HEAVY MASS PROJECTILE IMPACT ON THIN AND MODERATELY THICK UNIDIRECTIONAL FIBER/EPOXY LAMINATES

Abstract

BALLISTIC IMPACT TESTS WERE CONDUCTED USING HARD STEEL CYLINDRO-CONICAL PROJECTILES OF MASS RANGING BETWEEN 550 TO 570GMS WITH THREE NOSE GEOMETRIES AGAINST UNIDIRECTIONAL GLASS-FIBER REINFORCED EPOXY COMPOSITE PLATES OF VARYING STACKING SEQUENCE AND THICKNESS. GAS GUN PROJECTILE LAUNCHER SETUP WAS USED TO ACCELERATE THE PROJECTILES. THE DAMAGE EVOLUTION, FAILURE PATTERN, BALLISTIC LIMIT AND ENERGY ABSORPTION BY EACH TARGET SET WERE DETERMINED EXPERIMENTALLY. EXPERIMENTAL STUDY SHOWS THAT THE NOSE GEOMETRY OF HEAVY PROJECTILE HAS VERY LESS INFLUENCE ON THE ENERGY ABSORPTION AND BALLISTIC LIMIT FOR THIN TARGETS WHEREAS IT PLAYS A MAJOR ROLE WITH INCREASING THICKNESS OF THE LAMINATES. IT WAS ALSO CONFIRMED FROM THE EXPERIMENTAL STUDY THAT DELAMINATION WAS NOT A MAJOR FAILURE MECHANISM FOR THIN LAMINATES BUT HAS CONSIDERABLE EFFECT ON THICK LAMINATES. SEVERE DELAMINATION AND DAMAGE WERE OBSERVED IN THICK LAMINATES. VARYING THE STACKING SEQUENCE NEITHER SHOWED MARKED DEVIATION IN BALLISTIC LIMIT NOR ENERGY ABSORPTION, BUT SHOWED DIFFERENCE IN DELAMINATED AREA ESPECIALLY IN THICK TARGETS. RESULTS SHOW THAT, WHILE THE AMOUNT OF ENERGY ABSORBED BY THE COMPOSITE WAS DIFFERENT FOR ALL THREE PROJECTILES, THEY SHOWED SIMILAR TRENDS - ENERGY ABSORBED INCREASED WITH VELOCITY UP TO A CRITICAL IMPACT VELOCITY BEFORE IT STARTS TO DECREASE. A MATHEMATICAL MODEL BASED ON ENERGY BALANCE PRINCIPLE AND RESISTIVE FORCES ACTING ON THE PROJECTILE DURING PERFORATION WAS DEVELOPED TO THEORETICALLY CALCULATE THE BALLISTIC LIMIT. THE THEORETICAL VALUE CORRELATES WELL WITH THE EXPERIMENTAL VALUE.