Conventional Nondestructive Evaluation Methods Research Articles

Multi-Defect Detection in Additively Manufactured Lattice Structures Using 3D Electrical Resistance Tomography

Cellular lattice structures possess high strength-to-weight ratios suitable for advanced lightweight engineering applications. However, their quality and mechanical performance can degrade because of defects introduced during manufacturing or in-service. Their complexity and small length scale features make defects difficult to detect using conventional nondestructive evaluation methods. Here we propose a current injection-based method, electrical resistance tomography (ERT), that can be used to detect damaged struts in conductive cellular lattice structures with their intrinsic electromechanical properties. The reconstructed conductivity distributions from ERT can reveal the severity and location of damaged struts without having to probe each strut. However, the low central sensitivity of ERT may result in image artifacts and inaccurate localization of damaged struts. To address this issue, this study introduces an absolute, high throughput, conductivity reconstruction algorithm for 3D ERT. The algorithm incorporates a strut-based normalized sensitivity map to compensate for lower interior sensitivity and suppresses reconstruction artifacts. Numerical simulations and experiments on fabricated representative cellular lattice structures were performed to verify the ability of ERT to quantitatively identify single and multiple damaged struts. The improved performance of this method compared with classical ERT was observed, based on greatly decreased imaging and reconstructed value errors.

Selection of optimal exciting frequency and Lamb wave mode for detecting wall-thinning in plates using scanning laser Doppler vibrometer

The continuous excitation-based scanning laser Doppler vibrometer (SLDV) has been gaining prominence as a defect-detecting tool because of its superior performance in discovering faults, such as thinning of structures, compared to conventional non-destructive evaluation methods. To date, the optimal test mode and frequency for interdigital transducers have been heuristically selected. Although this approach is effective for problems involving a small number of modes, heuristic algorithms have limitations with respect to problems involving multiple complex modes. Therefore, in this study, the determination of the inspection mode and frequency is formulated as an optimization problem, and the effective wavenumber and bandwidth of the high-pass and bandpass filters in signal processing are also considered. Numerical optimization examples show that the proposed method is effective and robust. An experiment with a thick plate with shallow defects was performed, and the quantitative images obtained showed the correct location of the defects with the proposed numerical optimal solution.

Structural integrity of DEMO divertor target assessed by neutron tomography

The divertor target plates are the most exposed in-vessel components to high heat flux loads in a fusion reactor due to a combination of plasma bombardment, radiation and nuclear heating. Reliable exhaust systems of such a huge thermal power required a robust and durable divertor target with a sufficiently large heat removal capability and lifetime. In this context, it is pivotal to develop non-destructive evaluation methods to assess the structural integrity of this component that, if compromised could reduced its lifetime. In this work we have demonstrated for the first time the feasibility of using neutron tomography to detect volumetric defects within DEMO divertor mock-ups with a spatial resolution of the order of hundreds of micrometers. Neutron tomography is applicable for studying complex structures, often manufactured from exotic materials which are not favourable for conventional non-destructive evaluation methods. This technique could be effectively used during research and development cycles of fusion component design or for quality assurance during manufacturing.

Characterisation of Friction Stir Weld Discontinuities by Non-destructive Evaluation

Friction stir weld (FSW) is an advanced metal joining process recently practised in aerospace industries with application spanning across other engineering fields as well. Friction stir welding being solid-state joining process, the weld is characterised by superior weld properties with proper parameter setting. The morphology of FSWs varies from other welds due to the plastic state formation of the material as against the liquid state of fusion encountered in conventional welding process. The nature of the discontinuities in these joints is significantly different. The presence of discontinuities in the welds due to its unique weld formation process has made the failure pattern in these products also unique. Hence, a comprehensive non-destructive evaluation (NDE) assessment of FSWs is attempted with different techniques and their detecting capability has been discussed. Conventional NDE methods, namely radiography, ultrasonics and eddy current techniques used in FSW discontinuity detection are discussed and compared for each type of discontinuity.

Cryo-Ultrasonic NDE: Ice-Cold Ultrasonic Waves for the Detection of Damage in Complex-Shaped Engineering Components.

Recent advances in computational methods, materials science, and new manufacturing processes are resulting in an unprecedented design flexibility which is driving the geometrical complexity of the components found in modern structures and machines. For safety-critical components, the geometrical complexity poses a significant challenge to the sensitivity of the existing nondestructive evaluation (NDE) methods available for the detection of manufacturing defects or damage that develops while a component is in service. Although X-ray computed tomography is the primary NDE method used to test these parts in current industrial practice, it is widely recognized that it has limited sensitivity to critical defects, such as cracks, especially in the presence of large size parts made of dense materials. The lack of sensitive NDE methods represents a major technology gap that could impede the acceptance of rapidly developing technologies, such as 3-D printing, for the production of safety-critical components. This paper attempts to bridge this gap by exploring the possibility of inspecting a complex-shaped part with ultrasonic waves after it has been encapsulated in ice, under the paradigm of what can be defined as cryo-ultrasonic NDE. The underpinning hypothesis is that through ice encapsulation a complex-shaped part can be transformed into a simple-shaped solid whose volume can be probed with ultrasonic waves, which are known to be highly sensitive to both pores and crack-like defects and over a wide range of material properties. Damage detection is then performed by analyzing cross-sectional images of the ice-encapsulated part obtained by applying migration methods to the ultrasonic signals measured by an array of transducers. This paper lays the foundation for cryo-ultrasonic NDE and presents the first experimental results demonstrating the possibility of imaging defects through multiple ice-metal interfaces. This paves the way to the detection of defects in complex-shaped parts containing internal vanes which have so far limited the use of conventional NDE methods.

Experiments and Analytical Modeling of Frequency-Targeted Laser Elastic Wave Generation and Detection in Aluminum Structures

AbstractPropagating solid elastic waves forms the basis of multiple nondestructive evaluation (NDE) and structural health monitoring techniques. The majority require direct sensor contact with the material or structure being tested. Conventional NDE methods such as ultrasonic testing have rigorous coupling requirements and limited ranges for damage or defect detection. These requirements and limitations make inspection of large areas or complex geometries slow and cumbersome or altogether impractical. Removing the requirement for contact between the sensor and structure could greatly relax the geometric and size limitations of current elastic wave–based NDE techniques. Laser-based excitation and detection of solid elastic waves are demonstrated capabilities; however, existing laser-based excitation techniques lack the precision and flexibility required by NDE methods that target specific wave modes or frequencies. This proof-of-concept study investigates using a pulsing laser for frequency controlled exci...

Damage Identification After Impact in Sandwich Composites Through Embedded Fiber Bragg Sensors

Based on the full-spectral response of fiber Bragg grating sensors, embedded at the facesheet-core interface, we identify the progression of failure modes in foam core sandwich composites during multiple, low-velocity impacts. By considering the characteristic shape of the reflected spectrum from the FBG sensor in the post-impact, residual strain state, it is shown that we can classify the extent of damage into one of three states. Unlike the previous FBG peak wavelength measurements; this identification does not require the full strain history to identify the current state of damage in the composite. The disparate material properties between the facesheet and core materials, which create significant challenges for conventional non-destructive evaluation methods, enhance the damage detection through large deformations in the core at the impact location with sharp strain gradients.

Ultrasonic evaluation of adhesive bonding: Journal of adhesion, Vol. 29, pp. 257–274 (1989)

Abstract The capabilities of existing ultrasonic nondestructive evaluation (NDE) methods for the strength-related properties of bonds in structural components is reviewed. The severe limitations of conventional NDE methods in yielding quantitative results are indicated. Some recent results of a joint theoretical and experimental program of research using leaky Lamb waves (LLW) in laboratory specimens are presented. The LLW technique is shown to have several advantages over conventional techniques. Potential applications of the technique to determine non-destructively the quality of bonds in a variety of models are discussed.

Ultrasonic Evaluation of Adhesive Bonding

Abstract The capabilities of existing ultrasonic nondestructive evaluation (NDE) methods for the strength-related properties of bonds in structural components is reviewed. The severe limitations of conventional NDE methods in yielding quantitative results are indicated. Some recent results of a joint theoretical and experimental program of research using leaky Lamb waves (LLW) in laboratory specimens are presented. The LLW technique is shown to have several advantages over conventional techniques. Potential applications of the technique to determine non-destructively the quality of bonds in a variety of models are discussed.