I began drafting a response regarding a failed frame last year. Did not need to use it in the end but the general points may help. Mine had a lifetime guarantee so I was in a stronger position that way, but your three year guarantee does not negate your case.
"The Consumer Rights Act 2015 requires goods to be of satisfactory quality (section 9(1)). The quality of the goods is satisfactory if they meet the standard expected of a reasonable person, taking into account factors such as description, price and other factors (section 9(2)). Other factors, such as statements made by the producer are also considered as part of the test (section 9(5)).
The bicycle was purchased in late 2017 for circa. £2,200.00 (a price reduced from the original sale price). This was a bicycle described by XXXX as capable of some gravel type riding (not that I used it for that) and came with a lifetime frame guarantee. Paragraph 105 of the explanatory notes of the Act explain a person has a limit of six years if they believe a breach of contract has occurred. In particular it refers to a breach of the goods being not of satisfactory quality in respect of the expectation of a reasonable person.
In light of that I believe the cost of the frame and advertised intended would mean a reasonable person would expect the bicycle to last longer than five years "
Sorry if I have missed the model of the frame. If it is a gravel bike you may have a stronger argument. Ideally look for a catalogue from the year it was made. I note on their website the latest gravel bike is described as being fit for Himalayan rides and uses titanium for ultimate strength. If you can find something saying similar about yours, a failure like yours after averaging 10 miles day would not appear reasonable given cost as well. If they do offer a longer warranty on current titanium frames it raises questions regarding if previous frames were not built to the same standards.
Hopefully you are in Strava so can evidence all the riding was on roads (if that was the case) and not on the gravel terrain the frame was made for (if it is a gravel frame).
If they bring in the might have been crashed argument ask them for proof of their assertion. Also highlight the lack of any scuff marks/crash damage.
The onus is on you, but not to prove the science regarding material failure. You have to prove it did not meet the test of a reasonable person, so the more evidence you can get in the basket the better.
Hope this helps. Only my own views and not offered with any expertise.
If all else fails take comfort in the fact it didn't snap whilst riding and it is a snapped frame, not a snapped body.
