Split Hopkinson Pressure Bar (SHPB) Firing System Redesign / Undergraduate Researcher
Overall Setup
Key Contributions
Firing System Redesign: Replaced the previous trigger mechanism with a spring-loaded piston actuated via air-venting, improving reliability and control.
Sensor Integration: Installed a dual pressure sensing system using analog gauges and Arduino-powered digital pressure transmitters for real-time monitoring and safer operation.
Engineering Calculations: Derived optimal spring constant (k) and valve flow coefficient (Cv) values to achieve precise launch conditions within the desired pressure range.
System Layout & Testing: Contributed to the mechanical and pneumatic design layout, prioritizing safety, repeatability, and ease of operation in a high-strain-rate testing environment.
Background / Goal
This diagram shows a typical Split Hopkinson Pressure Bar (SHPB) setup used to test materials under high strain rates. My role focused on redesigning the pneumatic firing system to launch the projectile cleanly from the gas gun. I calculated the required spring compression force and selected an appropriate solenoid with the required flow coefficient to achieve rapid chamber venting. By replacing the original three-way valve with a manual vent, I significantly reduced lag time and improved system responsiveness for consistent, high-speed material impacts.
Typical Setup
Our Setup
SHPB Pneumatic Firing System Redesign
Description
I replaced the original analog-only configuration with a dual-sensor system consisting of both pressure gauges and Arduino-based electronic transmitters for real-time monitoring and data acquisition. I integrated a firing solenoid with manual venting, added an automatic pressure relief valve, and updated the wiring layout for safe gas delivery from a 3000 psi tank to the launcher.
In addition to system design, I compiled a detailed part inventory (with traceable part numbers) and created wiring and PSI validation diagrams to ensure every component operated well below its pressure rating. This work enabled safer experimentation and streamlined troubleshooting for future users of the SHPB system.
To see more details related to the Arduino-based pressure transmitter, see my "Arduino-Based Remote Controller & Live Sensor" project.
Spring Constant & Flow Coefficient Calculations
Spring Constant Calculation
I calculated the required pressure to compress the internal spring within our SHPB setup. Assuming a spring constant of k=1lb/in, I analyzed the displacement from the spring’s free length to its compressed length, then calculated the resulting force and distributed it over the available surface area. This analysis yielded a required pressure of approximately 1.21 psi, confirming that our system's nitrogen operating pressure (≈100 psi) would be more than sufficient to trigger the projectile release reliably.
Cv Calculations for Solenoid Valve Selection
To ensure rapid depressurization of the gas chamber after firing, I calculated the flow coefficient (Cv) needed for our venting solenoid. By modeling the vent volume and applying gas dynamics equations with a target vent time of 1 millisecond, I solved for the minimum Cv needed to achieve the required mass flow rate. My analysis showed that valves with Cv values of 2.1 or higher would reduce chamber pressure in under 0.133 seconds. This informed our decision to switch from a slower three-way valve to a manual vent valve, significantly improving venting response time and system reset efficiency.