• TOPICS
    • Design
    • Manufacturing
    • Inspection
    • Heat Treating
    • Lubrication
    • Materials
    • The Gear Industry
    • Gears by Type
  • MAGAZINE
    • Current Issue
    • Departments
    • Archives
    • Subscribe
    • Advertise
  • NEWSLETTER
    • Subscribe
  • VIDEO
    • Gear Technology TV
      • Ask the Expert Live
      • Revolutions
    • Industry Videos
  • BLOGS
  • BUYER'S GUIDE
  • NEWS and EVENTS
    • Product News
    • Industry News
    • Events
  • ADVERTISING
    • Brand Awareness
      • Print: Display Advertising
      • Online: Web Banners & Keyword Banners
      • Online: Native Advertising (Sponsored Content)
      • E-mail: Custom, White Papers & Webinars
      • E-mail: Newsletter Sponsored Content (Native Advertising)
    • Response & Lead Generation
      • Online: Sponsored Content (Native Advertising)
      • E-mail: Newsletters
      • E-mail: Newsletter Sponsored Content (Native Advertising)
      • E-mail: Custom, White Papers & Webinars
      • Online: Buyers Guide
    • Print Advertising
      • Print: Display Advertising
      • Print: MPT Expo Showstoppers
      • Print: Buyers Guide
      • Print: Manufacturing sMart
      • Print: Specifications
      • MPT Expo Show Guide Advertising
    • Online Advertising
      • Online: Web Banners & Keyword Banners
      • Online: Native Advertising (Sponsored Content)
      • Online: Buyers Guide
      • Online: Specifications
    • E-mail Advertising
      • E-mail: E-Newsletters
      • E-mail: Newsletter Sponsored Content (Native Advertising)
      • E-mail: AGMA Industry News
      • E-mail: Custom, White Papers & Webinars
      • E-mail: Specifications
    • Special Promotions
      • Print: MPT Expo Showstoppers
      • Print: Buyers Guide
      • Print: Manufacturing sMart
      • MPT Expo Show Guide Advertising
  • CONTACT US
  • AGMA
    • Membership
    • Events
    • Education
    • Emerging Technology
    • AGMA Media
    • Standards
Subscribe
  • Sign In
  • Create Account
  • Sign Out
  • My Account
Home » Blogs » Editor's Choice » Fatigue Strength and Service Calculation of Gears

Editor's Choice
Editor's Choice RSS FeedRSS

Design / Manufacturing / Inspection / Materials / Bending Stress / Calculation / Fatigue / Fatigue Life / Fatigue Strength / Flank Modification / Module / Optimization / Root Stress / Software / Strength / Stress / Tooth Flank Modification / Tooth Root / Processes / Face Hobbing / Face Milling / Hobbing / Milling / Testing / Pitting / Bevel Gears / Cylindrical Gears / Spiral Bevel Gears
Matthew jaster
Matthew Jaster, Senior Editor, has a B.A. in journalism from Columbia College Chicago and has 15+ years of writing and editing experience in automotive, manufacturing, engineering, law and arts and entertainment. He's been with Gear Technology since 2007.

Fatigue Strength and Service Calculation of Gears

February 22, 2021
Matthew Jaster
No Comments
calculation

Bevel gear design is well-established. Flank geometry optimization is used worldwide to ensure satisfactory low-noise emissions and specific values for surface and bending stress.

But what about calculating the service life of gears? To its familiar KIMoS (Klingelnberg Integrated Manufacturing of Spiral Bevel Gears) software package, Klingelnberg has added a module for calculating the service life of a bevel or hypoid gear set that is based on the latest R&D work in service life calculation.

Designing bevel gears is a rather complex task. Unlike cylindrical gears, bevel gears are always designed in pairs. The design engineer must take numerous conflicting objectives into account, including minimum dimensions, maximum load capacity, noise reduction, and ease of manufacture on shop floor machines.

But one aspect is often left out: What about the gear’s fatigue strength?

If the maximum load on a tooth does not exceed the load limits of the material, the tooth returns to its initial state after the load is removed. This assumption is valid for several hundred load applications. But when we are talking about several million load applications, damage will occur at much lower loads than the load limits of the material. This phenomenon is known as fatigue.

Fig 2. Ease-off without tooth flank modification.

Fatigue strength testing – a core competence of OEMs and Tier 1 gear suppliers – is accomplished through time-consuming testing of transmissions. These tests are performed with an empirically defined load spectrum that inflicts the same damage that would occur under practical service conditions. One of the machines used for these endurance tests on bevel gears is the Oerlikon TS 30 bevel gear test stand.

What if we could calculate the service life of a bevel gear instead of having to subject each design to costly, time-consuming tests?

In the latest version of KIMoS, Klingelnberg makes it possible to calculate a bevel gear’s service life for specific operational loads, as well as for face hobbing design and face milling.

Fig 3. Ease-off with tooth flank modification.

To calculate the fatigue strength of a bevel gear, three basic elements must be known: the precise shape of the gear, the properties of the material, and the running conditions of the gear set. All of these elements are taken into account in KIMoS. Fatigue strength is calculated using Miner’s rule based on the linear cumulative damage hypothesis.

The cumulative damage to a gear pair can be predicted by combining the load spectrum, the load concentration on the tooth surface, as well as the bending stress in the tooth root and the cyclic stress-strain properties of the material. If the total cumulative damage for pitting and breakage is available, KIMoS can calculate the service life of the bevel gear set.

To generate a load spectrum with an extremely limited number of load cases, one of the counting methods must be used for the load cycles. If real load conditions comprising many different load cycles (for example with the rain flow method) are used to start with, these cyclic events can be counted, making it possible to convert real operational load cycles with an extremely reduced number of load cases into a load spectrum.

Will service life calculation of toothed gears replace endurance testing in the future?

The answer is a clear no. But calculating the fatigue strength enables an extremely effective comparison of different designs. The expected service life of a gewar pair can be estimated quite accurately when endurance test data exist for one of the designs.

That is why KIMoS gives the design engineer the ability to create a design that not only meets the geometry and noise emission requirements, but also takes fatigue life into account.

The following example shows two designs with the same dimensional data, but different with and without flank form modifications shown in Figure 2 and 3. The toothed gear data are z=13/38 teeth, the outside pitch diameter of the ring gear is 250 mm, and the hypoid offset is 20 mm.

This example shows the potential of tooth flank modifications. The design on the left has a service life of approx. 14 000 h, which is limited by the tooth root stress on the pinion. The design on the right has a service life of approx. 34 000 h, but here, too, the calculated cause of failure will be tooth breakage on the pinion.

Fig 4. Load spectrum and Wohler curves of the gear without tooth flank modification.

Not only does KIMoS empower the design engineer to optimize noise behavior and load capacity, but it also enables service life optimization of a gear set for specific load cases. This paves the way for new potential in lightweight design and enables more efficient and robust gear designs.

Fig 5. Load spectrum and Wohler curves of the gear with tooth flank modification.

www.klingelnberg.com

Post a comment to this article

Report Abusive Comment

Free Gear Technology Subscriptions
Subscribe
Free Gear Technology Subscriptions
Subscribe
FEATURED VIDEO
  • Marposs
    Marposs OptoCloud EDU
December 15, 2022
RECOMMENDED
  • Precision Equals Performance at ZPE GripTec

    October 12, 2022
    gt0922_Page_28_Image_0003.jpg
  • State of the Powder Metal Industry

    October 12, 2022
    gt0922_Page_30_Image_0001.jpg
  • The Afterglow of Furnaces North America 2022

    October 12, 2022
    gt0922_Page_20_Image_0001.jpg
  • Reigniting the Educational Infrastructure

    December 5, 2022
    gt1122_Page_20_Image_0001.jpg
  • Profile: Continuing Education and Training with the AGMA

    December 5, 2022
    gt1122_Page_26_Image_0001.jpg
  • Reigniting the Educational Infrastructure

    December 5, 2022
    gt1122_Page_20_Image_0001.jpg
  • Profile: Continuing Education and Training with the AGMA

    December 5, 2022
    gt1122_Page_26_Image_0001.jpg
  • Precision Equals Performance at ZPE GripTec

    October 12, 2022
    gt0922_Page_28_Image_0003.jpg
  • Subscribe
  • Advertise
  • Contribute
  • AGMA
Powered byAGMA
Copyright © 2023 Gear Technology
  • Privacy Policy
  • Contact