Search Results (59)

Masonry retaining walls are widely used in mountainous regions but are susceptible to progressive internal damage under environmental and operational loads, which is often difficult to detect through conventional visual inspection. To address this problem, this study proposes a baseline-free vibration-based damage identification method for existing masonry retaining walls. The method combines impulse response function (IRF) estimation with wavelet packet decomposition (WPD) and introduces a scalar damage index, termed the energy ratio standard deviation (ERSD). Unlike conventional WPD energy ratio deviation (ERD) vectors, ERSD condenses multi-band energy redistribution into a single positive scalar for each sensor location, thereby facilitating spatial interpolation and field-level damage localization without modal extraction. The method was validated through four monthly impact hammer tests on a masonry retaining wall in Zhenjiang, China. The results show that non-zero ERD vectors indicate vibration energy redistribution between successive monitoring states, while the spatial peak of ERSD identifies the most likely damage zone. The ERSD maximum occurred at point 5 and was confirmed by post-test visual inspection, which revealed a local crack of approximately 0.8–1.2 mm in the adjacent mortar joint. To avoid overfitting with the limited four-test dataset, the temporal trend of ERSD was evaluated using a linear regression and finite-difference progression rates rather than a high-order polynomial. The proposed method provides a practical preliminary screening tool for field damage localization; however, its quantitative damage severity calibration requires further validation using controlled stiffness-reduction tests and environmental compensation models. Full article

3D-printed concrete (3DPC) enables formwork-free automated construction with geometric flexibility and improved material efficiency, yet its engineering reliability remains limited by interlayer weakening generated during sequential deposition. This review critically examines the formation, cross-scale consequences, and control of weak interlayer interfaces in 3DPC. In most studies, the 3DPC printing interval ranges from 20 s to 120 min, and the average interfacial bond strength ranges from 0.1 to 16 MPa. Interfacial weakness arises from the asynchronous evolution of adjacent layers in terms of contact quality, rheological recovery, moisture exchange, and early-age hydration. This mismatch promotes pore enrichment, discontinuity of hydration products, reduced phase continuity, and consequent local mechanical softening. These defects govern interlayer bonding, crack propagation, anisotropy, and stress-transfer pathways, and their effects propagate from material properties to member response, structural performance, and durability degradation. Rather than treating the interface as a localized cold joint, this review frames it as a process-induced multiscale variable linking printing history, microstructure, mechanical response, transport behavior, and serviceability. Current research remains constrained by non-comparable testing methods, undefined quantitative thresholds, and models that still rely heavily on empirical calibration. Future work should establish standardized characterization, transferable interface descriptors, multiscale predictive models, real-time quality control, and design methods that explicitly incorporate interfacial variability. 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

Thermal degradation of the interfacial microstructure critically limits the service life of Zn-Al brazed Cu/Al joints. This work elucidates the stabilizing role of trace Ni (0.3 wt.%) in retarding interfacial deterioration during 200 °C isothermal aging for up to 1000 h. Microstructural evolution and micromechanical responses were probed via SEM, EDS, and nanoindentation. In Ni-free joints, continuous Zn influx triggers the decomposition of the massive CuAl₂ phase into a defect-ridden, Zn-rich lamellar structure, precipitating a sharp decline in shear strength from 57 MPa to 37.5 MPa. Conversely, Ni doping constructs a robust fine-grained interfacial architecture. The Ni-bearing coral-like layer exhibits exceptional morphological stability, while the underlying Cu-based transition layer undergoes in situ stratification and Zn ejection, functioning as a chemical buffer to intercept Zn diffusion. This microstructural reconfiguration enables Ni-doped joints to sustain a shear strength of ~55.2 MPa after 1000 h—matching the initial strength of Ni-free counterparts. The superior durability stems from the modulus softening of the stratified transition layer and a multi-stage crack deflection mechanism, offering a viable metallurgical strategy for robust Cu/Al interconnects. Full article

In this study, a small core diameter single mode fiber laser was applied to weld an 8 mm thick plate of 6061-T6 aluminum alloy. The microstructural evolution and mechanical properties of the laser welded aluminum alloy specimens were investigated in detail. The results indicated that fully penetrated welded specimens, free of welding defects like porosity, melt sagging, and hot cracking could be achieved by optimizing the processing parameters through response surface methodology. The upper part of the fusion zone consisted mainly of fine equiaxed dendrites, with secondary dendrite arm spacing (SDAS) of approximately 3–5 μm. While the lower region of the fusion zone exhibited pronounced microstructural coarsening, made up mostly of coarse columnar grains, along with some localized equiaxed grains, and an SDAS ranging from 8 to 12 μm. Both the fusion zone and heat affected zone (HAZ) were characterized by a “softened” hardness profile. The fusion zone featured a narrow region with the lowest microhardness across the welded joint with the microhardness value reducing to ~72% of the base metal (BM). Meanwhile, the microhardness of the HAZ was ~87.4% of the BM. The ultimate tensile strength of laser welded specimens was ~243.6 MPa, amounting to approximately 78.3% of the base metal. This study provides a fresh approach for welding medium-thick aluminum alloy plate using a high-quality laser beam, even at the kilowatt level with a fiber laser, and it shows a strong promise for applications in light-alloy manufacturing sectors such as automotive, rail transportation, aerospace, and beyond. Full article

Eggshell cracks are a critical factor affecting egg quality and food safety, with traditional detection methods often struggling to detect fine cracks, especially under multi-colored shells and complex backgrounds. To address this issue, we propose a non-destructive detection approach based on an enhanced three-dimensional convolutional neural network (3D-CNN), named 3D-CrackNet, integrated with hyperspectral imaging (HSI) for high-precision identification and localization of eggshell cracks. Operating within the 1000–2500 nm spectral range, the proposed framework employs spectral preprocessing and optimal band selection to improve discriminative feature representation. A residual learning module is incorporated to mitigate gradient degradation during deep joint spectral-spatial feature extraction, while a parameter-free SimAM attention mechanism adaptively enhances crack-related regions and suppresses background interference. This architecture enables the network to effectively capture both fine-grained spatial textures and contiguous spectral patterns associated with cracks. Experiments on a self-constructed dataset of 400 egg samples show that 3D-CrackNet achieves an F1-score of 75.49% and an Intersection over Union (IoU) of 60.62%, significantly outperforming conventional 1D-CNN and 2D-CNN models. These findings validate that 3D-CrackNet offers a robust, non-destructive, and efficient solution for accurately detecting and localizing subtle eggshell cracks, demonstrating strong potential for intelligent online egg quality grading and micro-defect monitoring in industrial applications. Full article

The fracture behavior of the Al₄Cu₉ intermetallic compound at the interface of impact-welded Cu/Al joints remains insufficiently explored through integrated multiscale modeling and experimental validation. In this study, molecular dynamic (MD) simulations, finite element (FE) analysis implemented in ABAQUS (version 2020) and a cohesive zone model (CZM) were combined with optical microscopy (OM) and scanning electron microscopy (SEM) observations of the interface and crack initiation zones in impact-welded Cu/Al specimens to investigate crack propagation mechanisms under different defect configurations. The experimental specimens consisted of 1060 aluminum (Al) and oxygen-free high-conductivity (OFHC) copper, fabricated via impact welding and subsequently annealed at 250 °C for 100 h. The interfacial morphology and crack initiation features obtained from OM and SEM provided direct validation for the traction–separation (T-S) parameters extracted from MD and mapped into the FE model. The results indicate that composite defects (blunt crack + void) cause a significantly greater reduction in fracture energy and stress intensity factor than single defects and that defect effects outweigh temperature effects within the range of 200–500 K. The experimentally observed crack initiation locations were in strong agreement with simulation predictions. This integrated simulation–experiment approach not only elucidates the multiscale fracture mechanisms of the Al₄Cu₉ interface but also provides a physically validated basis for the reliability assessment and optimization of aerospace Cu/Al welded structures. Full article

The widespread application of WE43 (Mg-4Y-2Nd-1Gd-0.5Zr) alloy castings in aerospace components is hindered by the frequent formation of defects such as cracks, pores, and especially yttria inclusions. These defects necessitate subsequent welding. However, using homologous WE43 filler wires often exacerbates these issues, leading to high crack susceptibility and reintroduction of inclusions. Herein, we propose a novel strategy of tailoring Y content in filler wires to achieve high-quality welded joint of WE43 sand castings. Systematic investigations reveal that reducing Y content to 2 wt.% (WE23) effectively suppresses oxide inclusion formation and significantly enhances the integrity of the joint. The fusion zone microstructure evolves distinctly with varying Y levels: grain size initially increases, peaking at 24 μm with WE43 wire, then decreases with further Y addition. Moreover, eutectic compounds transition from a semi-continuous to a continuous network structure with increasing Y content, deteriorating mechanical performance. Notably, joints welded with WE23 filler exhibit minimal performance loss, with ultimate tensile strength, yield strength, and elongation reaching 93.0%, 98.0%, and 97.4% of the sand-cast base metal, respectively. The underlying strengthening mechanisms and solute-second phase relationships are elucidated, highlighting the efficacy of optimizing Y content in welding wire design. This study provides valuable insights toward defect-free welding of high-performance Mg-RE alloy castings. Full article

In many areas such as the automotive, aircraft, and building industries, the high-strength aluminum alloy Al 7075 is frequently used due to its appropriate properties as a lightweight structural material. However, due to modest weldability, it is challenging to obtain high-quality welds with suitable mechanical properties, as cracks are generated while welding. Moreover, in order to avoid post-welding heat treatments and the use of complex welding equipment, in this paper the Al 7075 alloy is welded with MIG under longitudinal vibrations by using the Al 4043 alloy as filler material. As a consequence of strengthening the HAZ through precipitation, the mechanical and structural properties of the welded joints can be improved. These are investigated both under longitudinal forced vibrations at 50 Hz and without such vibrations. The results reveal improvements in terms of reducing the risk of hot cracking, obtaining a band structure free of porosity of the welds, improving the hardness of the welds under vibrations by 8.7% to 12.5%, and improving the tensile strength of the plates welded under vibrations by 12 to 15.5% in comparison to no vibrations. In relation to other welding procedures, the proposed procedure is more cost-effective and the weld quality is improved during the welding process. Full article

This study investigates two-sided pulsed-periodic laser welding of three-layer metal–polymer–metal (MPM) composite sheets composed of galvanized dual-phase steel (DPK 30/50+ZE) as outer layers and a polypropylene–polyethylene (PP–PE) core. Welding was performed using a Rofin StarWeld Performance pulsed Nd:YAG laser with controlled parameters: pulse energy (30–32 J), duration (6–8 ms), and frequency (up to 1 Hz). High-quality welds were achieved with penetration depths reaching 70% of the outer metal layer thickness and minimal defects. Microscopic analysis revealed distinct fusion and heat-affected zones (HAZ) with no evidence of cracks or porosity, indicating stable thermal conditions. Mechanical testing showed that the welded joints attained a tensile strength of approximately 470 MPa, about 80% of the ultimate tensile strength of the base metal, with an average elongation of 0.6 mm. These results confirm the structural integrity of the joints. The observed weld morphology and microstructural features suggest that thermal conditions during welding significantly affect joint quality and HAZ formation. The study demonstrates that strong, defect-free joints can be produced using basic beam-shaping optics and outlines a pathway for further improvement through the integration of diffractive optical elements (DOEs) to enhance spatial-energy control in multilayer structures. Full article

This investigation examines the corrosion behavior and mechanisms of 304 stainless steel shielded metal arc welding (SMAW) and gas metal arc welding (GMAW) joints in the simulated reservoir environment through electrochemical testing, stress-free hanging specimens and U-bend specimen immersion experiments, and microstructural characterization. The electrochemical results demonstrate that both welded joints exhibit a superior corrosion resistance in this environment, with a sensitivity of intergranular corrosion (IGC) below 1% and a corrosion rate below 0.005 mm/a. Increasing chloride concentrations elevate the passivation current densities for both the base metal and welded joints. The immersion testing revealed that after 90 days of exposure across the investigated chloride concentrations (50–300 mg/L), all welded specimens maintained surface integrity with no visible corrosion. Furthermore, U-bend specimens demonstrated no evidence of stress corrosion cracking, confirming a low stress corrosion susceptibility. Full article

The Sichuan Basin is a key area for shale gas energy exploration in China. However, the pore evolution mechanism and accumulation effect of the Lower Jurassic continental shale gas in the northeastern Sichuan Basin remain poorly understood. In this study, the pore structure characteristics of shale reservoirs and the dynamic accumulation and evolution of shale gas in the northern Fuling and Yuanba areas were systematically analyzed by adsorption experiments, high-pressure mercury injection joint measurement, and thermal simulation experiments. The results indicate the following: (1) The continental shale in the study area is predominantly composed of mesopores (10–50 nm), which account for approximately 55.21% of the total pore volume, followed by macropores (5–50 μm) contributing around 35.15%. Micropores exhibit the lowest proportion, typically less than 10%. Soluble minerals such as clay minerals and calcite significantly promote pore development, while soluble organic matter may block small pores during hydrocarbon generation, which facilitates the enrichment of free gas. (2) The thermal simulation experiment reveals that pore evolution can be divided into two distinct stages. Prior to 450 °C, hydrocarbon generation leads to a reduction in pore volume due to the compaction and transformation of organic matter. After 450 °C, organic matter undergoes cracking processes accompanied by the formation of shrinkage fractures, resulting in the development of new macropores and a significant increase in pore volume. This indicates that thermal energy input during the thermal evolution stage plays a key role in reservoir reconstruction. (3) The early Jurassic sedimentary environment controls the enrichment of organic matter, and the Cretaceous is the key period of hydrocarbon accumulation. Hydrocarbon generation and diagenesis synergistically promote the formation of gas reservoirs. The Cenozoic tectonic activity adjusted the distribution of gas reservoirs, and finally formed the enrichment model with the core of source–reservoir–preservation dynamic matching. For the first time, combined with dynamic thermal simulation experiments, this study clarifies the stage characteristics of pore evolution of continental shale and identifies the main controlling factors of shale gas accumulation in the Lower Jurassic in northeastern Sichuan, which provides a theoretical basis for continental shale gas exploration and energy resource development, offering important guidance for optimizing the selection of exploration target areas. Full article

In this study, a series of unrelieved cutting tests was conducted to analyze the effect of joints on rock cutting using a conical pick. The tests were performed on jointed rock mass specimens with joint spacings (J_s) of 30, 60, and 90 mm and at cutting depths of 3, 6, 9, and 12 mm. For each case, the distance between the cutting path and the joint plane (d) was varied from 0.1J_s to 0.5J_s. The cutting force decreased as the distance from the joint plane increased but reached the level observed in intact rock at the midpoint between adjacent joint planes (d = 0.5J_s). Regardless of joint spacing, the cutting force reached its minimum when d was between 0.2J_s and 0.3J_s. The rock fragmentation zone extended beyond the joint plane when d was 0.1J_s but became confined within the joint plane from around 0.2J_s to 0.3J_s. These results indicate that the influence of the joint is most pronounced within this range. Three types of crack propagation patterns were observed near the joint plane: (1) cracks that terminate at the joint along the shortest path, (2) cracks that pass through the joint and reach the opposite free surface, and (3) cracks that end at a free surface located just inside the joint plane. These observations suggest that the reduction in cutting force can be attributed to shorter crack propagation paths due to the presence of the joint. This study contributes to a better understanding of the cutting behavior of jointed rock masses when using a conical pick. Full article

A total of 0.3%C-Cr-Mo-V steel, a high-strength alloy steel widely used in rocket motor housings, suspension systems in high-performance vehicles, etc., is noted due to its high strength-to-weight ratio. However, its high carbon equivalent (CE > 1%) makes it challenging to weld, as it is prone to brittle martensitic formation, which increases the risk of cracking and embrittlement. The present paper focuses on enhancing the microstructure and mechanical properties of 0.3% C-Cr-Mo-V steel by gas tungsten arc welded (GTAW) joints, utilizing post-weld heat treatment and cooling strategies (PWHTCS). A systematic experimental approach was employed to ensure a defect-free weld through dye penetrant testing (DPT) and X-ray radiography techniques. Subsequently, test specimens were extracted from the welded sections and subjected to PWHT protocols, including hardening, tempering, and rapid quenching using air and oil cooling (AC and OC, respectively) mediums. Results show that OC has enhanced tensile strength and hardness while simultaneously maintaining and improving ductility, ensuring a well-balanced combination of strength and toughness. Fractography analysis revealed ductile fracture in AC samples, whereas OC weldments exhibited a mixed ductile–brittle fracture mode. Thus, the findings demonstrate the critical role of PWHTCS, with OC, as an effective method for achieving enhanced mechanical performance and microstructural stability in high-integrity applications. Full article

This study attempts to use fly ash as the brazing filler additive to increase the sustainable use of coal-fired power plant by-product materials. The experimental results show that adding 5 wt% fly ash into the Ag paste filler contributes to the interfacial reactions in heterogeneous reactive air brazing (RAB) of the ZrO₂ and Crofer alloy. The Ag-rich phase dominates the brazed zone. The interfacial reaction layers contain oxidation of the Cu-Ti coating layer, Crofer alloy, and the Si/Al-rich oxides from the fly ash particles. The 5% fly ash RAB joint maintained airtightness for 280 h under 2 psig helium at room temperature. When the test temperature was raised to 600 °C for 24 h, the pressure of the joint assembly still did not drop. When the fly ash addition was increased to 10 wt%, the joint assembly was no longer leak-free at room temperature. Many visible voids and cracks exist in the brazed zone and at the ZrO₂/braze and braze/Crofer interfaces. A high volume fraction of the fly ash particles results in many brittle Si/Al-rich oxides in the joint after RAB, and the fracture of these oxides significantly deteriorates the airtightness of the joint. This study shows the feasibility and potential of introducing 5 wt% fly ash particles to the Ag-rich paste filler during the RAB of ZrO₂ and Crofer for airtight applications. Full article