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Split Hopkinson Presssure Bar

Split Hopkinson Presssure Bar

Additional Information:

What is a Split Hopkinson Pressure Bar?
A Split Hopkinson Pressure Bar (sometimes called a Kolsky bar or SHPB) is an apparatus used to characterize the unique stress-strain response of materials during dynamics loading. They make use of interesting wave mechanics by measuring the part of a stress wave that does not go into a material to work backwards and determine the effects felt by a sample material. These devices are sold commercially for around $20,000 but with a research group at Northeastern University, I have been working to design and construct a miniature SHPB in order to characterize the stress-strain response of polymers and metals during loading achieving a strain rate in the order of 1000-4000 s^-1 for 20% of this price.

My research:
Each SHPB must be custom made for a desired family of materials (metals, polymers, ceramics...etc) and a target strain rate range. Typically, SHPB apparatuses achieve strain rates in the order of 100 – 1000 s^-1 and are around 20m in length but my research group is interested in characterizing strain rates several magnitudes greater than this.

My tasks as part of this group has been to learn the relevant theory behind the SHPB and develop a method to allow for our desired high strain rates. The method that I have worked for the past year to develop requires the device to be shrunk from 20m to < 5m in total length to impart a shorter incident pulse. In doing so I have developed what is known as a miniature SHPB because it is miniature.

After months of research and parameter calculation I worked to develop an FEM simulation in Abaqus to model the device and determine the strain rates that will be achieved. Once all the ground work was done and all of our key parameters were set, I worked to produce the rest of the device: I developed a gas gun to accelerate a striker utilizing fluid mechanics knowledge, coded a velocity measurement system and launch system using Arduino, and made an in depth CAD model detailing every part of the apparatus in order to make sure that we were on track to start constructing the device.

Recently, my group was able to get to Northeastern University’s Innovation Campus in Burlington, Massachusetts to start the assembly process of our device. The assembly took us a few days to complete and now we are moving into the more laborious task of calibrating the system. The SHPB functions based on a few key assumptions, one of which being the imparting of a one-dimensional wave pulse. To reach this idealized condition, I put a lot of effort into making sure of precise manufacturing tolerances for integral components, but the system still needs to be meticulously axially aligned to yield correct results.

Split Hopkinson Presssure Bar
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