AbstractsEngineering

A need exists to develop manufacturing technologies for armor alloys that can replace risk-sensitive welding. Armor materials have poor formability at room temperature and are prone to cracking even at modest bend radii. An Induction assisted bending process has been successfully performed using titanium alloy Ti-6Al-4V. The main objective of this work was to develop optimized procedures for induction assisted hot bending of titanium and steel armor. The response of several armor alloys to high temperature straining and the effect of induction bending on their mechanical properties and microstructure were evaluated. A methodology for characterization and testing of armor materials which supports the development of induction bending procedures was also developed. The results of this research have expanded the elevated temperature data for several grades of alloy Ti6-4 and for three armor steel alloys. The latter included single grades of rolled homogeneous armor (RHA), high hard armor (HHA) and Armox 440 steel. Induction bent plates of grade 5 Ti6-4 were characterized using optical and scanning electron microscopy. Utilizing a mandrel radius of 50 mm, crack free induction bends were made in ½” thick grade 5 plates at temperatures as low as 427 °C. Using a 12.5 mm mandrel radius resulted in cracking at bending temperatures below 621 °C. The surface roughness of the plates may have provided stress concentration sites for crack initiation. Also, voids were discovered near the surface and in front of crack tips using optical and scanning electron microscopy. These voids provide evidence for a possible crack propagation mechanism. The depth of the cracks and the void locations were utilized to calculate the strain associated with these defects. This was used to generate a strain vs. deformation temperature plot that can be utilized by manufactures as a process development and control tool. Heating of Armox 440 below the A1 temperature resulted in over tempering and a significant softening with a drop in hardness to 28 HRc from 47.6 HRc in the as-delivered condition. Straining of this still below the A1 temperature at 700 °C resulted in significant loss of room temperature tensile strength. These results illustrate the need for a post bend heat treatment of Armox 440 to restore the mechanical properties. A methodology for characterization and testing of armor materials has been established, which supports the development of induction bending procedures that can be applied to other materials. This methodology includes: 1) hot ductility testing to determine the optimum temperature range for induction bending; 2) metallurgical characterization and hardness testing to evaluate the material response to elevated temperature exposure; and 3) high temperature straining followed by room temperature tensile testing and hardness testing to evaluate the effect of induction bending on mechanical properties. The test results are utilized to generate an optimal strain vs. temperature process control window for…