Flyer Plate Impact Tests Research Articles

Gas Gun Flyer Plate Impact Testing of Stainless Steel Deposited by Low Pressure Plasma Spraying and Cold Gas Dynamic Spraying

Understanding shock wave propagation behavior in coatings is valuable for predicting their performance in high-velocity impacts. Samples of stainless steel were deposited by low pressure plasma spray and cold gas dynamic spraying. The sound speeds of the deposits were measured, and the deposits were tested in flyer plate impact tests in a gas gun to determine the shock propagation and porosity compaction properties. The most porous sample was tested to determine its equation of state, while the other samples were tested to measure shock wave profiles as a function of deposition parameters. Comparison of the results between the coatings and to reference wrought stainless steel shows the effect of deposition conditions on the dynamic behavior of the deposits. Higher deposit density leads to higher sound speed. The shock speed for the highest porosity plasma sprayed deposit was below that of wrought stainless steel. The Hugoniot elastic limit stress for cold sprayed deposits is higher than that for plasma sprayed deposits due to the higher degree of cold work. Porosity crush up times were found to vary with the total porosity of the deposit. Better understanding of the behavior of these deposits under extreme impact conditions is demonstrated.

Microstructure of CrMnNi Cast Steel After Explosive-Driven Flyer-Plate Impact at Room Temperature and Below

A low-carbon metastable austenitic CrMnNi cast steel was investigated under shock conditions in a flyer-plate impact test. The samples were impacted by aluminum flyer-plates with impact velocities of 620 ± 30 m/s. Depending on deformation temperature and strain rate, the material exhibited different deformation mechanisms (dislocation glide, martensitic transformation, and mechanical twinning), which determined the microstructural evolution and mechanical behavior. Flyer-plate impact tests were carried out at 213 K and 293 K (−60 °C and +20 °C). A soft recovered sample revealed microstructural changes directly after impact. The subsequent microstructural investigations via light-optical microscopy and scanning electron microscopy revealed that transformation-induced plasticity (TRIP effect) was the primary deformation mechanism. Moreover, it was possible to quantify the martensite volume fraction by different methods and to identify the hcp e-martensite phase as an intermediate transformation stage. A decrease in temperature also increased the driving force for the martensitic transformation.

Lagrangian analysis led design of a shock recovery plate impact experiment

Shock recovery techniques, such as the flyer-plate impact test, are used to examine a material that has been subjected to a single well-defined shock, followed by a single release wave. One of the key requirements of this type of technique is that the process should be such that any change found in the sample after recovery, can only be attributed to the shock process alone. Therefore, the principal problem for a test specimen-fixture assembly is that it is designed such that the loading history of the recovered specimen is known. This has motivated this research through the analysis led design of a shock recovery experiment. The choice of Lagrangian Finite Element Analysis for this design work was driven by the method's ability to accurately track history variables (for plastic deformation) and treat contact interactions which are crucial in this problem.Starting from an initial configuration, LS-Dyna has been used to analyse in detail the resulting wave propagation to ensure the generation of a uniaxial strain state in the specimen through Lagrangian distance-time diagrams. These iso-maps enabled the identification of potential shortcomings with the initial design, in terms of the transmission of contact and the influence of radial release waves at the different boundaries between specimen and supporting fixture rings.The benefits of using Lagrangian Finite Element Analysis for this design work are its ability to track history variables (for plastic deformation) and contact treatment. Based on these findings, a new configuration was developed, which consists of an array of concentric rings that support the specimen. During shock formation in the specimen, these rings progressively transfer the loading in the impact direction and radially away from the specimen, acting as momentum traps and preventing unwanted release waves from affecting the strain state experienced by the specimen.Comparing distance time diagrams between original and proposed configurations, a design sensitivity analysis was performed, where the new geometry resulted in a decrease of both the residual velocity (−38%) and radial displacement (−27%) of the target when compared to the original setup.

Micromechanisms of deformation in high-purity hot-pressed alumina

A high-strength aluminum oxide was produced by vacuum hot pressing high-purity, submicron-size alumina powders. The uniaxial compressive fracture strength was strongly strain-rate sensitive and varied from 5.5 GPa at 10 −4 s −1 to 8.3 GPa at 10 3 s −1. A Hugoniot elastic limit of about 11.9 GPa was determined from flyer plate impact tests. The deformation/fracture process was examined using both uniaxial stress and uniaxial strain conditions. Under a uniaxial stress condition, microplasticity was observed in the form of aligned dislocations that appeared similar to shear bands in metals. Under a uniaxial strain condition, extensive dislocation activity, grain boundary microcracking and occasional twins were observed. Based on the experimental results and microscopic observations, possible mechanisms responsible for the observed high strength and high strain-rate sensitivity in this alumina are discussed.