Numerical modeling of compaction induced defects in thick 2D textile composites

Significance 

The past few decades have witnessed an incredible advance in the use of composite structures in engineering and construction applications. Fiber reinforced composite materials have undoubtedly revolutionized traditional design concepts in engineering circles by creating new and exciting possibilities for high performance applications. In determining the performance and feasibility of composite structures, the quality of the final part is always critical.

Manufacturing of composite parts involves two main steps: forming and compaction. The forming process ensures that the material conforms to the desired shape, while the compaction is responsible for attaining the needed thickness and fiber volume fraction. Both steps require the material to deform, however, if the deformations exceed the limits of the material, defects (commonly wrinkles) may occur. Process modelling helps understand the limits of the material in respect to the manufacturing process, providing a powerful tool for eliminating unwanted deformations when integrated in the early stages of the design process.

Process modeling of textile composites has primarily focused on the forming of planar textiles into three-dimensional shapes, aiming to capture defects resulting from the large shear strains caused by the process. Although compaction induced defects are smaller in magnitude, their impact on the parts performance is equally as severe and their presence is often less noticeable, therefore developing effective modelling tools for predicting these defects is a key research priority. On this account, University of Bristol researchers: Dr Adam Thompson, Joseph McFarlane, Dr Jonathan Belnoue, and Professor Stephen Hallett developed a new modeling approach for predicting compaction induced defects in thick textile composites. The work is currently published in the journal, Materials and Design.

Briefly, the authors extended the conventional finite element forming models to include the through-thickness compliance of the textiles. The textiles were modelled in a continuous manner using mutually constrained membrane and shell elements to accommodate different stiffness forms such as low out-of-plane bending, high tensile, and non-linear shear stiffnesses. Instead of using material behaviors to capture the through-thickness compliance of the material, the new model used a penalty contact relationship. Simulation of the compaction of stacked textile layers was conducted to analyze their deformation behaviors. Finally, the simulation results were compared to the experimental data to validate the feasibility of the model and determine the relationship between the defect formation and the design and manufacturing parameters.

Results demonstrated an effective simulation of the compaction process of thick two-dimensional textile components. By introducing the compliant penalty contact, the authors accurately determined the mechanical response during the compaction process through surface interactions rather than through material behavior. The formation of the compaction-induced wrinkle defects as well as their magnitude, location, and shape were predicted. Furthermore, the design parameters such as lay-up and part design, as well as manufacturing process i.e. vacuum bagging procedure, exhibited a significant influence on the formation and magnitude of the wrinkles.

In summary, University of Bristol scientists successfully developed a new numerical modeling approach that takes into consideration the through-thickness compliance of the textile material during forming simulations. The model was experimentally validated, and the influence of design and manufacturing parameters on the formation of defects was established. The key parameters included the configuration of the vacuum bags, fiber orientation and tool profile. The method offers a new approach for modeling and predicting compaction-induced defects. In a statement to Advances in Engineering, the authors explained that the main benefit of this approach is the ability to simulate a wide range of conditions, making it possible to examine the effect that different parameters within the design space and manufacturing capabilities have on the final part. Through this, a better understanding of the mechanisms behind compaction induced defects can be gained and used to help inform part design and manufacturing process.

Numerical modeling of compaction induced defects in thick 2D textile composites - Advances in Engineering

About the author

Adam Thompson is currently a Senior Research Engineer at the Bristol Composite Institute (University of Bristol). He completed his BEng in Mechanical Engineering with Composites at Plymouth University, UK, in 2013 before moving to the University of Bristol to undertake his PhD in process modelling of composite materials. Since the completion of his PhD in 2017 he has worked within the Bristol Composite Institute, developing numerical methodologies to overcome pressing engineering challenges within the Aerospace sector. His research is focused on the development of process modelling tools to inform mechanical performance models for both organic and ceramic matrix composites.

About the author

Joseph McFarlane is currently an Engineer and Project Manager for East African Piling in Uganda. He obtained his MEng in Engineering Design from the University of Bristol in 2020. During his studies he conducted a 2-year research project into optimising the design and installation of XL monopile foundations for offshore wind turbines. He also participated in a research project into characterising wrinkle formation in composite manufacturing processes. During this project he collected experimental data to validate results from the numerical model presented in this research article.

About the author

Jonathan Belnoue is a Research Fellow at Bristol Composites Institute (University of Bristol). He obtained his D.Phil in Engineering Science from the University of Oxford in 2011. In the last 8 years, his research has focused in the development of extremely efficient, physics-based numerical models that can simulate the manufacturing process of real-size composite structures. Some his current research interest include the use of numerical models to help mitigate manufacturing-induced defect in composites, the use of simulations to support the development of new manufacturing processes and the creation of composite manufacture digital twins.

About the author

Stephen Hallett completed his BSc in Mechanical Engineering at the University of Cape Town, South Africa, in 1993 before being awarded a Rhodes Scholarship to undertake his D. Phil in Engineering Science at the University of Oxford, UK, graduating in 1997.

He is currently Professor in Composite Structures at the Bristol Composites Institute at the University of Bristol and Director of the Composites University Technology Centre supported by Rolls-Royce. He is well known for his work on the understanding of the physical properties of composite materials and structures, through data rich experimentation and numerical modelling. He is the author of over 150 refereed journal publications.

Reference

Thompson, A., McFarlane, J., Belnoue, J., & Hallett, S. (2020). Numerical modelling of compaction induced defects in thick 2D textile compositesMaterials & Design, 196, 109088.

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