Joint Mechanics Research Articles

Comprehensive assessment of lower limb alignment and forces during dance landings under fatigue

This study investigates the impact of fatigue on Lower Limb Alignment (LLA) and Ground Reaction Forces (GRF) during dance landings, intending to understand how fatigue-induced changes affect joint mechanics and stabilization in trained dancers. Thirty dancers (mean age: 23.4 years) with a minimum of three years of training in high-impact dance forms, such as ballet and contemporary dance, participated in the study. A within-subject experimental design assessed each participant’s landing mechanics before and after a fatigue-inducing protocol. Kinematic data were captured using a 3D motion capture system, while kinetic data were recorded with force plates. Joint angles at the hip, knee, and ankle were measured during the landing’s initial contact, peak force, and stabilization phases. Vertical and medial-lateral GRF and time to stabilization (TTS) were also analyzed pre- and post-fatigue. The fatigue protocol consisted of plyometric exercises and repetitive dance-specific movements designed to mimic the physical demands of a dance performance. Measurements were taken immediately after the fatigue protocol and at intervals of 15 min, 1 h, 24 h, and 48 h post-fatigue to assess both immediate and delayed effects of fatigue. Significant changes in joint angles were observed across all phases of the landing. Post-fatigue, hip and knee flexion increased significantly at initial contact (hip: +2.7°, knee: +3.6°, p < 0.05), reflecting compensatory adjustments for impact absorption. Ankle dorsiflexion also increased significantly during stabilization (+2.7°, p = 0.028). Vertical GRF increased across all phases post-fatigue (initial contact: +4.4 N/kg, p = 0.009), indicating a reduced ability to absorb impact forces efficiently. TTS was significantly prolonged at all post-fatigue intervals, particularly within the first 15 min post-exertion (+34 ms, p = 0.008), suggesting impaired neuromuscular control and balance.

Three degrees of freedom rigid-soft coupling biomimetic hip joint driven by dielectric elastomer

Abstract Dielectric elastomer (DE) has an attractive combination of high energy density, large strain, and fast response. A growing number of DE actuators are being used as driving materials in rigid-soft coupling joints. For better structural design, the mapping relations from the musculoskeletal system of the human hip joint to the biomimetic hip joint mechanism have been established. Inspired by the human musculoskeletal system, the configuration of the three-degree-of-freedom rigid-soft coupling hip joint based on DE is proposed. The configuration includes six soft-driving limbs and one passive rigid limb. The soft-driving limb driven by the fiber-constrained dielectric elastomer actuator (FCDEA) does not contain passive rigid joints. Based on the Gent material model, the electromechanical coupling model of FCDEA is established. A mapping model is established between the voltage applied to the soft-driving limb of the biomimetic hip joint and the posture of the moving platform in the case of deflection and torsion. A single FCDEA is prepared and its electro-responsive deformation performance is tested through experiments. As a demonstration, a prototype of the biomimetic hip joint is developed. After applying voltage, the deflection angle and the torsion angle of the biomimetic hip joint are tested and the curve of voltage and rotation angle is drawn. The experimental results agree well with the theoretical predictions. This article can provide theoretical references for improving the performance of rigid-soft coupling hip joints.

Seismic performance of joints in coal ash slag concrete frames

This paper presents experimental investigations on the joints of concrete frame beams and columns with 20% coal ash slag replacing cement. The failure mechanism of concrete frame joints with coal ash slag as a cement replacement is examined, focusing on the impacts of two scenarios—concrete with 20% coal ash slag and ordinary concrete—on the failure mode and seismic performance of beam-column joints, as well as the influence of varying concrete strength grade when the coal ash slag content is 20%. The main research variables are the presence of coal ash slag in the concrete and the concrete strength grade. Findings reveal typical failure modes at the beam-end flexural plastic hinge, progressing through stages of initial cracking, yielding, limit, and failure. Joints without coal ash slag exhibit 10.3–16.2% higher ductility, while those with 20% coal ash slag show a 14% improvement in bearing capacity. The C50 joint with 20% coal ash slag outperformed the C40 joint in bearing and energy dissipation, with robust hysteretic curves meeting seismic requirements. Thus, replacing 20% of cement with coal ash slag enhances durability and seismic performance of concrete components.

Bio-Mechatronics Development of Robotic Exoskeleton System With Mobile-Prismatic Joint Mechanism for Passive Hand Wearable-Rehabilitation

The World Health Organization (WHO) estimates that 15 million people are affected by stroke each year, causing deterioration of the upper limb, which is reflected in 70-80% of them, decreasing the performance of daily activities and quality of life, mainly affecting hand functions. Thus, the purpose of this study is to present a high-quality alternative to recover muscle tone and mobility, consisting of a hand-exoskeleton for passive rehabilitation. It covers a motion protocol for each finger and pressure sensors to give a safety pressure range during the gripping function. The bio-design method covers standards (ISO 13485 and VDI 2206) based on biomechanic and anthropometric fundamentals, where Fusion 360 was used for mechanical development and electrical-electronic circuit schematics. The prototyping process was based on 3D printing using polylactic acid (PLA); also, the actuators were servomotors DS3218, the pressure sensors were RP-C7.6-LT, and the microcontroller was Arduino Nano. The system has been validated by the Institute of Research in Biomedical Sciences (INICIB) at the Ricardo Palma University, where the novelty of this work lies in the introduction of a new mobile-prismatic joint mechanism. In conclusion, favorable results were achieved regarding the complete flexion and extension of the fingers (91.6% acceptance rate, tested in 100 subjects), so the next step proposes that the wearable device will be used in the Physical Medicine and Rehabilitation Departments of Medical Centers. Doi: 10.28991/ESJ-2024-08-06-02 Full Text: PDF

Influence of Stretch Speed and Arousal State on Passive Ankle Joint Mechanics.

Studies investigating the mechanisms influencing maximum passive joint range of motion (ROMmax) and stiffness have not objectively assessed the possible influence of stretch speed and/or arousal state. The purpose of this study was to assess the effects of arousal state and stretch speed on healthy individuals ROMmax, stiffness, gastrocnemius medialis, and soleus electromyographic activity (EMG). Fourteen participants performed one familiarization and then one testing session on separate days in the laboratory. In the familiarization (Session 1), participants practiced fast (30°/s ankle dorsiflexion) and slow (5°/s) plantar flexor stretches on an isokinetic dynamometer with the knee extended. In the experimental session (Session 2), they performed two slow, then two fast, stretches under three randomized arousal conditions: control (no music), arousing, and relaxing music. Dorsiflexion ROMmax, ankle joint stiffness, muscle activity during stretch, mean heart rate, and perception of arousal were measured. Perception of arousal was greater in the arousing than relaxing condition (p = 0.001). ROMmax was greater during fast (69.1° ± 7.8°) than slow stretches (64.9° ± 10.8°; p = 0.002) with no effect of arousal. Stiffness and EMG were higher at faster speeds, with a significantly greater percentage of stiffness observed in the arousing than the other conditions during faster stretches (p = 0.04). ROMmax was greater at the faster stretch speed despite greater stiffness and muscle activities being produced during the stretch. Thus, despite reflexive muscle activity and viscosity being higher during faster stretches, a greater, not lesser, ROMmax was observed. Arousal state, at least when altered by music, did not seem to affect ROMmax but somewhat influenced stiffness in the faster stretches.

Effect of a variable electrode force on the LME crack formation during resistance spot welding of 3G AHSS

AbstractIn the pursuit of lightweight vehicles, third-generation advanced high-strength steels (3G AHSS) with increased mechanical properties are desired to be used for critical components. However, the exposure of these zinc-coated AHSS to the manufacturing conditions during resistance spot welding can trigger liquid metal embrittlement (LME), possibly compromising the mechanical properties. As the reproducibility of LME cracks in resistance spot welding is a challenge, the effect on the static and dynamic mechanical properties of the welds is not yet fully clarified and therefore a distinction between critical and non-critical cracks is not implemented in current standards. To achieve this, it is necessary to provoke LME cracks of a given size, for example by increasing the welding current, reducing the electrode force and hold time, or using manufacturing discontinuities. Due to its significant effect on the heat input and the tensile stresses during the resistance spot welding process, which impacts the LME crack propagation, the focus of this paper is on the electrode force. An expulsion-free decreasing force profile, which consists of a force run-in, force decrease, and force run-out time, has been derived in a two-stage Face-Centered-Central-Composite design of experiment for an electrogalvanized third-generation advanced high-strength steel (3G AHSS) DP1200 HD. The crack location, length, depth, and nugget geometries were investigated for each weld. With the decreasing force profile, it was possible to generate type A, B, and C cracks by parameter adaption, with type B and C cracks being the most dominant. The type C crack formation was investigated by aborting the welding process in defined time steps and the LME cracking mechanism was confirmed by welding dezincified samples. Based on the investigations carried out, the force profile was found suitable for generating different LME crack sizes to further investigate the mechanical joint properties as it was able to reproducibly generate defined cracks without expulsion and excessive electrode indentation while maintaining a minimum nugget diameter.

Experimental and analytical study on CFST column-steel beam joints with stiffening ring and stirrups under high axial compression ratio

Super high-rise structures frequently employ concrete-filled steel tubular (CFST) column-steel beam joints with stiffening ring because of its superior performance. This study examined the structural behavior of high axial compression ratio stiffening ring joints with stirrups in the column. Three 1/2-scaled joints with different stirrup arrangements and axial compression ratios were designed and tested. Apart from analyzing the hysteresis behavior, skeleton curve, stiffness degradation, energy dissipation, and steel strain of each specimen, an investigation was conducted into the failure mechanisms of the specimens under low cycle reciprocating load on the beam end. Furthermore, a three-dimensional nonlinear solid finite element (FE) model was developed for the joint. The results of the FE analysis and the experimental data agreed well regarding failure modes, hysteresis curves, and steel strain. Furthermore, the energy dissipation allocation mechanism of joints with various parameters was revealed. The results show that the seismic performance of the stiffening ring joint with stirrups was excellent, and stirrup confinement effectively improved the seismic performance of stiffening ring joints. Under a high axial compression ratio of 0.8, the joint with stirrup exhibited bending failure at the beam end, avoiding the phenomenon of column end bending failure in traditional specimens. In addition, the stiffening ring joint underwent a transition from beam energy dissipation to column energy dissipation when the beam-column flexural capacity ratio reached 1.39. The study's findings can serve as a guide for engineers using stirrups in square CFST column-steel beam joints with stiffening rings.

Efficient development of subject-specific finite element knee models: Automated identification of soft-tissue attachments

Musculoskeletal disorders impact quality of life and incur substantial socio-economic costs. While in vivo and in vitro studies provide valuable insights, they are often limited by invasiveness and logistical constraints. Finite element (FE) analysis offers a non-invasive, cost-effective alternative for studying joint mechanics. This study introduces a fully automated algorithm for identifying soft-tissue attachment sites to streamline the creation of subject-specific FE knee models from magnetic resonance images. Twelve knees were selected from the Osteoarthritis Initiative database and segmented to create 3D meshes of bone and cartilage. Attachment sites were identified in three conditions: manually by two evaluators and via our automated Python-based algorithm. All knees underwent FE simulations of a 90° flexion–extension cycle, and 68 kinematic, force, contact, stress and strain outputs were extracted. The automated process was compared against manual identification to assess intra-operator variability. The attachment site locations were consistent across all three conditions, with average distances of 3.0 ± 0.5 to 3.1 ± 0.6 mm and no significant differences between conditions (p = 0.90). FE outputs were analyzed using Pearson correlation coefficients, randomized mean square error, and pairwise dynamic time warping in conjunction with ANOVA and Kruskal-Wallis. There were no statistical differences in pairwise comparisons of 67 of 68 FE output variables, demonstrating the automated method’s consistency with manual identification. Our automated approach significantly reduces processing time from hours to seconds, facilitating large-scale studies and enhancing reproducibility in biomechanical research. This advancement holds promise for broader clinical and research applications, supporting the efficient development of personalized musculoskeletal models.

Time-dependent changes in medial meniscus kinematics and attachment strength after anterior root injury and repair in a large animal model.

This study investigated joint kinematics and attachment tensile mechanics following resection of the medial meniscus anterior attachment. A secondary objective investigated the repair of the attachment. Yucatan minipigs underwent unilateral surgery for either Injury (en bloc) resection of the anterior attachment of the insertional ligament, (a portion of the cranial medial meniscotibial ligament) or Repair (immediate repair with a suture anchor), with the contralateral knee as Intact control. Evaluation at 6 weeks and 6 months included joint kinematics measured from MRI acquired under knee compression and tensile testing of the attachment. Injury resulted in large levels of meniscus extrusion, despite the development of a fibrovascular scar. At 6 weeks, the meniscus extruded 1.95 mm more than Intact; at 6 months, this extrusion was reduced to 0.77 mm. Under an applied 1× body weight load, the meniscus further extruded and was not different with treatment or time. During attachment tensile testing, elongation was 0.6 mm for Intact, following Injury, elongation was 2.7 mm at 6 weeks and was partially restored to 1.5 mm at 6 months. Despite this, the cartilage wear worsened over time. Repair was inadequate to avoid the extrusion or cartilage wear seen in the injury group at 6 weeks, so it was not continued for the 6-month group. This study demonstrates that while meniscus injury is useful to study cartilage degeneration, a holistic consideration of the role of the meniscus itself, including its changing material properties and its impact on joint mechanics during injury, repair, and rehabilitation, are key factors contributing to overall joint health.

Analysis of the Influence of Adhesive, Geometry, and Manufacturing Processes on Mixed Mode Stress Ratio in Single Lap Shear Adhesive Joint Structures of Aluminum and Composite Plates

In aircraft structures, composite plate joints often present significant challenges. Mechanical fastenings such as pins, bolts, or rivets require holes to be drilled in the plates, which reduces the strength of the laminate due to stress concentrations around the hole edges. These joints frequently become sources of structural failure in aircraft. Therefore, the design of composite plate joints is crucial to maintain structural integrity. Adhesive joints offer several advantages over mechanical joints, including the ability to join two different materials, more uniform stress distribution along the joint, and reduced weight since no bolts or rivets are needed. The most common adhesive joint design is the Single Lap Joint (SLJ), which is popular due to its simple geometry and high structural efficiency. However, the main drawback of the SLJ is load eccentricity, which leads to secondary bending and undesirable normal stresses along the adhesive edges. The hypothesis of this study is that SLJ conditions with optimal shear strength can be achieved through the right combination of adhesive type, bond surface preparation, and joint configuration. This study analyzes the influence of various adhesive materials, joint designs, and manufacturing methods using numerical modeling methods, validated with analytical approaches and ASTM standard testing. Numerical modeling is conducted using the finite element method with a cohesive zone model (CZM) approach to examine stress distribution in various cases, such as the impact of geometry, adhesive thickness, and joint length. The normal and shear stress distribution along the joint is found to significantly affect the strength of the SLJ, highlighting the importance of careful design and material selection in these applications.

Formation mechanism of ZrC-SiC joint prepared by pulsed-current assisted diffusion bonding

For pulsed-current assisted diffusion bonding of ZrC-SiC composite, the required joining temperature and joint formation mechanism showed great difference with grain-size. Compared to base-materials with a grain-size of 3–5 μm (m-ZS), the joining temperature of n-ZS (grain-size ∼1 μm) could be reduced by 100 °C while maintaining the same joint efficiency. Moreover, the straight bond-line of m-ZS joint was eliminated by strain-induced grain-boundary migration, but causing by the straight interface due to the pining effect of interfacial SiC, shear strength of the joint bonded at 1700 °C is only 81.7 % of the substrate. In contrast, pulsed-current enhanced the vaporization-deposition mechanism in n-ZS joint, resulting in massive formation of nano-scale ZrC particles at interface. At 1700 °C, the cross-interface growth of nano-particles contributed to a seamless joining, and the joint microstructure and shear strength are consistent with those of the base-materials.

Experimental Investigations on Thermo-mechanical Behavior and Failure Mechanisms of Hybrid Bonded-bolted Plain-woven Composite Joint

This paper focuses on the thermo-mechanical coupling behavior and failure mechanisms of single-lap bonded, bolted, and hybrid bonded-bolted plain-woven composite joints. Quasi-static tension tests were conducted on these three types of joints at -50 ℃, -20 ℃, +23 ℃, +70 ℃ and +120 ℃, respectively. Based on the experimental results, the failure mechanisms and hybridization effect of the hybrid joint under temperature impact were analyzed and discussed. It is shown that i) failure load in the bonding stage of the hybrid joint is significantly lower than that of the bonded joint. ii) The increasing temperature not only leads to the decreasing joint performances of joints but also the transition of failure modes for the bonded joint and hybrid joint. iii) Compared with the bonded joint and bolted joint, no significant improvement is observed in the joint strength and joint stiffness of the hybrid joint, which is due to the high stiffness of the adhesive and the thread embedment-induced adhesive failure. iv) Although the hybridization effect is not sensitive to the temperature of -50 ℃ and -20 ℃, it shows a strong relation with the temperature of +120 ℃, which is probably due to the premature adhesive failure.

Impact of knee geometry on joint contact mechanics after meniscectomy.

Finite element modeling has served as a cornerstone in understanding knee joint mechanics post-meniscectomy, yet the influence of varying knee geometries remains unknown. The present study aimed to fill that gap by employing statistical shape modeling to generate knee models from MRI data of 31 human knees, capturing the population's knee size and shape variations. Finite element simulations were conducted to replicate intact, partial, and total medial meniscectomy conditions during standing. The results revealed a substantial shift in load distribution from the medial to lateral compartment following medial meniscectomy with its magnitude depending on knee geometry. Cartilages experienced variable degrees of pressure changes at different sites, which could also be different for fluid and contact pressures. While changes in joint size led to somewhat predictable alterations in contact pressure, variations in joint shape resulted in unexpected changes in contact and fluid pressures, emphasizing the need for computational simulations. The average knee geometry exhibited the lowest contact and fluid pressures under the given loading and boundary conditions, in contrast to knees with shapes deviating from the average. This study highlights the significance of individual knee shape in the biomechanical outcome of meniscectomy, potentially explaining the variability in clinical outcomes observed post-surgery.

Fatigue fracture mechanism and life prediction of steel-aluminium clinched joints under different stress ratios

Vehicle bodies are subject to complex random loads during travelling, making it imperative to investigate the effects of different stress ratios on the body joining structure. To investigate the fatigue performance of steel-aluminium clinched joints under different stress ratios, fatigue experiments were conducted on these joints subjected to different load levels at stress ratios of -0.4, 0.1, and 0.4. The fracture mechanism of steel-aluminium clinched joints under different stress ratios was investigated through analysis of the joint's fracture morphology and the composition of abrasive chips using Scanning Electron Microscope and Energy Dispersive Spectroscopy. A fatigue life prediction model for steel-aluminium clinched joints was developed by employing the modified Paris formulation of the Wallker equation. The results indicate that joint failure can be classified into three main forms: lower sheet fracture, upper sheet pull-off accompanied by lower sheet fracture and reaching infinite life (2 million times). The lower sheet of a fatigue failure specimen in a steel-aluminium clinched joint exhibited a novel form of fretting damage known as lower sheet inter-plate fretting wear. Furthermore, the application of Walker's improved Paris formula proved to be highly effective in accurately predicting the fatigue life of steel-aluminium clinched joints under different stress ratios, with the predicted results demonstrating excellent agreement with experimental findings.

User experience of lower extremity exoskeletons and its improvement methodologies: A narrative review.

In this review, user experience (UX) of recent lower limb exoskeletons (LLEs) and its improvement methodologies are investigated. First, statistics based on standardised and custom UX evaluations are presented. It is indicated that, LLE users have positive UX, especially in the aspects of safety, dimension and effectiveness. Further, overall, UX levels of ankle and hip-knee exoskeletons are higher than those of other exoskeleton types; unilateral LLEs have higher mean UX levels than that of the bilateral ones. Then, design practices for improving UX are studied; the focused points are burden reduction and improvement of device fit. The former is achieved through lightweight design and approaches that reduce device's moment of inertia (MOI) at mechanical joints. Works on the latter refer to the endeavours to enhance static and dynamic fit; they mainly rely on the optimisations of human-robot interface (HRS) and endeavours to rectify misalignment of axes of mechanical and anatomic joints, respectively. The following section is control approaches to enhance wearing comfort level; it is mainly focused on adaptive, interaction and compensation-based controls. Finally, existing problems and future directions are stated and prospected respectively.

Nonlinear Vibrations of Low Pressure Turbine Bladed Disks: Tests and Simulations

One of the most effective methods to limit the mechanical vibrations of bladed disks is the use of friction damping at mechanical joint interfaces. Unfortunately, dedicated tests to assess the impact of mistuning and the effectiveness of friction dampers are uncommon. This paper presents an original design of an academic demonstrator to perform an experimental analysis of the dynamic response of a tip-free bladed disk with under-platform dampers (UPDs), including an identification of intrinsic and contact mistuning introduced by the UPDs. The 48-blade disk was tested in a vacuum spinning rig by using permanent magnets. Vibration measurements were performed with the Blade Tip-Timing system. Tests were simulated using the Policontact tool, which predicted the average experimental nonlinear response in the presence of UPD, confirming the tool’s ability to capture the general nonlinear dynamic behavior of the mistuned bladed disk. This study presents a novel approach combining experimental Blade Tip Timing (BTT) with numerical simulations using Policontact (ver. 3.0) software and a model update based on experimental evidence to validate nonlinear dynamic responses. It distinguishes between intrinsic and contact mistuning effects, providing new insights into their impact on bladed disk vibrations. Additionally, a comparison of aluminum and steel UPDs reveals that steel offers a 26% greater damping efficiency due to its higher density and preload, significantly improving vibration reduction.

Knee joint mechanics during gait after anterior cruciate ligament reconstruction using a partial or full thickness quadriceps tendon autograft at 2 years after surgery.

Despite quadriceps weakness in individuals after quadriceps tendon anterior cruciate ligament reconstruction (QT-ACLR), and its association with knee joint mechanics, no studies have addressed gait mechanics in both partial-thickness (PT-Q) and full-thickness (FT-Q) options for QT-ACLR. To assess gait mechanics across a QT-ACLR cohort. We hypothesized that QT-ACLR would show changes in knee joint mechanics compared to control participants (CON) and nonoperated limbs. Additionally, we hypothesized that FT-Q operated limbs would show greater changes compared to PT-Q and CON. Retrospective cohort study. University-affiliated sports medicine institute. Sixteen patients who underwent QT-ACLR (7 FT-Q: Age (years) = 28.6 ± 7.3, post-op (months) = 23.5 ± 10.7, 9 PT-Q: Age = 25.2 ± 4.3, post-op = 24.4 ± 11.7) were recruited and compared to 11 CON (age = 23.4 ± 4.8). Participants underwent gait testing with force plate integrated motion capture. Mixed repeated-measures analyses of covariance, adjusted for gait speed, were used to determine significant main effects or interactions in peak knee flexion angle, sagittal knee range of motion, peak internal knee extension moment (KEM), and peak internal knee flexion moment. When measured an average of 2 years after surgery, no main effect for limb or limb by depth interaction were detected. A significant effect by group was observed for peak KEM (p = .03, η2 = .27) and peak knee flexion angle (p = .04, η2 = .24) in the loading response phase. FT-Q (p = .02) and PT-Q (p = .03) showed lower KEM compared to the CON group in both limbs. The FT-Q group showed lower peak knee flexion angle compared to the CON group (p = .01). Knee joint symmetry may be recovered 2 years following QT-ACLR, but lower KEM compared to CON for both graft options and lower peak knee flexion angle than CON for the FT-Q group may indicate a need for further investigation in QT-ACLR.

Effects of structural parameters on the load distribution unevenness in CFRP hybrid bonded‐bolted joint

AbstractCarbon Fiber Reinforced Polymer (CFRP) Hybrid Bonded/Bolted (HBB) joint structures are distinguished for their superior jointing performance among current mechanical joint systems, making them a favored option for mechanical joints. These structures are characterized by many structural parameters, with the relationship between these parameters and jointing performance being notably complex. Additionally, the laminate's brittleness and the uneven distribution of bolt loads in multi‐bolt joint structures impair the overall jointing performance. To investigate the impact of structural parameters on the uneven load distribution within CFRP HBB joint structures and improve their jointing performance, a finite element analysis (FEA) model grounded in 3D Hashin failure criterion is developed. Validation of the model with experimental data confirmed the uneven load distribution among bolts in multi‐bolt joints. The study elucidated the influence of changes in structural parameters (overlap length, bolt‐hole spacing, and clearance fit) on the uneven load distribution and the connection strength of CFRP HBB joint structures. A negative correlation is found between the unevenness of load distribution and connection strength, offering insights for enhancing and researching connection strength in CFRP HBB joint structures.Highlights Developed a FEA model based on the 3D Hashin failure criterion for CFRP Bonded‐Bolted joints. Identified key factors affecting HBB joint load distribution and jointing performance. Evaluated the impact of overlap length, bolt‐hole spacing, and clearance fit on CFRP joints. Suggested design optimizations for enhancing the performance of HBB joints.

Microstructural and mechanical properties of laser-welded molybdenum joints with the addition of nano-sized ZrC in the weld pool

Effects of adding nano-sized ZrC in the fusion zone (FZ) on the microstructures and properties of laser-welded joints of pure molybdenum (Mo) and underlying mechanisms were explored. Compared with the joints without ZrC, the average microhardness of the FZ increases from 180 HV to 330 HV, the tensile strength of joints grows from 32 MPa to 386 MPa, and the fracture mode of joints switches from intergranular fractures to that dominated by cleavage fractures, after adding ZrC. ZrC, ZrO2, and Mo2C are detected in the FZ after adding ZrC. ZrC and ZrO2 is mainly found on grain boundaries (GBs). ZrC is able to deplete O in the FZ, thus decreasing the amount of harmful molybdenum (Mo) oxides on GBs, so it plays a role in purifying and strengthening GBs. ZrC, ZrO2, and Mo2C particles not only hinder dislocation movement and GB movement, but also serve as effective heterogeneous nucleation cores and therefore can refine grains in the FZ. The average grain size in the FZ of the joint without ZrC is 47.6 μm, while it is 28.4 μm after adding ZrC, which reduces by 40.3 % compared with the former. The significant improvement of the joint strength after adding ZrC is a result of joint action of dispersion strengthening, fine-grain strengthening, and GB purification.

The application of 3D printing technology in the design of sandwich panels

Composite materials including sandwich panels can offer a number of advantages such as excellent strength to mass ratio or stiffness to mass ratio. Sandwich panels can find their application in many industrial sectors where the mass and mechanical properties are critical. Despite these and many other advantages, the use of sandwich panels is associated with many problems, which stem from their structural composition (weak core with high shear stiffness connecting two skins with high in plane stiffness). This composition can cause problems in joining the sandwich panels to each other and to other parts by means of mechanical joints. To solve these problems, there exist many accessories such as inserts. The main objective of this paper is to present the development, manufacturing, and testing of plastic inserts for sandwich panels made by Fused Deposition Modelling 3D printing technology.