Improving Quality of a Truck Fender Using Ply Draping Modelling - C122

 

Improving Quality of a Truck Fender Using Ply Draping Modelling
Case study
Document Type	Case study
Document Identifier	122
Themes	Materials deposition and consolidation management Residual stress and dimensional control management Quality/inspection management
Tags	Deposition Forming Development to production Reinforcement architecture Process modelling Quality
Objective functions	Cost Maintain Rate Maintain Quality Increase
MSTE workflow	Development

Summary

A lightweight truck fender was required for a semi-trailer that displayed the carbon fibre weave to achieve an aesthetically pleasing design. Initial prototypes suffered from wrinkles and visual inconsistencies from overlapping plies. A draping analysis was performed to determine a suitable manufacturing approach. A flat pattern was produced based on the analysis results that improved the consistency and aesthetics of the production parts.

Challenge

The geometry of the truck fender consisted of a doubly curved surface. A 0/90 bi-directional stitched carbon fibre fabric had been selected for manufacturing. The stitched architecture limited the ability of the 0/90 fibre bundles from shearing relative to each other. This made it challenging to conform the fabric around the geometry of the fender. Wrinkles that were visually unacceptable appeared in the parts when the initial prototypes were manufactured. The manufacturing technicians started adding ply darts (cuts) during the layup process, but the darts ruined the continuous fibre aesthetic that was desired. It also resulted in inconsistency between parts because each manufacturing technician applied the darts at different locations.

Approach

When a fabric is draped over a doubly curved surface the fibres undergo in-plane shearing to conform to the geometry. The fibres eventually reach a maximum shear angle that locks the fibres from further shear deformation. When deformation continues past this angle the fabric begins to deform out-of-plane resulting in wrinkles in the part. Ply draping modelling can be used to predict changes in fibre orientation due to draping, as well as the location of wrinkles. Adjustments of the ply draping start location and initial ply orientation can change the draping results. Additionally, the inclusion of ply darts can help to eliminate wrinkles (see Ply Draping Modelling for Structural Analysis and Manufacturing).

Fabric lock angle was the key material parameter required for the draping analysis. Standardized tests such as picture frame and bias extension exist to quantify fabric lock angle, but these were not readily available for this project. Instead, a manual approach was adopted that was less accurate, but provided sufficient data to successfully complete the project.

A square section of fabric was cut from the material roll. A smaller square was sketched onto the fabric while ensuring the material remained flat and undistorted. Two fingers were placed diagonally opposite of each other outside of the sketched square and then slid away from each other. When the fabric began to distort out-of-plane, the angle between the lines of the sketched square was measured using a protractor. This angle was subtracted from 90° to calculate the lock angle of the fabric as shown in Figure 1. The measured lock angle for the stitched biaxial carbon fibre fabric was 35°.

Figure 1 – Lock angle measurement.

The next step in the analysis was to set up the finite element model. Care was given in deciding the appropriate mesh size for the analysis . It was important to choose a mesh size that was small enough to accurately capture geometry changes that could affect the draping process. However, it was also important not to use too small a mesh as this dramatically increased the processing time. The final mesh selection is shown in Figure 2.

Figure 2 – Meshed model.

To perform the draping analysis the solver required definition of the layup starting point, initial fibre orientation, lock angle, and location of ply darts. Each solver has different methods of displaying the output of the analysis. As shown in Figure 3, the solver used in this analysis displayed two arrows on each element that indicated the longitudinal and transverse fibre orientation for that specific element. Red arrows indicated the shear angle exceeded the lock angle. The solver also provided an option to look up the numerical value of the shear angle for each element via a spreadsheet.

Figure 3 – Draping starting point at bottom centre.

Initial trials focused on selecting the starting point of the draping process as well as the initial direction of the fabric. Changes to these two parameters were shown to change the distortion in the fabric. The first iteration selected a starting point at the bottom and centre of the fender. This led to good conformity near the starting point of the layup, but the lock angle was exceeded once the fabric reached the curvature leading to the top of the fender as shown in Figure 3.

After some initial trials the most effective starting point was found to be at the apex of the fender with the initial direction of the fabric running along the length of the fender. The preliminary results displayed in Figure 4 showed that the fabric could successfully drape over the top of the fender without exceeding the lock angle, but as the fabric moved away from the top of the fender it began to exceed the lock angle as it draped over the sides. However, this approach showed promise as the pattern was symmetric resulting in a symmetric cutting template that made manufacturing easier.

Figure 4 – Draping starting point at top centre.

Based on the preliminary draping results it was determined that darts would be required to prevent wrinkling in the part. The finished fender needed to have a continuous carbon fibre surface that was not marred by cuts and overlaps in the fabric. The plan was to paint the edges of the fender, so this gave an opportunity to hide the required darts and leave the centre section continuous. The advantage of performing the draping analysis was that several options for dart locations could be investigated in a relatively short amount of time. The initial trial involved adding nine short darts along each side of the fender. The darts were stopped short of the curvature leading to the top of the fender as shown in Figure 5. The subsequent draping analysis showed that inclusion of these darts resulted in very little change in the draping results. Many areas still exceeded the lock angle as shown in Figure 6.

Figure 5 – Short darts

Figure 6 – Short darts analysis results

Another attempt increased the length of the darts so they extended over the curvature and stopped at the top of the fender. Initially only four darts on each side were included as shown in Figure 7. The results shown in Figure 8 demonstrated a clear reduction in the number of elements that exceeded the lock angle. However, the number of darts wasn’t sufficient to completely eliminate potential wrinkles.

Figure 7 – Four long darts on each side

Figure 8 – Four long darts on each side analysis results

Additional darts were added along the edge of the part, each of which extended over the curvature to the top of the fender. Nine darts were included on each side as shown in Figure 9. This change eliminated the elements that exceeded the lock angle as shown in Figure 10. It took approximately ten iterations to reach the final design. The goal of the process was to eliminate the wrinkling while minimizing the size and number of required darts.

Figure 9 – Nine long darts on each side

Figure 10 – Nine long darts on each side analysis results

Once the dart locations were finalized the software created a flat pattern of the fabric based on the part geometry and the length and location of each dart. The flat pattern was used to manufacture a physical template that was implemented during production of the fenders. The manufacturing technicians used the template to consistently cut the fabric to the correct shape. The technicians then laid up the part using the pre-cut fabric and the same starting location that was defined in the analysis (top centre of the fender).

Figure 11 – Flat pattern.

Outcome

Performing a draping analysis of the fender allowed for a quick investigation of options to reduce wrinkling in the part. The analysis helped to identify the ideal layup starting location and direction, as well as determine the appropriate length and locations for ply darts. The creation of a flat pattern that was used as a cutting template enabled the production of fenders without wrinkles and with a consistent, high quality aesthetic look.

Figure 12 – Fender finished product.

Related pages

• See Webinar on Fiber Architecture
• See Webinar on Fabric Forming
• See page on Ply Draping Modelling for Structural Analysis and Manufacturing

Related pages

Page type	Links
Introduction to Composites Articles
Foundational Knowledge Articles	Conduction - A118 Convection - A106 Glass transition temperature (Tg) - A210 Heat of reaction - A114 Viscosity (resin) - A203
Foundational Knowledge Method Documents	How to measure gel time - M101 How to measure reinforcement content (and corresponding matrix content) - M109
Foundational Knowledge Worked Examples
Systems Knowledge Articles
Systems Knowledge Method Documents
Systems Knowledge Worked Examples
Systems Catalogue Articles
Systems Catalogue Objects – Material
Systems Catalogue Objects – Shape
Systems Catalogue Objects – Tooling and consumables
Systems Catalogue Objects – Equipment	Rheometer - A357
Practice Documents	Maintaining equivalency during cure for different fibre architectures - P118 Ply Draping Modelling for Structural Analysis and Manufacturing - P174 Practice for Developing a Deposition Step - P157 Practice for developing a thermal transformation process step - P105 Troubleshooting part quality during cure when changing the reinforcement - P131
Case Studies	Cost Comparison Study of a GFRP Leisure Boat Hull Manufacturing Method; Spray Up vs Resin Infusion - C115 Improving Quality of a Truck Fender Using Ply Draping Modelling - C122 Optimizing Cost vs Weight for Low Production Volume Parts - C112 SAMPE Canada - CKN - CANCOM Student Competition: Case Study - C121 Troubleshooting of room temperature processes for large recreational and industrial parts - C100
Perspectives Articles	Case Study: Optimizing a Press Moulding Process - A324 Composite materials engineering webinar session 1 - Introduction - A120 Composite materials engineering webinar session 2 - Constituent Materials - Fiber - A121 Composite materials engineering webinar session 5 - Manufacturing processes - Introduction - A124 Composite materials engineering webinar session 6 - Manufacturing processes - Prepreg processing - A125 Composite materials engineering webinar session 7 - Manufacturing processes - Liquid composite moulding - A126 Composites Process Simulation: A Review of the State of the Art for Product Development - A283 Dr. Anoush Poursartip's cdmHUB global composites expert webinar - A136 Fabric Forming: how it affects design and processing, and how simulation can address this - A310 Fibre Architecture: Availability, pros and cons, and selection for my application - A309 Interview with Prof. Kevin Potter - A134 Pultrusion of Thermoplastic Composites - A334 Simulation models for rapid liquid composite molding - A333.0

About	Help

Carbon fibres are composed of large aromatic sheets similar to those in graphite. These graphitic layers form the basic structural units in the shape of ribbons. The structure of carbon fibre ribbon is believed to be a columnar arrangement of disoriented graphite crystallites parallel to the ribbon length. The idealized tetragonal crystallites are stacked above one another, with slight disorientation between the crystals in the direction of fibre axis, trapping sharp needle like voids, where the boundaries between the stacks represent the disordered regions.

The use of multiphysics models to predict the outcome of real-world scenarios. May be analytical (closed form, "hand calculations") or computational (implementation on computers is required due to the large number of calculations involved. e.g. finite element method, finite difference method)

Most often in composite materials engineering, modelling refers to either:

• Process modelling (predicting manufacturing outcomes, or the inverse problem of predicting manufacturing parameters to achieve a desired outcome), or
• Performance modelling (predicting the stiffness/strength/suitability of a structure, or the inverse problem of the material properties and dimensional requirements to achieve a desired stiffness/strength/suitability of a structure)

(same as "Simulation")