Ndt & E International最新文献

Development in aerospace technology makes it increasingly important to understand the thermal-mechanical behavior of materials subject to high temperature ranging from 2000°C to 3000 °C. In this work, a simple and low-cost Ultraviolet-Digital Image Correlation (UV-DIC) system composed of a CCD camera, a telecentric lens and a single UV bandpass filter was proposed for deformation measurement at up to 3000 °C. Hafnium carbide (HfC) powder was used as the speckle pattern material. To verify the UV-DIC system and the speckle pattern, the coefficient of thermal expansion (CTE) of graphite heated by electric current was measured from 25 °C to 3000 °C. The results show that the system can effectively suppress strong heat radiation at up to 3000 °C, and that the prepared speckle pattern can withstand 3000 °C. Comparison of the measured CTE of graphite with that in the existing database verifies the feasibility and accuracy of the proposed method. The proposed method and technology lay the foundation for further development of the DIC in ultra-high temperature deformation measurement.

We propose an alternative method for processing infrared thermography (IRT) data based on a thermal 1-layer model. The method is based on the analogy of the Shock Response Spectrum (SRS) analysis for mechanical systems (ISO 18431). A thermal Q-factor, similar to the resonance sharpness (Q-factor) of a mechanical oscillator, is introduced as a parameter for selecting a specific thermal 1-layer model. Two main aspects of this method and corresponding properties have been considered: the strictly model-based treatment of this methodology and an empirical introduction of additional bandpass filters. The method is validated with two practical examples: for a homogeneous polymer sheet with blind holes and an inhomogeneous plate made of carbon fiber reinforced polymer (CFRP) with artificial defects, the capability of defect detection is compared with established methods. The comparison of the results with the commonly used data processing methods of IRT as Pulsed Phase Thermography (PPT) and Modified Differential Absolute Contrast (MDAC) shows equivalent or sometimes improved performance.

Nondestructive estimation of residual stresses has been a major challenge in engineering. Herein, the collinear Lamb wave mixing method is proposed for residual stress measurement in metal plates under immersion ultrasonic testing. Numerical simulations have been conducted to investigate the influences of excitation parameters on the performance of the wave mixing method. The results showed that the receiver position and cycle numbers of primary waves affect the amplitude of the method, and optimal excitation parameters recommended. Ultrasonic immersion experiments are conducted on two types of plate-like specimens using the collinear Lamb wave mixing method. Experimental results showed that the proposed method is effective for measuring the residual stress in metal plates. The immersion ultrasonic testing can significantly reduce the influence of inconsistent coupling conditions between the transmitters and the specimen on experimental results, therefore it is more reliable than conventional contact testing.

The challenge of detecting cracks in powder metallurgy (PM) components has been a topic of interest for many years, with no practical commercial solution currently in place. This study employs enhanced truncation-correlation photothermal coherence tomography (eTC-PCT) to visualize 3D cracks within PM automotive parts. Through the application of effective diffusion-wave reversal techniques, blurred infrared thermophotonic images of subsurface defects (cracks) in (“green”) compressed metal PM components were restored to their original geometric resolution over the entire depth range. This approach enabled the creation of 3-dimensional depth-resolved photothermal tomographic images and cross-sectional mappings of cracks. The developed technique reveals the precise spatial dimensions of surface and subsurface cracks, reaching depths of down to 3 mm (not an upper limit) that conventional thermal imaging cannot access due to limitations imposed by the depth-integrated nature of conventional thermal-wave imaging, the properties of PM materials, and the physics of spreading diffusion. The super-resolution method was further applied to a sintered automotive part, specifically validating the efficacy of eTC-PCT for non-destructive imaging (NDI) in manufactured automotive components. Diffusion reversal imaging shows promise as a non-destructive testing (NDT) tool, with potential applications in a wide range of manufactured products, including both the green and sintered stages of automotive component production.

A non-contact optical inspection method for detecting voids in translucent composites is presented. Structured laser light is used to illuminate the inspected part. As the light penetrates the matrix, it scatters and is reflected from internal structures, rendering them perceptible in close proximity of the laser illumination. A systematic image acquisition and scanning approach is employed along with image processing to reconstruct and visually represent the internal composition of the inspected part. Experiments involving translucent epoxy and polyester based composites demonstrate capability to detect voids with depths reaching up to 5 mm. The detection depth is predominantly influenced by the light transmittance properties of the matrix, as well as the density and quantity of fiber layers. The arrangement of the camera and laser on the same side of the inspected part facilitates the examination of parts with varying thicknesses. The presented method is intended for automated inspection in mass production by leveraging its non-contact characteristics and high operational velocity.

Some studies indicate that for specific defect detection in eddy current testing (ECT), the transmitter-receiver (T-R) probe models with tangential rectangular transmitter coil exhibit effective detection performance. In this context, mutual inductance being a crucial parameter. The calculation of mutual inductance for vertically oriented T-R coils is more intricate compared to that of parallel T-R coils, which is currently predominantly focused on circular mutual inductance analysis. This paper presents a closed-form formula for the mutual inductance of rectangular T-R coils oriented vertically to the conductor based on the method of the second-order vector potential approach. In this model, a form function concerning the coil's position and shape is defined, allowing convenient extension to T-R coils of arbitrary shapes and positions. Simultaneously, the validity of the theory is tested against experimental measurements on different positions and frequencies of coil systems above an aluminum plate. The results indicate good agreement between theoretical and experimental results within the 100 Hz to 100 kHz range. Consequently, this model can offer guidance for the calculation of mutual inductance for vertically oriented rectangular T-R coils in ECT.

Effectively determining the size and thickness distributions of corrosion damages is a vital problem in nondestructive testing (NDT). In this article, a new approach is introduced that employs magnetostrictive transducers (MST) to excite the first dispersive shear horizontal mode (SH1), and utilizes the DCD-FWI (deep convolutional descent full waveform inversion) to provide comprehensive thickness mapping in just 1 s. Compared with traditional imaging techniques, DCD-FWI network is an intrinsically full waveform inversion (FWI) based method, which yields reliable imaging results in large scale finite element simulations. Moreover, the shorter wavelength and resistance to water loading of SH guided waves bring about reliable imaging results. Combined with these advantages, the high energy transfer efficiency of the MST enhances the proposed method's robustness, as demonstrated by guided wave tomography experiments on aluminum plates.

In this paper, the modulated step-heating thermography is proposed for opaque coating thickness measurement. The surface is heated by a modulated heating flux at a frequency that the thermal wave is confined within the coating layer. The DC component of the thermal signal is normalized by the amplitude of the AC component to cancel out the influences from the variations in heating intensity, surface absorptivity and emissivity, resulting in a linear correlation to the coating thickness. Meanwhile, it eliminates the need for tedious frequency trail and the issue of the nonmonotonicity as suffered in conventional thermography. Both theoretical and experimental results confirmed the effectiveness. Specimens with thickness ranging from 100 to 400 μm are measured with a relative error within ±7.9 %.

We present a methodology to size the area and depth of horizontal metallic inclusions of unknown geometry, embedded in insulators, using lock-in inductive thermography. The method is based on averaging the amplitude and phase thermograms along circles concentric with the center of the heated region. We present an analytical calculation of the surface temperature distribution produced by a horizontal circular heat source, taking into account conductive coupling with the air, and we propose to fit the averaged data to this model. We present lock-in thermography data on resin samples containing embedded calibrated circular and rectangular Cu slabs that we excite inductively. The results indicate that it is possible to determine the area and depth of rectangular heat sources with aspect ratio below 1.5 with accuracy better than 10 %.

Carbon fiber reinforced polymer (CFRP) is widely used in modern industries, and damages may occur from manufacturing to utilization, highlighting the importance of CFRP detection. As being a multi-phase structural material, the CFRP's mesostructural features contained in eddy current signals can obscure macroscopic defect characteristics. Phase rotation is a common method for eddy current signal processing, but the specific criteria for evaluation of processing effect are lacking. This paper proposes three reliable criteria for assessment of the phase rotation processing effects of Transmitter-Receiver (T-R) probe signals, namely: signal overlap ratio (SOR), signal-to-noise ratio (SNR), and image average gradient (IAG). To begin, the SOR serves as a crucial indicator for assessing signal similarity and the degree of overlap, with a low SOR indicating the method's effectiveness in distinguishing defect characteristics. Subsequently, by comparing the SNRs of images, the clarity of defects under different rotation angles can be effectively quantified. Finally, a novel criterion, i.e. the IAG, is introduced. What distinguishes this criterion is its higher degree of automation, facilitating a comprehensive evaluation of processing effects without excessive subjective intervention. After analyzing these criteria, it is clear that the IAG criterion excels in automation and objectivity for evaluating eddy current signal processing effects.