D2 Ultrasound C-Scan

Topic

This model inspects the laminate non-destructively using ultrasound via the pulse-echo technique: a transducer emits an ultrasonic pulse into the laminate, and subsequently receives the echo generated whenever the pulse encounters an interface between two distinct regions of the material. Because the pulse generates an echo at each interface it encounters, the interior of the laminate can be inspected without causing damage.

The time-of-flight of the ultrasonic pulse—the interval between the pulse's emission and the receipt of its echo—determines the depth of the defect that generated the echo; since the pulse travels at a known speed within the laminate, the distance traveled before reflection is derived directly from this elapsed time. A longer time-of-flight corresponds to a greater defect depth, while a shorter time-of-flight corresponds to a shallower depth.

Whether the ultrasonic pulse generates an echo at a specific interface depends on the acoustic impedance contrast at that interface: when the two regions meeting at the interface have significantly different acoustic impedances, a large portion of the pulse is reflected rather than continuing on its path. A higher acoustic impedance contrast results in a higher reflection coefficient—the fraction of the pulse reflected at the interface—while a lower contrast results in a lower reflection coefficient. An especially high reflection coefficient at a specific interface within the laminate indicates the presence of a delamination, a void, or another internal defect: the air occupying the gap of a delamination or void has an acoustic impedance vastly different from that of the surrounding solid laminate, and this sharp contrast is precisely what—based on the established relationship—produces a reflection coefficient far higher than that of the sound interior of the laminate. The fact that this reflection coefficient is so high allows that specific point in the laminate to be identified as an internal defect.

Thus, this model—utilizing the ultrasonic pulse-echo inspection method introduced at the start—specifically addresses another model in the set: the one describing laminate delamination. By using the pulse's time-of-flight to determine the defect's depth and the high reflection coefficient to identify the defect specifically as a delamination, this model experimentally confirms exactly where and when the delamination propagation criterion described by that other model was met within the laminate.

ID:4423