Surface Topography Influences on Structural Life Prediction

Topography describes the complex form of a surface--the undulations which make up its character. Topography comes in all shapes and forms; what is true for the surface of our planet is also true for the surfaces of engineered structures. If you have ever driven across the Flint Hills in south-eastern Kansas, you probably recognize that the only indicator you have that you are climbing a hill is that the engine rpm goes up ever so slightly. These hills have little in common with the hills of south-eastern Kentucky, yet on an ordinary road atlas, they are labeled “hills” just the same. It is not until you look at these regions on a topographic map that the differences become clear. In an engineered structure, sometimes topography is important, and other times it is not. When we produce, for example, a residual strength analysis, the assumption of a pristine surface is the norm. For many types of analyses and under many criteria, this is acceptable. However, surface integrity is often critical to proper function of a structure. Ignoring the form of a surface, or the deviation of a surface from its intended form, either from improper machining, accidental damage, wear, or corrosion, can have profound structural implications.