Lap splice adhesive on aircraft9/23/2023 ![]() ![]() This basic mechanism has not been identified, and one of the objectives of the work is to see to what extent the mechanism is revealed by a fracture analysis of the MSD cracks. Moreover, it indicates that there is some mechanism which keeps longer cracks from running away from shorter ones, or, equivalently, a mechanism for shorter cracks to catch-up with longer cracks. This regularity suggests that nucleation of the cracks must not be overly difficult. One of the most striking features of MSD observed in joints of some test sections and in the joints of some of the older aircraft fuselages is the relative uniformity of the fatigue cracks from rivet to rivet along an extended row of rivets. The effect MSD has on the ability of skin stiffeners to arrest the growth of long skin cracks is a particularly important topic that remains to be addressed. Most of this work is documented in the proceedings of previous symposia on the aging aircraft problem. Fatigue testing efforts have included flat coupon specimens, two-dimensional lap joint tests, and full scale tests on specimens designed to closely duplicate aircraft sections. Fracture analyses previously carried out include small-scale modeling of rivet/skin interactions, larger-scale two-dimensional models of lap joints similar to that developed here, and full scale three-dimensional models of large portions of the aircraft fuselage. Multi-site damage (MSD) is receiving increased attention within the context of problems of aging aircraft. Results of a fracture mechanics analysis relevant to fatigue crack growth at rivets in lap joints of aircraft skins are presented. Preliminary results on the fracture analysis of multi-site cracking of lap joints in aircraft skins Other effects, such as temperature and potential, as well as the impact of the environment on fatigue crack growth have also been studied. The extent and morphology of the attack in artificial lap joints has been compared to studies of corroded samples from actual aircraft. Laboratory studies have also included exposure tests involving artificial lap joints exposed to various simulated bulk and crevice environments. The statistically significant ions have been used to create a second generation solution. Additional tests have determined the relative importance of each of the detected ions in model solutions used for future predictive tests. Electrochemical analyses of the behavior of AA2024-T3 in these solutions gave corrosion rates of up to 250 microns per year (10 mpy). After determining the species present and their relative concentrations, the resultant solution was reproduced in bulk and electrochemical tests were performed to determine the corrosion rate. Measurements of pH of wetted corroded surfaces indicated an alkaline occluded solution. Over twenty different ions have been detected. CE analysis has been performed on over sixty corrosion product samples removed from both civilian and military aircraft. Capillary electrophoresis (CE) is used to identify the ionic species contained in corrosion product samples removed from fuselage lap splice joints. A protocol for collecting and identifying the chemistry of airframe crevice corrosion has been developed. The objective of this work is to develop a laboratory corrosion test protocol to identify the chemistry to which lap joints are exposed and to develop a model of the corrosion within the joints. Fuselage lap-splice joints are a particularly important structural detail in this regard because of the difficulty associated with detection and measurement of corrosion in these occluded regions. The complexity of airframe structure lends itself to damage resulting from crevice corrosion. Determination of the Corrosive Conditions Present within Aircraft Lap-Splice Joints ![]()
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