|Home||The Split Hopkinson Bar Apparatus(also known as Kolsky Apparatus) is composed of a striker bar, an incident bar, the test specimen and the output bar. A rectangular compression wave of well defined amplitude and length is generated in the incident bar when it is impacted by the striker bar. Once this wave reaches the test specimen part of it transmits through it and part of it reflects back through the incident bar. From one dimensional wave propagation analysis we can determine high strain rate stress-strain curves from the measurements of strain in the incident and output bars. In order to obtain correct wave propagation the striker bar must reach necessary velocity before it hits the incident bar.|
|Milestones||Two major subsystems play important role in wave generation process. Stress Generating System that consists of gas reservoir, quick opening valve(or irys/ membrane),vacuum pump, stopper, launch tube, striker, incident and transmitter bar. Stress Determination System consists of strain gages, bridges, amplifiers and oscilloscope.|
|Team Members||This project will focus on the design of the Stress Generating System. In this system the reservoir acts as an accumulator for a measured amount of gas under high pressure. Before each testing, the reservoir is charged to the desired pressure from compressed gas cylinder. Later during firing gas is suddenly released trough a quick opening valve into the launch tube and behind the striker. Expansion of this gas behind the striker accelerates it down the launch tube.|
reservoir, launch tube and the striker thus constitute a unified system
for converting potential gas energy into a useful striker kinetic energy.
It is assumed for the first approximation for design purpose that
the gas obeys the perfect gas laws and that expansion occurs
adiabatically. Furthermore it is assumed that the amount of energy loss in
the system is negligible. Thus a relationship among the pressures,
volumes, velocity and mass may be obtained by equating the potential
energy of gas and the kinetic energy of the striker.
Stress Generating System will undergo a testing phase in the EXPERIMENTAL PART of the project. We are planning to conduct the following tests:
1. Portable vacuum pump performance testing to determine actual suction required during the retrieval process of the striker bar.
2. Velocity measuring testing. This experiment will determine the actual pressure-velocity curve of the striker bar. It will consist of designing, building and testing of the Velocity Measuring Apparatus (VMA),(based on photo resisting elements and the duration of the laser light transmittance). We are also considering the usage of standard accelerometer in the portion of this experiment to compare the results with the corresponding results obtained from VMA.
3. Examination of the strains present in the crucial components present during the operation of the apparatus.
4. If time permits we will conduct several destructive dynamic testing on samples of our choice.
The experimental part milestones are included on the Milestones Page of the project.