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**[Abstract]**
This study investigates the fatigue life and failure mechanisms of a glass fiber/nylon 66 composite rolling bearing manufactured using a short fiber injection molding process. Through comprehensive fatigue testing, the research provides essential insights into the performance and reliability of such bearings, offering valuable guidance for their design and application in industrial settings.
**Keywords:** composite rolling bearing; fatigue test; failure analysis
**Test Research on the Fatigue Behavior of Composite Rolling Bearings**
Zhang Li, Yang Yong, Zhang Heng
(Luoyang Institute of Technology)
**[Abstract]**
This paper presents a detailed investigation into the fatigue behavior of composite rolling bearings made from glass fiber-reinforced nylon 66. The study focuses on analyzing the fatigue life and failure modes under different loading conditions. A practical and efficient testing method is proposed, which can be used to evaluate the safety and service life of composite bearings. This research contributes significantly to the development and application of advanced composite materials in bearing technology.
**Keywords:** composite rolling bearings; fatigue test; fatigue failure
**1. Introduction**
Composite rolling bearings are widely used in various industries due to their excellent wear resistance, corrosion resistance, heat resistance, and low noise characteristics. Compared to traditional metal bearings, they offer lower cost and better dimensional stability. However, the fatigue behavior of composite materials differs significantly from that of metals. Factors such as load frequency, temperature, and material heterogeneity lead to more scattered fatigue life data, making conventional metal fatigue testing methods unsuitable.
To address this, this study conducts a fatigue test on a glass fiber/nylon 66 composite rolling bearing. A truncated test method is employed to estimate the fatigue life distribution, and the results are analyzed using the Weibull distribution model. The findings provide a solid foundation for improving the design and application of composite bearings in real-world engineering scenarios.
**2. Experimental Studies**
**2.1 Test Specimens and Equipment**
A total of 25 sets of 204-type composite rolling bearings were tested. These bearings were manufactured using a short fiber injection molding technique with nylon 66 reinforced by glass fibers. The production process involved meltable alloy core injection molding. For comparison, 25 sets of 204-type plastic bearings made of pure nylon 66 were also tested.
The testing was conducted using a JB-30 type rolling bearing fatigue tester. Both types of bearings were subjected to radial loads—588 N for the composite bearings and 392 N for the plastic ones. All tests were performed under oil lubrication with the same rotational speed of 12,800 rpm.
**2.2 Test Method**
Due to the high variability in fatigue life data, statistical analysis is essential. A fixed-number censored test was used, where 15 sets of bearings were terminated after a certain number of cycles. The remaining bearings were observed until failure or the end of the test. This method allows for an efficient estimation of the life distribution without requiring full testing of all samples.
**2.3 Data Processing**
The Weibull distribution was found to be the most suitable model for describing the fatigue life of the bearings. The failure probability function is given by:
$$ F(L_0) = 1 - \exp\left[-\left(\frac{L_0}{\beta}\right)^e\right] $$
Where $ L_0 $ is the number of revolutions (in units of $ 10^6 $), $ e $ is the shape parameter, and $ \beta $ is the characteristic life. Using the best linear unbiased estimation method, the parameters for the composite bearings were calculated as $ e = 5.756 $ and $ \beta = 4.467 \times 10^6 $, while for the plastic bearings, $ e = 3.02 $ and $ \beta = 7.104 \times 10^6 $.
**2.4 Monitoring Fatigue Failure**
During the test, both temperature monitoring and sound analysis were used to detect early signs of fatigue failure. As the bearing operates, the temperature gradually rises until it stabilizes. When fatigue occurs, the temperature increases again due to increased friction. Additionally, changes in the sound emitted by the bearing during rotation were used to identify failure.
**3. Test Results and Analysis**
**3.1 Fatigue Life**
By plotting the fatigue failure probability on a double logarithmic scale, the relationship between life and failure probability becomes linear. According to international standards, 90% of bearings should survive at least $ 10^6 $ revolutions before failure.
For the 204-type composite bearing under a load of 588 N, the rated fatigue life at a 10% failure probability was found to be $ 3.1 \times 10^6 $ revolutions. In contrast, the plastic bearing had a rated life of $ 2.2 \times 10^6 $ revolutions under a load of 392 N. 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 pitting, spalling, and chipping caused by repeated stress exceeding the material's endurance limit.
- **Plastic Flow**: Occurs when excessive contact stress leads to deformation or melting of the bearing surfaces.
- **Wear**: Involves material loss from the contact surfaces, often resulting in increased clearance and reduced performance.
- **Related Failure**: May occur between the bearing and its housing due to relative motion.
These failure modes provide critical insights into the mechanical behavior of composite bearings under dynamic loading.
**4. Conclusions**
(1) A total of 25 composite rolling bearings were tested using a fixed-number censored method. The Weibull distribution was successfully applied to estimate the fatigue life, demonstrating the feasibility of using statistical models for composite materials.
(2) The 204-type composite bearing showed a rated fatigue life of $ 3.1 \times 10^6 $ revolutions under 588 N load, proving the potential of composite materials in bearing applications.
(3) Four distinct failure mechanisms were identified, offering important references for improving the design, performance, and reliability of composite rolling bearings.
This research not only enhances the understanding of composite bearing behavior but also supports the broader adoption of these materials in industrial applications.
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