Measurements for stress sensing of composites using tailored piezospectroscopic coatings
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Chromium-doped α-alumina is naturally photo-luminescent with spectral properties that are characterized by R-lines with two distinct peaks known as R1 and R2. When the material is subjected to stress, shifts in the R-lines occur, which is known as the piezospectroscopic (PS) effect. Recent work has shown that improved sensitivity of the technique can be achieved through a configuration of nanoparticles within a polymer matrix, which can be applied to a structure as a stress-sensing coating. This study demonstrates the capability of PS coatings in mechanical tests and investigates the effect of nanoparticle volume fraction on sensing performance. Here, measurements of spectral shifts that capture variation in stress of the coating during mechanical testing and in the region of substrate damage showed that stress contours are more noticeable on a soft laminate than hard laminate. It was found that the 20 % volume fraction PS coating showed the most distinct features of all the coatings tested with the highest signal-to-noise ratio and volume fraction of α-alumina. Post failure assessment of the PS coatings verified that the coatings were intact and peak shifts observed during mechanical testing were due to the stress in the substrate. The results suggest the ability to design and tailor the “sensing” capability of these nanoparticles and correlate the measured stress variations with the presence of stress and damage in underlying structures. This study is relevant to nondestructive evaluation in the aerospace industry, where monitoring signs of damage is of significance for testing of new materials, quality control in manufacturing and inspections during maintenance.Keywords:
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Nondestructive test methods (NDT) are available for the assessment of many types of defects in existing structures including: the evaluation of reinforcing steel corrosion, determination of defect location, accurate assessment of the member sizes, and reinforcement locations. The use of these methods has increased as engineers and owners become aware of their capabilities. However, recent experiences have suggested that the integration of the NDT results into the evaluation process is lagging, and often the results of the NDT program end up as little more than report filler. Worse, the lack of NDT verification can result in incomplete or erroneous conclusions about the structure. Integration of NDT results into the evaluation process requires an understanding of both the output of the test methods and how the results impact structural performance. The successful integration of NDT results into the evaluation process is described.
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AIM]To investigate the differ ence between the assays of coated tablets with removed coating or without remove d coating. [METHODS]It was proved by mathematical analysis that the re was a theoretical differece between the assays of coated tablets with removed coating or without removed coating, under the condition of no influence of coat ing matericals on the assay. [RESULTS]After removing coating, the assaying result attenuated because of the loss of the tablet core, meanwhile th e residual coating had no influence on the assaying result. [CONCLUSION] When coating materials dont interfere with the assay of coated tablets, the direct assay without removed coating is feasible.
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The coating binder in cross-section of coating layer will be migrated, the binder concentration will be different in z-direction of coating layer, which affect some properties of coated paper. The paper studied the effects of coating progress on binder migration and affected factors. The z-direction distribution of the coating binder which was tagged with Br in coating layer and its concentration in coating surface were examined quantitatively by using SEM-EDXA and ESCA analysis. During coating process the drying rate, dwell time from coating device to dryer and coating weight affect the binder migration. The mechanism of binder migration was proposed. The results indicated that the degree of binder migration is directly proportional to the drying temperature and coating weight, but reduces with extending the dwell time.
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Three kinds of new NDT techniques have been developed.In this paper the development and application of nondestructive test technique at home and abroad in concrete beam are presented .The first type of NDT methods are based on the mechanical principle of stress wave propagation,such as impactecho method,spectral analysis of surface wave method,acoustic emission technique and ultrasonic pulse method etc.The second type is the electromagnetic wave propagationbased NDT methods,taking ground penetrating radar as an example.The third type of NDT method makes use of radiography as the medium of detection,for instance,infrared thermography and computerized tomography etc.In terms of practical experience,these techniques play an important role in increasing the accuracy and speed of many NDT investigations.
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Abstract Material state characterization is often performed using nondestructive evaluation (NDE) techniques with an objective to either understand or evaluate the microstructural state of the material or indirectly determine the damage that may have occurred in the material during manufacturing or service. Understanding material state is crucial, since material properties define the material's ability to perform its designed function. A number of nondestructive evaluation/nondestructive testing/nondestructive inspection (NDE/NDT/NDI) sensors are available to measure properties of a material. Basic laws of physics dictate the function of the sensor. This article attempts to explain the physics behind eddy current, ultrasonic, and acoustic emission sensors routinely used in NDI of aircraft structures.
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Eddy current nondestructive testing is one of nondestructive testing methods(NDT),it is important in testing the metal material.In this article,introduce the development of NDT input frequency from single frequency,multi-frequency to frequency-band first,then introduce field-quantity analysis of NDT,especially present the data processing and finite element method of numerical calculation.this article is tried to expound the status and development of eddy current nondestructive testing.
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The development in materials technology has produced stronger, lighter, stiffer, and more durable electrically insulating composites which are replacing metals in many applications. These composites require alternative inspection techniques because the conventional nondestructive testing (NDT) techniques such as thermography, eddy currents, ultrasonic, X-ray and magnetic particles have limitations of inspecting them. Microwave NDT technique employing open-ended rectangular waveguides (OERW) has emerged as a promising approach to detect the defects in both metal and composite materials. Despite its promising results over conventional NDT techniques, OERW microwave NDT technique has shown numerous limitations in terms of poor spatial resolution due to the stand-off distance variations, inspection area irregularities and quantitative estimation in imaging the size of defects. Microwave NDT employing OERW in conjunction with robust artificial intelligence approaches have tremendous potential and viability for evaluating composite structures for the purpose mentioned here. Artificial intelligence techniques with signal processing techniques are highly possible to enhance the efficiency and resolution of microwave NDT technique because the impact of artificial intelligence approaches is proven in various conventional NDT techniques. This paper provides a comprehensive review of NDT techniques as well as the prospect of using artificial intelligence approaches in microwave NDT technique with regards to other conventional NDT techniques.
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Abstract Nondestructive testing (NDT) includes several highly efficient techniques for the estimation of the physical and mechanical properties of structural timber. However, NDT results are affected by several factors [moisture content (MC), temperature, specimen dimensions, sensor positioning and grain angle, timber-sensor coupling, etc.], of which wood MC is the most important. Scientific research on MC influence in NDT measurements started in the 19 th century, and 2018 was the first year that a MC adjustment for NDT measurements was published in a European standard (EN14081-2). Although MC influence on NDT has been studied for more than 170 years, MC adjustment factor research is important nowadays because it is widely used in the industry. Currently, NDT device manufacturers develop their own MC adjustment factors adapted to their equipment and species. This paper presents an exhaustive review of MC adjustments for different types of NDT equipment, as proposed by several authors from the 19 th century to date, and a discussion of factors affecting MC adjustments.
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This paper describes an approach to planning and performing nondestructive testing (NDT) on a structure. It applies to NDT in general, but it is most relevant to inspections of large composite structures using thermographic NDT (TDNT) and other imaging NDT techniques in which defects are detected by pattern recognition or image analysis. Realistic problems are listed.
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