A New Method Using Pseudovelocity-Based Fatigue Analysis to Determine the Effectiveness of Acoustic Fields Used for Acoustic Testing

Abstract

Abstract This paper summarizes results from the use of advanced adaptive multiple-input, multiple-output (i.e., MIMO) control for direct field acoustic testing to excite an aluminum-honeycombed 1.22 m × 2.44 m (4 ft × 8 ft) test panel with MSI-DFAT's near-diffuse acoustic field and four nondiffuse acoustic fields using three panel orientations, and two speaker configurations. The five fields have the same overall sound pressure level (OASPL) and 1/3-octave sound-pressure-level (SPL) spectrum. Test and analysis results demonstrate a dependence of the test panel's response characteristics to each acoustic-field excitation, showing that the near-diffuse field excites experimental-modal-analysis-identified test panel modes effectively, whereas nondiffuse fields excite these modes ineffectively. Differences are attributed to the relative diffuseness of fields. Partial fatigue damage values from 20 accelerometer locations are determined from pseudovelocity (PV) outputs from single-degree-of-freedom (SDOF) models at each modal frequency excited by their response time histories, for each acoustic field, to quantify the relative ability of acoustic fields to detect workmanship flaws of typical test articles. Fatigue-damage values are obtained from PV response time histories of SDOF models at identified modal frequencies, which are rainflow-cycle counted with the partial-damage coefficients calculated using the Palmgren-Miner rule. A new form of vibro-acoustic gain based on PV power spectral densities (PSDs) is also introduced and correlated with these experimental results, since the PV response PSDs of a test article undergoing random vibration are proportional to modal stress at their frequencies. This paper shows that the modal stress caused by acoustic-field types is an important consideration for acoustic testing of satellites and other spacecraft, since using a nondiffuse field may result in an acoustic test that doesn't detect workmanship flaws in a test article, even though the acoustic environment is achieving the same specified OASPL and average acoustic 1/3-octave SPL spectrum.