Fatigue Testing of Rigid Plastics (JIS K 7118)

Significance of the topic

Plastic components in automotive, aerospace and consumer goods are subject to repeated loads that can lead to fatigue failure over time.
Accurate characterization of fatigue behavior in rigid plastics is essential to ensure product safety and performance under prolonged cyclic stresses.

Study Objectives and Overview

This study demonstrates fatigue testing of rigid PVC and polycarbonate (PC) according to JIS K7118 using a tabletop dynamic and fatigue testing system.
The aim is to evaluate static and dynamic mechanical properties and establish relationships between maximum stress, specimen temperature, and fatigue life for two representative polymers.

Methodology

Static tensile tests were performed at 50 mm/min to determine the ultimate tensile strength of each material.
Fatigue tests were conducted in load control up to 1×10^6 cycles with a stress ratio of 0.1 and frequency adjusted to keep the specimen surface temperature below 30 °C.
Surface temperature monitoring was achieved using a radiation thermometer with blackbody paint applied to the specimen.

Used Instrumentation

• Servopulser EHF-L tabletop dynamic and fatigue testing system
• Servo Controller 4830
• 5 kN load cell and ±25 mm actuator stroke
• Non-shift screw-type grips (prototype)
• FT-H10 radiation thermometer

Main Results and Discussion

Static tests yielded ultimate tensile strengths of 74.7 MPa for rigid PVC and 64.05 MPa for PC.
Specimen temperature remained below 30 °C across all fatigue conditions by adapting test frequency.
S-N data showed decreasing cycles to failure with increasing maximum stress for both materials.
Heating effects were more pronounced at higher stress levels, emphasizing the need for real-time thermal control during cyclic loading.

Benefits and Practical Applications

The described setup enables standardized fatigue characterization of engineering plastics in compliance with JIS K7118.
Real-time temperature monitoring and high-accuracy dynamic control support reliable material screening, design validation, and quality assurance in R&D and industrial testing laboratories.

Future Trends and Potential Applications

Integration of automated jigs and advanced data analytics could further enhance throughput and insight into fatigue mechanisms.
Extension of this approach to additional polymer types and composite materials may support broader application in lightweight structural components.
Predictive modeling combined with in situ thermal measurements promises improved lifetime forecasts for polymer-based parts.

Conclusion

The tabletop Servopulser EHF-L system, coupled with precise temperature control, provides an effective platform for fatigue testing of rigid plastics under JIS standards.
This methodology delivers critical data on mechanical endurance and thermal behavior, facilitating safer and more durable polymer designs.

References

1) Takeshi Kunio: Materials System, 6 (1987), 7-19