Composite attachment: the Trek bottom bracket
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Bottom bracket failures have been one of the most common failures in the composite bicycle frames produced by the Trek Bicycle Corporation. The bottom bracket is the portion of the frame that supports the crank and pedals. An aluminum insert is chemically adhered to the composite shell of the Trek frames with an epoxy. This insert is the attachment point for the crank assembly, so it is exposed to cyclical and often relatively large loads. The most common failure is a disbond in the epoxy. This research analyzed a composite bicycle frame using finite element analysis software to help determine the stresses in the frame about the point of failure. A model of the entire frame and a more detailed model of the bottom bracket region were constructed to perform the analysis. The model of the frame was analyzed using a static analysis and loads specified by Trek. Results from the frame model were then applied to the bottom bracket model for analysis. Stresses as high as 320 MPa (46,500 psi) resulted. The stresses and the resultant strains cause the failure. A different epoxy resin or a different manufacturing process will be required to remedy this problem.
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Includes bibliographical references: leaf 19.
Mallard, David (1998). Composite attachment: the Trek bottom bracket. Texas A&M University. Available electronically from