PREDICTION OF SHAPE DISTORTIONS IN COMPOSITE WING STRUCTURES

Abstract

SHAPE DISTORTIONS AND WARPAGE ARE A MAJOR SOURCE OF PROBLEMS FOR COMPOSITE MANUFACTURERS. THESE DISTORTIONS ARE USUAL-LY ACCOMPANIED BY BUILT UP RESIDUAL STRESSES. THEY CAN DEFORM A COMPONENT SO THAT IT BECOMES USELESS. IT ALSO HAS THE CAPABILITY TO REDUCE THE STRENGTH OF THE STRUCTURE. IN THIS PAPER, THE THREE-DIMENSIONAL VERSION OF THE CONSTITUTIVE MODEL ORIGINALLY PROPOSED BY SVANBERG AND HOLMBERG IS EMPLOYED TO PREDICT THE WARPAGE OF A WING PLANFORM. THE MODEL TAKES INTO ACCOUNT IMPORTANT MECHA-NISMS SUCH AS THERMAL EXPANSION, RESIN SHRINKAGE AND FROZEN-IN STRAINS DEVELOPED DURING CURING CYCLES. THE MODEL WAS IMPLEMENTED INTO ABAQUS FINITE ELEMENT CODE AS A USER SUBROUTINE UMAT. THE MACROMECHANICAL PROPERTIES OF EACH COMPOSITE LAYER WERE PRE-DICTED USING A MICROMECHANICS BASED APPROACH, IMPLEMENTED INTO MATLAB. RESULTS SHOW THAT WINGS WITH CROSS PLY LAMINATES WITH REDUCING THICKNESS ALONG THE SPAN EXPERIENCED MORE WARPAGE THAN QUASI-ISOTROPIC LAMINATES. FURTHERMORE, FOR WINGS WITH EQUAL THICK-NESS ALONG THE SPAN, THE RESULTS SHOW THAT THE QUASI-ISOTROPIC LAM-INATES EXPERIENCED MORE WARPAGE THAN CROSS PLY LAMINATES. LASTLY, THE RESULTS SHOW THAT WINGS WITH PROGRESSIVELY REDUCING THICKNESS EXPERIENCE TWIST THAT IS VARYING FROM THE WING ROOT TO THE WING TIP WHILE WINGS WITH A CONSTANT THICKNESS EXPERIENCE TWIST MAINLY AT THE CENTRE OF THE WING