Sensitivity analysis with Stiffness Injection

What is stiffness injection?

The Stiffness Injection (SI) method consists of changing the stiffness of one or more components of a physically existing assembly, introducing extra (virtual) spring and/or damper elements. This is possible using the Virtual Point Transformation and Dynamic Substructuring technologies. Stiffness injection is applied to a component in an assembly, where all transfer paths are already measured and defined. With SI, you add and/or remove stiffness between the DoFs on the active and passive sides of a component. As a result, you calculate new assembly FRFs using Dynamic Substructuring.

Why use stiffness injection?

You usually perform Stiffness Injection at a later stage of a vehicle development process. This is because SI consists of modifying the full-vehicle FRFs by adding and/or removing stiffness to a single component. For this reason, you need the assembled system physically available, with all transfer paths defined and measured.

Theoretically, you can apply SI to any component, between its active and passive sides. Practically, SI is mainly applied to bushings, where you add or remove stiffness to make them stiffer or softer. You use the stiffness injection technology for two main reasons:

1. To optimize the stiffness of one element of the already existing assembly.
2. To study the effects of the durability of bushings (likely the final bushing stiffness will differ from the original one).