In this lecture prof C. Kassapoglou talks about the how problem of skin-stiffener separation arises and how to determine the stresses at the interface.

After clearly defining the problem he starts by explaining the Euler-Lagrange equation, which is a differential equation can be used to minimize or maximize a function using calculus of variations. He then writes out the stress equilibrium equations and applies them to a generalized case to find expressions that can be used in the Euler-Lagrange equation to find a minimized solution.

Finally the Euler-Lagrange equation is applied on the stress relations, and known boundary conditions are used to find an expression for the skin-stiffener interface stresses.