Made to measure…Holes.

Who are you?: Nick Brown
What is your role?: EngD Researcher
What is your work about?: Thermally Assisted Piercing of Thermoplastic Composites


Figure 1: X-ray image of a hole created by displacing material

I beg your pardon?: Over the last 4 years I have been developing a novel method of making holes in composite materials, specifically carbon fibre reinforced plastics, as part of my doctoral research with the University of Surrey and TWI. If you think of the many ways to make holes then you will no doubt be thinking of a technique that involves removing material. What my research was looking into was a way of making a hole without removing material. This technique creates a hole by pushing the material into another place (or displacing it) and leaving a hole that can be used for fastening or to allow gases or liquids to travel through (Figure 1).

OK. Why?: Why would we want to move material rather than remove it? Well, if we take a carbon fibre composite and drill a hole in it then we are cutting and/or removing the carbon fibres to create the hole. The problem with this is that the carbon fibres are there to give the composite its strength. So if we can push the fibres to the side of the hole, and not cut them out, then we can keep more of the fibres intact and retain more of the strength that makes composites so useful in engineering.
And?: What I found in my research was that by making adjustments to the way I created my holes, the strength would vary quite significantly. To understand why this was happening I looked into the microstructure of the composites and how they were changing when I created my holes. What I found was that when moving the material during the process the carbon fibres would be bunched and compacted into some areas and pulled away from other areas. This had a dramatic effect on the strength of my specimens when testing them under different conditions.
So what?: When comparing the strength of my specimens with specimens that were conventionally drilled, I found that the strength could be increased by up to 20% in some situations or reduced by up to 30% in other situations. This not only varied according to the test used, but also when I varied the process settings. From one perspective this could mean that the holes are only good for certain situations, when created in a particular way.
Final Thought: The way I like to see it is that these holes can be tailored for their application…or ‘made to measure’.

For more information on Nick’s work click on this made to measure link: 
TWI’s Made to Measure Holes