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A technique for measuring dynamic friction coefficient under impact loading
1College of Science, National University of Defense Technology, Changsha, Hunan 410073, China.
The Review of Scientific Instruments
|October 3, 2014
Summary
A novel split Hopkinson pressure bar setup with a wedge-shaped incident bar was developed to test dynamic friction coefficients under impact. This method directly calculates friction coefficients from measured forces without assumptions, revealing changes during loading.
Area of Science:
- Materials Science
- Mechanical Engineering
- Tribology
Background:
- Dynamic friction coefficients are critical for understanding material behavior under impact loading.
- Existing methods often require assumptions or complex theoretical derivations for friction coefficient calculation.
- A need exists for a direct, assumption-free method to measure dynamic friction under combined compressive and shear stress.
Purpose of the Study:
- To develop and validate a novel experimental setup for measuring dynamic friction coefficients under impact.
- To investigate the friction coefficient evolution and slip behavior of PTFE/aluminum 7075 friction pairs.
- To provide a direct calculation method for dynamic friction coefficients without theoretical assumptions.
Main Methods:
- A modified split Hopkinson pressure bar (SHPB) technique utilizing a wedge-shaped incident bar for combined compressive and shear loading.
- Integration of quartz transducers for direct force history measurement and an optical apparatus for interfacial slip monitoring.
- Experimental testing of PTFE/aluminum 7075 friction pairs and simulation using explicit finite element method (FEM) code LS-DYNA.
Main Results:
- The novel SHPB setup successfully measured time-resolved dynamic friction coefficients and slip histories.
- For PTFE/aluminum 7075, the average friction coefficient in the stable plateau was 0.137, with maximum normal pressure of 52 MPa and slip velocity of 1.5 m/s.
- FEM simulations confirmed that constant pressure and slip velocity can be achieved with specific incident pulse shapes, predicting potential for higher pressures and velocities with specialized friction pairs.
Conclusions:
- The developed wedge-shaped SHPB setup offers a direct and reliable method for determining dynamic friction coefficients under impact.
- The study demonstrates that friction coefficients are not constant during impact loading and vary with slip.
- The methodology is adaptable for various friction pair geometries and can be extended to explore extreme conditions of pressure and velocity.
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