Rapid, Approximate Multi-axis Vibration Testing

Abstract

Sequential single-axis vibration testing strategies often produce over-testing when qualifying system hardware. Rarely does the test article experience equivalent cumulative vibration response between laboratory and service environments when using traditional single-axis testing methodologies. Multi-axis excitation techniques can simulate realistic service environments, but the hardware and testing-strategies needed to do so tend to be costly and complex. Test engineers instead must execute sequential tests on single-axis shaker tables to excite each degree of freedom, which the previous two decades of vibration testing literature have shown to cause extensive over-testing when considering cross-axis responses in assessing the severity of the applied test environments. Traditional assessments assume that the test article responds only in the axis of excitation, but often significant response occurs in the off-axes as well. This chapter proposes a method to address the over-testing problem by approximating a simultaneous multi-axis test using readily available, single-axis shaker tables. By optimizing the angle of excitation and the boundary condition through dynamic test fixture design, the test article can be rapidly and inexpensively tested using a single-input, multiple-output (SIMO) test in a way that approximates a multiple-input, multiple-output (MIMO) test. This chapter shows the proposed method in simulation with a 2D finite-element box assembly with removable component (BARC) model attached to springs with variable stiffness. The results include quantified test quality assessment metrics with comparison to standard sequential testing. The proposed method enables wide access to rapid, approximate multi-axis testing using existing hardware, thereby reducing the over-conservatism of sequential single-axis tests and requisite over-design of systems.