Flexural Strength Research Articles

Enhanced Degradability of Thiol-Ene Composites through the Inclusion of Isosorbide-Based Polycarbonates.

Open reduction internal fixation metal plates and screws remain the established standard-of-care for complex fracture fixation. They, however, have drawbacks such as limited customization, soft-tissue adhesions, and a lack of degradation. Bone cements and composites are being developed as alternative fixation techniques in order to overcome these issues. One such composite is a strong, stiff, and shapeable hydroxyapatite-containing material consisting of 1,3,5-triazine-2,4,6-trione (TATO) monomers, which cures through high energy visible light-induced thiol-ene coupling (TEC) chemistry. Previous human cadaver and in vivo studies have shown that patches of this composite provide sufficient fixation for healing bone fractures; however, the composite lacks degradability. To promote degradation through hydrolysis, new allyl-functionalized isosorbide-based polycarbonates have been added into the composite formulation, and their impact has been evaluated. Three polycarbonates with allyl functionalities, located at the termini (aPC1 and aPC2) or in the backbone (aPC3), were synthesized. Composites containing 1, 3, and 5 wt % of aPCs 1-3 were formulated and evaluated with regard to mechanical properties, water absorption, hydrolytic degradation, and cytotoxicity. Allyl-functionalized polycaprolactone (aPCL) was synthesized and used as a comparison. When integrated into the composite, aPC3 significantly impacted the material's properties, with the 5 wt % aPC3 formulation showing a significant increase in degradation of 469%, relative to the formulation not containing any aPCs after 8 weeks' immersion in PBS, along with a modest decrease in modulus of 28% to 4.01 (0.3) GPa. Osteosyntheses combining the aPC3 3 and 5 wt % formulations with screws on synthetic bones with ostectomies matched or outperformed the ones made with the previously studied neat composite with regard to bending stiffness and strength in four-point monotonic bending before and after immersion in PBS. The favorable mechanical properties, increased degradation, and nontoxic characteristics of the materials present aPC3 as a promising additive for the TATO composite formulations. This combination resulted in stiff composites with long-term degradation that are suitable for bone fracture repair.

High-strength tile production from yellow clay with high silicon dioxide content and its reflection in ultraviolet and visible regions

Presently, there is an increasing global demand for high-quality raw materials in tile production owing to rapid urbanization. In addition, the issues of insufficient reserves and low-quality clays are resolved by exploring the potential of environmentally friendly Bilecik yellow clay with high SiO2 content. In this study, the feasibility of producing high-strength earthen tiles from yellow clay, which has a higher SiO2 content than that of commercially used clays, is investigated. X-ray diffraction, field-emission scanning electron microscopy, and X-ray fluorescence spectroscopy are employed to analyze yellow clay. The tiles are produced in the Hatipoglu Günes Tile and Brick Industry Inc. factories. Galette tiles are obtained using a vacuum press device. Then, the galette tiles are fired at temperatures of 900, 950, and 1000 °C in an electric and Hoffman furnace. The tile fired at 1000 °C exhibits the highest transformed flexural strength (305.371 kg/cm2), which is 2.55 times higher than that specified in the TS EN 1304:2016 standard (Turkish standard-European norm). In addition, reflectance measurements are performed in ultraviolet and visible regions through UV–VIS and Fourier-transform infrared spectroscopy; the results confirmed that the galette tiles are reflected in the UV-C region. Therefore, it can be concluded that galette tiles exhibit sterilization and disinfectant effects under appropriate conditions. The usability of yellow clay with high SiO2 content in industry, the availability of high-strength products, and its production stages will create an important database for literature.

Coconut fiber and fly ash polymer hybrid composite treated silane coupling agent: Study on morphology, physical, mechanical, and thermal properties

Composite materials made from natural ingredients are currently being developed by researchers as materials that are more environmentally friendly. Hybridization techniques used in making composite materials continue to progress, involving the combination of several raw materials with similar or different properties, such as organic/organic, organic/inorganic, and inorganic/inorganic. In this research, coconut fiber which is an organic material is combined with fly ash which is an inorganic material. The contrasting properties of these two raw materials prompted the evaluation of their combination by including a silane coupling agent, which facilitates the bonding of organic and inorganic components. The essence of this research is to test the effect of adding silane coupling material on several parameters, namely physical properties (density, water absorption, and thickness swelling), mechanical properties (tensile strength, tensile modulus, elongation, and flexural strength), and thermal properties. To prepare coconut fiber, alkaline treatment is used to remove hemicellulose and lignin. Then, the coconut fiber was soaked in a 5 % vinyltrimethoxysilane (TVS) solution by weight. The addition of silane coupling material affects the physical properties of the composite resulting in a decrease in water absorption by 33 % and a decrease in thickness swelling by 0.3 %. The inclusion of silane coupling agent led to an increase in tensile strength, tensile modulus, and flexural strength, while elongation decreased by 20 %. Thermal properties analysis showed that the silane treatment affected the decomposition of the composite material, reducing it by 2 % from 90 % without the coupling agent to 88 % with the coupling agent.

A cost-effective way to utilize low-grade Ti-rich clay: Preparing cordierite-mullite composite ceramics for thermal storage

Cordierite-mullite composite ceramics were prepared by solid-state method using Panzhihua low-grade Ti-rich clay, talc, and alumina. Influences of cordierite/mullite ratio, sintering temperature, and the chemical composition of clay on the phase composition, microstructure, physical properties, and thermal properties were investigated in detail. The results showed that the impurity oxides inside the Ti-rich clay had a great ability of forming liquid. Above 1300 °C, the reaction between TiO2 of the clay and Al2O3 produced stable Al2TiO5, which was conducive to decreasing the coefficient of thermal expansion (CTE). At 1300–1350 °C, the secondary mullitization caused the volumetric expansion, decreasing the bending strength and increasing the CTE. The optimum ratio of cordierite to mullite ranged from 90:10 to 80:20, and the sample fired at 1400 °C exhibited the lowest water absorption and porosity (0.64 % and 1.56 %, respectively), optimal bulk density, and bending strength (2.59 g cm−3 and 87.79 MPa), as well as better CTE, thermal conductivity, and thermal storage density (2.91 × 10−6 °C−1, 4.11 W/(m⋅K) (30 °C), and 1181 kJ kg−1, respectively). Compared with the reported values of cordierite-based thermal storage ceramics prepared by using the high-grade clay or minerals, the obtained samples showed the advantages such as lower costs for raw materials, higher bending strength, higher thermal conductivity (1.63–2 times higher), low CTE, and high thermal storage density. This study demonstrated that the low-grade Ti/Fe-rich clay has excellent cost-effective potential for the preparation of thermal storage ceramics.

Optimization of poplar wood shavings bio-pretreated with Coriolus versicolor to produce binderless fiberboard using response surface methodology

Free formaldehyde is released due to the addition of aldehyde-based adhesives during the production of fiberboard. This is harmful to human health and pollutes the environment, and for that reason binderless fiberboard has become a research hotspot. There have been reports about pretreatments with white-rot fungi or lignocellulase to produce binderless fiberboard, but there have been no such reports about optimizing the bio-pretreatment conditions. In this study, poplar wood shavings were used for fiberboard production, and the bio-pretreatment conditions with Coriolus versicolor were studied using response surface methodology. After single-factor optimization, the central levels of bran, molasses, and magnesium sulfate were obtained. Further optimization was carried out using Box-Behnken design to study the influence of the factors. A second-order polynomial equation was obtained, and the low p-value (0.001) implied that the model was highly significant. The optimized bio-pretreatment conditions for modulus of rupture (MOR) of the fiberboard were obtained by ridge analysis as 3.021 g of bran, 8.907 g of molasses, and 0.27 g of magnesium sulfate. Under the optimized conditions, MOR of fiberboard reached 27.21±0.64 MPa, which was 2.2 times that of the control fiberboard. Bio-pretreatment with C. versicolor should be a good choice to produce a high-strength binderless fiberboard.

Ecuadorian Woods: Building Material Selection Using an Entropy-COPRAS Comparative Analysis Based on the Characterization of Ecuadorian Oak and Guayacan Timber.

Considering that global awareness for sustainable development has risen to face environmental damages, different building materials have been considered from a mechanical perspective. In this sense, considering the richness of South America regarding its woods, the Guayacan and the Ecuadorian oak timbers have not been previously characterized. The present research has performed mechanical, thermal, and moisture content characterizations to acknowledge the benefits of considering these materials for the building industries. In this sense, Guayacan has been shown to have lower thermal conductivity, making it ideal for thermal insulation; the oak from Manabi showed the best compressive strength; while the oak from El Oro stands with the best tensile strength; and the oak from Loja showed the best modulus of elasticity. On the other hand, all the materials were compared by multicriteria decision methods to select the best, by using the COPRAS method driven by the objective entropy-weighted method, showing that the oak from Loja is the best choice considering the advantage that presents with the modulus of elasticity. In this sense, it is concluded that regarding the mechanical properties, there is not much difference for the compression, bending, and tensile strength; nevertheless, for the modulus of elasticity the oak from Loja stands out, making it a factor to be considered in the selection of a wood for building applications that is corroborated through multicriteria decision methods.

3D printing of continuous metal fiber-reinforced recycled ABS with varying fiber loading

Purpose The current study aims to develop a 3D-printed continuous metal fiber-reinforced recycled thermoplastic composite using an in-nozzle impregnation technique. Design/methodology/approach Recycled acrylonitrile butadiene styrene (RABS) plastic was blended with virgin ABS (VABS) plastic in a ratio of 60:40 weight proportion to develop a 3D printing filament that was used as a matrix material, while post-used continuous brass wire (CBW) was used as a reinforcement. 3D printing was done by using a self-customized print head to fabricate the flexural, compression and interlaminar shear stress (ILSS) test samples to evaluate the bending, compressive and ILSS properties of the build samples and compared with VABS and RABS-B samples. Moreover, the physical properties of the samples were also analyzed. Findings Upon three-point bend, compression and ILSS testing, it was found that RABS-B/CBW composite 3D printed with 0.7 mm layer width exhibited a notable improvement in maximum flexural load (Lmax), flexural stress at maximum load (sfmax), flex modulus (Ef) and work of fracture (WOF), compression modulus (Ec) and ILSS properties by 30.5%, 49.6%, 88.4% 13.8, 21.6% and 30.3% respectively. Originality/value Limited research has been conducted on the in-nozzle impregnation technique for 3D printing metal fiber-reinforced recycled thermoplastic composites. Adopting this method holds the potential to create durable and high-strength sustainable composites suitable for engineering applications, thereby diminishing dependence on virgin materials.

Exploring flexural performance and abrasion resistance in recycled brick powder-based engineered geopolymer composites

BackgroundDue to growing global concerns regarding the management of construction waste, this study investigates the feasibility of creating engineered geopolymer composites by replacing traditional industrial by-products (slag) with construction waste, specifically recycled brick waste powder.ResultsPolyvinyl alcohol fibers were incorporated into the engineered geopolymer composite mixtures. The substitution of slag with recycled brick waste powder was carried out at varying percentages: 0, 20, 40, 60, 80, and 100%, resulting in six different engineered geopolymer composite mixtures. The study evaluated the flexural strength, sorptivity, water absorption, and abrasion resistance of the engineered geopolymer composites, and also, microstructural characterization was conducted using scanning electron microscopy. The findings demonstrated that incorporating recycled brick waste powder into the engineered geopolymer composite mixes resulted in a decrease in flexural strength by 35.59% and a notable increase in midspan deflection by 339% when slag was replaced. Concurrently, there was a significant rise in water absorption and sorptivity by approximately 304 and 214%, respectively, when slag was entirely substituted with recycled brick waste powder. Conversely, abrasion resistance decreased, with the inclusion of recycled brick waste powder resulting in an 84% increase in volume change. The scanning electron microscopy (SEM) analysis showed active geopolymerization of recycled brick waste powder within the engineered geopolymer composite mixtures.ConclusionsThe results of this investigation demonstrate that it is feasible to produce engineered geopolymer composites using recycled brick waste powder instead of slag. The greater ductility and increased midspan deflection point to areas that require further optimization, even in spite of the observed decreases in flexural strength and abrasion resistance. The SEM examination reveals an active geopolymerization, highlighting the potential of recycled brick waste powder to produce environmentally friendly and sustainable construction materials. These results offer a good starting point for further studies that try to maximize the durability and performance of these composites.

Impact of high Al2O3 content on the microstructure, mechanical properties, and wear behavior Al–Cu–Mg/Al2O3 composites prepared by mechanical milling

Metal matrix composites are increasingly being recognized as new wear-resistant materials. The main purpose of this study is to investigate the microstructure, mechanical properties, and wear resistance of Al–Cu–Mg alloy matrix composites reinforced with high contents of Al2O3 particles. Moreover, the effects of 10, 20, and 40 wt% Al2O3 contents on the microstructure, mechanical properties, and dry wear resistance of the Al–Cu–Mg matrix composites are studied. The results show that the θ (CuAl2) phase ratio increases with increasing Al2O3 contents. The hardness values of the samples also increase with increasing Al2O3 contents. The highest tensile and flexural strengths are measured as 284 and 562.9 MPa, respectively, and these values are obtained for the composite material reinforced with 10 wt% Al2O3 particles. The continuous increase in the hardness of the samples with increasing Al2O3 content may cause the lowest volume loss for the 40 wt% Al2O3-reinforced composite. The friction surfaces show that the wear surfaces comprise adhesion, delamination, and smear layers. Overall, compared to the Al2O3-reinforced composite samples, pure Al–Cu–Mg alloy samples show approximately 2 times more mass gain.

Exploring Damage Patterns in CFRP Reinforcements: Insights from Simulation and Experimentation.

Carbon Fiber Reinforced Polymers (CFRP) have become increasingly significant in real-world applications due to their superior strength-to-weight ratio, corrosion resistance, and high stiffness. These properties make CFRP an ideal material for reinforcing concrete structures, particularly in scenarios where weight reduction is crucial, such as in bridges and high-rise buildings. The transformative potential of CFRP lies in its ability to enhance the durability and load-bearing capacity of concrete structures while minimizing maintenance costs and extending the lifespan of the infrastructure. This research explores the impact of reinforcing structural elements with advanced composite materials on the strength and durability of concrete and reinforced concrete structures. By integrating Carbon Fiber Reinforced Polymer (CFRP) reinforcements, we subjected both rectangular and T-section concrete beams to comprehensive three-point bending tests, revealing a substantial increase in flexural strength by 45% and crack resistance due to CFRP reinforcement. The study revealed that CFRP reinforcement increased the flexural strength of concrete beams by 45% and improved crack resistance significantly. Additionally, the load-bearing capacity of the beams was enhanced by 40% compared to unreinforced specimens. These improvements were validated through finite element simulations, which showed a close alignment with the experimental data. Furthermore, an innovative simulation study was conducted using a finely tuned finite element numerical model within the Abaqus calculation code. This model accurately replicated the laboratory specimens in terms of shape, dimensions, and loading conditions. The simulation results not only validated the experimental observations but also provided deeper insights into the stress distribution and failure mechanisms of the reinforced beams. Novel aspects of this study include the identification of specific failure patterns unique to CFRP-reinforced beams and the introduction of an enhanced interaction model that more accurately reflects the composite behavior under load. In CFRP-reinforced beams, specific failure patterns were identified, including flexural cracks in the tension zone and debonding of the CFRP sheets. These patterns indicate the points of maximum stress concentration and potential weaknesses in the reinforcement strategy. The study revealed that while CFRP significantly improves the overall strength and stiffness, careful attention must be given to the bonding process and the quality of the adhesive used to ensure optimal performance. These findings contribute significantly to the understanding of material interactions and structural performance, offering new pathways for the design and optimization of composite-reinforced concrete structures. This research underscores the transformative potential of composite materials in elevating the structural integrity and longevity of concrete infrastructures.

Fabrication of Si3N4 ceramics with improved thermal conductivity by carbothermal reduction and two‐step sintering

AbstractSi3N4 ceramics with improved thermal conductivity and mechanical properties were prepared by carbothermal reduction and two‐step sintering. The addition of 2 wt% C led to the development of an intergranular phase YNSiO2 with reduced oxygen content. Notably, setting the pre‐sintering temperature at 1450°C promoted the formation of a rough bimodal morphology within the Si3N4 ceramics. Furthermore, an extended holding period at 1850°C resulted in additional grain growth and the elimination of intergranular phases. The Si3N4 specimens produced at 1450°C for 3 h followed by 1850°C for 8 h, incorporating 2 wt% C, exhibited a notable continuity between Si3N4 grains. The thickness of the grain boundary layer was only about 1 nm, and the N/O atomic ratio of the intergranular phase was measured to be 0.42. Consequently, the resulting thermal conductivity, flexural strength, and fracture toughness of Si3N4 specimens were found to be 101 W·m−1·K−1, 712 ± 29 MPa, and 7.7 ± 0.2 MPa·m1/2, respectively. Compared with samples without C additive and directly sintered at 1850°C for 8 h, the Si3N4 specimens produced in this work showed a significant increase of more than 50% in thermal conductivity and about 17% in fracture toughness.

Mechanical Properties and Microscopic Study of Recycled Fibre Concrete Based on Wind Turbine Blades.

In recent years, wind energy has begun to receive a significant amount of attention as clean energy is utilised and demanded in large quantities, resulting in a sharp increase in the use of wind turbines. The demand for wind turbines has gradually risen due to the clean and recyclable nature of wind energy. The current blade life of wind turbines in China is about 20 years, which means that the disposal of obsolete used blades can become a difficult problem in the future. Therefore, this study is of great significance to explore the regeneration performance of the blades after recycling and disposal. In this paper, wind turbine blades were mechanically recycled into recycled macrofibres, which were added to concrete as a reinforcing material to make wind impeller fibre concrete (WIC), and the three proportion ratios of 1%, 1.5%, and 2% were explored to compare the performance. The performance of WIC was also evaluated and its performance was compared to that of glass fibre concrete (GC). In addition, the material physical properties of second-generation recycled aggregate concrete (RAC) based on WIC were explored. The strength and peak strain variations and their causal mechanisms were analysed both macroscopically and microscopically by means of the classical mechanical tests (compression and bending tests), SEM, and XRD. The results show that the compressive strength of WIC was negatively correlated with the fibre content and increased by 6.04-18.12% compared to that of ordinary concrete (OG), with a maximum of 19.25 MPa; the flexural strength was positively correlated with the fibre content, with an increase of 5.37-18.5%. The microstructural analysis confirmed the macroscopic results and the intrinsic model better validated the experimental results.

Enhancing Hydraulic Lime Mortar with Metakaolin: A Study on Improving Restoration Materials for Historic Buildings.

This study investigates the enhancement of hydraulic lime mortar (HLM) using varying contents of metakaolin (MK) to improve its application in the restoration of historic buildings. Samples from historic structures were analyzed, and the effects of different MK contents on the physical and mechanical properties of HLM were examined. The reaction mechanism and microstructural changes were evaluated using XRD and SEM analysis. The results indicated that increasing MK levels in HLM led to a decrease in fluidity, with fluidity reducing by 4.8% at 12% MK. The addition of MK increased water consumption for standard consistency by 5.4% and shortened the final setting time by 10.2%. MK consumption promoted secondary hydration, enhancing compressive strength by up to 98.1% and flexural strength by up to 55.1%, and increasing bonding strength by 26.9%. The density of HLM improved with MK addition, slightly reducing moisture content by 4.5% and water absorption by 4.6%, while the water vapor transmission properties decreased by 50.9%, indicating reduced porosity. The elastic modulus of the mortar increased significantly from 2.19 GPa to 7.88 GPa with the addition of MK, enhancing rigidity and crack resistance. The optimal blend for restoration materials was found to be 9.0% MK and 25.0% heavy calcium carbonate and was characterized by moderate mechanical strength, enhanced early strength, commendable permeability, minimal risk of cracking, and ease of application. This blend is highly suitable for the rehabilitation of historic structures.

Improving thermal conductivity of Al/SiC composites by post-oxidization of reaction-bonded silicon carbide preforms

High thermal conductivity aluminium-based silicon carbide (Al/SiC) composites were successfully fabricated through post-oxidization of reaction-bonded silicon carbide preforms (RS preforms), utilizing vacuum pressure infiltration technology. The study investigated the regulation of interfacial reactions in conventional sintering and reaction sintering. Conventional sintering introduced a large amount of SiO2, which negatively impacted the thermal conductivity of the Al/SiC composite, but the reaction sintering not. The proposed post-oxidization treatment of RS preforms effectively removed residual carbon from the SiC particle surfaces, thereby forestalling the formation of Al4C3. Furthermore, the post-oxidization treatment effectively formed lightweight SiO2 deposits onto the surface of SiC particles, improving Al-SiC interfacial wettability and reducing thermal resistance, thereby enhancing composite thermal conductivity. Notably, the thermal conductivity of the post-oxidized sample exhibited an increase of 6.5% compared to the untreated sample. The study also evaluated the impact of particle size distribution on volume fraction and thermal properties. The optimized Al/SiC composites yielded thermal conductivity, coefficient of thermal expansion, bending strength, and Young’s modulus values of 237.3 W/m K, 8.5 × 10−6/°C, 325 MPa, and 75.9 GPa, respectively.

Enhancement mechanism of microbial mineralization modified coal gangue aggregate properties

Preparing concrete with coal gangue as the aggregate has significant environmental and economic advantages. Nevertheless, the fundamental characteristics of the manufactured concrete are significantly impacted by the high water absorption and low strength of coal gangue aggregate. The present study employs the microbial-induced carbonate precipitation (MICP) technique to efficiently enhance the characteristics of coal gangue aggregate (CGA). Starting from the circumstances of microbial mineralization, the effects of pH, temperature, and time on the capacity of bacteria for mineralization were taken into consideration. Following solution immersion treatment with varying concentrations of urea, calcium ions, and bacterial solution, the patterns of water absorption, crushing index, apparent density, and ultrasonic pulse resistance of CGA were examined. The precipitates produced by microbial mineralization, the micro-morphology, and the pore structure of the aggregate surface were all characterized, and the mechanism of the modification of CGA by MICP was revealed through the use of scanning electron microscopy (SEM), X-ray diffractometer (XRD), and nuclear magnetic resonance (NMR) techniques. Investigations were also conducted on the mechanical characteristics of modified coal gangue aggregate concrete. The results showed that the water absorption and crushing index of the CGA with optimal modification effect (M-CGA) decreased by 18.5 % and 24.1 %, respectively, which was attributed to the fact that the calcium carbonate formed in the cracks and pores of the CGA filled the aggregates and prevented the penetration of water. The 28-day compressive strength, split tensile strength, and flexural strength of modified coal gangue aggregate concrete prepared from M-CGA were increased by 8.13 %, 13.88 %, and 8.53 %, respectively. MICP is an effective method to improve the properties of CGA, which is conducive to the waste recycling of coal gangue.

Improving the Interfacial Adhesion of Long Carbon Fiber-Reinforced Polyamide 6 Composites by Electrochemical Oxidation and Polyethylenimine-Carboxymethyl Cellulose Grafting.

Carbon fiber (CF)-reinforced thermoplastic composites have notable ascents in various sectors and applications. For high-performance composites, strong interfacial adhesion between the polymer matrix and the CF is crucial. This is achieved by introducing functional groups on the CF surface. In this paper, a water-based surface treatment was applied to long carbon fibers to enhance the interfacial bonding with the polyamide 6 (PA6) matrix. For that, PEI and CMC were grafted onto the surface of carbon fibers after electrochemical oxidation. The PEI-CMC sizing reduced the carbon fiber/water contact angle to 26.42° from 111.69°. The clear improvement in wettability resulted in a 164.8% increase in the interfacial strength of 26.7 MPa after the application of PEI-CMC sizing on carbon fibers (CFs). The resultant tensile and flexural strength increased by 19.3 and 11.7% from 2009.6 and 378.3 MPa for desized CF/PA6 composites to 250.3 and 422.7 MPa for PEI-CMC-sized CF/PA6 composites, respectively. Moreover, the fractured surface morphologies were also investigated to confirm the enhancement of mechanical properties. The proposed one-step electrochemical oxidation and water-based sizing procedure is found to be promising for the production of high-performance long-fiber-reinforced thermoplastic composites.

Microstructure and radiation shielding characteristics of PVA fiber-reinforced ultra-high performance concrete

The application of nuclear technologies simulates the development of radiation shielding materials. Traditional heavy-weight concrete used for radiation shielding is limited in practical construction due to the poor mechanical properties and durability. This study developed a PVA fiber-reinforced ultra-high performance concrete (UHPFRC) with magnetite as heavy aggregates used for radiation shielding. Due to the scientific skeleton design, UHPFRC exhibits superior mechanical properties, with compressive strength and flexural strength reaching up to 121.9 MPa and 23.2 MPa, respectively. The microstructure of UHPFRC was investigated in detail and the results revealed that the incorporation of PVA fibers refined the pore structure of UHPFRC. The interfacial transition zone between magnetite aggregates and cementitious matrix in UHPFRC was much denser than that in traditional concrete due to the low water to binder ratio. The gamma and neutron radiations shielding capacity of UHPFRC were evaluated by the combination of actual measurement and simulation. By introducing light nuclei and refining the pore structure, the incorporation of PVA fibers improved the neutron radiation shielding capabilities of UHPFRC by 5.1%.

A Forward Sensitivity Analysis and Design of U-Shaped Bellows Considering the Radial Compensation Capability Under Internal Pressure

Abstract Bellows serve as integral component within a piping system, which withstand radial displacement loads and internal pressure loads. This study investigates the sensitivity analysis of structure design parameters, such as convolution height, convolution pitch, ply thickness, and convolution number, on radial compensation capability of U-shaped bellows under internal pressure. The influences of the geometric parameters on the strength performance of U-shaped bellows under internal pressure and radial displacement loads are also investigated. A forward design process considering the sensitivity of the structural parameters of the bellows to the bending stiffness and strength is provided. In order to improve the radial displacement compensation ability and to obtain better pressure resistance performance, a mathematical model is established to describe the performance of bellows, and multi-object optimization of bellows is conducted. The results show that the ply thickness has the greatest impact on bending stiffness and strength, and the optimized model has lower stiffness and higher strength compared to the initial model.

Interface strengthening for carbon fiber‐reinforced poly(ether‐ether‐ketone) laminated composites by introducing fluorene‐containing branched poly(aryl‐ether‐ketone)

AbstractFluorene‐containing branched poly(aryl‐ether‐ketone) (BFPAEK) with terminal hydroxyl groups is synthesized by random copolycondensation reaction; then, the CF@BFPAEK/PEEK laminated composite is prepared by the “powder impregnation‐high temperature compression molding” method with poly(ether‐ether‐ketone) (PEEK) as the matrix and BFPAEK‐modified carbon fiber (CF@BFPAEK) as the reinforcement. When the content of branched units in BFPAEK is 10% and the coating amount of BFPAEK on the carbon fiber (CF) surface is 3 wt%, the CF@BFPAEK/PEEK laminated composite has outstanding mechanical properties, with an interlaminar shear strength (ILSS) of 57.3 MPa and flexural strength of 589.4 MPa, which are 80.2% and 44.3% higher than those of the pure CF/PEEK laminated composite (31.8 and 408.4 MPa), respectively. After 288 h of hydrothermal aging and high/low‐temperature alternating aging, the corresponding retention rate of ILSS and flexural strength are respectively 87.9% and 84.7%, higher than those of pure CF/PEEK laminated composites (74.5% and 70.4%). The thermal conductivity coefficient and temperature for 5% weight loss of CF@BFPAEK/PEEK laminated composite are 1.85 W m−1 K−1 and 538.0°C, respectively.

Yield line-based design of fibre reinforced concrete: assessment of suitability of material models

The present research is intended to address the adequacy of flexural toughness-based material models such as equivalent and residual flexural strength, and the deflection limits at which these parameters are estimated for design of fibre reinforced concrete (FRC), for various applications such as slabs-on-grade/pavements. The work is an experimental study using FRC concrete mixes with individual and hybrid combinations of hooked-end steel (SF) and macro polypropylene fibres (PF). The experimental investigation consisted of toughness testing unnotched and notched prisms and square slabs, prepared with a typical grade of concrete used for FRC pavement applications. To validate the material models, a comparison was made between the theoretical moment/load calculated based on material flexural toughness parameters and the actual moment obtained from slabs using actual yield line formed during testing. From the study it is observed that overall, both equivalent (from unnotched prism test) and residual (from notched prism test) flexural strength, are suitable for designing FRC slabs, however the equivalent strength parameter shows better correlation to the slab response. The results also indicate that the hybrid mixes of PF and SF, with a higher volume fraction of 0.6% Vf, shows a marginal increase in flexural performance, in comparison to the mixes with lower volume fraction but no or minimal synergy due to hybridisation.