Electromagnetic Interference in Measurements of Radial Stress During Split Hopkinson Pressure Bar Experiments

Area of Science:

• Geotechnical Engineering
• Materials Science
• Experimental Mechanics

Background:

• Split Hopkinson pressure bar (SHPB) tests are crucial for soil characterization under dynamic loading.
• Plane strain conditions are typically achieved using rigid confining rings, enabling radial stress inference.
• Previous SHPB experiments have reported anomalous electromagnetic interference (EMI) obscuring radial stress data.

Purpose of the Study:

• To identify the source of electromagnetic interference in SHPB tests on soils.
• To develop methods for mitigating EMI for reliable radial stress measurements.
• To improve constitutive modeling of soils under blast and impact conditions.

Main Methods:

• Utilized an induction coil to detect the source of anomalous signals.
• Conducted comparative experiments using sand and rubber specimens.
• Analyzed signals to differentiate between interference from equipment and specimen deformation.

Main Results:

• Identified magnetised pressure bars (martensitic stainless steel, 440C) as the source of EMI.
• Demonstrated that induced currents in gauge lead wires are the primary cause of interference.
• Confirmed that deforming soil specimens contribute minimally to the observed EMI.

Conclusions:

• The movement of magnetised pressure bars induces currents, causing EMI in radial stress measurements.
• Recommendations are provided to reduce EMI, enabling more accurate soil characterization.
• Accurate radial stress data is essential for developing robust soil constitutive models for dynamic events.