Standard Practice for Matrix Array Ultrasonic Testing of Composites, Sandwich Core Constructions, and Metals

Importancia y uso:

5.1 The procedures described in this practice have proven utility in the inspecting (1) monolithic polymer matrix composites (laminates) for bulk defects, (2) metals for corrosion during the service life of the part of interest, (3) thickness checks, (4) adhesive bonding of metals, composites, and sandwich core constructions, (5) coatings, and (6) composite filament windings. Both unpressurized and, with suitable precautions, pressurized materials and components are inspected.

5.2 This practice provides guidelines for the application of longitudinal wave examination to the detection and quantitative evaluation of damage, discontinuities, and thickness variations in materials.

5.3 This practice is intended primarily for the testing of parts to acceptance criteria most typically specified in a purchase order or other contractual document, and for testing of parts in-service to detect and evaluate damage.

5.4 MAUT search units provide near-surface resolution and detection of small discontinuities comparable to phased array transducers. They may or may not be capable of beam steering. The advantage of MAUT for straight-beam longitudinal wave inspections is the ability to provide real-time C-scan data, which facilitates data interpretation and shortens inspection time. Depending on inspection needs, data can be displayed as A-, B-, or C-scans, or three-dimensional renderings. Toggling between pulse-echo and through transmission ultrasonic (TTU) modes without having to use another system or changing transducers is also possible.

5.5 The MAUT technique has proven utility in the inspection of multi-ply carbon-fiber reinforced laminates used in primary aircraft structures.11

5.6 For ultrasonic testing of laminate composites and sandwich core materials using conventional UT equipment consult Practice E2580. Consult Practice E114 for ultrasonic testing of materials by the pulse-echo method using straight beam longitudinal waves introduced by a piezoelectric element (transducer) with diameters of 3.2 mm to 28.6 mm (¹/₈ in. to 1¹/₈ in.) in contact with the material being examined and usually presented in an A-scan display.

5.7 This practice is directed towards the evaluation of discontinuities detectable at normal beam incidence. If discontinuities or material integrity at other orientations are of concern such as through cracks and welds, alternate scanning techniques are required.

5.8 Procedure A, Pulse Echo—Pulsed energy is transmitted into materials, travels in a direction normal to the contact surface, and is reflected back to the search unit by discontinuity or boundary interfaces, which are parallel or near parallel to the contacted surface. These echoes return to the search unit, where they are converted from mechanical to electrical energy and are amplified by a receiver. The amplified echoes (signals) are displayed as A-, B-, or C-scans, or three-dimensional renderings. Types of information that may be obtained from the pulsed-echo straight-beam practice are (1) apparent discontinuity size, (2) depth location of discontinuities, (3) material properties such as velocity of sound in the material, and similarly, the thickness of a material, and (4) the extent of bond and unbond (or fusion and lack of fusion) between two ultrasonic conducting materials if geometry and materials permit. In addition to detecting volumetric discontinuities such as delaminations (Fig. 3), ultrasonic thickness measurements can be made with MAUT search units in pulse-echo mode on basic shapes and products of many materials, and on precision machined parts, to determine wall thinning in process equipment caused by corrosion and erosion (Fig. 4).

FIG. 3 Detection of Delamination in Flat Panel Carbon-fiber Reinforced Composite Using Matrix Array Ultrasonic Testing Showing Typical A-, B- and C-Scans and a Three-dimensional Rendering (Pulse-Echo Method)

FIG. 4 Detection of Wall Thinning Corrosion in 3.5 mm Thick Aluminum Plate Using Matrix Array Ultrasonic Testing (Pulse-Echo Method)

5.9 Procedure B, Through Transmission—In TTU, a transducer on one side of a part transmits an ultrasonic pulse to an aligned receiving transducer on the other side (Fig. 2). Alignment between the two transducers is often accomplished by automation. Attenuation or absence of the pulse coming to the receiving transducer indicates the presence of a defect. Advantages of TTU over pulse-echo include less attenuation of sound energy, absence of transducer ringing, and less of an effect of defect orientation on transmitted signal. However, two-sided access is necessary, and like pulse-echo, vertical defects such as through cracks are difficult to detect. Applications include inspection of plate and bar stock after manufacturing, and detection of disbonds in materials with high attenuation properties that hinder sound propagation, such as multiple bond layers, honeycomb cores (Fig. 5), and foam cores.

FIG. 5 Detection of Disbond in an Impact-Damaged Region of a Sandwich Construction Consisting of a Graphite Fiber Reinforced Facesheet and an Aluminum Honeycomb Core Using Matrix Array Ultrasonic Testing (Through-Transmission Mode)

5.10 This practice does not discuss nonlinear resonant ultrasonic spectroscopy, ultrasonic spectral analysis, use of angle beams, transverse waves, and guided waves that can be used to assist in bond characterization in composites or sandwich constructions.12 Air coupled ultrasonic inspection using MAUT search units to detect skin-to-core disbonds in sandwich constructions is also not discussed.

Subcomité:

E07.06

Volúmen:

03.04

Número ICS:

19.100 (Non-destructive testing), 49.025.01 (Materials for aerospace construction in general)

Palabras clave:

composites; corrosion; delamination; disbond; flat panel composites; foreign object debris (FOD); honeycomb core; laminates; matrix array transducer; matrix array ultrasonic testing (MAUT); nondestructive evaluation (NDE); nondestructive inspection (NDI); nondestructive testing (NDT); polymeric matrix composites (PMC); porosity; pulse-echo; sandwich constructions; straight beam; thickness measurement; through transmission ultrasound (TTU); ultrasonic testing (UT);