01 Significance of Bearing Fatigue Testing

• Verify design and theory: Use test data to validate the accuracy and reliability of bearing strength calculations (such as contact strength and rolling fatigue strength) based on standards like ISO, ABMA, and JIS.
• Evaluate materials and processes: Compare the impact of different materials (e.g., GCr15, 渗碳 bearing steel), heat treatment processes (e.g., quenching and tempering, carburizing and quenching), and manufacturing processes (e.g., grinding, superfinishing) on bearing fatigue life.
• Establish basic databases: Obtain reliable S-N curves (stress-life curves) and P-S-N curves (probability-stress-life curves) to provide valuable raw data for subsequent bearing design.
• Quality control and comparison: Serve as the final inspection of product quality or for comparing the performance of bearing products from different suppliers.
• Research failure mechanisms: Conduct in-depth observation and analysis of the entire process of fatigue crack initiation, propagation, and final fracture to provide directions for design improvement.

02 Design of Standard Bearings

Key Design Features of Standard Bearings

• Standardized geometric parameters:
  • Basic dimensions: Adopt standard values such as inner diameter (d), outer diameter (D), and width (B) in line with ISO or national standards.
  • Rolling element parameters: Standardize the number, size, and shape (e.g., spherical, cylindrical) of rolling elements to ensure consistent load distribution.
  • No special modifications: Avoid any structural modifications such as optimized raceway profiles or enhanced cage designs. This eliminates the impact of modifications on load transfer, returning the test conditions to the most basic operating state and directly reflecting the intrinsic performance of materials and processing technologies.
   
• Strict control of materials and processes:
  • Uniform material batches: Bearings in the same test must be made of steel from the same heat to ensure consistent chemical composition.
  • Consistent heat treatment: All bearings undergo heat treatment in the same batch with the same process parameters, ensuring high consistency in key indicators such as core hardness, surface hardness, effective hardening layer depth, and residual austenite content.
  • High-precision manufacturing: Generally, it is required to meet Grade 5 or higher precision specified in GB or ISO standards to minimize the interference of manufacturing errors on load distribution.
   

Common Types of Standard Bearings

• ISO standard bearings: Internationally recognized universal standard bearings, defining unified geometric parameters (e.g., deep groove ball bearings 6200 series, tapered roller bearings 30200 series) and test methods. Widely used in material performance testing and lubricant evaluation.
• SKF standard test bearings: Developed by Swedish bearing manufacturer SKF, featuring strict process control and high dimensional accuracy. Commonly used in advanced fatigue life testing and new material verification.

03 Types of Fatigue Tests

1. Rolling Contact Fatigue Test

• Test purpose: Determine the bearing's ability to resist surface spalling and pitting. Focus on the maximum contact stress between rolling elements and raceways.
• Test design:
  • Test rig: Mostly adopts power-flow closed-loop test rigs. This system forms cyclic power internally through a torque loading device, requiring only an external motor to compensate for losses such as friction, making it energy-efficient and high-performance.
  • Loading method: Apply a constant cyclic load (stress ratio R ≈ -1 or R ≈ 0.1) to the test bearing, simulating the alternating load during actual operation.
  • Failure criterion: The service life endpoint is determined when surface spalling area reaches a specified proportion of the raceway (e.g., 3% or 5%), or when destructive pitting (large and deep pits leading to sharp increases in vibration and noise) occurs.
   
• Application and output:
  • Generate S-N curves: By applying different stress levels to a group of bearings, record the number of cycles until failure, and plot the rolling contact fatigue S-N curve. This curve is the fundamental basis for selecting allowable stress in bearing design.
  • Evaluate lubricants: This test is a key standard for assessing the extreme pressure and anti-wear performance of bearing oils. Different lubricant formulations significantly affect the pitting life of bearing surfaces.
   

2. Cage Fatigue Test

• Test purpose: Evaluate the cage's ability to resist fatigue damage under cyclic impact and friction. Focus on the stress concentration areas of the cage, such as pockets and ribs.
• Test design:
  • Test rig: Use special cage fatigue test rigs that simulate the actual motion state of the cage, including rotational speed, rolling element impact, and lubrication conditions.
  • Loading method: Apply cyclic impact loads to the cage through rolling elements at a specified rotational speed, simulating the dynamic interaction during high-speed operation.
  • Failure criterion: Determine failure when the cage exhibits cracks, deformation, or breakage that affects the normal operation of the bearing.
   
• Application and output:
  • Optimize cage design: Provide data support for improving the cage's structural strength, material selection, and manufacturing processes.
  • Verify service life: Ensure the cage can match the bearing's overall service life under extreme operating conditions.
   

04 Test Procedures and Analysis

Test Planning