Increase In Axial Load Research Articles

Cyclic behavior of oval hollow section (OHS) beam-columns

This paper seeks to gain an in-depth understanding of the seismic behavior of oval hollow section (OHS) beam-columns through experimental and numerical investigations. Quasi-static tests on nine OHS beam-column specimens with varying tube thicknesses, axial load ratios and bending directions are conducted, where the failure mode, yield/ultimate strength, ductility, and energy dissipation-related quantities are discussed in detail. Following the experimental program, a numerical study on a total of 360 OHS beam-column models with broadened section and material parameters is further conducted, and design recommendations for OHS beam-columns subjected to seismic conditions are proposed. Among other findings, the study reveals that local buckling at the fixed base is the governing failure mode for the considered members, but the failure mechanism varies under different bending directions. The flat web plate of the OHS is a critical area which is prone to local buckling, although stable post-buckling behavior can be exhibited. Earlier local buckling and more severe damage to the column base are induced when the axial load increases, resulting in decreased ductility. The plastic moment resistance is better mobilized with the increase in the tube thickness and when under major axis bending. The parametric study finally leads to practical ductility-oriented and strength-oriented design curves, where both least-square regression and lower-bound solutions are provided.

Modeling of Thermal Contact Resistance of Ball Screws Considering the Load Distribution of Balls

Abstract A new analytical method for the modeling of the thermal contact resistance of ball screws considering the load distribution of balls is proposed in this research. The load on balls is analyzed by the force analysis of ball screws, and then, the thermal contact resistance is obtained by the minimum excess principle and Majumdar–Bhushan (MB) fractal theory. The proposed method is validated by experimental results. The comparison with experimental and former results indicates that it is an effective method to evaluate the thermal contact resistance of ball screws. On that basis, effects of axial load, axial pretension, and geometry error of balls are discussed. It is concluded that the thermal contact resistance of ball screws increases along with axial load increase. The load on balls all decreases with axial pretension increase, and the thermal contact resistance of ball screws decreases with the axial pretension increase as well. When the axial load is applied on the nut in an axial-pretension ball screw, the load distribution in Nut A or B becomes less homogenized when the nut moves from nut position parameter ξ = 0 to 1. When the nut moves to ξ = 0.25, the thermal contact resistance will reach a minimum value, and it gets a maximum value at the nut position ξ = 1. The interval range of load and thermal contact resistance are obtained via uncertain analysis. It is concluded that the geometry error has much greater effects on the balls far away from the spacer.

Experimental Research on Bending Bearing Capability of Grouted Double Mortise‐Tenon Joint for Prefabricated Metro Station Structure

The grouted mortise‐tenon joint, invented as the connection between the large prefabricated elements, is the most important component in the prefabricated underground structures. This paper conducts analysis of load‐carrying capacity performance and failure mode with 1 : 1 prototype test in key working direction of different double mortise‐tenon joint types for the prefabricated metro station. The resistance moment is developed and used to analyze the bending bearing characteristic curve, and the corresponding test results of each stage of the characteristic curve are described in detail. In addition, the bending bearing performance of different types of double‐tenon joints under different load conditions is compared. The test results clarify the ultimate failure mode of double‐tenon joint and the variable bearing capacity characteristics of the joint with the increase in axial load and explain the bearing performance of each stage. It is also found the auxiliary pretightening device is helpful to delay the appearance of cracks and improve the bearing capacity, especially when it is set on the tension side. The research results have important application value for the joint design of prefabricated metro station structures.

Research on comprehensive stiffness characteristics of angular contact ball bearings under multi-factor coupling condition

In order to research the dynamic performance of angular contact ball bearings of high-speed motorized spindles in detail, based on Hertz contact theory and bearing quasi-static model, considering the influence of centrifugal force, gyroscope moment and thermal effect on bearing operation, the modified quasi-static model is established to calculate the bearing contact stiffness. Then, considering the influence of temperature on the dynamic viscosity of lubricating oil, film stiffness model of bearing is also presented. On the basis, the bearing comprehensive stiffness model is proposed, and the influences of combined load and rotational speed on the bearing stiffness are investigated. The results show that as the speed increases, the radial contact stiffness increases, while the axial and angular contact stiffness decrease, the dynamic viscosity of the lubricating oil decreases, the film stiffness decreases and the comprehensive radial, axial and angular stiffness decrease. With the increase of axial load, the radial, axial and angular contact stiffness increase, the comprehensive stiffness increases. When the radial load increases, the radial, axial and angular contact stiffness decreases, while the comprehensive stiffness increases. It is found that the comprehensive stiffness considering the temperature is larger than without consideration of the temperature.

Analyzing Vibration Mechanism of Angular Contact Ball Bearing with Compound Faults on Inner and Outer Rings

This paper investigates a method to dynamically model compound faults on the inner and outer rings of an angular contact ball bearing as well as their effects on its dynamic behavior. Gupta’s dynamic modeling method is used to consider changes in the deformation and direction of the contact load when the ball passes through the damaged area and to develop a dynamic model of compound faults in the angular contact ball bearing. The step‐changing fourth‐order Runge–Kutta method is used to solve the dynamic compound fault model. The time‐domain signal of vibration responses in the case of a single fault in the inner and outer rings exhibited a certain periodicity, and the frequency of faults in the envelope spectrum was clear. By comparison, the periodicity of compound faults was not clear. The signals of compound faults were decomposed by the dual‐tree complex wavelet transform to identify their characteristic frequency. Errors occurred between the characteristic frequency of the theoretical fault and its simulated value. They increased with the rotational speed and decreased with an increase in axial load, whereas the influence of radial load on them was minor. For compound faults on the inner and outer rings of an angular contact ball bearing, this study provides a modeling method that can describe changes in the deformation and direction of the contact load when the ball passes through the damaged area of the inner and outer rings. The work here can provide an important foundation for fault identification in angular contact ball bearings.

Behaviour of steel columns with realistic boundary restraints under standard fire

The significance of the occurrence of linearly varying rotational restraint with an increase in temperatures during building fires is outlined. A detailed parametric study conducted on seven hundred and twenty specimens using ABAQUS® investigates the effect of linearly varying rotational restraint on the stability of steel columns under standard fire was presented. Surface plots are drawn to understand the interactive effect of slenderness ratio of a column, axial boundary restraint, and temperature (buckling and critical) with linearly varying rotational restraint for different pre-applied axial load and moment ratios. The prevalence of axial force (Pbuckle/PO) at the ends of the columns due to axial restraint against thermal expansion is also assessed and plotted for the above parameters considered. It was found that buckling temperature and buckling load decreases with an increase in pre-applied axial load and moment while critical temperature variation was insignificant. The interaction equation useful for designers is proposed based on the non-linear regression analysis for assessing the critical temperature of steel columns under standard fire. It was found that the Euro code interaction equation (Eq. 4.21) predicted the critical temperature of a column with varying rotational restraint with reasonable accuracy.

Mechanical behavior of 3D printed syntactic foam composites

A three-dimensional printed (3DP), polymer based syntactic foams are developed using hollow glass micro balloons (GMB) dispersed in high density polyethylene (HDPE). This work presents the buckling and vibration response of 3D printed foams subjected to axial compression. The buckling load is estimated using Modified Budiansky Criteria (MBC) and Double Tangent Method (DTM) through the load–deflection plots. The first three natural frequencies and their mode shapes are computed as a function of axial compressive load. It is noted that the natural frequency reduces with an increase in axial compressive load. It is also observed that with an increase in GMB %, the natural frequencies and critical buckling load increases. In mode-1, the natural frequency decreases in pre-buckling regimes and increases exponentially in post-critical loading conditions. Analytical solutions obtained from the Euler-Bernoulli-beam theory are compared with experimental results. It is noted that the fundamental frequency approaches zero when the axial load is equal to the critical load. The critical buckling load is estimated through the vibration correlation technique and compared with the results obtained using DTM and MBC methods. The property map is plotted for buckling load against the density of various composites.

Vibro-acoustics response of an isotropic plate under non-uniform edge loading: An analytical investigation

Analytical studies carried out on the vibro-acoustic response behavior of an isotropic plate under non-uniform edge loads subjected to steady-state mechanical excitation is presented. An analytical method based on the energy approach is used to calculate the buckling load (Pcr). Free and forced vibration responses of the plate are obtained using an analytical method based on Reddy's third-order shear deformation theorem (TSDT) while sound radiation behavior is analyzed using Rayleigh Integral. Results revealed that Pcr is significantly influenced by the nature of non-uniform edge load. Similarly, natural frequencies reduce with an increase in axial compressive load due to a reduction in structural stiffness. Vibration and acoustic resonant amplitudes are affected by the intensity of the compressive load. Sound transmission loss reduces with an increase in compressive load magnitude and the effect is significant in the stiffness dominant region.

Fretting fatigue damage mechanism of Nickel-based single crystal superalloys at high temperature

A novel high temperature fretting fatigue test apparatus was developed to investigate the fretting fatigue mechanism of Nickel-based single crystal (NBSX) superalloys at elevated temperature. The fretting fatigue tests were carried out under 5 loading conditions at 600°C. Results showed that the fretting fatigue life decreased with the increase of axial load and normal load. Metallographic observations revealed that surface peeling, delamination occur at the contact area. Energy dispersive spectrum (EDS) analysis showed that the surface material was oxidized, and the oxides will be compacted onto the contact surface and form a glazed layer. Besides, many micro cracks are observed at the contact surface that are nearly perpendicular to the fretting direction. These micro cracks would either be eliminated due to the large relative displacement or grow into the main crack, which are supposed to be the dominant source of fretting fatigue failure. Multiple fretting fatigue cracks initiate at the contact leading edge area and grow along the (100) plane that is nearly perpendicular to the fretting direction. Then the crack propagation direction will deflect from (100) plane to a series of {111} planes and the specimen eventually failed. The combined effect of fretting wear and crystallographic slip is the cause of fretting fatigue failure.

Feasibility of textile fabrics for strengthening of concrete column

Renovation and rehabilitation of concrete structures become inevitable when structures reach their service life. Rehabilitation or strengthening of concrete structures using fiber reinforced polymers and textile reinforced mortar are the most common and effective methodologies. However, these rehabilitation techniques are expensive hence cheaper alternatives need to be explored for sustainable concrete structures. Current research program was planned to investigate the efficiency and effectiveness of textile reinforced mortar using locally available textile fabrics on upgrading structural performance of concrete columns. Six locally available fabrics were characterized to select best fabrics for strengthening of concrete columns. Plain Concrete Columns (PCC) were strengthened using epoxy and mortar and selected fabrics with different number of layers. All specimens were tested under uniaxial compression. Results revealed that an increase in axial load carrying capacity ranging between 32% and 58% can be achieved using fabrics along with epoxy. On replacing epoxy with cement mortar, a further increase of up to 23% can be achieved under specific conditions. The use of three layers of textile fabrics might be considered effective as on addition of further layers, the strength gain is not significant. The presented results indicate that the use of textile fabrics may prove to be a promising method of upgrading column’s structural performance.

A Study on the Friction Dynamic Response of Asphalt Pavement Considering the Unevenness

In order to quantitatively analyse the influence of pavement unevenness on the stress of asphalt pavement, a tire-road coupling model with stable rolling was established. Sinusoidal wave is used to describe the pavement unevenness, and based on the established tire-road coupling model, different conditions of axle load and base elastic modulus are used to analyse the influence of unevenness on the dynamic response of asphalt pavement. The results show that the influence of unevenness on vertical stress of asphalt pavement increases with the increase of axial load. As the elastic modulus of base increases, the vertical stress of asphalt layer will decrease, while the vertical stress of base layer increases. But the influence of unevenness on dynamic response of asphalt pavement cannot be eliminated. Therefore, the unevenness should be taken into account in the simulation of real road surface.

Axial Load Monitoring for Concrete Columns Using a Wearable Smart Hoop Based on the Piezoelectric Impedance Frequency Shift: A Feasibility Study

Concrete columns are critical in supporting the weight of an entire structural frame and also play a key role in force transferring among structural members. Therefore, integrity of the columns, especially their axial load bearing capacity, directly affects the stability and safety of the entire structure. In this study, a wearable smart hoop is designed to monitor the axial load of the concrete columns. The smart hoop measures the shift in impedance frequency of its integrated piezoelectric transducer and correlates the frequency to the structural state of the column. In order to validate the feasibility of the smart hoop, an experiment on two concrete columns with different dimensions is carried out. The smart hoop is installed on each column. Then, an increasing axial load was applied onto the specimen, and the admittance of the PZT patch is acquired under different load levels by using an impedance analyzer. Finally, frequencies corresponding to the peak and trough in the susceptance of the admittance signal are collected as the monitoring index to estimate the axial load variation on the specimen. The experimental results demonstrated a downward shift in frequency corresponding to an increase of axial load. The results validate the feasibility of the wearable smart hoop in monitoring axial load for concrete columns and show potential for retrofit on existing columns.

Dynamic mechanical characteristics and fracture mechanism of gas-bearing coal based on SHPB experiments

To investigate the dynamic characteristics and fracture mechanisms of gas-bearing coal samples, a split Hopkinson pressure bar experimental system (SHPB-GAS) was built, using which dynamic impact experiments of gas-bearing coal were performed. Stress wave signals were collected and processed to analyze changes in strain characteristics with time. Relationships between dynamic strength, failure strain, and various factors such as axial static load, confining pressure, gas pressure, and impact load were analyzed. Our results show that dynamic strength and failure strain increased with the increase of confining pressure and impact load, but decreased with the increase of axial static load and gas pressure. Furthermore, evolution of dynamic cracks and failure mode of gas-bearing coal were analyzed, with the results indicating that samples presented axial tension fracture under the combination loading (axial static load, confining pressure, gas pressure and impact load). The effects of these four factors on the fracture evolution in coal samples were then discussed. Under these conditions, the fracture mechanism of gas-bearing coal was investigated and the effects of shear stress and normal stress on the fracture surface were illustrated. Our findings show that gas flow over the coal surface will increase shear stress along the fracture surface, in turn inducing coal fracture.

Effect of load, sliding distance and sliding velocity on the wear properties of aluminum alloy AA5052

Aluminum alloys are widely used in engineering applications. In motion established contact applications, wear is an inevitable phenomenon. In this study, the wear mechanism of AA5052was explored using pin-on-disc tribometer. The wear test parameters namely load (kg), sliding distance (m), and velocity (m/s) were varied according to central composite design. The wear tracks of the worn specimens were observed using high-resolution scanning electron microscope and the elemental composition was analysed using energy dispersive X-ray spectroscopy. A hybrid model integrating the linear function and radial basis function was developed to explore the effect of load, sliding distance, and sliding velocity on the wear rate of the AA5052 alloy. The results indicate that increase in axial load and sliding distance decreases the wear rate of the AA5052 alloy.

Transverse Bending and Vibration Characteristics of a Simply Supported Discontinuous Beam under Axial Loads

An abrupt change of stiffness may occur at the interface of discontinuous beams, and the transverse stiffness and vibration characteristics of this part of the beam can be significantly different from those of the remaining beam. In this paper, the relationship between the internal force and the displacement of discontinuous beams is analyzed based on the Timoshenko beam theory, and the equations for the deflection curve and free vibration of a simply supported beam under axial load are analytically derived. The normal function of the transverse vibration equation is obtained by separating variables, while the endpoint displacement is derived using the method of transfer matrix. The deflection and free vibration frequency of the discontinuous beam under different axial loads and connection stiffness were calculated. The results show that with an increase of stiffness, the deflection and free vibration frequency decreases and increases exponentially respectively. Moreover, the free vibration frequency of each order decreases with an increase of axial load, and the lower order frequency is more dependent on the axial load.

Experimental method for identifying high-coercive permanent magnets

A bench was developed and a method for identifiying a pilot batch of high-coercive permanent magnets (HcPM) made of the same brand of neodymium-iron-boron alloy (NdFeB) was proposed. The tested samples from the trial amount of HcPM have the shape of a disk, a rectangular prism and an axial direction of magnetization. The criterion for the identification of the HcPM in each trial amount is their identical volume magnetization, which is taken into account by the standard deviation of the constructed experimental curves of the interaction electromagnetic force for each test sample of a permanent magnet from the trial amount with a magnetic reflector when the distance between them changes. As a magnetic reflector, a more powerful permanent magnet with a disk shape and a height exceeding the height of the permanent magnet test sample is used. Neglecting the procedure of identification of the HcPM from the trial amount leads to disruption of the electromagnetic systems incorporating them, for example, during the development of synchronous electric machines inductors based on permanent magnets, shaft beating, increased vibration of the operating elements, an increase in radial and axial load on the bearings, reduced service life and failure of electric machines during operation are observed.

Non-spherical single cone bit tooth failure analysis and tooth load test

Single cone bit is frequently used in slim-hole drilling field. To solve the problems of the spherical single cone bit during drilling process, a new type of single cone bit is designed, and field test is carried out. In this paper, the statistical analysis of tooth wear is done, and the causes of cutting tooth wear and protects radial tooth eccentric wear are analyzed in detail. In order to figure out the causes of tooth failure, the tooth load of non-spherical single cone bit was measured by experiment method and the change regularity of tooth load was statistically analyzed. The results show that the axial load is greater than the tangential load and radial load during drilling process. The axial load increase is more obvious with increase of weight on bit (WOB), but the tangential load and radial load change less. With increase of axle tilt angle of bit axis, the axial load and tangential load is reduced at the end of cone, but the radial load is increase. However, the axial load, tangential load and radial load of other's tooth is increase with increase of axle tilt angle of bit axis. The experiment results explained the cause of tooth wear, and it was important to understand the mechanism of tooth wear, optimize the structure parameters of bit, and understand the movement of bit in the well.

Dynamic axial contact stiffness analysis of position preloaded ball screw mechanism

This article establishes an axial contact stiffness model of position preloaded ball screw mechanism based on Hertz contact theory. The analysis of dynamic axial contact stiffness is one of the foundations of the research on the dynamic characteristic of the ball screw feed drive system. The model takes into account the coupling relationship between the contact angle and the normal contact force, as well as the coupling relationship between the elastic deformation and the contact deformation coefficient. The static and dynamic axial contact stiffness characteristics of the preloaded ball screw mechanism are studied. The numerical analysis result shows that the static contact stiffness of the preloaded ball screw mechanism increases with the increase in the preload and decreases with the increase in the axial load. The dynamic contact stiffness of the preloaded ball screw mechanism increases with the increase in the screw’s rotational speed. The variation range of dynamic contact stiffness increases with the increase in axial load under the same preload. And the variation range of dynamic contact stiffness decreases with the increase in preload under the same axial load. The axial contact stiffness model established in this article can be used to analyze either static or dynamic contact stiffness of position preloaded ball screw mechanism.

Modeling and application of thermal contact resistance of ball screws

Aiming at determining the thermal contact resistance of ball screws, a new analytical method combining the minimum excess principle with the MB fractal theory is proposed to estimate thermal contact resistance of ball screws considering microscopic fractal characteristics of contact surfaces. The minimum excess principle is employed for normal stress analysis. Moreover, the MB fractal theory is adopted for thermal contact resistance. The effectiveness of the proposed method is validated by self-designed experiment. The comparison between theoretical and experimental results demonstrates that thermal contact resistance of ball screws can be obtained by the proposed method. On this basis, effects of fractal parameters on thermal contact resistance of ball screws are discussed. Moreover, effects of the axial load on thermal contact resistance of ball screws are also analyzed. The conclusion can be drawn that the thermal contact resistance decreases along with the fractal dimension D increase and it increases along with the scale parameter G increase, and thermal contact resistance of ball screws is retained almost constant along with axial load increase before the preload of the right nut turns into zero in value. The application of the proposed method is also conducted and validated by the temperature measurement on a self-designed test bed.

Influence of Incremental Impact on the Damage of Coal‐Rock under Unidirectional Constraint

Taking the briquette sample as research object, the influence of the incremental impulse (momentum) on the damage of coal‐rock under different uniaxial axial pressure was studied by using the self‐developed pendulum impact dynamic loading test device, cooperating with the ultrasonic detection device. Meanwhile, the influence of constant impulse on the damage degree of coal‐rock was compared. The results show that the damage degree of coal‐rock increases with the increase of the impulse, and the damage fitting curve is upward concave, indicating that the coal sample tends to accelerating failure. Moreover, with the increase of axial pressure, the variation gradient of the damage degree of coal‐rock tends to moderate and the cumulative damage degree decreases under the same impulse, and the impact resistance of coal‐rock increases. When the impulse is constant, the damage degree of coal‐rock increases with the number of impact, and the damage curve is upward convex, indicating that coal‐rock has a tendency to slow down the damage. The cumulative damage degree of coal‐rock decreases with the increase of axial pressure, and the number of impact needed to destroy coal‐rock is increased. In addition, the damage model of coal‐rock was proposed, and the criterion of coal‐rock damage was obtained, which shows that the damage degree of coal‐rock increases with the increase of impact load and decreases with the increase of static axial load.