Automated detection of fatigue cracks on the faying surface within high load transfer bolted specimens

摘要

Boeing is currently conducting evaluation testing of the Comparative Vacuum Monitoring (CVM~(TM) system offered by Structural Monitoring Systems, Ltd (SMS). Initial testing has been conducted by SMS, with further lab tests to be performed at Boeing. Testing has been conducted on high load transfer dog bone type specimens. A notch was cut at one of the bolt holes and a CVM sensor installed on both sides of the plate. The doublers were added and a single line of 4 bolts along the longitudinal center line were used to attach the doubler plates to the dog bone type specimen. In this way, a high load transfer situation exists between the two halves of the dog bone specimen and the doubler plates. The CVM sensors are slightly over 0.1mm (0.004") in thickness and are installed directly upon the faying surface of the dog bone specimen. Testing was conducted on an Instron 8501 Servohydraulic testing machine. The standard laboratory equipment offered by SMS was used for crack detection. This equipment included the Kvac (vacuum supply) and the Sim8 (flow meter). The Sim8 was electrically connected to the Instron machine so that as soon as a crack was detected, fatigue loading was halted. The aim of the experiment was for CVM to detect a crack on the faying surface of the specimens at a length of 1.27 +- .25 mm (0.050" +- 0.010"). This was accomplished successfully.