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1.1 This practice covers procedures for matrix array ultrasonic testing (MAUT) of monolithic composites, composite sandwich constructions, and metallic test articles. These procedures can be used throughout the life cycle of a part during product and process design optimization, on line process control, post-manufacturing inspection, and in-service inspection.

1.2 In general, ultrasonic testing is a common volumetric method for detection of embedded or subsurface discontinuities. This practice includes general requirements and procedures which may be used for detecting flaws and for making a relative or approximate evaluation of the size of discontinuities and part anomalies. The types of flaws or discontinuities detected include interply delaminations, foreign object debris (FOD), inclusions, disbond/un-bond, fiber debonding, fiber fracture, porosity, voids, impact damage, thickness variation, and corrosion.

1.3 Typical test articles include monolithic composite layups such as uniaxial, cross ply and angle ply laminates, sandwich constructions, bonded structures, and filament windings, as well as forged, wrought and cast metallic parts. Two techniques can be considered based on accessibility of the inspection surface: namely, pulse echo inspection for one-sided access and through-transmission for two-sided access. As used in this practice, both require the use of a pulsed straight-beam ultrasonic longitudinal wave followed by observing indications of either the reflected (pulse-echo) or received (through transmission) wave.

1.4 This practice provides two ultrasonic test procedures. Each has its own merits and requirements for inspection and shall be selected as agreed upon in a contractual document.

1.4.1 Test Procedure A, Pulse Echo (non-contacting and contacting) is at a minimum a single matrix array transducer transmitting and receiving longitudinal waves in the range of 0.5 MHz to 20 MHz (see Fig. 1). This procedure requires access to only one side of the specimen. This procedure can be conducted by automated or manual means. Automated and manual test results may be analyzed in real time or recorded and analyzed later.

FIG. 1 Test Procedure A, Pulse Echo Apparatus Set-up for a Composite Panel (Left) and Metal Plate (Right) Using One-sided Access

1.4.2 Test Procedure B, Through Transmission (non-contacting and contacting) is a combination of two transducers. One transmits a longitudinal wave and the other receives the longitudinal wave in the range of 0.5 MHz to 20 MHz (see Fig. 2). This procedure requires access to both sides of the specimen. Typically, the signal transmitting and signal receiving transducers are perpendicularly aligned with each other. This is normally achieved using a yoke transducer holder arrangement, which attaches the two transducers to a single point but deploys them on opposite sides of the structure. Through transmission inspections are also permitted without the use of a yoke transducer holder. This is due to the capacity for improved manual alignment via the matrix array transducers, whereby the live C-scan display enables visual confirmation of accurate alignment, and facilitates re-alignment if needed. This procedure can be conducted by automated or manual means. Automated and manual test results may be imaged or recorded.

FIG. 2 Test Procedure B, Through Transmission Apparatus Set-up using Two-sided Access

1.5 Other contact methods such as angle-beam techniques using shear waves to characterize welds, or surface-beam techniques using Lamb waves to detect impact damage in composite panel structures are not covered.

1.6 This practice does not specify accept-reject criteria.

1.7 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.

1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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 straightbeam longitudinal waves introduced by a piezoelectric element (transducer) with diameters of 3.2 mm to 28.6 mm (⅛ in. to 1⅛ 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 Test 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 Test 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 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.