宽音频扫描加载的电子剪切散斑技术在多层粘接板结构无损检测中的应用

本文利用宽音频自动扫描加载的电子剪切散斑干涉技术对多层粘接板结构进行了时实检测，结果表明，这种方法能够同时测定板的多个位置、大小和形状各不相同缺陷，迅速准确地对多层粘接板结构质量作出判断，同时根据到试过程中记录的共振频率等各种信息，可以进一步对被测部分的振动位移及缺陷深度进行定量分析．     

剪切散斑干涉与有限元优化计算相结合实现缺陷参数的定量求解

本文将剪切散斑干涉与有限元优化分析相结合，对薄壁压力容器缝缺陷进行了定量检测，通过对优化计算结果和已知的缺陷参数所构成的目标函数的求解，获得了较为精确的缺陷参数识别结果。     

碳纤维悬挂支臂疲劳损伤实验研究

对碳纤维复合材料某型飞机垂直尾翼方向舵悬挂支臂完成了谱载疲劳、冲击损伤、损伤扩展和剩余强度试验，采用超声波检查方法对其全过程的损伤状态进行了跟踪实验研究，其结果与位移等试验一致．     

Comparative analysis on thermal non-destructive testing imagery applying Candid Covariance-Free Incremental Principal Component Thermography (CCIPCT)

Thermal and infrared imagery creates considerable developments in Non-Destructive Testing (NDT) area. Here, a thermography method for NDT specimens inspection is addressed by applying a technique for computation of eigen-decomposition which refers as Candid Covariance-Free Incremental Principal Component Thermography (CCIPCT). The proposed approach uses a shorter computational alternative to estimate covariance matrix and Singular Value Decomposition (SVD) to obtain the result of Principal Component Thermography (PCT) and ultimately segments the defects in the specimens applying color based K-medoids clustering approach. The problem of computational expenses for high-dimensional thermal image acquisition is also investigated. Three types of specimens (CFRP, Plexiglas and Aluminium) have been used for comparative benchmarking. The results conclusively indicate the promising performance and demonstrate a confirmation for the outlined properties.     

Pitfalls in the experimental recording of ultrasonic (backscatter) polar scans for material characterization

The ultrasonic polar scan (UPS), either in transmission, reflection or backscatter mode, is a promising non-destructive testing technique for the characterization of composites, providing information about the mechanical anisotropy, the viscoelastic damping, the surface roughness, and more. At present, the technique is merely being used for qualitative purposes. The limited quantitative exploration and use of the technique can be primarily ascribed to limitations of current theoretical models as well as the difficulty to perform accurate, and more importantly, reproducible UPS experiments. Over the last years, we have identified several potential pitfalls in the experimental implementation of the technique which severely deteriorate the accurateness and reproducibility of a UPS. In this paper, we make an inventory of the most important difficulties, illustrate each of them by a real experiment and present a feasible mediation, either numerical or experimental in nature. Once the experimental set-up is fine-tuned to overcome these pitfalls, it is expected that the recording of high-level UPS experiments, in combination with numerical computations, will facilitate the technique to become a fully quantitative non-destructive characterization method.     

Ultrasonic study of wheat flour properties

In this work, the wheat flour properties are investigated using ultrasound techniques. Moreover, the flour samples were also characterized by means of well established techniques such as protein content, Alveograph and Mixolab®. A set of 35 dough samples, made of wheat flours with diverse physical and quality properties, were studied. The obtained results shown that ultrasound measurements can detect changes in the dough consistency induced by proteins and also by gelatinization of the starch. Furthermore, ultrasound measurements can be related to parameters indicative of the proteolytic degradation or softening of the dough due to protease activity. Thus, ultrasound can be considered a low cost and rapid tool, complementary to conventional test, for wheat flour characterization.     

Nondestructive damage assessment in fiber reinforced composites with the pulsed ultrasonic polar scan

This study investigates the use of both amplitude and time-of-flight based pulsed ultrasonic polar scan (P-UPS) as a sophisticated non-destructive damage sensor for fiber reinforced composites. Focus is put on stiffness related damage phenomena, which are in general difficult to monitor nondestructively, and their associated signature in the P-UPS image. Various composite samples, with different damage states, have been inspected at multiple material spots with the P-UPS technique. The results demonstrate the capability of the P-UPS method to obtain a unique signature of the local material damage characteristics. Several indicators in the acquired P-UPS images have been identified from which the type and level of material degradation can be obtained. The P-UPS extracted characteristics are fully supported by simulations, conventional tests as well as visual inspection.     

Determination of thermal wave reflection coefficient to better estimate defect depth using pulsed thermography

Thermography is a promising method for detecting subsurface defects, but accurate measurement of defect depth is still a big challenge because thermographic signals are typically corrupted by imaging noise and affected by 3D heat conduction. Existing methods based on numerical models are susceptible to signal noise and methods based on analytical models require rigorous assumptions that usually cannot be satisfied in practical applications. This paper presents a new method to improve the measurement accuracy of subsurface defect depth through determining the thermal wave reflection coefficient directly from observed data that is usually assumed to be pre-known. This target is achieved through introducing a new heat transfer model that includes multiple physical parameters to better describe the observed thermal behaviour in pulsed thermographic inspection. Numerical simulations are used to evaluate the performance of the proposed method against four selected state-of-the-art methods. Results show that the accuracy of depth measurement has been improved up to 10% when noise level is high and thermal wave reflection coefficients is low. The feasibility of the proposed method in real data is also validated through a case study on characterising flat-bottom holes in carbon fibre reinforced polymer (CFRP) laminates which has a wide application in various sectors of industry.     

Understanding a time reversal process in Lamb wave propagation

This study investigates the time reversal process (TRP) of Lamb wave signals which are transmitted and received by piezoelectric transducers bonded on plate-like structures. A number of previous studies have paid attention to spatial and temporal refocusing capability of an original excitation through the TRP in highly dispersive and complex media. However, when the TRP is applied to Lamb waves in a homogeneous regular waveguide, the refocusing capability is limited due to permanent residual side bands even if the duration of the time reversed signal increases. Based on the reciprocity of elastodynamics and linear piezoelectricity, theoretical interpretation is conducted for the main and residual side bands of the reconstructed signal in the time domain. In particular, the interpretation includes the temporal effect of velocity and amplitude dispersions, the existence of multimodes, and the reflections from boundaries during the TRP. Then, numerical and experimental tests are conducted to validate the theoretical findings of this paper. Practical issues for the successful implementation of the TRP of Lamb waves are briefly addressed as well.     

Application of laser ultrasonic technique for non-contact detection of drilling-induced delamination in aeronautical composite components

The detection of drilling-induced delamination in composite components is a vital and challenging task in aviation industry. Numerous key components of aircrafts are made of composite materials, and drilling is often a final operation during assembly. Drilling-induced delamination is a very serious defect that significantly reduces the structural reliability, but it is rather difficult to be detected effectively due to its special location. A novel application of laser ultrasonic technique for the detection of drilling-induced delamination in composites is presented in this paper. A carbon fiber reinforced plastic laminate with drilling holes was made as specimen. A laser ultrasonic system was constructed and experiments were performed to detect the drilling-induced delamination, 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, and the morphology features of the delamination are imaged clearly by laser ultrasonic C-scan testing. The results proved that the laser ultrasonic technique is a feasible and effective method for the detection of drilling-induced delamination in composite components.