Hinge Model Research Articles

High-Resolution Measurements of Velocity and Shear Stress in Leakage Jets From Bileaflet Mechanical Heart Valve Hinge Models.

In flow through cardiovascular implants, hemolysis, and thrombosis may be initiated by nonphysiological shear stress on blood elements. To enhance understanding of the small-scale flow structures that stimulate cellular responses, and ultimately to design devices for reduced blood damage, it is necessary to study the flow-field at high spatial and temporal resolution. In this work, we investigate flow in the reverse leakage jet from the hinge of a bileaflet mechanical heart valve (BMHV). Scaled-up model hinges are employed, enabling measurement of the flow-field at effective spatial resolution of 167 μm and temporal resolution of 594 μs using two-component particle image velocimetry (PIV). High-velocity jets were observed at the hinge outflow, with time-average velocity up to 5.7 m/s, higher than reported in previous literature. Mean viscous shear stress is up to 60 Pa. For the first time, strongly unsteady flow has been observed in the leakage jet. Peak instantaneous shear stress is up to 120 Pa, twice as high as the average value. These high-resolution measurements identify the hinge leakage jet as a region of very high fluctuating shear stress which is likely to be thrombogenic and should be an important target for future design improvement.

Crack Tip Opening Angle as a Fracture Resistance Parameter to Describe Ductile Crack Extension and Arrest in Steel Pipes under Service Pressure

The angle between two element sides representing the crack tip is defined as the crack tip opening angle (CTOA). Its critical value is used as a criterion of fracture resistance for characterizing stable tearing in thin metallic materials. Various methods are used for determination of the CTOA. Optical microscopy is one of the most common methods as well as fitting of experimental load-displacement diagrams by the finite element method (DIC). Additionally, analytical analysis using the experimental load-displacement curve method (SSM) derived from the plastic hinge model of deflection in three-point bending of a ductile specimen is applied. This approach assumes a constant rotation centre distance. Values of CTOA for API 5L X65 pipe steel found by three methods—DIC, CNM, and SSM—are given. Values of CTOA given by these three methods are similar and close to 20°. A discussion on the different parameters used to characterize the fracture resistance of running cracks in a pipe under service pressure is presented. The energy of fracture at impact determined by Charpy or drop-weight tear test (DWTT) tests and the critical J energy parameter are considered as well as the yield locus after damage, cohesive zone energy, and CTOA is another approach. One notes that CTOA is assumed to be constant during stable crack extension and decreases linearly with crack length during the instable and primary phase. A numerical technique to describe a ductile running crack using the node release technique and using CTOA as the fracture resistance criterion is presented. This method is compared with three different two-curve methods (TCMs): the Battelle, high strength line pipe (HLP), and HLP-Sumitomo methods. The Batelle TCM, as the oldest method, based on Charpy energy, gives a strongly conservative prediction. Predictions by the CTOA method are close to those obtained by the HLP-Sumitomo one.

Ultimate analysis of steel structures based on fiber hinge model and time-varying structure theory

Oversize deformations and local damages may occur in steel structures due to inappropriate design, inadequacy of construction, improper uses and some other factors. Such damages could produce serious safety problems and shorten the service life of the structures. We proposed in this paper an effective and accurate method for analyzing the ultimate bearing capacity of steel framework based on the fiber hinge model and time-varying structure theory. A detailed study was conducted to investigate a cantilever column with I shaped cross section. The effects of cross section division and fiber hinge unit length on computation accuracy were investigated using SAP2000 finite element software. The proposed method was then applied to a real-life engineering problem, in which the steel structure of a mechanical building was gradually damaged under the action of uneven foundation settlement. The detailed information was obtained for the whole structural damage process as well as for the structural improvements after reinforcement. The results presented in this paper provided valuable information for strengthening of the damaged structures that are usually difficult to obtain in field detection, as well as the critical information for evaluating the structure conditions. In addition, the results in this paper could also provide useful information for safety assessment of new constructions.

Structural performance of final lining according to the rock load shape

The purpose of this study is to analyze the structural performance of the lining according to the magnitude as well as shape of rock load. Four cases of rock load shape were applied on the final lining (concrete lining) to perform structural analysis using beam spring model. This study includes two contents; firstly, the stability of the lining was analyzed using capacity diagrams. Secondly, the serviceability of the lining was analyzed using the cracked hinge model. While assessing the stability of the lining, FS = 2.45 was used according to LRFD specifications. The stress-crack opening relationship, represented by g(w) function, was used to assess the serviceability of the lining. The critical parameters used in this study are the K0 condition, load direction and application of the wedge load. Based on the results obtained after analysis, it was concluded that the K0 condition could change the thrust force-bending moment relationship which affects the stability and serviceability of the lining. Rock load in vertical direction affected the lining more than that in horizontal direction. Lastly, the development of wedge load proved to be more adverse than the application of larger uniform rock load on the lining.

Computational modeling of a dynamic knee simulator

Knee replacement surgery has made a huge evolution during the past decades. For further improvements of knee arthroplasty, dynamic knee simulators are used for fully instrumented ex-vivo tests. This paper provides a closer look at the validation of the rig. Therefore, a hinge model is constructed, resulting in an unambiguous evaluating method. The actual position of the ankle and the reaction forces at the ankle are measured and compared with the simulations. The results indicate an excellent agreement between the outcome of the numerical simulations and the measured values. The kinematics and kinetics of the rig are accordingly considered as validated. In the future, the behaviour of a more realistic knee representation will be evaluated.

Direct analysis for high-strength steel frames with explicit-model of residual stresses

This paper proposes a direct analysis method (DAM) for design of high-strength steel members and frames allowing explicit modeling of residual stresses. A section analysis technique, based on quasi-Newton iterative scheme, is employed taking into account for the effects of residual stress. Two distributed patterns of residual stress for the welded box-sections and H-sections fabricated by high-strength steel are discussed. To consider second-order effects associated with initial imperfections and the highly inelastic behavior along the member length, the curved arbitrarily-located-hinge (ALH) element is introduced. A plastic fiber hinge model using the sectional strength-iteration surfaces is proposed for modeling of material yielding. Finally, several examples are given for verifying the accuracy and validity of the proposed method. The distinct feature of this paper is about the development of a versatile numerical procedure accounting for residual stress and geometric imperfections separately and independently for stability design of high-strength steel members.

Fuzzy multi-objective optimization for movement performance of deep-notch elliptical flexure hinges.

Compared with commonly used flexure hinges, deep-notch elliptical flexure hinges are more suitable for flexible mechanisms with high precise transmission requirements. The rotation stiffness model of deep-notch elliptical flexure hinges was built first, and the compliance matrix was analyzed and solved by using Newton-Cotes quadrature formula to simplify the calculation of compliance coefficients; on the other hand, the fuzzy multi-objective optimization model with distribution was constructed, and a detailed example was given out to validate the effectiveness of the fuzzy optimization. The experiment results show that the desired angular displacement α(z) around the z axis is increased by 30.13%; while the undesired α(y) that around the y axis is decreased by 15.74% in experiment. The line displacements of Δ(y) and Δ(z) along the Y and Z axes are decreased by 18.15% and 47.69%, respectively. All the optimization data show that after the fuzzy optimization, the rotation capacity of z axis has been raised, and the motion capacity of the undesired directions has been restrained, so that the movement precision and the performance of the deep-notch elliptical flexure hinge can be improved, which is more suitable for the optical waveguide packaging positioning platform with high precision transmission.

Performance of reinforced concrete columns under bi-axial lateral force/displacement and axial load

Accurate and realistic assessment of the performance of columns in general and those in critical locations that may cause progressive failure of the entire structure, in particular, is significantly important. This performance is affected by the load history, pattern and intensity. Current design code does not consider the effect of load pattern on the load and displacement capacity of columns. In the study reported here, monotonic material models, cyclic rule, and plastic hinge models have been utilized in a fiber-based analytical procedure, validated against experimental data. Comparison of the analytical predictions and experimental data, through moment–curvature and force–deflection analyses, confirmed the accuracy and validity of the analytical algorithm and models. The analytical model was then used in a parametric study considering the effects of axial load variation and lateral force/displacement paths on the flexural strength and energy dissipation capacity of reinforced concrete columns.

Damped leaf flexure hinge.

Flexure-based mechanism like compliant actuation system embeds complex dynamics that will reduce the control bandwidth and limits their dynamic positioning precision. This paper presents a theoretical model of a leaf flexure hinge with damping layers using strain energy method and Kelvin damping model. The modified loss factor of the damped leaf flexure hinge is derived, and the equivalent viscous damping coefficient of the damped leaf hinge is obtained, which could be used to improve the pseudo-rigid-model. The free vibration signals of the hinge in three different damping configurations are measured. The experimental modal analysis also is performed on the three kinds of damped leaf flexure hinges in order to evaluate their 1st order bending natural frequency and vibration-suppressing effects. The evaluation of modified loss factor model also is performed. The experimental results indicate that the constrained layer damping can enhance the structure damping of the hinge even if only single damping layer each side, the modified loss factor model can get good predicts of a damped leaf flexure hinge in the frequency range below 1st order natural frequency, and it is necessary that the dimensional parameters of the damping layers and basic layer of the hinge should be optimized for simplification at the mechanism's design stage.

Experimental validation of relationship between fracture parameters J and CTOD for SE(B) and SE(T) specimens during ductile crack growth

In structural assessments, the crack driving force is usually estimated numerically based on the \(J\)-Integral definition because its determination is well established in many finite element codes. The nuclear industry has extensive fracture toughness data expressed in terms of \(J\)-Integral and huge experience with its applications and limitations. On the other hand, the material fracture toughness is typically measured by CTOD parameter using the plastic hinge model or double-clip gauge technique. The parameter CTOD has a wide acceptance in the Oil and Gas Industry (OGI). Also, the OGI has a lot of past data expressed in terms of CTOD, and the people involved are very familiar with this parameter. Furthermore, CTOD parameter is based on the physical deformation of the crack faces and can be visualized and understood in an easy way. There is a unique relationship between \(J\) and CTOD beyond the validity limits of linear elastic fracture mechanics for stationary cracks. However, if ductile crack propagation happens, the crack tip deformation profile and stress–strain fields ahead of the crack tip will change significantly when compared to the static case. Thus, the stable crack propagation may change the well-established relationship between \(J\) and CTOD for stationary cracks compromising the construction of resistance curves \(J\)-\(\Delta a\) from CTOD-\(\Delta a\) data or vice versa. A search in the open literature was undertaken to get experimental measurements of \(J\)-Integral and CTOD data including ductile crack growth. Then, using theoretical relations developed in previous work, predictions for CTOD values from \(J\) values are performed and directly compared with the experimental values. The present results provide additional understanding of the effects of ductile crack growth on the relationship between \(J\)-Integral and CTOD for standard fracture specimens. Specific procedures for the evaluation of CTOD-R curves using SE(T) and SE(B) specimens are proposed.

Earthquake induced torsion in buildings: critical review and state of the art

The problem of earthquake induced torsion in buildings is quite old and although it has received a lot of attention in the past several decades, it is still open. This is evident not only from the variability of the pertinent provisions in various modern codes but also from conflicting results debated in the literature. Most of the conducted research on this problem has been based on very simplified, highly idealized models of eccentric one-story systems, with single or double eccentricity and with load bearing elements of the shear beam type, sized only for earthquake action. Initially, elastic models were used but were gradually replaced by inelastic models, since building response under design level earthquakes is expected to be inelastic. Code provisions till today have been based mostly on results from one-story inelastic models or on results from elastic multistory idealizations. In the past decade, however, more accurate multi story inelastic building response has been studied using the well-known and far more accurate plastic hinge model for flexural members. On the basis of such research some interesting conclusions have been drawn, revising older views about the inelastic response of buildings based on one-story simplified model results. The present paper traces these developments and presents new findings that can explain long lasting controversies in this area and at the same time may raise questions about the adequacy of code provisions based on results from questionable models. To organize this review better it was necessary to group the various publications into a number of subtopics and within each subtopic to separate them into smaller groups according to the basic assumptions and/or limitations used. Capacity assessment of irregular buildings and new technologies to control torsional motion have also been included.

A subject-specific musculoskeletal modeling framework to predict in vivo mechanics of total knee arthroplasty.

Musculoskeletal (MS) models should be able to integrate patient-specific MS architecture and undergo thorough validation prior to their introduction into clinical practice. We present a methodology to develop subject-specific models able to simultaneously predict muscle, ligament, and knee joint contact forces along with secondary knee kinematics. The MS architecture of a generic cadaver-based model was scaled using an advanced morphing technique to the subject-specific morphology of a patient implanted with an instrumented total knee arthroplasty (TKA) available in the fifth "grand challenge competition to predict in vivo knee loads" dataset. We implemented two separate knee models, one employing traditional hinge constraints, which was solved using an inverse dynamics technique, and another one using an 11-degree-of-freedom (DOF) representation of the tibiofemoral (TF) and patellofemoral (PF) joints, which was solved using a combined inverse dynamic and quasi-static analysis, called force-dependent kinematics (FDK). TF joint forces for one gait and one right-turn trial and secondary knee kinematics for one unloaded leg-swing trial were predicted and evaluated using experimental data available in the grand challenge dataset. Total compressive TF contact forces were predicted by both hinge and FDK knee models with a root-mean-square error (RMSE) and a coefficient of determination (R2) smaller than 0.3 body weight (BW) and equal to 0.9 in the gait trial simulation and smaller than 0.4 BW and larger than 0.8 in the right-turn trial simulation, respectively. Total, medial, and lateral TF joint contact force predictions were highly similar, regardless of the type of knee model used. Medial (respectively lateral) TF forces were over- (respectively, under-) predicted with a magnitude error of M < 0.2 (respectively > -0.4) in the gait trial, and under- (respectively, over-) predicted with a magnitude error of M > -0.4 (respectively < 0.3) in the right-turn trial. Secondary knee kinematics from the unloaded leg-swing trial were overall better approximated using the FDK model (average Sprague and Geers' combined error C = 0.06) than when using a hinged knee model (C = 0.34). The proposed modeling approach allows detailed subject-specific scaling and personalization and does not contain any nonphysiological parameters. This modeling framework has potential applications in aiding the clinical decision-making in orthopedics procedures and as a tool for virtual implant design.

The soil effect on the seismic behaviour of reinforced concrete buildings

This paper investigates the soil effect on seismic behaviour of reinforced concrete (RC) buildings by using the spread plastic hinge model which includes material and geometric nonlinearity of the structural members. Therefore, typical reinforced concrete frame buildings are selected and nonlinear dynamic time history analyses and pushover analyses are performed. Three earthquake acceleration records are selected for nonlinear dynamic time history analyses. These records are adjusted to be compatible with the design spectrum defined in Turkish Seismic Code. Interstory drifts and damages of selected buildings are compared according to local soil classes. Also, capacity curves of these buildings are compared with maximum responses obtained from nonlinear dynamic time history analyses. The results show that, soil class influences the seismic behaviour of reinforced concrete buildings, significantly.

Planar Flexible Hinges With Curvilinear-Axis Segments for Mechanisms of In-Plane and Out-of-Plane Operation

The new design class and related analytic compliance-matrix model of planar flexible hinges with curvilinear longitudinal axes is presented here. The proposed approach enhances and generalizes the existing design and modeling variants dedicated to straight-axis and circular-axis hinge configurations. In-plane and out-of-plane small-displacement compliances are derived for standalone curvilinear-axis hinges as well as for hinges that are formed by serially connecting several curvilinear- and straight-axis segments. The general algorithm is further utilized to derive the compliance model of symmetric hinges, which utilizes a reduced number of compliances defining half the hinge. To illustrate the modeling/design procedure, a new flexible hinge is introduced and studied whose half portion comprises a constant-thickness parabolic-axis segment and a straight-axis segment of elliptically varying thickness. The resulting analytical compliances are validated by finite element simulation (FEA). Two compliant mechanisms that incorporate the new hinge design are studied in terms of specific performance qualifiers.

Multimodal Pushover Analysis for R.C. Bridges

In recent years, Italian technical-scientific community has increased its interest on the evaluation of the seismic response of existing structures. Among this wide range of structures, reinforced concrete bridges stand out for their strategic relevance and technical complexity. Most of these structures were built between 60ies and 70ies, according to design procedures which ignored nowadays knowledge in seismic engineering. Thus, the necessity to evaluate the real strength capacity of these structures with modern analysis techniques has become essential, leading to the determination of their safety level in case of an earthquake. In particular, for the assessment of several bridges of a motorway network, a multi-modal pushover analysis approach has been considered. This analysis technique allows considering the nonlinear behaviour and the complex dynamic response of such structures without exceeding in high computational costs. Some basic rules were defined (constitutive laws of materials, finite element type, plastic hinge models, etc.) for the modelling of bridges, in order to guarantee homogeneous comparable results among different structures of a network. At the end, some of the results are compared to see the variation of the verification level with respect to both the number of modes considered and the analysis’s accuracy in terms of number of loading steps.

様々なき裂深さを持つ鋼の3点曲げ試験における塑性回転因子

Since Crack tip opening displacement (CTOD) has been proposed as a fracture mechanics parameter CTOD in 1960s CTOD is widely used in steel structure industries for toughness evaluation of the materials and/or defect assessment of the welded structures based on the fitness for service standard. National standard in each country and also ISO standard have been established which is a similar procedure to the firstly standardized DD19 in British Standard Institution in 1972. The CTOD calculation is composed of plastic hinge model which assumes rotational deformation around the specific point. Standard range of crack length to width ratio (a0/W) is limited to be from 0.45 to 0.5. In the last 15 years, the discussion of CTOD has revived at a chance of the J based CTOD proposal in ASTM. The J based CTOD is capable of CTOD calculation in the wide a0/W range. CTOD evaluation using single edge notched tension (SENT) specimen with a sallow crack is also desired by industries at the same time. However, the capability of rotational CTOD evaluation in the wide a0/W range has not completely been concluded, yet. In this study, aiming to propose the new calculation method of CTOD, the rotational deformation is examined in the a0/W range from 0.05 to 0.70, and the applicability of rotational CTOD calculation for a shallow cracked specimen is discussed.

The Analyse on Stiffness Model of 3-PPSR Flexible Parallel Robot

In order to achieve greater workspace motion, it’s designed a high aspect ratio 3-PPSR flexible parallel robot, driven by a piezoelectric motor, connected by flexible hinges, which has the advantages of simple structure, non singular, seamless, high motion precision. Because of the stiffness of the system directly affecting the motion accuracy, load bearing performance, according to the characteristics of high aspect ratio flexible hinge, It’s established the mathematical model of flexible hinge through finite element method. Using method of integral stiffness, conbined coordination equation with force balance equation, the flexible stiffness model of system is obtained. Finally, through using Ansys, it’s confirmed the validity of the theoretical model by comparing of the theoretical stiffness model results with the finite element analysis of the model results, to provide a reliable guarantee for optimization and analysis of kinematics and dynamics of flexible parallel robot.

Development of a Rotation Algorithm for Earthquake Damage Diagnosis

In the attempt to develop simple damage detection algorithms that can be embedded in structural monitoring systems for rapid condition assessment following a large earthquake, a new algorithm is developed that characterizes structural damage, based on the residual drift following a strong motion. The residual drift is estimated from rotations computed from strong motion structural response acceleration measurements taken at key points on the structure. The Paulay and Priestley (1992) plastic hinge model is used to evaluate the residual drift, given rotation measurements at points on a single column. The algorithm is tested using data collected from a set of reinforced concrete single-column shaking tests, performed at the University of Nevada, Reno, and the University of California, Berkeley. Results from the tests indicate that the rotation algorithm can potentially be used for detecting and quantifying damage to single-column structures using one rotation measurement. Additional calibration and further testing of the algorithm will be necessary to reduce possible overestimation of the residual drift present on the column due to the simplicity of the column deformation model. Nevertheless, the results serve as an initial proof of concept that can be useful and very practical as a rapid damage estimation technique.

Accuracy evaluation of a new stereophotogrammetry-based functional method for joint kinematic analysis in biomechanics.

The human joint kinematics is an interesting topic in biomechanics and turns to be useful for the analysis of human movement in several fields. A crucial issue regards the assessment of joint parameters, like axes and centers of rotation, due to the direct influence on human motion patterns. A proper accuracy in the estimation of these parameters is hence required. On the whole, stereophotogrammetry-based predictive methods and, as an alternative, functional ones can be used to this end. This article presents a new functional algorithm for the assessment of knee joint parameters, based on a polycentric hinge model for the knee flexion-extension. The proposed algorithm is discussed, identifying its fields of application and its limits. The techniques for estimating the joint parameters from the metrological point of view are analyzed, so as to lay the groundwork for enhancing and eventually replacing predictive methods, currently used in the laboratories of human movement analysis. This article also presents an assessment of the accuracy associated with the whole process of measurement and joint parameters estimation. To this end, the presented functional method is tested through both computer simulations and a series of experimental laboratory tests in which swing motions were imposed to a polycentric mechanical analogue and a stereophotogrammetric system was used to record them.

Effects of confinement reinforcement and concrete strength on nonlinear behaviour of RC buildings

This paper investigates the effects of confinement reinforcement and concrete strength on nonlinear behaviour of reinforced concrete buildings (RC). For numerical application, an eleven-storey and four bays reinforced concrete frame building is selected. Nonlinear incremental static (pushover) analyses of the building are performed according to various concrete strengths and whether appropriate confinement reinforcement, which defined in Turkish seismic code, exists or not at structural elements. In nonlinear analysis, distributed plastic hinge model is used. As a result of analyses, capacity curves of the frame building and moment-rotation curves at lower end sections of ground floor columns are determined. These results are compared with each other according to concrete strength and whether appropriate confinement reinforcement exists or not, respectively. According to results, it is seen that confinement reinforcement is important factor for increasing of building capacity and decreasing of rotations at structural elements.