For accuracy and efficiency quasi-static analyses require the application of loading that is as smooth as possible. Sudden, jerky movements cause stress waves, which can induce noisy or inaccurate solutions. Applying the load in the smoothest possible manner requires that the acceleration changes only a small amount from one increment to the next. If the acceleration is smooth, it follows that the changes in velocity and displacement are also smooth.
Abaqus has a simple, built-in smooth step amplitude curve that automatically creates a smooth loading amplitude. When you define a smooth step amplitude curve, Abaqus automatically connects each of your data pairs with curves whose first and second derivatives are smooth and whose values are zero at each of your data points. Since both of these derivatives are smooth, you can apply a displacement loading with a smooth step amplitude curve using only the initial and final data points, and the intervening motion will be smooth. Using this type of loading amplitude allows you to perform a quasi-static analysis without generating waves due to discontinuity in the rate of applied loading. An example of a smooth step amplitude curve is shown in Figure 1.
Figure 1. Amplitude definition using a smooth step amplitude curve.
