Engineers spend significant time optimizing individual components, but assemblies often fail somewhere else entirely: at the interfaces connecting those components. Bolted joints, welds, press fits, bearing seats, bonded surfaces, and other connections are where loads transfer from one part to another, and where local stresses can become significantly different from those predicted for the individual components.
A bolted joint, for example, introduces holes, contact surfaces, preload, and friction. A weld changes local geometry and material properties while potentially introducing residual stress. A press fit creates contact pressure that depends on the dimensional variation of two separate components. Each interface adds conditions that cannot be understood by analyzing either part independently.
Real operating conditions make these interactions even more important. Vibration can loosen fasteners, cyclic loading can initiate fatigue cracks near joints, thermal expansion can alter fits, and misalignment can create unexpected contact loads. A component may be perfectly strong in isolation while the connection transferring force into it becomes the system’s weakest point.
This is why load-path analysis should continue across the entire assembly. Engineers need to understand how forces enter a component, how they travel through it, and how they transfer into the next component. Contact geometry, fastening strategy, tolerances, material combinations, and expected movement all become part of the reliability calculation.
A reliable assembly is more than a collection of reliable parts. The connections between those parts must survive the same loads, cycles, environments, and manufacturing variation as the components themselves. Finding those vulnerable interfaces early can prevent failures that individual part analysis may never reveal.