double-arrowLaboratory Equipment

The Dynamic Mechanics of Materials Laboratory is equipped with a compression split Hopkinson bar (SHB) apparatus for high strain rate compression experiments.  The apparatus, see Figure 1,  is comprised of three 0.5 in. diameter Ti-6Al-4V bars. The compression loading wave is generated by firing a striker bar into the end of the incident bar using a gas gun. The incident and transmitter bars are 6 ft. long and comprised of Ti-6Al-4V. The waves during a test are measured at the center of both the incident (Gage A) and transmitter (Gage B) bars, see Figure 1. At both locations, four 1000 Ohm strain gages are connected in a full Wheatstone bridge circuit configured to measure axial load. The compression SHB apparatus at the Dynamic Mechanics of Materials Laboratory is shown in Figure 2.

Specimens, typically small cylinders, are placed between the bars. The contact surfaces between the specimen and the bars are lubricated to minimize friction and "barreling" deformation. Typical strain rates of 400 to 8000 s-1 are achievable on this apparatus.

Click here for sample compression SHB data from the apparatus shown in Figure 2.

Some materials require large sample sizes to maintain their aggregate mechanical characteristics.  These sample sizes may be too large for the apparatus in Figure 2 to accomodate.  Because of this, the Dynamic Mechanics of Materials Laboratory has designed and constructed a large diameter compression SHB.

Sketch of a compression split Hopkinson bar apparatus.
 Sketch of a compression split Hopkinson bar apparatus.
Figure 2. Compression split Hopkinson bar apparatus at the Dynamic Mechanics of Materials Laboratory.
Figure 2. Compression split Hopkinson bar apparatus at the Dynamic Mechanics of Materials Laboratory.

 

More detail on this experimental technique can be found in the following reference:

Gray, G.T., “Classic Split-Hopkinson Pressure Bar Testing”, Mechanical Testing, Vol. 8, ASM Handbook, ASM International, 2000.