Archives of Civil and Mechanical Engineering最新文献

The impact of the gradient nanostructures on the fatigue properties of aluminum alloys remains limited. The ultrasonic surface rolling process (USRP) was utilized in this study to generate the gradient nanostructure on the surface of 7075 aluminum alloy, and the high fatigue properties with the stress ratio R =  – 1 were following tested. The findings indicated that the fatigue limits of 3- and 6-passes-treated samples were found to reach 225 MPa (125%) and 200 MPa (100%), respectively, surpassing those of untreated sample. The characterizations of scanning electron microscope (SEM), laser confocal scanning microscope (LCSM), and X-ray diffractometer (XRD) showed a positive correlation between the number of rolling passes and the enhancement of the gradient hardening layer and residual compressive stress, contributing to the improvement in fatigue limit. Meanwhile, the SEM analysis of the fracture indicated that the fatigue crack initiation site was altered as a result of surface modification, and the crack initiation point of the 3-passes-treated sample was located further from the surface. Additionally, finite-element simulation was employed to analyze the stress distribution across the cross-section, and the fatigue risk coefficient R_f was used to quantify the impact of residual stress distribution and surface hardening on the crack initiation site. The results demonstrated that USRP not only altered the surface condition of the aluminum alloy but also changed its stress distribution in the cross-section. The combined effect of the two controlled the crack initiation site and the fatigue life of the 7075 aluminum alloy.

Modern society witnessed a remarkable surge in urban mobility with the proliferation of micro-mobility sharing services. However, this transformation has also led to a worrisome increase in severe accidents and injured users. In addition, conventional helmets are significantly lacking in sustainability. This research investigates the feasibility and safety aspects of a novel bicycle helmet concept using cork as a protective liner. In comparison to traditional synthetic foams, cork offers eco-friendly advantages, such as recyclability and superior protection against multiple impacts. The newly proposed helmet is designed to provide enhanced sustainability and convenience, maintaining compliance with the EN 1078:2012+A1 standard whilst offering the capability to flatten for easy storage and transportation. Numerical simulations were conducted to optimise the design concept, and impact tests, in accordance with the European standard, were performed using physical prototypes categorised into three types of design configuration. The results from the standard impact test were outstanding, with the best performing configuration demonstrating a performance 36.8% below the standard’s threshold. This falls within the average performance range of a regular bicycle helmet made entirely of petrol-derived materials. Furthermore, it exhibited safe head injury criterion levels, indicating a minimal risk of severe head injury.

This study presents the integration of two Arrhenius-constitutive model parameters, activation energy (Q) and the Zener–Hollomon parameter (Z), into a numerical model to evaluate their correlation with the microstructural evolution of AA6082 wheel forging. Isothermal tests powered by a Gleeble machine were conducted to establish the constitutive model of AA6082 material, with deformation temperatures and strain rates varying between 350–560 °C and 0.05–15 s⁻¹, respectively. Two types of Arrhenius methods were employed: strain-compensated Arrhenius and artificial neural network (ANN)-enhanced Arrhenius. The key difference between the two methods is that the former ignores the effects of deformation temperature and strain rate when determining the activation energy (Q) value, while the latter considers these factors. Integrating activation energy and Zener–Hollomon parameters into a numerical model by directly inputting the mathematical equation from the strain-compensated Arrhenius method resulted in significant overfitting at certain nodes and elements. To address this issue, a new approach using trilinear interpolation and behavior-based clamping methods on Q values generated by the ANN–Arrhenius method proved effective. Additionally, the ANN–Arrhenius method demonstrated superior accuracy, reducing the prediction’s average absolute relative error (AARE) from 3.14% (strain-compensated Arrhenius method) to 1.10%. A comparative study of the distribution of Q and Z values in numerical model simulations, alongside average grain size and shape examined with an optical microscope, revealed that the Q and Z parameters are beneficial for predicting grain characteristics in final workpieces. This study aims to bridge the gap in implementing activation energy and Zener–Hollomon parameters in more realistic forging scenarios and with more complex workpiece designs.

The shear bearing capacity of confined concrete columns subjected to lateral cyclic loading is an important mechanical property in investigating seismic behavior of concrete buildings. However, it is still difficult to accurately predict shear bearing capacity of confined concrete columns using traditional analysis methods owing to its complex mechanical principle and indeterminate multivariable interrelationship. In this paper, an experimental study of 15 confined concrete columns subjected to lateral cyclic loading was conducted to explore the seismic behavior of confined concrete columns. Moreover, ANN and SVR models were established to accurately estimate the shear bearing capacity of confined concrete columns based on a reliable test database consisting of 121 specimens conducted in this study and published literatures. Nine key parameters were considered as input variables, including cross-sectional area of core concrete, unconfined concrete compressive strength, shear span ratio, axial compression ratio, volumetric ratio of transverse reinforcement, yield strength of transverse reinforcement, longitudinal reinforcement ratio, yield strength of longitudinal reinforcement, and confinement type. Additionally, the model sensitivity analysis was conducted to investigate the impact of parameters on shear bearing capacity of confined concrete columns. Finally, the ANN and SVR models were evaluated by comparing with five existing predicted methods and experimental results indicating that the ANN and SVM models have enough accuracy and reliability in predicting shear bearing capacity of confined concrete columns subjected to lateral cyclic loading.

This study investigates the problem of concavity formation on the ends of parts manufactured on CNC skew rolling mills. Numerical modeling and Taguchi method were used to determine the effects of the main parameters of skew rolling (i.e., forming angle, skew angle, reduction ratio, temperature, steel grade, dimeter ratio, velocity ratio) on the depth of concavities formed on the product ends. The simulations showed that the only parameter to have a significant impact on the concavity depth was the reduction ratio. The FEM results were then used to establish equations for calculating concavity depth and allowance for excess material with concavity. For more universality, the established equations took into account the billet diameter. The experimental validation showed high agreement between the numerical and the experimental concavity depths.

The microstructure of SiC ceramic particle-reinforced FeCoNiCrAl high-entropy alloy specimens prepared by laser cladding was observed, and the effects of SiC and Al content and laser process parameters on the microstructure of laser cladding high-entropy alloy were analyzed. The results show that increasing the scanning speed and laser power or reducing the powder feeding rate is conducive to obtaining smaller grains and forming a denser microstructure. However, when the laser power and scanning speed are too large, pores and unmelted powder will appear. Increasing the content of SiC ceramic particles significantly increases the number of heterogeneous nucleation points, resulting in a decrease in the grain size in the cladding layer and a more tortuous grain boundary, which is conducive to improving comprehensive performance. However, when the SiC content is too high, defects, such as cracks and inclusions, are prone to occur. With the increase of Al content, the grain size in the cladding layer increases first and then decreases.

Electromagnetic forming (EMF) has unique advantages in processing metallic materials owing to the high-strain effect. However, it possesses poor shape-control ability for workpieces and is not suitable for forming materials with low conductivity. To address this, an electromagnetic-driven forming method with a metal driven ring is proposed to achieve Lorentz force transforming and shape control of the workpiece. The effectiveness of this method and ring configurations on the deformation behavior of AA1060-H24 aluminum alloy sheets, along with the forming mechanism, have been thoroughly investigated in combination with experiments and simulations. Results demonstrate that the introduction of the driven ring can adjust the Lorentz force generated on the sheet, resulting in a flat-topped profile with a uniform deformation ratio of 0.62, which increases by 100% compared to that without a driven ring. Meanwhile, it is discovered that the uniform deformed area, forming shapes, and targeted deformation areas can be controlled by regulating the ring configurations, which indicates that the proposed method possesses good adaptability and flexibility in shape control. Moreover, it has also been validated and applied in forming low-conductivity titanium sheets, which can be deformed into a flat-topped shape. This work provides an effective approach for shape control by aggregating the Lorentz force on the driven ring, which is essential for broadening the scope of EMF technology within the domain of sheet metal processing.

Post-machining of metal additive-manufactured (AMed) nickel-based alloy components is one of the efficient approaches to reduce surface roughness and enhance surface quality. Although the white layer formed on the wrought nickel-based alloy surface after machining has been deeply investigated, the formation mechanism of the white and dark layers generated on AMed nickel-based alloy still faces challenges. In this study, the white and dark layer formation on laser powder bed fusion (LPBF)-fabricated Inconel 625 alloy surface after turning was determined. Then various material characterization techniques were adopted to comprehensively analyze the microstructure, texture and phase constituent concerning the white and dark layers. Obvious intragranular misorientation change, great concentration of high angle grain boundaries and grain refinement occurred beneath the machined surface. Strongly refined grains in nanometers and noticeable plastic deformation with slight grain division along with disappeared dense dislocations were revealed correspondingly within the white and dark layers. Phase transformation was absent from the machined surface despite cutting parameters. Dynamical crystallization (DRX) following shear deformation dominated the formation of the white layer while plastic deformation was responsible for dark layer formation. The findings were beneficial to understanding the occurrence of damages initiated from machined surfaces during service.

In order to study the hydroforming simulation process of variable cross-section shaped tubular automobile longitudinal arm and the influence law of key factors on its forming quality, and to provide guidance for its engineering application. Firstly, the numerical simulation and experimental analysis of hydroforming are carried out on variable diameter tube with similar characteristics to the longitudinal arm hydroforming, and the correctness of the built finite element model and numerical simulation method is verified through experiments. Then, according to the structural characteristics of the automobile longitudinal arm parts, determine the longitudinal arm hydroforming process and the main molding parameters, and analyze the molding process by numerical simulation. According to the simulation results, the effects of hydroforming initial internal pressure, initial feeding, friction coefficient and shaping pressure on the wall thickness characteristics and shaping rules of the longitudinal arm are investigated, and the hydraulic expansion test of automobile longitudinal arm is carried out on the basis of the optimal loading path obtained. The results show that: in the case that the initial internal pressure does not reach the cracking pressure, the initial internal pressure and initial axial feeding has a greater impact on the wall thickness of the automobile longitudinal arm, reduce the friction coefficient can improve the material flow performance, improve the uniformity of the wall thickness of the parts, and appropriately increase the shaping pressure can improve the dimensional accuracy of the longitudinal arm molding and the molding quality. It is verified by experimental comparison that the whole process of automobile longitudinal arm forming simulation based on bending-hydraulic forming has high feasibility, and a relatively good loading path can be obtained to provide reference for practical engineering applications.

In the present research, the static bending analysis of a three-layer sandwich cylindrical panel with a re-entrant auxetic honeycomb core and polymeric face sheets reinforced with graphene nanoplatelets (GNPs) resting on an elastic foundation in a thermal environment is investigated. The mechanical properties of the nanocomposite GNP-reinforced face sheets are calculated using the Halpin–Tsai model along with the rule of mixture. The heat conduction equation is solved in the thickness direction to provide the exact profile of the temperature distribution. The panel is modeled based on the third-order shear deformation (TSDT), the elastic foundation is modeled according to the Pasternak foundation model, and the governing equations and boundary conditions are derived via the minimum potential energy principle. The differential quadrature method (DQM) is employed to solve the governing equations under various boundary conditions in longitudinal and circumferential directions. The convergence and accuracy of the modeling are confirmed and influences of different parameters on the deflection and stress distribution are studied including the inclined angle of the re-entrant cells, thermal environment, mass fraction and distribution patterns of the GNPs, the thickness of core-to-thickness of panel ratio, and the boundary conditions.