Compressive Strength Behavior Research Articles

Cement kiln dust and polypropylene fiber in expansive clay improvement

For civil engineers, expansive soils pose a great deal of difficulty because of their sensitivity to volume changes with different moisture levels. These difficulties are compounded by the widespread occurrence of swelling clay, which can seriously harm infrastructure, especially in arid or semi-arid areas. The geotechnical qualities of these soils have been improved through the use of various additives and techniques, resolving this problem and making the soils suitable for building. Numerous stabilization techniques, nevertheless, may have negative environmental effects. Therefore, it is imperative to investigate the use of local waste or by-products to stabilize soil in order to preserve the environment and lower stabilization costs, especially in road construction projects.To address these issues, an experiment was conducted to determine how locally obtained cement kiln dust (CKD), both alone and combined with polypropylene fibers, affected the properties of plastic clay soil, also referred to as expansive clay from Cheffia.The main objective of this study is to assess how well different CKD percentages (from 5% to 25%) stabilize soil while improving its mechanical and physical properties. The study also aims to explain how the addition of polypropylene fiber affects the unconfined compressive strength and compaction behavior of the soil in the optimal CKD-soil mixture. The results of the analysis show that the addition of cement kiln dust (CKD) significantly improved the studied soil's workability, compaction, and strength. Additionally, adding polypropylene fibers strengthens the clay's resistance to compression, which presents encouraging opportunities for reducing the difficulties brought on by expansive soils in civil engineering applications.

Experimental analysis of the compressive behaviour of perforated brick masonry using digital image correlation

The paper presents an experimental program on the characterisation of the mechanical behaviour of perforated brick masonry (PBM) under uniaxial compression. The study is aimed to provide a better understanding on the compressive strength and elastic behaviour of a kind of masonry hardly dealt with in the literature. The mechanical response of the investigated masonry shows actually two complexities, linked respectively to the perforated nature of the bricks and the asymmetric cross-section of the units. The latter feature is particularly recurrent in exposed brickwork composed of perforated bricks, whenever one of the face shells has a larger thickness than the other one. For this purpose, an experimental campaign was carried out on units and PBM subjected to uniaxial compressive loading. The mechanical response of PBM is investigated to accurately determine the masonry Young’s modulus and the compressive strength. Measurements obtained with conventional sensors are compared with those derived from the Digital Image Correlation (DIC) technique. Lastly, the experimental findings in terms of compressive strength and Young’s modulus are cross-referenced with the estimations derived from empirical criteria available in Eurocode 6 and ACI 530.1–02.

Hybridization of concrete by the inclusions of kaolin, alumina and silica fume: Performance evaluation

Concrete is the prime source, which fulfils the applications for construction in various forms. The prime roles of concrete industries are reducing material usage, enrichment of compressive strength, and flexural strength of concrete usage. This research focuses on recycling kaolin (mining waste) and silica fume, a great potential material for replacing coarse aggregate gravel stone and fine aggregate sand in conventional concrete as a hybrid. The developed concrete contained 5% nano alumina (Al2O3), 10% of kaolin waste (KW), and 5, 10, and 15% of silica fume (SF), and its behavior like compressive strength, flexural strength, water absorption, and acid attack behavior is studied. The molecular structure of crystalline is analyzed via X-ray diffraction (XRD). The 15% SF blended with 5% alumina and 10% KW cured within 28 and 90 days recorded high compressive and flexural strength (44 ± 1.76 MPa and 4.3 ± 0.17 MPa). XRD pattern proved their alumina, SF, and KW and found that the concrete blended with 5% alumina, 10% KW, and 15 wt% SF(90 days cured concrete) showed low water absorption (3.1 ± 0.12%). The effect of sulfuric acid behavior on weight reduction was 0.78% compared to CC1 (concrete cube without Al2O3, SF, and KW).

Study on the Influence of Contact Surface Characteristics on Strength and Fracture Evolution of Layered Cemented Backfill (LCB)

The stability of backfill plays a crucial role in the process of mine operation. In this study, author combined indoor experiments, surface fitting, numerical simulation, and theoretical derivation to investigate how the filling times (FTs), cement tailings ratio (CTR), and minimum CTR filling position (MCFP) affect the uniaxial compressive strength (UCS) and fracture evolution behavior of LCB. The findings demonstrate that an augmentation in FTs reduces the UCS of LCB. Moreover, the highest strength ratio resulting from diverse MCFP amounts to 2.25 times. When once filling, backfill sustain damage as a result of cracks penetrating, whereas LCB that are filled multiple times first encounter damage at the layered contact surface, followed by the gradual spread of cracks until penetrate the LCB. Through an interactive regression model, it is evident that FTs, CTR, and MCFP significantly affect the UCS. Additionally, the interaction between CTR and MCFP has a considerable impact on the UCS. Based on numerical simulation, an increase in FTs results in a wider large displacement area generated by the backfill, leading to greater horizontal and vertical displacement. The MCFP has a significant impact on the lateral displacement and maximum stress of the backfill. Theoretical derivation verifies that MCFP at the top or middle layer results in an increase in the UCS, which is consistent with the experimental findings and numerical simulation. This paper elaborates on the mechanical mechanism behind the interaction between CTR and MCFP. These findings can provide a foundation for assessing the durability and stability of LCB in subsequent stages.

Enhancement on compressive strength of Bangkok clay cement using novel high-strength polyethylene fibers

This study aims to investigate the effect of novel high-strength polyethylene fibers on the unconfined compressive strength (UCS) behavior of concrete produced with admixed Bangkok clay cement. Bangkok clay samples were prepared at a liquid limit of 88% and were added to ordinary Portland cement (OPC) at 2, 4, 6, 8 and 10% by weight; polyethylene fibers were also added at 0.5, 1.0, 1.5, 2.0 and 2.5% by volume. These samples were cured for 7, 14, and 28 days and subjected to an unconfined compressive test. From the test results, the cement content of 8% by weight was the optimum, and a polyethylene fiber content of 1% by volume is recommended. Moreover, the novel high-strength polyethylene fiber with 0.2 mm in diameter and 6 mm in length provided the maximum UCS value.

Electron beam powder bed fusion additive manufacturing of Ti6Al4V alloy lattice structures: orientation-dependent compressive strength and fracture behavior

High porosity level lattice structures made using electron beam powder bed fusion additive manufacturing (EBPBF) need to be sufficiently strong and the understanding of the mechanical anisotropy of the structures is important for the design of orthopedic implants. In this work, the combined effects of loading direction (LD), cell orientation, and strut irregularity associated with EBPBF of Ti6Al4V alloy lattices on the mechanical behavior of the lattices under compressive loading have been studied. Three groups of simple cubic unit cell lattices were EBPBF made, compressively tested, and examined. The three groups were [001]//LD lattices, [011]//LD lattices, and [111]//LD lattices. Simulation has also been conducted. Yield strength (σy-L) values of all lattices determined experimentally have been found to be comparable to the values predicted by simulation; thus, EBPBF surface defects do not affect σy-L. σy-L of [001]//LD lattices is 1.8–2.0 times higher than those of [011]//LD and [111]//LD lattices. The reason for this is shown to be due to the high stress concentrations in non-[001]//LD samples, causing yielding at low loading levels. Furthermore, plastic strain (εp) at ultimate compression strength of [001]//LD samples has been determined to be 4–6 times higher than the values of non-[001]//LD samples. Examining the tested samples has shown cracks more readily propagating from EBPBF micro-notches in non-[001]//LD samples, resulting in low εp.

Modeling the influence of lime on the unconfined compressive strength of reconstituted graded soil using advanced machine learning approaches for subgrade and liner applications.

In the field of soil mechanics, especially in transportation and environmental geotechnics, the use of machine learning (ML) techniques has emerged as a powerful tool for predicting and understanding the compressive strength behavior of soils especially graded ones. This is to overcome the sophisticated equipment, laboratory space and cost needs utilized in multiple experiments on the treatment of soils for environmental geotechnics systems. This present study explores the application of machine learning (ML) techniques, namely Genetic Programming (GP), Artificial Neural Networks (ANN), Evolutionary Polynomial Regression (EPR), and the Response Surface Methodology in predicting the unconfined compressive strength (UCS) of soil-lime mixtures. This was for purposes of subgrade and landfill liner design and construction. By utilizing input variables such as Gravel, Sand, Silt, Clay, and Lime contents (G, S, M, C, L), the models forecasted the strength values after 7 and 28 days of curing. The accuracy of the developed models was compared, revealing that both ANN and EPR achieved a similar level of accuracy for UCS after 7 days, while the GP model performed slightly lower. The complexity of the formula required for predicting UCS after 28 days resulted in decreased accuracy. The ANN and EPR models achieved accuracies of 85% and 82%, with R2 of 0.947 and 0.923, and average error of 0.15 and 0.18, respectively, while the GP model exhibited a lower accuracy of 66.0%. Conversely, the RSM produced models for the UCS with predicted R2 of more than 98% and 99%, for the 7- and 28- day curing regimes, respectively. The RSM also produced adequate precision in modelling UCS of more than 14% against the standard 7%. All input factors were found to have almost equal importance, except for the lime content (L), which had an average influence. This shows the importance of soil gradation in the design and construction of subgrade and landfill liners. This research further demonstrates the potential of ML techniques for predicting the strength of lime reconstituted G-S-M-C graded soils and provides valuable insights for engineering applications in exact and sustainable subgrade and liner designs, construction and performance monitoring and rehabilitation of the constructed civil engineering infrastructure.

The surface treatment of PVA fibres to enhance fibre distribution and mechanical properties of foam concrete

Fibres are often used to improve the mechanical properties of foam concrete. However, the poor dispersion of PVA fibres in foam concrete significantly restricts their reinforcement efficiency. Limited studies have been conducted on improving the distribution of PVA fibres in a cementitious matrix, particularly in relation to foam concrete. This is noteworthy because pore structure, which can be significantly influenced by the fibres and fibre treatment agents, is a critical parameter that affects the mechanical properties of foam concrete. Therefore, this study employed polar agents (non-ionic surfactants) to treat the fibre surface, aiming to enhance the distribution and reinforcement efficiency of PVA fibres in foam concrete. In view of safety and feasibility, two non-hazardous polar agents, namely PEG-PPG-PEG (designated as PA A) and Polyoxyethylene (20) cetyl ether (designated as PA B), were used to treat the PVA fibres. The impact of fibre treatments on fibre dispersion and pore structure was investigated, and the compressive strength and flexural behaviour of foam concrete were measured before and after the treatments. PA A was found to be unsuitable for fibre treatment due to its poor bonding with the fibre surface. On the other hand, PA B exhibited good bonding with PVA fibres, resulting in enhanced fibre dispersion and pore structure in the foam concrete. Compared to plain foam concrete, the fibres treated with PA B increased the compressive and flexural strength by 47.4 % and 190.3 %, respectively. Moreover, the treated fibres (by PA B) were observed to improve the 0.8 mm toughness of foam concrete by 27.2 %.

Effects of Noncrosslinked Polyvinyl Alcohol Fluid Loss Additive on the Compressive Strength and Viscosity of Class G Cement Slurries

Summary Limiting the fluid loss from the cement slurry to the adjacent formation by using additives is essential for maintaining the slurry’s water/cement ratio. The present work focuses on the effect of noncrosslinked polyvinyl alcohol additive (PVOH), a widely used fluid loss additive (FLA), on the compression strength and rheological behavior of Class G cement pastes. Results of the current study show that the PVOH surfactant characteristic and its absorptive mechanism interfere not only with the hydration process but also with the physical properties and compressive strength of cement pastes, such as porosity, permeability, and early age strength, which revealed the importance of using a defoamer when PVOH is present in the mixture. In the absence of a defoamer, the PVOH additive generates foam in the mixed cement paste samples, which results in increased porosity and reduced compressive strength of the hardened cement paste. Moreover, regarding rheology, increasing the PVOH concentration increased the effective viscosity when evaluating flow curves. Therefore, this study demonstrates a systematic method for assessing the possible effects of cement paste additives, such as PVOH and defoamer, providing a physical and mechanical approach rather than just chemical to evaluate additives’ influence on the mixtures. This method should consider different additives in combination with PVOH to test cement paste stability and to obtain specific working recipes.

Compressive properties of AlSi10Mg lattice structures with novel BCCZZ and FCCZZ configurations fabricated by selective laser melting

PurposeThis paper aims to examine the static compression characteristics of cell topologies in body-centered cubic with vertical struts (BCCZ) and face-centered cubic with vertical struts (FCCZ) along with novel BCCZZ and FCCZZ lattice structures.Design/methodology/approachThe newly developed structures were obtained by adding extra interior vertical struts into the BCCZ and FCCZ configurations. The samples, composed of the AlSi10Mg alloy, were fabricated using the selective laser melting (SLM) additive manufacturing technique. The specific compressive strength and failure behavior of the manufactured lattice structures were investigated, and comparative analysis among them was done.FindingsThe results revealed that the specific strength of BCCZZ and FCCZZ samples with 0.5 mm strut diameter exhibited approximately a 23% and 18% increase, respectively, compared with the BCCZ and FCCZ samples with identical strut diameters. Moreover, finite element analysis was carried out to simulate the compressive response of the lattice structures, which could be used to predict their strength and collapse mode. The findings showed that while the local buckling of lattice cells is the major failure mode, the samples subsequently collapsed along a diagonal shear band.Originality/valueAn original and systematic investigation was conducted to explore the compression properties of newly fabricated lattice structures using SLM. The results revealed that the novel FCCZZ and BCCZZ structures were found to possess significant potential for load-bearing applications.

The role of intrinsic soil properties in the compressive strength and volume change behavior of unstabilized earth mortars

Despite the growing interest in earthen construction, there is critical lack of reliable experimental data on the soil properties which mostly affect the engineering characteristics of the dried building material. Therefore, the main objective of this research was to explore the influence of some of these properties, namely clay fraction content, Specific Surface Area (SSA), Cation Exchange Capacity (CEC), chemical and mineralogical composition and various forms of iron and calcium carbonate on earth mortars. The initial trigger for this research was the extraordinary compressive strength of four earth mortars prepared with different soils. So, these four soils, along with seven others from previous research, were thoroughly examined using soil science techniques to investigate the link between soil properties and compressive strength and linear shrinkage of earth mortars. A relationship between the compressive strength to CEC ratio and dry density was found, highlighting the decisive role of clay activity as expressed by CEC, in earthen materials properties. According to linear regression and dominance analysis, the strongest correlation was exhibited by SSA followed by CEC, demonstrating that compressive strength is largely dependent on these two properties. Less strong correlation was found for clay fraction content, while poorly ordered/amorphous iron oxides were found to correlate with strength and shrinkage, but their contribution requires further research. Regarding the mineralogical properties, it was found that the mortars that achieved the highest strengths contained poorly crystalline smectite clays. Finally, even significant differences in soil chemical composition did not necessarily lead to different mortar properties.

Rheological and mechanical behavior study of eco-friendly cement mortar made with marble powder

The work aim is to investigate the rheological and mechanical behavior of eco-friendly mortar made with marble powder. Marble have used as sand by total substitution of natural sand and as additional materials by partial substitution of cement. Firstly, rheological tests were carried out on the cement pastes in order to studying the effect of cement substitution by marble powder on the rheological behavior. Secondly, our study is devoted to evaluate the mechanical performances (flexural strength, compressive strength, mechanical behavior and ultrasonic pulse velocity) of a fluid mortar such as the case of the self-compacting mortars elaborated with the marble powder as addition materials and as a sand. The mechanical test results show that a significantly improved of compressive strength and mechanical behavior of an ecological cement mortar made with marble waste as a natural sand. However, marble-based mortars with 100% of marble sand have given a mechanical strength similar to that obtained by control cement mortar (100% natural sand). It was also noted that it can be obtained an ecological cement mortar made with 30% of marble powder as an addition supplementary materials. This leads to a reduction in cement consumption cad a reduction in CO2 gas emissions caused by cement production.

Investigations into magnesium oxide carbon sequestration foamed concrete: Mechanical performance, microstructure and environmental benefits

This paper proposes an innovative preparation measure for magnesium oxide (MgO)-based foamed concrete. Carbon dioxide (CO2) foam has been introduced into the sample as a substitute for air foam, resulting in a novel formulation referred to as MgO carbon sequestration foamed concrete (MCFC). This innovation facilitates the setting and hardening of MgO-based foamed concrete under ambient conditions. Basic mechanical properties were tested at three different ages. At the age of 28 days, the resultant MCFC has demonstrated mechanical performance comparable to conventional Portland cement-based foamed concrete including unconfined compressive strength and stain-stress behavior. Through SEM NMR and X-ray CT, the MCFC sample exhibited an increasingly compact matrix and an evolving distribution of pore structure as time progressed. Furthermore, a comprehensive life cycle assessment has revealed that MCFC has the potential to reduce carbon emissions by up to 50% when compared to conventional cement-based foamed concrete. The results imply that MCFC presents itself as a viable alternative to conventional PC-based foamed concrete, offering equivalent mechanical performance while delivering superior environmental advantages for engineering applications.

Optimization of non-bearing splice connection in GFRP short columns by manual testing and finite element analysis

Connection designs are established to ensure the stability of joined cut sections, the joints so designed should be based on the optimal performance as per the requirements. The connection joints so established should not be based on just strength but reliability and durability as well. This study focuses on tackling one of the major issues faced when using Glass Fibre Reinforced Polymers (GFRPs) as construction materials, which is based on the abrupt failure of the material under critical or maximum loading. Connection designs are established in GFRP short column H-sections based on Bolted Splicing connections by Eurocode 3 for steel splicing connections. A total of seven Connection designs are established using bearing and non-bearing splicing connections. A total of five models for each connection is established for manual testing and Finite Element Analysis (FEA) is used to simulate and analyze these connection designs. Parameters such as ultimate load, displacement at ultimate load, stiffness, compressive strength, failure mode, load versus displacement behavior graph, and percentage compressive strength compared to the un-cut section are provided in this study. The strongest specimen in this study displaced 128% and 127.7% compressive strength compared to an un-cut GFRP H-section when tested using manual testing and FEA accordingly.

A comprehensive assessment of green concrete incorporated with municipal solid waste incineration bottom: Experiments and life cycle assessment (LCA)

To reduce the high carbon emissions in the concrete field and facilitate the sustainable development of concrete, in this study, we repurposed high-volume municipal solid waste incineration bottom ash (MSWIBA) as a supplementary cementitious materials (SCMs) for the production of concrete at different percentages (0%, 10%, 20%, 30%, 40%, 50% and 60%). The influence of MSWIBA on the compressive strength, hydration, microstructure and heavy metal leaching behaviour of concrete was investigated. The results showed that a high volume of MSWIBA will reduce the compressive strength (from 56.81 MPa to 12.65 MPa) because aluminium produces hydrogen in an alkaline environment and excessive incorporation of MSWIBA leads to insufficient active substances. The content of ettringites and calcium silicate hydrate (C-S-H) initially increases (from 0.286 ％ to 0.405 ％ and from 0.635 ％ to 0.893 ％) and subsequently decreases (from 0.405 ％ to 0.275 ％ and from 0.893 ％ to 0.500 ％) as the proportion of MSWIBA in the mixture gradually increases due to the aluminium salt content reacting with the sulfate and pozzolanic reactivity of MSWIBA. In addition, compared with those in MSWIBA, the amounts of leachable hazardous ions (Cu, Pb, Cr, As and Hg) in concrete were effectively reduced by 87.1%, 83.3%, 70.0%, 90.3%, and 89.3%, respectively. Additionally, the measured heavy metal leaching met Chinese specification requirements. Life cycle assessment (LCA) was employed to evaluate environmental impacts (EIs), and it was found that using MSWIBA as a SCM can reduce the EI by 7.5 ％− 44.1 ％ (from 2.58E-11 to 1.56E-11) when the replacement cement ratio of MSWIBA is from 10 ％ to 60 ％. By normalizing the EI indices, it was found that the global warming potential (GWP) and eutrophication potential (EP) were the main contributors to the EI. Finally, a model was established to assess the comprehensive performance, including the environmental impact, compressive strength, porosity, apparent density, and ecology-strength efficiency, of the different MSWIBA formulations, and the comprehensive performance improved when the MSWIBA percentage was 30%.

Comparative analysis of self-cure and dual cure-dental composites on their physico-mechanical behaviour.

Clinical practitioners may have become familiar with the rapid transformation of dental composites. However, they may not scientifically understand the factors influencing the mechanical and physical properties. Scientific knowledge of filler-resin interaction can significantly improve clinical understanding of resin composites. Several independent studies have examined the mechanical and physico-mechanical properties of dental resin composites; however, no comprehensive study has examined the influence of fillers and resin materials on the physico-mechanical properties of both self-cure and dual-cure composites. This study performed investigations on the physico-mechanical behaviour of four commercially available dual-cure dental composites (Bioactive, Fill Up!, Surefil One, Cention N) and two commercially available self-cure dental composites (Stela Capsule and Stela Automix). Test specimens for flexural and compressive strength, microhardness, fracture toughness, and hydrolytic behaviour were prepared and tested as per respective standards. The data sets were statistically analysed using one-way ANOVA and Tukey's post-hoc comparison. There was a substantial variation in flexural strength and modulus values in this study, ranging from 32.0 to 113.4 MPa and 2.36 to 12.07 GPa, respectively. Similarly, there were significant differences in compressive strength between the materials in this study, ranging from 119.3 to 223.5 MPa. The highest fracture toughness value was found to be 1.41 MPa.m0.5 , while the lowest value was 0.43 MPa.m0.5 . Variations in surface microhardness were significant (24.11-68.0 N/mm2 ), which correlated with the filler content. Water sorption and solubility demonstrated high variations among materials, with Surefil One exceeding ISO 4049 thresholds significantly. A linear correlation can be established between surface microhardness (HV) and flexural and compressive moduli, as well as filler content (wt.%). However, both flexural and compressive strengths are impacted by the resin's constituent monomers and the resin-filler matrix's cross-linking capability. Additionally, factors such as filler size, shape, and the cross-linking ability of the resin-filler matrix play a crucial role in fracture toughness and the propagation of cracks within the restoration. Also, resin monomers and filler particle size affect the hydrolytic degradation characteristics of composites, which can also affect their mechanical properties. © 2023 Australian Dental Association.

The Effects of Steel Fibres and Expansive Agents on the Compressive Behaviour of Circular Concrete-Filled Steel Tube Columns (CFSTCs)

Concrete filled steel tube columns (CFSTCs) are commonly used in large-span bridges and high-rise buildings. As the shrinkage of concrete may lead to significant degradation in the mechanical performance of CFSTCs, expansive concrete or fibre reinforced concrete is usually employed to improve the mechanical performance of CFSTCs. This study presents an experimental analysis of the combined effects of expansive agents and steel fibres on the axial compressive behaviour of circular CFSTCs. 13 CFSTCs were designed and manufactured using concrete mixes with varying expansive agent rates and steel fibre contents. The time-dependent expansive behaviours of the specimens were monitored during the concrete curing period. Then, the 13 specimens were tested under axial compression load. The failure modes, compression load-axial strain relationship, hoop strain and axial strain relationship, and ductility were investigated. The results demonstrated that the combined addition of expansive agents and steel fibres would substantially improve the compressive strength and ductile behaviour of CFSTCs.

Experimental and FEA Analysis of Bonded Connection in Glass Fiber-reinforced Polymer Short Column

Glass Fibre Reinforced Polymer (GFRP) is a synthetically manufactured material that is derived by compressing multiple layers of glass fiber in a resin matrix. GFRPs can be used as compressive members and hold good compressive strength. These materials display a brittle mode of failure at maximum loading and this aspect is the major disadvantage of these materials. This study intends to tackle this disadvantage by designing and analyzing a connection method called non-bearing spliced connection by Eurocode 3 based on BS EN 1990 and BS EN 1991 guidelines. The connections are established using only bonding as the type of connection. There are two types of bonds established in this study based on the thickness of the epoxy used to establish the bonded connection. A 2 mm thick bond and a 5 mm thick bond are used to create 5 samples of each bond thickness samples. A detailed study of their behavior is established in this study by testing them manually and by using Finite Element Analysis (FEA). The required properties such as failure load, maximum displacement, stiffness, compressive strength, failure modes, and load versus displacement graph behavior are compared and explained in detail in this study.

Continuous surface cap model for ultra-high-performance concrete under static and low strain rate loadings: Calibration, experiment, and simulation

The ultra-high compressive strength and ductile tensile behavior of ultra-high-performance concrete (UHPC) make it promising in the application of civil and crashworthy facilities. Although numerous experimental studies have been conducted to investigate the performance of UHPC, studies on the methods for simulating the behavior of UHPC are few. In this paper, an overview of widely used constitutive models of concrete-like materials in hydrocode was presented first, and then a comprehensive calibration of the continuous cap surface (CSC) model was performed to simulate the mechanical behavior of UHPC under static and low strain rate loadings. Four groups of parameters: (1) failure surface parameters; (2) cap and hardening parameters; (c) damage parameters; and (4) strain rate parameters were systematically calibrated via extensive available material test data of UHPC with uniaxial compressive strength ranging from 101 MPa to 238 MPa. A calculation method was proposed to address the inconsistency of existing conclusions regarding the fracture energy of UHPC, which significantly affects the modeling of UHPC damage. Moreover, a method was proposed to convert the engineering uniaxial tensile strain of UHPC to the true uniaxial tensile strain, and so does the tensile fracture energy of UHPC. To validate the accuracy of the calibrated CSC model in simulating the behavior of UHPC under static loading, uniaxial tension and compression tests of UHPC samples and three-point bending tests of steel-UHPC-steel composite beams were conducted and simulated. Existing triaxial compression tests of UHPC cylinders were simulated to validate the accuracy of the calibrated CSC under confinement. Moreover, low-velocity impact tests of UHPC columns were simulated to further validate the reliability of the calibrated CSC model to capture the structural behavior of UHPC members under low strain rate loading. It was found that the calibrated CSC model showed excellence in simulating the material properties of UHPC and the structural behavior of UHPC members under static and low strain rate loadings.

Significant reduction in friction and wear of an ultrafine-grained single-phase FeCoNi alloy through the formation of nanolaminated structure

Reducing friction and wear has long posed a challenge for metallic components under dry sliding conditions. This study unveils a significant reduction in friction and wear of a single-phase ultrafine-grained FeCoNi multi-principal element alloy (MPEA). Through a comparative analysis of the sliding wear behaviors of single-phase ultrafine-grained CoCrFeMnNi and FeCoNi alloys with different stacking fault energies and detailed microstructure characterization, we found that despite having a similar initial microstructure and even a 20% lower hardness, the FeCoNi alloy exhibited a remarkable 52% reduction in coefficient of friction, and more notably, a wear rate three orders of magnitude lower than that of CoCrFeMnNi. The significantly reduced friction and wear can be attributed to the remarkable disparities in wear-induced surface microstructures between the two alloys during repetitive sliding. The sliding wear of FeCoNi alloy triggers the formation of a nanolaminated structure with excellent strain-hardening capacity and substantial deformation plasticity, as evidenced by micropillar compression tests. Conversely, the twinning-active CoCrFeMnNi alloy induces the formation of an equiaxed nanograin layer which exhibits a high compressive strength but catastrophic failure behavior after the onset of yielding, and thus deteriorates the wear resistance. The findings provide significant insights into fundamental understanding of the plastic deformation of single-phase MPEAs during wear and guide the design of wear-resistant alloys.