Gear Test Research Articles

Simulation, Fabrication and Testing of UAV Composite Landing Gear

This study concerns the use of the fused filament fabrication technique to create models of the landing gear of an unmanned aircraft. These components are made of filament with short fibers (chopped fibers) of carbon fiber and fiberglass. In order to identify the material with the high mechanical strength, the designed models were subjected to a finite element analysis and to a three-point bending test, followed by a microscopic examination of the tested components. Following a comparative study, both the finite element analysis results and the three-point bending test results provided similar results, with a relative error of 2%, which is acceptable in the aviation field. After analyzing all the results, it was found that the carbon fiber-reinforced polymer material has the highest mechanical performance, with a bending strength of 1455 MPa. Among the fused filament fabricated landing gears, the one with the best mechanical performance was polyethylene terephthalate with short carbon fiber, which had a bending strength of 118 MPa. Microscopic analysis of the landing gear models, manufactured by the fused filament fabrication process, indicated the typical defects of composite filaments: voids and interlayer voids.

Performance of selective laser sintered polyamide spur gear under dry and lubricated conditions

The durability of a selective laser sintered (SLS) polyamide gear was evaluated using an in-house gear test rig under dry and oil-lubricated conditions. The lubricated SLS gear exhibited inferior contact fatigue performance at lower torques than that under dry conditions. Cyclic contact stress coupled with sliding motion diffuses the lubricating oil into the porous subsurface and reduces the contact fatigue strength of the gear tooth. The failure of the SLS gear under dry conditions exhibited the polishing effect, thermal softening with surface cracks, and thermal bending at 1.8, 2.5, and 3.5 Nm, respectively, whereas failure of the SLS gear under the oil-lubricated condition was only pitting for all the considered conditions. The lubricated gear exhibited superior performance at a higher torque than the gears in the dry-running condition, owing to its improved thermal stability.

Applying ionic liquids as oil additives for gearboxes: Going beyond the state of the art by bridging the nano-scale and component level

Ionic liquids (ILs) have been used effectively in many applications for reducing problems related to friction and wear. In this work, the potential of ILs as an anti-wear and extreme pressure lubricant additive for high load-carrying gearbox applications such as helicopter transmissions has been studied. Two halide-free ILs: {{rm{P}}_{8881}}{left({{rm{BuO}}} right)_2}{rm{PO}}_2^ - (1) and {{rm{P}}_{8881}}{left({{rm{MeO}}} right)_2}{rm{PO}}_2^ - (2), which are blended at 5 wt% each into a standard non-additivated FVA2 base oil (BO) are examined. Their solid—liquid interface, friction and load-carrying capacity, and wear (scuffing) behavior are studied on the nano-, lab-, and component-scale, respectively, at a different range of temperature and loading conditions by using the atomic force microscopy (AFM), Schwing—Reib—Verschleiß (SRV) friction tests, and Brugger tests, as well as forschungsstelle für zahnräder und getriebebau (FZG) back-to-back gear test rig. The AFM analysis shows nearly no change of adhesion over the full range of studied temperature for the IL blends compared to the BO. Similarly, IL blends demonstrate a very stable coefficient of friction (COF) of around 0.16, which even decreases with increasing test temperatures ranging from 40 to 120 °C. A clear reduction in COF up to 25% is achieved by adding only 5 wt% of the investigated ILs in the BO, and the Brugger tests also show a pronounced enhancement of load-carrying capacity. Finally, on the component-scale, a significant improvement in gear scuffing performance has been observed for both used IL blends. A detailed characterization of the wear tracks from the SRV friction tests via the transmission electron microscopy (TEM) revealed the formation of a phosphate (P—O)-based amorphous tribo-chemical layer of about 20 nm thickness. Therefore, this work may present an approach for ILs to be used as an additive in conventional lubricants due to their ability to enhance the lubrication properties, making them an alternative lubricant solution for high load-carrying gearbox applications.

In situ investigation of the influence of varying load conditions on tooth deformation and wear of polymer gears

A new method for in situ deformation and wear measurement of polymer gears has been developed at the LKT and validated for polyamide-66 (PA66) gears at constant loading torque and rotational speed. This contribution contains a more comprehensive validation of the newly developed test method by examining polybutylenterephtalate (PBT) gears under varying loading conditions. The deformation test method is based on measuring and analysing the timing differences between the index pulse signals of rotary encoders on the input and output shaft of the test rig. Since the total tooth deformation is a combination of different effects, such as elastic and plastic deformation, thermal expansion and wear, different testing modes with a low and a high torque level are implemented to separate the effects of elastic deformation on the one hand and plastic deformation and wear on the other hand. As a consequence, the new test rig design allows a deeper understanding of the wear and deformation behaviour of polymer steel gear sets over time. This potential is used to analyse the interactions of different loading conditions on the time-dependent deformation of plastic gears. The influence of both, different transmitting torques and rotational speeds is examined.The test method shows good correlation with well-established ex situ measurements for different combinations of rotational speeds and loading torques and thus could be validated. Long-term gear tests under varying rotational speeds and loading torques show increasing wear and deformation at higher speeds and torques confirming the state of the art described in the literature. In addition, the time dependent deformation behaviour at different load conditions due to superposition of wear and plastic deformation could be analysed in detail.

Failure analysis of POM ternary nanocomposites for gear applications: Experimental and finite element study

The main purpose of the present study is to assess the failure behavior of polyoxymethylene/carbon black/CaCO3 ternary nanocomposite gears by employing an experimental gear test setup and a gear renewal technique. The failure-related factors including surface temperature, tooth wear, and failure analysis at macro- and micro-scales were studied. The tooth surface temperature was measured continuously based on an online-measuring approach. The tooth wear was calculated using microscopic images and software analysis. The maximum contact stress on meshing teeth surfaces was specified by finite element analysis. According to SEM micrographs, the application of both nanostructures contributed to a more uniform distribution of each nanophase within the POM matrix. The gear test results indicated an enhanced tooth resistance and service life of up to 58% and 125%, respectively, for ternary nanocomposites relative to neat POM gears. The tooth surface temperature was reduced for nanocomposite gears due to the promoted heat transfer and thermal stability. The tooth deformation and cracking were highly suppressed for ternary nanocomposite gears at failure. The evaluation of teeth surface damages at micro-scale revealed the suppression of plastic flow and material adhesion for ternary nanocomposites.

Analyzing the Life Prediction of Spur Gear based on Vinyl Ester with Different Fibre Proportion

The gear is an essential part of every mechanical power transmission system, as well as most industrial rotating machinery. Gears may grow to dominate as the most effective mechanism for transmitting power in future machines due to their high degree of durability and compactness. The vinyl ester resin have high strength and low frictional of porous carbon material. The Vinyl ester resin is used as a reinforced material in plastic gear. In this work, Vinyl Ester and Glass fiber composite material with different proportions were equipped for strengthen cast plastic gear. The spur gear pair was used as the test gears, and the glass transition temperature and fatigue tests were used to determine the gear's life span. Finally, the composite gear has to be analyzed.

A Study on Preparation and Property Evaluations of Composites Consisting of TPU/Triclosan Membranes and Tencel®/LMPET Nonwoven Fabrics.

This study investigated eco-friendly antibacterial medical protective clothing via the nonwoven process and characteristic evaluations. Firstly, Tencel® fibers and low melting point polyester (LMPET) fibers (re-sliced and granulated from recycled PET bottles) were mixed at different ratios and then needle punched at diverse needle rolling depths. The influences of manufacturing parameters on the Tencel®/LMPET nonwoven fabrics were examined in terms of mechanical properties, water vapor transmission rate, and stiffness. Next, Tencel®/LMPET nonwoven fabrics were combined with thermoplastic polyurethane (TPU)/Triclosan antibacterial membranes that contained different contents of triclosan using melt processing technology. The resulting Tencel®/LMPET/TPU/Triclosan composites were characterized via different measurements; an optimal bursting strength of 86.86 N, an optimal horizontal tensile strength of 41.90 N, and an optimal stiffness along the MD and CD of 8.60 cm were recorded. Furthermore, the Tencel®/LMPET/TPU/Triclosan composites exhibited a distinct inhibition zone in the antibacterial measurement, and the hydrostatic pressure met the requirements of the EN 14126:2003 and GB 19082-200 disposable medical protective gear test standards.

Time-resolved ex situ Raman/FT-IR spectroscopic study of structural changes in polymeric gears during operation: Towards the development of operando spectroscopic systems for polymer gears

In this study, time-resolved ex situ Raman and Fourier transform infrared (FT-IR) spectroscopy were performed to monitor structural changes in a polyamide (PA) 66 gear during operation and reveal the failure mechanisms of the material. A gear test was performed using a lab-built gear tester, which is a power-absorption type. Raman and FT-IR analyses were performed on the side gear surfaces around the root of the gear (at the side of the active flank), where a bending stress is continuously loaded during operation. The results showed that the crystallinity changed, amide related bonds were broken, trans-gauche (TG) transformation occurred, and a change in the inner stress condition of the PA66 gear occurred over time. It was concluded that these changes interact with each other during operation and are related to the failure of the PA66 gear, such as the initiation of the plastic gear degradation.

Proximate Model of Gear Drive Units Based on Dimensional Analysis for Wear Process Evaluation

Excessive wear of gears will not only cause noise and vibration in the transmission system, but also reduce transmission efficiency and accuracy in severe cases, causing irreversible losses to the transmission system. It is desirable to develop a micro-gear unit model for evaluating the wear process and predicting the failure time of large gear units (such as wind turbine gear units), reducing losses due to sudden failures. Based on the Buckingham pi-theorem of dimensional analysis and Hertz formula, the similarity ratio of each parameter of the gear wear process was proposed. The maximum equivalent stress is calculated by establishing the FEM model and comparing it with the theoretical contact stress calculated by the Hertz formula, and the results were relatively consistent. Two pairs of gear friction and wear experiments with similar parameters were carried out to compare the wear evolution performance of two similar gears. The friction performance process of the test gears was observed by particle counter and analytical ferrograph. The results show that the friction and wear processes of the two groups of gears with similar parameters have a certain correlation, which was consistent with the proposed similarity model. The similarity model combined with the observation results of abrasive particles has a certain application value for the evaluation of the wear state of the transmission system.

Experimental research of wear-fatigue interaction of gears

Gear failures are commonly caused by wear and fatigue and past research on gear failures has primarily focused on individual failures. A gear testing machine was developed to explore the mechanism of gear wear-fatigue interaction, and four sets of wear-fatigue interaction tests were performed by changing the operating conditions of the gear drive by regulating the quantity of lubricant in the test gearbox. The K-S test method was used to investigate the gear life distribution under wear-fatigue interaction. The frequency domain properties of the wear-fatigue interaction were compiled and analyzed using Fast Fourier Transform (FFT) analysis. A coordinate measuring machine was implemented to obtain the exact amount of wear at each stage of the gear test. The mechanism of gear wear-fatigue interaction was analyzed by scanning electron microscope observation of tooth surfaces. The results are as follows. The life distribution under wear-fatigue interaction obeys a log-normal distribution. With the increase of the lubrication the pitting fault occurs, the fault gear rotation frequency and its harmonic frequency appear in the low frequency region, and its amplitude increases with the increase of the pitting fault. In the high-frequency region, a sideband with the faulty gear rotation frequency as the interval appears around the meshing frequency and its two times frequency, and its amplitude increases with the increase of the pitting fault. With the decrease of lubrication, the gear wear failure increases, the amplitude of the meshing frequency and its two times frequency increases in the high frequency region. In the gear transmission process, wear and fatigue exist in a competitive relationship of mutual constraints.

A combined experimental-numerical approach for life analysis and modeling of polymer-based ternary nanocomposite gears

The life assessment of polyoxymethylene (POM), POM/carbon black (CB), and POM/CB/nano precipitated calcium carbonate (NPCC) ternary nanocomposite gears was carried out using experimental and numerical techniques. The gear life tests were conducted under constant loading up to failure. Finite element analysis (FEA) was utilized to calculate contact and root stress values. The characterization tests indicated the proper particle-polymer adhesion and the uniform distribution of nanoparticles in the matrix. According to experimental gear tests, POM/CB/3NPCC gears showed the highest lifetime at all applied loads, attributed to synergetic reinforcing effects of CB and NPCC in the POM matrix. The SEM examination of tooth microstructure displayed a smooth surface, characterized by minor indications of surface crack, plastic flow, and debris formation, with the application of 1.5 and 3 wt% NPCC, against pristine POM. The finite element analysis of gears indicated that the single tooth area, during teeth contact, was shorter than the theoretical value. In addition, the contact and root stress values were higher for nanocomposite gears than pristine POM. The experimental and numerical data were applied to obtain the stress-life diagrams for pristine POM and POM nanocomposites and propose a model for life prediction of the gear samples.

Wide-range fiber Bragg grating strain sensor for load testing of aircraft landing gears

The impact load borne by landing gear during the take-off and landing of aircraft is an important parameter in structural health monitoring. A wide-range fiber Bragg grating (FBG) strain sensor with a surface-attached carbon fiber matrix is designed to measure the strain and load of aircraft landing gear structures for monitoring requirements. The sensor's performance was tested, and its strain sensitivity is 1.14 pm/μɛ. In addition, a multivariate linear load regression method was proposed, which can simultaneously monitor and predict the three-way load of landing gear, and the ground static loading test was carried out to verify the feasibility of this method. The result shows that the regression load error calculated by this method is within 5%, which meets the actual engineering requirements.

Efficiency and temperature of spray lubricated superfinished spur gears

Gearboxes are one of the most power dense systems used today, and in certain instances their limiting factor is the ability to evacuate heat from the gear contact. This work analyses the efficiency (i.e. heat generation) and tooth temperature in the three lubricating conditions dip, into mesh spray and out of mesh spray for superfinished gears which are then compared to ground gears. A back-to-back gear test rig is employed to test maximum contact pressures at the pitch of 0.59 to 0.96 GPa and pitch velocities from 0.5 to 20 m/s at a controlled lubricant temperature of 90 °C. The results show superfinished gears have higher mesh efficiency and lower gear tooth and bulk temperatures, hence lower heat flux compared to ground gears in all lubricating conditions.

Analysis of retraction performance of aircraft landing gear in high and low temperature environment

Abstract In order to solve the problem that the internal mechanism parameters of the aircraft landing gear are difficult to measure and retractable, the retractable performance of the landing gear under high and low temperature environments is studied. This paper simplifies the retractable mechanism of the landing gear by analyzing the motion mechanism of the aircraft landing gear. The degree of freedom of the retractable mechanism is calculated to verify the accuracy of the simplified rear landing gear retraction mechanism. The simulation model of landing gear retraction mechanism under high and low temperature environment is constructed by Patran. The component deformation and shaft clearance of the retractable mechanism under low temperature (-55°C) and high temperature (74°C) environments are analyzed from the overall and detail dimensions. The quantitative effect of ambient temperature on the deformation of the retractable mechanism of the landing gear is studied. Then Adams is used to establish the kinematics simulation model of the retractable mechanism, and the friction coefficient of the kinematic pair under different ambient temperatures is incorporated. Based on the historical data of the high and low temperature environmental test of the landing gear, the correctness of the model is verified. The influence of the environmental temperature on the driving torque, movement angle and movement time of the retractable mechanism is quantified. The problem that the deformation parameters and motion characteristics of the retractable mechanism of the landing gear are difficult to measure is solved, and the research method of retractable performance of the landing gear mechanism under different ambient temperatures is formed.

Failure analysis of nylon gears made by additive manufacturing

Additive manufacturing enables fast manufacturing of polymer gears directly from a 3D model. Failed polymer gears can be replaced easily and quickly using many different materials. Mechanical and thermal characteristic of gears manufactured using additive manufacturing are mostly dependent on selected manufacturing parameters and material. In this research, the influence of the most important manufacturing parameter (infill percentage) on failure types and service life of additive manufactured nylon gears is experimentally investigated. The experimental tests were carried out using a custom-made gear testing device. Samples with 20, 40, 60, 80 and 100% of infill volume were tested. Infill type, shell thickness, and manufacturing speed were the same for all samples. Service life of gears was tested and failure types were characterized.

Optimization of disc geometry and hardness distribution for better transferability of fatigue life prediction from disc to FZG tests

FZG tests have become a standard for the determination of fatigue lifetime and other key operational parameters in gear applications. This testing configuration is considered to be closer to the real-field application than other rigs such as twin disc testers, although FZG requires a significantly more complex sample preparation in addition to not allowing for the variation of key test parameters. Despite the fact that DIN 3990 recommends the use of disc tests if no other gear test results are available, it must be noted that the transferability of results from twin disc to FZG gear tests has not been properly assessed in the available literature.For the present study, gears made of case hardened 22MnCr5 with different carburisation depths were tested under lubricated conditions using a FZG test rig. The results, including S–N curves, were compared with twin-disc tests performed by the authors with modified disc geometries, in order to assess the transferability of the results between both configurations. Additionally, worn samples have been characterised in terms of residual stresses and microstructure for one case hardening depths in FZG tests at different tooth flank locations and compared with disc tests. It has been found that a good match between FZG and twin disc test rig results can be found for an appropriate twin disc sample geometry and hardness distribution, opening the way for transferability between both test configurations.

Use of transmission error for a quantitative estimation of root-crack severity in gears

Gear transmission error (TE) has been acknowledged as a prominent diagnostic tool in condition monitoring. Its advantages vs vibration include being closer to the source and less affected by transmission path effects. TE has recently demonstrated its enormous capabilities in gear wear severity assessment. For crack diagnostics, despite some promising preliminary results, a methodology for an accurate and reliable TE-based estimation of crack size was previously not available. In order to achieve this result two main obstacles needed to be overcome: (i) the removal of dynamic TE effects due to speed and (ii) the separation of profile error and compliance-related tooth deflections. This paper proposes a new crack-severity-estimation methodology that solves these problems. The proposed technique exploits different speeds and loads, often experienced by geared transmissions, and includes an automated identification of the cracked tooth and a crack-depth estimation based on a comparison with a theoretical tooth stiffness model. The proposed methodology is validated using experimental encoder measurements collected from a spur gear test rig with artificially seeded root cracks.

Experimental and numerical analysis of laminated carbon fibre-reinforced polymer gears with implicit model for coefficient-of-friction evaluation

Abstract Laminated composites have so far received little attention as a potential material for gear drive applications. In the presented study, the thermomechanical performance of a newly developed type of epoxy impregnated, autoclave-cured carbon fibre-reinforced polymer gear—running in pair with a steel pinion—was analysed, using a combination of experimental and numerical approaches. The employed methods enabled the identification of the composite’s mechanical, thermal, and tribological characteristics, as related to the studied gear pair application. A newly proposed, finite-element-analysis-based iterative procedure enabled an implicit evaluation of the analysed material pair’s coefficient of friction (COF), which is a key parameter in determining the gear pair’s thermomechanical characteristics. For the considered material pair, a value of 0.34 was identified for the coefficient in the quasi-steady region. As the coefficient is strongly correlated with frictional heat generation and significantly affects the surface shear stress, it can consequently have a meaningful influence on the composite’s wear rate. The developed COF identification procedure was validated using a reciprocating cylinder-on-flat tribological test method. The composite gear’s service life was additionally tested at various running loads, resulting in pitch contact pressures ranging between 400 and 540 MPa. Lifetime gear test results showed a markedly superior performance compared to the high-temperature thermoplastic polyether ether ketone, which is typically employed in the most demanding polymer gear applications. Several methods are additionally proposed that could further improve the developed composite gears’ performance.

Application research on active disturbance rejection control algorithm and test of electro-hydraulic steering gear

Application research on active disturbance rejection control algorithm and test of electro-hydraulic steering gear

Effect of layer orientation on the single tooth bending fatigue strength of polymer gears manufactured by selective laser sintering

This study investigates the influence of tooth layer orientation on the bending fatigue behaviour of Nylon 12 spur gears manufactured by a selective laser sintering process in an ‘on-edge’ configuration. The test gears were submitted to single tooth bending fatigue tests, and the thermal response of gears was recorded using Infrared thermography. The surface morphology of failed teeth was examined using microscopy. The effect of tooth layer orientation on the fatigue strength of selective laser sintering gears was evaluated by testing each tooth configuration. The tooth configurations with the highest and lowest strength were 40° and 160°, respectively. The performance of selective laser sintering gears was compared with that of injection moulded Nylon 66 gears. The injection moulded, selective laser sintering 40°, and selective laser sintering 160° gear teeth were tested at multiple loads to investigate the high cycle fatigue and low cycle fatigue behaviour. The bending fatigue life was highest for the injection moulded gears in both low cycle fatigue and high cycle fatigue regimes. The surface temperature was higher in selective laser sintering gears, with 160° configuration exhibiting the highest temperature. The difference between the temperatures of selective laser sintering 40° configuration and injection moulded gear magnified as the applied load increased. Consequently, the strength of the selective laser sintering 40° configuration with respect to injection moulded gear deteriorated in the low cycle fatigue region. Fractography indicated that crack propagation in selective laser sintering 40° and selective laser sintering 160° configurations were cross-laminar and inter-laminar, respectively. In the cross-laminar mode of propagation, the crack propagation was impeded by the layer structure. However, the crack propagation was expedited in the inter-laminar mode, as the crack path was along the interlayer region, which presents a path of least resistance.