MESO-SCALE RESIDUAL STRESS ANALYSIS OF THERMOPLASTIC COMPOSITES
Topic(s) : Experimental techniques
Co-authors :
Onur YUKSEL (NETHERLANDS), Buse ATAC (TURKEY), Baris CAGLAR (NETHERLANDS)Abstract :
Residual stresses are inherently formed in composite materials and affect their mechanical properties [1]. Despite the extensive research in the literature on residual stress and internal variability in fiber reinforced polymer composites (FRPCs), a comprehensive experimental analysis providing insights about the residual stresses in meso-scale throughout the whole cross-section remains absent. Building on prior studies on processing-structure-properties relationship [2,3], this study addresses the critical need to characterize internal residual stresses in thermoplastic composites, focusing on the influence of internal structure of individual layers and interlaminar interaction. The motivation lies in enhancing the understanding of how processing and internal structure affect the performance of structural components, particularly the residual stress field.
The present work delves into the intricate relationship between the tool, the outer layers and the inner layers for the residual stress formation. A novel experimental methodology was developed for the internal residual stresses analysis in laminated thermoplastic composites, considering the influence of stacking sequence and interlaminar resin rich layers. The experimental approach involves cutting the consolidated thermoplastic laminate and collecting micrographs on the face closer to the cutting section before and after the orthogonal cutting depicted in step 4 as schematically shown in Fig.1. Digital image correlation (DIC) was performed on these micrographs to analyze the resulting displacement field caused by the stress release via cutting. Optimal DIC parameters are determined using virtually deformed micrographs with fibers acting as random speckle pattern. A numerical model was developed to back calculate the released stress locked in during the manufacturing, based on the experimentally observed displacement fields.
For the experimental investigation, three different carbon fiber reinforced low-melt polyaryl ether ketone (LM-PAEK) laminates were consolidated in an hot press. The stacking sequences were [04\904]S and [02\902\02\902]S for the first two laminates. The third laminate was manufactured with the latter stacking sequence with additional 200 micron thick LM_PAEK films in between the outer and their adjacent layers to examine the influence of shear lag [4].
A preliminary DIC result belonging to a sample from the second laminate is depicted in Fig.2, where the observed displacement field is in line with the expected tensile residual stress in the middle 90 degree layers. By using experimental approaches, this study provides crucial insights into the interplay between internal variability and residual stress fields such as the influence of variable ply thickness or resin rich layers on the residual stress. The findings contribute to optimizing manufacturing processes and improving the overall performance of structural components in continuous fiber-reinforced polymers.
The present work delves into the intricate relationship between the tool, the outer layers and the inner layers for the residual stress formation. A novel experimental methodology was developed for the internal residual stresses analysis in laminated thermoplastic composites, considering the influence of stacking sequence and interlaminar resin rich layers. The experimental approach involves cutting the consolidated thermoplastic laminate and collecting micrographs on the face closer to the cutting section before and after the orthogonal cutting depicted in step 4 as schematically shown in Fig.1. Digital image correlation (DIC) was performed on these micrographs to analyze the resulting displacement field caused by the stress release via cutting. Optimal DIC parameters are determined using virtually deformed micrographs with fibers acting as random speckle pattern. A numerical model was developed to back calculate the released stress locked in during the manufacturing, based on the experimentally observed displacement fields.
For the experimental investigation, three different carbon fiber reinforced low-melt polyaryl ether ketone (LM-PAEK) laminates were consolidated in an hot press. The stacking sequences were [04\904]S and [02\902\02\902]S for the first two laminates. The third laminate was manufactured with the latter stacking sequence with additional 200 micron thick LM_PAEK films in between the outer and their adjacent layers to examine the influence of shear lag [4].
A preliminary DIC result belonging to a sample from the second laminate is depicted in Fig.2, where the observed displacement field is in line with the expected tensile residual stress in the middle 90 degree layers. By using experimental approaches, this study provides crucial insights into the interplay between internal variability and residual stress fields such as the influence of variable ply thickness or resin rich layers on the residual stress. The findings contribute to optimizing manufacturing processes and improving the overall performance of structural components in continuous fiber-reinforced polymers.