High strain rate testing using the SHPB -- Help please

[Ben_P_1992]

I am a part C mechanical engineering student and require some advice for my individual project, which is based on the high strain-rate testing of a particular glass filled composite material using a split-Hopkinson pressure bar (SHPB) experiment.

I gathered the results on a SHPB test rig and have external data which is being used for comparative analysis to verify my results, however the Young's modulus of the material seems to be way off (It should be about 5-6GPa!) I was hoping somebody had some experience with this experiment or had any ideas as to why this has occurred? Please see the graph below- the gradient of my results should match that of the two curves labelled Finland Test.

https://www.physicsforums.com/attachments/upload_2015-5-2_21-31-21-png.82985/

The data used was gathered from strain gauges mounted on the maraging steel 250 pressure bars. The measured voltage and time was then manipulated with a program (this program has been used in previous experiments and outputted matching results for different materials.) The only inputs required for this program is the elastic wave speed of the pressure bars and their modulus of elasticity as well as the specimen dimensions pre-testing. I am confident that these inputs are correct, and have even played about with the inputs for both (varied the Young's modulus from 160GPa to 220GPa in 10GPa intervals) to see how the Young's modulus is affected, but there is little effect. Please see the graph below:

https://www.physicsforums.com/attachments/upload_2015-5-2_21-37-34-png.82986/

I am very stuck and am not quite sure how to explain why this happening. Any help or advice would be much appreciated.

Thanks,

Ben

 

[leafjerky]

Hey Ben, sorry I'm afraid I won't be of much help as I haven't made it as far as you, but I just wanted to let you know your pictures are not coming up. Just letting you know so you can fix it so someone who can help you will be able to.

 

[Ben_P_1992]

Thanks for the heads up. The pictures are attached here.https://www.physicsforums.com/attachments/upload_2015-5-2_21-31-21-png.82985/
https://www.physicsforums.com/attachments/upload_2015-5-2_21-37-34-png.82986/

 

[afreiden]

Your images are still broken.
You say that this test setup has been successfully used before, but were those previous materials as soft as yours?