ABSTRACT The wear of the barrel mainly occurred at the forcing cone, which greatly changed the projectile engraving characteristics and the gun’s inner ballistic characteristics. To further reveal the projectile-engraving dynamic characteristics of the large caliber wear gun, a parametric structural model of the worn barrel was proposed and regular meshed. A finite element model of the projectile dynamic engraving process was established under different barrel wear amounts, which considering the change of internal ballistic parameters caused by wear. The numerical calculation results were in good agreement with the experimental results and the projectile dynamic engraving characteristics under different barrel wear amounts were analyzed. The results indicated that with the wear intensified, the chamber pressure-boosting rates and projectile engraving resistance decreased, the projectile velocity and angular velocity at the end of the engraving process increased due to the projectile’s total engraving displacement increasing. As the barrel wear increased, the average stress on the belt element gradually decreased and the stress on the inner barrel liner reduced, the belt unit proportion sheared by the forcing cone was reduced. When the barrel wear was greater than 2.4 mm, the front belt showed a flattening phenomenon, which changed the groove shape and stress-strain state of the copper belt.

Abstract Stainless steel (SS) 316 is extensively used in aerospace, marine, and nuclear industries because of its superior mechanical properties and corrosion resistance. Nevertheless, its microstructure and mechanical behavior are greatly affected by welding-induced thermal cycles. In this research, the influence of Tungsten Inert Gas (TIG) welding on the microstructural development and mechanical properties of analogous SS316 weldments is explored. A multi-pass (two-pass) TIG welded process was used, and the weld joints were characterized by microstructural characterization, tensile testing, microhardness testing, and infrared (IR) thermography. IR thermography was used to record temperature gradients during welding at various stages, indicating heat buildup and thermal gradients influencing microstructural development. Microstructural analysis indicated columnar dendrites in the fusion zone and grain coarsening in the heat-affected zone (HAZ). Mo and Cr segregation in inter-dendritic areas was seen, and these can affect corrosion resistance and mechanical performance. Tensile test results revealed that the weld joints had an ultimate tensile strength (UTS) of 636–640 MPa with minor fluctuations because of heat build-up. Among the three tensile-tested specimens, two exhibited failure in the HAZ. However, specimen 3 failed just adjacent to the weld zone, suggesting that localized heat input at the commencement of welding influenced the failure location. Microhardness analysis revealed a hardness value of 94–99 HV in the weld and 97–99 HV in the HAZ, which followed grain refinement and thermal effects. The results of this research offer significant information on the optimization of welding parameters to improve joint performance, ensuring the reliability of SS316 components in critical applications.

Abstract Deep geotechnical engineering requires grouting technology to ensure project safety. However, the interlayered geological conditions of layered rock formations make grouting effectiveness difficult to predict and guarantee. Therefore, it is of significant practical value to investigate the diffusion mechanism of grouting within layered rock masses further. First, this study developed a true triaxial grouting physical testing system to reveal the influence of water-to-cement ratio (W/C) and injection rate on grout diffusion. The evolution of acoustic emission characteristics under different grouting parameters was compared and analyzed. Furthermore, potential fracture mechanisms within layered rocks were identified through moment tensor inversion. The results indicate that cement slurry spreads more readily within weak layers at low injection rates and W/Cs, facilitating generation of multiple small-scale fractures. Peak fracturing pressure exhibits a positive correlation with the injection rate and a negative correlation with W/C. Acoustic emission localization results indicate that higher injection rates facilitate slurry diffusion perpendicular to weak layers. Furthermore, a hydraulic-mechanical-damage coupled model for simulating grouting in layered rocks was developed using COMSOL Multiphysics software. By numerical simulation, the regulatory mechanisms of weak layer dip angle and in-situ stress on dominant diffusion directions were revealed. Compared results revealed that when longitudinal stress was the maximum principal stress, a steeper weak-strength layer inclination tended to confine slurry within high-strength layers. However, the initial cracking pressure first decreased then increased with weak layer inclination, approaching its minimum at 45°. This work systematically investigates the fracture mechanism induced by grouting in layered rocks by integrating laboratory physical tests with numerical simulations that account for weak layer dips and in-situ stress fields. The relevant findings and insights provide valuable practical references for underground geotechnical engineering.

ABSTRACT Five-axis milling of free-form surfaces requires simultaneous optimization of toolpaths and continuously varying tool orientations. However, most commercial CAM workflows focus only on geometric simulation and neglect critical physical quantities such as cutting forces, leading to force spikes, tool deflection and surface inaccuracies. This study proposes an integrated optimization framework that combines automatic toolpath generation from STEP/B-Rep models with solid-model-based extraction of cutter–workpiece engagement (CWE). The CWE data are transformed into entry and exit immersion parameters and undeformed chip thickness to enable mechanistic cutting-force prediction. Tool orientations are then optimized using a curvature-aware parameterization method and a particle swarm optimization (PSO) algorithm. Numerical validation on representative free-form surfaces demonstrated that the proposed method reduced the maximum cutting force from 214 N to 170 N (a 20.6% reduction) compared with the original path. A secondary optimization stage incorporating polynomial-fitted force smoothing decreased force fluctuation amplitude by over 40%, resulting in both smoother tool-axis trajectories and improved machining stability. By integrating geometric modeling, physical simulation and metaheuristic optimization, the proposed PSO-based framework provides a quantitatively verified improvement in force-aware toolpath planning. The approach can be readily incorporated into existing CAD/CAM environments for efficient and reliable five-axis machining of complex free-form surfaces.

Abstract Under alternating axial external forces, threaded fasteners are prone to fatigue failure. At present, the main focus is on improving material strength to optimize fatigue resistance; most of these methods have greatly increased the cost. Plastic strengthening is a traditional method that does not increase the cost, is easy to operate and can effectively improve the fatigue resistance. Without changing the fastener, the fatigue resistance can be enhanced to a certain extent by simply pre-tightening it beyond the target clamping force and then untighten it to the target clamping force. However, currently there is no clear specification for the maximum pre-tightening force that exceeds the target clamping force. Too strong or too weak maximum pre-tightening force may cause micro-cracks in the fastener or fail to be effectively strengthened. In addition, the strengthening mechanism of the threaded structure has not been clearly explained. This study, the relationship between the strengthening level and the using conditions is clarified through experiments and finite element stress analysis, and the plastic strengthening mechanism is revealed, which is also of guiding significance for the plastic strengthening of other structures.

Abstract Understanding the movement and deposition patterns of granular materials is important for understanding the landslides and dry granular flow hazards in mountainous regions. This study investigates the influence of grain size distribution, characterized by median grain size (D50) and sorting coefficient (Sc), on the moving and deposit characteristics of dry granular materials using an inclined channel coupled with a horizontal tank. The experiments involved measuring the entry speed (V0), runout distance (LR), maximum width (W) and the final deposit shape profiles under varying channel slopes (θ = 25°, 30° and 35°). To comprehend the influence of grain size distribution and channel slopes on the entry speed, an empirical equation is provided relating V0 to D50, Sc and θ using multiple linear regression analysis. The results demonstrate that as the channel slope increases, the runout distance and entry speed increase, while the deposit width decreases. Empirical equations relating the entry speed with the runout distance and maximum width are also provided to further demonstrate the influence of entry speeds on the deposit characteristics. Additionally, the analysis of the grain size distribution within the final deposits revealed a distinct pattern, with coarser grains settling toward the Tail and finer grains accumulating in the Middle and Front. Granular materials with higher Sc exhibit higher grain size segregation, resulting in a more heterogeneous deposit in the horizontal tank. The empirical relationships for entry speed derived in this study provide a quantitative framework for predicting granular flow behavior based on grain size distribution, sorting coefficient and channel slope. These findings can be applied to granular flow modeling and may help improve predictions of landslide mobility.

Abstract Classical viscoelastic models constructed using linear springs and dashpots are the most common models for analyzing viscoelastic behaviors, and the core of these models is their constitutive equations. Compared to other derivation methods, the Laplace transform method is preferably chosen for deriving the constitutive equations of classical viscoelastic models because of the systematic nature of this method. In literature, the initial conditions associated with stress and strain are all assumed to be zero in deriving the constitutive equations of classical viscoelastic models using the Laplace transform method, but it is a paradox to make such an assumption, since the initial conditions are not necessarily all zero in general. In this article, we present the derivation of the constitutive equations of some classical viscoelastic models using the Laplace transform method under the assumption that the initial conditions are not necessarily all zero. It is believed that this is the most systematic and general approach for deriving the constitutive equations of classical viscoelastic models. The derivations demonstrate that the constitutive equation of a classical viscoelastic model is actually the same no matter the initial conditions are assumed to be all or not all zero. Hence, in practice, it is reasonable and recommended to assume the initial conditions are all zero for largely simplifying the derivation process when using the Laplace transform method for deriving the constitutive equation of a classical viscoelastic model.

Abstract To address the challenges associated with conducting large-scale and complex acoustic vibration experiments on dual-layer cylindrical shells, which are both difficult and costly, this paper proposes a method that predicts the vibrational response of a full-scale dual-layer cylindrical shell using the vibrational response of a single-layer scaled-down model. Finite element models of both the full-scale dual-layer cylindrical shell and its scaled-down counterpart were developed using Virtual.Lab Acoustic software. The vibrational responses of these models were analyzed within the 100–500 Hz frequency range, and a comparative analysis was conducted to validate the accuracy of the scaling method and the similarity of vibrational responses. The results indicate that the displacement ratio between the scaled-down model and the original model aligns closely with the geometric scaling factor. Furthermore, the similarity coefficients of the vibrational responses for both the inner and outer shells of the scaled-down model exceed 0.9, confirming the effectiveness of the proposed approach.

ABSTRACT In this study, a modified hybrid optimization algorithm (HOA) is presented to address the limitations inherent in traditional optimization techniques, particularly for multi-objective problems. This HOA integrates a genetic algorithm, an artificial neural network and a mathematical programming scheme. The integration aims to overcome the computational inefficiencies and convergence issues present in standalone methods. The effectiveness of the proposed HOA is first validated through two standard test cases. In addition, further results are reported for multi-criteria optimization of the process-induced thermal-mechanical behavior of an anisotropic conductive film (ACF)-based ultra-thin chip-on-film (ACF-UTCOF) package, where the objectives are the minimization of package warpage and adhesive peeling stress, and the maximization of contact stress in the micro-joints. Besides, two different HOA models are proposed, and their results are compared in terms of solution accuracy and efficiency. To explore the residual behaviors of the ACF-UTCOF package during fabrication, a process-dependent modeling technique that incorporates both transient thermal and nonlinear contact finite element analysis and ANSYS element death-birth technique is introduced. The effectiveness of this approach is demonstrated through experimental validation.

Abstract Based on a traditional wingtip endplate configuration, four wingtip variant configurations with delta winglet shapes were designed to explore their tip-vortex suppression effects. Each delta winglet configuration consists of a rectangular wing and a pair of tip-mounted delta winglets. The wingtip vortex flow characteristics of the wingtip endplate configuration and delta winglet configurations I–IV were experimentally investigated under different attack angles (α = 0–20°) and downstream cross-sections (x/c = 1.04–2.2) at Re = 154 032. The results indicate that the variation of α or x/c greatly affects the tip-vortex cores’ number, shape, area, location, vorticity level and circulation for the five wingtip configurations due to continuous interactions between their positive and negative vorticity regions. The wingtip endplate configuration’s total or parasitic drag always rises at a higher rate than those of the delta winglet configurations I–IV at α = 0–20°. Furthermore, for any of the five wingtip configurations, the induced-drag variation trend with α depends on the positive and negative vorticity regions’ circulation variations with α. At α = 0–20°, the maximum proportions of induced drag relative to total drag for the wingtip endplate configuration and delta winglet configurations I–IV are 39.41, 41.04, 37.70, 38.02 and 39.42%, respectively. By further comparing the lift-drag performances of the five wingtip configurations, it can be observed that the delta winglet configuration II exhibits better lift-drag efficiency due to its superior drag performance.