Search Results (5,670)

Recently, rotary friction welding has been used to join magnesium alloys. FRW uses friction heat to bond magnesium alloys with aluminium alloys. Combining these light alloys can provide many promising applications in the industry. The welding parameters such as friction and upsetting force, rotational speed, and welding time play a significant role in determining the joint strength. The paper presents a new approach to multi-objective optimisation of friction welding process parameters for AZ91D/AA6082 alloy joints. Multi-objective optimisation is based on artificial neural networks and genetic algorithms as non-conventional AI techniques. The methods were used to determine the following optimal welding process parameters: friction force, upsetting force and friction time for simultaneously maximised tensile strength and minimised metal loss (shortening) during welding. The ultimate tensile strength and metal loss of the friction welding joints were studied numerically and experimentally. Moreover, the influence of welding parameters on the ultimate tensile strength and shortening of friction joints was also studied. A genetic algorithm successfully found a set of welding parameters for which the joint strength increases from 24 to 81 MPA and the joint shortening decreases from 8.25 to 0.23 mm. The results show that a low friction force and upsetting force give a high value of tensile strength and the lowest shortening of the bimetal joints. Full article

The increasing demand for sustainable construction practices has prompted the exploration of innovative materials, such as waste plastics, to enhance both the environmental and mechanical performance of concrete, particularly for rigid pavements. This review investigates the mechanical properties of concrete incorporating four types of waste plastics—high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyvinyl chloride (PVC), and polypropylene (PP). The primary focus is on how these materials affect key mechanical properties, including compressive strength, tensile strength, and flexural strength. The analysis reveals that HDPE and PP, at optimal levels (5–10%), can enhance flexural and crack resistance, making them suitable for non-structural applications. Conversely, LDPE and PVC tend to reduce both compressive and tensile strengths at higher substitution levels due to poor bonding with cementitious materials. Despite these challenges, incorporating waste plastics into concrete presents significant environmental and economic benefits, including plastic waste reduction and lower reliance on natural aggregates. The review also highlights the need for further research on improving plastic–cement bonding through surface treatments and hybrid mix designs. This study contributes to the growing body of knowledge aimed at promoting the use of waste plastics in concrete, offering insights for the development of sustainable, high-performance construction materials. Full article

The utilization of ecological and cost-effective construction materials has emerged as a critical necessity in contemporary circumstances. It is essential to investigate the use of repair mortar as opposed to epoxy, which offers adhesion to concrete, to guarantee structural integrity under dynamic stresses. In this study, we performed an experimental and computational analysis of the load-bearing capacity of repair mortar to evaluate the adhesion between reinforced concrete structural elements and a geogrid. We performed triaxial bending, compression, splitting, shear bond strength, angle, and adhesion tests on specimens, which were constructed from repair mortar. We constructed 10 × 10 × 50 cm unreinforced beam specimens and 15 × 25 × 200 cm reinforced concrete beams and wrapped the geogrid in the stress zones of the beams by bonding it with repair mortar. We then performed four-point flexural tests on the geogrid specimens wrapped with repair mortar in the tensile zones of these beams. The mechanical properties obtained from these experiments allowed us to create a numerical model. For the first time in the literature, this study investigated the effectiveness of repair mortar compared with epoxy, as well as the innovative use of repair mortar to improve adhesion between the concrete surface and the geogrid. In the literature, reinforcement materials encasing concrete structural elements have utilized epoxy; however, an example of the application of a geogrid wrapped around structural elements with repair mortar has not been previously published. It was concluded that epoxy, effective in adhering to building materials for reinforcement, can bond with structural elements reinforced with a geogrid using repair mortar and may serve as an alternative to epoxy. Full article

The interface weakening process of bonded-layer composite structures is calculated, simulated, and experimentally investigated using ultrasonic longitudinal waves. Firstly, the reflection coefficients of echoes are calculated theoretically. Subsequently, a time-domain simulation model of bonded-layer composite structures is established. The propagation law of ultrasonic waves in bonded-layer composite structures is obtained. The relationship between different bonding interface states and the ultrasonic reflection characteristics are investigated through ultrasonic experiments on bonded composite structures. The theoretical calculation, simulation, and experimental results are as follows: when the bonding strength of the bonding layer changes from weak to strong, the amplitude of the first echo gradually decreases, the amplitude of the second echo progressively increases, and the amplitude of the third echo is basically unchanged; when the bonding strength of the upper interface changes from weak to strong, the amplitudes of the first and the second echoes are same as in the previous variation whereas the amplitude of the third echo slightly increases; when the bonding strength of the lower interface changes from weak to strong, the amplitudes of the first and the third echoes remain essentially unchanged, but the amplitude of the second echo progressively increases in the experiment compared with the theoretical calculation and simulation. In addition, the time of the first echo remains broadly unchanged, and the times of the second and the third echoes gradually decrease under all conditions. Full article

The durability of carbon fiber-reinforced polymer (CFRP) bars in marine environments is essential for their application in seawater–sea sand concrete (SWSSC), especially under cyclic loading conditions. While previous studies primarily focused on static bonding performance, the effects of seawater immersion and dry–wet cycles on bond fatigue behavior at CFRP–SWSSC interfaces remain underexplored. This study investigated the bond fatigue performance of CFRP bars and SWSSC under seawater immersion and dry–wet cycling conditions. Eighteen CFRP bar-SWSSC bond specimens were divided into three categories and prepared for static and fatigue pull-out tests. The effects of varying stress levels (fatigue upper load/static bond ultimate load) after seawater immersion and dry–wet cycling on fatigue failure modes, bond–slip behavior, and fatigue characteristics were evaluated. The results show that seawater immersion and dry–wet cycling significantly degrade the performance of bonds between CFRP bars and SWSSC, with an average bond strength reduction of 10.31%. These conditions reduce fatigue cycles and stiffness while increasing bond–slip (relative displacement at the bar–concrete interface) and residual–slip (displacement after unloading). Moreover, dry–wet cycling has a greater negative impact on fatigue bond performance than seawater immersion. Higher fatigue stress levels exacerbate damage and crack propagation at the CFRP–SWSSC interface, leading to significant increases in both bond–slip and residual-slip. Under similar conditions, higher stress levels enhance bond stiffness. However, excessively high stresses may lead to bond fatigue failures. Using experimental data and existing fatigue bond–slip constitutive models, a customized model for CFRP bars in SWSSC was developed. These findings highlight that marine environments and fatigue loading severely impair bond performance, thereby emphasizing the importance of careful design for marine applications. The proposed model offers a reliable framework for predicting bond–slip behavior under fatigue conditions, enhancing the understanding of CFRP–SWSSC interactions and supporting the design of durable marine infrastructure. Full article

Hybrid hydrogels from protein–polymer conjugates are biomaterials formed via the chemical bonding of a protein molecule with a polymer molecule. Protein–polymer conjugates offer a variety of biological properties by combining the mechanical strength of polymers and the bioactive functionality of proteins. These properties allow these conjugates to be used as biocompatible components in biomedical applications. Protein–polymer conjugation is a vital bioengineering strategy in many fields, such as drug delivery, tissue engineering, and cancer therapy. Protein–polymer conjugations aim to create materials with new and unique properties by combining the properties of different molecular components. There are various ways of creating protein–polymer conjugates. PEGylation is one of the most common conjugation techniques where a protein is conjugated with Polyethylene Glycol. However, some limitations of PEGylation (like polydispersity and low biodegradability) have prompted researchers to devise novel synthesis techniques like PEGylation, where synthetic polypeptides are used as the polymer component. This review will illustrate the properties of protein–polymer conjugates, their synthesis methods, and their various biomedical applications. Full article

Graphene oxide (GO) has attracted significant attention as a nano-reinforcement for cement-based materials, owing to its exceptional mechanical properties and abundant surface functional groups. However, the precise mechanisms governing its effects in cement composites remain inadequately understood due to inconsistencies and gaps in the existing literature. This review conducts a comprehensive analysis of the dispersion and reinforcement effects of GO in cement materials, focusing on three key areas: (1) challenges associated with achieving uniform dispersion of GO in the high-pH environment of cement slurries and potential strategies to address them; (2) the influence of GO on the macroscopic properties of cementitious composites, including workability, load-bearing capacity, flexural strength, fracture resistance, and durability; and (3) the reinforcement mechanisms of GO, encompassing its role in hydration kinetics, alterations to the calcium-silicate-hydrate (C-S-H) structure, and bonding interactions at the cement matrix interface. Furthermore, recent advancements in optimizing the dispersion and reinforcement effects of GO, such as surface modification techniques, are explored, emphasizing its potential for multifunctional and intelligent applications. This review aims to provide engineering professionals with the latest insights into the application of graphene oxide as a nano-reinforcement in cement-based composites, while offering valuable guidance and direction for future research in this field. Full article

Paper is an essential material in daily life, yet its widespread use contributes significantly to waste, which poses environmental hazards. In Indonesia, paper waste is one of the most substantial types of solid waste. Recycling waste paper into new, usable products offers both environmental and economic benefits. This study investigates the tensile strength, tearing strength, and microstructure of recycled paper produced using 70 g HVS waste paper, coconut husk fibers, NaOH as a chemical treatment, and tapioca powder as an adhesive. NaOH concentrations were varied at 2%, 4%, 6%, and 8% to assess their effects on the mechanical properties of the recycled paper. Results from tensile strength tests indicated that the highest tensile strength, 2.2774 MPa, was achieved with a 6% NaOH concentration, while the lowest tensile strength, 1.1065 MPa, was observed at a 4% NaOH concentration. Tearing strength tests showed that the highest tearing strength of 2.6145 MPa was obtained with a 4% NaOH concentration, whereas the lowest tearing strength of 1.8481 MPa was observed at an 8% NaOH concentration. Microstructural analysis of the fracture and tear zones revealed non-uniform fiber pullout, highlighting the influence of NaOH concentration on fiber bonding. These findings provide insights into optimizing NaOH concentration for improved mechanical properties in recycled paper products. Full article

Approaches to retain or improve wave-transparent composite properties received ongoing attention. Silica glass fiber composites are being utilized in wave transparency applications owing to their excellent dielectric properties. During operational service life, they are exposed to ambient and harsh environments, which degrade their performance and properties. The objective is to evaluate the progressive degradation of silica fiber wave-transparent composite material’s properties and overall performance. Silica fiber/epoxy wave-transparent composites (SFWCs) were fabricated by stacking high-silica glass cloth (HSG) plies via multi-layer compression and curing at 150 °C (14 hrs) and were investigated upon one-year real-time weathering and 20-year accelerated aging (Hallberg peck model). The morphology of one-year-aged SFWC composite was found to be better than that of 20-year-aged SFWC, where relatively weakened interfacial bonding and composite structure were observed. One year weathering the dielectric constant (ε_r) was increased to 4.34%, and dielectric loss (δ) was found to be 5.6%, whereas upon accelerated conditions (equivalent to 20 yrs of ambient conditions), ε_r was significantly raised 30.63% from its original value (3.2), and δ was increased 22.8% (0.035). In the 20-year aged SFWC composite, the maximum absorbed moisture was 3.1%. Tensile strength dropped from 147.8 MPa to 136.48 MPa, and compressive strength from 388.54 MPa to 374.41 MPa. Upon aging (from 1 year of weathering to 20 years of accelerated aging), SFWC composite properties and functional performance were lowered but remained reasonable. SFWC properties, as revealed by microscale characterization, can contribute to the determination of the impact of deterioration and useful service life in respective microelectronics wave transparency applications. Full article

This paper presents a comprehensive study of the mechanical properties of lime-based mortar in an acidic environment, employing both experimental analysis and machine learning to model techniques. Despite the extensive use of lime-based mortar in construction, particularly for the strengthening of structures as externally bonded materials, its behavior under acidic conditions remains poorly understood in the literature. This study aims to address this gap by investigating the mechanical performance of lime-based mortar under prolonged exposure to acidic environments, laying the groundwork for further research in this critical area. In the experimental phase, a commercial hydraulic lime-based mortar was subjected to varying environmental conditions, including acidic solution immersion with a pH of 3.0, distilled water immersion, and dry storage. Subsequently, the specimens were tested under flexure following exposure durations of 1000, 3000, and 5000 h. In the modeling phase, the extreme gradient boosting (XGBoost) algorithm was deployed to predict the mechanical properties of the lime-based mortar by 1000, 3000, and 5000 h of exposure. Using the experimental data, the machine learning models were trained to capture the complex relationships between the stress-displacement curve (as the output) and various environmental and mechanical properties, including density, corrosion, moisture, and exposure duration (as input features). The predictive models demonstrated remarkable accuracy and generalization (using a 4-fold cross-validation approach) capabilities (R² = 0.984 and RMSE = 0.116, for testing dataset), offering a reliable tool for estimating the mortar’s behavior over extended periods in an acidic environment. The comparative analysis demonstrated that mortar samples exposed to an acidic environment reached peak values at 3000 h of exposure, followed by a decrease in the mechanical properties with prolonged acidic exposure. In contrast, specimens exposed to distilled water and dry conditions exhibited an earlier onset of strength increase, indicating different material responses under varying environmental conditions. Full article

Interfacial shear fracture behavior of C18150Cu/1060Al/C18150Cu trilayered composite at different temperatures, which was fabricated by high-temperature oxygen-free hot rolling technology. The interfacial microstructure, interfacial shear strength, interfacial shear fracture morphology, and microstructure near the shear fracture were systematically investigated. The results reveal that the composite exhibits a metallurgical and mechanical bonding interface, along with mechanical interlocking between the copper and aluminum. As the testing temperature increases, the interfacial shear strength decreases. At temperatures below 150 °C, the strength remains stable, but it sharply decreases at temperatures above 150 °C. Specifically, the interfacial shear strength is 56.8 MPa at room temperature and 20.9 MPa at 350 °C. When the testing temperature is below 100 °C, the interfacial shear fracture predominantly occurs at the interface between the copper alloy and intermetallics. Also, aluminum is attached to the copper surface of the shear fracture, and the size and quantity of attached aluminum increase with the increase in temperature. When the testing temperature exceeds 100 °C, curled aluminum appears on the copper layer, and a large number of intermetallics are attached to the aluminum surface. This indicates that the bonding strength between intermetallics and aluminum is higher than that between intermetallics and copper. Full article

A simple short-flow thermo-mechanical treatment (TMT) named L-ITMT (consisting of three steps: solution, warm deformation, and solution) was applied to ultra-high-strength Al-10.0Zn-2.7Mg-2.3Cu alloy to study the influence of the deformation degree on the particle distribution, resolubility, microstructure evolution, recrystallization mechanism, formation and development of deformation bonds, and mechanical properties. Increasing the rolling deformation during the L-ITMT process can effectively break up the second phase at the grain boundary and promote its dissolution, which is beneficial to aging precipitation strengthening and improves the strength of the alloy. The dominant mechanism changes from recovery to recrystallization when the deformation degree reaches 80%. As the strain increases, the deformation band becomes flatter and eventually becomes nearly parallel to the RD direction, promoting the occurrence of geometric recrystallization or continuous recrystallization (CRX). Under high-strain conditions, the formation mechanisms of recrystallized grains include discontinuous recrystallization (DRX), CRX, and particle-stimulated nucleation (PSN), but the main contributions to the formation of large-area fine-grained bands are CRX and PSN. The results showed that as the deformation degree increased from 10% to 80%, the improvement of solid solubility and grain refinement in the short-flow TMT process increased the ultimate tensile strength (701 MPa), yield strength (658 MPa), and elongation (11.3%) of the alloy by 15.7%, 10.8%, and 842%, respectively. This shows that the short L-ITMT process has a synergistic effect in significantly improving the plasticity and maintaining the strength of this ultra-high strength Al-Zn-Mg-Cu alloy. Full article

Fly ash and granulated blast furnace slag are both bulk industrial solid wastes. Using these two raw materials to completely replace cement and prepare alkali-activated fly ash slag concrete (AAFSC) at room temperature can not only efficiently utilize industrial solid waste and reduce the carbon footprint, but also reduce the economic cost and technical difficulty of construction, which is of great significance for promoting the sustainable development of the concrete industry. In this article, the content of fly ash accounted for 80% of the total precursor (fly ash + slag), and a mixed solution of sodium silicate and sodium hydroxide was used as alkali activator to prepare AAFSC by curing at room temperature. The effects of alkali equivalent and activator modulus on compressive strength, impermeability, water absorption, and microstructure were systematically studied and compared with ordinary Portland cement concrete. The conclusions drawn were as follows. The 7-day compressive strength of AAFSC was lower than that of cement concrete, while its 28-day compressive strength was 104.86% to 131.94% of that of cement concrete. AAFSC exhibited excellent impermeability protection performance. The water absorption rate of AAFSC was lower, with A8M1 having a water absorption rate of 2.13%, which was only 60.86% of cement concrete. Through microscopic analysis, it was found that the alkali-activated fly ash slag cementitious matrix had good bonding with the aggregate, and there existed fly ash particles with different degrees of reaction. The Ca/Si value of AAFSC was smaller than that of cement concrete. Full article

Heavy metal powders driven by explosions can enhance the near-field lethality of explosive warheads by forming a quasi-pressure field while reducing collateral damage at medium and long ranges. Incorporating polymers into high-content metal powders prevents powder sintering under explosive high pressure, enhancing dispersion uniformity and making them promising for controllable warhead applications. To describe the mechanical behavior of materials under impact loading, this paper investigates the dynamic and static mechanical properties and constitutive modeling of tungsten powder/polytetrafluoroethylene (PTFE) composites. Quasi-static compression tests and split Hopkinson pressure bar (SHPB) dynamic tests were conducted on composites with varying tungsten contents (0 wt%, 70 wt%, 80 wt%, and 90 wt%) and particle sizes (200 μm, 400 μm, and 600 μm), obtaining compressive stress–strain curves over a strain rate range of 0.001 to 3610 s⁻¹. The compressive strength of the composites slightly decreased with increasing tungsten particle size but increased with higher tungsten content. Under quasi-static compression, the compressive strength of the composites with 70 wt% and 80 wt% tungsten was lower than that of pure PTFE. This was due to the bonding strength between the tungsten particles and the resin being weaker than the cohesion within the resin. Additionally, the random distribution of the tungsten particles in the matrix led to shear cracks propagating along the phase interfaces, reducing the compressive strength. The compressive strength of the composites with 90 wt% tungsten exceeded that of pure PTFE, as the packed arrangement of the tungsten particles increased the material strength through particle extrusion and friction during compression. Under dynamic impact, the compressive strength of the composites was higher than that of pure PTFE, primarily due to particle extrusion and friction effects. The composites exhibited significant strain rate sensitivity, with both the compressive strength and critical strain increasing quasi-linearly with the strain rate. Based on the experimental data, a damage-modified Zhu–Wang–Tang (ZWT) viscoelastic model was employed to fit the data, effectively characterizing the uniaxial compressive constitutive behavior of tungsten powder/PTFE composites. Full article

Annealing is a commonly used post-processing method for composite thin strips but suffers from drawbacks such as long processing time, high energy consumption, and susceptibility to oxidation. Replacing annealing with electric pulse treatment (EPT) can address these issues. In this study, a specially designed fixture was used to investigate the effects of pulsed current on the bonding strength of T2 copper (Cu)/304 stainless steel (SS) composite thin strips. The initial strip, with a 50% reduction rate, was prepared using a two-high mill, resulting in a Cu/SS composite strip with a thickness of 0.245 mm. Pulsed current treatment was applied with peak temperatures ranging from 350 °C to 600 °C. The results showed that EPT significantly improved the bonding strength. A pulsed current of 55 A resulted in the highest average peel strength of 10.66 ± 0.93 N/mm, with a maximum Fe content on the Cu side of 7.39 ± 0.84%, while a pulsed current of 65 A resulted in the highest Cu content on the SS side, reaching 57.54 ± 2.06%. This study demonstrates that EPT effectively controls the deformation behavior and interface state of composite strips, producing Cu/SS composite thin strips with high bonding strength. Full article