Mechanical Preload Research Articles

Impact of homeostatic body hydration status, evaluated by hemodynamic measures, on different pain sensitization paths to a chronic pain syndrome

Contrasting findings on the mechanisms of chronic pain and hypertension development render the current conventional evidence of a negative relationship between blood pressure (BP) and pain severity insufficient for developing personalized treatments. In this interdisciplinary study, patients with fibromyalgia (FM) exhibiting clinically normal or elevated BP, alongside healthy participants were assessed. Different pain sensitization responses were evaluated using a dynamic 'slowly repeated evoked pain' (SREP) measure, as well as static pain pressure threshold and tolerance measures. Cardiovascular responses to clino-orthostatic (lying-standing) challenges were also examined as acute re- and de-hydration events, challenging cardiovascular and cerebrovascular homeostasis. These challenges involve compensating effects from various cardiac preload or afterload mechanisms associated with different homeostatic body hydration statuses. Additionally, hair cortisol concentration was considered as a factor with an impact on chronic hydration statuses. Pain windup (SREP) and lower pain threshold in FM patients were found to be related to BP rise during clinostatic (lying) rehydration or orthostatic (standing) dehydration events, respectively. These events were determined by acute systemic vasoconstriction (i.e., cardiac afterload response) overcompensating for clinostatic or orthostatic cardiac preload under-responses (low cardiac output or stroke volume). Lower pain tolerance was associated with tonic blood pressure reduction, determined by permanent hypovolemia (low stroke volume) decompensated by permanent systemic vasodilation. In conclusion, the body hydration status profiles assessed by (re)activity of systemic vascular resistance and effective blood volume-related measures can help predict the risk and intensity of different pain sensitization components in chronic pain syndrome, facilitating a more personalized management approach.

Effects of deformations and angular ring misalignment on dynamic properties for ball bearing under different preload mechanisms

Effects of deformations and angular ring misalignment on dynamic properties for ball bearing under different preload mechanisms

Study on the preload loss mechanisms of CFRP-steel hybrid bolted joint under transverse cyclic loading

There is bolt preload loss under vibration in the aircraft rudder, of which the connected parts are steel beam and CFRP panel, and the fastener is bolts and self-lock jet nuts. Based on the above phenomenon, this paper analyzes rotational loosening, washer wear, composite progressive damage, and plastic deformation condition of CFRP-steel hybrid self-lock bolted joint under transverse cyclic loading by experiments and finite element simulations, and subsequently analyzes the preload loss mechanisms. The results showed that washer wear was the main factor leading to the preload loss under long-term loading, and even this factor accounted for 70% of the total preload loss when the aluminum washer was used. During short-term loading, local slip and stress redistribution among threads, plastic deformation, and composite damage accounted for 30%, 50%, and 20% of the total preload loss respectively. To prevent preload loss, the wear-resistance of the washer should be improved, and the plastic deformation on the bolt and the damage in the composite material should be reduced.

Influence of surface stress on the mechanical response of nanoporous metals studied by an atomistically informed continuum model

The influence of surface stresses on the deformation behavior of nanoporous metals is considered to be the main reason for the tension-compression asymmetry observed in atomistic simulation studies of nanoporous metals. While it is difficult to differentiate between the contributions of linear and non-linear elasticity, dislocation activity, topology and surface stresses from atomistic simulations, continuum mechanics allow to disentangle these effects by systematically varying the applied constitutive relations. In this study, we investigate the elastic response of a nanoporous Au and Ag structure, both by molecular statics simulations and an elastic continuum model, which includes surface stresses and elastic anisotropy. The 3-dimensional periodic atomistic nanoporous structure is triangulated and transferred to the continuum model, where periodicity, elastic anisotropy, and surface stresses are considered. The results show that surface stress acts as a mechanical pre-load and that the elastic response is sensitive to the loading direction. An asymmetric behavior is observed in the elastic regime. Moreover, we show that sites, where dislocation activity is starting, show high von Mises stresses.

Recent Patents for the Motorized Spindle Preload Mechanism

Background: The motorized spindle preload technology is one of the motorized spindle key technologies, and adjusting the preload according to the working conditions can effectively improve the dynamic performance of the motorized spindle and enhance the machining accuracy. Objectives: Review the preload mechanism development, introduce various preload mechanisms, and show research status in recent years. Then to explore and predict the future development of preload technology through the analysis of the overall preload mechanism. Methods: Search for different kinds of patents and literature about spindle preload structure in recent years. Through structural research and comparison with the traditional preload mechanism, to review the structure principle of various preload mechanisms at the present stage, then shown the advantages and disadvantages of each structure. Result: According to the patents and research of the preload mechanism in recent years, classification introduced the piezoelectric ceramic preload device, electromagnetic preload device, and hydraulic preload device, and so on. Introduce their advantages and existing problems in detail, then comprehensively compare the advantages and disadvantages of various mechanisms in control and mechanism. Finally, discuss the prospects and development directions of preload technology. Conclusion: With the further development of technology, high-precision products have higher requirements for machine tools, such as low latency, low heat generation, high efficiency, and long life. People use electromagnetic force, air pressure, hydraulic pressure, and other methods, to control the magnitude of the preload, maintain the performance of the motorized spindle at a high level. Compared with the traditional quantitative preload, their applicable working conditions are more extensive and accuracy is higher. However, various new preload methods still have certain shortcomings and need further improvement.

Rotordynamic Analysis of Piezoelectric Gas Foil Bearings with a Mechanical Preload Control Based on Structural Parameter Identifications

This paper presents a rotordynamic analysis and experimental characterization of a novel concept of a controllable gas foil bearing (C-GFB) with piezoelectric (PZT) actuators. The C-GFB consists of bump foil structures and three PZT actuators, and the PZT actuators push the bump foil structures in different displacements according to the driving voltage, enabling preload control. In order to predict the piezoelectric preload according to the driving voltage, an equivalent spring model for PZT actuators and foil structures is introduced. In addition, PZT parameters (a piezoelectric constant and stiffness) are measured through parameter identification tests using a latch. Next, static lubrication analysis for C-GFB reveals that the gas-film pressure reduces the effect of piezoelectric preload by up to a maximum of 11%, because the piezoelectric actuator has structural compliance so that it is structurally deformed by the pressure. Finally, nonlinear orbit simulation is performed, and the performance of real-time vibration control of C-GFB is evaluated. The real-time preload control is carried out at ~32.6 krpm, where the rotordynamic instability sufficiently occurs. As the driving voltage increases, the instability suppression and delay effect increase. In particular, when controlled at 150 V, the onset speed of the instability increases to 79.1 krpm. Consequently, this study demonstrates that the GFB with piezoelectric preloads is a simple, effective, and real-time method to improve the rotordynamic stability.

First-in-Human Experience of Mechanical Preload Control in Patients With HFpEF During Exercise

Exercise intolerance remains one of the major factors determining quality of life in heart failure patients. In 6 patients with heart failure with preserved ejection fraction (HFpEF) undergoing invasive cardiopulmonary exercise testing, balloon inflation within the inferior vena cava (IVC) was performed during exercise to reduce and maintain pulmonary arterial (PA) pressures. Partial IVC occlusion significantly reduced PA pressures without reducing cardiac output. Partial IVC occlusion significantly reduced respiratory rate at matched levels of exercise. These findings highlight the importance of pulmonary pressures in the pathophysiology of HFpEF and suggest that therapies targeting hemodynamics may improve symptoms and exercise capacity in these patients.

The Effects of Mechanical Preload on Transmural Differences in Mechano-Calcium-Electric Feedback in Single Cardiomyocytes: Experiments and Mathematical Models.

Transmural differences in ventricular myocardium are maintained by electromechanical coupling and mechano-calcium/mechano-electric feedback. In the present study, we experimentally investigated the influence of preload on the force characteristics of subendocardial (Endo) and subepicardial (Epi) single ventricular cardiomyocytes stretched by up to 20% from slack sarcomere length (SL) and analyzed the results with the help of mathematical modeling. Mathematical models of Endo and Epi cells, which accounted for regional heterogeneity in ionic currents, Ca2+ handling, and myofilament contractile mechanisms, showed that a greater slope of the active tension–length relationship observed experimentally in Endo cardiomyocytes could be explained by greater length-dependent Ca2+ activation in Endo cells compared with Epi ones. The models also predicted that greater length dependence of Ca2+ activation in Endo cells compared to Epi ones underlies, via mechano-calcium-electric feedback, the reduction in the transmural gradient in action potential duration (APD) at a higher preload. However, the models were unable to reproduce the experimental data on a decrease of the transmural gradient in the time to peak contraction between Endo and Epi cells at longer end-diastolic SL. We hypothesize that preload-dependent changes in viscosity should be involved alongside the Frank–Starling effects to regulate the transmural gradient in length-dependent changes in the time course of contraction of Endo and Epi cardiomyocytes. Our experimental data and their analysis based on mathematical modeling give reason to believe that mechano-calcium-electric feedback plays a critical role in the modulation of electrophysiological and contractile properties of myocytes across the ventricular wall.

Experimental and theoretical investigation of rotordynamic characteristics of a rigid rotor supported by an active bump-type foil bearing

This study aims to investigate the rotordynamic characteristics of a rigid rotor supported by an active bump-type foil bearing (ABFB) with real-time controllable mechanical preload. ABFB is composed of a traditional bump-type foil bearing with controlling substructures that consist of flexure hinges, lever amplifiers and piezoelectric stack actuators (PZTs). The structure realises the adjustment of bearing's mechanical preloads by actively controlling the DC voltage on the PZTs (U). Experimental investigations based on rotordynamic test rig are performed to measure the effects of ABFB on rotordynamic responses of rotor-ABFB system. Combined with the dynamics of the active control structures and modified link-spring model, linear and nonlinear mechanical models of the rotor-ABFB system are established, and the rotordynamic responses of the rotor are predicted. Both the experimental and theoretical results verify the possibility of building active rotor-gas foil bearing systems. Moreover, the effects of rotor unbalance on the rotordynamic responses of the rotor-ABFB system are investigated.

Study of the Stiffness Matrix of Preloaded Duplex Angular Contact Ball Bearings

This paper studies the stiffness characteristics of preloaded duplex angular contact ball bearings. First, a five degrees-of-freedom (5DOF) quasi-static model of the preloaded duplex angular contact ball bearing is established based on the Jones bearing model. Three bearing configurations (face-to-face, back-to-back, and tandem arrangements) and two preload mechanisms (constant pressure preload and fixed position preload) are included in the proposed model. Subsequently, the five-dimensional stiffness matrix of the preloaded duplex angular contact ball bearing is derived analytically. Then, an experimental setup is developed to measure the radial stiffness and the angular stiffness of duplex angular contact ball bearings. The simulated results match well with those from experiments, which prove the validity of the proposed model. Finally, the effects of bearing configuration, preload mechanism, and unloaded contact angle on the angular stiffness and the cross-coupling are studied systematically.

Active bump-type foil bearing with controllable mechanical preloads

Abstract This paper presents an active bump-type foil bearing (ABFB), in which mechanical preloads can be actively adjusted by controlling the driving voltages of piezoelectric actuators (PZTs) to create a variable multiple-lobe clearance and enhance bearing performance. A theoretical model that couples active and compliant foil structures is proposed, and static load–deformation tests and measurements of airborne drag torque on the basis of a prototype bearing are conducted at different driving voltages. Tests results show that the proposed active structure is feasible and effective in controlling mechanical preload. Moreover, the static and dynamic performances of ABFB are discussed. This work lays foundation for the further study of active control methods in gas foil bearings.

A comparative study and stiffness analysis of angular contact ball bearings under different preload mechanisms

The dynamic performance of angular contact ball bearings is greatly affected by preload force and preload mechanisms. In the present research, a comparison model is built to analyze the stiffness of angular contact ball bearings under different preload mechanisms. In the first part, the elastic deformation of inner ring of bearing produced by assembling stress and centrifugal stress is calculated. Then the differences of two different types of preload on the action mechanism of bearings are discussed. Based on these, a comparative model of ball bearing and stiffness with respect to different preload mechanisms is proposed. Finally, the influences of the inner ring interference value, rotating speed and radial load on the bearing characteristics and stiffness are discussed in detail. The results show that under fix-positon preload, the bearing have a better stability of stiffness, and the inner ring interference value and rotating speed also have a significant influence on the bearing dynamic properties and stiffness. In addition, the proposed model is validated by comparing the results obtained by the proposed method with those from the other literatures and experiments.

Miniature preload mechanisms for a micro ultrasonic motor

We propose the smallest preload generation mechanisms that provide force between the rotor and the one cubic millimeter stator in a micro ultrasonic motor. Miniaturizing the preload mechanism is key for implementation of a micro ultrasonic motor with the best performance into micro devices. In this paper, we evaluate two kinds of preloads that exert in the axial and radial directions: an axial preload mechanism and a radial preload mechanism. The experiments clarify how both preload mechanisms improve motor performance measures such as angular velocity, torque, and efficiency. The micro ultrasonic motors with both preload mechanisms generated torque over 10μNm at the experimentally optimized preload of approximately 6g. By designing the miniature preload mechanisms using a micro coil spring, the preload mechanisms are miniaturized with similar motor performance. At present, they represent the smallest and most powerful ultrasonic motors with preload mechanisms.

A smart experimental technique for the optimization of dielectric elastomer actuator (DEA) systems

In order to aid in moving dielectric elastomer actuator (DEA) technology from the laboratory into a commercial product DEA prototypes should be tested against a variety of loading conditions and eventually in the end user conditions. An experimental test setup to seamlessly perform mechanical characterization and loading of the DEA would be a great asset toward this end. Therefore, this work presents the design, control and systematic validation of a benchtop testing station for miniature silicon based circular DEAs. A versatile benchtop tester is able to characterize and apply programmable loading forces to the DEA while measuring actuator performance. The tester successfully applied mechanical loads to the DEA (including positive, constant and negative stiffness loads) simulating biasing systems via an electromagnetic linear motor operating in closed loop with a force/mechanical impedance control scheme. The tester expedites mechanical testing of the DEA by eliminating the need to build intricate pre-load mechanisms or use multiple testing jigs for characterizing the DEA response. The results show that proper mechanical loading of the DEA increases the overall electromechanical sensitivity of the system and thereby the actuator output. This approach to characterize and apply variable loading forces to DEAs in a single test system will enable faster realization of higher performance actuators.

Rotordynamic Analysis of an Oil-Free Turbocharger Supported on Lobed Gas Foil Bearings—Predictions versus Test Data

This article presents the predictions of the rotordynamic performance of oil-free turbochargers (TCs) for various lobed gas foil bearings (GFBs) with the first-generation bump-type configuration and compares these predictions to the measured test data reported earlier. The three-lobed GFBs used for the simulations have increased bearing clearances and mechanical preloads with a fixed minimum bearing clearance, thus yielding larger average bearing clearances and higher wedge effects at the same time. The engine-induced TC housing excitation is found to have no influence on the critical speeds and damping ratios of the rotor rigid modes. The synchronous and asynchronous GFB analyses imply decreases in destabilizing forces for the highly lobed GFBs. The predicted critical speed and damping ratio of the TC rotor supported on the lobed GFBs demonstrate increasing system natural frequency and enhanced rotordynamic stability with increasing mechanical preload. The rotordynamic and bearing analyses of the lobed GFBs validate the beneficial effects of the mechanical preload on the rotordynamic stability of GFBs even with an increased average bearing clearance, which leads to a decreased bearing friction torque as well.

Effects of Mechanical Preload and Bearing Clearance on Rotordynamic Performance of Lobed Gas Foil Bearings for Oil-Free Turbochargers

This article presents the results of experimental studies on the effects of mechanical preload and bearing clearance on the rotordynamic performance of lobed gas foil bearings (GFBs) for oil-free turbochargers (TCs). The lobed GFBs have a first-generation bump-type configuration within a lobe-like inner surface bearing housing. Five test GFBs were fabricated and used for experiments: three circular GFBs and two lobed GFBs. The GFB clearance was measured via GFB displacement versus static load testing. The TC housing vibrations were identified via impact tests and engine driving tests, demonstrating that the TC housing was subjected to engine-induced excitations and TC housing resonances. The second-order harmonic of the engine speed appeared to be most noticeable in the rotor motions due to the engine-induced excitations. Measurements of the rotordynamic performance of the test GFBs were conducted during a series of TC rotor speed-up and slow-down tests for an oil-free test TC driven by the diesel vehicle engine. An increase in the bearing clearance of the circular GFBs led to significant reductions in the onset speed of subsynchronous (OSS) motion. In contrast, the lobed GFBs with larger preloads and for an identical minimum assembly clearance value resulted in a delay in OSS with increasing whirl frequencies. Furthermore, the lobed GFBs increased the TC speeds at engine idle, implying a reduction in the bearing friction. Consequently, the test results suggested that lobed GFBs with the proper combination of mechanical preload and bearing clearance are able to simultaneously improve the rotordynamic performance and reduce the friction losses.

Fracture strength of yttria‐stabilized tetragonal zirconia polycrystals crowns with different design: an in vitro study

The aim of this study was to evaluate the effect of different types and design of zirconia frameworks as well as the effect of different veneering ceramics on the fracture strength of crowns. The importance of different abutment materials was also evaluated. Eighty cores, 40 in a fully-sintered zirconia material and 40 in a pre-sintered zirconia material were made. Twenty cores of each material were made with a core of even thickness shape (ES) and 20 were made with a core with anatomical shape (AS). The cores were divided into subgroups and veneered with one of two different veneering ceramics: a porcelain and a glass-ceramic material. In total eight groups of 10 crowns were made. They were all cemented onto abutments made of resin. One extra group of 10 AS, pre-sintered zirconia cores veneered with glass-ceramic were made and cemented onto titanium abutments. All crowns underwent thermocycling and mechanical pre-load and were finally loaded until fracture. AS crowns withstood significantly higher loads than ES crowns (P-value <0.001), and crowns with titanium abutments withstood significantly higher loads than crowns supported by abutments made of inlay pattern resin (P-value <0.001). Three types of fracture were noted: minor and major fracture of the veneering ceramic, and complete fracture through core and veneer. ES crowns showed significantly more major fractures of the veneering ceramic than AS crowns. This in vitro study indicates that the design of the core, as well as the abutment support, significantly influences fracture load and fracture mode of yttria-stabilized tetragonal zirconia polycrystals crowns.

A comparative study on the dynamics of high speed spindles with respect to different preload mechanisms

This paper presents the effects of bearing preload mechanisms on the dynamic performance of high speed spindles. The comparisons of two main types of bearing preload—“constant” and “rigid”—mechanisms are provided using a mathematical model as well as experiments. Based on the Timoshenko beam element theory coupled with a nonlinear model of angular contact ball bearings, the dynamics of the spindle shaft, housing, and bearings system is modeled as a nonlinear function of preload mechanism and amplitude, spindle speed, and external cutting loads. The mathematical model of the spindle is experimentally validated by comparing the predicted and measured static displacements, mode shapes, frequency response functions, and natural frequencies under different conditions. The performance of spindles under rigid and constant force preload is investigated systematically using a mathematical model under various conditions. It is shown, among other things, that at high speeds and under cutting loads the rigid preload mechanism is more efficient in maintaining the dynamic stiffness of spindles than constant preload.

Response of Rotary Blood Pumps to Changes in Preload and Afterload at a Fixed Speed Setting Are Unphysiological When Compared With the Natural Heart

Responses of four rotary blood pumps (Incor, Heartmate II, Heartware, and Duraheart) at a single speed setting to changes in preload and afterload were assessed using the human left ventricle as a benchmark for comparison. Data for the rotary pumps were derived from pressure flow relations reported in the literature while the natural heart was characterized by the Frank-Starling curve adjusted to fit outputs at different afterloads reported in the literature. Preload sensitivity (mean ± SD) for all pumps at all afterloads tested was 0.105 ± 0.092 L/min/mm Hg, while afterload sensitivity was 0.09 ± 0.034 L/min/mm Hg-values that were not significantly different (t-test, P = 0.56). By contrast, preload sensitivity of the natural heart was over twice as high (0.213 ± 0.03 L/min/mm Hg) and afterload sensitivity about one-third (0.03 ± 0.01 L/min/mm Hg) the values recorded for rotary pumps (t-test, P < 0.001). Maximum preload sensitivity and minimum afterload sensitivity allow the right and left ventricles to synchronize outputs without neural or humoral intervention. This theoretical study reinforces the need to provide preload sensitive control mechanisms of sufficient power to enable the pump and left ventricle in combination to adapt to changes in right ventricular output automatically.

Predicting the Effect of Compressive and Tensile Residual Stresses in Fracture Mechanics Specimens

This paper considers the prediction of the effects of tensile and compressive residual stress in fracture mechanics specimens by the application of a mechanical pre-load. This is considered in the context of a ‘C’ shape specimen which is mechanically pre-tensioned or pre-compressed to produce, respectively, a compressive or tensile residual stress in the region where the crack is introduced. Finite-element analysis is performed to simulate the pre-loading and the subsequent fracture loading of the cracked specimens. The finite-element predictions are compared with experimental data including residual stress measurements using neutron diffraction. A discussion is presented on modelling and material issues pertaining to the use of mechanical pre-loading as a means for introducing residual stress.