Crippling of stiffeners

In this subject, Prof. C. Kassapoglou talks about local failure modes of stiffeners, which do not cause the structure to lose all load carrying capabilities. This behavior is called crippling, and is preferable over total failure modes such as column buckling since your structure retains some strength after initial failure.

He starts by writing out general equations for a stiffener on an elastic foundation, for a multitude of boundary conditions, followed by an example of using graphite pins under an angle with respect to the facing as core of a sandwich material. He then proceeds to tell about the main topic of the lecture, the crippling of stiffeners. He makes a distinction between segments of the stiffener cross section which have either one or no edge free, and compares the analytic results with actual testing data.

After the break, a case of an aircraft fire is discussed, and what considerations are when repairing composite structures. At the end of the lecture the practical implications of radius regions in the cross section are discussed, and examples are given of how to deal with them.

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