This article presents the basic principle, characteristics, advantages, and disadvantages of resonant ultrasound spectroscopy (RUS) methods in additive manufacturing. It focuses on the two types of RUS methods: the swept-sine method and the impulse excitation method. Representative significant results for additively manufactured complex parts obtained with the different RUS systems are also shown. The article also presents the basic principle and examples of nonlinear RUS methods.

This article focuses on ultrasonic testing (UT) applied to metallic additive manufacturing (AM) parts, presenting the basic principles of UT. It provides a detailed discussion on postprocess UT inspection of powder-bed-fusion-manufactured samples and directed-energy-deposition-manufactured samples.

Of the many different nondestructive evaluation (NDE) techniques, ultrasonic inspection continues to be the leading nondestructive method for inspecting composite materials, because measurements can be quantitative and the typical defect geometries and orientations lend themselves to detection and characterization. This article focuses on the three common methods for ultrasonic nondestructive inspection of plastics, namely pitch-catch, through-transmission, and pulse-echo, as well as the three basic types of ultrasonic NDE scans: the A-scan, B-scan, and C-scan. The discussion includes the linear and phased array systems that are sometimes used for large-scale inspection tasks to reduce scan times, the various gating and image processing techniques, and how ultrasonic data are interpreted and presented. A brief section on future trends in ultrasonic inspection is presented at the end of the article.

Nonlinear ultrasonic nondestructive examination (NDE) techniques are based on nonlinear interaction of ultrasonic waves with the material to be characterized and defects to be detected. This article introduces the basic principles of nonlinear material-wave interaction, the origin of intrinsic nonlinearity in intact solids, and the main mechanisms of excess nonlinearity in damaged metals. It describes the measurement methods for nonlinear ultrasonic materials characterization and flaw-detection. The article schematically illustrates the instrumentation used for measurements of longitudinal wave and Rayleigh surface acoustic waves. It concludes with information on the applications of nonlinear ultrasonics.

Ultrasonic inspection is a family of nondestructive methods in which beams of high-frequency mechanical waves are introduced into materials, using transducers, for the detection and characterization of both surface and subsurface anomalies and flaws in the material. This article describes the basic equipment in ultrasonic inspection systems, and lists the advantages and disadvantages of these systems. It discusses the applications of ultrasonic inspection and also the general characteristics of ultrasonic waves in terms of wave propagation, longitudinal waves, transverse waves, surface waves, and lamb waves. The article reviews the major variables in ultrasonic inspection, including frequency, acoustic impedance, angle of incidence, and beam intensity. It discusses the attenuation of ultrasonic beams and provides information on the pulse-echo and transmission methods for implementing ultrasonic inspection.

This article describes the basic features of electromagnetic acoustic transducers (EMATs) and discusses their existing and some potential uses within the field of ultrasonic nondestructive evaluation (UNDE). It provides sufficient basic and practical information to make an informed choice when considering the transducer to be used for any particular UNDE application. The article describes how different types of EMATs operate and presents their fundamental and some practical limitations. It summarizes the representative literature for electromagnetic acoustic transducer UNDE applications. Some successful uses of EMATs are mentioned to illustrate the depth, range, and potential of commercial EMAT applications. The article concludes with information on the commercial sources for EMAT systems and components.

Guided wave testing (GWT) is a method of nondestructive evaluation for the inspection of pipelines. This article focuses mainly on explaining GWT as it is applied in routine established use, covered by standards, in the oil and gas industry and also introduces some of the other contexts in which its use is growing in other evolving applications. It discusses the various guided wave modes and their selection criteria. The article provides information on considerations for mode control and the sensitivity of the GWT to the defect. It also shows some examples of advanced GWT.

A number of nondestructive evaluation (NDE) methods, such as radiography, ultrasound, and eddy current, are available to detect flaws in solid materials. This article describes the fundamental aspects of these NDE methods in terms of operation principles. It presents some examples of the methods performed on various types of flaws resulting from solid-state welding processes.

The success of a reliable non-destructive evaluation (NDE) application depends greatly on the expertise and thoroughness of the NDE engineering that is performed. This article discusses the general considerations of NDE in terms of NDE response and NDE system management and schedule. It describes the NDE engineering and NDE process control, along with some case studies related to the applications of NDE. The article reviews various models for predicting NDE reliability, such as ultrasonic inspection model, eddy current inspection model, and radiographic inspection model. It concludes with an example that illustrates the integration of an ultrasonic reliability model with a CAD system.

Additive manufacturing (AM) is the process of joining materials to make parts from three-dimensional (3D) model data, usually layer upon layer, as opposed to subtractive manufacturing and formative manufacturing methodologies. This article discusses various defects in AM components, such as porosity, inclusions, cracking, and residual stress, that can be avoided by using vendor recommended process parameters and approved materials. It describes the development of process-structure-property-performance modeling. The article explains the practical considerations in nondestructive evaluation for additively manufactured metallic parts. It also examines nondestructive testing (NDT) inspection and characterization methods for each of the manufacturing stages in their natural order. The article provides information on various inspection techniques for completed AM manufactured parts. The various electromagnetic and eddy current techniques that can be used to detect changes to nearsurface geometric anomalies or other defects are also discussed. These include ultrasonic techniques, radiographic techniques, and neutron imaging.

Time-of-flight diffraction (TOFD) is an ultrasonic technique used to detect diffracted waves from crack tips and to size the cracks from the arrival times of those waves. This article discusses the basic considerations and provides information on probe selection, gain setting, and instrumentation of TOFD. It describes the numerous effects that result from modifying the probe characteristics. The article provides the American Society of Mechanical Engineers (ASME), the European Committee for Standardization (CEN), and the International Standardization Organization (ISO) recommendations for the reference blocks according to applicable codes and standards. It also provides the ASME, CEN, and ISO recommendations for examination of welds. The article concludes with information on the interpretation and analysis of TOFD images with an aid of sizing algorithms.

Laser-ultrasonics is a particular implementation of ultrasonic nondestructive inspection in which ultrasound is generated and detected by lasers. This article discusses the various mechanisms that ensure ultrasound generation and explains the possibility to get the equivalent of phase-array by numerical processing of an array of previously acquired laser-ultrasonic signals. The article describes the ultrasound generation by thermoelastic mechanism and ablation or vaporization. It illustrates the principle of optical detection of ultrasound with confocal Fabry-Perot interferometer and photorefractive two-wave mixing interferometer. The article concludes with information on the industrial applications of laser-ultrasonics, including thickness measurement, flaw detection, and material characterization.

The potential for introducing defects during processing becomes greater as the relative density of pressed and sintered powder metallurgy (PM) parts increases and more multilevel parts with complex geometric shapes are produced. This article discusses the potential defects in pressed and sintered PM parts: density variations, compaction and ejection cracks, microlaminations, poor degree of sintering, and voids from prior lubricant agglomerates. It describes the various methods applicable to green compacts: direct-current resistivity testing, radiographic techniques, computed tomography, and gamma-ray density determination. The article also discusses the methods for automated nondestructive testing of pressed and sintered PM parts: acoustic methods-resonance testing, eddy current testing, magnetic bridge comparator testing, ultrasonic techniques, radiographic techniques, gamma-ray density determination, and visual inspection.

This article focuses on nondestructive inspection of steel bars. The primary objective in the nondestructive inspection of steel bars and wire is to detect conditions in the material that may be detrimental to the satisfactory end use of the product. The article discusses various types of flaws encountered in the inspection of steel bars, including porosity, inclusions, scabs, cracks, seams, and laps. Inspection methods, such as magnetic-particle inspection. liquid penetrant inspection, ultrasonic inspection, and electromagnetic inspection, of steel bars are also described. The article provides a discussion on electromagnetic systems, eddy-current systems, and magnetic permeability systems for detection of flaws on steel bars. It concludes with a description of nondestructive inspection of steel billets.

This article considers the two primary methods used for ultrasonic inspection: pulse-echo and the transmission methods. Pulse-echo inspection can be accomplished with longitudinal, shear, surface (Rayleigh), or Lamb (plate) waves using a diverse range of transducers. The article discusses the principles of each of these inspection methods. It describes the applications and the basic data formats for single-element transducer-based systems, including A-scans, B-scans, and C-scans. The article provides information on electronic equipment used for ultrasonic inspection. It also describes how specific material conditions produce and modify A-scan indications. The article provides information on the controls and their functions for the display unit of the electronic equipment. It describes the techniques used for the identification and characterization of flaws, namely, surface (Rayleigh) wave and ultrasonic polar scan techniques.

This article provides an overview of the characteristics of Rayleigh waves plus methods for generation and detection of waves, including using piezoelectric transducers or noncontact techniques such as lasers, electromagnetic acoustic transducers, or air-coupled ultrasonics. It reviews the methods for using Rayleigh waves for defect detection and materials characterization, alongside nonlinear ultrasonic inspection and surface acoustic wave (SAW) microscopy. The article concludes with information on the standards that use Rayleigh waves for nondestructive evaluation (NDE) of different structures.

This article discusses the inspection/reference standards that are absolutely critical for proper application of ultrasonic inspection systems. Many of the standards and specifications for ultrasonic inspection require the use of standard reference blocks. The article lists the variables that should be considered when selecting standard reference blocks and describes the three types of standard blocks ordinarily used for calibration or reference: area-amplitude blocks, distance-amplitude blocks, and blocks of the type sanctioned by the International Institute of Welding. It reviews the determination of area-amplitude and distance-amplitude curves of a straight-beam pulse-echo ultrasonic inspection system. The article discusses the three principal conventional manual ultrasonic sizing techniques: 6 dB drop technique, maximum-amplitude technique, and 20 dB drop technique. It provides information on the dimension-measurement applications of ultrasonic inspection methods.

Adhesive-bonded joints are extensively used in aircraft components and assemblies where structural integrity is critical. This article addresses the problem of how to inspect bonded assemblies so that all discrepancies are identified. It describes several inspection techniques and presents drawbacks and limitations of these techniques. Generic flaw types and flaw-producing mechanisms are listed in a table. The article discusses metal-to-metal defects, adherend defects, honeycomb sandwich defects, repair defects, and in-service defects. It reviews the methods applicable to the inspection of bonded structures, including visual inspection, ultrasonic inspection, X-ray radiography, and neutron radiography. The evaluation and correlation of inspection results are also discussed. The article concludes with information on the effects of ultrasonic wave interference in the ultrasonic inspection of adhesive-bonded joints.

Nondestructive inspection (NDI) methods for cast iron are used to ensure that the parts supplied perform as required by the purchaser. This article focuses on the principal nondestructive methods used to inspect for anomalies in cast irons and to determine if the volume, shape, size, or number of these anomalies exceeds the maximum allowed by the purchaser. The nondestructive methods include visual inspection, dimensional inspection, liquid penetrant inspection, magnetic-particle inspection, eddy-current inspection, radiographic inspection, ultrasonic inspection, resonant testing, and leak testing. The technique, strengths, and weaknesses of each of the nondestructive methods are also discussed.