Archives of Civil and Mechanical Engineering最新文献

In the present research, the static bending analysis of a three-layer sandwich cylindrical panel with a re-entrant auxetic honeycomb core and polymeric face sheets reinforced with graphene nanoplatelets (GNPs) resting on an elastic foundation in a thermal environment is investigated. The mechanical properties of the nanocomposite GNP-reinforced face sheets are calculated using the Halpin–Tsai model along with the rule of mixture. The heat conduction equation is solved in the thickness direction to provide the exact profile of the temperature distribution. The panel is modeled based on the third-order shear deformation (TSDT), the elastic foundation is modeled according to the Pasternak foundation model, and the governing equations and boundary conditions are derived via the minimum potential energy principle. The differential quadrature method (DQM) is employed to solve the governing equations under various boundary conditions in longitudinal and circumferential directions. The convergence and accuracy of the modeling are confirmed and influences of different parameters on the deflection and stress distribution are studied including the inclined angle of the re-entrant cells, thermal environment, mass fraction and distribution patterns of the GNPs, the thickness of core-to-thickness of panel ratio, and the boundary conditions.

The study investigated the physicasl characteristics and mechanical performance of fly ash-based geopolymer composites when exposed to high temperatures. Geopolymer composites were produced using fly ash as an aluminosilicate-rich raw material and a combination of sodium silicate and sodium hydroxide as an alkaline activator. In this context, the study also examined the impact of partially replacing metakaolin (7.5% and 15% by weight). Furthermore, the study aims to examine the impact of adding fiber (basalt and carbon types) on the physical, mechanical, and high-temperature properties of geopolymer composites. The physical properties investigated were unit weight, apparent porosity, water absorption, and capillary water absorption, while the strength performances investigated were flexural and compressive strengths. To monitor the effect of high temperatures on the strength characteristics of the geopolymer composites, the mixtures were exposed to temperatures of 200 °C, 400 °C, and 600 °C. Besides, SEM images were provided to illustrate the degree of geopolimerization. The results indicated that metakaolin replacement yielded mixtures having higher unit weight, but lower apparent porosity and water absorption. The results indicated that metakaolin replacement yielded mixtures having a higher unit weight, reaching an increase of about 5%, but lower apparent porosity and water absorption, with decreases reaching 18.3% and 20%, respectively. The metakaolin-blended geopolymer composites resulted in better strength performance and resistance to high temperatures. Raising the metakaolin replacement level from 0 to 15% led to an increase of 17.3% in flexural strength. The compressive strength of the composites subjected to a temperature of 200 °C exhibited an increase of over 10%. Notably, this rate of increment was observed to be nearly 20% higher in nonfibrous composites. Fiber addition decreased the compressive strength up to about 21%, while increasing the flexural strength up to 65%. Strength performance improved at 200 °C, but decreased at higher temperatures up to 600 °C. The geopolymer composites experienced significant mass loss when exposed to high temperatures.

In recent years, fiber-reinforced polymer-polyvinyl chloride (FRP-PVC) tubular cylinders have been widely used in civil engineering applications. Concrete-filled FRP-PVC tubes possess excellent mechanical behavior and high durability. In this work, a composite reinforcement system with basalt fiber reinforced polymer (BFRP) strips wrapped around the surface of polyvinyl chloride (PVC) tubes is proposed for existing concrete cylinders. In addition, the effectiveness of the composite reinforcement system is evaluated and the working mechanism is studied. Monotonic axial compression tests are conducted on 39 concrete cylindrical specimens, and the parameters studied includs the number of BFRP layers, the net spacing of BFRP strips, and the type of reinforcement. The test results demonstrate that the bearing capacity of specimens with BFRP strips was enhanced by 8.42% up to 45.43% compared to unreinforced concrete cylinders. While, the bearing capability of BFRP-PVC reinforced specimens increase by 26.54% up to 62.30% compared with the control group specimen. Furthermore, a strength model that considers equivalent constraint effect coefficients is proposed based on existing strength models. The difference between the predicted results and the experimental results is within 15%. Research has shown that the reinforcement effect of the composite system is significant, and the research results can provide reference for engineering practice.

In this study, geopolymers (GMs) were produced using basalt fiber, polyamide fiber, and polypropylene fiber-reinforced and ground blast furnace slag (GBFS) waste ceramic powder (WCP). In the initial phase of the study, the optimal ingredient proportions were identified, and an ideal geopolymer was selected based on its highest compressive strength. Subsequently, at the second stage of the study, various fibers with differing proportions were incorporated into the ideal geopolymer, and the resulting properties were evaluated through laboratory testing. In the third stage, the optimal GMs were determined through a holistic approach, employing a multi-criteria decision-making method. A total of ten mixtures, comprising 23 properties (230 parameters in total), were subjected to a multi-criteria decision support method (TOPSIS). The optimal GM mixture with the proportions and suitable components was identified. The findings indicated that a 20% substitution of WCP with GBFS resulted in an optimal and cost-effective mixture in a 10 M NaOH solution, serving as a reference point or ideal unreinforced mixture in this research. With regard to the addition of fibers, all three types of fibers were observed to enhance the compressive, flexural, and splitting tensile strength of the WCP–GBFS-based GM. Maximum compressive strength was observed to be 60.15 MPa, while the flexural strength was 12.98 MPa and the splitting tensile strength was 3.45 MPa for the polyamide fiber (PA)-reinforced GM. Furthermore, all reinforced GMs exhibited enhanced abrasion resistance, with the inclusion of polypropylene fibers yielding the best results. Additionally, these fiber-reinforced GMs demonstrated significant resistance to high temperatures, even as temperatures increased. The TOPSIS results indicated that PA0.8 was the optimal GM, and its components with suitable components were recommended as a sustainable net zero/low CO₂ emission building material.

One-step (F100) and three-step (F30-60-40) hot forging of Al_0.35CoCrFeNi alloy was investigated to achieve a uniform equiaxed grain structure. In the as-cast and forged state, only a single-phase face-centered cubic structure was observed. The formation of twins, recrystallized and partially recrystallized grains in the volume of the samples was observed depending on used forging process. To predict uniform grain-size formation numerical simulation of the hot-forging process was used. The numerical model was calibrated and validated by means of measured compression experimental data of as-cast Al_0.35CoCrFeNi alloy before forging. Thermal analysis using finite element analysis was used to simulate cooling of sample during the relocation from the furnace on the lower die. Simulations were run under different thermo-mechanical conditions and the regions for the formation of dynamically recrystallized grains were predicted. Room temperature mechanical properties were evaluated after F100 and F30-60-40 hot-forging process. The F30-60-40 hot forging optimized the grain size, which was evident in the very small dispersion of the room temperature mechanical properties in tension. Elongation after F30-60-40 hot forging increased by 17%. The correlation between temperature, equivalent stress, equivalent plastic strain, microstructure, tensile properties, and strain-hardening behavior is discussed.

In recent decades, the quest for high-performance materials—those that combine low weight with high mechanical strength—has intensified. A promising solution involves composites reinforced with fiber and a polymeric matrix. However, these composite materials often exhibit deficiencies in crashworthiness. To address this issue, we investigated the incorporation of shape memory alloys, specifically nickel–titanium (NiTi), into the laminate structure. This study aimed to develop an equation, using a design of experiments approach, capable of predicting the energy absorption capacity of fiberglass and epoxy resin matrix composites upon impact, with integrated NiTi wires. Additionally, we proposed a model through numerical simulation using the finite element method to correlate with experimental analyses, thereby establishing a reliable model for future research. We selected the appropriate NiTi alloy (martensitic or superelastic) for the impact specimens through a full factorial design and dynamic mechanical analysis. After choosing the statistically superior superelastic wire, we manufactured test specimens using vacuum assisted resin transfer molding. These specimens, designed with three variables (diameter, spacing, and position in the laminate), followed a fractional factorial design. The drop-weight impact tests, conducted according to the ASTM D7136 standard, demonstrated increased energy absorption when NiTi wire was included in the composite. A non-linear numerical simulation (dynamic analysis) was performed, and its results—showing an excellent correlation with experimental data (above 95%)—validated the model.

In this work, tantalum-doped tungsten boride ceramic coatings were deposited from a single sputtering target with the radio frequency (RF) and high-power impulse magnetron sputtering (HiPIMS) methods. Two-inch torus targets were synthesised from pure elements with the spark plasma sintering (SPS) method with a stoichiometric composition of W_1-xTa_xB_2.5 (x = 0, 0.08, 0.16, 0.24). Films were deposited with RF and HiPIMS power suppliers at process temperatures from RT to 600 °C. The substrate heating and the energy of the ionised material impacting the substrate increase the surface diffusivity of adatoms and are crucial in the deposition process. The results of SEM and XRD investigations clearly show that the addition of tantalum also changes the microstructure of the deposited films. The coatings without tantalum possess a finer microstructure than those with 24% of tantalum. The structure of films is homogeneous along the film thickness and composed mainly of columns with a (0001) preferred orientation. Deposited coatings are composed mainly of P₆/mmm α-WB₂ structures. The analysis of nanoindentation results allowed us to determine that ceramic coatings obtained with the HiPIMS method possess hardness above 41 GPa and a ratio of hardness to reduced Young modulus above 0.1. The thickness of HiPIMS-deposited films is relatively small: only around 60% of the RF magnetron sputtered coatings even when the average power input was two times higher. However, it has been shown that the RF coatings require heating the substrate above 400 °C to obtain a crystalline structure, while the HiPIMS method allows for a reduction of the substrate temperature to 300 °C.

This study investigates the influence of polymer interlayers on the mechanical properties and fracture behavior of friction stir welded EN AW-2024-T3 aluminum alloy joints. Aqualock AL 6002 (Adhesive_1) and 3M Adhesion Promoter 86A (Adhesive_2) were selected as polymeric sealants for EN AW-2024-T3 aluminum alloy interfaces. Force analysis revealed that the choice of polymer interlayer significantly affects the axial force during welding, with Adhesive_1 joints showing a significant reduction in force compared to other variants. The axial force during FSW in Adhesive_1 was 18% less than in Adhesive_2. Cross-sectional analysis revealed distinct features in joint morphology and defects, with Adhesive_1 joints exhibiting favorable thermal stability and minimal defects compared to Adhesive_2 joints. Tensile strength analysis showed a significant increase in load capacity for the Adhesive_1 (9470N) joint, while the Adhesive_2 (5030N) joint exhibited reduced strength due to inadequate heat flow. The Adhesive_1 joint showed a 93% increase in tensile strength compared to Adhesive_2. The mixing of Adhesive_2 with the joint area produced hard complex particles that reduced the strength of the final joint. Fracture analysis revealed complex fracture mechanisms, with Adhesive_1 joints exhibiting ductile fracture zones and Adhesive_2 joints exhibiting quasi-cleavable intergranular cracking. Microhardness distribution analysis showed variation between the joint variants, with Adhesive_2 joints showing higher microhardness in the weld nugget.

Tubular components of aluminium alloys find application in body-in-white to achieve weight reduction owing to growing demand of fuel efficiency in new age vehicles. However, fabrication of tubes through conventional extrusion route are restricted by tube size, cost and expensive dies. Therefore, tubular structures of AA 5083 (length to diameter ratio 2.5) were successfully fabricated cost-effectively adopting friction stir welding (FSW) process by designing an indigenous setup and a concave shoulder tool. Subsequently, the effect of weld zone (WZ) on crushing characteristics of welded tubes were assessed by compressing these tubes in axial and lateral directions between two flat platens. It was detected that the welded tubes underwent concertina mode of deformation during axial crushing, showing that the WZ had negligible impact on the collapse pattern. However, in lateral crushing formation of plastic hinge started from the WZ due to its thinning during welding. It is noteworthy that the WZ could withstand severe plastic deformation under non-linear strain path without any failure because of increase in its strength by approximately 87% as compared to base material (AA 5083), and less inhomogeneity amongst various zones. The specific energy absorption of tubes was found to be approximately 30 and 1.6 kJ/Kg during axial and lateral crushing, respectively. These values were found to be comparable with that of extruded tubes crushed under the above loading conditions reported in existing literature. The findings of the present work will encourage automotive industries to implement FSWed tubes as thin-walled energy absorbers to sustain different loadings during an event of crash.

In this study, we investigated the use of graphene as a reinforcement material in magnesium alloy (AZ91) composites. The composites were prepared through stir-casting followed by a novel strength improvement process using T6 heat treatment and equal channel angular pressing (ECAP). Microstructural analysis through X-ray diffraction and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy substantiates new phases, including magnesium carbide (MgC₂), which produce enhanced mechanical properties along with grain refinement after T6 heat treatment and ECAP. The addition of graphene increased the mechanical properties of the samples to 0.1 wt% graphene in the as-cast sample. However, the hardness and strength of 0.2 wt% graphene decreased because of agglomeration under the as-cast condition. Following two passes of ECAP, a 49.22% increase in hardness was observed in the composite, whereas the yield and ultimate tensile strength increased by 64.38% and 80.42%, respectively. The load transfer mechanism contributed to the strengthening of the AZ91/graphene composites and exhibited satisfactory interfacial bonding between the matrix and reinforcement. Ductile fractures were predominantly observed in T6- and ECAP-treated samples.