Fatigue Testing of Carbon Fiber Reinforced Thermoplastic (CFRTP)

Importance of the Topic

Carbon fiber-reinforced thermoplastic composites combine high specific strength with excellent moldability and recyclability. Mass-production techniques such as injection and press molding reduce costs and support automotive applications. Assessing fatigue performance under repeated loading is critical for reliability and safety in transport structures.

Objectives and Study Overview

This study aimed to evaluate the fatigue behavior of randomly oriented CFRTP using a tabletop dynamic and fatigue testing system with specialized composite grips. Key goals included minimizing grip-induced damage and obtaining reliable S-N data.

Methodology and Instrumentation

Static and fatigue tests were carried out at room temperature on specimens prepared from 3 mm thick plates of randomly oriented CFRTP. Static tensile tests established baseline strength. Fatigue tests spanned up to 1×10^6 cycles at 10 Hz with a stress ratio of 0.1 and maximum stress levels from 35 to 55% of static strength.

Instrumentation

• Servopulser EHF-L tabletop dynamic and fatigue tester
• 20 kN load cell
• ±25 mm actuator stroke
• Servo Controller 4830
• Non-shift screw-type grips with fine file teeth
• Windows software for controller operation

Results and Discussion

Static tests yielded an average ultimate tensile strength of 191.3 MPa (CV 6%). Fatigue tests at various stress fractions showed stable sine-wave control and central specimen failure enabled by the new grips. The S-N diagram confirmed the expected inverse relationship between stress amplitude and cycles to failure.

Benefits and Practical Applications

• Improved fatigue evaluation accuracy through reduction of grip-induced failures
• Reliable S-N data for CFRTP design in automotive and transport structures
• High-precision dynamic control facilitating repeatable testing protocols

Future Trends and Opportunities

Ongoing development may include tailored grip geometries for diverse composite forms, adaptive control algorithms for real-time fatigue monitoring, and integration with digital twins for predictive maintenance. Extending to other thermoplastic matrix composites can broaden industrial applications.

Conclusion

The Servopulser EHF-L system combined with newly designed composite grips enables accurate fatigue assessment of CFRTP, enhancing material qualification processes and supporting lightweight, mass-producible composite structures for next-generation transport equipment.