Consolidation-driven wrinkling in carbon/epoxy woven fabric prepregs

An experimental and numerical study

Significance 

Due to their lightweight and improved mechanical properties, composite materials are gradually replacing their metallic counterparts in various industrial applications. They are, however, highly susceptible to defects formed in their uncured state when the plies (additively stacked to form the part 3D shape) are very compliant. Amongst these defects, fiber-path defects such as in-plane waviness and out-of-plane wrinkling can particularly affect composite structures’ mechanical performance. Therefore, a thorough understanding of the ply wrinkling can enhance manufacturing throughput to produce cost-effective and lighter parts by enabling the production of fewer parts with critical defects and the use of lower safety factors.

Previous studies on ply wrinkling have concentrated on characterizing, simulating and understanding the wrinkle formation and formability in woven fabrics. However, consolidation-induced defects have remained largely under explored despite their practical significance in ensuring defect-free formability. To date, several studies have investigated the key parameters influencing the formation of fiber-path defects in thermoset prepregs. However, these studies are characterized by the trial-and-error physical trials which are both expensive and time consuming. This, together with increasing geometric complexity, has necessitated the devolvement of new numerical methods for simulation and increasing the comprehension of the processes involved in composite manufacturing.

A recent research article published in the journal, Composites Part A and authored by Dr Armin Rashidi and Professor Abbas Milani from the University of British Columbia together with Dr Jonathan Belnoue, Dr Adam Thompson and Professor Stephen Hallett from the University of Bristol, investigated the formation of manufacturing-related defects during the consolidation of carbon-fiber epoxy woven fabric prepregs. The numerical and experimental study aimed to predict the defects that arise due to the consolidation process and clarify the critical parameters responsible for the defect formation mechanisms.

Briefly, the consolidation model utilized for the fabric prepregs was an extension of one previously verified for UD prepregs. The coupled forming and consolidation FE-based modelling scheme integrated through-thickness compaction and inter-ply shear behavior of the individual plies, presented in the form of compliant penalty contact. Several experiments on C-sections and L-sections were conducted to validate the approach’s practicability and improve the understanding of the wrinkling of fabric prepregs. The numerical and experimental results were analyzed and compared to explore the significance of various parameters.

The authors demonstrated that even though the compaction model accounted for both bleeding and squeezing flow, the experimental results showed that only the bleeding flow was observed in the textile prepregs. This was confirmed by experimental observations. The key factors responsible for the formation of wrinkles included the tool geometry, laminate bulk factor, and boundary conditions. One of the main advantages of the presented approach is its versatility and applicability to a wide range of geometries as well as its computational efficiency.

In summary, a combination of numerical and experimental approaches was used to provide further insights into the process-driven mechanisms governing the formation of manufacturing-induced out-of-plane defects associated with fabric prepreg composites. The in-plane and out-of-plane behaviors of the woven fabric were effectively captured using the presented scheme. The experimental and numerical results were in good agreement, and the applicability of the model was successfully verified using a series of industrial relevant cases. In a statement to Advances in Engineering, the authors explained that their study has now set the foundations for industrial uptake of virtual manufacturing of composites.

Reference

Rashidi, A., Belnoue, J., Thompson, A., Hallett, S., & Milani, A. (2021). Consolidation-driven wrinkling in carbon/epoxy woven fabric prepregs: An experimental and numerical studyComposites Part A: Applied Science and Manufacturing, 143, 106298.

Go To Composites Part A: Applied Science and Manufacturing

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