Monitoring of Carbon Fiber-Reinforced Old Timber Beams via Strain and Multiresonant Acoustic Emission Sensors

This paper proposes the monitoring of old timber beams with natural defects (knots, grain deviations, fissures and wanes), reinforced using carbon composite materials (CFRP). Reinforcement consisted of the combination of a CFRP laminate strip and a carbon fabric discontinuously wrapping the timber element. Monitoring considered the use and comparison of two types of sensors: strain gauges and multi-resonant acoustic emission (AE) sensors. Results demonstrate that: (1) the mechanical behavior of the beams can be considerably improved by means of the use of CFRP (160% in bending load capacity and 90% in stiffness); (2) Acoustic emission sensors provide comparable information to strain gauges. This fact points to the great potential of AE techniques for in-service damage assessment in real wood structures.The experiments were supported by the companies DÁVILA Restauración de Monumentos and DRIZORO® S.A.U, under research contract No. 3546. The authors also gratefully acknowledge the important contribution of lab technicians David Jiménez and Ismael Romero

Acoustic emission monitoring of wood materials and timber structures: A critical review

The growing interest in timber construction and using more wood for civil engineering applications has given highlighted importance of developing non-destructive evaluation (NDE) methods for structural health monitoring and quality control of wooden construction. This study, critically reviews the acoustic emission (AE) method and its applications in the wood and timber industry. Various other NDE methods for wood monitoring such as infrared spectroscopy, stress wave, guided wave propagation, X-ray computed tomography and thermography are also included. The concept and experimentation of AE are explained, and the impact of wood properties on AE signal velocity and energy attenuation is discussed. The state-of-the-art AE monitoring of wood and timber structures is organized into six applications: (1) wood machining monitoring; (2) wood drying; (3) wood fracture; (4) timber structural health monitoring; (5) termite infestation monitoring; and (6) quality control. For each application, the opportunities that the AE method offers for in-situ monitoring or smart assessment of wood-based materials are discussed, and the challenges and direction for future research are critically outlined. Overall, compared with structural health monitoring of other materials, less attention has been paid to data-driven methods and machine learning applied to AE monitoring of wood and timber. In addition, most studies have focused on extracting simple time-domain features, whereas there is a gap in using sophisticated signal processing and feature engineering techniques. Future research should explore the sensor fusion for monitoring full-scale timber buildings and structures and focus on applying AE to large-size structures containing defects. Moreover, the effectiveness of AE methods used for wood composites and mass timber structures should be further studied

Acoustic emission monitoring of wood materials and timber structures: A critical review

The growing interest in timber construction and using more wood for civil engineering applications has given highlighted importance of developing non-destructive evaluation (NDE) methods for structural health monitoring and quality control of wooden construction. This study, critically reviews the acoustic emission (AE) method and its applications in the wood and timber industry. Various other NDE methods for wood monitoring such as infrared spectroscopy, stress wave, guided wave propagation, X-ray computed tomography and thermography are also included. The concept and experimentation of AE are explained, and the impact of wood properties on AE signal velocity and energy attenuation is discussed. The state-of-the-art AE monitoring of wood and timber structures is organized into six applications: (1) wood machining monitoring; (2) wood drying; (3) wood fracture; (4) timber structural health monitoring; (5) termite infestation monitoring; and (6) quality control. For each application, the opportunities that the AE method offers for in-situ monitoring or smart assessment of wood-based materials are discussed, and the challenges and direction for future research are critically outlined. Overall, compared with structural health monitoring of other materials, less attention has been paid to data-driven methods and machine learning applied to AE monitoring of wood and timber. In addition, most studies have focused on extracting simple time-domain features, whereas there is a gap in using sophisticated signal processing and feature engineering techniques. Future research should explore the sensor fusion for monitoring full-scale timber buildings and structures and focus on applying AE to large-size structures containing defects. Moreover, the effectiveness of AE methods used for wood composites and mass timber structures should be further studied

Recent Advancements in Non-Destructive Testing Techniques for Structural Health Monitoring

Structural health monitoring (SHM) is an important aspect of the assessment of various structures and infrastructure, which involves inspection, monitoring, and maintenance to support economics, quality of life and sustainability in civil engineering. Currently, research has been conducted in order to develop non-destructive techniques for SHM to extend the lifespan of monitored structures. This paper will review and summarize the recent advancements in non-destructive testing techniques, namely, sweep frequency approach, ground penetrating radar, infrared technique, fiber optics sensors, camera-based methods, laser scanner techniques, acoustic emission and ultrasonic techniques. Although some of the techniques are widely and successfully utilized in civil engineering, there are still challenges that researchers are addressing. One of the common challenges within the techniques is interpretation, analysis and automation of obtained data, which requires highly skilled and specialized experts. Therefore, researchers are investigating and applying artificial intelligence, namely machine learning algorithms to address the challenges. In addition, researchers have combined multiple techniques in order to improve accuracy and acquire additional parameters to enhance the measurement processes. This study mainly focuses on the scope and recent advancements of the Non-destructive Testing (NDT) application for SHM of concrete, masonry, timber and steel structures

Mechanical Strength of Sic Composite Tubing Under Uniaxial and Multiaxial Loading

Silicon carbide fiber reinforced silicon carbide matrix composite is one of the candidate materials for accident tolerant nuclear fuel cladding concepts. In a Nuclear power plant, the reactions between the fuel, cladding, and coolant in a potential loss of coolant accident(LOCA) are of utmost importance to ensure safety in the accident tolerance of such plants. It is for this reason that SiC(silicon carbide) composite tubes have been selected as a possible alternative to the older Zirconium based cladding methods currently used in the industry, which were a partial cause of the Fukushima 2011 meltdown. To serve as fuel cladding, a material must be able to withstand certain stresses and strains in high temperature environments, and the use of SiC composite is due to its low reactivity with steam and it’s capability or maintaining high strength at high temperature. In studying the SiC composite to ensure its safety in actual usage, many different techniques are being employed to create a full knowledge of the material. The goal of this study is to better understand the mechanical behavior of SiC composite tubing, particularly its mechanical strength under uniaxial and multi-axial loading situations. This will be accomplished by compiling testing results for multiple uniaxial and multiaxial testing scenarios. These include, burst testing, axial testing, torsion testing, torsion-burst testing, and tension-torsion testing. By encapsulating all 5 of these testing scenarios, the general profile of a sample’s failure strength can be created as a function of principal stress direction in the sample. The analysis of the various strengths of the material in different conditions were accomplished by various measurement methods. These methods were comprised of stress and strain observation and calculations, through use of strain gauges and general stress measurement techniques and equations, DIC digital image correlation to verify loading angles and strains created by testing, AE acoustic emission to analyze sample failure by use of sound analysis and matrix/fiber failure events, and x-ray computed tomography(XCT) to analyze post-failure samples. Samples were tested accordingly to map a failure profile for samples with the specific triaxial fiber architecture. This failure map was created to show the ability of a sample to resist failure when the principal stress is pointed to a given direction on the samples. The triaxially braided samples provided by General Atomics showed an abnormal weakness in torsional loading, which has a 45° principal stress angle. The samples proved strongest in the 2 uniaxial testing methods, and the samples in combined loading had the notable strength drop-off the closer the principal stress load angle reached 45° from either starting at 0° (hoop) or 90° (tensile). The samples had the highest tensile strength in the axial direction, due to the triaxial braid giving the most support to tensile loading due to fiber orientation. It was hypothesized after post processing that torsional strength drop-off could be due to the braid angle and orientation

Avaliação de métodos ultrassônicos para o monitoramento da degradação em fadiga de tubos de PRFV

A busca incessante por materiais leves e com boa resistência química e mecânica tem sido uma das principais forças motrizes para o desenvolvimento dos materiais compósitos. No entanto, os materiais compósitos laminados do tipo PRFV (Polímero Reforçado com Fibra de Vidro) são de natureza anisotrópica, heterogênea e com alta atenuação acústica, o que dificulta a inspeção e monitoramento através de métodos acústicos e torna a avaliação de integridade estrutural desses materiais bem mais desafiadora quando comparada com componentes metálicos. Neste trabalho é realizada uma avaliação do potencial de métodos ultrassônicos para o monitoramento da degradação de tubos de PRFV submetidos a fadiga. Duas diferentes técnicas de monitoramento foram avaliadas, uma baseada em ultrassom convencional/volumétrico (com ondas do tipo longitudinal) e outra baseada em ondas guiadas, para ambas técnicas foram utilizadas diferentes metodologias de inspeção. Para a técnica de ondas guiadas foram analisadas, por meio de índices de dano, diferentes métricas como atenuação, alteração de fase e mudanças no espectro de frequência. O efeito da temperatura também foi analisado para cada uma das métricas avaliadas. Para avaliação dos métodos os mesmos foram aplicados para monitoramento de tubos de PRFV submetidos a ensaio de fadiga com razão de carregamento R=0,1 aplicada através de variação da pressão interna. Como referência indicativa do grau de degradação do material foram utilizadas as variações de um estimador da propriedade elástica nas direções longitudinal e circunferencial as quais foram determinadas a partir do monitoramento de deformações superficiais com extensômetro de resistência elétrica. Os resultados demonstraram que a técnica de ultrassom convencional não foi satisfatória para as condições metodológicas utilizadas neste trabalho. Já a técnica de ondas guiadas mostrou potencial para monitoramento da degradação do material desde que aplicados os métodos adequados para análise dos resultados. Os resultados obtidos pela técnica de ondas guiadas mostraram um comportamento semelhante às variações da propriedade elástica detectadas com o monitoramento das deformações. Além disso, foi possível verificar quantitativamente qual métrica mais adequada para detecção de danos de fadiga em materiais compósitos. Sendo assim, esses métodos abrem oportunidades promissoras que contribuem para a utilização da técnica de ondas guiadas em sistemas de avaliação da integridade estrutural em dutos fabricados em PRFV.The endless search for lightweight materials with good chemical and mechanical resistance has been one of the main driving forces for the development of composite materials. However, GFRP (Glass Fiber Reinforced Plastic) laminated composite materials are anisotropic, heterogeneous and have high acoustic attenuation, which makes the inspection and monitoring through acoustic methods difficult and makes the structural integrity assessment of these materials much more challenging when compared to metallic components. In this study, an evaluation of the potential of ultrasonic methods for monitoring the degradation of GFRP pipes subjected to fatigue is performed. Two different monitoring techniques were evaluated, one based on conventional/volumetric ultrasound (with longitudinal waves) and the other based on guided waves, for both techniques different inspection methodologies were used. In the guided wave technique different metrics such as attenuation, phase shift, and changes in the frequency spectrum were analyzed using damage indexes. In addition, the effect of temperature was analyzed for each of the metrics evaluated. In order to perform the evaluation, the methods were applied for monitoring GFRP pipes subjected to fatigue testing with loading ratio R=0.1 applied by varying the internal pressure. As an indicative reference of the material degradation degree, the variations of an estimator of the elastic property in the longitudinal and circumferential directions were used, which were determined from the monitoring of surface deformations with an electrical resistance strain gauge. The results showed that the conventional ultrasound technique was not satisfactory for the methodological conditions used in this work. The guided waves technique showed potential for monitoring the degradation of the material since the appropriate methods are applied to analyzing the results. The results obtained by guided wave technique showed a similar behavior to the elastic property variations detected with the strain monitoring. Furthermore, it was possible to quantitatively verify which metric was most suitable for detecting fatigue damage in composite materials. Thus, these methods open promising opportunities that contribute to the use of the guided wave technique in structural integrity assessment systems in GFRP pipelines