Fatigue test load identification using weighted modal filtering based on stress

• The fatigue test is modeled with a linear state space model.
• A modal filter is applied to find the modal excitations.
• The mode shapes are given weights proportional to their stress contribution in critical points.
• Experiments indicate that the proposed procedure enables a more accurate reproduction of the stress in the test setup.

Laboratory reliability testing is an important part of the vehicle development process. Test rigs are designed to reproduce accelerations or other sensor readings in a controlled environment and criteria on the duration of testing without failure are used to assure quality. An apparent difficulty of this procedure is that the damage at a point is only indirectly coupled to the accelerations measured in other points. In this paper, it is proposed to use a modal shape filter, and control the test such that the shapes that are generating stress in critical points are reproduced. A selective weighting of the mode shapes allows for accurate reproduction of the stress, and hence the damage, also in circumstances when the exact location of the excitation force cannot be reconstructed in the test. The proposed procedure is applied in two different experiments; the first aiming to reproduce the stress in a cantilever beam, and the second aiming to reproduce the stress in a truck cabin suspension.