|
Composite sandwich structure has been widely used in aerospace due to its
lightweight, high stiffness and strength. The quality of the structure is crucial to
durability and structural integrity of the rehabilitated the structure, Delaminations,
debonding and water ingressing to honeycomb are typical defects in the structure.
Defects in the structure will influence the quality of product. Pulse thermography has
been an effective NDE method in recent ten years. The technique uses pulse to excite
the specimen, because the presence of subsurface defects reduce the diffusion rate,
then temperature difference between defect area and sound area will be measured by
an infrared camera. Subsurface defects become visible with time delays, it is a
non-contact, quickly inspection method. Pulsed infrared thermography has been
widely used in aerospace and mechanical manufacture industry because it can offer
non-contact, quickly and visual examinations of defects. It is a meaningful research
topic to study on quantitative testing with the structure rapidly and non-destructively.
Sandwich composites with aluminum facesheet and aluminum honeycomb cores are
chosen as study objectives. Some back-drilled holes with different sizes and depths in
the specimen are used to simulate delaminations between plies in the strcuture .The
paper presents a method for defining the boundaries, quantitatively estimating the
sizes of the flaws in the CFRP using pulsed infrared thermography. Processing
captured data using splinefitting, measuring the size of the defects by calculating the
pixels numbers that exceed the detection threshold and computing areas of defects by
binary image. Compared with the designed sizes and areas having defects, the results
show that the method offers more than 90% accuracies with reference to the sizes of
artificial flaws embedded in the CFRP sheet. The experimental results demonstrate
the feasibility of using detection threshold to inspect the CFRP sheet. The curve of the detection threshold and depth obtained could be applied for practical inspection.
|
