(Dr. Tom Kurfess, advisor)
"Systems Development for High Temperature, High Strain Rate Material Testing
Hardened Steels for Plasticity Behavior Modeling"
Hard turning is a more flexible process than grinding with respect to component production changeover. Therefore, as lot sizes continue to decrease due to policies such as just in time manufacture, hard turning is becoming a viable and desirable However, because hard turning is a relatively new process, it is not being optimally employed. This is due to the fact that the process itself is not well understood. To better understand the material removal mechanics in hard turning, empirical data must be developed that provide insight into the behavior of hardened steels at high temperatures, large strains and at high strain rates.
To assess material behavior, a Split Hopkinson’s Pressure Bar (SHPB)
apparatus was used as the experimental facility at the Georgia Institute of
Technology. This set-up is capable of testing materials at relatively high rates
of strain which are comparable to strain rates found in machining operations.
The SHPB is a standard material testing apparatus. However, an induction heater
for high temperature testing was integrated into the SHPB for this research.
Testing was done from room temperature up to 900° C in increments of 100°
C. The new experimental apparatus was able to generate data that have not been
available to researchers in the past. The new system was used to obtain flow
stress data for three types of hardened steels: AISI 52100, 1070 and 1050. Subsequently,
this set-up will be useful for testing specific materials from which high temperature
flow stress data is required. Finally, this flow stress data is used to suggest
an empirical model that best characterizes the specific material behavior. In
the future, the flow-stress data and empirical model will be used to implement
hard turning simulation models and FEM packages.