Overview

In the previous blogs, we have introduced the following topics:

1. The challenges of switching to composites design
2. State of the art in composites design for manufacturability

Continuing from the previous blog, this blog highlights the fundamentals of composites design and provides a step-by-step guide for achieving such a design. The key difference of the approach presented here is that it considers manufacturing and material as an integral part of the design process. The table of content is provided below with the links to quickly jump to respective sections:

• Fundamentals of design thinking in composites
• Steps in the process flow of designing the composites part
  • Set out a design objective
  • General design requirements and their implications
  • The operational environment and design criteria
  • Key attributes to keep in mind for lightweight structure design
  • Choice of materials, manufacturing with structural analysis
• Key takeaways

Fundamentals of design thinking in composites

The two basic decisions in designing a composite part are the selection of materials and the form of construction to be employed. This blog outlines the design requirements, constraints, principles, and decisions.

The materials choice is a compromise between technical, manufacturing, commercial and strategic factors. The form of construction is chosen to obtain substantial weight savings at acceptable manufacturing cost, paying particular attention to four technical factors that dominate the design.

1. Design for integrity in the presence of built-in and accidentally induced stress raisers
2. Design for structural stability
3. Design for integrity in a service environment including the effects of humidity and elevated temperature exposure
4. Design and test margins to give adequate allowance for anticipated variability of structural performance.

Steps in the process flow of designing the composites part

1. Set out a program objective

• To design, develop, manufacture, and demonstrate by testing parts made from composites
• To embody design principles and methods of manufacture that are likely to be adopted for small to medium-volume production to:
  • Save at least X % of structure weight compared with the corresponding structure in the existing metallic shape
  • Embed sensor for Structural health monitoring
  • Combine multiple smaller components into a single large component
  • Integrate with the digital supply chain by automating and digitizing the workflow
• To maintain standards of safety at least equal to the present metal part and embody design principles to satisfy future damage tolerance requirements
• To embody materials and manufacturing methods suitable for evolution into cost-competitive structures.
  

2. General design requirements and their implications

• The main structure will be able either replace or would adapt to the new design of the assembly
• Boundary geometry identical to the metal part;
• Key features for operations
• Mounting points
• Moving elements/hinges and sensors
• Load cases
  

3. The operational environment and design criteria

• Environmental degradation
• Variability and safety margins
• Notch sensitivity and damage tolerance
  

4. Key attributes to keep in mind for lightweight structure design

1. First design decision based on literature/proven design with lightweight design principles as follows
   1. Minimize the amount of material to convey forces
   2. Search for fully stressed designs
   3. Design Stress fields, not components
   4. Avoid bending stresses: girder beams to be decomposed in the truss system
   5. Tension forces can be conveyed  over long distances and compression forces over short distances
   6. Short-circuiting forces reduce the use of resources
2. New design exploration only when existing designs do not meet the requirements
3. Skin design
4. Internal member design
5. Joining interface design
6. Design for manufacturing review
7. Any changes/consideration- return to step 1 (structural design)
   

5. Choice of materials, manufacturing with structural analysis

1. Select feedstock from Rovings, prepregs, woven fabrics, Knitted fabrics, non-crimp fabrics, etc. [free and paid databases are listed here 1 2 3]
   
2. Process selection based on
   1. Component geometry
   2. Scale of production
   3. Tooling
   4. Part size
   5. Automation
      
3. Structural performance for the probable routes
   1. Preliminaries
   2. Thickness, mass, and material cost
   3. Process costs

Key Takeaways

• Identify what is the goal of the redesign/design process
• Define the key goals that the new part will achieve
• List out an application and operational  requirements for the part
• Before diving into the design process make sure lightweight design principles are in check
• Go through the iterative process of the design until the design, process, and material are not meeting most of the set-out criteria.

Are you ready to leverage your composite manufacturing with an all-in-one AFP solution? Contact Pravin Luthada or James Kuligoski via LinkedIn now to schedule a demo.

About Addcomposites

Addcomposites is the provider of the Automated Fiber Placement (AFP) ecosystem - including the Fiber Placement System (AFP-XS), 3D Simulation and Programming Software (AddPath), and Robotic Cells (AddCell). With the leasing program for the AFP system (AFPnext), composites manufacturers can work with thermosets, thermoplastics, dry fiber placement, or in combination with 3D Printers on a monthly basis.

References

• https://architecture.mit.edu/sites/architecture.mit.edu/files/attachments/lecture/LightweightStructures.pdf
• https://sci-hub.hkvisa.net/10.1016/j.paerosci.2014.03.003
• Selection of composite materials and manufacturing routes for cost-effective performance

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