What does a dull thud indicate when inspecting a composite panel using the ring test?

A dull thud during the ring test of a composite panel indicates separation of the laminates. This test involves tapping the surface of the panel to listen for the sound it produces; a sharp, ringing sound typically signifies structural integrity, while a dull thud suggests that there may be delamination happening. Delamination occurs when the layers within the composite panel are not properly bonded, allowing for separation, which compromises the panel's strength and performance. Recognizing the sound produced during this test is crucial for assessing the overall condition of the panel and ensuring it meets safety and performance standards. Thus, a dull thud is directly associated with laminate separation and indicates a problem that needs to be addressed.