Neha Yadav1*, Karol Wachtarczyk 2, Pawel Gąsior 2, Ralf Schledjewski1, Jerzy Kaleta2

1Processing of Composites Group, Department Polymer Engineering and Science, Montanuniversität Leoben, Otto-Glöckel-Strasse 2/3, 8700 Leoben, Austria
2Department of Mechanics, Materials and Biomedical Engineering, Wrocław University Of Science And Technology, Smoluchowskiego str. 25, 50-370 Wrocław, Poland
*neha.yadav@unileoben.ac.at

Residual stresses generated during automated tape layup process adversely affect the layup quality and have detrimental effect on the mechanical properties. These stresses may result in various defects arising in the laminate such as delamination, matrix cracking, fiber buckling and shape distortion [1, 2]. Tensile and flexural properties and fracture toughness during service life might also be impaired [3]. Shape distortion for flat parts happens in the form of warpage and so far, trial and error approach is used to rectify such distortions [4], which is both expensive and time consuming.
Inline monitoring of residual stress is crucial to understanding the relationship between distortion and process parameters. Recognizing such parameters will help in minimizing stress and limiting the laminate distortion. To further assess the effects of these stresses on mechanical properties structural health monitoring (SHM) is required.
For the present work, fiber Bragg gratings (FBG) sensors are integrated inside the laminate as they can be used for both inline measurements during the process and SHM. Regular FBG sensors are used to evaluate the effect of tool temperature on residual stress for unidirectional layup. Highly birefringent (HiBi) FBG sensors are used to assess both axial and transverse stress for cross-ply layup. It is found that tool temperature has a direct effect on the residual stress. As the cooling rate decreases, so does the residual stress, leaving the laminate distortion free. The effect on mechanical properties of such stresses is also discussed.
References
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