A modified Kolsky bar system for testing ultrasoft materials under intermediate strain rates

Area of Science:

• Materials Science
• Mechanical Engineering
• Dynamic Testing

Background:

• Traditional Kolsky bars are unsuitable for ultrasoft materials due to limitations in strain rate and pulse duration.
• Testing soft materials requires specialized equipment capable of handling low-amplitude stresses and long loading pulses.

Purpose of the Study:

• To modify a Kolsky bar apparatus for testing ultrasoft materials at intermediate strain rates (10-100 s⁻¹).
• To develop a reliable data acquisition method for dynamic testing of soft materials using long loading pulses (5-50 ms).

Main Methods:

• A 25 mm aluminum Kolsky bar was modified with an 800 mm steel striker and a 2.5 mm soft rubber pulse shaper.
• A laser gap gauge was employed for direct measurement of sample deformation.
• Piezoelectric transducers embedded in the bars monitored low-amplitude dynamic stresses.

Main Results:

• The modified Kolsky bar successfully generated ultralong loading pulses (5-50 ms).
• Direct deformation measurement via laser gap gauge proved feasible for ultrasoft materials.
• The system effectively monitored low-amplitude dynamic stresses during testing.

Conclusions:

• The modified Kolsky bar system is a viable tool for dynamic characterization of ultrasoft materials.
• This approach overcomes the limitations of traditional strain gauge methods for long loading pulses.
• The feasibility was demonstrated using a commercial foam rubber sample.