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In the above set of equations, it can be shown that , due to moment balance! Furthermore, we begin by making valid assumptions with regards to our problem of interest. First, we assume that there is no body force (b = 0) anywhere in our model. In addition, we model our problem as a plane stress problem, which means that all of the out-of-plane stress components involving -direction, can be assumed to equal zero (σ_θ = τ_θr = τ_θz = 0). These assumptions lead to the following simplifications:
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