Bicycle components failure

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 Although steel has a fatigue endurance limit certain parts of the frame are stressed above this limit and are prone to fatigue cracking. The rear triangle, comprising the chainstays and seatstays are particularly vulnerable.

On the opposite side, the associated cracked point had caused surface corrosion. Notice that the cracks had occurred close to the brazed-on cross member. The heat affected zone associated with brazing and welding usually reduces the endurance limit and raises the chance of fatigue crack initiation.

A metallurgical investigation of the extent of the heat affected zone is in progress. The manufacturers did not fulfil their "lifetime" guarantee in this instance by suggesting that damaged paintwork caused corrosion, which in turn initiated fatigue.