Axial Preloading Research Articles

Dynamic Compressive Test of Gas-Containing Coal Using a Modified Split Hopkinson Pressure Bar System

In deep mine, coal is usually subjected to coupled high gas pressure and static compressive stress. The coal may be also subjected to dynamic loading due to the sudden fracture of hard roof during mining. In our previous study, the behaviour of gas-containing coals with initial gas pressure was investigated subjected to uniaxial static compression. In this study, the dynamic compressive behaviour of gas-containing coals with gas pressure and static axial preloading is investigated using a modified Split Hopkinson Pressure Bar (SHPB) system. The dynamic behaviours of gas-containing coals under SHPB tests are studied by varying initial gas pressure and axial static preloading. The testing results include strain measurements and energy dissipation. In addition, the wave impedance method is used to quantify damage of gas-containing coals under coupled gas-static-dynamic load. It is found that the dynamic compressive strength of gas-containing coal under coupled load decreases with the increasing initial gas pressure. The gas-containing coal with higher gas pressure and axial static preloading is more vulnerable to dynamic loading. The findings can be applied to mining design or support design in deep mining of high-gas-containing coal seam.

Laser shape setting of superelastic NiTi wire: effects of laser beam power and axial pre-load

Shape setting is one of the most important steps of the production route of shape memory alloys, because the programmed shape and functional properties, such as the shape memory effect and the superelasticity, can be fixed. The conventional NiTi shape setting is performed throughout a low temperature (400 °C–500 °C) furnace treatment of constrained material. Recently, it was demonstrated the feasibility of an advanced method, based on using a laser beam scanning, to induce the functional performances on thin NiTinol wires. We studied the effects of the principal process parameters, like laser power and axial pre-load, on functional properties, microstructure and cycling of straight laser annealed Nitinol thin wires. The collected results were then compared to the performances obtained with the commercial wires. It was demonstrated that optimal superelastic behavior can be achieved by optimizing the laser power, while the variation of the applied stress did not affect the wire performances. Laser treated wires shown reduced mechanical hysteresis compared the commercial reference one.

Biomechanical Evaluation of Transforaminal Lumbar Interbody Fusion and Oblique Lumbar Interbody Fusion on the Adjacent Segment: A Finite Element Analysis

To analyze the biomechanical changes of lumbar adjacent segment by comparing the biomechanics after the surgery of transforaminal lumbar interbody fusion (TLIF) and oblique lumbar interbody fusion (OLIF). The finite element model of the L1-S1 was reconstructed via computed tomography scan images. The models of TLIF and OLIF were constructed and analyzed. A 400-N vertical axial pre-load was imposed on the superior surface of L1 and a 10-N·m moment was applied on the L1 superior surface along the radial direction to simulate 4 different physiological motions: flexion, extension, bending, and torsion. The range of motion (ROM) and the intradiscal pressure (IDP) were evaluated and compared with investigate the biomechanical influences of TLIF and OLIF on the adjacent segments (L3-L4 and L5-S1). Compared with the normal model, TLIF and OLIF in all motion patterns increased the ROM and the IDP of adjacent segments. However, the ROM and the IDP between TLIF and OLIF had no significant difference. The biomechanical analysis showed that both TLIF and OLIF can increase ROM and IDP. It indicates that TLIF and OLIF probably increase the potential risk of adjacent segment degeneration similarly.

The effect of follower load on the intersegmental coupled motion characteristics of the human thoracic spine: An in vitro study using entire rib cage specimens

The mechanical coupling behaviour of the thoracic spine is still not fully understood. For the validation of numerical models of the thoracic spine, however, the coupled motions within the single spinal segments are of importance to achieve high model accuracy. In the present study, eight fresh frozen human thoracic spinal specimens (C7-L1, mean age 54 ± 6 years) including the intact rib cage were loaded with pure bending moments of 5 Nm in flexion/extension (FE), lateral bending (LB), and axial rotation (AR) with and without a follower load of 400 N. During loading, the relative motions of each vertebra were monitored. Follower load decreased the overall ROM (T1-T12) significantly (p < 0.01) in all primary motion directions (extension: −46%, left LB: −72%, right LB: −72%, left AR: −26%, right AR: −26%) except flexion (−36%). Substantial coupled motion was found in lateral bending with ipsilateral axial rotation, which increased after a follower load was applied, leading to a dominant axial rotation during primary lateral bending, while all other coupled motions in the different motion directions were reduced under follower load. On the monosegmental level, the follower load especially reduced the ROM of the upper thoracic spine from T1-T2 to T4-T5 in all motion directions and the ROM of the lower thoracic spine from T9-T10 to T11-T12 in primary lateral bending. The facet joints, intervertebral disc morphologies, and the sagittal curvature presumably affect the thoracic spinal coupled motions depending on axial compressive preloading. Using these results, the validation of numerical models can be performed more accurately.

A new application of Fe-28Mn-6Si-5Cr (mass%) shape memory alloy, for self-adjustable axial preloading of ball bearings

A new application of Fe-Mn-Si based shape memory alloys (SMAs) was developed under the form of truncated cone-shaped module, for self-adaptive axial preload control in angular contact bearings. The modules were processed by high-speed high-pressure torsion (HS-HPT), from circular crowns cut from axially drilled ingots of Fe-28Mn-6Si-9Cr (mass%) SMA. The specimens were mechanically tested in the hot rolled state, prior to HS-HPT processing, demonstrating free-recovery shape memory effect (SME) and high values for ultimate tensile stress and strain as well as low cycle fatigue life. The HS-HPT modules were subjected to static loading–unloading compression, without/with lubrication at specimen-tool interface, both individually and in different coupling modes. Dry compression cycles revealed reproducible stress plateaus both during loading and unloading stages, being associated with hardness gradient, along cone generator, caused by HS-HPT processing. Constrained recovery tests, performed using compressed modules, emphasized the continuous generation of stress during heating, by one way SME, at a rate of ∼9.3 kPa/%. Dynamic compression tests demonstrated the capability of modules to develop closed stress–strain loops after 50 000 cycles, without visible signs of fatigue. HS-HPT caused the fragmentation of crystalline grains, while compression cycles enabled the formation of ε hexagonal close-packed stress-induced martensite (ε), which is characterized by a high density of stacking faults. Using an experimental setup, specifically designed and manufactured for this purpose, both feasibility and functionality tests were performed using HS-HPT modules. The feasibility tests proved the existence of a general tendency of both axial force and friction torque to increase in time, favoured by the increase of initial preloading force and the augmentation of rotation speed. Functionality tests, performed on two pairs of HS-HPT modules fastened in base-to-base coupling mode, demonstrated the capacity of modules to accommodate high preloads while maintaining both axial force and friction torque at constant values in time. These preliminary results suggest that, for the time being, the modules can operate only as single use applications, more effective during the running-in period. This bevahior recommends HS-HPT modules as a new application of Fe-Mn-Si SMAs, with the potential to be used for the development of new temperature-responsive compression displacement systems.

A new method for measuring the rotational accuracy of rolling element bearings

The rotational accuracy of a machine tool spindle has critical influence upon the geometric shape and surface roughness of finished workpiece. The rotational performance of the rolling element bearings is a main factor which affects the spindle accuracy, especially in the ultra-precision machining. In this paper, a new method is developed to measure the rotational accuracy of rolling element bearings of machine tool spindles. Variable and measurable axial preload is applied to seat the rolling elements in the bearing races, which is used to simulate the operating conditions. A high-precision (radial error is less than 300 nm) and high-stiffness (radial stiffness is 600 N/μm) hydrostatic reference spindle is adopted to rotate the inner race of the test bearing. To prevent the outer race from rotating, a 2-degrees of freedom flexure hinge mechanism (2-DOF FHM) is designed. Correction factors by using stiffness analysis are adopted to eliminate the influences of 2-DOF FHM in the radial direction. Two capacitive displacement sensors with nano-resolution (the highest resolution is 9 nm) are used to measure the radial error motion of the rolling element bearing, without separating the profile error as the traditional rotational accuracy metrology of the spindle. Finally, experimental measurements are performed at different spindle speeds (100-4000 rpm) and axial preloads (75-780 N). Synchronous and asynchronous error motion values are evaluated to demonstrate the feasibility and repeatability of the developed method and instrument.

Behaviour of steel-jacket retrofitted RC columns with preload effects

Steel jacketing is an efficient way to retrofit reinforced concrete columns. Previous studies focused on the performance improvement without considering the preloads on the original columns. The preloads might inevitably affect the structural performance of the retrofitted columns. Comprehensive experimental and numerical studies on the behaviour of steel-jacket retrofitted RC columns with preload effects are presented in this paper. Twenty-nine steel jacketing columns with different steel tube thicknesses, axial preloading levels and load eccentricities are tested under concentrically or eccentrically compressive loading.The experimental results are discussed and illustrate that the effects of preloading levels on the axial compression strength of the retrofitted columns are negligible while increasing the preloads could decrease the eccentric compressive strength. A fibre element model is developed to predict the behaviour of the retrofitted columns. The material non-linear behaviour of all the components considering the steel tube and stirrup confining effects on the concrete as well as the preloading action are taken into account in the model. The model is validated by comparing its results with the experimental results. Extensive parametric studies are undertaken by using the proposed numerical model to elucidate the effects of axial and moment preloading and the effects of preloads with various other parameters on the performance of the retrofitted columns.

Vibration Characteristics of Tapered Roller Bearings with Roller Diameter error

This study investigates the vibration characteristics of tapered roller bearings with the presence of error in roller diameter. A general model for tapered roller bearing with five degree-of-freedom was adopted with taking into account the error in roller diameter. Then, the effect of one single errored roller and multiple errored rollers on the vibration behaviour of tapered roller bearing was investigated. Simulation results confirmed that the bearing vibration frequencies are equal to cage rotational frequency in the case of axial preloading, and multiple of cage rotational frequency in the case of combined loadings, irrespective of the error magnitude, the number or position of errored rollers, which, however, significantly affect the vibration amplitude of bearing.

Root cause analysis of rotary shouldered pin-box connection failure

The threaded rotary shouldered connection considered in this study has been utilized in the oil and gas industry in drilling operations. A rotary shouldered pin-box connection failed during drilling operations in the field. The failure is investigated by employing numerical, analytical and experimental methodologies. The pin-box connection studied in this study is loaded by three different loads in the field. These loads are make-up torque, axial load due to dead weight of the drilling pipes and bending load due to axial misalignment in the drill-hole. The root-cause of a failure of a rotary shouldered pin-box connection requires careful examination of these three loads. This study was focused on make-up torque loading, which is one of the three loadings applied on the connection in the field during drilling operations. The main goal in this study is to accurately determine the axial pre-load force due to applied make-up torque of 57,000ft.lbs to the pin-box connection. Rosette type strain gages were employed to measure the axial pre-load in the connection. The calculated pre-load force in the connection due to applied make-up torque is documented in this publication.

Dynamic study of anti-backlash gears and angle-contact ball bearing based on a simplification of the Hertz contact theory

The contact stiffness of a mechanical joint surface has a significant influence on the assembly resonance frequency by affecting the stiffness matrix of the kinetic equation. The Hertz contact theory is improved and facilitated to found a mapping relationship between the assembly process parameters and contact stiffness, which is applied in the anti-backlash gear and the angle-contact ball bear to establish reduced model of transmission system. The anti-backlash gear can be simplified using a contact of two cylinders in reduced model, and the rotational resonance frequency of the transmission system can be increased through torsional spring preloading, while the angle-contact ball bearing can be facilitated into a contact of two spheres in reduced model, and the translational resonance frequency of the transmission system can be enhanced through axial preloading. The contact stiffness in anti-backlash gear is calculated and converted considering the driving torque and gear preloading, while the contact stiffness in angle-contact ball bearing is improved and merged by multiplying a correction factor [Formula: see text] in axial preloading. By adding corresponding non-massive rigid auxiliary elements, the transmission system model composed by the anti-backlash gear and the angle-contact ball bear is established to simulate the dynamic performance in ADAMS software. The frequency response values of the transmission system agree well with the theoretical value. Thus, the complex theoretical calculation formulas can be replaced by the simplified model.

G1100105 軸方向予圧を用いた大容量ハイブリッド減速装置の高効率化の研究

G1100105 軸方向予圧を用いた大容量ハイブリッド減速装置の高効率化の研究

Does total disc arthroplasty in C3/C4-segments change the kinematic features of axial rotation?

We analyze how kinematic properties of C3/C4-segments are modified after total disc arthroplasty (TDA) with PRESTIGE® and BRYAN® Cervical Discs. The measurements were focused on small ranges of axial rotation (<0.8°) in order to investigate physiologic rotations, which frequently occur in vivo.Eight human segments were stimulated by triangularly varying, axially directed torque. By using a 6D-measuring device with high resolution the response of segmental motion was characterised by the instantaneous helical axis (IHA). Position, direction, and migration rate of the IHA were measured before and after TDA. External parameters: constant axially directed pre-load, constant flexional/extensional and lateral-flexional pre-torque.The applied axial torque and IHA-direction did not run parallel. The IHA-direction was found to be rotated backwards and largely independent of the rotational angle, amount of axial pre-load, size of pre-torque, and TDA. In the intact segments pre-flexion/extension hardly influenced IHA-positions. After TDA, IHA-position was shifted backwards significantly (BRYAN-TDA: ≈8mm; PRESTIGE-TDA: ≈6mm) and in some segments laterally as well. Furthermore it was significantly shifted ventrally by pre-flexion and dorsally by pre-extension. The rate of lateral IHA-migration increased significantly after BRYAN-TDA during rightward or leftward rotations.In conclusion after the TDA the IHA-positions shifted backwards with significant increase in variability of the IHA-positions after the BRYAN-TDA more than in PRESTIGE-TDA.The TDA-procedure altered the segment kinematics considerably. TDA causes additional translations of the vertebrae, which superimpose the kinematics of the adjacent levels. The occurrence of adjacent level disease (ALD) is not excluded after the TDA for kinematical reasons.

Fundamental Study about Hybrid Speed Increasing and Reducing Power Transmission Device (The Analyses and Experiments in the Case of Using Axial Preload)

Fundamental Study about Hybrid Speed Increasing and Reducing Power Transmission Device (The Analyses and Experiments in the Case of Using Axial Preload)

Behavior of Normal- and High-Strength Confined Concrete

The objective of this study was to evaluate and model the behavior of concrete under triaxial compression using various loading paths and to better understand the mechanism of confinement. A total of 110 cylindrical specimens 54 mm (2.1 in.) in diameter and 110 mm (4.3 in.) long were tested in which variables included unconfined concrete strength, lateral confining pressure, level of damage caused by axial preload, and active or simulated passive confinement. The confined strengths of up to 107, 177, and 314 MPa (15, 26.7, and 45.5 ksi) were observed, respectively, for concretes with unconfined strengths of 36, 84, and 120 MPa (5.2, 12.1, and 17.4 ksi). The results suggest that concrete subjected to axial preloads of up to 80% of unconfined strength can be retrofitted without losing any significant benefits of confinement. Analytical models, essential to model the confinement mechanism, are proposed for dilation behavior of confined normal-strength concretes (NSCs) and high-strength concretes (HSCs) under triaxial compression.

Experimental study on bearing preload optimum of machine tool spindle

An experimental study is conducted to investigate the possibility and the effect of temperature rise and vibration level of bearing by adjusting axial preloads and radial loads in spindle bearing test rig. The shaft of the test rig is driven by a motorized high speed spindle at the range of 0~20000 rpm. The axial preloads and radial loads on bearings are controlled by using hydraulic pressure which can be adjusted automatically. Temperature rise and radial vibration of test bearings are measured by thermocouples and Polytec portable laser vibrometer PDV100. Experiment shows that the temperature rise of bearings is nonlinear varying with the increase of radial loads, but temperature rise almost increases linearly with the increase of axial preload and rotating speed. In this paper, an alternate axial preload is used for bearings. When the rotating speed passes through the critical speed of the shaft, axial preload of bearings will have a remarkable effect. The low preload could reduce bearing vibration and temperature rise for bearings as well. At the others speed, the high preload could improve the vibration performance of high speed spindle and the bearing temperature was lower than that of the constant pressure preload spindle.

Implications of the center of rotation concept for the reconstruction of anterior column lordosis and axial preloads in spinal deformity surgery

In thoracolumbar deformity surgery, anterior-only approaches are used for reconstruction of anterior column failures. It is generally advised that vertebral body replacements (VBRs) should be preloaded by compression. However, little is known regarding the impact of different techniques for generation of preloads and which surgical principle is best for restoration of lordosis. Therefore, the authors analyzed the effect of different surgical techniques to restore spinal alignment and lordosis as well as the ability to generate axial preloads on VBRs in anterior column reconstructions. The authors performed a laboratory study using 7 fresh-frozen specimens (from T-3 to S-1) to assess the ability for lordosis reconstruction of 5 techniques and their potential for increasing preloads on a modified distractable VBR in a 1-level thoracolumbar corpectomy. The testing protocol was as follows: 1) Radiographs of specimens were obtained. 2) A 1-level corpectomy was performed. 3) In alternating order, lordosis was applied using 1 of the 5 techniques. Then, preloads during insertion and after relaxation using the modified distractable VBR were assessed using a miniature load-cell incorporated in the modified distractable VBR. The modified distractable VBR was inserted into the corpectomy defect after lordosis was applied using 1) a lamina spreader; 2) the modified distractable VBR only; 3) the ArcoFix System (an angular stable plate system enabling in situ reduction); 4) a lordosizer (a customized instrument enabling reduction while replicating the intervertebral center of rotation [COR] according to the COR method); and 5) a lordosizer and top-loading screws ([LZ+TLS], distraction with the lordosizer applied on a 5.5-mm rod linked to 2 top-loading pedicle screws inserted laterally into the vertebra). Changes in the regional kyphosis angle were assessed radiographically using the Cobb method. The bone mineral density of specimens was 0.72 ± 22.6 g/cm(2). The maximum regional kyphosis angle reconstructed among the 5 techniques averaged 9.7°-16.1°, and maximum axial preloads averaged 123.7-179.7 N. Concerning correction, in decreasing order the LZ+TLS, lordosizer, and ArcoFix System outperformed the lamina spreader and modified distractable VBR. The order of median values for insertion peak load, from highest to lowest, were lordosizer, LZ+TLS, and ArcoFix, which outperformed the lamina spreader and modified distractable VBR. In decreasing order, the axial preload was highest with the lordosizer and LZ+TLS, which both outperformed the lamina spreader and the modified distractable VBR. The technique enabling the greatest lordosis achieved the highest preloads. With the ArcoFix System and LZ+TLS, compression loads could be applied and were 247.8 and 190.6 N, respectively, which is significantly higher than the insertion peak load and axial preload (p < 0.05). Including the ability for replication of the COR in instruments designed for anterior column reconstructions, the ability for lordosis restoration of the anterior column and axial preloads can increase, which in turn might foster fusion.

Effect of previous cyclic axial loads on pile groups

Numerous piles are often subjected to the combination of cyclic axial and cyclic lateral loads in service, such as piled foundations for offshore platforms which may suffer swaying and rocking motions owing to wind and wave actions. In this research, centrifuge tests were conducted to investigate the effect of previous cyclic axial loads on the performance of pile groups subjected to subsequent cyclic lateral loads. Different pile installation methods were also applied to study the different behaviour of bored and jacked pile groups subjected to cyclic loads. During lateral load cycling, it is seen that cyclic axial loads to which pile groups were previously subjected could reduce the pile cap permanent lateral displacement in the first lateral load cycle but do not influence the incremental rate of permanent displacement in the following lateral load cycles. Moreover, it is found that previous cyclic axial loads could improve the pile cap cyclic lateral secant stiffness, especially for the pre-jacked pile group. When rocking motions were induced by cyclic lateral loads, pile groups subjected to cyclic axial loads before have smaller permanent settlement than those without the cyclic axial loading effect. The designers of piles that are intended to resist significant lateral loads without excessive deformations in service may wish to deploy cyclic axial preloading, accordingly.

Comparison of Self-Drilling and Self-Tapping Cervical Spine Screws Using ASTM F543-07

Abstract ASTM F543-07 is used to evaluate insertion load (Annex A4), driving torque (A2), and axial pullout (A3) characteristics of self-tapping metallic medical bone screws. F543-07 was designed to evaluate screws that utilize a pre-drilled pilot hole and was not intended for self-drilling screws. The objectives of this study were to (1) adapt the F543-07 test methods to allow evaluation of both self-drilling and self-tapping screws and (2) quantify differences in performance between the two screw types. For all three tests (A4, A2, A3) appropriately sized pilot holes were pre-drilled into the surrogate test medium for all the self-tapping screw designs per ASTM F543-07. No pilot holes were created for the self-drilling screws. During the insertion load tests (A4), a constant rotation was applied to the screws under an initial, near-zero axial force state. While monitoring axial load, torque, and displacement, the axial load was gradually increased. The maximum load at which there was a marked increase in torque and displacement on the graph was indicative of the force required to engage the self-drilling or the self-tapping feature. To measure driving torque (A2), a constant rotation was applied. To maintain screw driver–screw contact, a constant-force axial pre-load was required. The axial insertion load, determined during the insertion load testing (A4), was used as the preload for the driving torque testing. Axial pullout testing (A3) measured the axial tensile force required to remove a screw from the test medium. Quantifiable differences in mean insertion load, driving torque, and pullout load were found, demonstrating that these methods are able to discern differences in performance between different screw designs. Finally, this study demonstrated it is possible to adapt the test methods outlined in ASTM F543-07 to evaluate the insertion load, driving torque, and axial pullout performance of self-drilling screws in addition to self-tapping screws.

Design of hollow and concrete filled steel and stainless steel tubular columns for transverse impact loads

The behaviour of hollow and concrete filled thin-walled steel tubular members subjected to transverse impact was previously investigated experimentally and theoretically. The members were restrained axially and rotationally at their ends. In this paper the study is extended to investigate nominally identically sized stainless steel tubes, tested experimentally under the same conditions. Comparisons between the performance of the two materials are made. Both the steel and stainless steel tubular members, hollow and concrete filled, are then modelled numerically. The FE models are validated against the experiments, and subsequently extended to investigate the general behaviour of such members when used as columns or other axially load bearing structures. The influences of axial pre-load, rotational restraint at the member ends, axial restraint, metal material properties and concrete filling, are investigated. In particular, their effect on the capacity of the members to absorb transverse impact energy. A general design procedure for metal tubular members with or without concrete filling subjected to transverse impact is developed, in a format aligned with current static structural steel specifications.

Alternative Mechanical Structure for LARP Nb$_{3}$Sn Quadrupoles

An alternative structure for the 120 mm Nb3Sn quadrupole magnet presently under development for use in the upgrade for LHC at CERN is presented. The goals of this structure are to build on the existing technology developed in LARP with the LQ and HQ series magnets and to further optimize the features required for operation in the accelerator. These features include mechanical alignment needed for field quality and provisions for cold mass cooling with 1.9 K helium in a helium pressure vessel. The structure will also optimize coil azimuthal and axial pre-load for high gradient operation, and will incorporate features intended to improve manufacturability, thereby improving reliability and reducing cost.