Search Results (3,323)

This study investigates the seismic response of a natural draft reinforced concrete cooling tower subjected to spatially varying earthquake ground motion, with particular emphasis on nonlinear material behavior, damage evolution, and stiffness degradation. The analysis is based on a constitutive description of concrete using the Concrete Damaged Plasticity (CDP) model, enabling the representation of tensile cracking, compressive crushing, and irreversible plastic deformation under cyclic dynamic loading. Two structural configurations of the lower shell region–a locally thickened shell and a bottom ring-stiffened solution–are examined from the perspective of material performance and damage control. Spatially varying seismic excitation is defined using a real earthquake record from the Carpathian Flysch region, with wave passage and incoherence effects calibrated from in-situ measurements. Nonlinear time-history analyses, performed to capture the coupling between material degradation mechanisms and global structural response, demonstrate that the seismic performance of the cooling tower is controlled primarily by local material behavior rather than global dynamic characteristics. Spatial variability of ground motion activates complex deformation modes, leading to pronounced tensile damage, plastic strain accumulation, and stiffness degradation in the lower shell region. The structural variant with thickened lower zone of the shell exhibits extensive material deterioration, including the formation of a continuous plastic zone and irreversible deformation associated with damage localization. In contrast, the ring-stiffened configuration effectively limits damage propagation, reduces plastic strain by up to 80%, and maintains predominantly elastic material response with significantly lower stiffness degradation. The bottom ring stiffener is shown to provide superior performance by mitigating damage evolution of the concrete structure under spatially non-uniform seismic loading. The study highlights the critical role of advanced constitutive material modeling in capturing the realistic seismic behavior of reinforced concrete shell structures and demonstrates that structural strengthening strategies should be evaluated based on their ability to control material degradation mechanisms. Full article

The hydrogen embrittlement (HE) behavior of an Fe–18Mn–8Al–1C–5Ni lightweight steel containing a fine and uniformly distributed B2 phase and κ-carbide was investigated by slow strain rate tensile testing with in situ hydrogen charging. Hydrogen charging reduces the elongation from 28.2% to 11.2%, while preserving an ultimate tensile strength above 1100 MPa and yielding an HE index of 60.2%. A thermal desorption analysis reveals a multi-peak desorption curve corresponding to diffusible hydrogen, hydrogen reversibly trapped at κ-carbides, and hydrogen strongly bound at the B2/γ interfaces, revealing a hierarchical hydrogen trapping behavior. Electron backscatter diffraction and electron channeling contrast imaging analyses near the fracture head region further reveal that localized hydrogen enrichment at the B2/γ boundaries induces severe stress concentration and interfacial weakening, shifting the fracture mode from ductile micro-void coalescence in air to hydrogen assisted intergranular and interphase cracking. This study clarifies the distinct roles of coherent κ-carbide and B2/γ interfaces in hydrogen trapping and crack initiation, offering a microstructure-based perspective for designing high-strength, HE resistant lightweight steels. Full article

In this study, 310S austenitic stainless-steel was welded using a laser with varying amounts of Nb to systematically investigate the effect of Nb on solidification cracking susceptibility, mechanical properties, and corrosion resistance of the weld. Under the present experimental conditions, the critical restraint width was higher for the 0.58 wt.% Nb and 1.45 wt.% Nb welds than for the Nb-free and 2.3 wt.% Nb welds, indicating that Nb addition affected the solidification cracking response of the weld. At low-to-moderate Nb contents, Nb can aggravate compositional segregation and increase the presence of low-melting-point liquid films, thereby increasing cracking susceptibility. At higher Nb contents, the reduced cracking susceptibility was accompanied by microstructural refinement and changes in the distribution of Nb-rich constituents during solidification. With increasing Nb content, the number of precipitated phases in the weld increases, mainly distributed at the austenite grain boundaries in granular, elongated, and chain-like forms. The introduction of Nb generally increases the microhardness and tensile strength of the welded joint, attributed to grain refinement strengthening and solid-solution strengthening. The reduction in area first increased and then decreased, suggesting that excessive Nb addition may reduce ductility because of the increased amount of grain-boundary precipitates and local strengthening heterogeneity. With increasing Nb content, the Ir/Ia ratio decreased from 67.6% to 52.2%, suggesting improved intergranular corrosion resistance. This improvement is likely related to the preferential reaction of Nb with carbon, which may suppress the formation of Cr-depleted zones at grain boundaries. Overall, Nb addition improved the corrosion resistance and increased the hardness and tensile strength of the weld; however, its effect on solidification cracking susceptibility was non-monotonic, indicating that careful control of Nb content is required to balance cracking susceptibility, mechanical properties, and corrosion resistance. Full article

Polymer insulation layers such as polyimide (PI) have gradually replaced inorganic dielectric layers (SiO₂, SiCN) in the integrated packaging process of hybrid bonding (HB). PI can fill the gaps in the thermal compression bonding process and help to obtain a good Cu/Polymer bonding interface. At present, the existing post-crack double cantilever beam tensile test (PBC-DCB) has been successfully applied to the quantitative measurement of bonding strength of hybrid bonding with inorganic materials, but this method only considers elastic behavior. Since PI exhibits viscidity, elasticity and plasticity, knowing how to correlate these properties to the bonding process is challenging. Whether PBC-DCB is suitable for the characterization of PI bonding is unclear. This paper presents a comprehensive experimental and finite element analysis (FEA) study on the PI–PI bonding interface. Firstly, nanoindentation experiments and simulations are performed on the prepared PI interface to obtain key elasticity and plasticity parameters. Then, the bonding strength is characterized by the PBC-DCB test. Theoretical and experimental results show that the plasticity of PI causes energy dissipation during stretching, resulting in a deviation of approximately 2.51% compared with pure elasticity. Based on experimental data, the Cohesive Zone Model (CZM) FEA method is used to simulate the crack propagation. The results indicate that the Embedded Process Zone (EPZ) model can accurately describe crack initiation and delamination behavior, with a margin of error of about 3.61%. Finally, based on the EPZ CZM, defects such as bonding void and wafer warpage are further discussed in relation to bonding strength measurement. Full article

Titanium matrix composites (TMCs) are increasingly vital in aerospace for their high specific strength and wear resistance, with compositional gradient design serving as a key strategy to mitigate thermophysical mismatches between ceramic and metal phases. This study utilized laser-directed energy deposition with concurrent wire-powder feeding (LDED-WP) to fabricate TiC/Ti6Al4V gradient composites, employing a laser power of 2700 W, wire feed rates of 110–150 cm/min, and calibrated powder feed rates ranging from 50.22 to 497.13 g/h. Along the build direction, the TiC content was progressively increased from 10 wt.% to 60 wt.%. Investigations into microstructural evolution revealed that the reinforcement morphology transitions from chain-like eutectic TiC to dendritic primary TiC, while the lamellarα-Ti width refines significantly from 4.07 ± 1.15 μm to 0.45 ± 0.29 μm. EBSD analysis confirmed that higher TiC concentrations weaken the characteristic <001> solidification texture, reducing intensity from 11.24 to 7.64. Furthermore, KAM analysis highlighted that thermal expansion and elastic modulus mismatches trigger substantial geometrically necessary dislocation (GND) accumulation at interfaces. Consequently, Vickers hardness improved by 164% along the gradient, peaking at 950 HV. Although the composite achieved an ultimate tensile strength of 630 MPa, the elongation was limited to 2.4% due to crack nucleation in TiC-rich regions and interfacial instability. Full article

This study presents a mechanics based analytical framework for predicting the flexural–shear capacity of reinforced concrete (RC) beams strengthened with Engineered Cementitious Composites (ECCs) and a hybrid ECC–GFRP near surface mounted (NSM) system. Building upon previously reported experimental observations, the present work aims to establish rational prediction models capable of capturing the interaction between flexural and shear mechanisms in strengthened beams. The analytical approach integrates sectional analysis for flexural capacity with a modified truss analogy for shear resistance, explicitly incorporating the strain hardening tensile contribution of ECC and the tensile and confinement effects of GFRP reinforcement. An interaction based failure criterion is subsequently employed to identify the governing failure mode under combined flexural shear actions. The proposed model is validated against experimental results obtained from twenty seven beam specimens with varying flexural and shear reinforcement ratios and strengthening configurations. The predicted ultimate loads show good agreement with experimental values, with an average deviation within ±10%. The analytical framework accurately captures the transition between flexural dominated, combined flexural–shear, and diagonal tension failures observed experimentally. Results demonstrate that ECC significantly enhances ductility and shear crack control, while the hybrid ECC–GFRP system provides substantial strength enhancement with a controlled shift in failure mode. Overall, the developed analytical models offer a reliable and computationally efficient tool for predicting the flexural–shear capacity and failure behavior of ECC and hybrid ECC–GFRP-strengthened RC beams, supporting performance based design and practical strengthening applications. Full article

The application of ultra-high performance concrete (UHPC) in the hogging moment region significantly enhances the crack resistance of concrete slabs of composite girders with integrated piers, while also providing economic benefits. To investigate the crack resistance performance and develop a calculation method for crack width in hogging moment region of steel–UHPC–normal concrete (NC) composite girders, a full-scale bending test was conducted. Based on the test results, the post-cracking residual tensile strength of UHPC was determined according to the energy equivalence principle. A calculation method for reinforcement stress incorporating the tensile contribution of UHPC at a cracked section was proposed and then the applicability for current design codes for crack width calculation was evaluated. For the UHPC–NC interface, a corresponding crack width calculation method was developed. The results indicate that cracks initiated on the surface of the NC layer beneath the UHPC overlay at the cantilever root. Then cracks developed in sequence at the top surface of the UHPC layer cantilever root, the UHPC–NC interface, and the mid-plane of the girder-to-pier joint. Ultimately, UHPC cracks exhibited a “numerous and closely spaced” distribution, whereas NC cracks were “few and widely spaced.” When the residual tensile strength of UHPC at cracked section was considered, the mean value and average coefficient of variation in the ratios of calculated to measured reinforcement stresses for different sections were 1.07 and 0.10, respectively, which can be further used for crack width calculation. The mean ratios of code-predicted to measured UHPC crack widths for different sections using the Chinese code, French code, and European code were 1.10, 0.98, and 1.13, respectively, with corresponding average coefficients of variation of 0.25, 0.33, and 0.28; the Chinese code is recommended for UHPC crack width prediction. For the UHPC–NC interface, an expression for crack width calculation was derived using the comprehensive theory, and the mean ratio of calculated to measured values and the coefficient of variation were 1.08 and 0.18, respectively, demonstrating good predictive accuracy. Full article

Ultra-high molecular weight polyethylene (UHMWPE) fibers have recently emerged as a promising reinforcement material in fiber-reinforced concrete (FRC). To investigate the synergistic effects and reinforcing mechanisms of fibers with different elastic moduli within the concrete matrix, a series of hybrid fiber-reinforced concrete (HFRC) specimens were prepared by incorporating 0.25 vol%, 0.5 vol%, and 0.75 vol% carbon fibers (CFs) or polypropylene (PP) fibers into concrete containing 1 vol% UHMWPE fibers. The mechanical performance of the prepared composites was systematically evaluated through compressive, splitting tensile, flexural, and drop-weight impact tests. The experimental results indicate that concrete reinforced solely with UHMWPE fibers exhibits higher compressive strength but lower tensile strength, flexural strength, ductility, and impact toughness than the hybrid fiber systems. For both UHMWPE-CF and UHMWPE-PP hybrid concretes, the initial cracking impact resistance and failure impact resistance increased progressively with increasing CF or PP content. At equivalent fiber volume fractions, UHMWPE-PP hybrid concrete demonstrated superior resistance to initial cracking, whereas UHMWPE-CF hybrid concrete exhibited better post-failure impact resistance. Furthermore, fractal theory was employed to quantitatively characterize the impact damage behavior of HFRC specimens. The impact damage evolution equation is established by using the two-parameter Weibull distribution model. The findings provide theoretical and experimental support for the design and optimization of hybrid fiber-reinforced concrete subjected to impact loading. Full article

Concrete, when used in construction, is prone to internal micro cracks that compromise its strength, flexibility, durability and lifespan. To address this, self-healing concrete technologies using microbial-induced calcium carbonate precipitation (MICP) have gained significant attention. The objective of this study was to focus on the preparation of a bacterial consortium (BV) composed of Bacillus cereus and Vibrio natriegens, selected for their specific characteristics to produce calcium carbonate under alkaline conditions. These bacterial strains with nutrients were added in optimised proportions to the concrete mixes and evaluated their healing potential. The effectiveness of the bacterial consortium on the self-healing potential of concrete was investigated. Similarly, the performance of this consortium was assessed across three different water–cement (w/c) ratios: 0.40, 0.45, and 0.50. These variations were selected to investigate the influence of moisture availability and mixed porosity on bacterial activation and crack healing efficiency. Mechanical tests like flexural strength, split tensile strength and compressive strength were performed to assess the structural recovery. Durability tests such as acid resistance, water absorption, and non-destructive tests like ultrasonic pulse velocity were also performed. Based on these investigations, a 0.40 w/c ratio of bacterial consortia (0.40 BV) showed the best performance. These results indicate that the bacterial consortium can significantly improve the self-healing properties of concrete, particularly at low w/c ratios. Full article

Underground Compressed Air Energy Storage (CAES) is a promising large-scale energy storage technology, yet its long-term operational safety is constrained by progressive tensile damage accumulation in lining structures under cyclic thermo-mechanical loading. Conventional steel-lined caverns are costly, while ordinary reinforced concrete linings require excessive reinforcement due to their limited tensile capacity, compromising the economic viability of CAES. This study proposes a Reinforced-Steel Fibre Concrete (R-SFC) lining as the structural load-bearing layer of CAES caverns, in which the steel fibres provide tensile and crack-propagation resistance and the rebars contribute supplementary tensile capacity. A 2D coupled thermo-mechanical damage-plasticity finite element model was developed in COMSOL Multiphysics and verified using published in situ monitoring data from operating CAES caverns. Parametric analyses of the steel fibre volume fraction, lining thickness, rebar diameter, and cavern diameter were then performed. The results show that the R-SFC lining significantly improves crack propagation resistance, reducing the maximum tensile damage by 41.3% relative to conventional reinforced concrete while lowering steel consumption. Within the lining–rock system, the concrete lining and the surrounding rock jointly resist the radial compressive load, while the steel fibres and rebars bear the hoop tensile stress. A thickness-to-diameter ratio of 1/8 to 1/5 is identified as the recommended geometric design range to balance lining damage against surrounding rock loading. Finally, an MOPSO algorithm coupled with a PSO-BP surrogate model is employed to balance lining tensile damage against cavern dimensions, yielding optimised parameter combinations particularly suitable for cavern diameters around 4 m. The study findings may provide a new lining solution and design reference for cost-effective and high-reliability underground gas storage. Full article

This study examined the stress corrosion of Alloy 625 in Cl⁻ + S₂O₃²⁻ solutions using digital holography in combination with electrochemical methods. Without elastic tensile stress, intergranular corrosion (IGC) occurred, due to the higher activity of grain boundaries compared to the grain interior and to preferential adsorption of sulfur (produced by S₂O₃²⁻ decomposition) at these boundaries. Digital holography observations showed that IGC initiated at certain grain boundaries and propagated to adjacent boundaries, even in the absence of elastic tensile deformation. Applying elastic tensile stress (260 MPa, ~46% σy) increased the defect density within the oxide film, thereby enhancing corrosion and anodic currents, and inducing river-like cracks. Although elastic tensile stress suppressed IGC, it simultaneously promoted stress corrosion cracking (SCC), as the stress exerted a stronger accelerating effect on corrosion than the grain-boundary did. Digital holography allowed in situ monitoring of the stress corrosion process in Alloy 625, demonstrating that cracks initiated via localized corrosion/IGC and subsequently propagated along the direction of the applied stress. Full article

Acoustic emission (AE) is a vital non-destructive technique for monitoring damage in materials, yet its simulation via the Discrete Element Method (DEM) has historically been limited to material-scale analysis. This research presents a novel application of block-based DEM to simulate AE signals in masonry structures at the structural scale under quasi-static in-plane loading. Using a simplified micro-modeling approach, the study first validates the method by monitoring crack initiation and AE energy in single mortar bed joints under tensile and shear conditions. The methodology is then scaled to a large-scale masonry wall panel (1.835 × 1.170 × 0.15 m³) subjected to monotonic shear loading. A critical finding is the influence of local damping; a reduced damping ratio of 0.3 is recommended to preserve the kinetic energy necessary for capturing clear velocity signals. Numerical results show strong agreement with experimental force-displacement and cumulative AE energy curves, confirming the model’s robustness. Furthermore, frequency analysis of the simulated signals successfully distinguishes between tensile and shear failure modes. This study fills a significant gap in the literature by demonstrating that DEM is an effective predictive tool for structural-scale failure analysis and AE monitoring in heterogeneous masonry. Full article

The inherent heterogeneity of coal significantly influences cutting efficiency, directly impacting energy consumption and dust generation in mining operations. To investigate this effect, this study established a heterogeneous coal model using PFC 2D 5.0, assigning strength parameters based on the Weibull distribution. The influence of the heterogeneity index (λ) on macroscopic strength, brittleness, and micro-crack propagation during coal cutting was systematically analyzed, and comparisons were made with homogeneous models of varying uniaxial compressive strength (UCS). The results show that as λ increases, both UCS and Brazilian tensile strength (BTS) increase exponentially, approaching the values of the homogeneous models, with BTS exhibiting greater sensitivity to λ than UCS. The brittleness index also increases with λ. During cutting, a higher λ leads to more concentrated crack propagation and stress distribution, as well as a reduced proportion of shear cracks, indicating a shift toward a more controllable fragmentation mode. Correspondingly, the specific energy (SE) for cutting decreases monotonically with λ, reflecting enhanced cutting efficiency, a trend attributed to the reduced energy dissipation from shear friction and the homogenization of internal stress distribution. Compared with homogeneous models, the heterogeneous models produce a more complex crack network and a greater number of cracks at lower strength levels, though these differences diminish as λ increases. These findings provide theoretical insights for optimizing cutting parameters to reduce energy consumption and minimize uncontrolled fracturing in efficient coal resource exploitation. Full article

In this study, the two-dimensional aligned steel fiber-reinforced micro-expansive concrete (2D) was prepared, aiming to address the inherent vulnerabilities of concrete, such as early-age shrinkage cracking and low tensile ductility. For this purpose, the steel fibers and expansive agent were utilized. Furthermore, the planar rotating magnetic field was used to randomly distribute the steel fibers in a two-dimensional plane. In order to verify its superior mechanical and shrinkage properties, the compressive, fracture and drying shrinkage tests were carried out. The results demonstrate that the 2D alignment method enhances the fiber utilization efficiency. Compared with fiber-free groups, the compressive strength and fracture parameters of specimens incorporating steel fibers were improved. Furthermore, compared with randomly distributed steel fiber-reinforced micro-expansive concrete (RD), the 2D alignment method made the cubic compressive strength and fracture energy improve 8–14.2% and 19.4–110%, respectively. Additionally, the advantage of the fiber 2D alignment method was also reflected in the inhibition of drying shrinkage. Compared with normal concrete, the 180-day shrinkage strain of the 2D1.2 group was reduced to 200 με (only 19.5% of that of normal concrete, or 30.6% of that of micro-expansive concrete). Mechanistically, these superior performances are fundamentally governed by a coupling effect: chemical shrinkage compensation and physical alignment constraint. Full article

To investigate the shear performance of steel fiber-reinforced high-strength concrete (SFRHSC) corbels subjected to concentrated loading, an experimental program was executed on six specimens featuring welded anchorage for the upper longitudinal reinforcement. The control variables included shear span-to-depth ratios of 0.2 to 0.5 and steel fiber volume fractions of 0%, 0.75%, and 1.50%. During the testing phase, strain evolution within the steel reinforcement and concrete matrix was monitored to analyze the structural deformation sequence and ultimate failure modes. Anchored in the Mohr–Coulomb failure criterion and the foundational strut-and-tie model (STM) framework, a softened strut-and-tie calculation approach for corbel shear capacity was formulated; this method explicitly accounts for the softening effect of the steel fiber-reinforced concrete (SFRC) and incorporates a size effect correction. The established shear capacity calculation model, alongside STM-based provisions from ACI 318-19, EN 1992-1-1, and CSA A23.3-19, was deployed to forecast the shear capacities of the six fabricated specimens and 18 additional units sourced from existing literature. Ultimately, a rigorous comparative analysis was conducted between the theoretical predictions generated by each method and the empirical test data. The results indicate that the failure process of the SFRHSC corbels primarily involves three distinct stages: initial cracking, through cracking, and ultimate failure. The addition of steel fibers can alleviate stress concentration at cracks and limit crack growth, thereby improving the tensile performance of the cracked concrete. Test results indicate that the strain in the longitudinal tensile reinforcement increased with the shear span-to-depth ratio but decreased as the steel fiber volume fraction increased. At the point of specimen failure, all longitudinal tensile reinforcement had reached the yield strength, while the horizontal stirrups only partially yielded. The concrete strain distribution across the normal section of the corbel did not follow the plane section assumption. Furthermore, incorporating steel fibers increased both the cracking load and the ultimate load of the corbel normal sections. The mean value of the experimental-to-predicted ratios obtained from the STM provisions of various international codes was 1.453, with a variance of 0.029, indicating conservative calculation results. In contrast, the mean value of the experimental-to-predicted ratios for the calculation model developed in this study was 1.048, with a variance of 0.004, demonstrating closer agreement with the experimental results and less dispersion. Simultaneously, by explicitly considering the softening effect in SFRHSC and the size effect, it provides a better prediction for the shear capacity of corbels. Full article