John D. Cinnamon

Metallographic Examination and Validation of Thermal Effects in Hypervelocity Gouging

In this work, a gouged section of 1080 railroad rail steel is examined using metallographic techniques to characterize the nature of the damage. The gouging was performed by a rocket sled at Holloman Air Force Base, riding on VascoMax 300 steel shoes at 2.1 km/s. The damaged rail is evaluated in detail to examine material phase changes, shear bands, and heat effects. The results are compared to samples of the virgin material, machined and prepared exactly as they are prior to the Holloman AFB High Speed Test Track (HHSTT) runs. The gouged section was examined using optical microscopy, scanning electron microscope (SEM), and other techniques. The resulting microstructure is presented and compared to the virgin material. Material mixing, shear band formation, and significant thermal damage, consistent with a high energy gouging event, are confirmed. In addition, the material phase change evident in this approach allows us to estimate the thermal conditions present during the formation of the gouge. This thermal history establishes a profile by which related research in gouge simulation can be validated against. A one-dimensional heat conduction model is presented that validates the cooling rates required to generate the presented microstructure.

Johnson‐Cook Strength Model Constants for VascoMax 300 and 1080 Steels

High strength steels, VascoMax 300 and 1080, are characterized under tension at strain rates of ∼1/s, ∼500/s, ∼1000/s, and ∼1500/s and at high temperatures using the quasi‐static and split Hopkinson bar techniques. The data on 1080 steel exhibited a typical strain hardening response, whereas Vasco‐Max 300 steel showed diminishing flow stress beyond yielding because of localized necking in gauge section of the tested specimens. The tension data are analyzed to determine the Johnson‐Cook (J‐C) strength model constants for the two steels. The flow stress values for VascoMax are adjusted to account for necking, and the corrected J‐C model is developed.

Investigation of a Scaled Hypervelocity Gouging Model and Validation of Material Constitutive Models

In an effort to improve the accuracy and validate the performance of a hypervelocity gouging model developed for the shock-wave physics code CTH, the physical dimensionality of an impact problem at the Holloman Air Force Base High-Speed Test Track is mathematically scaled. The resulting scaled impact problem is sized for laboratory experimental testing and modeled. The contact schemes and approaches to friction available in CTH are summarized. In addition, results of a hypervelocity laboratory gouging experiment are presented. CTH is used to model these experimental tests, and the modeling efforts are validated. These efforts enhance the ability of a previously developed full-scale gouging model to be improved and validated.

Metallographic Examination of Thermal Effects in Hypervelocity Gouging

In this work, a gouged section of 1080 railroad rail steel is examined using metallographic techniques to characterize the nature of the damage. The gouging was performed by a rocket sled at Holloman Air Force Base, riding on VascoMax 300 steel shoes at 1.5 to 3.0 km/sec. Similar in approach to Gerstle, et al. [1], the damaged rail is evaluated in detail to examine material phase changes, shear bands, and heat effects. The results can be compared to samples of the virgin material, machined and prepared exactly as the rail and shoe are prior to the Holloman AFB High Speed Test Track (HHSTT) runs. The gouged section was examined longitudinally and in a transverse manner using optical microscopy and a Scanning Electron Microscope (SEM). Pictures are presented of the resulting microstructure. Comparisons to the virgin material confirm material mixing consistent with a high energy gouging event. In addition, the material phase change evident in this approach allows us to estimate the non-equilibrium thermal conditions present during the formation of the gouge. The creation of shear bands, predicted by the previous modeling efforts, is also confirmed.Copyright

Further Refinement and Validation of Material Models for Hypervelocity Gouging Impacts

The gouging impact phenomenon which occurs at the Holloman Air Force Base High-Speed Test Track during hypervelocity impact testing is examined further. The material constitutive models for VascoMax 300 and 1080 steel are refined, and extended into the high-strain-rate regime, using results from flyer plate impact experiments. These experiments are simulated using the hydrocode CTH to improve the material strength models at high strain rates. The improved viscoplastic models are then validated by comparing laboratory hypervelocity impact tests to CTH simulations. The final material models are then used in sled/rail impact simulations for the Holloman Air Force Base High-Speed Test Track gouging problem. These full-sled simulations match previous experimental findings extremely well.

Refinement of a Hypervelocity Gouging Model for the Rocket Sled Test

In an effort to improve the accuracy of current numerical models of the hypervelocity gouging impact phenomenon at the Holloman Air Force Base High Speed Test Track (HHSTT), several investigations were conducted. First, a metallurgical study of a gouged rail section is summarized that quantifies the nature of the non-equilibrium thermodynamic event. Second, the current CTH model of the sled/rail interaction is scaled mathematically to determine the feasibility of a laboratory experiment to generate gouging. Additionally, the various material contact schemes in CTH are evaluated to determine the most accurate approach in the gouging impact problem. Next, the absence of specific constitutive models for 1080 steel and VascoMax 300 (which are the materials of interest in the HHSTT gouging problem) is addressed with Split Hopkinson Bar characterization. These models are validated by comparison to Taylor Impact Tests conducted on the same materials. Finally, the two coatings used at the HHSTT to mitigate gouging are experimentally compared using the Taylor test. Conclusions are drawn from the experimentation and numerical modeling efforts with regard to the gouging phenomenon.Copyright