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**[Abstract]**
This study investigates the fatigue life and failure mechanisms of a glass fiber/nylon 66 composite rolling bearing manufactured through a short fiber injection molding process. Through a series of fatigue tests, the research provides valuable insights into the performance and reliability of composite bearings, offering a reference for their design and practical application in industrial settings.
**Keywords**: composite rolling bearings; fatigue test; failure analysis
**Test Research on the Fatigue of Composite Rolling Bearings**
Zhang Li, Yang Yong, Zhang Heng
(Luoyang Institute of Technology)
**[Abstract]**
This paper presents a fatigue test on composite materials used in rolling bearings, focusing on the fatigue life and failure behavior of glass-fiber-reinforced nylon 66 mosaic bearings produced via injection molding. The study introduces a reliable testing method that supports the design and application of composite rolling bearings.
**Keywords**: composite rolling bearings; fatigue test; fatigue failure
**1. Introduction**
Composite rolling bearings are widely used in various industrial applications due to their excellent wear resistance, corrosion resistance, heat resistance, and dimensional stability. They also help reduce vibration and noise while maintaining a low cost. However, the fatigue properties of composites differ significantly from those of metals. Composite materials are more sensitive to loading frequency and temperature, leading to more scattered fatigue data. Therefore, traditional metal-based fatigue testing methods are not suitable for composites. This study explores an effective and convenient fatigue test method for composite bearings, ensuring their safety and reliability and promoting their broader use in industry.
**2. Experimental Studies**
**2.1 Test Specimens and Equipment**
A total of 25 sets of 204 composite rolling bearings were tested. These bearings were made of nylon 66 reinforced with short glass fibers, using a meltable alloy core injection molding process. The testing was conducted using a JB-30 type rolling bearing fatigue tester.
**2.2 Test Method**
Due to the high variability in bearing fatigue life, statistical methods were employed to analyze the data. A truncated test method was used, which is simple and efficient. In this method, a certain number of samples are tested until failures occur, and the remaining samples are censored. This approach allows for accurate estimation of the life distribution parameters.
In the experiment, a radial load of 588 N was applied to the 204-type composite bearings, with oil lubrication and a truncation number of 15. The testing speed was set at 12,800 r/min, and all test conditions were kept consistent. For comparison, 25 sets of 204 plastic bearings made of nylon 66 were also tested under similar conditions, with a radial load of 392 N and oil lubrication using 20# oil.
**2.3 Data Processing**
The study found that the Weibull distribution better fits the fatigue failure data than the normal distribution. The life of the bearings follows a two-parameter Weibull distribution, expressed as:
F(L₀) = 1 - exp[-(L₀ / β)^e]
where Lâ‚€ = 10ⶠrevolutions, e is the slope parameter, and β is the characteristic lifetime parameter. Using the best linear invariant estimation method, the parameters were calculated. For composite bearings, e = 5.756 and β = 4.467 × 10â¶. For plastic bearings, e = 3.02 and β = 7.104 × 10â¶.
**2.4 Monitoring of Fatigue Failure**
To monitor fatigue failure, a surface thermometer was used to track temperature changes during operation. As the bearing operates, the temperature gradually rises until it stabilizes. When fatigue occurs, the temperature increases further due to increased friction. Additionally, sound monitoring was used to detect changes in the bearing’s condition during rotation.
**3. Test Results and Analysis**
**3.1 Fatigue Life**
By taking the double logarithm of the Weibull equation, a linear relationship was established. The fatigue failure probability diagram for 204-type composite and plastic bearings is shown in Figure 2. According to international standards, 90% of bearings should reach at least 10ⶠrevolutions before failure.
From the results, the rated fatigue life of the 204-type composite bearing under a 588 N load was found to be 3.1 × 10ⶠrevolutions, while the plastic bearing had a rated life of 2.2 × 10ⶠrevolutions under a 392 N load. This indicates that the composite bearing has a 50% higher load capacity and significantly improved fatigue life.
**3.2 Fatigue Fracture Characteristics**
Four main failure modes were identified through microscopic observation:
- **Surface Fatigue**: Includes rolling contact fatigue, pitting, chipping, and exfoliation.
- **Plastic Flow**: Occurs when contact stress exceeds endurance strength, causing deformation or melting.
- **Abrasive Wear**: Leads to material loss and increased clearance between components.
- **Associated Wear**: Can occur between the bearing and its housing due to relative motion.
Each bearing may experience multiple failure modes simultaneously.
**4. Conclusions**
(1) The study used a fixed-number censored test method and the linear invariant estimation technique to determine the Weibull parameters of the bearing life, providing a simple and effective approach for data analysis.
(2) The 204-type composite bearing demonstrated a rated fatigue life of 3.1 × 10ⶠrevolutions under a 588 N load, confirming the feasibility of using composite materials in rolling bearings.
(3) Four major failure modes were identified, offering important guidance for the design, performance evaluation, and reliability improvement of composite rolling bearings.
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