Design of a Split Hopkinson Pressure Bar facility for dynamic material characterization

It is important to know the mechanical response of materials over a full range of strain rates. In machining and stamping, or in ballistic type events such as bullet penetration, shell impacts, and explosive blasts, strain rates of 100 s-1 to 10,000 s-1 or even higher for hyper-velocity impacts, are achieved. A Split Hopkinson Pressure Bar facility is generally used to study the mechanical response of materials at these strain rates. The Split Hopkinson Pressure Bar produces precise data which can be used to study the dynamic response of materials. Over the last 70 years the Split Hopkinson Pressure Bar has been subject to many scrutinous studies which push the boundaries of materials it can test. In this thesis, the design of a compressive Split Hopkinson Pressure Bar facility is presented. The Split Hopkinson Pressure Bar is designed to obey the fundamental assumptions: one-dimensional and undispersed wave propagation as well as uniaxial loading of the specimen. Each subsystem of the compressive Split Hopkinson Pressure Bar is closely examined to outline its role in obeying these assumptions as well as its role in obtaining accurate data acquisition, then a design of each subsystem is presented. The presented facility improves accuracy, functionality, and ease of operation compared to previous work. Improvements in strain gage design increased the maximum attainable impact velocity from 40 m/s to at least 50 m/s. The Split Hopkinson Pressure Bar facility is thoroughly tested to verify the design. The dynamic response of aluminum 6061-T6511 is tested between strain rates of 1,000 s-1 and 6,300 s-1 to verify the accuracy of the facility. Testing showed that the response of 6061-T6511 is strain rate dependent which is consistent with literature. The flow stress of 6061-T6511 increases as strain rate increases from 350 MPa to 400 MPa at a rate of about 0.009 MPa-s. The dynamic response of polycarbonate is reported at strain rates between 1,000 s-1 and 7,000 s-1. The flow stress increases by about 8.2% over the range of strain rates. Super activated carbon and a super activated carbon composite is also studied using aluminum pressure bars, specifically designed for soft materials.M.S.Includes bibliographical reference