Search Results (104)

In view of the severe performance requirements of high-strength drill pipe joint in deep drilling engineering, 130 ksi high-strength and toughness drill pipe joint is taken as the research object. Thermal deformation behavior and precision forming process of a new composition system joint are investigated. Wire-cut specimens (ϕ10 × 15 mm) are tested on a Gleeble-3500 machine under 900–1200 °C and 0.01–10 s⁻¹, with EBSD for microstructure observation. Results show that the small- and large-angle grain boundary cooperate to obtain the mixed structure of high dislocation density, fine substructure and fine grain, which makes the phase transformation products more fine and uniform. Combined with the finite element numerical simulation and experimental verification system, the effects of billet temperature, strain rate and die temperature on the microstructure and macro properties of the joint are analyzed, and the optimal combination of parameters is determined, including 880 °C billet temperature, 20 mm/s punch speed and 300 °C die temperature. The optimization scheme aims to achieve grain refinement and flow stress control, obtain fine and uniform tempered sorbite structure with grain size grade 10.0, and also achieve the optimal comprehensive strength and toughness, which can provide a theoretical basis and technical path for the industrial production of high-performance drill pipe joints. Full article

Cold forging backward extrusion is mainly employed in the manufacturing of axisymmetric cup-like components used extensively in automotive and aerospace assemblies due to the process-induced strength that has a pivotal role in such applications. Although cold forging backward extrusion yields mechanically robust components, it demands high forces, subjecting tooling to immense stress, thereby restricting process capacity. The process encounters hindrances in gaining widespread industrial acceptance due to frequent failures of die elements, necessitating proper die design and control of major influencing factors for process viability and cost-effectiveness. The punches in backward extrusion are often susceptible to failures when processing steel billets. The punch service life is significantly affected by geometrical attributes, the type of steel undergoing deformation, and tool manufacturing aspects. Hence, the present study evaluates punch performance in cold forging backward extrusion using optimized geometrical attributes, manufactured through a design of an experimental approach comprising an L9 orthogonal array. The manufacturing factors considered are punch material, hardness, and advanced surface coating. Punches were designed for two industrial components using powder metallurgy (PM) steels—S600, S290, and S590, heat treated to 60–66 HRC, and coated via physical vapor deposition with TiN, AlTiN, and TiAlCN. Punch performance was analyzed against existing industry practices, and the strategy demonstrated improved productivity. Punch performance was determined based on the number of forgings produced before wear- and fatigue-induced failures. Significant improvements in punch performance were witnessed in both high-speed steel (HSS) and PM punches with optimized geometries. Fractographic investigations were carried out on fractured punches and analyzed, focusing on the coating’s effect on the thermal aspects of the punches. The proposed study will assist the cold-forging industry in determining appropriate variables to minimize forming responses, thereby enhancing tool life. The research also benefits industries by enhancing process robustness and improving process efficiency with respect to cost and time. Full article

Head injuries remain one of the major health concerns in contact sports such as boxing. Despite the widespread use of protective gloves and helmets, their biomechanical effectiveness in mitigating head acceleration and reducing brain injury risk remains uncertain. This study aims to biomechanically assess available boxing equipment solutions and identify the brain–skull system’s response to physical forces from a boxing punch. A dedicated experimental setup was developed using mini triaxial accelerometers and a high-speed camera to measure head accelerations in a Primus unbreakable dummy. Tests were performed using gloves of different masses (0 oz, 10 oz, and 16 oz) and three head protection configurations: no helmet, rugby helmet, and boxing helmet. The resultant accelerations were analyzed and compared across test conditions. Peak wrist accelerations ranged from 195.00 to 271.77 m/s², while head accelerations did not exceed biomechanical injury thresholds. The boxing helmet, composed of multilayer polyurethane foam, did not consistently decrease acceleration; in some cases, it produced higher overloads due to increased head mass and moment of inertia. A rugby helmet made of open-cell EVA (ethylene vinyl acetate) foam with lower density exhibited more favorable energy-dissipation characteristics under low-impact conditions. Glove mass also influenced acceleration differently between male and female participants, likely due to variations in punch velocity and force generation. This work is a pilot study using two trained adult volunteers to validate the combined IMU–video measurement framework. The results serve as hypothesis-generating mechanistic observations rather than population-level effect estimates. Protective effectiveness in boxing depends on a complex interaction between material properties, geometry, and user biomechanics. Optimal equipment design should balance energy absorption and mass to minimize both linear and rotational accelerations. Future studies should integrate advanced material modeling and finite element simulations to support the development of adaptive, lightweight protective systems. Full article

With the continuous growth of highway traffic volume and the increasing proportion of heavy vehicles, vehicle–bridge collisions have emerged as a significant accidental hazard threatening the safe operation of bridge infrastructure. Systematic investigation of the collision resistance of critical bridge components is therefore essential for the development of rational anti-collision design strategies and reliable risk assessment methods. Focusing on the representative disaster scenario of high-speed heavy vehicles impacting concrete bridge piers, this study first develops a finite element model of an RPC beam and validates its reliability through impact experiments. The validated modeling approach is then extended to bridge piers, where a high-fidelity finite element model established using ANSYS/LS-DYNA 2020 is employed to simulate the vehicle–pier collision process and to systematically investigate collision force characteristics, bridge damage evolution, and collision response behavior. The results show that the established reactive powder concrete (RPC) beam model, validated through drop hammer impact tests, reliably captures the impact-induced damage and dynamic response of concrete members. During heavy-vehicle impacts, the vehicle head and cargo compartment successively interact with the pier, generating two distinct collision force peaks, with the peak force induced by the cargo compartment being approximately 38.2% higher than that caused by the vehicle head. Severe damage is mainly concentrated within the impact region, characterized by punching shear failure on the impact face, tensile damage on the rear face, and shear failure near the pier top. The collision-induced structural response is dominated by horizontal displacement, which remains below 10 mm during the vehicle head impact but exceeds 260 mm under the cargo compartment impact. Significant displacements are also observed in the cap beam, with maximum horizontal and vertical values of 24 mm and 19 mm, respectively. These findings provide valuable insights into the impact behavior and failure mechanisms of concrete bridge piers, offering a sound theoretical basis and technical support for anti-vehicle collision design, collision-resistant structural optimization, bridge damage assessment, and the refinement of relevant design specifications. Full article

This study investigates the two-dimensional (2D) steady-state frictional contact behavior of functionally graded piezoelectric material (FGPM) coatings under a high-speed rigid cylindrical punch. An electromechanical coupled contact model considering inertial effects is established, while a layered model is employed to simulate arbitrarily varying material parameters. Based on piezoelectric elasticity theory, the steady-state governing equations for the coupled system are derived. By utilizing the transfer matrix method and the Fourier integral transform, the boundary value problem is converted into a system of coupled Cauchy singular integral equations of the first and second kinds in the frequency domain. These equations are solved semi-analytically, using the least squares method combined with an iterative algorithm. Taking a power-law gradient distribution as a case study, the effects of the gradient index, relative sliding speed, and friction coefficient on the contact pressure, in-plane stress, and electric displacement are systematically analyzed. Furthermore, the contact responses of FGPM coatings with power-law, exponential, and sinusoidal gradient profiles are compared. The findings provide a theoretical foundation for the optimal design of FGPM coatings and for enhancing their operational reliability under high-speed service conditions. Full article

Formability testing is a fundamental method for determining sheet metal’s susceptibility to deep drawing operations. This article presents the results of formability analysis of several batches of 0.7 mm thick cold-rolled DX56D+Z100-M-C-O steel sheets. As part of the preliminary tests, mechanical properties of the tested steel sheets were determined. The ARAMIS digital image correlation system was used to determine the formability of sheet metal during the hemispherical punch stretching test. The stretching tests were conducted over a wide range of strain rate variations between 2 mm/min and 17 mm/min. A total of 540 individual geometry measurements were taken to analyze the test material’s formability. It was observed that with increasing strain rate, the strength properties increased, while the plastic properties decreased. From the perspective of formability, the margin of plasticity (the ratio of yield strength to tensile strength) deteriorated with increasing strain rate in tensile tests. Forming limit curves revealed that at higher strain rates, the metal sheet’s formability decreased. A reduction in the safety margins with an increasing hemispherical punch stretching test speed was also observed. Full article

The modern coinage industry ensures dimensional and weight precision, as well as improved surface quality, for its products. The speed of coin mass production requires increased performance for used machines and tools. Despite these, error incidence cannot be excluded. Some of these errors are recorded inside the punching machine and generate clipped blank disks; on their turn, those malformed disks lead to the clipped coins. In the first part, the paper presents the premises underlying the appearance of clipped blanks. There are some exemplified coins having different types of clips: curved, straight, and ragged. The literature review in the coinage field covers the following subjects: coin and die behavior under the striking load, viewpoints on 3D modeling, and finite element method (FEM) analysis, insights on various striking errors, with most of them more or less valued as collection metal pieces. The paper’s main purpose is outlined as follows: to study, using the available modern techniques, the particularities of different clipped coin types. In the second part of the paper, we introduced the adequate tridimensional (3D) model, for parts such as the die, collar, and the coin. It follows the assembled model corresponding to each studied case, which consists of the obverse and reverse striking dies and the collar, having inside them the coin. For each of the models, based on the initial conditions, the finite element analysis was performed. The paper’s last part presents the analysis’ results, the discussions, and the conclusions. Full article

Warm deep drawing is an effective special deep drawing technique for improving the forming limits of difficult-to-form materials such as aluminum alloys, magnesium alloys, and stainless steels. This paper experimentally investigated the effect of a combined variable process path, which integrates a variable punch speed (VSPD) and a variable blank holder force (VBHF) path, on the warm deep drawing performance of an A5182 aluminum alloy sheet at 300 °C (where the strain rate sensitivity index m equals 0.11). Experiments demonstrated not only a reduction in the forming time and an improved wall thickness uniformity, but also an improvement in the forming limits. The significant improvement in the forming characteristics is discussed in terms of the theoretical three-dimensional process window (SPD-BHF-flange reduction ratio (ΔDR*) space) consisting of the fracture limit and flange wrinkling limit derived from deep drawing theory, and it was shown to be consistent with the experimental results. Finaly, the novel combined VSPD/VBHF process path successfully achieved deep drawing with a challenging drawing ratio (DR) of 3.3. Full article

Carbon fiber-reinforced polymer (CFRP) laminates are extensively utilized in aerospace and advanced engineering fields because of their outstanding strength-to-weight ratio and superior fatigue durability. However, despite their high in-plane strength and stiffness, CFRP laminates are inherently susceptible to delamination. This weakness stems from the relatively low interlaminar strength of the resin-rich interfaces between layers compared to the much stronger in-plane fiber reinforcement. During mechanical processes such as drilling and punching, out-of-plane stresses and interlaminar shear forces develop, concentrating at these weak interfaces. This study investigates the delamination behavior of CFRP laminates with 3 to 7 plies under drilling and punching, focusing on the effects of ply count and drilling speed. Experimental tests were conducted using an 8 mm punch and drill bit at 2500, 3000, and 3500 rpm, reflecting typical workshop practices for M8 fastener holes. Scanning electron microscopy (SEM) analyses at different magnifications were used to quantify delamination extent. A three-dimensional finite element model was created in ABAQUS/Explicit, integrating the Hashin failure criterion to predict damage initiation within the plies and cohesive surfaces to simulate interlaminar delamination. The analyses show that with proper support, punching can approach the damage levels of drilling for thin CFRP plates, but drilling remains preferable for thicker laminates due to better integrity and tool longevity. Full article

Accurate forecasting of springback continues to pose a significant challenge in sheet metal forming processes. The present paper presents a numerical model designed for the precise prediction of springback, allowing for a deeper understanding of plasticity behavior during cold forming operations in sheet metals. The key contribution of this model is the introduction of a non-associated anisotropic constitutive model featuring nonlinear mixed isotropic–kinematic hardening. This model is derived from Hill’48 quadratic function and it was implemented into ABAQUS 6.13 software environment through the user defined UMAT subroutine. For improved precision, kinematic hardening parameters specific to 5083 aluminum sheet metal were meticulously derived from cyclic shear experiments. Our results demonstrate the model’s strong capability in predicting springback during the U-bending operation, achieving remarkable accuracy. The design of experiments DOE is used as a statistical method to optimize the number of experiments and analyze the effects of key input factors. In this study, sheet thickness, punch speed, and sampling angle relative to the rolling direction (RD) are examined at different levels to assess their impact on folding force and springback. The strong agreement between experimental results and theoretical predictions confirms the accuracy and reliability of the proposed models in estimating folding force and springback. Full article

In the cold extrusion forming of thin-walled, specially shaped holes in aviation motor brush boxes, non-uniform metal flow can easily induce local stress concentrations on the punch, thereby accelerating wear. Reducing the punch wear and equivalent stress is therefore critical for ensuring the forming quality of such thin-walled features and extending the service life of the mold. In this study, a slender punch with a specially shaped cross-section was selected as the research object. The Deform-3D Ver 11.0 software, incorporating the Archard wear model, was employed to investigate the effects of five process parameters—extrusion speed, punch cone angle, punch transition filet, friction coefficient, and punch hardness—on the wear depth and equivalent stress of the punch during the compound extrusion process. A total of 25 orthogonal experimental groups were designed, and the simulation results were analyzed using the Taguchi method combined with range analysis to determine the optimal parameter combination. Subsequently, a multi-objective correlation analysis of the signal-to-noise ratios for wear depth and equivalent stress was conducted using the TOPSIS approach. The analysis revealed that the optimal combination of process parameters was an extrusion speed of 12 mm·s⁻¹, a punch cone angle of 50°, a punch transition filet radius of 1.8 mm, a friction coefficient of 0.12, and a punch hardness of 55 HRC. Compared with the initial process conditions, the integrated application of the Taguchi–TOPSIS method reduced the punch wear depth and equivalent stress by 21.68% and 42.58%, respectively. Verification through actual production confirmed that the wear conditions of the primary worn areas were in good agreement with on-site production observations. Full article

Objective: The purpose of this study is to investigate the effects of back squat (BS) and squat jump (SJ) on the maximum-striking strength and speed-striking strength of the jab and cross of elite male boxers, and to identify the time point of the post-activation performance enhancement (PAPE) induced by these two activation methods. Methods: A total of 29 Chinese male boxers were recruited to participate in four different intensities of muscle activation through BS and SJ exercises (BS_50%, SJ_50%, BS_80%, SJ_80%). The participants were tested on their jab and cross using specialized testing protocols at recovery intervals of 4, 8, 12, and 16 min (speed-striking strength testing was conducted first, followed by maximum-striking strength testing), and the maximum-striking strength and speed-striking strength of the athletes were recorded. Results: (1) Maximum-striking strength: For the jab, the results indicated that there were significant differences between BS_50% at 8 min and 12 min and the baseline (p < 0.01), and between SJ_50% at 4, 8, and 12 min and the baseline (p < 0.01). BS_80% showed significant differences at 12 min compared to baseline (p < 0.01), and the SJ_80% exhibited significant differences at 8 min (p < 0.05) and 12 min (p < 0.01) compared to baseline. For the cross, BS_50% demonstrated significant differences at 12 min compared to baseline (p < 0.01), and SJ_50% showed significant differences at 8 min and 12 min (p < 0.01). Both BS_80% and SJ_80% revealed significant differences at 8, 12, and 16 min compared to baseline (p < 0.01). (2) Speed-striking strength: For the jab, there were no significant differences between BS_50% and SJ_50% at all time intervals compared to baseline (p > 0.05). BS_80% showed a significant difference at 4 min compared to baseline (p < 0.05), and SJ_80% exhibited significant differences at 12 min compared to baseline (p < 0.01). For the cross, there were no significant differences between BS_50%, SJ_50%, and BS_80% at all time intervals compared to baseline (p > 0.05), while SJ_80% demonstrated significant differences at 8 min and 12 min compared to between (p < 0.01). The results showed that PAPE significantly enhanced maximum punch force at 8–12 min across several activation conditions. In contrast, improvements in speed-striking force were only observed following high-load squat jump (SJ at 80% 1 RM), with significant increases at 8 min for the cross and at 12 min for the jab, whereas BS or lower-load SJ produced no meaningful changes. Conclusions: PAPE activation significantly enhances the striking force of boxers at the recovery interval of 12 min, but the effect is influenced by the intensity and method of activation. High-load activation can enhance the striking strength of boxers more rapidly and sustainably, and high-load SJ are more beneficial for the speed-striking strength of boxers. Full article

Karate emphasizes technical precision, controlled movement, and the integration of strength and speed. Understanding the relationship between athletic performance and mechanical energy is essential for refining techniques. This study quantifies kinetic energy during mae geri (front kick) and gyaku tsuki (reverse punch) in elite and sub-elite athletes. Fourteen male black-belt karate athletes were divided into two groups: elite (n = 7) and sub-elite (n = 7). Physical attributes and muscular strength were assessed using isokinetic evaluations, while striking performance was analyzed through synchronized kinematic systems to measure linear and rotational kinetic energy at key joints. No differences in dynamometric strength were found between groups. However, elite athletes showed superior peak kinetic chain output, achieving higher peak velocities and kinetic energy in both techniques. For mae geri, elite athletes showed higher peak velocity (9.5 ± 0.8 vs. 8.5 ± 0.8 m·s⁻¹; p = 0.001) and kinetic energy (155.86 ± 54.06 vs. 124.42 ± 34.13 J; p = 0.012). In gyaku tsuki, elite athletes reached faster peak velocities (7.3 ± 0.8 vs. 6.1 ± 0.7 m·s⁻¹; p = 0.001) and kinetic energy (269.57 ± 18.62 vs. 214.44 ± 9.27 J; p = 0.008). These findings highlight the importance of peak kinetic chain output in karate. Full article

This study aimed to determine optimal forming conditions by comparing the compaction behavior and microstructural characteristics of two Fe-based Soft Magnetic Composite (SMC) powders, Somaloy 700HR 5P and Somaloy 130i 5P. A full factorial design was employed with powder type, compaction temperature, and punch speed as variables. Finite element modeling (FEM) using experimentally derived properties predicted density and stress distributions in toroidal geometries. 700HR 5P exhibited higher stress under most conditions, while both powders showed similar axial density gradients. Experimental results validated the simulations. SEM analysis revealed that 130i 5P had fewer microvoids and clearer particle boundaries. As revealed by TEM-EDS analyses, after heat treatment, both powders exhibited a tendency for the insulation layers to become more uniform and continuous. The insulation layer of 700HR 5P was relatively thicker but retained some pores, whereas that of 130i 5P was thinner yet exhibited smoother and more continuous coverage. XRD analysis indicated that both powders retained an α-Fe solid solution. These results demonstrate that powder properties, composition, and insulation stability significantly influence compaction and microstructural evolution. This work systematically compares the formability and insulation stability of two commercial Somaloy powders and elucidates process–structure–property relationships through an application-oriented evaluation integrating experimental design, FEM, and microstructural characterization, providing practical insights for optimal process design. Full article

Repairing veneer defects is the key to ensuring the quality of plywood. In order to improve the maintenance quality and material utilization efficiency during the maintenance process, this paper proposes a bidirectional maintenance method based on gear rack transmission and its related equipment. Based on the working principle, a geometric relationship model was established, which combines the structural parameters of the mold, punch, and gear system. Simultaneously, it solves the problem of motion attitude analysis of conjugate tooth profiles under non-standard meshing conditions, aiming to establish a constraint relationship between stamping motion and structural design parameters. On this basis, a constrained optimization model was developed by integrating multi-objective optimization theory to maximize maintenance efficiency. The NSGA-III algorithm is used to solve the model and obtain the Pareto front solution set. Subsequently, three optimal parameter configurations were selected for simulation analysis and experimental platform construction. The simulation and experimental results indicate that the veneer repair time ranges from 0.6 to 1.8 seconds, depending on the stamping speed. A reduction of 28 mm in die height decreases the repair time by approximately 0.1 seconds, resulting in an efficiency improvement of about 14%. The experimental results confirm the effectiveness of the proposed method in repairing veneer defects. Vibration measurements further verify the system’s stable operation under parametric modeling and optimization design. The main vibration response occurs during the meshing and disengagement phases between the gear and rack. Full article