Non-destructive testing of interfacial stiffness based on spring model for diffusion bonding interface of titanium alloy components with complex surface.

Ultrasonic testing is an important non-destructive testing method, which is sensitive to the defects in the diffusion bonding interface. Ultrasonic testing of diffusion bonding interfaces in complex-surface components is a challenge due to the geometry and the weak echo signal of the diffusion bonding defects. This paper proposes an interfacial stiffness characterization method based on the spring model for the ultrasonic testing of the diffusion bonding interface of titanium alloy complex-surface component. Finite element models for ultrasonic field are established to analyze the diffusion bonding defects response, the effect of complex surface, and the inconsistency of the bonding interface depth in ultrasonic testing of the titanium alloy complex-surface component. 15 MHz is recommended as the testing frequency of the diffusion bonding interface. Ultrasonic C-scan experiments are conducted using specimens with embedded artificial defects and a titanium alloy complex-surface component. The simulation and experimental results show that the novel interfacial stiffness characterization method can be applied to ultrasonic testing of the diffusion bonding interface (inclination angle less than 14°) in complex-surface components, and the ability to test defects at the diffusion bonding interface can be improved.

High-precision automatic identification method for dicentric chromosome images using two-stage convolutional neural network.

Dicentric chromosome analysis is the gold standard for biological dose assessment. To enhance the efficiency of biological dose assessment in large-scale radiation catastrophes, automatic identification of dicentric chromosome images is a promising and objective method. In this paper, an automatic identification method for dicentric chromosome images using two-stage convolutional neural network is proposed based on Giemsa-stained automatic microscopic imaging. To automatically segment the adhesive chromosome masses, a k-means based adaptive image segmentation and watershed segmentation algorithm is applied. The first-stage CNN is used to identify the dicentric chromosome images from all the images and the second-stage CNN works to specifically identify the dicentric chromosome images. This two-stage CNN identification method can effectively detects chromosome images with concealed centromeres, poorly expanded and long-armed entangled chromosomes, and tricentric chromosomes. The novel two-stage CNN method has a chromosome identification accuracy of 99.4%, a sensitivity of 85.8% sensitivity, and a specificity of 99.6%, effectively reducing the false positive rate of dicentric chromosome. The analysis speed of this automatic identification method can be 20 times quicker than manual detection, providing a valuable reference for other image identification situations with small target rates.

A novel non-destructive testing method for turbine disks using dual array ultrasonic transducer.

A novel dual array inspection method for detecting the diffusion bonding defects of superalloy turbine disk has been proposed in this study. The influence of relative position between the planar defect and acoustic source has been analysed, and based on which, the transmission and reception algorithm for the dual array method has been proposed. The time delay law of the dual array transducer for the complex turbine disk structure has been investigated. Finite-difference time-domain theory has been used to establish the numerical model of the dual array method. In the numerical simulations, the novel method has been applied for the superalloy turbine disk specimen with prefabricated defects at the depth of 18.3 m and 28.3 mm. Furthermore, the corresponding experiment has been conducted and verifies the reliability of the simulation. The novel method shows advantages in detecting small diffusion bonding defects in complex structure, assisting the manufacture of superalloy turbine disks, and ensuring the safety of aircrafts.

Rapid and automatic detection of micronuclei in binucleated lymphocytes image.

Cytokinesis block micronucleus (CBMN) assay is a widely used radiation biological dose estimation method. However, the subjectivity and the time-consuming nature of manual detection limits CBMN for rapid standard assay. The CBMN analysis is combined with a convolutional neural network to create a software for rapid standard automated detection of micronuclei in Giemsa stained binucleated lymphocytes images in this study. Cell acquisition, adhesive cell mass segmentation, cell type identification, and micronucleus counting are the four steps of the software's analysis workflow. Even when the cytoplasm is hazy, several micronuclei are joined to each other, or micronuclei are attached to the nucleus, this algorithm can swiftly and efficiently detect binucleated cells and micronuclei in a verification of 2000 images. In a test of 20 slides, the software reached a detection rate of 99.4% of manual detection in terms of binucleated cells, with a false positive rate of 14.7%. In terms of micronuclei detection, the software reached a detection rate of 115.1% of manual detection, with a 26.2% false positive rate. Each image analysis takes roughly 0.3 s, which is an order of magnitude faster than manual detection.

A Method for Prediction of Ultrasonic Detectability of Interface Gap Defects on TC4 Diffusion-Bonded Joints.

An analysis method for the detectability of defects on the TC4 (Ti-6Al-4V) diffusion bonding interface was proposed in this study. First, a semi-analytical model of the liquid-solid coupling acoustic field with attenuation characteristics was constructed. Based on this, a method for the selection of transducer parameters was investigated for effective focus on the diffusion bonding interface. Second, according to the characteristics of defects on the diffusion bonding interface, an acoustic response model for diffusion bonding defects was established based on Kirchhoff approximation. The detectability of defects on the diffusion bonding interface was analyzed using transducers of different frequencies with different diffusion bonding interface gaps. Finally, an experiment was conducted to verify the reliability of the simulation. The analysis method proposed shows the advantages in the selection of suitable parameters for detecting specific diffusion bonding interface gaps, providing theoretical predictions of the detectability of diffusion bonding interface defects.

Inspection of disbonds in titanium alloy honeycomb sandwich structures with different skin thicknesses using linear frequency-modulated thermography.

This paper reports the linear frequency-modulated thermography inspection of disbonds in titanium alloy honeycomb sandwich structures with different skin thicknesses. A three-dimensional finite element model of a titanium alloy honeycomb sandwich structure is built. The maximum value of the phase difference between the disbond defect region and the nondefective region is used to optimize the heating duration and frequency bandwidth. Three titanium alloy honeycomb sandwich structure specimens, with a skin thickness of 0.6 mm, 0.85 mm, and 1.2 mm, respectively, are manufactured, in which skin-to-core disbond defects are prepared. The linear frequency-modulated thermography experiments are carried out on the specimens. The correlation algorithm is used to process the infrared image sequences. The experimental results show that linear frequency-modulated thermography can realize the fast and efficient inspection of the disbonds in titanium alloy honeycomb sandwich structures with different skin thicknesses. For skin thickness ranges from 0.6 mm to 1.2 mm, a heating duration of 22 s and a frequency range of 0.01 Hz-0.21 Hz are recommended.

Application of Ultrasonic Array Method for the Inspection of TC18 Addictive Manufacturing Titanium Alloy.

Ultrasonic arrays have been investigated for inspecting the quality of special materials. Unfortunately, non-destructive testing and evaluation (NDT&E) of internal defects in additive manufacturing (AM) materials are difficult due to the anisotropy and the coarse grain. To solve the problem, this paper brings forward research on the inspection of TC18 AM titanium alloy products using an ultrasonic array. Firstly, a three-dimensional acoustic field distribution of different ultrasonic array transducers is established to design an optimal detection solution for an AM titanium alloy. Then, a total focusing method (TFM) for the ultrasonic annular array transducer is proposed and its imaging method is analyzed. Besides, the relation between ultrasonic group velocities in a TC18 AM specimen with different propagating angles is measured using the full matrix capture (FMC) method. Based on the measurements, the anisotropy of the AM titanium alloy is discussed and the TFM algorithm of annular array is optimized as well. Finally, C-scan experiments are conducted on the specimen with a height of 55 mm using the linear ultrasonic array transducer of the conventional focusing method and the TFM of annular array transducer, respectively. The results show that the TFM of annular array has higher accuracy in quantifying the defects of flat bottom holes and transverse holes with a diameter of 0.8 mm. In addition, the detection results of different forming directions are analyzed and the 3D imaging of defects in the specimen is realized based on FMC data. The TFM of annular array is an innovative ultrasonic testing technology with high resolution for AM titanium alloy products.

Numerical Simulation and Experimental Study of Fluid-Solid Coupling-Based Air-Coupled Ultrasonic Detection of Stomata Defect of Lithium-Ion Battery.

Aiming at the characteristics of the periodic stacking structure of a lithium-ion battery core and the corresponding relationship between the air-coupled ultrasonic transmission initial wave and the wave propagation mode in each layer medium of a lithium-ion battery, the homogenized finite element model of a lithium-ion battery was developed based on the theory of pressure acoustics and solid mechanics. This model provided a reliable method and basis for solving the visualization of ultrasonic propagation in a lithium-ion battery and the analysis of ultrasonic time-frequency domain characteristics. The finite element simulation analysis and experimental verification of a lithium-ion battery with a near-surface stomata defect, near-bottom stomata defect and middle-layer stomata defect were performed. The results showed that the air-coupled ultrasonic transmission signal can effectively characterize the stomata defect inside a lithium-ion battery. The energy of an air-coupled ultrasonic transmission signal is concentrated between 350-450 kHz, and the acoustic diffraction effect has an important influence on the effect of the ultrasonic and stomata defect. Based on the amplitude response characteristics of the air-coupled ultrasonic transmission wave in the stomata defect area, a C-scan of the lithium-ion battery was performed. The C-scan result verified that air-coupled ultrasonic testing technology can accurately and effectively detect the pre-embedded stomata defect and natural stomata defect in a lithium-ion battery, which is able to promote and expand the application of the technology in the field of electric energy security.

Inspection of butt welds for complex surface parts using ultrasonic phased array.

Detection of weld defects for complex surface parts has always been a difficult point in ultrasonic testing because the geometry complexity makes it difficult to arrange transducers and determine the propagation paths of acoustic beams. In this paper, the linear friction weld of the engine blade is taken as an example of the butt weld in complex surface parts, and the application of the ultrasonic array testing method is carried out. Firstly, the propagation properties of acoustic waves in the inspection area are analysed based on both the Snell's law and the acoustic pressure reciprocating transmittance (APRT). According to the inspection requirements, this study establishes a full-coverage inspection solution using multi-array transducers. Secondly, the whole inspection area is divided and the wedge parameters in each subarea are iteratively designed. Thirdly, based on the finite element method (FEM), a response simulation model of the ultrasonic array is established to testify the feasibility and validity of the inspection scheme. Lastly, experiments are conducted on the blade specimen welded by linear friction welding (LFW). The inspection results of different weld positions clearly identify the prefabricated crack defects, showing that the proposed method can fulfill the rapid and accurate inspection for the butt weld of complex surface parts.

A dicentric chromosome identification method based on clustering and watershed algorithm.

Aiming at the problem of low efficiency of dicentric chromosome identification counting under the microscope, this paper presents a joint processing algorithm combining clustering and watershed. The method first uses clustering and watershed algorithm to segment the original chromosome image, and then identifies the individual chromosomes. The results show that when the equivalent width Y parameter is selected m = 1, n = 1, the true positive rate of dicentric chromosome identification is 76.6%, and positive predictive value is 76.6% in high dose, which is higher than the threshold algorithm for the true positive rate (63.9%) and positive predictive value (63.5%). The number of identified dicentric chromosomes can be used for dose estimation. When 500 cells are used for identification and dose estimation, the dose estimation pass rate can reach 80% in high dose. But for low dose, more cells should be used to identify to increase the dose estimation pass rate.

Detection of disbonds in multi-layer bonded structures using the laser ultrasonic pulse-echo mode.

The laser ultrasonic technique with a pulse-echo mode has been investigated to detect disbonds in a multi-layer bonded structure and a quantitative method has been proposed to evaluate the defect sizes. The simulations were carried out to analyze influences of spot sizes on the characteristics of laser ultrasonic reflected waves, the interaction of laser ultrasonic reflected waves with disbonds, and quantitative characterization on disbonds. A noncontact laser ultrasonic inspection system has been established to perform a series of experiments to verify the theoretical results. Laser ultrasonic C-scans based on reflected shear waves can clearly redraw appearances of disbonds in the adhesive bond. The proposed quantitative method can evaluate the sizes of disbonds within a reasonable error range. Moreover, the experimental data are in good agreement with the simulation results. Therefore, a combination of the laser ultrasonic pulse-echo mode and the proposed quantitative strategy is practical for accurate detection of disbonds in multi-layer bonded structures.

Application of P4 Polyphase codes pulse compression method to air-coupled ultrasonic testing systems.

Air-coupled ultrasonic testing systems are usually restricted by low signal-to-noise ratios (SNR). The use of pulse compression techniques based on P4 Polyphase codes can improve the ultrasound SNR. This type of codes can generate higher Peak Side Lobe (PSL) ratio and lower noise of compressed signal. This paper proposes the use of P4 Polyphase sequences to code ultrasound with a NDT system based on air-coupled piezoelectric transducer. Furthermore, the principle of selecting parameters of P4 Polyphase sequence for obtaining optimal pulse compression effect is also studied. Successful results are presented in molded composite material. A hybrid signal processing method for improvement in SNR up to 12.11dB and in time domain resolution about 35% are achieved when compared with conventional pulse compression technique.

Step-heating infrared thermographic inspection of steel structures by applying least-squares regression.

This paper reports the application of the least-squares regression method in the step-heating thermographic inspection of steel structures. The surface temperature variation of a slab with finite thickness during both the step-heating phase and the cooling-down phase is presented. A mild steel slab with holes of various depths and diameters is chosen as the specimen. The step-heating thermographic inspection experiments are carried out on the specimen with different heating times. The heating as well as the cooling-down phases are recorded with an infrared camera and are analyzed separately by linear regression of the double logarithmic temperature increase versus time plots. Three statistics of the linear regression, the slope, the coefficient of determination, and the F-test value, are used to create image maps according to the processing results. The signal-to-noise ratio of each map is calculated to evaluate the performance of the three imaging methods with different durations of heating time and cooling time. The results prove that the F-test value maps present a good performance for the sequences of the step-heating phase, while the slope maps present a good performance for the sequences of the cooling-down phase. The optimal heating time and cooling time for a steel structure are also concluded. The comparison with the results of the thermographic signal reconstruction (TSR) method proves that the least-squares regression method has better detectability and a higher inspection efficiency.

Inspection of disbonds in multilayer dissimilar metal structure using lock-in thermography.

This paper reports the characterization of disbonds between a steel plate and a lead plate on the surface of the lead using lock-in thermography. Based on the photothermal model, the excitation frequency of the bonding specimen with the steel plate and the lead plate is optimized. A lock-in thermography testing system is established to inspect the specimen. The Fourier transform method is used to process the infrared image sequences. To improve the signal-to-noise ratio (SNR), a fuzzy c-means (FCM) algorithm is used to process the phase matrix. The influence of number of clusters on the processing results is researched, and the optimal value of clusters number is obtained. The shearing phase technique is used to evaluate the size of the disbonds quantitatively. The measurement results of the artificial disbonds in the specimen show good agreement with the actual values. The results prove that FCM is effective in enhancing the SNR of the phase image, which makes it feasible for the quantitative determination of defect size by the shearing phase technique.

Application of laser ultrasonic method for on-line monitoring of friction stir spot welding process.

Application of a laser ultrasonic method is developed for on-line monitoring of the friction stir spot welding (FSSW) process. Based on the technology of FSSW, laser-generated ultrasonic waves in a good weld and nonweld area are simulated by a finite element method. The reflected and transmitted waves are analyzed to disclose the properties of the welded interface. The noncontact-laser ultrasonic-inspection system was established to verify the numerical results. The reflected waves in the good-weld and nonweld area can be distinguished by time-of-flight. The transmitted waves evidently attenuate in the nonweld area in contrast to signal amplitude in the good weld area because of interfacial impedance difference. Laser ultrasonic C-scan images can sufficiently evaluate the intrinsic character of the weld area in comparison with traditional water-immersion ultrasonic testing results. The research results confirm that laser ultrasonics would be an effective method to realize the characterization of FSSW defects.

Detection of drilling-induced delamination in aeronautical composites by noncontact laser ultrasonic method.

A novel application of the laser ultrasonic technique for the detection of drilling-induced delamination in composite components of aircrafts is proposed. Numerous key components of aircrafts are made of composite materials, and drilling is often a final operation during assembly. Drilling-induced delamination significantly reduces the structural reliability, and it is rather difficult to be detected effectively and automatically. The laser ultrasonic technique is a promising method to solve the problem. This paper investigates the characterization of drilling-induced delamination in composites by a noncontact laser ultrasonic method. A carbon fiber reinforced plastic laminate with drilling holes is prepared as a specimen. The characterization of drilling-induced delamination with laser-generated ultrasonic waves is investigated theoretically and experimentally, and the morphology features of the delamination are obtained by laser ultrasonic C-scan testing. The results prove that the laser ultrasonic technique is effective for the detection of drilling-induced delamination in composite components, and it is a feasible solution for evaluating the drilling quality during assembly.

Ultrasonic characterization of delamination in aeronautical composites using noncontact laser generation and detection.

The characterization of delamination in composite plates with ultrasonic waves generated and detected by lasers is presented. Composite materials have become one of the most important structural materials in the aviation industry because of their excellent mechanical properties, such as high specific stiffness and antifatigue. This paper reports a new application of the laser ultrasonic technique to perform nondestructive detection of carbon-fiber-reinforced plastic (CFRP) and continuous-fiber-reinforced ceramic matrix composites (CFCCs) containing artificial internal defects, based on propagation characteristic of ultrasonic waves generated by pulse laser with a wavelength of 1064 nm and pulse duration of 10 ns. A laser interferometer based on two-wave mixing is used to measure ultrasonic wave signals. The main advantage of this technique over conventional ultrasonic testing techniques is the ability to carry out detection without using coupling agents. The research results prove that the laser ultrasonic technique is effective for the detection of internal defects in both CFRP and CFCC composite components, which should promote and expand the application of the technique in the aviation industry.

Effects of experimental variables on the nonlinear harmonic generation technique.

Harmonic generation is a promising technique for measuring small changes in the microstructure of components. Its extreme sensitivity is a benefit for detection, but results in a high degree of variability in any measurements taken. This paper characterizes the effects of experimental variables throughout the measurement signal path, establishing their relative importance and making suggestions for the best way to take measurements using harmonic generation. A model is used to predict the harmonic amplitude as a function of position and thereby account for alignment inaccuracy, explaining the effects of this key experimental variable. Finally, the potential effect of all of the variables on damage detection is discussed.