Impact testing is a crucial component of materials science and engineering, used to assess the behavior of materials under various dynamic loading conditions. Gas guns are versatile tools employed in impact testing to generate controlled high-velocity impacts. Whether you are testing materials for aerospace applications, automotive safety, or researching the behavior of materials in extreme conditions, adhering to best practices when using gas guns is essential to ensure the accuracy and reliability of your results. In this article, we explore the best practices for gas gun impact testing.
The Best Practices for Successful Impact Testing
1. Ensure Safety
Before diving into the specifics of gas gun operation, it’s paramount to emphasize safety. Impact testing can involve high velocities and forces that can be dangerous if not properly managed. Always adhere to the range or building safety protocols as well as any listed requirements for the equipment. In addition, ensure that all personnel involved are well-trained and equipped with appropriate safety gear. At minimum this should be eye protection and hearing protection. Also make sure that the gas gun you are using has safety systems installed. Note the safety systems of the Sydor gas gun below.
2. Familiarize Yourself with the Gas Gun:
Understanding the gas gun’s design, components, and capabilities is fundamental for its successful operation. Gas guns come in various configurations, including single-stage and two-stage designs, each with its own advantages and limitations. Familiarize yourself with the specific gas gun you are using, and consult the manufacturer’s manual for guidance in order to maximize your chance of success.
In the case of the Sydor Gas Gun, it is a single stage system rated for 300 bar with an interlock safety, and electronic firing mechanism. If provided with a firing tunnel, any access doors will be wired into the interlock system to enhance safety. Finally, Sydor’s gas gun, if over pressurized, will slowly vent excess gas via an exhaust tube facing down range to under the 300 bar mark.
3. Consider Your Test Objectives:
Clearly define your test objectives before conducting any impact test. This includes determining the desired impact velocity, the type of projectile, and the specimen to be tested. Having a well-defined purpose for your testing will help guide your experimental setup and data analysis.
As an example, a common test is the use of fragment simulating projectiles against armor samples, there are many international standards that call for this test with NATO AEP1 (STANAG)2 2920
4. Calibrate and Validate:
Making sure that any measurement equipment being used with the gas guns such as pressure transducers, strain gauges, velocity screens and other sensors are properly calibrated. Validation of the gas gun’s performance is equally important. Validation tests are designed by the user of the gas gun system; however, a common test could be the use of reference materials with known impact properties to confirm that your gas gun is operating as expected. Common measurement equipment for impact testing would be velocity measurement systems such as Sydor’s Infra-Red Velocity Screens or a High Speed Video Camera
5. Prepare Specimens Properly:
Carefully prepare your test specimens to ensure consistency and reproducibility. Specimen dimensions, geometry, and surface finish should meet established standards or specifications. Surface imperfections or defects on the specimen can significantly affect test results. These features of the test specimens should also be recorded within the test reports.
6. Select Projectiles that Match Objectives:
Selecting the appropriate projectile is crucial. The projectile should have properties that closely match your test objectives. Factors to consider include mass, shape, and material composition. Ensure that the flyer is properly machined or manufactured to minimize variations.
Many test standards will provide this information, however if custom projectiles are being used then this the factors mentioned above must be considered and tested prior to data collection.
7. Carefully Manage Propellant and Pressure:
The type and quantity of propellant gas used in the gas gun determine the velocity of the projectile. Properly manage the propellant load and pressure to achieve the desired impact velocity. Keep in mind that excessive pressure can damage the gas gun or create dangerous conditions.
The Sydor Gas Gun can run on three different types of gas; Compressed Air, Nitrogen and Helium. Compressed air being the densest gas, it will provide the slowest velocities, but it is the easiest to obtain. Helium being the least dense will provide the fastest velocities but may be more difficult to source.
8. Extract Meaningful Results with Data and Analysis:
Invest in high-quality data acquisition systems, such as Sydor’s Integrated Range Instrumentation to record the impact event accurately. This includes capturing high-speed images, measuring force, strain, and other relevant parameters. Conduct thorough data analysis to extract meaningful insights from your test results.
9. Maintain Environmental Controls:
Environmental conditions such as temperature and humidity can influence material behavior. Whenever possible, maintain consistent environmental conditions during testing. If variations cannot be avoided, ensure that they are documented and accounted for in your analysis.
10. Ensure Proper Documentation and Reporting:
Maintain detailed records of all aspects of your impact tests, including setup, calibration, and results. Proper documentation is essential for replicability and for reporting findings in scientific publications or engineering reports.
11. Continuous Improvement:
After each impact test, evaluate the results and the testing process for opportunities for improvement. This could include refining specimen preparation techniques, optimizing gas gun parameters, or enhancing data analysis methods.
In conclusion, gas guns are powerful tools for conducting impact testing in various scientific and engineering fields. Following best practices ensures the safety of personnel, the reliability of results, and the advancement of knowledge in ballistics, effectiveness of armor, materials science and engineering. By adhering to these guidelines, researchers and engineers can conduct impactful experiments that contribute to the development of safer and more resilient materials and structures.
If you need more help in deciding on which path to take, our ballistics experts are happy to assist you. Please click on the link below to see more of what Sydor Technologies offers and arrange a personalized meeting with an expert.
1 Approved Engineering Practices
2 Standardized Agreement