ON MICRO-BUCKLING OF UNIDIRECTIONAL FIBER-REINFORCED COMPOSITES BY MEANS OF COMPUTATIONAL MICROMECHANICS

Abstract

THE MICRO-BUCKLING SENSITIVITY TO FIBER MISALIGNMENT WITHIN A UNIT CELL DOMAIN IS INVESTIGATED IN THIS PAPER BY MEANS OF AN EXPLICIT REPRESENTATION OF THE GEOMETRY OF THE IMPERFECT FIBER WITHIN THE CONTEXT OF KINEMATICAL AND MATERIAL NON-LINEAR BEHAVIOR. TWO TYPES OF FIBER IMPERFECTIONS ARE CONSIDERED: A HELICOIDAL SHAPE, WHICH NEEDS A 3D MODEL; AND A SINUSOIDAL PLANE SHAPE (2D IMPERFECTION). BOTH IMPERFECTION MODELS ARE CHARACTERIZED BY A MAXIMUM MISALIGNMENT ANGLE OF THE FIBER WITH RESPECT TO THE IDEAL OR PERFECT CONFIGURATION, AS IS USUALLY CONSIDERED IN THIS FIELD. A TOTAL OF 238 CASES WERE COMPUTED; IN TERMS OF IMPERFECTION TYPE (EITHER 2D OR 3D), FIBER VOLUME FRACTION, FIBER ARRANGEMENT (SQUARE OR HEXAGONAL ARRAY), ORIENTATION FOR 2D MODELS, AND MISALIGNMENT ANGLE. TWO LOAD CASES, CONSTRAINED AND UNCONSTRAINED TRANSVERSE STRAIN, WERE CONSIDERED. ASSUMING PERIODIC BOUNDARY CONDITIONS, HOMOGENIZATION WAS CARRIED OUT TO OBTAIN MACROSCOPIC STRESSES. THE RESULTS INDICATE THAT THERE IS HIGH IMPERFECTION-SENSITIVITY FOR SMALL MISALIGNMENT ANGLES; ON THE OTHER HAND, THE TYPE OF IMPERFECTION AND THE FIBER ARRANGEMENT DO NOT HAVE A LARGE INFLUENCE ON THE RESULTS. THUS, THE MICRO-BUCKLING PROBLEM IS GOVERNED BY FIBER VOLUME FRACTION AND FIBER MISALIGNMENT. NUMERICAL RESULTS ARE COMPARED WITH AN ANALYTICAL MODEL AVAILABLE IN THE LITERATURE. SOME DESIGN RECOMMENDATIONS ARE PRESENTED.