Accurate analysis of bolted joint stiffness is critical for assessing the dynamic characteristics of mechanical equipment structures. Under repeated tightening conditions, thread contact stiffness is the predominant factor affecting joint stiffness and structural dynamic response. This study establishes a spring oscillator model for bolted joints incorporating thread contact stiffness. A computational method for asperity stiffness on contact surfaces is developed by integrating Hertz contact theory with a cosine contour model. The thread surface topology is characterized using non-contact 3D laser scanning microscopy, enabling acquisition of high-resolution point cloud data. The analysis of point cloud data reveals a progressive enhancement of contact stiffness with increasing tightening cycles. A hammer-impact modal test is conducted to study the vibration response of the bolted joint structure. The frequency shifts in structural modes reveal the effects of repeated tightening and torque variations on bolted joint stiffness. Experimental validation confirms the consistency between the proposed model and the contact stiffness of bolted joints.

The textures, shearing performance, and specific strengthening mechanism of the composite joints with heterogeneous phase aging at 600 °C

Reciprocating wear mechanism of U75V flash-welded rail joints under the combined effects of chloride ions and ice

UV-B radiation reduced the susceptibility of Brachionus plicatilis to microplastics by decreasing their toxic effects and bioaccumulation.

Abstract Rehabilitation robotics offers a promising approach to enhancing recovery in patients with musculoskeletal or cerebrovascular injuries. This article presents the development and validation of a novel variable-stiffness joint (VSJ) that replaces large motors to generate resistive forces, thereby facilitating controlled recovery of muscle tone. For a revolute joint mechanism, we show that a constant output force can be maintained by adjusting stiffness, as demonstrated through simulation studies. Further validation was conducted through prototype experiments with volunteer participants, confirming that spring-length control enables modulation of joint stiffness and maintains a constant force at the link's end regardless of the rotation angle or trajectory.

The mechanical joint surface is commonly simplified as smooth or Gaussian-distributed, while its actual non-Gaussian characteristics significantly affect fretting wear behavior. A non-Gaussian fretting wear model, characterized by the 3D morphology of actual machined surfaces, is established to accurately reveal the fretting wear mechanism of joint interfaces. Firstly, the Fast Fourier Transform is adopted to construct non-Gaussian surface models consistent with actual surface characteristics. Secondly, the non-Gaussian surface fretting wear model is developed through ABAQUS and the UMESHMOTION wear subroutine. Finally, the effects of kurtosis, skewness, standard deviation, material properties and friction coefficient are explored. The conclusions illustrate non-Gaussian surfaces demonstrating the positive skewness and high kurtosis exhibit the most pronounced local stress concentration and maximum wear depth compared to smooth and Gaussian surfaces. Non-Gaussian surfaces exhibiting negative skewness and low kurtosis demonstrate more uniform stress distribution and better wear resistance under identical conditions. The wear depth in the non-Gaussian surface increases significantly with rising the standard deviation, elastic modulus of materials, and friction coefficients.

ABSTRACT Multifunctional materials (MFMs) exhibit multiple useful functions without complex joint mechanisms. Compared with soft MFMs, metallic MFMs are desired due to their superior mechanical properties and durability. However, the design and fabrication of MFMs are daunting tasks, requiring the organic integration of multiple metals and alloys during manufacturing processes. Additive manufacturing, especially directed energy deposition (DED), has the potential in this regard due to its capability to deposit multimaterials site‐specifically. Through carefully programmed printing paths, novel applications arise and achieve functionalities unseen before. Here, we showcase the versatility of such techniques by four case studies of metallic MFMs: (i) tuning magnetic lifting force, (ii) securely and durably embedding information as material fingerprints, (iii) improving conventional ferrofluidic seals, and (iv) possessing programmable mechanical properties. This work demonstrates the possibilities of using DED to achieve multifunctionalities in metallic materials and provides enlightenment to a wide range of engineering applications.

Segmental piles with mechanical joints(hereinafter, mechanically-jointed piles), as an improved pile type, have been widely adopted in construction projects. Due to their structural differences from conventional single piles, their mechanical responses diverge significantly, particularly under lateral loading. Gaps form at the mechanical joint between two single pile segments in mechanically-jointed piles, amplifying distinctions in mechanical response compared to conventional piles. To investigate the mechanical behavior of mechanically-jointed piles under lateral loading, this study develops a calculation theory for mechanical response based on the *m*-method-a standard approach for conventional single piles. The theory's feasibility is validated via numerical simulations. Results indicate that numerical simulation align closely with *m*-method calculations: pile head displacement error is 4.8%, rotation error 6.2%, maximum bending moment error 24.9%, and maximum shear force error 8.2%. Comparative analysis of conventional single piles and mechanically-jointed piles with free ends reveals that under lateral loading, mechanically-jointed piles exhibit approximately 30% larger pile head displacement and approximately 55% greater rotation than conventional piles, indicating reduced deformation resistance. However, the results indicate that the mechanically-jointed pile can effectively reduce the maximum bending moment in the pile shaft. This reduction suggests a potential for optimizing the pile design and enhancing its lateral resistance performance under certain conditions.

The bonding behavior of the Ni-based superalloy CM247LC during transient liquid phase (TLP) bonding is strongly governed by filler metal chemistry, particularly boron activity. In this study, the time-dependent bonding mechanisms of CM247LC joints fabricated using a high-boron MBF-80 filler and a low-boron MBF-20 filler are systematically compared to clarifying the transition between reaction-dominated brazing and diffusion-assisted TLP bonding. Microstructural analyses reveal that MBF-80 promotes the formation of a persistent, reaction-stabilized interlayer characterized by strong boron localization and the development of boron-rich intermetallic reaction products. These features kinetically suppress diffusion-assisted homogenization and prevent isothermal solidification, resulting in pronounced chemical and mechanical discontinuities across the joint. In contrast, MBF-20 enables progressive boron depletion, suppression of stable intermetallic accumulation, and interfacial smoothing, leading to diffusion-assisted chemical redistribution and partial isothermal solidification. This evolution is accompanied by gradual convergence of hardness profiles toward that of the CM247LC base metal, indicating improved mechanical continuity. These results demonstrate that joint hardness alone is insufficient for evaluating bonding quality in CM247LC. Instead, controlled microstructural evolution governed by low-boron filler chemistry is essential for achieving chemically and mechanically compatible joints. The present work establishes a clear mechanistic link between filler metal composition and bonding behavior, providing guidance for the design of reliable TLP bonding strategies in Ni-based superalloys.

BackgroundUnderstanding the impact of different motor learning strategies on injury-related movement patterns is essential for designing effective ACL injury mitigation programs. This study aimed to compare the effects of three motor learning strategies linear pedagogy (LP), nonlinear pedagogy (NLP), and differential learning (DL) on improving biomechanical indicators related to ACL injury risk in male basketball players with dynamic knee valgus, while considering motor competence (MC) as a moderating factor.MethodsNinety male student-athletes (mean age = 19.29 ± 0.93 years) with prior basketball experience and clinically confirmed dynamic knee valgus were categorized into high and low MC groups based on the standardized BOT-2 test. Participants were randomly assigned to six intervention groups (combining training type and MC level). Each group received a single one-hour training session according to their respective instructional method. Three-dimensional kinematic and kinetic data were collected synchronously using an eight-camera motion capture system (120 Hz) in combination with a force plate. Assessments were conducted at pre-test, post-test, retention (24 h later), and transfer (48 h later).ResultsThe results showed that the NLP with high MC improved knee flexion, reduced abduction loads, and lowered GRF, effects retained at 24–48 h. Additionally, individuals with higher MC consistently outperformed their lower-competence peers across all conditions.ConclusionsThe findings underscore the importance of dynamic, interaction-based training design and the need to consider individual MC. Consequently, NLP may be beneficial in corrective and injury-mitigation programs, particularly for athletes with high MC. The observed improvements in joint mechanics indicate a reduced risk of ACL injury, and the findings support the potential use of nonlinear pedagogy in preventive training programs.Clinical trial numberIRCT20250527065941N1 on 14/06/2025.

Bolted joints are widely used in a variety of engineering applications. However, their loosening significantly increases the risk of structural failure. In this work, a refined finite element model of the bolted joint was developed to investigate the initiation and evolution of loosening under transverse cyclic loads. Loss curves of bolt preload and residual torque with different influencing factors, namely bolt preload, transverse load amplitude and thread friction coefficient, were obtained by finite element analysis. The effect of residual torque on the initiation of loosening was revealed based on the analysis of mechanical state. Results showed that the non-uniform stress distribution at the threads tends to become uniformly distributed under transverse cyclic loads. On the contact surface of bolt head, stress distribution and slip state varied periodically with the transverse cyclic loads. The analysis of the evolution of stress and contact state provides a new perspective for elucidating the loosening mechanism of bolted joints.

Inconsistent outcomes of treatment of labral injuries in the overhead athlete suggest that deficiencies exist in the current knowledge about the roles of the labrum in overhead throwing athletes. These may include inadequate knowledge of labral anatomy and optimum glenohumeral joint (GHJ) mechanics, inadequate knowledge of the pathoanatomy and pathomechanics that create the clinical dysfunction and symptoms, or use of nonanatomic surgical techniques. These deficiencies suggest that a different perspective regarding labral anatomy and GHJ mechanics may provide a basis for examination and guidance for further scholarship and treatment. This perspective is based on the principle of form follows function, which states that the form, the shape or structure of an object, should be based on its intended function, or purpose, and can be utilized to address these deficiencies. It integrates anatomy/form and mechanics/function to provide more effective knowledge and resources for evaluation and treatment. Based on this perspective, this clinical commentary will review and discuss the mechanical function of the GHJ-to optimize task-specific ball-and-socket kinematics, concavity/compression, and dynamic GHJ stability in the overhead throwing athlete; the form of the glenoid labrum, its 3-component mechanical anatomy, and associated biceps tendon-labral complex, which exists to achieve that function; and the demonstrated alterations to the form that result in alteration of function. Alterations to the form, representing various types of labral injury, produce mechanical consequences in GHJ kinematics and contact pressures that can be associated with clinical symptoms and dysfunction. Surgical techniques that address restoring and optimizing the form by re-creating the 3-component mechanical anatomy have been demonstrated to restore the joint kinematics and contact pressures to the intact state. This perspective also provides implications regarding evaluation techniques and treatment guidelines and may serve to provide insights into the development of more effective techniques for restoration of the form that can optimize the function.

Given the strong ties to data sharing and the responsible use of resources, reproducibility of modeling and simulation practice is of paramount importance in science. Computational models in orthopaedics provide insight into healthy and injured joint mechanics and can inform clinical decision-making. The KneeHub project investigated the influence of modelers? decisions and thus, their "art" in simulation and modeling; five teams developed and calibrated knee models using the same experimental data. Model benchmarking evaluated the predictive ability of the models under loading scenarios that were not considered in the development and calibration process. The objective of this study was to evaluate the accuracy of predictions of knee-specific joint biomechanics for benchmark scenarios of simulating a resected anterior cruciate ligament (ACL) using models of one knee and a combined pivot shift loading using models of another knee. The models predicted the major trends in kinematics and kinetics; however, differences were observed between experimental data and between the teams. Predictions of internal-external rotation had the largest errors. While calibrated models were tuned to a similar set of conditions (albeit with different decisions), the optimized stiffness and reference length/strain of ligament structures may not fully reproduce the contributions of these structures to joint kinematics that were measured experimentally in the benchmark scenarios. As researchers often extend models beyond the conditions used to calibrate them, quantifying model accuracy and limitations with benchmarking represents a crucial step toward reproducibility and can help establish best practices for credible modeling in our community.

Giant cell tumor of bone (GCTB) occurring in the femoral head and neck region presents significant therapeutic challenges due to its complex anatomy and aggressive biological behavior. This study aimed to analyse the clinical outcomes of preoperative denosumab therapy combined with curettage after surgical dislocation of the hip in the treatment of GCTB at the femoral head and neck region. Between 2016 and 2023, a total of 16 patients with GCTB in the femoral head and neck were treated at the authors' institution, of whom 14 eligible and included in the study (6 males/8 females, aged 17-35 years). All patients received three cycles of Denosumab therapy preoperatively, with treatment response monitored and therapeutic efficacy was assessed according to Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 criteria. Subsequently, surgical dislocation of the hip combined with curettage of the lesion was performed. Regular postoperative follow-up was conducted to monitor for complications. Imaging studies were used performed to evaluate surgical site status, local recurrence, and distant metastasis. Limb function and hip joint function were assessed preoperatively and at 1 year postoperatively using the Musculoskeletal Tumor Society (MSTS) score and Harris Hip Score (HHS), respectively. All 14 patients underwent a full course of preoperative denosumab therapy and underwent successful surgery, with a follow-up period of 24-50 months (mean 38.2 ± 9.0 months). No postoperative complications observed. Imaging revealed shrinkage of residual cavities, blurred boundaries, progressive bone sclerosis, and trabecular bone regeneration at the surgical site. Functional assessments demonstrated significant improvements in MSTS scores (preoperative: 22.3 ± 1.3 compared with postoperative: 27.6 ± 1.2, P <0.001) and HHS (preoperative: 72.4 ± 3.1 compared with postoperative: 88.9 ± 4.3, P <0.001). All patients achieved excellent functional status (MSTS >25, HHS >82) with preserved joint mechanics. Preoperative denosumab therapy achieved partial remission (PR) in 79% (11/14) and stable disease (SD) in 21% (3/14) patients according to RECIST 1.1 criteria. At final follow-up, no patients experienced local recurrence or metastatic progression. Denosumab treatment combined with curettage after surgical dislocation of the hip successfully treated GCTB in the femoral head and neck. The safety profile of denosumab as adjuvant therapy was favorable, with no drug-related complications observed. Postoperatively, native hip joints were preserved in all patients, with satisfactory functional outcomes and no evidence of tumor recurrence or metastasis.

Gait pathomechanics in early-stage knee osteoarthritis: do non-traumatic and post-traumatic patients walk differently?

Marfan syndrome (MFS) is a connective tissue disorder caused by structural changes in fibrillin-1 and is associated with muscle weakness and joint pain. The understanding of lower extremity (LE) joint mechanics associated with joint pain in people with MFS is limited. The goal of this study was to assess LE joint mechanics during the sit-to-stand (STS) task in people with MFS compared with asymptomatic controls. Sixteen people with MFS and 16 sex- and body mass index-matched controls were tested in this study. All participants performed the STS task at a self-selected speed. Peak LE joint extensor moments, moment impulses, moment durations, time to task completion, total support moment (TSM), and each joint’s contribution to the TSM were evaluated. People with MFS took longer to perform the task and exhibited lower peak knee extensor moments and higher peak ankle plantar flexor moments compared with controls. Higher LE joint extensor moments impulses and moment durations were observed in people with MFS. People with MFS performed the STS task using a higher TSM with higher ankle contributions to the TSM. People with MFS exhibit altered LE joint mechanics during the STS task and utilize a more ankle joint dominant strategy.

Damage mechanisms of high-temperature titanium alloy laser-welded joints during hot deformation: A multiscale in situ study

Study on damage mechanism and wear behavior of rail welding joints under controlled kinetic energy

Microstructure evolution and interfacial healing mechanism of GH4098 Ni-base superalloy joints produced by hot-compression bonding

Purpose The purpose of this study is to explore the size effect on shear mechanical behavior of microscale ball grid array (BGA) structure Cu/SAC305/Cu solder joints with different heights under current stressing, and to reveal the influence mechanism of current and solder joint’s height on shear performance and fracture behavior. Design/methodology/approach A dynamic mechanical analyzer was used in conjunction with a constant current power supply to conduct shear mechanical testing of solder joints under current stressing with current densities from 6.0 × 103 to 1.1 × 104 A/cm2. Meanwhile, temperature, current density, stress and strain distribution in solder joint are analyzed in combination with finite element simulation to further reveal the evolution mechanism of mechanical behavior of solder joint. Findings This study reveals that the shear size effect in solder joints originates from the weakened constraint effect of the intermetallic compound (IMC)/substrate interface on the solder matrix with increase of joint height. Furthermore, incorporating in situ current stressing demonstrates that greater joint height leads to greater heat accumulation at identical current densities, resulting in monotonic degradation of shear strength with greater joint height. Simultaneously, greater joint height intensifies current crowding and strain mismatch at the solder/IMC interface, promoting interfacial fracture. These findings are rigorously supported by decline-rate trends and a finite element (FE)-validated simulation mechanism chain (including stress triaxiality, temperature, current density and stress/strain fields), establishing quantitative thresholds for interfacial fracture initiation. Originality/value This study extends previous research on shear size effect of solder joints by incorporating in situ current stressing. The coupling influence of joint height and current stressing was revealed by a FE-validated mechanism chain, and relevant quantitative thresholds was established, providing critical data and theoretical support for evaluating the reliability of microscale BGA-structured solder joints under current stressing.