Preload Loss Research Articles

Modeling of Ball Screw–Nut Interface Stiffness With Wear (Ball Screw Wear Dynamics)

Abstract The effects of wear, preload loss, and missing balls on the dynamics of ball screw drives in machine tools are modeled and incorporated into the finite element model of the drive assembly for condition monitoring. The contacts between the ball–nut and ball–screw are modeled using Hertzian springs, whose stiffnesses vary as a function of the worn contact area. These contact stiffnesses are then transformed to the finite element nodes on the nut and screw. The frequency response functions at the motor shaft and table, which can be measured by commercial computer numerical control (CNC), are predicted for various faults at different positions of the table. The experimentally validated model demonstrates that the faults primarily affect the first coupled torsional-axial mode of the ball screw drive and can be utilized for automated condition monitoring of ball screw drives.

Robust feature design for early detection of ball screw preload loss

The ball screw is a critical device for precision linear motion control that has widespread applications in industrial robots, computer numerical control (CNC) machines, and high-precision leveling systems, among others. Because high-precision positioning is ensured by the addition of a preload to the ball screw system, it is crucial to detect and monitor the loss of preload at the earliest possible stage of degradation. The degradation process of the ball screw can be characterized in two stages: the initial reduction of preload without backlash, followed by a loss of preload with an emergence of backlash. To explore the change of the ball screw dynamics caused by degradation, a novel fixed cycle feature test (FCFT) is implemented in combination with multi-level mass experiments and a run-to-failure (RTF) test. The relationships of the ball screw dynamics with preload, worktable mass, and axis position are investigated, with a focus on the axial natural frequency as an indicator of preload loss. Experimental results validate the axial natural frequency’s role as a reliable early detector of preload loss for interventive use in a prognostic system.

Research on Influencing Factors of Cable Clamp Bolt Elastic Interaction in Cross-Ocean Suspension Bridges

Suspension bridges are the most common type of bridge used to cross the ocean. The cable clamps in suspension bridges clamp the main cables by bolt preload, but the elastic interaction of the bolts reduces the preload, which is detrimental to the force in suspension bridges. However, research on the factors influencing the elastic interaction of cable clamp bolts in suspension bridges is currently limited. This paper aims to explore the law of influence of external factors on the elastic interaction of bolts through a combined approach of theoretical analysis, full-scale experiment, and finite element simulation. The results indicate that the average preload loss was reduced by about 27% when the elastic modulus was increased by about 110%. The average preload loss was reduced by about 45% when the bolt center distance was increased by 75%. The number of bolts has a small effect on the elastic interaction, which can be ignored. When the preload of bolt installation was increased by 133%, the average preload loss was reduced by approximately 125%, which was almost a linear relationship. Tightening the bolt from the center bolt creates greater elastic interaction. The conclusions can provide suggestions for reducing the elastic interaction of bolts in the design and construction of suspension bridge cable clamps.

Research on the anti-slip performance of arc groove cable clamps

Cable clamps are crucial for connecting component and transmitting prestress in cable structures. The anti-slip performance of the cable clamp is an important factor affecting the stability and safety of the structure. This paper introduces a novel test device to evaluate the anti-slip performance of arc groove cable clamps, and anti-slip performance experiments are performed on four arc groove cable clamps and four straight groove cable clamps. Long-term high strength bolt preload loss tests are conducted to investigate the loss pattern. Furthermore, seventeen parametric finite element models are developed to analyze the effects of groove bending angle, bolt length, cable force, and pressure plate stiffness on the anti-slip performance of arc groove cable clamps. It is found that the arc groove cable clamp exhibits a higher anti-slip bearing capacity, with a friction coefficient equivalent to that of the straight groove cable clamp, both exceeding 0.2. The bolt preload stabilizes at a certain value after 96 h of screwing the bolt, while it stabilizes after 24 h of tensioning the cable. The increase in the bolt length and angel of arc groove, as well as the reduction in the stiffness of the pressure plate, have a positive impact on the anti-slip bearing capacity of the arc groove cable clamp. There is a critical cable force that results in the lowest anti-slip bearing capacity of the arc groove cable clamp. These research results provide valuable insights for the design and engineering application of arc groove cable clamps.

Method of accumulation of preload loss of bolted joints due to rotational self-loosening caused by cyclic, transversal excitation

This paper presents a new method to experimentally characterize the rotational self-loosening behavior of bolted joints. Furthermore, a method to calculate the preload loss due to certain relative displacements of the clamped parts was developed. The method obtains all required calculation parameters from the experimental tests performed and neither needs further experimental determination of friction coefficients nor numerical simulations to predict the preload loss. The method accumulates the preload loss of load cycles. Thereby, it can be used to estimate the time a machine can operate until a critical amount of preload is lost. Non-linear dependencies of the preload loss to the displacement amplitude and the remaining preload are considered. The calculation method also applies to load cases with variable load amplitudes. This is validated experimentally.

Simulation of Preload Relaxation of Bolted Joint Structures under Transverse Loading

In this study, based on the Iwan model, the connection interface of the bolted joint structure subjected to lateral loads was simulated and comparatively analyzed. Commercial finite element software was used to model the bolted joint structure. Monotonic lateral loads and cyclic displacement loads were applied to the model. The changes in the preload force of the bolted connection structure, as well as the changes in the sticking zone and stress state of the connection interface, were analyzed, and the loading results of monotonic load and cyclic displacement load were compared. The results show that the contact interface stress decreases with the increase in displacement load, and this increase is also a nonlinear relationship, which is approximately in phase with the trend of the contact surface slip curve. The amount of contact surface stress loss and the amount of preload loss are not directly related to the magnitude of the initial preload, regardless of the loading conditions. The contact surface is also circular under any form of displacement loading, whether it is stressed or slipped. The amount of preload loss is proportional to the amount of bolt compression for that variable.

Preload relaxation behavior and its influence on the mechanical performance of bolted carbon fiber‐reinforced thermoplastic sheet molding compound joints

AbstractIn this study, the relaxation of the initial tightening preload of bolted carbon fiber reinforced thermoplastic sheet molding compound (CFRTP‐SMC) joints was experimentally investigated under different temperatures and initial preload conditions. The influence of preload relaxation on the bolted structures was evaluated using static bearing tests, whereas the failure modes during the test were verified based on metallographic observations. The experimental results indicate that the speed of the preload relaxation can be accelerated by increasing the temperature and initial preload. The static bearing strength of the bolted SMC material decreased with a continuous increase in the preload loss. Furthermore, the existence of a lateral preload protected the material around the assembly hole from buckling, resulting in a higher static bearing strength. The shielding effect of the preload was weakened after the relaxation of the initial preload.Highlights Elevated temperature and initial preload can expedite the relaxation process. Preload loss will result in a declined static bearing performance. Initial tightening preload can protect the bolted SMC material from buckling.

Mechanism and control of preload force loss of precast structural joint bolts under freeze–Thaw environments

Bolt-connected precast buildings are increasingly prevalent, especially due to their efficient force transfer and accelerated construction processes. However, in cold climates, special attention must be directed towards the effects of freeze-thaw (F-T) damage on concrete at bolt connection sites. This study conducted an accelerated F-t-test to investigate how concrete F-T damage influences the preload force of the connection bolts. The changes in bolt preload forces across F-T cycles were monitored using advanced fiber optic sensing technology. To mitigate preload force loss, silicone rubber sleeves were introduced into the bolts. Results indicate a correlation between initial preload force and subsequent preload loss, with lower initial preloads leading to greater losses. Additionally, the concrete's frost resistance significantly affects preload force loss, with less resistant specimens showing marked preload decreases. A notable risk of brittle damage arises after 3 to 6 F-T cycles if a 4 mm gap between the bolt and concrete exists, attributed to water freezing and expansion within the gap. Concrete specimens subjected to our proposed mitigation strategies effectively withstand over 140 F-T cycles, substantially lowering crack damage risks.

Comparison of three implant systems under preload loss: A finite element analysis validated by digital image correlation methods.

This study evaluated the effects of screw preload loss on three implant systems, both in silico and in vitro. Three finite element analysis (FEA) models of implant restorations were created using bone-level (BL, 4.8×12 mm; BLX, 4.5×12 mm) and tissue-level (TL, 4.8×12 mm) implant systems. The screws in each group were subjected to preloads of 100 N and 200 N, with an additional 130 N load applied to the crown tops. An in vitro study of the principal strain was conducted using digital image correlation (DIC) under the same conditions as for the FEA models. The results were evaluated for von Mises stress, principal strain, and sensitivity index. During loading, the highest stress levels were observed in the implants and screws. In the BL group, the screws experienced the highest von Mises stress at 466.04 MPa and 795.26 MPa in the 100 N and 200 N groups, respectively. The BLX group showed the highest von Mises stress at 439.33 MPa and 780.88 MPa in the implants in the 100 N and 200 N groups. Sensitivity analysis revealed that the screws and abutments in the TL group were significantly more affected by the preload changes. The abutment in the TL group was particularly sensitive to preload changes compared with those in the BL and BLX groups. Variations in the preload significantly affect the stress distribution in implants and screws. Maintaining screw preload stability under loading is crucial in clinical practice to prevent mechanical failure.

Seismic Resilience Evolution of Shield Tunnel with Structure Degradation

The structural performance of shield tunnel structures is highly susceptible to degradation under complex environmental loads, with the most common manifestation being bolt preload loss. In this study, a shield tunnel numerical simulation model was established to analyze the seismic response of shield tunnels with varying degrees of bolt preload loss. Firstly, the deformation patterns of shield tunnel structures under seismic loads were analyzed. Subsequently, ellipticity and joint opening were selected as seismic resilience assessment indicators based on the mechanical response. A seismic resilience assessment model was then established, including three states: normal state, affected state, and recovered state. The results show a direct relationship between the recovery capacity of tunnel structures and the initial performance of the lining structure, as well as the magnitude of the load. The lower the degree of structure degradation, the greater the structural recovery capacity. Additionally, there is a positive correlation between residual deformation and the initial performance loss of shield tunnel structures, as well as the intensity of seismic loads. This study contributes to enriching the theoretical framework for the seismic resilience assessment of shield tunnels, which have significant implications and provide valuable references for engineering safety.

Effect of abutment type and creep behavior on the mechanical properties of implant restorations in the anterior region: A finite element analysis.

This study aimed to assess the effect of abutment variation and creep on dental implant restorations. Three finite element analysis (FEA) models of implant restorations were created, which were restored by conventional one-piece abutment (CA), hybrid abutment crown (HAC), and multi-unit abutment (MUA). The contacts were considered intimate (no friction), except for implant/abutment, abutment/screw, and abutment/screw/crown (HAC) attachments. The related mechanical parameters were used to improve the authenticity of the study. Instantaneous loads and constant loads (100 s) of 130 N were applied at a 30° angle to the palatal portion of the crown. Results were qualitatively and quantitatively evaluated using the equivalent von Mises stress, micro-gap distance of the implant-abutment interface (IAI), preload changes, and safety index. The stress state of each component differed depending on the restoration type, from CA and HAC to MUA. Implants and screws were the structures that suffered the most stress under instantaneous loads. Each metal structure exhibited a substantial decrease in stress during a constant loading period. The screws of the MUA abutment showed more preload loss (62.1 N) after constant loads for 100 s. MUA base produced less micro-gap (0.72 μm) at the IAI when it was compared with the CA group (0.93 μm) and HAC group (3.29 μm). The abutment type influences the mechanical properties and performance of implant restorations. The creep effect decreases the maximum stress level and increases the safety factors of each structure, indicating that stress-related mechanical complications may not occur more easily.

Study on the Seismic Response of Shield Tunnel Structures with the Preload Loss of Bolts

Shield tunnels can experience preload loss in their connecting bolts during the operational phase, leading to changes in tunnel structure stiffness, which, in turn, affect the seismic performance of shield tunnels. A refined three-dimensional model of shield tunnel was established using the finite element method to study the impact of preload loss in connecting bolts on the seismic dynamic response of shield tunnels. An artificial viscoelastic boundary was used to simulate the propagation of seismic waves from an infinitely distant field. This study investigated the effects of different levels of preload loss on the seismic response of shield tunnels. In addition, the Arias intensity, which can reflect the degree of seismic impact on structures, was used to analyse the extent of damage to the tunnel. The conclusions drawn from the study are as follows: As the level of preload loss increases, the tightness of the segments during the static phase gradually deteriorates, and the maximum joint opening during the seismic loading phase continues to increase. Post-earthquake non-recoverable ellipticity and radial deformation progressively increase with an increase to preload loss level. Overall tunnel damage becomes more significant with the degree of preload loss increases depending on the Arias intensity. Preload loss leads to a decrease in the overall structural stiffness and an increase in longitudinal relative displacement. In conclusion, preload loss also affects structural failure mode and seismic performance. These research findings are of reference value for enhancing the seismic performance of shield tunnel structures and ensuring engineering safety.

Non-destructive detection of high-strength wind turbine bolt looseness using digital image correlation

Looseness of high-strength wind turbine bolts is one of the main types of mechanical failure that threaten the quality and safety of wind turbines, and how to non-destructively detect bolt loosening is essential to accurate assessment of operational reliability of wind turbine structures. Therefore, to address the issue of looseness detection of high-strength wind turbine bolts, this paper proposes a non-destructive detection method based on digital image correlation (DIC). Firstly, the mathematical relationships between the inplane displacement component of the bolt’s nut surface, the bolt’s preload force loss and the bolt loosening angle are both deduced theoretically. Then, experimental measurements are respectively conducted with DIC with different small bolt loosening angles. The results show that the bolt loosening angle detection method based on DIC has a detection accuracy of over 95%, and the bolt’s preload force loss evaluated by the deduced relationship has a good agreement with the empirical value. Therefore, the proposed DIC-based bolt loosening angle detection method can meet the requirements of engineering inspection, and can achieve quantitative assessment of preload forces loss of wind turbine bolt.

Screw preload loss under occlusal load as a predictor of loosening risk in varying dental implant designs

PurposeScrew loosening is a critical aspect of an implant design, as it can lead to implant failure. This study proposes a methodology and qualitatively assesses the potential of screw loosening risk for various types of screw heads and implant fixture-abutment connections. It is assumed that the risk of screw loosening is related to the drop in loosening moment under occlusal loads. The methodology and an assumption is verified by confronting the results with laboratory tests. MethodsNumerical simulations supplemented with semi-empirical equations were employed to estimate a loosening moment change under occlusal loads. The loosening risk was estimated by comparing the value before and after application of a compressive occlusal load of 150N. The procedure was carried out for 289 implant designs with smooth transition between flat to tapered shape of a screw head and an fixture-abutment connection. All analyses were conducted using Abaqus software. Pearson and Spearman correlation coefficients for normalised change in a screw loosening moment drop has been computed for numerical and laboratory tests. ResultsThe statistical analysis (Pearson, ρ = 0.8, Spearman, rs = 0.85) indicates very high correlation and confirms that the general tendencies observed in laboratory tests are reflected in the proposed procedure. The procedure was used for various geometries and the following results are presented: a screw loosening drop, implant stiffness and a tightening moment. The loosening moment drop achieves the extreme values of 6% and 24%. The biggest drop is an effect of a conical implant-abutment connection and a flat screw head while the lowest was recorded for a flat implant-abutment interface regardless of a screw head type. A low drop is also observed for a strongly conical screw head. ConclusionsThe proposed methodology exhibited very good correlation when confronted with laboratory tests, supporting a screw preload reduction under occlusal load as a key factor in screw loosening. Analysis across a wide spectrum of implant designs revealed geometry significantly impacts loosening potential under occlusal loads. Two key features were identified as favourable - an abutment-fixture butt joint and a tapered screw. The results also enable prediction of qualitative geometry effects on loosening risk.

Loss of preload of unprotected bolted joints considering environmental effects: A comparative study

An experimental program, with the aim to investigate and understand the preload loss behaviour of single-bolted double-lap joints subjected to environmental effects, was conducted in this paper. Four bolt types including plain bolts, galvanised bolts, stainless steel bolts and glass fibre reinforced polymer (GFRP) bolts were investigated and three environmental scenarios (i.e. indoor, outdoor and seawater immersion) were covered to represent varying degrees of environmental severities. Steel bushes attached with strain gauges were used to obtain strain variations continuously for such bolted joints with various bolt types under different environments. Severer environments clearly introduced earlier and higher preload loss. The bolted joints with galvanised bolts and stainless steel bolts showed larger preload loss compared to those using plain bolts in seawater immersion scenario; and the preload of joints with GFRP bolts dropped to nearly zero after a certain time of exposure under seawater immersion scenario. Modelling work was then developed to describe the preload loss over time, where the effects from environmental scenario (outdoor and seawater immersion scenarios) and bolt type (plain, galvanised and stainless steel bolts) were considered and also the initial rapid preload loss can be considered.

Preloaded bolted connections with duroplastic gap filling materials

AbstractIn steel construction, bolted connections are preloaded either for load‐bearing capacity reasons or for serviceability reasons. Single and multi‐section connections of wind turbines, offshore plants, bridges etc. are typical application examples. Imperfections due to fabrication and assembly may lead to a gap formation and consequently pose a risk e.g. for the controlled application of the required preload level as well as for the prevention of cavity corrosion. Therefore, the formation of gaps must be kept to a minimum. In cases where packing plates cannot be used, gap filling materials might be an alternative for gap compensation.MM1018 of Diamant Polymer GmbH represents a two‐component reaction resin system based on epoxy resins. Within the framework of the German (ZIM) cooperation project “Bri‐San‐T ‐ DuroFüllSta”, systematic investigations into the use of MM1018 (liquid and pasty) in preloaded bolted connections were carried out. In addition to the determination of slip factors according to EN 1090 2, Annex G under consideration of various practical boundary conditions such as gap thickness, curing time, temperature and surface condition, also relaxation tests were carried out to determine possible preload losses over the service life of the structure. The presented contribution intends to provide an insight into the main experimental findings for the gap filling material MM1018.

Experimental Investigations on load‐bearing Capacity and characteristic Preload of Lockstud Systems

AbstractThe joining technology Lockstud System combines the advantages of a bolt thread for making a tapped thread joint and the advantages of a lockbolt. On the tapped thread joining side, the bolt has a metric ISO thread. On the assembly side, the bolt has a grooved geometry like lockbolts of type A, B and C. This article publishes results on the mechanical‐technological properties, the assembly process with the initial preload, the preload losses due to embedding under long period of time and the load‐bearing capacity subjected to static and fatigue normal stress for Lockstud systems of nominal diameters M12, M16 and M20 (strength grade 10.9) compared to conventional bolt assemblies and lockbolt systems.

Effect of Antirotational Two-Piece Titanium Base on the Vertical Misfit, Fatigue Behavior, Stress Concentration, and Fracture Load of Implant-Supported Zirconia Crowns.

This study investigated the effects of antirotational titanium bases on the mechanical behavior of CAD/CAM titanium bases used for implant-supported prostheses. The aim was to assess the impact on the marginal fit, fatigue behavior, stress concentration, and fracture load of implant-supported CAD/CAM zirconia crowns. Forty titanium implants were divided into two groups: those with antirotational titanium bases (ARs) and those with rotational titanium bases (RTs). Torque loosening and vertical misfit were evaluated before and after cyclic fatigue testing (200 N, 2 Hz, 2 × 106 cycles). Fracture resistance was assessed using a universal testing machine (1 mm/min, 1000 kgf), and failed specimens were examined with microscopy. Three-dimensional models were created, and FEA was used to calculate stress. Statistical analysis was performed on the in vitro test data using two-way analysis of variance and Tukey's test (α = 0.5). Results show that the presence of an antirotational feature between the implant and titanium base reduced preload loss and stress concentration compared to rotational titanium bases. However, there were no differences in vertical misfit and resistance to compressive load.

Short implants: Influence of different diameters, torques, and transmucosal heights of straight prosthetic abutments on screw preload loss after cycling.

This study evaluated the influence of different implant diameters, insertion torques, and transmucosal heights on the loosening of abutments installed on short implants, after mechanical cycling. The Morse taper connection implants (n=96) tested were 5mm high, divided according to the platform diameter: 4 or 6mm. A universal abutment was coupled to each implant (with different transmucosal heights: 1 or 5mm). The sets were subdivided into 20- and 32-Ncm torque. After the cycle fatigue test, the detorque values were measured with a digital torque indicator. After mechanical cycling, the mean detorque values obtained for the abutment with 20-Ncm insertion torque were lower than for implants with 32-Ncm insertion torque, regardless of the platform diameter or transmucosal height. In the 20-Ncm torque group, there was no statistically significant difference in the detorque values between platform diameters or transmucosal heights. Otherwise, for 32-Ncm sets, a smaller platform diameter (4mm), and a longer transmucosal height (5mm) showed the lowest detorque values. In conclusion, implants placed with 32-Ncm insertion torque and abutments with 1mm transmucosal height and a 6mm implant diameter demonstrated the highest detorque values.

Pull-out behavior of torque-controlled expansion anchors in HPSFRC under different installation conditions

To study the pull-out behavior of torque-controlled expansion(TCE) anchors on high-performance concrete(HPC) and high-performance fiber-reinforced concrete(HPSFRC) substrates, 28 pull-out tests are set up. Different installation conditions of anchors, including the embedment depth(Hef) and the preload torque(Tinst), and the types of substrates, including no-fiber HPC and HPSFRC with 1% fiber content, are considered in the test. The split tensile(ft) and compressive strengths(fcu) of concrete are measured to evaluate the influences of fibers on the properties of concrete. Pull-out tests are conducted TCE anchors installed in C70 HPC/HPSFRC cylinder specimens by the displacement-control loading method. From test results, the relationship between failure mode, load-displacement behavior, pullout load-bearing capacity(Nu) and installation factors (Hef, Tinst, etc.) are analyzed. The preload loss law of the fastener system within 24 h is monitored. It is found that the larger Tinst leads to a larger preload loss rate, and the loss in Tinst tends to be stable within 5–7 h. A modified model of Nu of TCE anchors in HPSFRC is proposed. The prediction accuracy of the modified model and the existing models (CCD model, Toth et al's model) is compared; both CCD and Toth et al's model underestimate Nu, which would lead to uneconomical over-design, and the prediction results of the modified model are in a good agreement with the experimental results.