Dynamic Tensile Testing Using a Three-Dimensional DIC Analysis System
—Observation of Strain Distribution and Measurement of Strain in Polypropylene Just before Fatigue Failure—
Previously, it was often difficult to predict the appropriate fatigue life during fatigue testing that applied dynamic test forces or strains at high speeds due to stress concentration in the areas measured with conventional strain measurement methods that use contact-type sensors. For this reason, in recent years, analysis by digital image correlation (DIC) has attracted attention as a testing technique that can be used to accurately evaluate the static and dynamic mechanical characteristics of materials in the elastic and plastic ranges. The fatigue characteristics of such materials can now be comprehensively evaluated by installing a three-dimensional DIC analysis system in the fatigue and durability testing machine.
Dynamic (Fatigue) Tensile Testing
EHF-U Series Hydraulic Fatigue and Durability Testing Machine
Three-Dimensional Digital Image Correlation System Setup
| Instrument Used | EHF-U series hydraulic fatigue and durability testing machine |
|---|---|
| Control Method | Stress control, upper tensile stress 20 MPa and lower tensile stress 2 MPa |
| Test Speed | 2 Hz |
| Strain Measurement | Q400 3-dimensional digital image correlation system 35 mm fixed-focus lens Istra4D control and analysis software for image correlation (Dantec Dynamics K.K.) Frame rate: 10 fps KFG-2-120-D16-11L1M2S strain gauge (Kyowa Electronic Instruments Co., Ltd.) (affixed to back side of sample) DC-97A dynamic strain gauge (Tokyo Measuring Instruments Laboratory Co., Ltd.) |
| Test sample | JIS K 7161 1A Polypropylene |
Fatigue DIC Analysis Example
Principal Strain-Time Diagrams
(Virtual Strain Gauge Measurement)
In-Plane Principal Strain Distribution (Confirmation of Strain Concentration Locations)
Note: The virtual strain gauge is a function included in the DIC analysis software that can measure displacement at any arbitrarily specified point on the sample observation surface.
- Enables detailed evaluation of in-plane strain during the fatigue failure process.
- Data is continuously acquired during the measurement time of one fatigue test cycle, so the strain distribution can be evaluated during hysteresis.
- Enables fatigue evaluation from peak-to-peak data acquisition.
Static Tensile Testing
Test Sample and Jigs
Comparison of Stress-Strain Curves
(Comparison of Strain Gauge and Virtual Strain Gauge)
In-Plane Principal Strain Distribution
- Large-strain region that exceeds the measurement limit of strain gauges
- Enables various strain measurements and evaluation of strain distribution at arbitrary points.