Influence Of Preload Research Articles

Analysis of the fracture response of anchored rock under three-point bending from experimental and numerical perspectives

The stability and bearing capacity of fractured surrounding rock in underground engineering are affected by the support conditions. In this study, an anchored rock unit was selected as an object for fracture mechanics three-point bending tests by varying the anchorage position. The results showed that the fracture toughness (KIC) of the anchored specimens showed a decreasing trend with the increase in the distance of the bolt center from the crack tip (Da), while exhibiting an increase of 21.18 ∼ 135.32 % in comparison to the unanchored specimens. The change in axial force of the bolt with time can be classified into three stages: initial change, significant elevation, and liner increase. Besides, the sensitivity of the anchored specimens to the crack opening distance was significantly reduced and the ultimate tensile strains were commonly larger than the unanchored. Meanwhile, a numerical model consistent with the properties of the medium was developed using the PFC-FLAC coupling method. The simulation results show that the anchorage position and preload influence the mechanical parameters such as KIC and the bolt-enhanced fracture energy (Gb), while improving the stress concentration phenomenon at the crack tip.

Influence of preload on the tribological performance of MoS2/GO composite lubricating coating

Lubrication is one of the key factors to ensure the reliable operation of sliding parts for some critical components in aerospace. The most favorable lubrication performance of the lubricating film is always achieved after the initial period or the pre-running-in period. In this work, the influence of preloads varying from 0.5 to 15 N on the tribological performance of molybdenum disulfide/graphene oxide (MoS2/GO) composite lubricating coating was studied. It was found that the coefficient of friction (COF) during the running-in period decreased from 0.17 at 0.5 N to 0.14 at 5 N, and stabilized at 0.14 with further increasing the normal load, indicated that the optimal stable COF was obtained at 5 N and negligible changes when load is further increased from 5 to 15 N. In contrary to the widely reported coatings that their tribological results deteriorate at high applied loads, the MoS2/GO composite lubricating coating here exhibits much lower COF under higher loads, with the COF decreased from 0.14 at 5 N to 0.03 at 100 N. The results suggests that the preload had a positive effect on the tribological performance of the MoS2/GO composite coating, the COF of the composite coating decreased with the increase of the preload, which further improved the tribological properties and even achieved the optimized lubrication condition, and the optimum preload was equal to or slightly higher than the steady-state load. This work provides a guiding idea for the selection strategy of the preload for optimal tribological performance of the solid lubricating coating.

Quantifying preload alterations using a sensitive chest-mounted accelerometer

Abstract Seismocardiography (SCG) is a technology where the chest wall vibrations from the beating heart are measured using a highly sensitive accelerometer. SCG offers continuous measurement of cardiac function and potential applications include remote monitoring, diagnostic assessments, prognostic health checks and biventricular pacemaker optimization. Aim In the current study we examined how changes in preload influence SCG time intervals, by acute saline infusion. Methods We included twenty-six subjects, sixteen subjects with cardiac disease such as hypertrophic cardiomyopathy, dilated cardiomyopathy, aortic valve disease or ischemic heart disease (age 45.8±17.7 years and 93% male) and ten subjects without known cardiac conditions (age 42.1±14.4 years and 70% male). SCG was recorded from the xiphoid process using a custom-made sensor before and after acute infusion saline (median 2.0 L). The SCG signals were sampled with 5000 samples per second in 60 seconds, the individual heartbeats were identified using a dedicated segmentation algorithm and an average SCG beat was computed and used for the data analysis. Using a recently proposed nomenclature the following SCG fiducial points was identified: Es which coinciding with mitral valve closure, Gs which to some degree coincides with aortic opening, Bd coinciding with aortic valve closure and Fd coinciding with mitral valve opening [1]. The Es-Gs time interval was used as a measure of isovolumetric contraction time (IVCT), the Gs-Bd time interval was used as an estimate of ejection time (ET) and the Bd-Fd time interval as an estimate of isovolumetric relaxation time (IVRT). Paired t-test was used to test for significant response after infusion, while a two sample t-test was used to test for a significant difference in the observed response in subjects with or with our cardiac disease. Results For two subjects SCG after infusion was not obtained thus, twenty-four subjects were included in the final data analysis. In the whole group, acute saline infusion shortened the IVRT (Bd-Fd) from 91.0±15.3 ms to 82.7±15.3 ms (p=0.004) and prolonged the ET (Gs-Bd) from 329.4±35 ms to 343.4±33 ms (p<0.001). There was no significant change in IVCT (Es-Gs) which was 39.5±15.1 ms at baseline and 38.1±14.9 ms post-infusion (p=0.88). There was no significant difference in response between subjects with or without cardiac disease. Conclusion Increase in preload shortened the SCG time intervals related to the isovolumetric relaxation period and prolonged the period related to ejection time. SCG time intervals capture changes in preload, which demonstrates that the SCG is a potential modality for quantification of cardiac dynamics. Funding Acknowledgement Type of funding sources: None.

Quantifying preload alterations using a sensitive chest-mounted accelerometer

Abstract Seismocardiography (SCG) is a technology where the chest wall vibrations from the beating heart are measured using a highly sensitive accelerometer. SCG offers continuous measurement of cardiac function and potential applications include remote monitoring, diagnostic assessments, prognostic health checks and biventricular pacemaker optimization. Aim In the current study we examined how changes in preload influence SCG time intervals, by acute saline infusion. Methods We included twenty-six subjects, sixteen subjects with cardiac disease such as hypertrophic cardiomyopathy, dilated cardiomyopathy, aortic valve disease or ischemic heart disease (age 45.8±17.7 years and 93% male) and ten subjects without known cardiac conditions (age 42.1±14.4 years and 70% male). SCG was recorded from the xiphoid process using a custom-made sensor before and after acute infusion saline (median 2.0 L). The SCG signals were sampled with 5000 samples per second in 60 seconds, the individual heartbeats were identified using a dedicated segmentation algorithm and an average SCG beat was computed and used for the data analysis. Using a recently proposed nomenclature the following SCG fiducial points was identified: Es which coinciding with mitral valve closure, Gs which to some degree coincides with aortic opening, Bd coinciding with aortic valve closure and Fd coinciding with mitral valve opening [1]. The Es-Gs time interval was used as a measure of isovolumetric contraction time (IVCT), the Gs-Bd time interval was used as an estimate of ejection time (ET) and the Bd-Fd time interval as an estimate of isovolumetric relaxation time (IVRT). Paired t-test was used to test for significant response after infusion, while a two sample t-test was used to test for a significant difference in the observed response in subjects with or with our cardiac disease. Results For two subjects SCG after infusion was not obtained thus, twenty-four subjects were included in the final data analysis. In the whole group, acute saline infusion shortened the IVRT (Bd-Fd) from 91.0±15.3 ms to 82.7±15.3 ms (p=0.004) and prolonged the ET (Gs-Bd) from 329.4±35 ms to 343.4±33 ms (p<0.001). There was no significant change in IVCT (Es-Gs) which was 39.5±15.1 ms at baseline and 38.1±14.9 ms post-infusion (p=0.88). There was no significant difference in response between subjects with or without cardiac disease. Conclusion Increase in preload shortened the SCG time intervals related to the isovolumetric relaxation period and prolonged the period related to ejection time. SCG time intervals capture changes in preload, which demonstrates that the SCG is a potential modality for quantification of cardiac dynamics. Funding Acknowledgement Type of funding sources: None.

To Review the Effect of Tightened and Loosened Torque on Two Different Implant–Abutment Connection Designs

Introduction: It is crucial to take care of stability between various implant parts for the general success rate of the reconstruction. Component fit, saliva contamination, machining accuracy, and screw preload influence the steadiness of implant–abutment connection. Loosening of abutment screws has been a well-known technical problem. Aim: The aim of this study was to gauge repeated tightening and loosening torque on two commercially available implant/abutment connection designs. Study Design: This was an in vitro study. Methodology: A total of 32 implant analogs samples using a metal die with, metal ring of 20mm x 20mm x 20mm in size and a hole in the center were prepared. For both the groups, the implant analog was axially threaded within bases. They were clasped at an edge parallel to the standard minimal bone position. A 35 N/cm torque was enforced, each implant and abutment connection in both the groups using toque ratchet. After 20 min, screws were loosened and detorque measurement was recorded up to ten times. Scanning electron microscope micrographs of selected screws also are presented. SPSS (21.0 version) was used for analyzing data. Results: The mean residual torque for Group 1 was − 51.45 and Group 2 was − 43.29. The RTq (%) was found to be significantly less (0.028*) among Group 2: conical connection as compared to Group 1: butt joint connection. Conclusion: The loosening torque was significantly less in conical connection as compared to butt joint connection.

Influence of Preload on Failure Modes of Hybrid Metal-Composite Protruding Bolted Joints

This paper presents the effects of torque preload on the damage initiation and growth in the CFRP (Carbon Fiber Reinforced Polymer) composite laminated adherent of the single-lap, single-bolt, hybrid metal-composite joints. A detailed 3D finite element model incorporating geometric, material and friction-based contact full nonlinearities is developed to numerically investigate the preload effects on the progressive damage analysis (PDA) of the orthotropic material model. The PDA material model integrates the nonlinear shear response, Hashin-tape failure criteria and strain-based continuum elastic properties degradation laws being developed using the UMAT user subroutine in Nastran commercial software. In order to validate the preload effects on the failure modes of the joints with hexagonal head bolts, experiments were conducted using the SHM (Structural Health Monitoring) technique. The results showed that the adherent torque level is an important parameter in the design process of an adequate bolted joint and its effects on damage initiation and failure modes were quite accurately predicted by the PDA material model, which proved to be computational efficient and can predict failure propagation and damage mechanism in hybrid metal-composite bolted joints.

Behavior of circular concrete-filled double steel tubular slender beam-columns including preload effects

The hollow circular steel tubes support the permanent and construction loads of several upper floors during the construction of a high-rise building structure before the concrete is filled into the steel tubes to form circular concrete-filled double steel tubular (CFDST) columns. The preloads acting on the steel tubes may cause a marked reduction in the performance of slender CFDST columns. This paper presents a numerical modeling technique underlying the method of fiber elements for quantifying the behavior of circular slender CFDST beam-columns loaded eccentrically with preloads acting on the hollow steel tubes. The numerical model considers the concrete confinement, second-order effects, initial geometric imperfection, deformations induced by preloads as well as geometric and material nonlinearities. The dynamic nonlinear equilibrium functions are solved using efficient computational solution algorithms developed. The validation of the numerical modeling technique is made by comparing computations with existing results obtained by experiments and finite element analyses. The influences of preloads on the structural behavior of slender CFDST beam-columns with various important parameters are investigated by means of utilizing the developed computer model. It is shown that the numerical modeling method is an efficient computational simulation and design tool for slender CFDST columns including preloads.

Nonlinear analysis of square concrete-filled double steel tubular slender columns incorporating preload effects

Thin-walled square and circular hollow steel tubes are designed to support the permanent and construction loads of several upper composite floors before filling the concrete into the tubes to form concrete-filled double steel tubular (CFDST) columns. The influences of preloads acting on the steel tubes on the structural responses of slender square CFDST columns have not been investigated either experimentally or numerically. This paper presents a fiber-based computational model for the determination of the interaction behavior of local and global buckling in axially and eccentrically loaded CFDST thin-walled square slender columns including preload effects. The computational modeling method accounts for the influences of the deformations induced by preloads, local-global interaction buckling, geometric imperfections, second-order, and geometric and material nonlinearities. The accuracy of the computational algorithms developed is validated by comparing computations with test data on concrete-filled steel tubular (CFST) columns and finite element results of double-skin CFST (DCFST) columns with preload effects. The computer algorithms are employed to quantify the influences of preloads on the local-global interaction buckling responses of CFDST columns with various important parameters. Proposed is a design method for calculating the ultimate loads of concentrically loaded slender square CFDST columns considering preloads. The computational and design models developed are shown to be efficient modeling and design tools for square CFDST slender columns taking into account the construction method of high-rise composite buildings.

Influence of Preloading and Deformation on the Grain Structure and Strength of the Ni3Al Intermetallic Compound Synthesized under Pressure

We have studied the influence of a preload applied to a starting elemental powder mixture and the strain in the product of high-temperature synthesis during a bulk exothermic reaction on the grain structure of the Ni3Al intermetallic compound and the temperature dependence of its strength. The results demonstrate that, during the bulk exothermic reaction responsible for the formation of the intermetallic compound under pressure in a closed press die, the average grain size varies along a vertical cut, from the minimum value on the upper and lower surfaces of the synthesized sample to the maximum value in its central part. As the preload applied to the starting powder mixture is raised, the average grain size decreases, whereas the general character of the grain size distribution in a cross section of the sample remains unchanged. Deformation of the high-temperature synthesis product in a press die with partial extrusion causes an appreciable grain size reduction, significantly averaging the grain size in the bulk of the synthesized sample, and raises the tensile strength of the intermetallic compound in the temperature range 20–1000°C.

Effect of pre-load on wave propagation characteristics of hexagonal lattices

The aim of this paper is to investigate the effect of the applied pre-load on wave propagating behaviors of hexagonal lattices in terms of band structures, band gap distributions and phase/group velocities. The structure is composed of the repeat elementary unit cell, and the elementary unit cell is assembled with the axial pre-loaded elastic Timoshenko beams. The finite element method is adopted to solve the wave propagation problems. By calculating the band structure, we show a lower band gap is produced when the negative pre-load is applied. Band gap distributions are also calculated to gain the insight into the effects of the applied pre-load and the geometric parameters (internal angles and the relative density) on the wave propagation. The shift of the frequencies at specific points of the Brillouin zone due to the effect of pre-load is quantified. Special attention is devoted to the effect of pre-load on the directional energy flow. The phase constant surfaces and phase/group velocities are obtained for different pre-loads in order to demonstrate the influence of pre-load on the directional wave motion.

Preliminary analysis on the preload influence on the behavior of offset half gas bearings

This paper deals with a preliminary computational analysis of the influence of the preload factor on the performance characteristics of gas-lubricated offset half bearings. A finite element procedure is devised to solve the lubrication equations rendered by a linearized perturbation method applied on the compressible Reynolds equation. High-order shape functions are employed in the fluid domain modeling to avoid numerical instabilities in the equation solver. Steady-state and dynamic performance characteristics of gas bearings with different values of preload are predicted at several operating conditions. Curves of the bearing characteristics are rendered to show the influence of the preload on the performance of offset half gas bearings at high speeds.

Influence of Preload and Retainer of Linear Ball Guides on Feed Drive System in Microscopic Motions

Influence of Preload and Retainer of Linear Ball Guides on Feed Drive System in Microscopic Motions

A Laboratory Test on the Vibration Mitigation Efficiency of Floating Ladder Tracks

With the rapid development of railway systems, increasingly more environmental concerns are focused on railway vibrations. The track solution with the mass-spring-damping principle can be the most effective and economical option to control train-induced ground vibrations. The effect of track vibration mitigation is usually described by insertion loss (IL). IL can typically be obtained by impulse tests in laboratories. To investigate the influences of preloads on IL, a dynamic laboratory experiment was performed on a floating ladder track. Two conditions were considered, a ladder sleeper with and without under sleeper pads (USPs). A modal test was performed, and then, an automatic falling weight system was used for the vibration reduction test. A preloaded car with a deadweight of 2.4 tons was employed. Different concrete masses, with a maximum of 5.4 tons of total weight were applied on the car. Ground vibrations and IL were analysed under these different preloaded weights. The results show that the first natural frequency of the floating ladder track was 33 Hz. When the preload was applied, the ground vibration and IL around the natural frequency were largely influenced. In addition, the values of IL in different frequencies had different sensitivities to the preloads.

The Influence of Preload on the Work of Angular Contact Ball Bearings

Abstract Optimum values of preload can be achieved in well-tried constructions and then applied in similar structures. For new structures, it is recommended to calculate the preload force and to test the correctness of calculation by means of experiments. In practice it may be necessary to introduce corrections, because not all real work parameters can be precisely known. Credibility of calculations depends, first of all, on the consistence between the assumptions concerning temperature conditions during work and elastic deformations of cooperating elements – first of all of a holder – and the real work conditions. The aim of the study is to determine how preload influences the work of a system of angular ball bearings, in relation to durability of bearing, moment of friction and rigidity of the bearing.

Identification of representative anisotropic material properties accounting for friction and preloading effects: A contribution for the modeling of structural dynamics of electric motor stators

Simulating the dynamic behavior and determining equivalent material properties for anisotropic models, superelements or structures subjected to preloads or friction remains a challenging issue. Amongst other practical applications, modeling interactions between the steel sheets in industrial magnetic cores of electric motor stators is a complex task, as it requires anticipating behavioral heterogeneities in the structure, and possibly represents significantly costly operations for performing modal or dynamic response simulations. In this article, a method for identifying equivalent material properties to anisotropic structures is developed, which is able to take into account the influence of preloads and friction on the material properties, later used in structural dynamics simulations. The proposed approach can be used with superelements, converting stiffness matrices into elasticity matrices. The method is first applied to a triclinic model, and recreates its elasticity matrix with little derivation. Then, an equivalent linear material is computed for a continuous structure under preloading. Compared at low frequencies, the vibration behavior of the preloaded structure and its equivalent effective media are in good agreement. The operation is repeated with a laminated stack under preloading. Again, the dynamic behavior of the equivalent structure shows good accuracy compared to the initial preloaded stack. Finally, the magnetic core of an electric machine stator is modeled with equivalent anisotropic material properties, accounting for friction and preload in the yoke's and the teeth's steel sheets. The simulation of the structure's low-frequency radial vibration modes is satisfying, and shows improvement compared to orthotropic properties.

Stability analysis of machine tool spindle under uncertainty

Chatter is a harmful machining vibration that occurs between the workpiece and the cutting tool, usually resulting in irregular flaw streaks on the finished surface and severe tool wear. Stability lobe diagrams could predict chatter by providing graphical representations of the stable combinations of the axial depth of the cut and spindle speed. In this article, the analytical model of a spindle system is constructed, including a Timoshenko beam rotating shaft model and double sets of angular contact ball bearings with 5 degrees of freedom. Then, the stability lobe diagram of the model is developed according to its dynamic properties. The Monte Carlo method is applied to analyse the bearing preload influence on the system stability with uncertainty taken into account.

Influence of large strain preloads on the viscoelastic response of rubber-like materials under small oscillations

The viscoelastic response predicted by linearized internal variables models in the case of small oscillations superimposed on a large static preload is investigated, comparing simple forms of the Zener and the Poynting–Thomson models. It is shown that both of them predict a preload dependency of the equilibrium linearized stress, but only the latter take into account such a dependency on the out-of-equilibrium part. Yet, the Zener model is much more frequently linearized as the Poynting–Thomson model. The formulation of each model for finite deformations is quickly reminded, before linearizing them around a large static preload. Finally, a comparison of the influence of preload on each model is proposed for uniaxial extension, before discussing which kind of model has to be chosen regarding theoretical and practical aspects.

Influence of Preload and Nonlinearity of Railpads on Vibration of Railway Tracks under Stationary and Moving Harmonic Loads

In railway track dynamics, the stiffness and damping properties of railpads have a significant effect on track vibration, decay rates as well forces transmitted to the track supporting structure. Many studies have shown that railpads exhibit pronounced nonlinear behaviour, with preload and frequency dependent properties. This paper presents a three parameter railpad model, together with its differential equation of motion and the required model parameters obtained from experimental data. A time domain model of a rail discretely supported on these railpads is then formulated using the finite element method. The model is subjected to static and dynamic loading in order to study the effects of preload and frequency on its dynamic behaviour. Results are shown as time histories and frequency spectra for the track displacements and reaction forces for various preload levels. They emphasise the necessity of accounting for nonlinear behaviour based on the large disparities (up to 20 dB) observed between the linear and nonlinear cases for the parameters used in this study.

Determination of Valanis model parameters in a bolted lap joint: Experimental and numerical analyses of frictional dissipation

In this work, Valanis model parameters, and their variation with bolt preload, were determined for a bolted lap joint, which consisted in two steel plates held together by a metric 12 screw. For this purpose, a series of transitory non-linear analyses were performed on the basis of a three dimensional finite element model of the bolted lap joint subjected to varying bolt preloads and tangential displacements. Curve fitting of hysteresis cycles obtained from numerical simulations allowed determination of Valanis model parameters as well as assessment of bolt preload influence on these parameters. In addition, the present numerical simulations provided information about the evolution of the contact state from stick to slip regimes between the bolted plates, reflecting the non-linear behaviour of the joint. Quasi-static tests at several preloads and tangential displacements conditions were conducted to validate Valanis model parameters previously obtained from numerical simulations. The present findings provided detailed information about the evolution of the aforementioned Valanis parameters with bolt preload. Thus, we confirmed that equivalent stiffness values corresponding to the macro-slip regime as well as the upper limit of the sticking regime (Et and σ0, respectively) are highly influenced by bolt preload levels. These results may prove useful to appropriately design bolted joints to be used under specific stiffness and damping criteria, and therefore reducing the vibration response of the joint.

공작기계 베어링 결합부의 전산 모델링

The bearing coupling section of machine tools is the most important factor to determine their static/dynamic stiffness. To ensure the proper performance of machine tools, the static/dynamic stiffness of the rotating system has to be predicted on the design stage. Various parameters of the bearing coupling section, such as the spring element, node number and preload influence the characteristics of rotating systems. This study focuses on the prediction of the static and dynamic stiffness of the rotating system with the bearing coupling section using the finite element (FE) model. MATRIX 27 in ANSYS has been adopted to describe the bearing coupling section of machine tools because the MATRIX 27 can describe the bearing coupling section close to the real object and is applicable to various machine tools. The FE model of the bearing couple section which has the sixteen node using MATRIX 27 was constructed. Comparisons between finite element method (FEM) predictions and experimental results were performed in terms of the static and dynamic stiffness.