Fatigue

GEAR TALK WITH CHUCK | 2019-05-09

My Story – Bob Handschuh

Most of us only think of NASA with regard to the “S” [Space] in its acronym. The first “A” [Aerospace] is just as important to its mission of s...

GEAR TALK WITH CHUCK | 2019-01-18

Lessons Learned the Hard Way

Chris’ account of p...

GEAR TALK WITH CHUCK | 2018-10-23

Appropriate Improvements

“Resto moding” a gearbox is not t...

GEAR TALK WITH CHUCK | 2018-10-04

Repairing Gears

Deadlines and budgets do not always allow for “first class” gearbox rebuilds. The challenge for rebuild shops is to find the fastest and most econo...

TECHNICAL ARTICLES | 2018-09-01

Influence of Different Manufacturing Processes on Properties of Surface-Densified PM Gears

The properties of both shot-peened and cold rolled PM gears are analyzed and compared. To quantify the effect of both manufacturing processes, the tooth root bending fatigue strength will be evaluated and compared to wrought gears.

INDUSTRY NEWS | 2018-08-13

International Gear Conference 2018

Lyon, France. Mechanical transmission components such as gears, rolling element bearings, CVTs, belts, chains, etc. are present in every industrial...

GEAR TALK WITH CHUCK | 2018-06-14

Options for Material Selection

Disclaimer: This is the policy I follow for material selection. Your situation may call for a different decision. You should not adopt this pol...

TECHNICAL ARTICLES | 2018-05-01

Prediction of Dynamic Factors for Helical Gears in a High-Speed Multibody Gearbox System

Accurate prediction of gear dynamic factors (also known as Kv factors) is necessary to be able to predict the fatigue life of gears. Standards-based calculations of gear dynamic factors have some limitations. In this paper we use a multibody dynamic model, with all 6 degrees of freedom (DOF) of a high-speed gearbox to calculate gear dynamic factors. The findings from this paper will help engineers to understand numerous factors that influence the prediction of dynamic factors and will help them to design more reliable gears.

TECHNICAL ARTICLES | 2018-03-01

Effect of Non-Metallic Inclusions on Bending Fatigue Performance in High Strength 4140 Steel

Three samples of quenched and tempered 4140 steel, with varying levels of oxygen and sulfur, were submitted to a series of bending fatigue tests.

GEAR TALK WITH CHUCK | 2017-12-14

Engineering Safety (Part Two)

To an engineer there are no accidents, only unanticipated consequences of situations that need to be better understood. We even have a rule about i...

INDUSTRY NEWS | 2017-10-10

Napoleon Engineering Services Announces Rolling-Contact Fatigue and Wear Testing

The largest independent bearing testing and inspection facility in the United States, Napoleon Engineering Services (NES) has announced t...

GEAR TALK WITH CHUCK | 2017-09-26

Where Did All the Big Projects Go?

Remembering the “good old days” too often or too fondly is an occupational hazard for a veteran blogger like me. I try to temper “story time” with ...

TECHNICAL ARTICLES | 2017-05-01

Performance and Machining of Advanced Engineering Steels in Power Transmission Applications - Continued Developments

It is becoming increasingly apparent that material properties can and will play a greater role than before in addressing the challenges most transmission manufacturers are facing today. Making use of materials' intrinsic fatigue properties provides a new design tool to support the market changes taking place.

GEAR TALK WITH CHUCK | 2017-01-12

The Essential Gear Book?

Continuing our discussion of gear training… What one book would you advise a newbie to purchase, read, and keep handy in the years ahe...

TECHNICAL ARTICLES | 2015-11-01

Knowing When Enough Is Enough

Detection of impending gear tooth failure is of interest to every entity that utilizes geared transmissions. However, it is of particular significance at the Gear Research Institute (GRI), where sponsored efforts are conducted to establish gear material endurance limits, utilizing gear fatigue tests. Consequently, knowing when a gear is about to fail in each and every test, in a consistent manner, is essential for producing reliable and useful data for the gear industry.

GEAR TALK WITH CHUCK | 2015-09-03

When Good Employees Screw Up

A friend of mine is the inspection department for a custom machine shop. He is also the process engineer and, occasionally, a machine operator. Rec...

TECHNICAL ARTICLES | 2014-08-01

Setting Load Parameters for Viable Fatigue Testing of Gears in Powertrain Axles Part I: Single-Reduction Axles

This presentation introduces a new procedure that - derived from exact calculations - aids in determining the parameters of the validation testing of spiral bevel and hypoid gears in single-reduction axles.

INDUSTRY NEWS | 2014-05-01

Industry News

The complete Industry News section from the May 2014 issue of Gear Technology.

ASK THE EXPERT | 2013-06-01

Worn Gear Contact Analysis

How does one perform a contact analysis for worn gears? Our expert responds.

FEATURE ARTICLES | 2012-06-01

Growing Pains - Renewables Hang on in Turbulent Energy Market

The turbines are still spinning. They’re spinning on large wind farms in the Great Plains, offshore in the Atlantic and even underwater where strong tidal currents offer new energy solutions. These turbines spin regularly while politicians and policy makers— tied up in discussions on tax incentives, economic recovery and a lot of finger pointing—sit idle. Much like the auto and aerospace industries of years past, renewable energy is coping with its own set of growing pains. Analysts still feel confident that clean energy will play a significant role in the future of manufacturing—it’s just not going to play the role envisioned four to five years ago.

TECHNICAL ARTICLES | 2010-11-01

Gear Fault Detection Effectiveness as Applied to Tooth Surface Pitting Fatigue Damage

A study was performed to evaluate fault detection effectiveness as applied to gear-tooth pitting-fatigue damage. Vibration and oil-debris monitoring (ODM) data were gathered from 24 sets of spur pinion and face gears run during a previous endurance evaluation study.

TECHNICAL ARTICLES | 2010-06-01

Bending Fatigue, Impact and Pitting Resistance of Ausform-Finished PM Gears

The powder metal (P/M) process is making inroads in automotive transmission applications due to substantially lower costs of P/M-steel components for high-volume production, as compared to wrought or forged steel parts. Although P/M gears are increasingly used in powered hand tools, gear pumps and as accessory components in automotive transmissions, P/M-steel gears are currently in limited use in vehicle transmission applications. The primary objective of this project was to develop high-strength P/M-steel gears with bending fatigue, impact resistance and pitting fatigue performance equivalent to current wrought steel gears.

TECHNICAL ARTICLES | 2009-11-01

Bending Fatigue Tests of Helicopter Case Carburized Gears: Influence on Material, Design and Manufacturing Parameters

A single tooth bending (STB) test procedure has been developed to optimally map gear design parameters. Also, a test program on case-carburized, aerospace standard gears has been conceived and performed in order to appreciate the influence of various technological parameters on fatigue resistance and to draw the curve shape up to the gigacycle region.

TECHNICAL ARTICLES | 2009-08-01

Effects of Axle Deflection and Tooth Flank Modification on Hypoid Gear Stress Distribution and Contact Fatigue Life

As is well known in involute gearing, “perfect” involute gears never work perfectly in the real world. Flank modifications are often made to overcome the influences of errors coming from manufacturing and assembly processes as well as deflections of the system. The same discipline applies to hypoid gears.

TECHNICAL ARTICLES | 2008-06-01

Study of the Correlation Between Theoretical and Actual Gear Fatigue Test Data on a Polyamide

In the past two years DSM has been conducting fatigue tests on actual molded gears in order to provide design data.

TECHNICAL ARTICLES | 2008-03-01

Methodology for Translating Single-Tooth Bending Fatigue Data to be Comparable to Running Gear Data

A method to extrapolate running gear bending strength data from STF results for comparing bending performance of different materials and processes.

TECHNICAL ARTICLES | 2007-03-01

Effects on Rolling Contact Fatigue Performance--Part II

This is part II of a two-part paper that presents the results of extensive test programs on the RCF strength of PM steels.

TECHNICAL ARTICLES | 2007-01-01

Effects on Rolling Contact Fatigue Performance

This article summarizes results of research programs on RCF strength of wrought steels and PM steels.

TECHNICAL ARTICLES | 2005-11-01

The Fatigue Endurance Limit: A Myth

Review of "Gigacycle Fatigue in Mechanical Practice," by Claude Bathias and Paul C. Paris

TECHNICAL ARTICLES | 2004-05-01

Evaluation of Bending Strength of Carburized Gears

The aim of our research is to clearly show the influence of defects on the bending fatigue strength of gear teeth. Carburized gears have many types of defects, such as non-martensitic layers, inclusions, tool marks, etc. It is well known that high strength gear teeth break from defects in their materials, so it’s important to know which defect limits the strength of a gear.

TECHNICAL ARTICLES | 2003-05-01

Characterizaton of Retained Austenite in Case Carburized Gears and Its Influence on Fatigue Performance

Carburized helical gears with high retained austenite were tested for surface contact fatigue. The retained austenite before test was 60% and was associated with low hardness near the case's surface. However, the tested gears showed good pitting resistance, with fatigue strength greater than 1,380 MPa.

TECHNICAL ARTICLES | 2002-01-01

Consideration of Moving Tooth Load in Gear Crack Propagation Predictions

Effective gear designs balance strength, durability, reliability, size, weight, and cost. Even effective designs, however, can have the possibility of gear cracks due to fatigue. In addition, truly robust designs consider not only crack initiation, but also crack propagation trajectories. As an example, crack trajectories that propagate through the gear tooth are the preferred mode of failure compared to propagation through the gear rim. Rim failure will lead to catastrophic events and should be avoided. Analysis tools that predict crack propagation paths can be a valuable aid to the designer to prevent such catastrophic failures.

TECHNICAL ARTICLES | 2001-05-01

Design Formulas for Evaluating Contact Stress in Generalized Gear Pairs

A very important parameter when designing a gear pair is the maximum surface contact stress that exists between two gear teeth in mesh, as it affects surface fatigue (namely, pitting and wear) along with gear mesh losses. A lot of attention has been targeted to the determination of the maximum contact stress between gear teeth in mesh, resulting in many "different" formulas. Moreover, each of those formulas is applicable to a particular class of gears (e.g., hypoid, worm, spiroid, spiral bevel, or cylindrical - spur and helical). More recently, FEM (the finite element method) has been introduced to evaluate the contact stress between gear teeth. Presented below is a single methodology for evaluating the maximum contact stress that exists between gear teeth in mesh. The approach is independent of the gear tooth geometry (involute or cycloid) and valid for any gear type (i.e., hypoid, worm, spiroid, bevel and cylindrical).

TECHNICAL ARTICLES | 2001-03-01

Austempered Gears and Shafts: Tough Solutions

Austempered irons and steels offer the design engineer alternatives to conventional material/process combinations. Depending on the material and the application, austempering may provide the producers of gear and shafts with the following benefits: ease of manufacturing, increased bending and/or contact fatigue strength, better wear resistance or enhanced dampening characteristics resulting in lower noise. Austempered materials have been used to improve the performance of gears and shafts in many applications in a wide range of industries.

TECHNICAL ARTICLES | 2000-11-01

Design Against Tooth Interior Fatigue Fracture

In a modern truck, the gear teeth are among the most stressed parts. Failure of a tooth will damage the transmission severely. Throughout the years, gear design experience has been gained and collected into standards such as DIN (Ref. 1) or AGMA (Ref. 2). Traditionally two types of failures are considered in gear design: tooth root bending fatigue, and contact fatigue. The demands for lighter and more silent transmissions have given birth to new failure types. One novel failure type, Tooth Interior Fatigue Fracture (TIFF), has previously been described by MackAldener and Olsson (Refs. 3 & 4) and is further explored in this paper.

REVOLUTIONS | 1999-07-01

Revolutions

Welcome to Revolutions, the column that brings you the latest, most up-to-date and easy-to-read information about the people and technology of the gear industry.

TECHNICAL ARTICLES | 1997-11-01

Gear Crack Propagation Investigations

A common design goal for gears in helicopter or turboprop power transmission is reduced weight. To help meet this goal, some gear designs use thin rims. Rims that are too thin, however, may lead to bending fatigue problems and cracks. The most common methods of gear design and analysis are based on standards published by the American Gear Manufacturers Association. Included in the standards are rating formulas for gear tooth bending to prevent crack initiation (Ref. 1). These standards can include the effect of rim thickness on tooth bending fatigue (Ref 2.). The standards, however, do not indicate the crack propagation path or the remaining life once a crack has started. Fracture mechanics has developed into a useful discipline for predicting strength and life of cracked structures.

FEATURE ARTICLES | 1997-09-01

Who's Who and What's What At Gear Expo '97

Below are listed the Gear Technology advertisers exhibiting at Gear Expo 97.

TECHNICAL ARTICLES | 1995-09-01

Comparison of Surface Durability & Dynamic Performance of Powder Metal & Steel Gears

Surface-hardened, sintered powder metal gears are increasingly used in power transmissions to reduce the cost of gear production. One important problem is how to design with surface durability, given the porous nature of sintered gears. Many articles have been written about mechanical characteristics, such as tensile and bending strength, of sintered materials, and it is well-known that the pores existing on and below their surfaces affect their characteristics (Refs. 1-3). Power transmission gears are frequently employed under conditions of high speed and high load, and tooth surfaces are in contact with each other under a sliding-rolling contact condition. Therefore it is necessary to consider not only their mechanical, but also their tribological characteristics when designing sintered gears for surface durability.

TECHNICAL ARTICLES | 1995-05-01

EHL Film Thickness, Additives and Gear Surface Fatigue

Aircraft transmissions for helicopters, turboprops and geared turbofan aircraft require high reliability and provide several thousand hours of operation between overhauls. In addition, They should be lightweight and have very high efficiency to minimize operating costs for the aircraft.

VOICES | 1993-01-01

Our Readers Discuss Gear Rattle, Gear Books, and Gear Tech

Investigation of Gear Rattle Phenomena The article by Messrs. Rust, Brandl and Thien was very interesting in its description of the problem and of some of the interactions which occur.

TECHNICAL ARTICLES | 1992-07-01

Comparing Surface Failure Modes in Bearings and Gears: Appearances vs. Mechanisms

In the 1960's and early 1970's, considerable work was done to identify the various modes of damage that ended the lives of rolling element bearings. A simple summary of all the damage modes that could lead to failure is given in Table 1. In bearing applications that have insufficient or improper lubricant, or have contaminants (water, solid particles) or poor sealing, failure, such as excessive wear or vibration or corrosion, may occur, rather than contact fatigue. Usually other components in the overall system besides bearings also suffer. Over the years, builders of transmissions, axles, and gear boxes that comprise such systems have understood the need to improve the operating environment within such units, so that some system life improvements have taken place.

TECHNICAL ARTICLES | 1991-05-01

Surface Pitting Fatigue Life of Noninvolute Low-Contact-Ratio Gears

Spur gear endurance tests were conducted to investigate the surface pitting fatigue life of noninvolute gears with low numbers of teeth and low contact ratios for the use in advanced application. The results were compared with those for a standard involute design with a low number of teeth. The gear pitch diameter was 8.89 cm (3.50 in.) with 12 teeth on both gear designs. Test conditions were an oil inlet temperature of 320 K (116 degrees F), a maximum Hertz stress of 1.49 GPa (216 ksi), and a speed of 10,000 rpm. The following results were obtained: The noninvolute gear had a surface pitting fatigue life approximately 1.6 times that of the standard involute gear of a similar design. The surface pitting fatigue life of the 3.43-pitch AISI 8620 noninvolute gear was approximately equal to the surface pitting fatigue life of an 8-pitch, 28-tooth AISI 9310 gear at the same load, but at a considerably higher maximum Hertz stress.

TECHNICAL ARTICLES | 1990-03-01

Influence of Lubrication on Pitting and Micropitting Resistance of Gears

Pitting and micropitting resistance of case-carburized gears depends on lubricants and lubrication conditions. Pitting is a form of fatigue damage. On this account a short time test was developed. The test procedure is described. The "pitting test" was developed as a short time test to examine the influence of lubricants on micropitting. Test results showing the influence of case-carburized gears on pitting and micropitting are presented.

TECHNICAL ARTICLES | 1990-01-01

Surface Fatigue Life on CBN and Vitreous Ground Carburized and Hardened AISA 9310 Spur Gears

Spur gear surface endurance tests were conducted to investigate CBN ground AISI 9310 spur gears for use in aircraft applications, to determine their endurance characteristics and to compare the results with the endurance of standard vitreous ground AISI 9310 spur gears. Tests were conducted with VIM-VAR AISI 9210 carburized and hardened gears that were finish ground with either CBN or vitreous grinding methods. Test conditions were an inlet oil temperature of 320 K (116 degree F), an outlet oil temperature of 350 K (170 degree F), a maximum Hertz stress of 1.71 GPa (248 ksi), and a speed of 10,000 rpm. The CBN ground gears exhibited a surface fatigue life that was slightly better than the vitreous ground gears. The subsurface residual stress of the CBN ground gears was approximately the same as that for the standard vitreous ground gears for the CBN grinding method used.

VOICES | 1987-07-01

No Surprise

For the last few years, the market has been tough for the U.S. gear industry. That statement will cause no one any surprise. The debate is about what to do. One sure sign of this is the enormous attention Congress and the federal government are now placing on "competitiveness."

TECHNICAL ARTICLES | 1986-09-01

Improved Gear Life Through Controlled Shot Peening

The search for greater gear life involves improvement in cost, weight and increased power output. There are many events that affect gear life, and this paper addresses those relating to fatigue, gear tooth pitting, fatigue strength losses due to the heat treating processes and shot peening technique. The capability of shot peening to increase fatigue strength and surface fatigue life eliminate machine marks which cause stress risers, and to aid in lubrication when properly controlled, suggests increased use and acceptance of the process.

INDUSTRY NEWS | 1986-01-01

The Process of Gear Shaving

Gear shaving is a free-cutting gear finishing operation which removes small amounts of metal from the working surfaces of the gear teeth. Its purpose is to correct errors in index, helical angle, tooth profile and eccentricity. The process can also improve tooth surface finish and eliminate, by crowned tooth forms, the danger of tooth end load concentrations in service. Shaving provides for form modifications that reduce gear noise. These modifications can also increase the gear's load carrying capacity, its factor of safety and its service life.

FEATURE ARTICLES | 1986-01-01

Effect of Shot Peening on Surface Fatigue Life of Carburized and Hardened AISI 1910 Spur Gears

Gear surface fatigue endurance tests were conducted on two groups of 10 gears each of carburized and hardened AlSI 9310 spur gears manufactured from the same heat of material

TECHNICAL ARTICLES | 1984-08-01

Maximum Surface Temperature of the Thermoplastic Gear in a Non-Lubricated Plastic-Steel Gear Pair

One of the major problems of plastic gear design is the knowledge of their running temperature. Of special interest is the bulk temperature of the tooth to predict the fatigue life, and the peak temperature on the surface of the tooth to avert surface failure. This paper presents the results of an experimental method that uses an infrared radiometer to measure the temperature variation along the profile of a plastic gear tooth in operation. Measurements are made on 5.08, 3.17, 2.54, 2.12 mm module hob cut gears made from nylon 6-6, acetal and UHMWPE (Ultra High Molecular Weight Polyethylene). All the tests are made on a four square testing rig with thermoplastic/steel gear pairs where the plastic gear is the driver. Maximum temperature prediction curves obtained through statistical analysis of the results are presented and compared to data available from literature.