Vacuum (partial) excitation involves the application of a change in pressure within an entrapped volume of air between a surface section and a vacuum hood frame. When a change (reduction) in pressure is applied (via a pump), a pressure bending load is applied to a partial section of the surface. A Laser Shearography sensor then measures the change in pressure, proportional to the out-of-plane bending strain, through a glass window on the vacuum hood frame. Vacuum (partial) excitation is defined in terms of a relative differential pressure between two applied pressure states.
Dantec Dynamics offers a vacuum hood system consisting of: a manual vacuum hood frame, two flexi-hoses and a pressure control unit (PCU). The manual vacuum hood is easy-to-use and can be connected simply, featuring two quick-release connection ports for the attachment of flexi-hoses and quick-clamp, mechanical locking feet. The locking feet only need to be re-clamped if the surface shape (topology) changes. The PCU is fully integrated into the Istra4D software and is capable of generating a (vacuum) pressure of -12 kPa within 5 seconds making it a reliable and fast excitation system for any application in conjunction with the FlawExplorer or FlawScout Laser Shearography senors.
With precision control, the setpoint pressure can achieved from any pressure level to an accuracy of +/- 5 Pa. Users can; perform both manual and automatic measurements using the pressure control unit and add/select any pressure level from a list. The recording procedure editor allows users the capability of adjusting the pressure level and camera acquisition on a clear measurement timeline. Manual procedures can also be logged and recorded into the recording procedure timeline for future editing.
Vacuum (partial) excitation delivers (usually) the best-quality and most reliable measurement results due to the accurate control of the loading and the stability of the setup. Additionally, it is the fastest method of excitation via the relatively quick and direct control of the loading mechanism (pump). It is usually an effective method for the inspection of; aluminium, glass-fiber (GFRP), carbon-fiber (CFRP), aramid-fiber (AFRP) laminates, sandwiches and honeycomb components.