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Yan, Shuang (2024) Predicting process-induced distortion for composite structures. PhD thesis, University of Nottingham.

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Abstract

Process-induced distortion (PID) is inevitable during the manufacturing of composite structures. A precise prediction of PID would benefit the design and manufacturing process so that the dimensional accuracy of the produced composite part is within tolerance. In this work, a sequentially coupled thermal-chemical and mechanical model was developed to predict the chemical, thermal and tool-part interaction (TPI) effects contributing to PID. The proposed model was based on the Cure Hardening Instantaneous Linear Elastic (CHILE) constitutive law and executed within ABAQUS finite element analysis, with the mechanical and thermal material properties defined through user subroutines.

As a starting point, this work presented a Matlab model based on forward discretisation method. This model provides a good opportunity to rapidly estimate the DoC and residual stresses distribution through the thickness of a laminate under an autoclave cure cycle, so that the validity and the effectiveness of the manufacturing recommend cure cycle (MRCC) could be examined.

This work then investigated the spring-in and warpage distortions in relating to the geometric features of composite structures. Subsequently, experimental and numerical investigations of PID in L-shaped laminates were performed. The specimens were manufactured using IM7/8552 UD prepregs under autoclave cure processing conditions. Factors contributing to the PID were isolated and the mechanism of each was discussed in details. The study found that the corner component of spring-in was primarily the results of chemical and thermal shrinkage, while the warpage in the flange part was found to have strong dependence on tool-part interactions.

The novelty presented in this work is to quantify TPI effects through a semi-empirical approach. An equivalent shear stress can be determined through a set of experimental data, so that it could be implemented in the modelling to replicate the warpage distortion occurred in the flat part of a laminate. The validity and limitations of the proposed TPI model on L-shaped laminates were also discussed.

Following that, the study extended its modelling approach to predict PID of laminated structure with thickness reduction along the length, exploring different ply-drop designs. Parameters include dropped ply orientation and number of dropped plies. This work found that the lay-up sequence at the ply-drop zone is crucial in determining the out-of-plane displacement. The study also found that the magnitude of warpage due to the TPI effect is still a major factor. Therefore, the importance of precise modelling of TPI effect was emphasised. The study also demonstrated that although mechanical performance is the design priority for tapered laminates, the PID could also be mitigated if handled properly in the design stage.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Warrior, Nicholas Mikhail, Matveev
Keywords:	Manufacture of composites; Forward discretisation method; Laminates; Residual stresses distribution; Manufacturing recommend cure cycle; Distortions; Ply-drop; Warpage
Subjects:	T Technology > TS Manufactures
Faculties/Schools:	UK Campuses > Faculty of Engineering > Department of Civil Engineering
Item ID:	77594
Depositing User:	Yan, Shuang
Date Deposited:	19 Jul 2024 13:55
Last Modified:	19 Jul 2024 13:55
URI:	https://eprints.nottingham.ac.uk/id/eprint/77594

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