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Troubleshooting part quality during cure when changing the reinforcement - P131

From CKN Knowledge in Practice Centre
Practice - A6Production Troubleshooting - A251Troubleshooting part quality during cure when changing the reinforcement - P131
Troubleshooting part quality during cure when changing the reinforcement
Practice document
Document Type Practice
Document Identifier 131
Objective functions
MSTE workflow Troubleshooting

Q: "I have used a given prepreg resin system to cure a wide variety of good quality parts, but having switched reinforcement types to lower cost, I can no longer make good quality parts with the same cure cycle."

A: It is likely that the change in reinforcement resulted in a significant change in the composite's material properties. Common properties to check would be the thermal conductivity, specific heat capacity, density, volume, thickness, and the coefficient of thermal expansion (CTE). If the specific heat capacity or mass of the reinforcement changed dramatically then so too would have the thermal mass of the composite. This will affect the thermal lag experienced by the composite during heat up and cooldown. A change in thermal conductivity, specific heat capacity, or density will have altered the thermal diffusivity of the reinforcement, and therefore the composite. This will affect the manner in which heat is distributed across the composite, potentially leading to hot and cold spots if the diffusivity is poor. In extreme cases, a change in thermal mass or thermal diffusivity may result in uneven cure. A change in the fibre volume fraction or ply thickness may have altered the exothermic response of the part which could have led to thermal degradation. This may manifest as reduced mechanical properties. Finally, if the CTE changed significantly, then the stress imparted onto the part by the tool during cure may be notable. If the part is deforming upon demoulding this may be the cause. Another potential cause for deformation following demoulding could be an uneven degree of cure (DOC).

Overview[edit | edit source]

Altering any aspect of the material will influence the composite's material properties. If the change in reinforcement is small, there may be no noticeable affect on quality. However, if the change is significant, it is possible that quality will be notably affected. If the thermal properties of the composite change significantly, then the consequences may influence not only the cure behaviour of the composite, but its flow and stress behaviour as well. As with all troubleshooting workflows, the best course of action is to list the defects, relate them to the changes made, and determine what may be the cause of those defects.

Thermal management considerations[edit | edit source]

Link to thermal management

From a thermal management perspective, 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:

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

Material deposition management considerations[edit | edit source]

Link to material deposition management

Content coming soon.

Flow and consolidation management considerations[edit | edit source]

Link to flow and consolidation management

Content coming soon.

Residual stress and dimensional control management considerations[edit | edit source]

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 [1][2]
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
Case Studies
Perspectives Articles


  1. [Ref] Daniel, Isaac M.; Ishai, Ori (2006). Engineering Mechanics of Composite Materials. Oxford University Press. ISBN 978-0-19-515097-1.CS1 maint: uses authors parameter (link) CS1 maint: date and year (link)
  2. [Ref] MatWeb LLC. "MatWeb: Online Materials Information Resource". Retrieved 9 September 2020.CS1 maint: uses authors parameter (link)

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Welcome to the CKN Knowledge in Practice Centre (KPC). The KPC is a resource for learning and applying scientific knowledge to the practice of composites manufacturing. As you navigate around the KPC, refer back to the information on this right-hand pane as a resource for understanding the intricacies of composites processing and why the KPC is laid out in the way that it is. The following video explains the KPC approach:

Understanding Composites Processing

The Knowledge in Practice Centre (KPC) is centered around a structured method of thinking about composite material manufacturing. From the top down, the heirarchy consists of:

The way that the material, shape, tooling & consumables and equipment (abbreviated as MSTE) interact with each other during a process step is critical to the outcome of the manufacturing step, and ultimately critical to the quality of the finished part. The interactions between MSTE during a process step can be numerous and complex, but the Knowledge in Practice Centre aims to make you aware of these interactions, understand how one parameter affects another, and understand how to analyze the problem using a systems based approach. Using this approach, the factory can then be developed with a complete understanding and control of all interactions.

The relationship between material, shape, tooling & consumables and equipment during a process step

Interrelationship of Function, Shape, Material & Process

Design for manufacturing is critical to ensuring the producibility of a part. Trouble arises when it is considered too late or not at all in the design process. Conversely, process design (controlling the interactions between shape, material, tooling & consumables and equipment to achieve a desired outcome) must always consider the shape and material of the part. Ashby has developed and popularized the approach linking design (function) to the choice of material and shape, which influence the process selected and vice versa, as shown below:

The relationship between function, material, shape and process

Within the Knowledge in Practice Centre the same methodology is applied but the process is more fully defined by also explicitly calling out the equipment and tooling & consumables. Note that in common usage, a process which consists of many steps can be arbitrarily defined by just one step, e.g. "spray-up". Though convenient, this can be misleading.

The relationship between function, material, shape and process consisting of Equipment and Tooling and consumables


The KPC's Practice and Case Study volumes consist of three types of workflows:

  • Development - Analyzing the interactions between MSTE in the process steps to make decisions on processing parameters and understanding how the process steps and factory cells fit within the factory.
  • Troubleshooting - Guiding you to possible causes of processing issues affecting either cost, rate or quality and directing you to the most appropriate development workflow to improve the process
  • Optimization - An expansion on the development workflows where a larger number of options are considered to achieve the best mixture of cost, rate & quality for your application.