3.1 HOW RIGID INTERLOCKS WORK

Integral mechanical attachments or integral interlocks are geometric features of two or more parts that when caused to come into contact and fully engage, prevent relative motion in certain directions of translation and/or rotation, including, when features physically interlock, unwanted separation in any or certain directions (see Chapter 2, Section 2.2). The interlocking features can pre-exist in the parts being brought together, having been created in the detail parts during their fabrication, or can be created once the parts are properly positioned in the intended assembly. The former situation occurs for both rigid and elastic interlocks, while the latter occurs for plastic interlocks (see Chapter 2, Section 2.3). Rigid integral mechanical attachments or rigid interlocks accomplish and retain assembly of parts by retaining their individual overall shapes and the shapes of the actual attachment or interlocking features throughout the process of part engagement, feature interlocking, and subsequent service as the assembly. Neither the parts nor the actual geometric features that allow and enable engagement and interlocking are intended to temporarily deflect as they do in elastic interlocks or permanently deform as they do in plastic interlocks.

To resist both temporary noticeable elastic deflection and permanent plastic deformation, rigid interlocks must be designed to remain rigid through the proper combination of their geometry (i.e., mass and shape-induced moment of inertia) and material (i.e., yield or flow strength for inherently ductile materials, fracture strength for inherently brittle materials, and elastic and/or shear modulus for...