a series of unconfined compression strength (UCS) tests were carried out in this research. Based on test results, an overall detrimental influence on the unconfined compressive strength (qu) was found due to low-temperature curing. Compared with cemented lean clay cured at a constant low temperature, an increase in qu was observed when the curing temperature rose again to 20°C, and the recovery in qu depends mainly upon the initial low-temperature curing time. The improvement in cement hydration was the main source in strength gain for cemented lean clay cured initially at 5°C/10°C. However, for cemented lean clay once cured at 0°C, the formation and thawing of pore ice damaged the soil structure and resulted in permanent damage to the development of strength. Moreover, the failure strain εf and secant modulus E50 were consistent well with qu when the temperature was not less than 5°C. For cemented lean clay used in this study, a curing temperature range of 5°C–20°C would guarantee adequate qu. [ABSTRACT FROM AUTHOR]

This study proposes a relation for the failure strain of externally bonded reinforcement on groove (EBROG) joints derived through multivariate regression analysis on the experimental results. In addition to the conventional parameters of concrete compressive strength and groove dimensions studied as independent variables, a novel descriptor variable of great effect, called width of fiber-reinforced polymer (FRP) sheet on a single groove, is also introduced for the first time. Using these descriptors and their variations, 27 specimens are strengthened via the EBROG method and subsequently subjected to the single lap-shear test. First, the proposed relation is assessed with respect to its goodness of fit using certain statistical indices, which reveals a good agreement between estimated and measured values. The relation is also verified in terms of its efficiency and accuracy through a comparison with a previous model using 65 specimens in three groups previously reported in the relevant literature. The comparisons indicate the superior accuracy of the proposed relation in estimating the failure strain of EBROG joints and its higher generality as compared to the rival model. [ABSTRACT FROM AUTHOR]

In this study, two types of cemented tailings backfill (CTB) were prepared by breaking up the waste clay bricks (WCB) from dismantled buildings and replacing part of the cement with brick powder and part of the tailings with brick aggregate. The mechanical properties of the modified CTB were investigated. The results showed that the strength of CTB with 10% brick powder content increased by 16.24% at the curing age of 28 days, while the content of 20% brick powder only decreased by 0.11%. The strength of the brick aggregate with less than 20% content can be increased at each curing age, and the strength of the 15% brick aggregate at the curing age of 7 d and 28 d is increased by 65.54 and 58.8%. The failure strain of the CTB-containing brick powder decreases with the extension of the curing time, and the failure strain of the CTB-containing brick aggregate decreases significantly at the curing age of 7 days. In addition, a three-stage damage constitutive model was established based on the results obtained in the present study, and the laboratory test results of CTB under uniaxial compression were effectively described with high confidence.

Automotive and construction industries demand for roll-formed high strength Dual-Phase steels due to their excellent structural performances and attractive appearances have increased dramatically over the last decade. However, their compromised ductility gives rise to problems and faces numerous manufacturing issues. These problems pertain to ductile fracture defect, which is often observed on tight radii during roll forming. The partial heating roll forming method is a recently proposed roll forming method alternative to the conventional cold roll forming method, aimed at reducing ductile fracture by partially heating only the bend areas. In this paper, the ductile fracture during the partial heating roll forming processes of DP980 high strength steel is evaluated by implementing the phenomenological Generalized Incremental Stress State Dependent Damage (GISSMO) model using the FE code LS-DYNA. To this aim, instability and fracture strains from the uniaxial, plane-strain, and shear tensile tests at different temperatures were evaluated. The basic tensile test results are in good agreement with the experimental results found in the literature. Subsequently, the instability and plastics strain at fracture from basic tensile tests were calibrated to numerical simulations of roll forming processes for ductile fracture predictions. Based on the results, the instability and fracture strain increase as the material's temperature increases. Moreover, the ductile fracture investigation of DP980 during the cold roll forming process showed that fractures were observed on the profile's bend areas. However, no visible cracks were observed on the partial heated roll-formed profile. [ABSTRACT FROM AUTHOR]

Fused depositional modeling (FDM) is one of the common methods for 3D printing of polymers, which is expanding in various industrial applications, scientific researches, and engineering applications due to its ability to make complex parts. In this research, molecular dynamics (MDs) simulation has been used to predict the physical and mechanical properties. Then, the mechanical properties of the printed parts were determined. The mechanical properties of 3D printed parts strongly depend on the correct selection of processing parameters. In this study, the effect of three important parameters such as infill density, printing speed, and layer thickness were investigated on the tensile properties of PLA specimens. For this purpose, standard specimens with four infill densities of 20%, 40%, 60%, and 80%, two speeds of 20 mm/s and 40 mm/s, and two thicknesses of 0.1 mm and 0.2 mm were printed and tested under quasi-static tensile test. In all printed specimens, the print angle is ± 45°. The obtained experimental outcomes from the tensile test revealed that with increasing the infilling density, the mechanical properties of the parts improve and increase significantly. However, at very high infilling densities, the samples behave more brittle, so in cases where the strength of the part is less important than its shape and appearance, a density of 40% is more suitable in terms of cost, material, and time savings. It was also noted that the printing speed has less effect on the mechanical properties of PLA parts. It was also observed that reducing the thickness of the layer, while slightly increasing the stiffness of the parts, makes the part extremely brittle, and on the other hand, it leads to increase in the dimensional accuracy and surface quality of the specimens. At infill density of 80%, the specimens had the highest stiffness and strength, but it exhibits a brittle behavior. Moreover, it can be deduced that by reducing the layer thickness although the modulus of elasticity increases a little, ductility is greatly affected. [ABSTRACT FROM AUTHOR]

Microbial-induced calcium carbonate precipitation (MICP) technology has been widely used in geotechnical engineering. The undrained and unconsolidated (UU) triaxial tests were conducted in this study to investigate the effect of bio-cementation concentration and treatment times on the mechanical behavior of MICP treated siliceous sands. Test results indicated that the strength of treated specimen is significantly affected by the bio-cementation concentration. The normalized σ′p/σ′p_u increases exponentially with treatment times and produced calcium carbonate. For the same treatment times, the higher the bio-cementation concentration, the larger the produced calcium carbonate and smaller corresponding failure strain. The void ratio and permeability of treated specimens decrease lineally with treatment times increase. The higher the used bio-cementation concentration, the larger the reduction of void ratio and permeability. SEM analysis illustrates that when the bio-cementation concentration is 0.5 mol/L, the crystal form of calcium carbonate is mainly spherical, while the concentrations are 0.7 mol/L and 1.0 mol/L, the crystal form of calcium carbonate is mainly block. This can explain from the perspective that the treatment effect of 0.7 mol/L and 1.0 mol/L bio-cement cementation is better than that of 0.5 mol/L. [ABSTRACT FROM AUTHOR]

Industrial waste calcium carbide residue (CCR) and ground granulated blast furnace slag (GGBFS) are used to solidify and improve clay. According to the unconfined compressive strength (UCS) test, the mass ratio of carbide slag to GGBFS, the influence of moisture content and the content of curing agent on the strength of solidified soil are studied. The characteristics of stress-strain curve and the change rule of failure strain are analyzed. The test results show that the hydration activity of GGBFS can be effectively activated by carbide slag, and the optimal ratio of carbide slag and GGBFS is 2:3. The UCS of solidified clay increases first and then decreases with the increase of the content of the curing agent and moisture content. The stress-strain curve of solidified soil can be divided into compaction stage, elastic deformation stage and failure stage. With the increase of UCS, the failure strain of solidified soil decreases as a power function while the deformation modulus increases linearly with the increase ofUCS, and decreases as a power function with the increase of failure strain. Used separately, the failure of carbide slag or GGBS solidified soil is plastic failure, and the failure strain increases with the increase of moisture content. However, the composite solidified soil is brittle failure, and its failure strain decreases with the increase of moisture content. The toughness index of solidified soil decreases with the increase of the content of curing agent. [ABSTRACT FROM AUTHOR]

This article presents data from the investigation of the thermal characteristics and mechanical behaviors of twelve different compositions of a polyurethane shape memory polymer (SMP). Each of the SMP compositions has a unique molar ratio of three monomers: (i) hexamethylene diisocyanate (HDI), (ii) N,N,N′,N′-Tetrakis(2-Hydroxypropyl)ethylenediamine (HPED), and (iii) Triethanolamine (TEA). The thermal characteristic datasets for each composition include the glass transition temperatures, as obtained from differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), and the thermal degradation thresholds, as found from thermogravimetric analysis (TGA). The mechanical behaviors of the SMPs are represented by the failure stresses and strains, as obtained by cyclic tensile testing and failure testing, respectively. The interpretation of these measurements as well as a discussion of the potential usage of candidate SMP compositions for medical devices can be found in the companion article by Kunkel et al. (2018) [1], “Synthesis and characterization of bio-compatible shape memory polymers with potential applications to endovascular embolization of intracranial aneurysms.”

Most of welded parts requires secondary forming process to meet the design requirements which makes the ductility of the joint an important parameter to be improved. To this end, we imped compensation layer of AA7075 aluminum alloy between two blanks of AA2024 aluminum alloy during friction stir welding. The effect of compensation layer width on the microstructure, microhardness, tensile strength and failure strain was investigated. XRD results showed that using AA7075 alloy compensation layer helped for precipitation of new intermetallic phases, Al2Cu and Mg2Zn, at the grain boundaries of Al grains. Tensile test results showed that the sample with 2 mm width compensation layer possess 18% improved strength and 54.4% improved failure strain compared with the joint without compensation layer. The failure strain of this joint was 16.8% which is almost that for AA2024 (17.2%). The improved strength was because of the grain refinement and the precipitation of Al2Cu and Mg2Zn intermetallics. While the improved failure strain was due to the higher content of Mg and Zn alloying elements in AA7075 alloy which precipitate on the grain boundaries facilitating the slipping between grains and provide more deformability of the global structure.

Maintaining the integrity of the major equipment in nuclear power plants is critical to the safety of the structures. In particular, the soundness of the piping is a critical matter that is directly linked to the safety of nuclear power plants. Currently, the limit state of the piping design standard is plastic collapse, and the actual pipe failure is leakage due to a penetration crack. Actual pipe failure, however, cannot be applied to the analysis of seismic fragility because it is difficult to quantify. This paper proposes methods of measuring the failure strain and deformation angle, which are necessary for evaluating the quantitative failure criteria of the steel pipe elbow using an image measurement system. Furthermore, the failure strain and deformation angle, which cannot be measured using the conventional sensors, were efficiently measured using the proposed methods.

Testing small amounts of extracted and recovered asphalt binder as used in construction allows for the acceptance of materials in accordance with traffic and climate requirements. This approach facilitates the sustainable use of resources and thus prepares the paving industry for the true circular economy. Oscillatory, creep, and failure tests in a rheometer are compared for the performance grading of 32 asphalt binders extracted and recovered from real-world contract samples. Films 8 mm in diameter and 0.5 mm thick were tested from 35 to −5 °C in dynamic shear, followed by shear creep at 0 and 5 °C, and finally in tertiary tensile creep at 15 °C. The enhanced protocol uses a very small amount of material in contrast to current methods, yet it provides comparable results. Phase angle measurements appear to be optimal for performance grading, but further field study is required to determine if additional binder properties such as stiffness and/or failure strain would be required for the control of cracking.

The uniformity, elasticity and hydrophobicity of methyltrimethoxysilane (MTMS)-based silica aerogels, which were prepared by using dimethyl sulfoxide (DMSO) as the solvent, were investigated. The as-prepared silica aerogels were characterized by means of scanning electron microscope, Fourier transform infrared, contact angle/interface system and electronic universal testing machine. The hydrophobicity of the MTMS-based silica aerogels could be adjusted by tuning the MTMS/DMSO molar ratios. The water contact angle of the MTMS-based silica aerogels could be as high as 160.2∘, suggesting its superhydrophobic property. It was found that all the MTMS-based silica aerogels had the typical three-dimensional porous structure. The failure strain of MTMS-based silica aerogels could be as high as 66.14%. [ABSTRACT FROM AUTHOR]

Featured Application: A non-contact digital image correlation technique is used to predict sandstone failure. Failure strain for the tested sandstone is estimated to be around 0.004. Finite element analysis verifies the accuracy of prediction results based on experiments. Investigation on the deformation mechanism of sandstone is crucial to understanding the life cycle patterns of pertinent infrastructure systems considering the extensive adoption of sandstone in infrastructure construction of various engineering systems, e.g., agricultural engineering systems. In this study, the state-of-the-art digital image correlation (DIC) method, which uses classical digital photography, is employed to explore the detailed failure course of sandstone with physical uniaxial compression tests. Four typical points are specifically selected to characterize the global strain field by plotting their corresponding strain–time relationship curves. Thus, the targeted failure thresholds are identified. The Hill–Tsai failure criterion and finite element simulation are then used for the cross-check process of DIC predictions. The results show that, though errors exist between the experimental and the theoretical values, overall, they are sufficiently low to be ignored, indicating good agreement. From the results, near-linear relationships between strain and time are detected before failure at the four chosen points and the failure strain thresholds are almost the same; as low as 0.004. Failure thresholds of sandstone are reliably determined according to the strain variation curve, to forecast sandstone damage and failure. Consequently, the proposed technology and associated information generated from this study could be of assistance in the safety and health monitoring processes of relevant infrastructure system applications. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Lime concrete and lime treatment are two attractive techniques for geotechnical engineers. However, researches have rarely been carried out to study the effects of moisture and capillary action due to increasing groundwater level on geotechnical properties of lime concrete. The aim of this study is to investigate the effects of curing time and degree of saturation on some of geotechnical properties of lime concrete such as unconfined compressive strength (UCS), secant modulus (Es), failure strain, brittleness index (IB), and deformability index (ID) using unconfined compression tests. First of all, geotechnical and chemical properties of used materials were determined. After curing times of 14 d, 28 d, 45 d, and 60 d in laboratory condition, the specimens were exposed to saturation levels ranging from 0 to 100%. The results showed that the moisture and curing time have significant effects on the properties of lime concrete. Based on the results of scanning electron micrograph (SEM) test, it was observed that the specimen was characterized by a rather well-structured matrix since both the filling of a large proportion of the coarse-grained soil voids by clay and the pozzolanic activity of lime led to retaining less pore water in the specimen, increasing the UCS and Es, and consequently resisting against swelling and shrinkage of the clay soil. Moreover, due to the pozzolanic reactions and reduction of water, by increasing the curing time and decreasing the degrees of saturation, UCS, Es, and IB increased, and ID decreased. Based on the experimental results, a phenomenological model was used to develop equations for predicting the properties in relation to the ratio of degree of saturation/curing time. The results showed that there was a good correlation (almost R2 > 90%) between the measured parameters and the estimated ones given by the predicted equations.

In this work, hybrid composite having linear gradation of carbon and glass fibers (functionally graded hybrid (FGH)) is made and its material properties are compared with classical sandwich hybrid (SH) laminates, i.e., carbon fibers in between glass fibers or vice versa. The performance of FGH composite is evaluated in tensile, compressive, and flexural loadings. Using analytical approach (rule of mixtures), hybrid effect w.r.t. carbon fiber or glass fiber laminates is determined in terms of strength and stiffness. It is observed that failure of FGH specimen is progressive, i.e., layer by layer failure, due to this high ductility is noticed in comparison with SH specimens except in compression. Stiffness and strength of FGH specimens are higher than SH specimens under tension, compression, and flexural. The FGH has shown 7–8% positive hybrid effect in flexural modulus w.r.t. carbon fiber reinforced polymer laminates. In terms of compressive strains, SH and FGH specimens have shown 526% and 380% positive hybrid effect w.r.t. carbon fiber laminates, respectively. Overall FGH is proved better in comparison with classical SH laminates. [ABSTRACT FROM AUTHOR]

Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Sakurai proposed hazard warning levels (HWLs) on the basis of the critical strain concept to evaluate the stability of tunnels. When the measured strain values remain smaller than HWL III, the stability of the tunnels is confirmed. The collapses occurred in a number of tunnels existing in Iran have questioned the accuracy of the Sakurai's criterion in spite of the smaller values of tunnel strains comparing to the HWL III. This study renders an account of the HWLs modified on the basis of the results of 162 uniaxial compression strength (UCS) tests conducted on ten types of rocks and soils. To this end, the UCS, critical strain and initial tangent modulus were first determined. Then, the upper and lower bounds of the critical strain were considered in UCS – critical strain and modified tangent modulus – critical strain graphs as the modified HWLs. According to the results, the modified HWLs are more accurate results regarding the tunnel stability conditions. [ABSTRACT FROM AUTHOR]

Abstract The effect of hydrogen on the ductility of metals is studied by incorporating the hydrogen diffusion process and the hydrogen enhanced localized plasticity (HELP) into a finite element program. A series of unit cell analyses are conducted under various stress states and the loading speed resulting in a steady state hydrogen distribution is determined. The evolution of the local stress and deformation states results in hydrogen redistribution in the material, which in turn changes the material's flow property due to the HELP effect. It is found that localized plastic deformation plays a major role in increasing the hydrogen concentration due to the newly generated trapping sites. The HELP effect promotes material failure by accelerating void growth, which is affected by the macroscopic stress state subjected by the material unit characterized by the stress triaxiality and the Lode parameter. For a constant Lode parameter, the effect of HELP on void growth and failure strain reduction increases with the stress triaxiality. For a constant stress triaxiality, the effect of HELP is highest when the Lode parameter is near 0. As the Lode parameter increases towards 1 or decreases towards −1, the HELP effect gradually diminishes. Highlights • A unit cell model is used to study the effect of hydrogen on ductile fracture. • Hydrogen diffusion and hydrogen enhanced localized plasticity are numerically modeled. • Loading speed corresponding to steady state hydrogen distribution is determined. • Effects of hydrogen on failure strain under different stress states are investigated. [ABSTRACT FROM AUTHOR]

Abstract The tungsten alloys reinforced by ZrO 2 were prepared using azeotropic distillation method combined with powder metallurgy method, and then the sintered tungsten alloys were swaged to obtain compact bars. The microstructures of W- x ZrO 2 (x = 0, 0.25, 1.0 and 1.5 wt%) alloys were investigated by means of SEM, XRD and TEM. The results show that ZrO 2 exist as a stable cubic phase in tungsten alloys by adding Y 2 O 3. Fine ZrO 2 particles (500–800 nm) are dispersed in the tungsten matrix, and thus refine the grain size and improve the physical properties and strength of tungsten alloys. With the increase of the ZrO 2 content, the relative density, hardness and compressive strength of tungsten alloys were all increased. The swaged W–1.5 wt%ZrO 2 alloy shows the finest microstructure with an average grain size of 47.18 μm, reducing 34.76% compared with that of pure tungsten. And thus, the swaged W–1.5 wt%ZrO 2 alloy achieves the highest compressive strength (1941.3 MPa) and failure strain (23.1%) at the same time, increasing 23.27% and 22.37%, respectively, compared with that of pure tungsten. Highlights • W-ZrO 2 alloys were prepared by azeotropic distillation and powder metallurgy process. • c-ZrO 2 particles (500–800 nm) were obtained and evenly distributed in W matrix. • ZrO 2 refined tungsten grain and improved strength and plasticity simultaneously. • Compressive strength of W-1.5%ZrO 2 alloys increases 23.27% in comparison with pure W. • Failure strain of W-1.5%ZrO 2 alloys increases 22.37% in comparison with pure W. [ABSTRACT FROM AUTHOR]

• Through the plate thickness compensation model, the target plates of different materials can meet the similarity requirements. • The concepts of Volume-failure strain and Volume-yield stress are introduced, which can better describe the high-velocity penetration problem involving fracture toughness. • After the compensation model is established, it is verified by analytical model and numerical simulation. This study aims to enable the use of target plates composed of different materials in the penetration problem through the H-method similarity framework. Since different fracture toughness can lead to imperfect similarity between models, the concepts of Volume-failure strain and Volume-yield stress are introduced, which can well describe the high-velocity penetration problem involving fracture toughness. To ensure that the initial velocity of the projectile does not change, the similarity distortion among scaled models composed of different materials and the prototype is compensated by changing the target plate thickness. The feasibility of the proposed method is preliminarily proven based on the analysis model of the dimensionless critical impact energy of the target plate and the residual velocity of the projectile during penetration. Moreover, numerical simulations of blunt projectiles penetrating steel plates are performed. By changing the target plate thickness, the similarity differences among scaled models composed of different materials are effectively resolved. The errors of the residual velocity and peak force are in a completely reasonable range. [Display omitted] [ABSTRACT FROM AUTHOR]

Investigation on the deformation mechanism of sandstone is crucial to understanding the life cycle patterns of pertinent infrastructure systems considering the extensive adoption of sandstone in infrastructure construction of various engineering systems, e.g., agricultural engineering systems. In this study, the state-of-the-art digital image correlation (DIC) method, which uses classical digital photography, is employed to explore the detailed failure course of sandstone with physical uniaxial compression tests. Four typical points are specifically selected to characterize the global strain field by plotting their corresponding strain−time relationship curves. Thus, the targeted failure thresholds are identified. The Hill−Tsai failure criterion and finite element simulation are then used for the cross-check process of DIC predictions. The results show that, though errors exist between the experimental and the theoretical values, overall, they are sufficiently low to be ignored, indicating good agreement. From the results, near-linear relationships between strain and time are detected before failure at the four chosen points and the failure strain thresholds are almost the same; as low as 0.004. Failure thresholds of sandstone are reliably determined according to the strain variation curve, to forecast sandstone damage and failure. Consequently, the proposed technology and associated information generated from this study could be of assistance in the safety and health monitoring processes of relevant infrastructure system applications.