Archives of Civil and Mechanical Engineering最新文献

The article describes to design the parameters of hot rolling and heat treatment technology in a way that would allow for permanent bonding of S355J2 and NANOS-BA® steel into one high-strength clad plates. In the article, guidelines for the hot rolling process of clad plates with two-stage heat treatment were described, which were then verified in a semi-industrial technological line. The materials obtained in this way in different initial states were subjected to metallographic and strength tests. Based on three technological variants of the process, S355J2/ NANOS-BA® clad plates were produced. After additional heat treatment, a nanobainitic microstructure of high strength and ballistic and abrasion resistance was created in the applied layer, which indicates the possibility of using this type of clad plate in the armaments, machine building, or construction industry.

In this paper, a pulse current assisted compression test platform is built to investigate the effects of temperature, strain rate, and current density on flow stress. Based on the Johnson-Cook model and considering the physical mechanism of the electroplastic effect, the constitutive equation for Inconel718 under pulsed current is constructed. By compiling the user subroutine Vumat and importing it into Abaqus for simulation, and comparing it with the electric pulse assisted turning experiment, the influence of electroplastic parameters (0–100 A) on chip morphology and cutting force is explored. The research results are expected to provide technical guidance for expanding the application field of Inconel718.

This study investigates the influence of friction stir welding parameters, specifically tool rotational speed and linear speed, on the electrochemical and mechanical properties of EN AW-6082-T651 butt joints. The research encompassed microstructural analysis, surface roughness measurements, potentiodynamic corrosion tests, hardness profile measurement, and static tensile testing. Results revealed that decreasing the linear speed or increasing the rotational speed during welding intensified heat input, leading to grain growth in the weld nugget zone. The smallest grain size of 3.46 ± 1.11 µm was achieved at 1000 rpm and 250 mm/min. Surface roughness was minimized at 1250 rpm and 200 mm/min, as excessive tool feed caused irregularities. Corrosion resistance improved compared to the parent material, attributed to fine-grained structures promoting compact passive layer formation. Hardness profiling indicated the lowest values in the heat-affected zone, particularly for joints produced at 1250 rpm and 200 mm/min due to the highest heat input and precipitate dissolution. Tensile testing confirmed fracture locations in the heat-affected zone, with maximum tensile strength reaching 69% of the base material and elongation approximately 30%.

Cementitious materials are often exposed to aggressive environments, which have a significant impact on their durability. Proper prediction of concrete corrosion helps to apply the right measures and technologies, to extend the service life of structures. Carbonation and cyclic freezing are recognized among the most common corrosive factors for concrete. Their progress is linked to the penetration of CO₂ and water into the concrete structure. Due to the random arrangement of aggregates and cement paste, concrete is an inhomogeneous material. Therefore, the progress of carbonation and frost-induced damage should be treated as random variables with appropriate probabilistic parameters. Experimental studies on concrete carbonation and freezing were conducted in accordance with the standards EN 12390–12 and EN 12390–9. As observed in the experiments, the progress of carbonation and frost damage of concrete could be described by zigzag, not necessarily monotonic functions. Stochastic differential equations (SDE) were employed to predict the behavior of concrete exposed to elevated CO₂ concentrations and cyclic freezing. The stochastic model consisted of a drift term, which described the general trend of concrete durability exposed to carbonation and frost cycles, as well as a diffusion term, which accounted for the stochastic features of inhomogeneous concrete microstructure. The Euler–Maruyama approximation with Milstein improvement was applied to model the realization of the stochastic changes in concrete microstructure/durability. The proposed approach predicted experimental results with high accuracy. The application of the Monte Carlo (MC) method with 100,000 SDE realizations allowed to calculate the statistical parameters of the processes, such as concrete carbonation and freezing cycles. The probabilistic parameters, such as expected values and standard deviations, calculated using the SDE_MC approach, were in good agreement with experimental results for both problems, i.e. decelerating concrete carbonation and accelerating concrete scaling.

High-speed penetration experiments were performed on traditional sintered 93W alloy (93W–5.4Ni–1.6Fe) and a novel 93W–La alloy (93W–5.5Ni–1.1Fe–0.4La) containing 0.4% La, to impact a 30CrMnMo target at a velocity of 1650 m/s. The results indicated that the incorporation of La enhanced the mechanical properties of the 93W alloy, resulting in an 8.41% increase in the penetration depth of the 93W–La alloy compared with the sintered 93W alloy. The parameters for the Johnson–Cook constitutive equations of the two types of penetrator materials were determined through quasi-static tensile tests and Split-Hopkinson Pressure Bar (SHPB) experiments. Numerical simulations of the high-speed penetration tests were conducted on the LS-DYNA platform using FEM and adaptive FEM–SPH methods. The simulation results were compared with experimental target impact test data, demonstrating that the adaptive FEM–SPH method had superior computational accuracy. The penetration characteristics of both penetrators were analyzed throughout the crater formation, stable penetration, and plugging stages. The 93W alloy penetrator retained a “mushroom head” shape at the tip throughout the penetration process, whereas the 93W–La alloy penetrator exhibited significant adiabatic shear sensitivity, leading to adiabatic shear failure and “self-sharpening” characteristics.

To precisely elucidate the deformation characteristics of Ti65 sheets under uniaxial and biaxial stress states during the superplastic forming (SPF) process, a series of uniaxial hot tensile and biaxial bulging tests were conducted to explore the superplastic deformation behavior within a temperature range of 900–960 °C and a strain rate range of 0.001–0.03 s⁻1. The deformation behavior and uniform strain under uniaxial stress states were characterized through the DIC real-time strain measurement system. In addition, the key microstructures evolutions during different stress states were characterized and analyzed to determine the deformation mechanisms. Based on the test results, the constitutive model for both uniaxial and biaxial behavior of Ti65 sheets was developed and calibrated. The results of this research indicated that Ti65 exhibited superplastic deformation at 940 °C—0.0014 s⁻1 and 960 °C—0.0075 s⁻1, which led to an enlargement of its forming limit. Simultaneously, the evolution mechanism of the microstructure under biaxial stress was revealed. As the temperature increased, the proportion of high angle grain boundaries rose, the grain size decreased, and the forming limit increased accordingly. The established constitutive model, which takes into account the evolution of the microstructure, successfully captured the forming limit points. The accuracy of the predicted uniaxial stress–strain and the bulging grain size reached 91.2% and 96.24%, respectively. This research provides theoretical guidance for the selection of the process window of titanium alloys.

Sapphire, known for its high hardness and excellent optical properties, is widely used in fields such as aerospace, optoelectronics and defense. Micro-milling technology for sapphire demonstrates significant potential in the field of sapphire surface processing due to its efficiency, high quality, low loss and flexibility. In this study, a double-edged helical polycrystalline diamond (PCD) micro-end mill with a diameter of 1 mm is designed and fabricated by electrical discharge machining (EDM). Then, the micro-slots on sapphire material are prepared with EDM-fabricated micro-end mills, and the surface quality, surface morphology, micro-milling forces and tool wear involved in micro-milling process are investigated. Experimental results indicate that three types of damages are observed on sapphire micro-slot surface including wavy cracks, individual small cracks and layered tear structures. The minimum surface roughness S_a for sapphire micro-slot obtained with PCD micro-end mill can reach to 0.73 µm. In addition, the major wear forms of PCD micro-end mill when machining sapphire include mechanical wear, thermal chemical wear, adhesive wear, and micro-chipping. The research of adopting PCD micro-end mills for sapphire holds significant application value, which can advance technological progress in machining efficiency and surface quality of hard brittle material.

H13 steel is a key material in the field of hot work dies. Despite its excellent strength and toughness, surface coatings are often needed to improve its hardness and wear resistance in high-temperature environments. In this research, laser cladding of Inconel 718 (IN718)/hexagonal boron nitride (h-BN) composite coatings on H13 steel is investigated to enhance its performance. The effect of process parameters on the macroscopic morphology, represented by the width-to-height ratio and dilution rate, is investigated to obtain coatings with enhanced interfacial bonding strength and improved metallurgical compatibility. The powder composition is determined by characterizing the microstructure, surface hardness, wear resistance, and other properties of composite coatings with varying h-BN content. Additionally, the roles of solution treatment and age hardening as post-treatment methods in further improving coating performance are evaluated. The results indicate that the composite coatings prepared under the applied laser cladding parameters exhibit no significant defects. The 35 wt.% h-BN composite coating (the optimal composition) demonstrates superior ambient/elevated-temperature hardness, 35.4% lower friction coefficient, and 76.8% reduced wear loss compared to the H13 steel substrate. As h-BN content increases, the volume of nitrides and borides in the coatings also rises. Precipitates such as alumina, Metal Carbide (MC), Metal Nitride (MN), and Laves phases are observed both inside and outside the grains, with grain sizes ranging from 5 to 100 µm. After solution treatment, the dissolution and diffusion of intergranular precipitates are evident. Following age hardening, hard phases enriched with B and N fully diffuse and precipitate at the grain boundaries. Post-treatment effectively releases residual stress in the coating, resulting in enhanced material properties. This research provides a novel strategy for surface strengthening of H13 steel in high-temperature applications.

In this article, the vibration analysis of a nanocomposite deep thick cylindrical shell surrounded by an orthotropic medium subjected to thermal load is studied. It is assumed that the shell is fabricated from a polymeric matrix reinforced with graphene nanoplatelets (GNPs) in which the volume fraction of the GNPs varies along the thickness based on several distribution patterns. The modeling of shell is carried out utilizing a quasi-3D shear theory which includes the thickness stretching. The modeling of the medium is conducted based on the orthotropic Pasternak model. The one-dimensional heat conduction equation is solved analytically to find the temperature profile through the thickness of the shell. Moreover, the dependency of properties of the materials on the temperature is considered. A semi-analytical solution is presented to determine the natural frequencies of the shell and associated mode shapes. The effects of several parameters on the natural frequencies are studied, including the mass fraction and distribution pattern of the GNPs, thermal loading, agglomeration parameters, boundary conditions, and characteristics of the orthotropic medium. Owing to considering the thickness stretching effect, removing shallow shell assumptions, and incorporating the agglomeration of the GNPs, the results of the presented work benefit from high accuracy and can be used in the design and analysis of thin to thick and shallow to deep nanocomposite cylindrical shells.