[home] [Personal Program] [Help]

---

Session: Session 19: Full-scale fatigue testing II
Session starts: Thursday 29 June, 15:40
Presentation starts: 15:40
Room: Theatre room: plenary

---

Eric Dionne (NRC)
David Backman (NRC)
C. André Beltempo (NRC)
Stéphane Brunet (NRC)
Benjamin B. Bolduc (NRC)

Abstract:
This paper describes the test campaign performed by the National Research Council Canada (NRC) on a disbonded F/A-18A/B/C/D Inner Wing Step Lap Joint (IWSLJ). Many disbonds have been reported by the F/A-18A/B/C/D fleet operator. The majority of the disbonds found are small relative to the size of the IWSLJ. The immediate effects of those disbonds and their changes in a long term are not well understood. The NRC is conducting a component test aimed at better understanding the effects of a partially disbonded IWSLJ on the F/A-18 wing structural integrity. This paper will summarize the objectives of the component test, as well as the approach used to address the test objectives, which combines several innovative techniques in the area of data sensing. This paper will summarize the test results to date as well as lessons learned. Residual Strength One of the primary purposes of this test is to evaluate the residual strength of a partially disbonded Stepped Lap Joint (SLJ) of the lower wing skin. For this purpose the United States Navy donated a retired wing with a pre-existing disbond similar to those found in the F/A-18A/B/C/D fleet. Static loads will be applied to the test article to demonstrate sufficient residual strength in presence of the small disbond. The test is performed at Room Temperature (RT) and loads are scaled up for temperature effects; this allows for a simpler test setup. Effect of Constant Amplitude Loading The second aim is to try to generate damage growth data for a common size of disbond in the SLJ. Repeated constant amplitude loads will be applied in an attempt to grow the disbond. The loads will be progressively increased and the disbond will be frequently inspected using customized non-destructive inspection techniques able to detect and measure disbond size and quantify the resulting growth. The data from the numerous sensors will also be monitored to detect if the disbond growth can be measured in a test environment. Load Redistribution The third aim is to evaluate the internal load distribution as a result of the disbond growth. The test article is equipped with over 250 strain gauges on the SLJ as well as on the surrounding structure as it is believed that new load paths will be created as the disbond grows. Digital Image Correlation (DIC) is also used on both the upper and lower SLJ with the anticipation it would detect a perturbation of the strain field at the tip of the disbond. Fiber optic sensors were also installed along the spars to detect load bypassing from the skin to spar caps. The sensor measurements will also be correlated to a Finite Element (FE) model of the wing in an effort to enable the development of FE models to replicate and predict more complex disbond scenarios.