Continuous Increase In Strength Research Articles

Shear banding suppression in Cu/TiZrNb nanolayered composites through dual crystalline/amorphous interfaces

Medium/high entropy alloys (M/HEAs)-based nanolayered composites have attracted intense scientific interest due to the improved mechanical properties. However, the shear banding (or shear instability) behavior of the M/HEAs-based nanolayered composites is rarely studied due to the lack of theoretical model to quantify the shear banding-induced strain localization. Herein, the size-dependent strengthening and shear instability behavior of Cu/amorphous TiZrNb nanolayered composites with individual layer thickness (h) of 2–100 nm was systematically investigated by using a combination of nano/microindentations and a detailed theoretical analysis. The results show that the strength of the Cu/TiZrNb composites obeys the trend of “smaller is stronger”. The size-dependent strengthening behavior of the samples with h in the range of 10–100 nm can be well described by the confined layer slip model, while the continuous increase in strength of those with h = 2 and 5 nm is related to the gradually amorphization of the Cu layers. It is intriguingly found that the shear instability of the Cu/TiZrNb composites shows a first-decrease-and-then-increase size dependence, which is apparently different from that of existing face-centered cubic/amorphous nanolayered composites that exhibits a monotonic size dependence. The non-monotonic trend leads to a significantly suppressed shear instability in the sample with h = 50 nm, in which only slight kinks are observed in microindentation. The enhanced resistance to shear banding is attributed to the dual crystalline/amorphous interfaces generated by the layered structure and the amorphous TiZrNb constituent layers that contains crystalline phase at h > 10 nm.

Setting time, sulfuric acid resistance, and strength development of alkali-activated mortar with slag & fly ash binders

This study evaluated the effect of initial molar ratios SiO2/Al2O3 and (CaO + SiO2)/Al2O3, on the setting time of mortar with alkali-activated Ground Granulated Blast Furnace Slag (GBS) and fly ash (FA) binders. The study also evaluated the chemical resistance of alkali-activated mortar and the effect of NaOH alkaline activator on resistance to sulfuric acid in particular. Mortar samples were cured at 22 ± 2 °C and 70% relative humidity (RH). Three GBS/FA binder combinations were evaluated: 1:1, 3:1, and 1:0 (100% GBS). Activation was done using a combination of sodium hydroxide, with concentrations from 10 mol/L to 16 mol/L, combined with sodium silicate solution. Chemical resistance was evaluated by immersing mortar samples in sulfuric acid. Geopolymer mortar samples cured in an open system exhibited an increase in compressive strength from the age of 1 day–28 days. However, at the age of 90 days, all air-cured mortar samples, irrespective of activator concentration, decreased in strength. Similar mortar specimens immersed in sulfuric acid 24 h after casting exhibited a continuous increase in strength until the age of 90 days. Water evaporates from an open system which may cause partial precipitation of dissolved silicates rather than the formation of geopolymer products. The medium containing the sulfuric acid provided a closed system simulating a physical barrier against evaporation, and making dissolved silicates available to participate in the formation of geopolymerization products. Setting time was found to have a stronger correlation with the initial molar ratio of (CaO + SiO2)/Al2O3, than the molar ratio SiO2/Al2O3. Several mathematical models for predicting splitting tensile strength were developed and the goodness-of-fit to test data was evaluated using the integral absolute error (IAE).

Multiscale insights into mechanical performance of a granite-based geopolymer: Unveiling the micro to macro behavior

Geopolymers (GPs), based on rocks and similar (waste) materials, have shown promising features as alternatives to Ordinary Portland Cement (OPC) in many applications. The properties of these materials can be tailored to a large degree, to meet the requirements of specific applications. This study presents a two-part granite-based GP system developed for wellbore sealant applications in Carbon Capture and Storage (CCS) operations. The system was modified by incorporating different concentrations of a Zn–K-based retarder. The performance of the GP system was then evaluated through consistency analyses, and uniaxial compressive strength (UCS) measurements. Further, the in-situ mechanical attributes of the GP system were assessed through tri-axial experiments at 90 °C and under varying confining pressures. Additionally, the morphology, mineralogy, and chemical composition of the hardened GP system were analyzed using X-ray diffraction (XRD), scanning electronic microscopy with energy dispersive spectroscopy (SEM-EDS), and Fourier transform infrared spectroscopy (FTIR). Consistency analyses revealed that slurries with higher retarder content exhibited improved fluidity but also longer setting times, which could result in fluid invasion and integrity issues. Accordingly, slurries with appropriate setting behavior were identified, striking a balance between rapid strength development and sufficient fluidity for downhole applications. The appropriate flow characteristics of the slurries and the stability of the solidified materials were also verified through rheological assessments, free-fluid tests, and sedimentation analyses. UCS measurements showed a continuous increase in strength for all GP samples, with optimized retarder content yielding the highest late-age mechanical strength. Tri-axial experiments showed that the in-situ Poisson's ratio, compressive strength, and compressive strength to Young's modulus ratio (C/E) of the GP system could be enhanced by 86.79%, 40.26% and 13.05%, respectively, through retarder content optimization. Furthermore, compressive strength and C/E ratios increased with higher confining pressure, while Poisson's ratio remained relatively constant. Moreover, XRD analyses revealed a transition from amorphous to crystalline phases within the GP system, depending on the retarder content, indicating enhanced network connectivity and the formation of new crystalline structures. FTIR analyses supported these observations, demonstrating the formation of new crystals and robust amorphous gels, indicating improved polycondensation and network connectivity in the GP system. Besides, SEM analysis of fractured samples exhibited distinct microstructural characteristics depending on the retarder content, with the optimized retarder content leading to higher crystallinity and more interconnected gel structures. These findings highlight the significance of microscale analysis alongside macroscale assessments when studying GP systems.

Effect of HPT straining and further natural aging on the structure and hardness of aluminum alloy 1965 with nanosized TM aluminides

Pre-quenched samples cut from a homogenized ingot of commercial aluminum alloy 1965 with a grain size of about 21 µm were compressed at 6 GPa and then strained by torsion up to 10 revolutions at room temperature. TEM, SEM and XRD analyses showed that the strengthening / softening of the alloy during further natural aging up to 500 hrs was controlled by simultaneous decomposition of the aluminum solid solution and recovery of its deformation structure. It was found that the two-level nanostructuring of the alloy (precipitates and matrix) is accompanied by more than twofold strengthening up to a hardness of about 250 HV. The main contribution was made by dislocation and structural hardening due to the formation of a highly work-hardened structure of the nanofragmented type. During subsequent aging, the change in hardness was controlled by both the preliminary strain and the aging time. A continuous increase in strength with strain and aging time was found in the samples after pressing and torsion up to 1 revolution. In other conditions, strengthening was preceded by softening, the magnitude and duration of which were also proportional to the strain. The nature of the alloy behavior and the role of nanosized aluminides of transition metals are discussed in details.

A sustainable approach in using construction and demolition waste materials in concrete

Purpose The purpose of this paper is to investigate the potential use of construction and demolition waste materials (C&DWM) as an alternative for natural fine aggregates (NFA), in view to solve the disposal problems caused due to landfills. In addition, to evaluate its suitability as a sustainable material, mechanical and durability properties have been performed on different proportions of concrete blending and the results recorded were compared with the reference concrete values. Design/methodology/approach In this research, the NFA were replaced at the proportion of 25%, 50%, 75% and 100% of C&DWM with a constant slump range of 130 mm–150 mm. This parameter will assess the consistency of the fresh concrete during transportation process. The characteristics of the end product was evaluated through various tests conducted on hardened concrete samples, namely, compressive strength, flexural strength, depth of penetration of water under pressure, rapid chloride penetration test, carbonation test and ultrasonic pulse velocity (UPV) test. All results recorded were compared with the reference concrete values. Findings The results demonstrated that the use of C&DWM in concrete portrayed prospective characteristics that could eventually change the concept of sustainable concrete. It was noted that the compressive and flexural strength decreased with the addition of C&DWM, but nevertheless, a continuous increase in strength was observed with an increase in curing period. Moreover, the increase in rapid chloride penetration and decrease in UPV over time period suggested that the concrete structure has improved in terms of compactness, thus giving rise to a less permeable concrete. The mechanical tests showed little discrepancies in the final results when compared to reference concrete. Therefore, it is opined that C&DWM can be used effectively in concrete. Originality/value This study explores the possible utilisation of C&DWM as a suitable surrogative materials in concrete in a practical perspective, where the slump parameter will be kept constant throughout the experimental process. Moreover, research on this method is very limited and is yet to be elaborated in-depth. This approach will encourage the use of C&DWM in the construction sector and in the same time minimise the disposal problems caused due to in landfills.

Investigation of flexural and creep behavior of epoxy-based nano-sized CaTiO3 particles

Abstractss Superior mechanical properties are the most needed in today’s new-made composites. Epoxy resins good properties make it a good choice to be used for making composites with desired requirements. However often, the inherent properties of the polymer alone are insufficient to meet the structural demands of an application. The major concern for polymeric material is its structural stability under constant loadings for long-term service. Targeting these issues, the current work investigates experimentally the flexural and creep behavior of polymer nanocomposites. For this purpose, different sets of polymer nanocomposites of epoxy resin (EPR) mixed with differing amounts of calcium titanate (CaTiO3) nano-particles and glass fiber (GF) were prepared. The flexural strength, flexural modulus, deflection at the peak were determined. Besides, the creep behavior was monitored by testing different samples for a duration of 24 ​h and the results show that good creep behavior was attended by adding glass fibre. Also, it was noted that the flexural strength at yield increases with increasing filler amount from 1 ​wt% to 7 ​wt%. However, the flexural strength at peak increases with increasing of filler up to 5 ​wt%. Moreover, by adding GF the flexural strength at the peak has a fluctuating change from decreasing to increasing at 0.1 ​wt % GF while adding 0.2 ​wt % of GF gives a continuous increase in strength.

Influence of metakaolin on the conversion and compressive strength of quaternary phase paste

AbstractApplication of calcium aluminate cement in construction faces the challenges of high manufacturing cost and volumetric instability associated with hydrates conversion. This work introduces a newly developed high‐performance Ca20Al26Mg3Si3O68 (Q phase)‐metakaolin (MK) composite binder. The influence of MK on the conversion and strength development of Q phase paste cured at 40°C was investigated. The mechanism of MK on the stability of synthetic hydrate was studied by solution chemistry, XRD, and NMR. The pure Q phase paste experiences a significant strength reduction due to hydrates conversion, whereas the Q phase paste containing 15% MK exhibits a continuous increase in strength. MK promotes the formation of CAH10, contributing to the refinement of pore structure and enhanced mechanical property. The AlV and AlIV dissolved from MK increase the concentration in the pore solution, and then the solubility of CAH10 decreases due to the common‐ion effect, thus inhibiting the subsequent precipitation of C3AH6. In addition, the release of dissolved alumina from MK considerably impedes silica dissolution, and consequently, the formation of C2ASH8 is hindered at a higher content of MK.

Cement-Free Refractory Concretes. Part 1. General Information. Hcbs and Ceramic Concretes

The general nature of the dependence of engineering and service characteristics of refractory concretes with an average cement content, and also low-cement (LCRC), ultra-low cement (ULCRC) and cement-free (CFRC), on the content of CaO (or HAC) in them is analyzed. Significant advantages of cement-free concretes are the reduced moisture content of the concrete mixture, which determines their increased density, a continuous increase in strength (absence of a softening temperature range typical for LCRC and ULCRC), and improved thermomechanical and operational characteristics. With use of CFRC, the insurmountable complexity of the LCRC and ULCRC connected with their initial heating in the dehydration temperature range of the HAC (up to 450°C) is resolved. The main provisions and stages of creating HCBS or artificial ceramic binders as a matrix system of ceramic concrete, i.e., LCRC with improved characteristics, are described. Classification of HCBS groups proposed by the author based on the chemical nature of their solid phase is considered.

Performance of Cement Mortar Exposed to Different Temperature and Curing Methods

Curing is an important process to achieve the specified concrete strength and durability. The objectives here is to determine the effect of four curing regimes on the development of mechanical properties for mortar specimens with mix proportions of 1:2.75 cement to sand by mass with W/C of 0.46, and with standard cube and prism dimensions, using OPC and SRPC; specimens tested under curing temperatures at 25 °C and 45 °C; to simulate the seasonal climatic conditions in Iraq. Curing methods adopted were: 1st: immersion in water, 2nd: wetting by using saturated covers, 3rd: curing by using wax-based compound, and 4th: by air curing. The specimens were examined at the ages of 3, 7, 14, and 28 days for density and mechanical properties. The study highlights that fully-saturated specimens in water is the recommended curing; as test results indicate that the highest mechanical properties were obtained. Considering the compressive strength as the criterion, curing by using wax-based compound came 2nd; and curing by saturated covers in 3rd position. This is true for temperatures at 25 °C and 45 °C; however, the experiments carried on OPC mortar show that increasing the temperature from 25 °C to 45 °C increases the early strength at 3 and 7 days by 16% and 22%, respectively; while the strengths at 14 and 28 days indicate an opposite manner; as the strength decreases when comparing the testing results at those ages by 23% and 17%. This is also valid for SRPC mortar and water-immersion curing for the same temperatures and corresponding ages; 25% and 19% increase at 3 and 7 days, respectively; but the results show that there was a continuous increase in strength at 14 and 28 days, by 29% and 33%, respectively. The study points out that immersion-curing in high temperatures is not recommended for OPC mortars after the age of 7 days; while it could be used for SRPC mortars.

The Effect of Processing Pass on the Microstructure and Mechanical Properties of a Friction Stir Processed As-Cast Mg-6 wt % Sn Alloy

In this study, as-cast Mg-6 wt % Sn alloy is subjected to one-pass and two-pass friction stir processing (FSP). The effect of processing pass on microstructure and mechanical properties of FSP Mg-6Sn alloy is investigated. It is found that one-pass FSP leads to the breakage and partial dissolution of the Mg2Sn phase in the stir zone (SZ) and two-pass FSP leads to the further dissolution and dynamic precipitation of the Mg2Sn phase. Dynamic recrystallization (DRX) takes place in the SZ of an Mg-6Sn alloy undergoing FSP. Compared to one-pass FSP, two-pass FSP brings about further grain refinement in the SZ. A strong {0001} basal texture is developed in the SZ of a Mg-6Sn alloy from FSP and the change of the sample region or processing pass has little influence on the texture. Compared to an as-cast Mg-6Sn sample, one-pass FSP brings about significant improvement in mechanical properties. Two-pass FSP leads to the further increase in yield strength (YS) and ultimate tensile strength (UTS) but elongation (EL) is reduced. The continuous increase in strength is attributed to the grain refinement and the dissolution and dynamic precipitation of Mg2Sn phase achieved by FSP.

Effect of Input Source Energy on SASW Evaluation of Cement Concrete Pavement

A series of spectral analyses of surface waves (SASW) tests were conducted on a cement concrete pavement by dropping steel balls of four different values of diameter (D) varying between 25.4 and 76.2 mm. These tests were performed (1) by using different combinations of source to nearest receiver distance (S) and receiver spacing (X), and (2) for two different heights (H) of fall, namely, 0.25 and 0.50 m. The values of the maximum wavelength (λmax) and minimum wavelength (λmin) associated with the combined dispersion curve, corresponding to a particular combination of D and H, were noted to increase almost linearly with an increase in the magnitude of the input source energy (E). A continuous increase in strength and duration of the signals was noted to occur with an increase in the magnitude of D. Based on statistical analysis, two regression equations have been proposed to determine λmax and λmin for different values of source energy. It is concluded that the SASW technique is capable of producing nearly a unique dispersion curve irrespective of (1) diameters and heights of fall of the dropping masses used for producing the vibration, and (2) the spacing between different receivers. The results presented in this paper can be used to provide guidelines for deciding about the input source energy based on the required exploration zone of the pavement.

VERSATILE ROSELLE GRAFT-COPOLYMERS: XRD STUDIES AND THEIR MECHANICAL EVALUATION AFTER USE AS REINFORCEMENT IN COMPOSITES

Roselle is rich in cellulose content and exists as waste bio-mass in abundance thorough-out the world. It has low weight and high tensile strength that promotes its use as backbone for graft copolymerization. Various reaction parameters for the graft co-polymerization of effective acrylate monomer onto stem fiber were optimized and used in binary mixture with six vinyl monomers to screen the change in properties of the fiber. These graft copolymers were characterized by advanced analytical techniques and evaluated for mechanical strength after being incorporated in polymer matrix based composite as reinforcement. . Cellulosic fiber possesses both crystalline and amorphous regions. The x-ray pattern of the crystalline polymer shows sharp peaks associated with the region of three dimensional order and the diffused features are characteristics of the molecularly disordered substances coexisting within itself. Lower crystallinity means higher amorphous content that may be more accessible to chemicals and water. Crystallinity is correlated to the strength of the fiber. On grafting crystal lattice of the polymer is disrupted but the strength of the material may add to reinforce the structure. However, if crystallinity is not affected on grafting then a continuous increase in strength can be obtained 11-14 . Hibiscus sabdariffa (Hs, Roselle) is found in abundance in nature through-out and has attained prominence as a jute substitute and attempts are being made to extend its cultivation in areas which are not favorable for jute cultivation. Good mechanical properties were found when injection-molded isotactic polypropylene/Roselle fiber composites were studied 15-16 , but still remain unexplored for its viability as substrate to grafting by vinyl monomers. The versatility of this chemical technique inspired the thoughts to implement it on the virgin Roselle fiber by using effective n-butyl acrylate as a principal monomer and its binary mixtures with acrylonitrile, 4-vinyl pyridine, methyl acrylate, acrylic acid, acrylamide and vinyl acetate to screen the change in the percentage grafting, morphology, crystallinity by FTIR, SEM and XRD studies and use the raw and the grafted fiber as reinforcement in Phenol- formaldehyde polymer matrix to form fiber -reinforced- composite for its comparative mechanical accreditation. The morphological transformation after use of binary vinyl monomeric mixtures for grafting by XRD and use of Sereni graft copolymers as reinforcement in polymer matrix based composites still remains unexplored.

Mechanical, microstructure and texture properties of interstitial-free steel and copper subjected to equal channel angular extrusion and cold-rolling

Interstitial-free steel and OFHC copper were subjected to 8 passes, route BC room temperature ECAE followed by cold-rolling up to 97.5% thickness reduction. Uniaxial tensile tests and Electron Back-Scattering Diffraction were used to characterise the evolution in mechanical properties, microstructure refinement and micro-texture. IF-steel showed continuous increase in strength whereas Cu returned reduced strength and a small gain in ductility at 97.5% reduction. In both metals substructure refinement was accompanied by an increase in high-angle boundary fraction, average misorientation and a slight increase in Σ3 boundaries. An evolution of crystallographic orientations from negative shear to predominantly cold-rolled textures after 95% and 97.5% reduction was observed in both metals.

Effect of grain shape and angularity on the undrained response of fine sands

The objective of this paper is to discuss the effect of grain shape and angularity on the undrained behaviour of sands. Four fine to medium (D50= 0.15–0.29 mm) and uniform sands were examined. These sands have similar and (or) identical grading curves, but differ with respect to the angularity of their grains. Under the electron scanning microscope two sands have rounded grains and the other two have subangular to angular grains. For sands with rounded grains, evidence of undrained behaviour undergoing systematic weakening (shear stress reduction after a transient peak deviator stress) is provided by torsional hollow cylinder tests. However, sands with the same grading curve and void ratio, but angular grains, show stable response with a continuous increase in strength after a transient peak. A small variation in the sand gradation, i.e., D50= 0.22 ± 0.07 mm, does not appear to alter the pattern of undrained response described earlier, with the angular sand (D50= 0.15) exhibiting stable response to shear and the rounded sands (D50= 0.22 and 0.29) having unstable response to shear. The stiffness characteristics of the sands are also presented. Triaxial compression tests were performed to confirm the pattern of response observed under torsional testing.

Comparison of two fine sands under torsional loading

In this paper the behaviour of two “standard research sands”, widely used for experimental purposes, is compared in a torsional hollow cylinder apparatus under monotonic and cyclic loading conditions. Both sands are fine and uniform with D50= 0.22 and 0.29 mm, respectively. However, their response to undrained monotonic loading at similar void ratios is dramatically different, with the finer sand showing strength reduction after peak and the coarser sand showing continuous increase in strength with torsional shear. The difference in response is mainly attributed to grain angularity and to a lesser degree to their grading. The results of drained torsional hollow cylinder tests show initial contraction followed by dilation. The stress ratio at phase transformation is uniquely defined by both drained and undrained tests for each sand. Cyclic loading instability is manifested by a sudden increase in shear strain and excess pore-water pressure leading to initial liquefaction. The instability initiates across the instability line for the sand showing strength reduction and across the phase transformation line for the sand showing continuous increase in strength with shearing. Both lines are defined under monotonic loading conditions. The liquefaction, stiffness, and damping characteristics of the sands are given in this paper.

Calcium Phosphate‐Based Resorbable Ceramics: Influence of MgO, ZnO, and SiO2 Dopants

Resorbable calcium phosphate (CaP)‐based biomaterials are important because they can significantly improve health care by shortening the time necessary for restoration of functional loading of grafted bones. Although synthetic CaPs show exceptional similarities to natural bone, however, they are deficient in one major area, in that they do not have the same mineral content of bone. The focus of our work is to understand the influence of dopants on the physical, mechanical, and biological properties of tricalcium phosphate (TCP) resorbable ceramics with special emphasis toward in vitro strength degradation and cell–materials interactions as a function of time. For this purpose, β‐TCP was doped with magnesia (MgO), zinc oxide (ZnO), and silica (SiO2). Those dopants were added as individual dopants, and their binary and ternary compositions. It was found that these dopants significantly influenced densification behavior and as sintered microstructures of TCP. In vitro mineralization studies in simulated body fluids (SBF) for 12 weeks showed apatite growth on the highly porous compositions either on the surface or inside. From scanning electron microscopic analysis it was evident that surface degradation occurred on all compositions in SBF. Compression strengths for samples up to 12 weeks in SBF showed that it is possible to tailor strength loss behavior through compositional modifications. The highest compression strength was found for binary MgO–ZnO doped TCP. Overall, samples showed either a similar strength level during the 12 weeks test period, or a continuous decrease or a continuous increase in strength depending on dopant chemistry or amount. In vitro human osteoblast cell culture was used to determine influence of dopants on cell‐materials interactions. All samples were non‐toxic and biocompatible. Dopant chemistry also influenced adhesion, proliferation, and differentiation of osteoblastic precursor cell line 1 (OPC1) cells on these matrices.