Stress Analysis of Instrument Panel Knobs 2000-01-0316

In this paper, hoop stresses in the hubs of plastic knobs used in instrument panels are analyzed. The objective is to provide analytical formulas for stresses due to knob assembly and temperature cycling. Insertion forces are estimated using simple beam equations to model spring deflection. These forces are used to predict stresses in the D-shaped hubs of the knobs, using equations for thick pressure vessels. Solutions for stresses due to thermal expansion mismatches between the plastic hub and metal spring are derived using a press-fit analogy. Finite element analysis (FEA) is used to supplement and validate the analytical results. The proposed simple calculations are useful for up-front design assessment, enabling the engineer to select appropriate dimensions for knob hubs, springs and shafts.