In high-load scenarios such as rail transit, heavy machinery, marine power, and aerospace transmission systems, gear tooth breakage not only reduces transmission efficiency but also poses the risk of severe equipment malfunctions. This article systematically analyzes the mechanism, common types, detection methods, and preventive measures of gear tooth breakage failure.

Definition of Gear Tooth Breakage

Gear tooth breakage refers to a failure mode where cracks form on the tooth surface or root during operation, eventually leading to tooth fracture. This failure typically occurs in gears subjected to high loads, impact loads, or long-term fatigue.

Typical Modes of Tooth Breakage

1. 1.

   Instantaneous Overload Breakage

   Commonly triggered by sudden jamming, startup impact, or abrupt load changes.

   Characteristic: Brittle fracture with a neat, flat fracture surface and almost no plastic deformation.

2. 2.

   Fatigue Breakage

   Repeated alternating loads cause stress concentration at the tooth root, leading to the gradual propagation of microcracks.

   Characteristic: The fracture surface generally consists of a fatigue initiation zone, a propagation zone (smooth with shell-like patterns), and an instantaneous fracture zone.

3. 3.

   Material Defect-Induced Breakage

   Inclusions, pores, or uneven heat treatment result in insufficient tooth root strength.

   Characteristic: Often occurs early in service; the fracture surface is rough, with visible defect-induced initiation points.

Key Causes of Tooth Breakage

Design Factors

• •

  Undersized tooth root fillet, causing severe stress concentration.

• •

  Poor tooth profile design, which amplifies meshing impact.

Material and Heat Treatment

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  Insufficient carbon content or a shallow carburized layer.

• •

  Uneven quenching, resulting in abnormal hardness gradients.

Manufacturing and Assembly

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  Machining tool marks or excessive surface roughness at the tooth root.

• •

  Assembly errors leading to actual loads far exceeding design values.

Operating Conditions

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  Overload operation.

• •

  Insufficient lubrication, which intensifies tooth surface impact.

Detection and Analysis Methods

Macroscopic Visual Inspection

• •

  Examine the characteristics of fracture surfaces using magnifying glasses or microscopes.

Metallographic Microscopic Analysis

• •

  Detect material structure, carbide distribution, and quenched layer depth.

Scanning Electron Microscopy (SEM) of Fracture Surfaces

• •

  Accurately identify fatigue initiation sites and crack propagation paths.

Finite Element Analysis (FEA)

• •

  Build gear models to calculate stress distribution at the tooth root and predict potential breakage risks.

Typical Case Study

A high-speed rail gearbox suffered tooth breakage within 2 years of operation. Failure analysis revealed that machining tool marks at the tooth root caused significant stress concentration, while contaminated lubricating oil intensified frictional impact—ultimately triggering fatigue cracks that propagated into full breakage.

Lesson Learned: Both machining quality control and lubrication management are indispensable.

Prevention and Optimization Measures