Hybrid Gear Performance Under Loss-of-Lubrication Conditions

Military application of composite gears - A brief study, 2022

Composite gears, characterized by their lightweight, corrosion resistance, noise reduction, and customization potential, find applications across diverse industries. They offer notable advantages in aerospace, naval, ground vehicle, unmanned aerial vehicle, and robotic systems.

2012

The following tendencies will be more pronounced in the future: • Metals will be increasingly substituted by plastics • Significant reductions in gear noise and vibration • Increase of the performance density (smaller models for same performance) • Use of special tooth forms (non-in volute tooting) Present thesis deals with phenomena of wear & suitable material investigation for the gears. It consists of eight chapters.

Journal of Advanced Mechanical Design, Systems, and Manufacturing

This article presents a lifespan testing analysis of polymer gears manufactured by cutting. Compared to injection molding, machine cutting provides higher accuracy of gear geometry. Two different tooth flank geometries were tested; i.e. involute and S-gears. In theory, S-gears have several advantages over involute gears due to the convex/concave contact between the matching flanks. The theoretical tooth flank geometry of S-gears provides more rolling and less sliding between the matching flanks, compared to involute gears. The convex/concave contact leads to lower contact stress, which in combination with less sliding means lower losses due to sliding friction and consequently less heat generated. The goal of our research was to prove that tooth flank geometry affects the lifetime of polymer gears, and to find the mechanisms and quantitative differences in the performance of both analyzed geometries. The gears were tested on specially designed testing equipment, which allows exact adjustment of the central axis distance. Two different material pairs (POM/POM and POM/PA66) of the drive and driven gears were tested. Each test was done at a constant moment load and a constant rotational speed. Several tests were conducted using the same conditions due to repeatability analysis. All the tests were performed till the failure of the gear pair and without lubrication. In lifespan testing, the polymer S-gears showed better performance and longer lifespan than involute polymer gears. means higher heat generation as a result of losses due to friction in contact. A more significant difference between the load capacities of both gear geometries was detected when testing the POM/PA66 material combination. Because the POM/POM material combination is tribologically incompatible, gears wear too quickly, tooth profile shape is no longer right and all of the advantages of the S-gear profile shape are lost. This time, tests were conducted under high loads in order to obtain results in a reasonable time. Overloading triggers the overheating failure mechanism. Practical applications often require material data after 10 or even 100 million load cycles. A different failure mechanism is expectedfatigue. For this reason, future tests will be carried out under lower load levels. Priority will be given to material pairs that are tribologically compatible and interesting for real applications (such as POM/PA).

Current and continuous increase in high performance aerospace transmission requirements need to be systematically approached from a dual point of view; deeper modelling capabilities of gear meshes and more reliable stress prediction analyses have to cope with finer gear materials strength characterisation.

Polymer based gears are finding major application where load carrying capacity is less with less requirement of maintenance. Since most of the application necessitates load/motion transmission in only one direction, asymmetric gears can replace conventional symmetric gears. In this work, usefulness of asymmetric polymer composite gears is established. Symmetric gear 20/20 asymmetric gears 20/34 were injection molded using unreinforced and 20 % glass fiber reinforced polypropylene materials. It is well established that polymer gears are less susceptible to contact fatigue failure due to its poor material Young’s modulus. Hence evaluation of bending fatigue performance would be more appropriate for the new material /design of polymer based gears. In this work, a fixture has been specially designed and developed to integrate with the servo hydraulic fatigue testing facility for bending fatigue evaluation of gear teeth. Unlike prior research work carried out, the present testing condition imitates the actual gear mesh condition so that localized loading conditions are significantly minimized. Test gear teeth were subjected to sinusoidal bending fatigue at various constant displacement magnitudes and at various frequencies of loading. Load carrying capacity for various gear teeth deflection was continuously measured and monitored. Addition of glass fiber reinforcement found to improve the bending load carrying capacity of both symmetric and asymmetric gears. Test gears found to exhibit improved performance at higher load frequency due to the strain rate sensitiveness of polymer based materials. Effective cantilever length of gear teeth found to improve the load carrying capacity of 34/20 over 20/34 asymmetric gears as well as symmetric gears. Thickness of weakest portion at the gear teeth root found to improve the load carrying capacity of 20/34 asymmetric gear over 20/20 symmetric gears. Keywords: Asymmetric gear, Bending fatigue, Injection moulding, Polymer gear, Composite.

IRJET, 2021

Due to its substantial strength and dependability, ferrous materials are commonly used in the automotive industry while also compromising on weight. To improve the vehicle's performance in terms of vibration, acceleration, and damping, lighter materials with higher strength than steel and approximately equivalent reliability can be employed. Carbon Fiber composite materials are roughly 78 percent lighter than ferrous alloys and have better strength per unit volume than steel. Metals with carbon fiber composites can be used in automobile gears to disrupt the vibration transmission pathway from the gear teeth to the center of the shaft, reducing total noise and weight without sacrificing load capacity. Carbon fiber composites directional characteristics are studied because of their anisotropic nature. Because of its greater torsional rigidity and impact strength, this material is suitable for drive shafts that must endure torsional forces, as well as suspension links that are subjected to fatigue loading. The goal of this project is to investigate the directional properties of carbon fiber composite materials, develop, analyse, and produce metal-carbon fiber composite gears, drive shafts, and suspension links, and test the product's and epoxy adhesive's long-term viability.

2018

Aerospace power transmission elements and units like gears and gearboxes are critical componentswhich need to be designed, manufactured and installed for a well performing fail-safe operation. Recent development of such components has seen rather satisfying improvements regarding different subjects like materials, design, manufacturing processes, surface treatment, etc. While cleanliness of material and special alloys help increase the strength of gear material, different design methods help reduce stresses under service loads. Similarly, different manufacturing methods help reduce surface burn like defects while material surface coatings help increase the resistance to wear and pitting like failures of both gears and bearings. Different examples of recent developments in aerospace gears and gearbox designs are provided in this paper to keep readers up to date with the aerospace power transmission technology. Keywords : aerospace, development, design, gear, gearbox, performance

The Proceedings of the JSME international conference on motion and power transmissions, 2017

The main advantages of polymer gears compared to metal gears are low manufacturing costs for mass production, vibration damping, and there is no need for a lubricant. In the literature and guidelines, the allowable gear endurance limits for bending and contact stresses are mainly given for polyamides (PA) and polyacetals (POM). A large number of suitable polymer gear materials is available, but the standards offer little support for the lifetime calculations of polymer gears from other materials. Therefore, the testing of gear geometry and materials combinations cannot be avoided in the design of an optimal gear drive. However, gear testing is very time-consuming and expensive, especially when testing several different material combinations in different testing conditions. By applying the upgraded accelerated testing procedure, gear test time and costs can decrease significantly. Determination of the gear temperature during meshing is needed for the precise calculation of plastic gears. The presented temperature calculation model is corrected and improved with input parameters, which were determined from the test results. Accelerated tests were conducted on different combinations of reinforced and unreinforced commercially available materials: PA6, PA66, POM and PPS. Glass and carbon fiber were used for reinforcement. The research goal was characterization of different material pairs with the coefficient of friction, time strength, wear, and the failure mechanism in relation to load cycles and load level. The paper's contribution are some general guidelines for selecting polymer material for gears, such as fiber reinforcement improves the allowable stress level at up to a few million load cycles; unreinforced polymers are better for a higher number of load cycles. Also, PTFE-the internal lubricant significantly reduces a coefficient of friction if added to PA polymers, and is less efficient in combination with POM.

IOP Conference Series: Materials Science and Engineering

There are many plastic materials (POM, PA66, PEEK, …) and material combinations available. The question is which combination is the correct one. It depends on many factors, like expected durability and price, means of production, e.g. injection moulding or cutting, lubrication, microstructure, fillers, etc. The available data bases and data sheets do not present conclusive results. So, it is of the utmost importance for a company to produce effective tests which could present correct results for each individual case. The gear tooth flank profile could be also optimized. S-gear shape is characterized by a convex concave contact in meshing start and end areas. This implies improved properties in comparison to involute gears, like lower contact pressure, less sliding and lower frictional losses, stronger root and improved oil film when lubricated. The paper presents some material properties for the combinations which were tested on the fatigue test benches, presents testing rigs, refer...

Journal of Materials Engineering and Performance, 2009

In this paper the contact fatigue resistance of gearwheel teeth, subjected to shot-peening treatment, was investigated experimentally and analytically. The main objective was the evaluation and prediction of fatigue crack initiation, propagation, direction, and rate. A specially designed experimental rig was used to test a number of spur gears with the following characteristics: (a) unhardened, thermally untreated unpeened surfaces, (b) thermally treated unpeened surfaces, (c) unhardened peened surfaces, and (d) thermally treated peened surfaces. The theoretical model assumed initiation and propagation of surface cracks of gears operating in the elastohydrodynamic lubrication regime while loading was due to simultaneous rolling and sliding. Finite element modeling was used for the calculation of the stress field at the gear teeth. Comparison of the experimental and analytical results showed considerable improvement in the contact fatigue strength of thermally treated gear teeth and especially those that underwent shot peening, which increased surface durability. The residual stresses induced by shot peening are mainly effective in stopping microcrack propagation. When shot peening is applied on thermally untreated gear teeth surface, it increases the contact fatigue life of the material by 17% at 7 3 10 5 loading cycles. If shot peening is applied on carburized gear teeth surfaces, it increases the surface fatigue life by approximately 8% at 10 6 cycles. Contact fatigue and eventual pitting are treated as a normal consequence of the operation of machine elements. To study this failure process different types of testing machines have been designed. The purpose of this paper is the presentation and evaluation of a new design experimental rig for studying contact fatigue damage of gear teeth subjected to different load patterns.