Three-Point Bending Fatigue Test and Crack Observation of Cracked Specimens Using SEM Servopulser

Significance of the topic

Material fatigue and fracture analysis at the micro-scale are critical for predicting component lifespan and enhancing safety. In-situ SEM observation during fatigue loading provides direct insight into crack initiation and growth.

Objectives and study overview

This work integrates a Scanning Electron Microscope with an electric-hydraulic fatigue tester to observe real-time crack development during three-point bending tests on notched stainless steel specimens.

• Determine static bending strength
• Perform fatigue tests at varied load levels
• Monitor micro-crack initiation and propagation

Methodology

A static three-point bending test at 5 mm/min established the maximum load. Fatigue tests then applied cyclic loads at stress ratio 0.1 and 20 Hz frequency. Specimens measured 36×4×2.5 mm with a central 0.5 mm notch.

Used instrumentation

• SEM Servopulser combining SEM and EHF-LV020k1A servopulser
• Servopulser EHF-L Series dynamic and fatigue testing machine
• 10 kN load cell and actuators ±10 mm SEM, ±25 mm EHF
• Controller 4830 with Windows software

Main results and discussion

The static test yielded 1138 N maximum load. Fatigue tests at loads from 638 to 405 N produced an S-N curve showing fewer cycles to failure at higher loads. In-situ imaging captured crack initiation around 5000 cycles and tracked growth to ~400 µm before failure at ~9826 cycles, with detailed crack tip morphology observed at magnifications up to 1000×.

Benefits and practical applications

• Real-time visualization of microfracture under load
• Improved accuracy in fatigue life prediction
• Applicable in materials R&D, QA/QC, and industrial analytics

Future trends and applications

Expanding in-situ SEM fatigue testing to diverse materials and complex loading scenarios. Integration of automated image analysis, high-speed detectors, and AI-driven crack detection will enhance throughput and predictive maintenance.

Conclusion

The SEM Servopulser and EHF-L system enable simultaneous mechanical evaluation and microscopic fracture observation, advancing understanding of crack dynamics and supporting improved material design and durability assessment.

Reference

• Nishikawa Y., Yano F. Three-Point Bending Fatigue Test and Crack Observation Using SEM Servopulser. Application News No. 01-00794-EN. Shimadzu Corp; Nov 2024.
• Three-Point Bending Fatigue Tests of Welded Material Using SEM Servopulser. Application News No. 01-00792-EN.
• Three-Point Bending Fatigue Tests of Carbon Fiber Reinforced Plastic Using SEM Servopulser. Application News No. 01-00793-EN.