Hail Damage
After the recent hail storm here in Melbourne at Christmas, I had a local rider contact me asking for a bike assessment. He said his road bike was on the roof rack on the car as he was driving home when the storm front hit. There was significant damage to his car, so he wanted to be sure his bike was still safe to ride.
He did a visual inspection and couldn't see any damage but thought he would bring it in to us to provide a professional assessment. I examined the bike first visually and also could not see any obvious damage, however when I did the Ultrasound scan a number of delamination indications became very obvious on the scan. All up there were 8 delaminations spread out across the top tube. The damage was akin to small hammer hits, which is pretty much what golf ball sized hail is, the top tube was the only tube on the frame damaged which makes sense as it was fully exposed to the hail.
It was recommended that the frame was unsuitable for use in this condition. Once again this shows the value of Ultrasound scans to find non visible damage and determine the safety of your bike.
Carbon bike repair featured in Mountain Bike Australia magazine
Raoul Luescher the director of Carbon bike repair is featured in the current issue of Mountain Bike Australia magazine. We often get asked if we repair MTB's as most of our repairs seem to be on road bikes. In the magazine article you can see the steps taken to perform a simple repair and also get an insight into some of the methods and materials used to ensure the highest quality structural repair to your ride.
You will also see one of Raoul's older MTB's from the 1990's as well as a new road bike that will top the scales at about 600g.
Follow the link or get a copy at the newsagent http://emag.mountainbikingaustralia.com.au/LandingPage.aspx#
A reproduction courtesy of MBA magazine can be found here. (1Mb)
Ausbike 2010 Seminar
I have uploaded the seminar that I presented at the Ausbike show in 2010.
The seminar gives some background info on carbon bikes, composite materials and some repair and inspection examples.
Click here to see a PDF version of the powerpoint file.
Compaction
Compaction is the process of bringing the individual fibre’s close to each other so they can transfer load to each other more effectively. Compaction plays another role of removing any trapped air that may cause voids or porosity in the laminate.
Compaction is very important because for the structure to perform as designed the individual fibre’s need to transfer the loads from one fibre to the next so the load can travel through the structure. The resin has strength and stiffness properties of about 1% of the fibre so it is important that the fibre can do the job it was intended to do. There is a misconception that compaction is only important to remove the excess “heavy” resin to reduce the weight of the part. This is false in that proper compaction provides not only a decrease in weight but an increase in strength and performance.
“The overall laminate will have lower strength than a properly consolidated laminate having the optimal per ply thickness, and will generally require more plies to achieve the desired strength”.
The Boeing Company
Common problems associated with compaction are:
Resin voids – Pockets of trapped air in the resin.
Porosity – Areas of fine air bubbles in the resin. (Like a Violet Crumble)
Resin pooling – Areas of resin rich pockets, often associated with a geometry change.
Resin rich – Area of excess of resin in the part
Resin poor – Area of insufficient resin in the part.
Thickness variability – Areas outside the optimum laminate thickness.
With bicycle frames problems often occur when designers use shapes that aren’t optimum such as tight corners and also at areas of sudden thickness change such as molded in cable guides.
For all these production flaws Ultrasound is the preferred method of inspection because the thickness can be measured and because ultrasound scans are very sensitive to porosity and planar defects.
Why don’t other carbon bike repairers use ultrasound?
One answer is cost however it is a little more complex than that.
To get set up with Ultrasound scanning equipment is expensive with a basic unit costing about $10 000. The prices go up from there with fully automated robotic systems costing up to $5 million. For aerospace repairs we use a portable unit with a typical cost of about $15 000 including the probes which cost about $1500 each. So as you can see from the numbers not many repair shops could afford such specialist equipment.
The main answer to this question however is the level of training and experience required.
The training required to use this equipment is very time consuming and expensive. It takes a typical aerospace technician many years of training to be certified in this inspection method. Experience is everything in this field, and that takes time to acquire, experience working with carbon composite and knowing the engineering involved with the part that is being inspected.
Most people are familiar with medical ultrasound scans, these differ significantly from the type of scans typically used on a carbon bike. Just like you go to a specialist medical technician if you need a scan on your body, you should go to a specialist carbon composite technician for your bike scan.
So as you can imagine it is not a simple process of buying a cheap unit and scanning parts, it takes years of training and specific knowledge to understand what the output signal is indicating.
Because we have this experience and equipment we are able to find damage that would not be found by any other methods, we can find the "undetectable" damage that others repairers don't know even exists. It isn't possible to repair damage when you don't know where it is!
This puts us at a significant advantage when it comes to accurately assessing if your bike is safe to ride or not.