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By Hossein Taheri, PhD
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Aerospace industries increasingly use composite materials for diverse parts and component manufacturing. For full utilization of the superior material and mechanical properties of composites in application and safety-critical aerospace components, reliable nondestructive testing (NDT) methods are required to prevent catastrophic failures. Meanwhile, aerospace industries also use a variety of sandwich core constructions and metals that require a high level of quality and integrity checked and confirmed by NDT methods.
Potential defects and damage mechanisms in aerospace composites need to be detected and evaluated to avoid unexpected sudden failures. Various NDT methods are used for damage detection and evaluation in a schedule-based manner to gather information of the remaining lifetime of structures or to perform a defect assessment. Matrix array ultrasonic testing (MAUT) is one of the newest techniques for material testing and inspection. Matrix arrays are a leading-edge transducer technology that enables ultrafast acquisition of volumetric data utilizing elements in a grid arrangement and available in a wide range of frequencies.
The new standard, titled Standard Practice for Matrix Array Ultrasonic Testing of Composites, Sandwich Core Constructions, and Metals Used in Aerospace Applications, was released in January 2023. This standard is included in ASTM Vol. 03.04: Nondestructive Testing (II): E2374 – Latest, and was developed by Subcommittee E07.06.
The procedures in this standard are for MAUT of monolithic composites, composite sandwich constructions, and metallic test articles. ASTM E3370 can be used throughout the lifecycle of a part, during product and process design optimization, online process control, post-manufacturing inspection, and in-service inspection.
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. Test procedure A is the pulse-echo (PE) method in noncontact and contact modes. In procedure A (PE mode), a matrix array transducer transmits and receives compression waves in the range of 0.5 to 20 MHz. Like other PE applications of ultrasonic testing, access to only one side of the specimen is sufficient. Test procedure B is the through-transmission (TT) method in noncontact and contact modes. In procedure B (TT mode), a combination of two transducers (one to transmit and one to receive the ultrasonic waves) is used. Procedure B requires access to both sides of the specimen and can be conducted in an automated or manual way.
ASTM E3370 procedures have proven utility in the inspection of monolithic polymer matrix composites, corrosion in metals, thickness variation checks, and adhesive bonding of metals, composites, and sandwich core constructions. However, it does not currently cover angle beam using shear waves or surface beam using lamb waves due to unavailability of the matrix technology.
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Hossein Taheri, PhD, is the Standards Editor for Materials Evaluation, htaheri@georgiasouthern.edu.
Reprinted from the June 2023 issue of Materials Evaluation. The electronic edition of ME is available at no cost to all ASNT members.