Plane Joint Research Articles

Development of An Anybody Musculoskeletal Model of The Thoroughbred Forelimb

Musculoskeletal injuries in horses are the main cause of retirement, rest, and death. To understand these injuries, it is necessary to study loads in muscles, tendons and ligaments. A musculoskeletal model makes it possible to consider all structures simultaneously and avoids invasive measurements. At present, most computational models of the equine limb described in the literature have been limited to the distal limb. The aim of this study was to create a preliminary musculoskeletal model of the whole equine forelimb and to run it with kinematic data collected during gait. The model was developed with the AnyBody Modelling System. It includes six limb segments, 11 muscle groups and 17 ligaments. Kinematic data were collected from the right forelimb of four Thoroughbreds at trot, right and left lead canter, and were then used in the model to compute sagittal plane joint excursions and ligament and tendon strains. The modelled joint excursions were in reasonable agreement with previous reports in the literature despite breed, gait and surface differences. Strain patterns of the tendons of the suspensory apparatus agreed with the literature, with maxima in mid-stance or at the end of stance. Strains in the distal palmar ligaments peaked in mid-stance, while strain in lacertus fibrosus peaked at the stance-swing transition. Tendon and ligament strains at canter were greatest when the measured forelimb was the trailing limb. Strain amplitudes varied against earlier models and these differences are discussed in relation to variations in methods, and especially in relation to attachment points of tendons and ligaments.

A 2D video-analysis scoring system of 90° change of direction technique identifies football players with high knee abduction moment

PurposeAbnormal joint biomechanics and poor neuromuscular control are modifiable risk factors for Anterior Cruciate Ligament (ACL) injury. Although 3D motion capture is the gold standard for the biomechanical evaluation of high-speed multidirectional movements, 2D video analysis is a growing-interest alternative because of its higher cost-effectiveness and interpretability. The aim of the present study was to explore the possible association between a 2D evaluation of a 90° change of direction (COD) and the KAM measured with gold standard 3D motion analysis.MethodsThirty-four competitive football (soccer) players (age 22.8 ± 4.1, 18 male and 16 females) were enrolled. Each athlete performed a series of pre-planned 90° COD at the maximum speed possible in a laboratory equipped with artificial turf. 3D motion analysis was recorded using 10 stereophotogrammetric cameras, a force platform, and three high-speed cameras. The 2D evaluation was performed through a scoring system based on the video analysis of frontal and sagittal plane joint kinematics. Five scoring criteria were adopted: limb stability (LS), pelvis stability (PS), trunk stability (TS), shock absorption (SA), and movement strategy (MS). For each criterion, a sub-score of 0/2 (non-adequate), 1/2 (partially adequate), or 2/2 (adequate) was attributed to the movement, based on objective measurements. The intra-rater and inter-rater reliability were calculated for each criterion and the total score. The Knee Abduction Moment (KAM) was extracted from the 3D motion analysis and grouped according to the results of the 2D evaluation.ResultsExcellent intra-rater reliability (ICC > 0.88) and good-to-excellent inter-rater reliability (ICC 0.68–0.92) were found. Significantly higher KAM was found for athletes obtaining a 0/2 score compared to those obtaining a 2/2 score in all the sub-criteria and the total score (20–47% higher, p < 0.05). The total score and the LS score showed the best discriminative power between the three groups.ConclusionThe 2D video-analysis scoring system here described was a simple and effective tool to discriminate athletes with high and low KAM in the assessment of a 90° COD and could be a potential method to identify athletes at high risk of non-contact ACL injury.Level of evidenceIV.

An experimental and analytical study of rate-dependent shear behaviour of rough joints

Understanding the shear behaviour of rough joints is of great significance for dealing with rock engineering problems. In many cases, rock joints are often subjected to dynamic loadings, which are usually caused by explosions, impacts or earthquakes, etc. Until now, the dynamic shear characteristics of rock joints have not been well understood. In the present study, we investigate joint shear behaviour at different shear rates and develop a rate-dependent constitutive model of rough joints. Testing results shows that the shear/frictional strength of joints with meso-roughness (i.e., planar joints) is independent on the shear rate, while the strength of joints with macro-unevenness (i.e., saw-toothed joints) increases with the shear rate. Under identical boundary conditions, the residual strength of joints with macro-unevenness approximates to the kinetic frictional strength of planar joints. Based on the testing results, the shear stress-displacement curve of rough joints was divided into four phases, i.e., linear elastic phase, shear hardening phase, shear softening phase and residual strength phase. A viscous joint model was thus proposed and validated through comparison with laboratory measurements. This new model correlates the static joint shear stiffness with dynamic one, and has the ability to describe the shear stiffness evolution during the whole shearing process. Based on the proposed model, a hypothesis about shear rate effects of rough joints was introduced and then verified through numerical modelling. The findings in this paper could facilitate better understanding the dynamic behaviour of rough joints and be useful for analyzing rock engineering problems with discontinuous rock masses.

Anatomical versus non-anatomical configuration of double coraco-clavicular tunnel technique in acromioclavicular joint reconstruction

PurposeHorizontal instability is a common problem after acromioclavicular joint injuries. The aim of this study was to evaluate if there is a difference regarding horizontal stability between an anatomical and a non-anatomical configuration of the double tunnel coraco-clavicular ligament reconstruction of the acromioclavicular joint.MethodsThirteen acromioclavicular joints of human cadaveric shoulders in ethanol-glycerin fixation were included in the study and underwent cyclic anterior and posterior translational testing at a load of 70 N using an electromechanical uniaxial testing machine. The shoulders were randomly assigned to the following groups: double coraco-clavicular tunnel technique in an anatomical configuration (DCTa) and double coraco-clavicular tunnel technique in an inverse configuration of the anatomical position (DCTb). The dislocation was recorded with a 3D optical measuring system.ResultsThe total horizontal displacement (p10 = 0.0221; p5000 = 0.082) was significantly higher for the non-anatomical reconstruction (DCTb) compared to the anatomical reconstruction (DCTa) after every measured amount of cycles. The increase in displacement for DCTb group was overall higher than the increase in displacement for DCTa group but without significance.ConclusionReconstruction of the CC ligaments in an anatomical configuration with two suture devices results in a significantly higher stability of the AC joint in the horizontal plane than reconstruction of the CC ligaments in a non-anatomical configuration. Based on the results of this biomechanical in vitro study, the use of a double coraco-clavicular reconstruction should focus on an anatomically correct position of the suture devices.

Kinematic and Temporospatial Changes in Children with Cerebral Palsy during the Initial Stages of Gait Development

ABSTRACT Purpose To identify changes in the gait kinematics and temporospatial parameters of children with bilateral Cerebral Palsy (CP) at 8 months after the onset of independent walking and identify differences to Typical Development (TD) children at the onset of independent walking and at 8 months follow up. Method Sixteen children with bilateral CP, GMFCS levels I and II, and 15 TD children were recruited. Gait kinematics and temporospatial parameters were recorded using a 3-D gait analysis system; the sagittal plane of the lower limb joints was analyzed. Baseline measurements were recorded at the individual’s onset of independent walking and follow up was after 8 months. Results Compared to baseline, children with bilateral CP demonstrated increased (mean difference ± SE) plantar flexion (11.79 ± 2.96), single support (0.04 ± 0.01), step length (0.2 ± 0.05) and stride length (0.4 ± 0.09), at follow up; all p < .05. Compared to TD children, they also had lower gait speed (0.16 ± 0.05), higher single support (0.02 ± 0.01) and lower maximum knee extension (9.14 ± 4.49) during the swing phase, at baseline and follow up (0.1 ± 0.04, 0.05 ± 0.01, 23.04 ± 4.17, respectively); all p < .05. Conclusion There are changes in the sagittal plane kinematics and temporospatial parameters of the gait during the first 8 months of independent walking. These indicate gait maturation changes and highlight the impact of walking experience on the gait characteristics of children with bilateral CP.

Effects of Overweight and Obesity on Running Mechanics in Children.

The purpose of this study is to determine differences in running mechanics between healthy weight (HW) children and children classified as OW/OB. Forty-two children (17 OW/OB, 25 HW) ran overground while kinematic and kinetic data were recorded using a motion capture system and force plate. Kinematic variables of interest included stance time, step length, and frontal and sagittal plane joint angles and excursions at the hip, knee, and ankle. Kinetic variables of interest included ground reaction forces and hip, knee, and ankle moments in the sagittal and frontal planes. The OW/OB group spent more time in stance, took shorter steps, displayed less hip flexion during the first half of stance, had greater ankle inversion at foot strike, had greater knee abduction throughout stance, and had smaller knee flexion, knee adduction, and hip adduction excursions. In comparing unscaled ground reaction forces, the OW/OB group displayed greater peak vertical force, vertical impact peaks, and vertical loading rates. The OW/OB group also displayed greater unscaled plantar and dorsiflexion moments, knee flexion and extension moments, ankle inversion moments, and knee and hip abduction moments. These data suggest that increased body weight in children is associated with changes in running mechanics. Higher joint moments and ground reaction forces may indicate increased injury risk or the development of joint degeneration among overweight/obese children.

Dickinsonia: mobile and adhered

AbstractThe classical genus of Ediacaran macroorganisms, Dickinsonia, was part of an extensive benthic marine community inhabiting the fields of microbial mats. The remains of Dickinsonia are commonly preserved in the position of adhesion to the habitat substrate. However, these were mobile organisms. In addition to the already known feeding traces of Dickinsonia, structures described as traces of motor activity are reported. Long parallel furrows, extending from the posterior end of the body imprint, are interpreted as imprints of ridges left by an organism moving along the surface of the substrate. Groups of differently shaped grooves laying in the depression that enhalo the Dickinsonia body imprints or accompany their individual areas are interpreted as imprints of ridges and cords of mucous material. They are considered to represent structures of self-determined stretching and lift-off of the body margins from the substrate. The rings and arcs of silt- and sand-sized mineral particles bordering the body imprints are composed of material that was supposedly brushed off from the surface of the microbial mat by Dickinsonia. They are considered traces of the adhesion of these organisms to the substrate. Accumulations of multidirectional pulling and tear-off structures, lacking the body imprint but accompanied by the joint plane passing into the overlying sediment and cutting through the bedding, are interpreted as escape traces. The dual modality of the behaviour (attachment and mobility) could indicate the adaptability of Dickinsonia to life in extremely shallow-water environments.

Kinematic and Kinetic Predictors of Y-Balance Test Performance.

BackgroundThe Y-Balance Test (YBT) assesses dynamic stability and neuromuscular control of the lower extremity. Several authors have analyzed kinematic predictors of YBT performance with conflicting results, but the influence of kinetic factors is not well understood.PurposeTo examine kinematic predictors of YBT performance and determine the joint kinetics which predict YBT performance.Study DesignCross-sectional study.MethodsThirty-one physically active individuals performed YBT trials on a force plate while whole body kinematics were recorded using a motion capture system. Sagittal, frontal, and transverse plane joint kinematics and joint moments were calculated at maximum reach in each YBT reach direction. Variables correlated with reach distances at the p < 0.2 level were entered into a stepwise linear regression.ResultsIn the anterior direction, knee flexion and torso rotation (R2=0.458, p<0.001) and knee extensor and hip abductor moments (R2=0.461, p<0.001) were the best kinematic and kinetic predictors of reach distance. In the posterior medial direction, hip flexion, ankle dorsiflexion, and ankle rotation accounted for 45.8% of the variance in reach direction (p<0.001) while hip and knee extensor, and hip abductor moments explained 72.6% of the variance in reach distance (p<0.001). In the posterior lateral direction, hip flexion and pelvic rotation (R2=0.696, p<.001) and hip extensor moments (R2=0.433, p=0.001) were the best kinematic and kinetic predictors of reach distance.ConclusionThe ability to generate large hip and knee joint moments in the sagittal and frontal plane are critical for YBT performance.Level of Evidence3.

Analysis and determination of the behavioral mechanism of rock bridges using experimental and numerical modeling of non-persistent rock joints

Presence of rock bridges (RB) in natural non-persistent discontinuity sets is an effective factor on the stability of rock structures. Investigations show that the bearing capacity of jointed rocks is changed with variation of different joint parameters. Therefore, in order to investigate the effect of parameters such as contact area and number of rock bridges, normal load, angle, length, and number of joints on shear strength of non-persistent rock joints and also to recognize the interaction of these parameters on the mechanical behavior of joints, experimental design methods of Taguchi and central composite design (CCD) were used for the sample generation, testing and numerical modeling. The effective parameters on the shear strength of jointed samples were obtained based on the previous studies. Using the Taguchi method, 16 samples were tested at CNL condition and the effect of parameters such as normal stress, number, and area of rock bridges was investigated. To evaluate other joints parameters, 30 experiments were designed using CCD method and examined using numerical modeling. Using the analysis of variance (ANOVA), it was found that the obtained models are statistically significant. According to the results of ANOVA, the area of rock bridges and the angle of joints showed the highest and the lowest effect on shear strength of coplanar and non-coplanar jointed samples, respectively. The results displayed that the dominant failure for planar non-persistent joints is pure shear and a combination of tensile and shear cracks is created from the both tips of adjacent joints. Moreover, it was found that the dominant failure of non-coplanar joints is the combination of shear and tension. Bonded particle model (BPM) and smooth joint model (SJM) were also applied for numerical modeling. A new method was considered for applying SJ to the models, which solved the interlocking problem during the test.

Functional alignment achieves soft-tissue balance in total knee arthroplasty as measured with quantitative sensor-guided technology.

Total knee arthroplasty (TKA) using functional alignment aims to implant the components with minimal compromise of the soft-tissue envelope by restoring the plane and obliquity of the non-arthritic joint. The objective of this study was to determine the effect of TKA with functional alignment on mediolateral soft-tissue balance as assessed using intraoperative sensor-guided technology. This prospective study included 30 consecutive patients undergoing robotic-assisted TKA using the Stryker PS Triathlon implant with functional alignment. Intraoperative soft-tissue balance was assessed using sensor-guided technology after definitive component implantation; soft-tissue balance was defined as intercompartmental pressure difference (ICPD) of < 15 psi. Medial and lateral compartment pressures were recorded at 10°, 45°, and 90° of knee flexion. This study included 18 females (60%) and 12 males (40%) with a mean age of 65.2 years (SD 9.3). Mean preoperative hip-knee-ankle deformity was 6.3° varus (SD 2.7°). TKA with functional alignment achieved balanced medial and lateral compartment pressures at 10° (25.0 psi (SD 6.1) vs 23.1 psi (SD 6.7), respectively; p = 0.140), 45° (21.4 psi (SD 5.9) vs 20.6 psi (SD 5.9), respectively; p = 0.510), and 90° (21.2 psi (SD 7.1) vs 21.6 psi (SD 9.0), respectively; p = 0.800) of knee flexion. Mean ICPD was 6.1 psi (SD 4.5; 0 to 14) at 10°, 5.4 psi (SD 3.9; 0 to 12) at 45°, and 4.9 psi (SD 4.45; 0 to 15) at 90° of knee flexion. Mean postoperative limb alignment was 2.2° varus (SD 1.0°). TKA using the functional alignment achieves balanced mediolateral soft-tissue tension through the arc of knee flexion as assessed using intraoperative pressure-sensor technology. Further clinical trials are required to determine if TKA with functional alignment translates to improvements in patient satisfaction and outcomes compared to conventional alignment techniques. Cite this article: Bone Joint J2021;103-B(3):507-514.

Visualization of 3D rock mass properties in underground tunnels using extended reality

The term extended reality (XR) refers to a family of technologies that cover Virtual Reality (VR), Augmented Reality (AR), and Mixed Reality (MR). The main benefit of XR is that it can offer a new viewpoint on the surrounding environment by augmenting it with digital data and visualizations. Recent developments of XR enable its deployment for rock engineering applications, including underground tunnels. In this paper, we demonstrate two cases of the use of XR in an underground tunnel to display spatial information on the tunnel surface. One of the tunnels in the Underground Research Laboratory of Aalto University (URLA) was digitized using Structure-from-motion (SfM) photogrammetry. As a result, a high-resolution 3D point cloud and textured model of the tunnel were created. Next, the rock joint planes were obtained semi-automatically from the digitized rock surfaces. The results are then represented in their actual positions in the tunnel geometry. In the first case, we used VR to display the rock joint planes on the textured model of the tunnel. In the second case, the data was displayed in real-time in tunnel conditions through a mobile device. The results demonstrate that XR technology can be successfully used in underground construction to digitize the workplace and provide a new perspective on the work environment, which can potentially lead to an increase in safety and productivity.

A Comparative Biomechanical Analysis during Planned and Unplanned Gait Termination in Individuals with Different Arch Stiffnesses

Although values of arch stiffness index (ASI) have been used to evaluate arch structure and injury susceptibility, investigations are limited regarding the influence of ASI on biomechanical characteristics during gait termination, which involves a challenging balance transition from walking to standing. This study aimed to explore plantar pressure distribution and lower extremity joint kinematic differences between individuals with both a stiff and flexible arch (SA and FA, respectively) during planned and unplanned gait termination (PGT and UGT, respectively). Following the calculation of ASI, sixty-five asymptomatic male subjects were classified and participated in two types of gait termination tests to acquire kinematic and plantar pressure data. Parameters were compared between SA and FA using a two-way ANOVA during PGT and UGT, respectively. UGT was found to have a larger range of motion on the hip joint in the sagittal plane and the knee joint in the transverse plane when compared with PGT. The differences in the kinematic characteristics of the lower limb joints caused by the difference in arch stiffness are mainly concentrated in the ankle and metatarsophalangeal joints. Plantar pressure data, represented by the maximum pressure, showed significant differences in the forefoot and rearfoot areas. These results suggest that ASI could change freedom of motion of the lower limb joints, and UGT tends to conduct a compensatory adjustment for the lower extremity kinetic chain. An understanding of the biomechanical characteristics of arch structures may provide additional insights into foot function and injury prediction during gait termination.

A state-of-the-art review of automated extraction of rock mass discontinuity characteristics using three-dimensional surface models

In the last two decades, significant research has been conducted in the field of automated extraction of rock mass discontinuity characteristics from three-dimensional (3D) models. This provides several methodologies for acquiring discontinuity measurements from 3D models, such as point clouds generated using laser scanning or photogrammetry. However, even with numerous automated and semi-automated methods presented in the literature, there is not one single method that can automatically characterize discontinuities accurately in a minimum of time. In this paper, we critically review all the existing methods proposed in the literature for the extraction of discontinuity characteristics such as joint sets and orientations, persistence, joint spacing, roughness and block size using point clouds, digital elevation maps, or meshes. As a result of this review, we identify the strengths and drawbacks of each method used for extracting those characteristics. We found that the approaches based on voxels and region growing are superior in extracting joint planes from 3D point clouds. Normal tensor voting with trace growth algorithm is a robust method for measuring joint trace length from 3D meshes. Spacing is estimated by calculating the perpendicular distance between joint planes. Several independent roughness indices are presented to quantify roughness from 3D surface models, but there is a need to incorporate these indices into automated methodologies. There is a lack of efficient algorithms for direct computation of block size from 3D rock mass surface models. • Review of automatic and semi-automatic methods for discontinuity characterization. • Focused on joint sets, orientation, persistence, spacing, roughness and block size. • Strengths and limitations of methods are discussed from a practical perspective. • Computation time, number of parameters, accuracy, and robustness are discussed. • Region growing was found fast and accurate for joint detection from LiDAR data.

Classification of a 3-RER Parallel Manipulator Based on the Type and Number of Operation Modes

Abstract The type/number of operation modes of a parallel manipulator (PM) may vary with the link parameters of the PM. This paper presents a systematic classification of a 3-RER PM based on the type/number of operation modes. Here, R and E denote revolute joint and planar joint, respectively. The 3-RER PM was proposed as a 4-degree-of-freedom (DOF) 3T1R PM in the literature. Using the proposed method, classification of a PM based on the type/number of operation modes can be carried out in four steps, including formulation of constraint equations of the PM, preliminary classification of the PM using Gröbner cover, operation mode analysis of all the types of PMs using primary decomposition of ideals, and identification of redundant types of PMs. The classification of the 3-RER PM shows that it has 13 types. Besides the two 4-DOF 3T1R operation modes, different types of 3-RER PMs may have up to two more 3-DOF or other types of 4-DOF operation modes. Motion characteristics of the moving platform of 3-RER PMs are also identified using Euler parameter quaternions. This work is the first systematic study on the impact of link parameters on the operation modes of the 3-RER PM and provides a solid foundation for further research on the design and control of 3-RER PMs and other multi-mode (or reconfigurable) PMs.

Verification of validity of gait analysis systems during treadmill walking and running using human pose tracking algorithm

BackgroundThe human tracking algorithm called OpenPose can detect joint points and measure segment and joint angles. However, the validity of gait analysis using OpenPose has not been examined yet. Research questionWhat is the validity of OpenPose-based gait analysis? MethodsTwenty-four healthy young people participated in this study. The participants were assessed during walking and running. Pelvic segment angles, and hip, knee, and ankle joint angles during treadmill walking and running were measured using VICON. Simultaneously, images were captured using digital cameras from the right and back sides. After processing with OpenPose, the corresponding angles were measured from the estimated joint points. To validate these estimations, linear regression analysis was performed, and intraclass correlation coefficients [ICCs (2, 1)] between the data obtained by OpenPose and VICON were calculated. Furthermore, the agreement between the data obtained by OpenPose and VICON was assessed by Bland–Altman analysis. ResultsFor most ranges of motion (ROM) in the sagittal plane, the hip, knee, and ankle joints had large coefficients of determination, without proportional biases. For most peak angles in the sagittal plane, the knee and ankle joints had large coefficients of determination without proportional biases, although the hip joint had nonsignificant coefficients of determination and proportional biases. In particular, for the hip flexion-extension ROM and peak knee flexion angle during running and the knee ROM during slow walking, the ICCs showed good to excellent agreement. However, for the parameters of the pelvis and hip joint in the frontal plane, there were nonsignificant coefficients of determination and poor ICCs with fixed and proportional biases. SignificanceThe lower limb ROM in the sagittal plane during gait can be measured by the OpenPose-based motion analysis system. The markerless systems have the advantage of being more economical and convenient than conventional methods.

A New Approach to Represent Impact of Discontinuity Spacing and Rock Mass Description on the Median Fragment Size of Blasted Rocks Using Image Analysis of Rock Mass

Several in-situ rock mass properties and blasthole parameters can affect the rock fragmentation. Because of the complexity of the variables affecting the fragmentation results of blasted rocks, to predict a proper value of the median fragment size has long been a difficult task. The blastability index (BI) represents the effect of five parameters of rock mass description (RMD), joint plane spacing (JPS), joint plane orientation, specific gravity and uniaxial compressive strength on the rock fragmentation. The median discontinuity spacing significantly varies with varying the scanline direction and an acceptable value of the median discontinuity spacing will not be expected in practice. The JPS rating also has a constant value of 20 for a wide range of joint spacing values between 0.1 and 1 m, whereas joint spacing can be in this range for most cases. A new method using image analysis of the in-situ rock mass was applied to represent JPS and RMD (belonging to one of the cases: friable, blocky and massive) as an alternative solution. The images contain the details of all individual discontinuities and interlocked in-situ small and large rock blocks. BI, rock strength factor, blasthole parameters, powder factor, fragment size distribution of blasted rock and in-situ block size distribution using image analysis technique were assessed in 15 zones of Sungun open pit copper mine, Angouran lead and zinc open pit mine, Bonab silica mine, Soufian limestone mine and Rashakan limestone mine. The results for rock mass properties and blasthole patterns cover a wide range using different mines. The fragment size distribution was assessed by Split Desktop program with proper delineating images using the Pixler software and blasting was carried out with electric delay detonators. The relations between fragment size and parameters such as in-situ block size (F50), σc, rating of joint plane orientation, powder factor (q), ϕh, Q and Lc were analyzed. The relations with high correlations were achieved by applying the new approach for the defined conditions. Not only the problem of assessing discontinuity spacing has been improved using this method but also the lower number of parameters that properly represent the factors affecting the rock fragmentation have been used. The results were also analyzed by the Sanchidrian and Ouchterlony model and modified Kuz–Ram models. The fragment size obtained by the new method in this study, Sanchidrian and Ouchterlony model and extended modified Kuz–Ram model by Cunningham (in: Proceedings of 3rd world conference on explosives and blasting, Brighton, 2005) after using correction factor [c(A)] significantly better fitted to the results than the modified Kuz–Ram models by Cunningham (in: Fourney, Dick (eds) Proceedings of 2nd international symposium on rock fragmentation by blasting, Keystone, 1987) and Gheibie et al. (Int J Rock Mech Min 46(6):967–973, 2009).

A generalized joint pyramid method for removability analysis of rock blocks: Theoretical formulation and numerical implementation

The traditional Block Theory divides a concave block into a finite number of convex sub-blocks before the removability analysis, and deals with the removability and kinematics independently, which are computationally inefficient. This paper proposes a new concept of removable domain, based on which a generalized joint pyramid (GJP) method is established to overcome the aforementioned limitations. The translational removability analysis of convex and concave blocks can be unified through GJP based on the fact that concave regions have no contribution to the removability and can thus be omitted accordingly, avoiding partition of concave blocks into convex sub-blocks. To achieve this, joints are classified as essential joints and redundant joints. Only essential joints are considered in kinematics analysis as the block will not penetrate the rock mass when sliding along the essential joints, and its motion changes once the essential joints are altered. Thereby, the number of joint planes in the removability analysis and the number of possible motion modes that need to be assessed in the kinematics analysis can be significantly reduced. The GJP method was implemented in the stereo-analytical method and its efficiency and effectiveness in the removability and kinematics analysis of translational motion were demonstrated through some generic scenarios.

Correlation dimension and bifurcation analysis for the planar slider-crank mechanism with multiple clearance joints

Joint clearance serves as a crucial element of nonlinearity in multibody systems. The quantization of the system chaos is conducive to not only the understanding of the nonlinear nature but the rationalization of system controlled parameters. In the present work, the system dynamics for the planar slider-crank mechanism with multiple clearance joints is depicted by the correlation dimension and bifurcation actions. Considering the obliqueness of the slider, the general configuration of the planar joint is proposed. Generalized coordinates and the Lagrangian approach are adopted to derive the dynamic motion equations. The effects of clearance size and driving speed on the bifurcations of the dynamic response are investigated. Furthermore, the fractal dimension of the strange attractor is identified by the correlation dimension from time series. Based on the Cao method, the Mutual Information (MI) function, and the Grassberger-Procaccia (G-P) algorithm, the controlled factors in the evaluation of correlation dimension are cautiously determined. Ultimately, the compound effect of translational and revolute clearance joints on the mechanism dynamics is featured. The numerical results testify that the correlation dimension of the slider displacement approximately saturates beyond a specific translational clearance value. Moreover, with the parameters used in this work, the complexity of system response seems to be more sensitive to the variation of translational clearance size than with the revolute joint.

Time-dependent behavior of rock-like specimen containing multiple discontinuous joints under uniaxial step-loading compression

Rock with multiple discontinuous joints widely exists in rock engineering, and its mechanical properties are complex, which greatly increases the difficulty of engineering design and construction. Time-dependent deformation characteristics and long-term strength evaluation of jointed rock masses remain poorly understood. In this work, the creep experiments of rock-like specimens with multiple discontinuous joints under uniaxial step-loading compression are carried out to explore the influence of joint geometry (rock bridge length, joint length, joint angle, and joint spacing) on creep strain, long-term strength, and failure pattern of specimens with multiple discontinuous joints. The following conclusions are drawn from the test results: 1) The deformation of jointed rock specimens has evident time-dependent effect, and the cumulative creep deformation increases as creep load increases; 2) The strength of jointed rock specimens under loading changes with time, and the ratio of long-term strength and creep peak strength ( σ∞/ σc) of the tested specimens ranges from 41% to 96%; 3) The distribution of initial joints affects the creep fracture modes of rock-like specimens. The rupture of rock-like specimens with different joints distribution is mainly caused by the growth of wing cracks and quasi-coplanar secondary cracks. Three different failure modes are observed from these specimens: i) tensile failure with cracks across the joint plane; ii) shear failure with cracks along the joint plane; and iii) tensile failure with cracks along the joint plane. Based on the principles of damage mechanics and fracture mechanics, a theoretical mechanistic model considering both the closure stage of pre-existing open joints and time-dependent propagation stage of new cracks is established. Considering the influence of joint length, joint angle and joint density, the evolution of creep strain of rock-like specimen with multiple discontinuous joints is analyzed. The theoretical model results agree well with the experimental results, which indicates that the established model can replicate the creep failure process of jointed rock mass. These theoretical and test results help us better understand the effect of multiple joints on the long-term behavior of rock mass.

Investigating the Effect of Interface Morphology in Adhesively Bonded Composite Wavy-Lap Joints

Joints and interfaces are one of the key aspects of the design and production of composite structures. This paper investigates the effect of adhesive–adherend interface morphology on the mechanical behavior of wavy-lap joints with the aim to improve the mechanical performance. Intentional deviation from a flat joint plane was introduced in different bond angles (0°, 60°, 90° and 120°) and the joints were subjected to a quasi-static tensile load. Comparisons were made regarding the mechanical behavior of the conventional flat joint and the wavy joints. The visible failure modes that occurred within each of the joint configurations was also highlighted and explained. Load vs. displacement graphs were produced and compared, as well as the failure modes discussed both visually and qualitatively. It was observed that distinct interface morphologies result in variation in the load–displacement curve and damage types. The wavy-lap joints experience a considerably higher displacement due to the additional bending in the joint area, and the initial damage starts occurring at a higher displacement. However, the load level had its maximum value for the single-lap joints. Our findings provide insight for the development of different interface morphology angle variation to optimize the joints behavior, which is widely observed in some biological systems to improve their performance.