EXPERIMENTAL STUDY OF BRASS PROPERTIES THROUGH PERFORATION TESTS USING A THERMAL CHAMBER FOR ELEVATED TEMPERATURES

Abstract

EXPERIMENTAL ANALYSIS ON STANDARD BRASS ALLOY HAS BEEN CARRIED OUT USING A HIGH PRESSURE GAS GUN. PERFORATION TESTS HAVE BEEN PERFOR-MED FOR A VARIETY OF IMPACT VELOCITIES FROM 40 TO 120 M/S IN ORDER TO STUDY THE MATERIAL BEHAVIOR AND TO DEFINE FAILURE MODES. THE SPECIMENS HAVE BEEN CUT FROM A STANDARD BRASS SHEET OF 1.0 MM THICKNESS TO FORM 130X130 MM TARGET PLATES. TWO SHAPES OF THE PROJECTILE WERE USED: THE CONICAL-HEADED WITH AN ANGLE OF 72° HAD 13 MM IN DIAMETER AND A MASS OF 30 G AND A BLUNT ONE OF THE SAME MASS. THE MATERIAL USED FOR MACHINING THE PROJECTILES WAS MARAGING STEEL WITH A HEAT TREATMENT TO REACH A YIELD STRESS OF 2.0 GPA. THE MAIN AIM OF THE STUDY HAS BEEN TO PROVIDE RESULTS USING AN INNOVATIVE THERMAL CHAMBER THAT ALLOWS TO HEAT SPECIMENS BEFORE IMPACT. THE RANGE OF AVAILABLE TEMPERATURES IS FROM THE ROOM TEMPERATURE UP TO 260 ˚C. THE TIME NECESSARY TO HEAT THE SPECIMEN AND TO STABILIZE ITS TEMPERATURE IS 20 MINUTES. THE THERMAL CHAMBER HAS BEEN SPECIALLY CALIBRATED FOR METALS SUCH AS BRASS. THE EXPERIMENTAL STUDY HAS ALLOWED TO DISCUSS THE BALLISTIC PROPER-TIES OF THE STRUCTURE. THE BALLISTIC RESISTANCE OF SHEET PLATES IS STRON-GLY DEPENDENT ON THE MATERIAL BEHAVIOR UNDER DYNAMIC LOADING AND CHANGES WITH TEMPERATURE. THE BALLISTIC PROPERTIES ARE ALSO INTENSELY RELATED TO INTERACTION BETWEEN THE PROJECTILE AND THIN BRASS TARGET. THE RESULTS IN TERMS OF THE BALLISTIC CURVE VR (RESIDUAL VELOCITY) VERSUS V0 (INITIAL VELOCITY) HAVE SHOWN THE EFFECT OF TEMPERATURE ON THE RESIDUAL KINETIC ENERGY AND THUS ON THE ENERGY ABSORBED BY THE PLATE, REVEALING A SOFTENING OF BRASS WITH TEMPERATURE INCREASE. AN INTERESTING OBSERVATION HAS BEEN MADE CONCERNING THE FAILURE PATTERN. IN CASE OF THE CONICAL PROJECTILE, THE USUAL NUMBER OF PETALS HAS VARIED BETWEEN 3 AND 4 FOR DIFFERENT IMPACT VELOCITIES, WHEREAS ITS NUMBER HAS INCREASED TO 6 AT ELEVATED TEMPERATURES AND AT IMPACT VELOCITIES CLOSE TO THE BALLISTIC LIMIT. THE SPECIMEN BEHAVIOR HAS BEEN CONFRONTED WITH AVAILABLE LITERATURE DATA. PRELIMINARY TEMPERATURE RECORDS WERE MADE USING A THERMAL IMAG-ING CAMERA. AS A NEXT STEP, NUMERICAL SIMULATIONS WILL EXTEND THE PERFORMED STUDY TO ANALYSE FAILURE MODES AS WELL AS TO PREDICT ADIABATIC HEATING DURING IMPACT.