Archives of Civil and Mechanical Engineering最新文献

Alkali-activated materials have gained increasing popularity due to their advantages in reducing carbon emissions and promoting environmental sustainability. To gain a comprehensive understanding of the early-stage properties and mechanisms of alkali-activated materials when mixed with various types of water, a study was conducted to investigate the impact of seawater, deionized water, and freshwater on the setting time, fluidity time, strength, and drying shrinkage rate of a slag and desulfurization gypsum composite alkali-activated material (SD-AAM). Additionally, the hydration products and microstructures of the SD-AAM were examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and thermogravimetric–differential scanning calorimetry (TG–DSC) to uncover the mechanisms by which mixing water influences these properties. The results indicate that seawater significantly enhances the strength of the SD-AAM after a 7-day curing age compared to deionized water. However, it also reduces fluidity, setting time, and drying shrinkage rate. This phenomenon can be attributed to the ability of seawater to accelerate the hydration process and facilitate the formation of Friedel’s salt. The strengthening effect of the seawater becomes increasingly pronounced as the curing age extends. Furthermore, Friedel’s salt is gradually enveloped by C–(A)–S–H gel, leading to a decrease in the ({text{Cl/Al}}) ratio when seawater is utilized, as evidenced by the combined results of SEM and EDS. In contrast, freshwater consistently exerts a detrimental effect on early-stage strength across various curing ages. These findings are significant for expanding the applications of alkali-activated materials in specialized engineering contexts.

Cork materials, valued for their sustainability and thermal insulating properties, are gaining use as eco-friendly alternatives to synthetic insulation in building facades, among other architectural, construction, and building applications. However, the ageing effects caused by weathering exposure are yet to be investigated. Understanding how these materials respond to outdoor environmental stressors is essential to ensure their long-term performance in facade systems and other exposed building elements. Therefore, this study examines the effects of accelerated ultraviolet (UV) ageing and freeze–thaw (FT) cycles on natural, agglomerated, and expanded cork’s structure, mechanical, thermal, and chemical properties. Each cork type underwent UV and FT ageing, simulating seasonal environmental conditions, and was subsequently analysed through scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), compressive mechanical testing, and thermal analysis. UV exposure leads to the degradation of the cellular structure in all types of cork, with particularly significant in expanded cork. On the other hand, FT cycles primarily affect agglomerated cork. FTIR analysis corroborates these structural changes from SEM observations, showing spectral changes associated with suberin and lignin degradation in UV-exposed cork. However, only expanded cork exhibits changed or erased bands when exposed to FT cycles. Mechanical testing indicates that UV exposure reduces the compressive strength of natural cork, whereas FT cycles led to a slight increase in the agglomerated one and a significant decline for natural and expanded cork. Thermal tests reveal that UV exposure increases thermal conductivity and specific heat in natural cork but reduces diffusivity, while agglomerated cork experiences an increase in conductivity and diffusivity for the same conditions. FT cycles generally increase the conductivity of all cork types, while thermal diffusivity decreases for expanded cork and decreases for both natural and agglomerated cork.

This research describes the formulation and experimental assessment of an environmentally sustainable ultra-high-performance concrete (UHPC) embedding both agricultural and industrial by-products. Although individual use of agricultural or ceramic waste in concrete has been explored, the combined effect of palm-based ashes and ceramic waste as fine aggregates (CWFA) on UHPC’s properties remains insufficiently investigated. Palm oil ash (POA) and palm leaf ash (PLA) were incorporated as partial substitutes for Portland cement (PC) in proportions of 10%, 20%, 30%, 40%, and 50%; concurrently, CWFA substituted quartz sand at replacement levels of 25%, 50%, 75%, and 100%. Nineteen distinct concrete mixtures were thus prepared and evaluated. Performance metrics comprised slump flow, compressive strength, permeability, scanning electron microscopy (SEM) analysis, and compressive strength retention under elevated-temperature conditions. Data revealed that the introduction of POA and PLA to an extent of 30% generally elevated the compressive strength in comparison to the reference matrix. The most effective mixture, POA30-C100, attained a peak compressive strength of 205.5 MPa at 90 days, exceeding the reference strength of 172.4 MPa. These results underscore the viability of repurposing agricultural and industrial residues for the sustainable fabrication of high-performance UHPC, thereby enhancing both material performance and ecological stewardship.

The present study investigates the dynamic tensile behaviour of a high-manganese austenitic TWIP steel (X45MnAl20-4) using a flywheel-based testing system, with emphasis on strain rate effects. Dynamic tensile tests with strain rates ranging from approximately 300 to 950 s⁻¹. The force vs. time signals were recorded during the course of tests. This allowed the true stress–true strain diagrams to be determined. It has been established that the propagation of elastic stress waves within the test stand construction caused oscillations in the σ_true-ε_true curves. The smoothing of these oscillations has been approached through the utilisation of a power function as an approximation. The influence of strain rate on the tested steel characteristics such as flow stress, plastic deformation work, and absorbed energy (SEA and VEA) was quantitatively evaluated on the basis of the obtained σ_true-ε_true curves. Microscopic observations confirmed that mechanical twinning is the predominant deformation mechanism in the steel studied, with increased twinning density and multisystem twinning under dynamic conditions. A comparison of the X45MnAl20-4 steel with other TWIP steels and DP steel has shown that it exhibits a competitive specific SEA value. This confirms its suitability for use in structural components operating under dynamic loading conditions. The findings of the study underscore the significance of accurate measurement data interpretation and selection of suitable correction methods when analysing the dynamic mechanical responses of TWIP steels by means of a flywheel machine.

The stacking fault energy (SFE)-governed synergy between twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) mechanisms delivers superior mechanical properties compared to either effect alone. However, precise knowledge of an optimal TWIP and TRIP balance remains elusive and holistic understanding on the contributions from both TWIP and TRIP effects to the mechanical properties is still lacking. In this study, we show that by carefully tailoring the SFE to approximately 10 mJ·m⁻² through adjustment of grain size and deformation temperatures, an optimal synergy between strength and ductility can be achieved in Fe–Cr–Ni austenitic steels with a variety of compositions. This synergy arises from the intricate manipulation of the sustained TWIP and TRIP effects. The optimal combination characterized by approximately 18% deformation twins and 50% strain-induced martensite is revealed by an SFE-dependent physical model which models the austenite → twin → α′-martensite transformation sequence. These findings offer valuable insights for the fast and cost-effective design of austenitic steels.

This study experimentally investigated the correlation between crystallographic, microstructural, and mechanical properties of Wire arc additive manufacturing (WAAM) fabricated ER70S-6 steel, especially focusing on the effects of layer height on the fabricated samples. To examine these properties, the samples were tested at different heights, i.e., bottom segment (BS), middle segment (MS) and top segment (TS). Then, the microstructure, grain scale boundaries, microhardness, and phase transformations were analyzed with scanning electron microscope (SEM), Energy-Dispersive X-ray Spectroscopy (EBSD), microhardness tester, and X-ray Diffractometer. Similarly, the mechanical behavior of ER70S-6 manufactured parts was measured along a vertical direction, i.e., building direction with a universal testing machine (UTM). The research shows that the mechanical properties of the same parts at different heights were not similar. The average microhardness and ultimate tensile strength of the constructed sample were reduced by 13.21% and 6.18%, respectively, from the bottom to the top of the sample. Based on this, it was found that changes in the cooling rate at different levels resulted in considerable variation in the microstructure. It is also concluded that a coarse-grained zone exists in samples along the building axis, with its growth toward the topmost part causing various changes in mechanical attributes such as ductility and strength.

This study investigates the potential use of Olive Pomace Bottom Ash (OPBA) as a partial cement replacement in self-compacting mortars (SCMs) to enhance sustainability in construction while addressing environmental concerns. A Central Composite Design (CCD) approach was used to investigate the effect of OPBA content (0–20%), limestone filler content (10–20%), and water-to-binder (W/B) ratio (0.4–0.5) on fresh properties, mechanical behavior, and water absorption potential of SCM. The results indicate that increasing the OPBA content typically decreased workability and strength while at the same time increasing water absorption potential. However, this effect can be mitigated by optimizing the filler content and W/B ratio. With low additions of OPBA (up to 10%), incorporating limestone filler showed a regular increase in strength. Statistical analyses using the central composite design method confirm that complex non-linear relationships among variables exist and that advanced optimization techniques are needed in mix design. An optimal mix was found to have 6.66% OPBA, 20% filler, and a W/B ratio of 0.42, with a desirability value of 0.927. This optimal mixture recorded a slump of 26.3 cm, flow time of 11.85 s, compressive strength of 48.66 MPa, flexural strength of 5.47 MPa, and water absorption of 11%. The above study indicates that OPBA is feasible in SCMs and could improve sustainability in the construction industry without compromising performance. These findings highlight OPBA feasibility in SCMs, promoting waste valorization and reducing cement consumption without compromising performance.

The utilisation of granite powder (GP) waste in cementitious composites is limited by its low reactivity and adverse effects on mechanical performance. This study investigates the mechanical activation of GP through grinding (GP-M) and sieving (GP-S) to optimise its physical properties and sustainability potential. The modified powders were characterised in terms of specific surface area (SSA), reactivity, loss on ignition, and alkali leachability. Cementitious composites were prepared with 20% and 40% cement replacement and evaluated for slump flow, setting time, strength development, and bulk density. Results show that grinding increases the SSA from 2890 cm²/g (raw GP) to 4290 cm²/g (GP-M), improving particle packing and enhancing compressive strength by up to 20% compared to unprocessed GP. Despite its low pozzolanic reactivity, GP-M acts as an effective filler, improving microstructure and maintaining compressive strengths above 40 MPa at 28 days for 20% replacement. Alkali leachability was also reduced, supporting long-term durability. A Life Cycle Assessment (LCA) indicates that replacing 40% of cement with GP-M reduces CO₂ emissions by over 50%, while maintaining acceptable mechanical properties. The proposed Mechanical Performance Ratio (MPR) and Environmental Performance Ratio (EPR) demonstrate that the most balanced performance was achieved in the GP-M20 and GP-S20 series, offering up to 12% CO₂ savings with minimal strength reduction. This study confirms that mechanically valorised granite powder is a viable, sustainable SCM, capable of reducing cement content while satisfying structural and environmental requirements in construction applications.

Explosive welding is an effective method for joining metals with dissimilar physicochemical properties. The Al/Ni system is particularly interesting due to the formation of intermetallic phases with unique mechanical and thermal properties, which makes these welds potentially applicable in industries, such as aerospace, energy, and chemical. Diffusion processes occurring at the interface between these metals play a significant role and can impact the durability of the connections. Therefore, this research focuses on the analysis of diffusion phenomena in Al/Ni welds formed by explosive welding and subjected to further annealing. It was investigated whether the technological parameters of the joining process, such as detonation velocity, which varied from 2000 to 2800 m/s or mutual localization of the colliding plates during the explosion, influence post-annealing interface transformations, in particular the sequence of the intermetallic phase formation, their thickness and growth mechanism. Welded clads underwent annealing at 500 °C for periods ranging from 0.5 to 168 h. After the heat treatment, microstructure and phase characterization of the interface zone were performed, with scanning and transmission electron microscopy, thanks to which the mechanisms and growth kinetics of the forming phases were determined. Additionally, for the first time, the anisotropy of the thermal expansion in explosively welded Al/Ni was examined with respect to the shock wave propagation and the accompanying microstructure evolution, providing a significant contribution to the engineering design of welds subjected to the thermal cycling. The thermal expansion coefficient was measured over the temperature range from ambient temperature to 500 °C and analyzed in relation to the welding conditions. Differences in the thickness of the two forming Al₃Ni and Al₃Ni₂ layers and their dominant growth mechanisms were observed for the individual clads. The effect of detonation velocity was particularly significant at 2000 m/s, where prolonged annealing led to weld degradation, thus limiting strength due to unfavorable welding conditions. The presence of porosity identified at the Al1050/Al₃Ni₂ interface was attributed to the Kirkendall effect accompanying the annealing procedure. Measurements of the thermal expansion coefficient revealed minor differences between samples, with the largest discrepancies observed for clads produced at 2400 m/s, which may be due to the less uniform initial microstructure of the interface. The obtained results indicate a relationship between explosive welding conditions and changes in the microstructure and physical properties of Al/Ni welds after heat treatment.

In the present research, free vibration of a truncated conical shell is investigated. The shell consists of three layers: a porous core and two carbon nanotube-reinforced nanocomposite (CNTs-RNC) facesheets. The structure is inserted in a thermal environment and also, is also subjected to a longitudinal magnetic field. The structure’s kinematics is modelled based on the first-order shear deformation theory (FSDT), and the modified coupled stress theory (MCST) is used to consider the scale effect. The equations of motion are derived using Hamilton’s principle, and then, the generalized differential quadrature method (GDQM) is employed to solve them under various combinations of boundary conditions. The effects of several parameters, including geometry, porosity coefficient, porosity distribution patterns, CNTs’ mass fraction and types, agglomeration coefficients, boundary conditions, and small-scale parameter are investigated. The results demonstrate that the natural frequency increases with increasing CNTs’ mass fraction and decreases with increasing porosity. These structures have a wide range of potential applications and can be used in microelectromechanical and nanoelectromechanical systems.