Eglin Team 3

Background:

The Air Force Research Laboratory (AFRL) has utilize a test to study material properties in extreme strain conditions developed during high velocity collisions called the Taylor Impact Test. The material properties exhibited during the collisions are important in the development of ordinance designed for penetrating armor. AFRL uses the data in comparison with data generated using finite element analysis to predict the changes the material will have as it impacted the armored surface. The information is crucial in the design of the ordinance’s functional characteristics. The engineers can estimate how far it will penetrate into the armor, the shape of projectile at various points during the penetration and the amount of energy transferred to the other side of the armor.

The Taylor Test is performed by accelerating cylindrical specimens to velocities near 200m/s and colliding them with a large incompressible flat surface. The impact is recorded using a high speed camera and examined to evaluate the changes in structure that occur during the test. The specimen cylinders are formed in standard diameters between 0.21 cal to 0.50 cal. The specimens tested have a defined shape property known as the length to diameter (L/D) ratio that can be adjusted for different tests. The L/D ratio is generally maintained at ten, but at times is varied to determine its affect on the material properties. The projectile is accelerated during the test using solid propellant and the velocity is varied by adjustments in the quantity of propellant used. The researchers have numerous charts and test data that is referenced to determine the propellant loading for the desired test parameters.

The purpose of this project is to upgrade the projectile velocity measurement system used during the Taylor Test. The test design currently employs two methods of velocity measurement: laser barriers and pressure transducers. The pressure transducers are mounted on the end of the firing mechanism and measure the differential pressure as the specimen travels out the barrel. The difference in time between the readings is converted to the velocity. Similarly, the lasers barriers produce a change in voltage when they are blocked by the specimen. The time difference between the voltage changes is converted to the velocity. The current laser barrier system has become outdated and is failing.

Design Specifications:

  1. The system must be able to measure specimen projectile speeds of at least 200m/s.
  2. Detector performance can not be affected by specimen material properties.
  3. The system must be able to accommodate specimens with cross-sectional diameters of .20 in to .50 in.
  4. Operation and calibration of the equipment must be able to be performed with no safety equipment
  5. Total system manufacturing and purchasing cannot exceed $1000.00 without a proposal.
  6. The new equipment must easily integrate into the existing system. Easy integration was defined to be:
    1. New detectors provide signals compatible with existing data acquisition system.
    2. Alterations to current safety equipment do not degrade the safety equipment integrity
    3. Alignment and calibration prior to use (after initial installation) should require less than one man-hour.