Maintaining equivalency during cure for different fibre architectures - P118

 

Maintaining equivalency during cure for different fibre architectures
Practice document
Document Type	Practice
Document Identifier	118
Themes	Thermal management Material deposition management Flow and consolidation management Residual stress and dimensional control management
Tags	Reinforcement architecture Continuous fibre reinforcement Reinforcement material Thermoset cure kinetics
Objective functions	Cost Maintain Rate Maintain Quality Maintain
MSTE workflow	Development
Prerequisites	Cure of thermosetting polymers Reinforcement properties Effect of material in a thermal management system

Q: "I have used a given resin system to cure a wide variety of good quality parts but am looking at switching reinforcement styles (such as to a tightly woven reinforcement). How do I ensure that I can continue to make good quality parts with the same cure cycle?

A: To ensure that the same cure cycle will work for both reinforcement types, the two composites must be similar from a chemical, physical, and mechanical perspective. If the material properties of the reinforcement have changed significantly, then you can likely expect an altered response. This includes thermal conductivity, specific heat capacity, density, volume, thickness, and the coefficient of thermal expansion (CTE). Moreover, if the change in reinforcement results in a change in fibre volume fraction or a change in the ply thickness, then you can again expect an altered response even with the same cure cycle. All else equal, a decrease in fibre volume fraction will result in a higher exotherm. If the fibre volume fraction is similar but the ply thickness is greater then the exotherm will again increase.

Regarding stress-induced defects, if the CTE of the new reinforcement has changed significantly this may result in part deformation upon demoulding. In such a case, the cure cycle or tooling may have to be altered to mitigate this problem.

These are just some of the considerations to weigh when changing the reinforcement.

Overview

Changing the fibre reinforcement alters the material properties of the composite. This is true at the ply level and the laminate level. Depending on how significant the change in reinforcement is, this could have minor or major ramifications on part quality. In order to ensure equivalent quality during cure, the chemical, physical, and mechanical response of the new composite (i.e. with the new reinforcement) must meet the same quality metrics as the old composite.

Thermal management considerations

Link to thermal management

From a thermal management perspective, this should be a minor change, but the following should be considered at a minimum:

1. Is the fibre different? Changing from carbon fibre to glass fibre is a significant change, but even different grades of the same fibre type can lead to changes in specific heat capacity, thermal conductivity, and thermal diffusivity of the reinforcement form. This can affect the thermal response of the system.
2. Is the fibre volume fraction (Vf) different? This can affect the composite properties, and again affect the thermal response of the system. To learn how to measure Vf, visit the following page: How to measure reinforcement content.
3. Is the ply thickness different? If so, the total laminate thickness will change, and this can again affect the thermal response of the system.

To learn more about the former two points, visit the following page:

• Effect of material in a thermal management system

To learn more about how laminate thickness may affect the thermal response of the system, visit the following page:

• Effect of shape in a thermal management system

Material deposition management considerations

Link to material deposition management

Content coming soon.

Flow and consolidation management considerations

Link to flow and consolidation management

Content coming soon.

Residual stress and dimensional control management considerations

Link to residual stress and dimensional control management

If the coefficient of thermal expansion (CTE) of the new reinforcement has changed significantly, then the residual stressed induced by the tool-part interaction will have also changed. This may act to increase or decrease the chance of part warpage upon demoulding depending on the disparity between the composite CTE and the tool CTE. A higher disparity will tend to increase CTE-induced deformation. Below is a table of common CTE values. Generally speaking, it is best to have tools with a low CTE for carbon fibre-epoxy composites.

CTE values for common tooling and part materials

Material	CTE (x10-6/°C)
Aluminum	23
Steel	11
Invar	0.6 to 1.5
Epoxy	45 to 62
Polyester	60 to 200
Vinylester	100 to 150
Carbon fibre (longitudinal)	-0.2 to -0.5
Carbon fibre (transverse)	10 to 15
E-glass fibre (longitudinal)	5
E-glass fibre (transverse)	5

Related pages

Page type	Links
Introduction to Composites Articles
Foundational Knowledge Articles
Foundational Knowledge Method Documents
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
Practice Documents	Maintaining equivalency during cure for different fibre architectures - P118 Troubleshooting part quality during cure when changing the reinforcement - P131
Case Studies
Perspectives Articles	Composite materials engineering webinar session 1 - Introduction - A120 Composite materials engineering webinar session 2 - Constituent Materials - Fiber - A121 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

References

About	Help

For polymer matrix composites (PMCs), resin refers to the matrix; the continuous material phase that binds the reinforcement together, maintains shape, and transfers load. Resins are divided into two main groups: thermosets and thermoplastics.

Volume fraction of either matrix or fibres with respect to total composite volume (matrix + fibre).

Engineered materials (designed to have specific properties) made from two or more constituent materials with different physical or chemical properties. The constituents remain separate and distinct on a macroscopic level within the finished structure.

A central processing theme in the manufacturing cycle. This theme is concerned with managing the thermal response of materials during storage and handling or parts/tools when they are subsequently heated.

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.