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A unique cascade test facility has been developed for use in the Wichita State University (WSU) water table. Although small in scale, the WSU water table has the advantage of low cost and the ease with which test conditions can be varied. Water table facilities have been used in the past for cascade experiments, especially as analogies for compressible flow visualization of turbine cascades. However, the lack of a quantitative measurement technique at low speeds has precluded the use of the water table as an analogy for testing subsonic compressors and turbines. In the present experiment, the hydrogen bubble flow visualization technique is used to generate bubble time lines, and a CCD (Charge Coupled Device) video camera system captures and digitizes these time line images. A VisualBASIC® computer program is then used to determine the wake velocity profile based on the difference in bubble line positions at successive intervals of time.

An aging aircraft accumulates fatigue cracks commonly referred to as multiple site damage (MSD). A simplified engineering fracture mechanics model, generally referred to as the linkup model (or plastic zone touch model), has been used with some success to describe the MSD fracture phenomenon in 2024-T3 aluminum panels. A disadvantage of the linkup model is that it gives excessively inaccurate results for some configurations. A modified linkup model has been developed through empirical analysis of test data taken from unstiffened panels with MSD cracks at open holes. The modified linkup model was then validated with test data from stiffened panels including single-bay panels with the lead crack centered between stiffeners and two-bay panels with the lead crack centered beneath a severed stiffener. Further validation of the modified linkup model was done with test data from panels with bolted lap joints. Test results were obtained from 112 different panels.

The residual strength of an aluminum panel with a centric hole and one cracked ligament was investigated experimentally. Each of the 7075-T6 aluminum panels which were tested included a cracked ligament of varying length on one side of the centric hole and an uncracked ligament on the other side of the hole. The failure of such a panel subjected to uniform tensile loading normally occurs according to the lower of two modes: brittle fracture or a net section type of yielding. On the other hand, the question of whether one or both ligaments fail is not easily answered. Results show that one or two ligament failure depends upon test conditions such as crack length and loading method. For short crack lengths, the uncracked ligament will fail almost simultaneously with the failure of the cracked ligament.