Archives of Civil and Mechanical Engineering最新文献

Four-dimensional (4D) printing has advanced beyond conventional three-dimensional (3D) printing by utilizing smart materials like Shape Memory Polymers (SMPs), allowing the fabrication of complex structures capable of altering their shape or properties in response to external stimuli such as heat. Despite their great potential, the lack of intrinsic electrical functionality in SMPs necessitates direct external thermal activation, which limits their use in critical engineering applications. While electroactive SMP nanocomposites enable Joule heating, the incorporation of conductive nanofillers often compromises the intrinsic shape memory, thermal, and mechanical properties of the polymer nanocomposite. This work addresses these limitations by utilizing conductive and flexible thermoplastic polyurethane (cTPU) filament as a heating element, forming a SMP/cTPU composite. The composite consisting of SMP matrix and cTPU filler is fabricated via dual-extrusion Fused Deposition Modeling (FDM) 3D printing. The integration of cTPU’s conductive network allows for electrothermal and remote activation of the SMP matrix, while preserving most of the intrinsic SMP properties. To study the performance of the proposed composite, a comparative assessment was conducted between the electrothermally activated SMP/cTPU composite and a conventionally heated SMP under similar conditions. The study shed insights into the fabrication and curing process, followed by evaluations of thermal stability, mechanical, and shape memory properties. The as-cured SMP/cTPU composite was successfully heated electrothermally, reaching its glass transition temperature (~ 55 °C), and exhibited consistent response over multiple electrothermal cycles. A shape memory cycle consisting of programming and recovery was conducted on a SMP/cTPU dumbbell specimen and characterized using Digital Image Correlation (DIC) and Infrared (IR) Thermography. The SMP/cTPU composite achieved a shape recovery ratio of approximately 73%, compared to 74% for the plain SMP. Moreover, SMP/cTPU composite showed faster recovery time as evidenced by the improved shape recovery rate. Mechanical testing further revealed a slight increase in elastic modulus and tensile strength, and improved deformation stability in the SMP/cTPU composite. This cost-effective, reproducible, and stable approach utilizes 3D printing to introduce electroactive functionality to intrinsic SMPs without compromising their inherent properties, while simultaneously enhancing the shape recovery rate and mechanical performance.

Low-carbon production of building materials as the core path of the “dual-carbon” goal, its important technological breakthrough lies in the maintenance of cementitious material properties through the replacement of cement by mineral admixtures to synchronize the realization of carbon emission reduction and ecological benefits win-win. In this paper, composite cementitious materials (CCM) were prepared using vanadium–titanium iron ore tailings (VTIOTs), and the effects of VTIOTs fineness, content and ion dissolution on the performance of CCM were investigated, the composition, structure and hydration mechanism of CCM hydration products were analyzed, and carbon emission calculation method and carbon reduction effect of CCM were evaluated. The results showed that the 28 d activity index of VTIOTs reached 69.4% when mechanical activation for 50 min. When the CCM mix ratio of VTIOTs: cement: silica fume (SF) is 2:7:1, the 28 d compressive strength was 39.7 MPa. The CCM with 30% VTIOTs could reduce the total exothermic heat of hydration by 27.01%. The hydration products of CCM were mainly C-S-H, calcium aluminate hydrate (C₃AH₆), ettringite (AFt) and some amorphous substances. It is recommended to use A₂ mix ratio, which reduces carbon emission by about 30% compared to cement, and ensures the mechanical properties of CCM with environmental benefits and achieve clean production of cement-based materials.

Topology optimization (TO) with genetic algorithm (GA) is a bio-inspired heuristic optimization technique. In practical applications, it suffers from unstable results, a large number of redundant computations, and low convergence rates. To address this issue, an improved GA, specifically tailored to TO by introducing a strong shape constraint and enriched information obtained from the embedded finite element analyses, is proposed in this study. The strong shape constraint adds a filter to all the individuals at the beginning of each iteration to prevent the analysis of topologies that would not lead to feasible structures. Meanwhile, multiple-input genetic operators leverage additional information from the finite element analyses to guide the mutation and reproduction process, accelerating the convergence rate to the optimal shape. Three case studies present the contributions of the proposed algorithm in terms of robustness, efficiency, and refinement compared to conventional GAs and the Solid Isotropic Material with Penalization (SIMP) method. The results show that the proposed algorithm achieves high robustness and the probability of convergence to impractical shapes is negligible, the computational cost is reduced to one half, the convergence is expedited (compared to conventional GAs), and a refined shape can be obtained and manufactured.

The heterostructure has been shown to enable metallic materials to achieve exceptional combinations of strength and ductility. However, the creation of novel heterostructures and the understanding of their deformation mechanisms remain significant challenges. In this study, 304 stainless steel (304ss) was subjected to a unidirectional twisting of 360° followed by annealing at temperatures ranging from 400 to 800 °C for 30 min. Microstructural characterizations using electron backscatter diffraction (EBSD) revealed the formation of two distinct types of global dual-gradient structures (GDGS) in the twisted and annealed 304ss. The mechanical properties of the GDGS 304ss were assessed through tensile tests, demonstrating superior combinations of high strength and ductility. The exceptional performance arose primarily from the interaction between the GDGS structures and martensitic transformation, which facilitated martensitic transformation (γ → α’) in the surface zones. Furthermore, the accumulation of geometrically necessary dislocations (GNDs) to accommodate the mechanical incompatibility between hetero-zones contributed to the synergistic enhancement of both strength and ductility.

Solid solution treatment is a common heat-treatment method for aluminum alloys. However, the traditional solid solution treatment in heating furnaces takes a long time and has low thermal efficiency. This paper used 6082-T6 Al alloy as the research object and studied the dissolution behavior of the second phase during the contact solid solution process using TEM and XRD. The results showed that a 2 mm 6082-T6 Al alloy sheet completed solution treatment in 28 s, which was much shorter than the 1800s required in the heating furnace. The main reason was that the extremely high heating rate of the contact solid solution inhibited the transformation and coarsening of the Mg₂Si phase, achieving rapid solid solution. Anchored in the established principles of dissolution kinetics, the study highlighted the effects of the secondary phase’s particle aspect ratio and heating rate. A dissolution kinetics model specifically for the Mg₂Si phase, in agreement with contact solid solution theory, was formulated and showed excellent agreement with experimental results.

Ultrasound measurements are used for monitoring the structural health of concrete. The elastic waves propagating in concrete structures are attenuated by scattering and intrinsic attenuation. Both quantities have to be determined for a detailed material characterization and for realistic numerical simulations of wave propagation in such structures. We present in this paper a numerical approach to determine the intrinsic attenuation of concrete. For this purpose, a realistic digital three-dimensional concrete specimen is created that accounts for correct volume fractions of aggregates of different sizes embedded into a mortar matrix. Using a viscoelastic finite difference scheme, we perform simulations of the ultrasound wave field in these digital models with different attenuation levels. The numerical observations are compared with results from ultrasonic measurements on a sample of saturated concrete to estimate the intrinsic attenuation. Embedded sensors are used for those long-term laboratory experiments. For this saturated concrete, we obtain Q=130 in a frequency band around 60 kHz.

Equivalent Rectangular Stress Block (ERSB) parameters, as presented in design codes, are commonly used by designers to determine the flexural capacity of glass fiber reinforced polymer - reinforced concrete (GFRP-RC) members. However, these parameters were originally developed for normal strength concrete (NSC) and often result in errors when applied to other types of concrete, such as fiber-reinforced concrete (FRC). This is primarily due to variations in the post-peak behavior of concrete in compression. To address this issue, an analytical model was developed using concrete constitutive models and validated against experimental data on GFRP-RC flexural members reported in the previous studies. The model incorporates key variables, including concrete compressive strength, fiber aspect ratio, fiber dosage, reinforcement ratio, and reinforcement type. A parametric study was then conducted, considering a wide range of concrete strengths and post-peak degradation rates. Based on the results, new ERSB parameter values were proposed as functions of concrete strength and post-peak strength degradation rate. The accuracy of the proposed parameters was evaluated for both conventional and non-conventional concrete types, such as FRC. The results demonstrate that the proposed ERSB parameters significantly improve the accuracy of flexural strength predictions compared to existing design methods. The proposed parameters can be adopted for various types of concrete, including FRC, with differing post-peak behaviors. This study concluded that considering the strength degradation rate of concrete, especially in fiber reinforced polymer reinforced concrete members where compression-controlled failure often governs the response-is a critical parameter in predicting the flexural strength that should be explicitly addressed in design codes. This study offers a unified method and the corresponding ERSB parameters, which can be adopted not only for conventional concrete but also for non-conventional concrete. It provides a simple and unified approach applicable to any type of concrete (including all types of FRC concrete, regardless of the type and amount of fibers), as long as the compressive strength and post-peak degradation are known.

Due to its several advantages over the conventional seismic design procedures, i.e., force-based and displacement-based, the energy-based seismic analysis and design procedures are anticipated to have the maturity to be included in the next-generation regulations and seismic design codes. However, extensive efforts are still required to reach a complete design methodology. This paper presents a comprehensive state-of-the-art review of the literature research on energy-based procedures in earthquake-resistant structural design. Starting with the earliest studies on the energy balance equations, it reviews the works carried out in the literature through the years in several categories, i.e., calculation of the seismic demands, development of the energy spectra, energy-based intensity measures, energy-based record selection and scaling, and energy-based structural design procedures. The reader will receive a complete review of energy-based analysis and design procedures in this paper, emphasizing unresolved issues and a list of existing research gaps.

The high environmental impact of ordinary Portland cement (OPC) in earth block stabilisation has prompted the search for sustainable alternatives. This study evaluates the use of thermoactivated recycled cement (RC), derived from hardened concrete waste (RCC), as a replacement for OPC in compressed earth blocks (CEB). A novel magnetic separation method was used to recover a high-purity cementitious fraction from concrete debris. Mechanical and microstructural performance of CEB with varying levels of OPC replacement (up to 100%) was assessed, along with the effect of replacing up to 40% of earth with construction and demolition waste (CDW). Microstructure was characterised using mercury intrusion porosimetry, nitrogen adsorption, and scanning electron microscopy. Despite RC higher water demand, compressive strength losses remained below 20% for 50% OPC replacement. Stabilisation with RC led to well-dispersed soil particles interposed with hydration products, resulting in a more refined mesoporosity than OPC CEB. Additionally, long-term shrinkage was lower than that of OPC CEB with equal water/binder. Incorporating up to 25% CDW increased compressive strength by as much as 29%, although it reduced surface hardness and abrasion resistance by up to 4% and 32%, respectively. Ultrasonic pulse velocity and sclerometric index correlated well with compressive strength (R² > 0.9), enabling practical non-destructive quality assessment. The results confirm that RCC is a viable alternative to OPC in earth stabilisation, offering comparable mechanical performance with significantly lower environmental impact. This work supports the practical application of recycled materials in sustainable masonry and provides guidance for future CEB design and production.

This study presents a novel intelligent hybrid seismic control system for a 10-storey shear building that integrates base isolation (BI) with an acceleration differential force-enhanced tuned mass damper inerter (BI-ADF-TMDI) and further extends it through active control to create the BI-ADF-ATMDI system. The key innovation lies in the mechanical configuration that connects the roof-mounted TMDI to the BI level via an inerter, as well as the incorporation of a passive acceleration differential force (ADF) mechanism that dissipates energy without requiring external power. To enhance adaptability, the system employs an active TMDI governed by a tilt-integral-derivative (TID) controller, whose parameters are optimally tuned using the multi-objective cheetah optimizer (MOCO) algorithm. Additionally, the MOCO algorithm is used to optimize the parameters of the three proposed systems: BI-TMDI, BI-ADF-TMDI, and BI-ADF-ATMDI. This study investigates the seismic performance of a structure equipped with these systems in comparison to an uncontrolled structure. Performance optimization was conducted using an artificial earthquake record, followed by rigorous validation across 23 diverse near-field seismic events. The results reveal that the BI-ADF-ATMDI system achieves significantly improved seismic performance as compared to its passive counterparts, demonstrating superior reductions in structural responses. All three proposed systems substantially outperform the uncontrolled structure, highlighting their effectiveness. Overall, this research establishes a robust methodology for system optimization and evaluation, contributing meaningfully to the advancement of seismic resilience in structural design.