Drop-weight Impact Testing Technology On Large Composite Structure

Composite structures are used widely in aircraft structures, but they are sensitive to low velocity impact damage and so research on impact resistance becomes more important. As impact tester of desk type is only adapted to standard specimen and cannot fulfill impact test on large structure parts. As a result, it is significant in engineering to develop the impact tester on large composite structure.Based on ASTM test standard, this paper firstly presents the technology requirements in impact test. And then a portable test instrument which could be used in large composite structure's impact is schemed out according to these requirements. The instrument uses force sensor to measure the impact force, and employ the optical sensor to measure impact and rebounding velocity; achieved the velocity-time history curve and force-displacement curve from the integration; the vibration frequency of the impact head parts are analyzed, which is proved to meet the test requirement. The measurement and control system is developed using LabVIEW.The impact test on a stiffened plate is carried out using this drop-weight impact tester. The vibration mode shapes of the stiffened plate at large and small span are obtained to examine the experiment method. The force-time history curve and force-displacement curve indicate the bend stiffness reduction due to the delamination. Damage form is also analyzed.The test instrument is also employed to produce the impact damage in wing box. Force signal is acquired to study the relationship between the maximum impact force and stiffness at the same impact energy. It is concluded that the maximum impact force increases as the stiffness of the impact site increases. The impact test on a co-cured wing box is carried out before the ultimate strength test. From the test curve, delamination or matrix crack happens first and then leads to a local stiffness reduction if the drop weight rebounds; while if it doesn't rebound but penetrates the plate, the stiffness remains stable in load increasing.