Tensile-Shear Fatigue Behavior of Aluminum and Magnesium Lap-Joints obtained by Ultrasonic Welding and Adhesive Bonding

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Non-destructive testing and fracture mechanics: A short discussion

A short discussion is provided on the relationship between non-destructive testing and fracture mechanics. The basic tasks behind this are to guarantee the safety of a component at a potential hazard loading event, to specify inspection intervals or, alternatively, of demands on non-destructive testing for a fixed inspection regime, to plan accompanying actions for cases of temporary continued operation of structures in which cracks have been detected, and, finally, fatigue strength considerations which take into account initial defects

Monitoring of fatigue crack growth in composite adhesively bonded joints using Fiber Bragg Gratings

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An acoustic emission approach to the structural health monitoring of historical metallic tie-rods

The application of Non-Destructive Testing and Structural Health Monitoring systems in historical buildings is of great interest due to the need to guarantee safety and conservation. The present memory focuses on the case study of the historical wrought iron tie-rods of Duomo di Milano, Italy. In recent years, two of these elements presented critical failures. Consequently, a monitoring methodology based on acoustic emission was defined. First, the fracture toughness of wrought iron was characterized by employing standard small-scale specimens taken from one of the failed tie-rods. Meanwhile, acoustic emission was acquired to define a methodology for detecting and localizing the damage events, separating those due to background noise by applying suitable pattern recognition algorithms. Subsequently, a tensile test was performed on a full-scale section of the same tie-rod. Before and after the test, phased-array ultrasonic testing and magnetic particle inspections were carried out to identify and map defects and their possible development due to load application. Finally, it was possible to conclude that magnetic inspections allow identifying the presence of surface defects effectively, phased-array testing estimates the geometry of the defect accurately, and acoustic emission is a promising technique for monitoring the structural integrity of historical metallic tie-rods

Analysis of peel and shear strains in cracked lap shear specimens subjected to fatigue loading using digital image correlation

Adhesive bonding presents many advantages, such as efficient manufacturing and improved structural performance [1]. However, in structures subjected to fatigue, cracks might initiate and propagate in joints, leading to in-service failure [2]. Most adhesively bonded joints are subjected to combination of peel and shear loads, so mixed I+II mode loading conditions are present [3]. In this work, Cracked Lap Shear specimens, which feature mixed I+II mode loading conditions, were tested under fatigue loading. During tests, crack growth was monitored using Visual Testing and Digital Image Correlation. With Digital Image Correlation, opening and sliding displacements in the bondline were extracted from the substrates’ displacement fields and compared against a Finite Element Model, revealing a highly strained process zone ahead of the crack tip. Results highlight the usefulness of DIC in capturing the deformation behaviour of adhesive joints under mixed mode loading conditions

Acoustic emission applied to mode I fatigue damage monitoring of adhesively bonded joints

The use of adhesively bonded joints has increased considerably due to their lightweight, relevant strength-weight ratio and possibility to join multi-materials. Nevertheless, there are still some challenges in the application of this kind of joints in primary structures, such as guaranteeing their reliability during the components’ useful life. Structural health monitoring methods are suggested to ensure in-service safety and reliability of adhesive joints. The acoustic emission appears promising because it can detect the elastic waves produced within the material when it is under damage or straining. This research focuses on mode I fatigue damage monitoring metallic double cantilever beam adhesively bonded joints using the acoustic emission method. Digital image correlation and visual evaluation were applied during fatigue interruptions to track the crack-tip position within the adhesive and correlate them with the acoustic emission outcomes. The acoustic emission method is susceptible and different kinds of waves (background, friction and damage) can be easily assessed during the tests, producing an immense amount of data. So, unsupervised artificial neural networks for patterning recognition were proposed. Self-organising maps and k-means algorithms were used for data clustering and then classified regarding their sources. Finally, the acoustic emission results, digital image correlation and visual evaluations were compared

Lymphatic Mapping for Endometrial Cancer

The staging for endometrial cancer is surgical and it should include both pelvic and para-aortic lymphadenectomy. The majority of endometrial cancers are diagnosed at early stage and lymphadenectomy gives no benefit for staging while adding surgical risks. Performing a systematic lymphadenectomy in very obese women is almost impossible. Preoperative lymphatic mapping (via planar lymphoscintigraphy, single photon emission computed tomography, or positron emission tomography) has poor correlation with surgical mapping of sentinel lymph nodes (SLNs), that has been proposed to avoid systematic lymphadenectomy in early stages. However, surgical SLN mapping is a very challenging procedure in endometrial cancer because the uterus has a complex lymphatic drainage. In the last 20 years, different authors used different tracers (vital stains, radioactive isotopes, or fluorescent dye), different sites of tracer injection (cervix, endometrium, or myometrium), and different surgical approaches (laparotomic, laparoscopic, or robotic) to find out the best procedure for SLNs identification. A well-designed, prospective, randomized, international multicenter tri¬al aimed at validating the accuracy of a uniform procedure is still lacking. In the meantime, to reduce the false-negative rate of intra-operative SLN mapping a surgical algorithm limits systematic pelvic lymphadenectomy to the hemi-pelvis without SLNs mapping and includes removal of any suspicious, although not mapped, node together with mapped SLNs

Analysis of peel and shear strains in cracked lap shear specimens subjected to fatigue loading using digital image correlation

Adhesive bonding presents many advantages, such as efficient manufacturing and improved structural performance [1]. However, in structures subjected to fatigue, cracks might initiate and propagate in joints, leading to in-service failure [2]. Most adhesively bonded joints are subjected to combination of peel and shear loads, so mixed I+II mode loading conditions are present [3]. In this work, Cracked Lap Shear specimens, which feature mixed I+II mode loading conditions, were tested under fatigue loading. During tests, crack growth was monitored using Visual Testing and Digital Image Correlation. With Digital Image Correlation, opening and sliding displacements in the bondline were extracted from the substrates’ displacement fields and compared against a Finite Element Model, revealing a highly strained process zone ahead of the crack tip. Results highlight the usefulness of DIC in capturing the deformation behaviour of adhesive joints under mixed mode loading conditions

A multi-sensor approach for volcanic ash cloud retrieval and eruption characterization: the 23 November 2013 Etna lava fountain

Volcanic activity is observed worldwide with a variety of ground and space-based remote sensing instruments, each with advantages and drawbacks. No single system can give a comprehensive description of eruptive activity, and so, a multi-sensor approach is required. This work integrates infrared and microwave volcanic ash retrievals obtained from the geostationary Meteosat Second Generation (MSG)-Spinning Enhanced Visible and Infrared Imager (SEVIRI), the polar-orbiting Aqua-MODIS and ground-based weather radar. The expected outcomes are improvements in satellite volcanic ash cloud retrieval (altitude, mass, aerosol optical depth and effective radius), the generation of new satellite products (ash concentration and particle number density in the thermal infrared) and better characterization of volcanic eruptions (plume altitude, total ash mass erupted and particle number density from thermal infrared to microwave). This approach is the core of the multi-platform volcanic ash cloud estimation procedure being developed within the European FP7-APhoRISM project. The Mt. Etna (Sicily, Italy) volcano lava fountaining event of 23 November 2013 was considered as a test case. The results of the integration show the presence of two volcanic cloud layers at different altitudes. The improvement of the volcanic ash cloud altitude leads to a mean difference between the SEVIRI ash mass estimations, before and after the integration, of about the 30%. Moreover, the percentage of the airborne “fine” ash retrieved from the satellite is estimated to be about 1%–2% of the total ash emitted during the eruption. Finally, all of the estimated parameters (volcanic ash cloud altitude, thickness and total mass) were also validated with ground-based visible camera measurements, HYSPLIT forward trajectories, Infrared Atmospheric Sounding Interferometer (IASI) satellite data and tephra deposits