The adhesive bonds option enables durability calculations on adhesive joints in metallic structures. Adhesive bonds are modeled with beam elements and grid point forces are used to determine line forces and moments at the edge of the glued flange. Approximate calculations of the strain energy release rate are made at the edge of the adhesive and, by comparison to the crack growth threshold, a safety factor is calculated.
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Adult sand flies mate soon after emergence; males locate females at resting sites or on vertebrate hosts, with the aid of pheromones [23]. Female sand flies usually lay 30-70 eggs during a single gonotrophic cycle, which are deposited in cracks and holes in the ground or in buildings, animal burrows and among tree roots [20]. The eggs require a microhabitat with high humidity in order to survive, but are not laid in water. Generally, one blood meal results in the production of a single batch of eggs [22].
Environmental interventions to eliminate sand fly breeding and resting sites in Fuenlabrada included removing organic waste, unwanted vegetation, wood piles and waste tips; cleaning drainpipes and watercourses; sealing sewage drains and electricity meters; plastering holes and cracks in the walls of buildings; placing wire mesh in the windows of sanitary basements and aeration tubes; eliminating rats and feral cat colonies and destroying hare and rabbit nesting grounds. Pyrethroid insecticides were applied on vegetation and water collection drainage systems in parks and urban areas close to leishmaniasis cases, around subterranean electricity networks, on walls covered with vegetation and in the sanitary basements of buildings.
Solution In Need Of A Problem. Acronym describing any pointlessly over-engineered gadget, system or service for which no real or meaningful demand exists: a sledgehammer to crack a nut, or a sales-centred approach to relationships. SINOAP represents push and persuade, rather than facilitate and enable; it reminds us of the importance of understanding and empathy. SINOAP is a also product or service designed from the supplier's perspective rather than from the customer's view. The acronym warns against inappropriate marketing or selling, where the proposition fits the supplier's or sales-person's needs (for profit, sales quota, commission, etc) but not the needs of the potential customer. (ack J Tallon)
Abstract:Human activity has required, since its origins, stones as raw material for carving, construction and rock art. The study, exploration, use and maintenance of building stones is a global phenomenon that has evolved from the first shelters, manufacture of lithic tools, to the construction of houses, infrastructures and monuments. Druids, philosophers, clergymen, quarrymen, master builders, naturalists, travelers, architects, archaeologists, physicists, chemists, curators, restorers, museologists, engineers and geologists, among other professionals, have worked with stones and they have produced the current knowledge in heritage stones. They are stones that have special significance in human culture. In this way, the connotation of heritage in stones has been acquired over the time. That is, the stones at the time of their historical use were simply stones used for a certain purpose. Therefore, the concept of heritage stone is broad, with cultural, historic, artistic, architectural, and scientific implications. A historical synthesis is presented of the main events that marked the use of stones from prehistory, through ancient history, medieval times, and to the modern period. In addition, the main authors who have written about stones are surveyed from Ancient Roman times to the middle of the twentieth century. Subtle properties of stones have been discovered and exploited by artists and artisans long before rigorous science took notice of them and explained them.Keywords: archeology; geology; fortification; durability; conservation; quarries; restoration; architecture
Electromagnetic methods such as eddy current, magnetic particle or radiographic and ultrasonic methods all introduce electromagnetic or sound waves into the inspected material in order to extract its properties. Penetrant liquid techniques can detect cracks in the test material by using either fluorescent or non-fluorescent dyes. In addition to these methods, scientists such as Shujuan et al. [2], Noorian et al. [3] and Aliouane et al. [4] have researched non-destructive testing based on a combination of electromagnetic and sound waves using electromagnetic acoustic transducers, best known as EMATs.
The principle of the eddy current technique is based on the interaction between a magnetic field source and the test material. This interaction induces eddy currents in the test piece [1]. Scientists can detect the presence of very small cracks by monitoring changes in the eddy current flow [5].
Eddy current testing permits crack detection in a large variety of conductive materials, either ferromagnetic or non-ferromagnetic, whereas other non-destructive techniques such as the magnetic particle method are limited to ferromagnetic metals. Another advantage of the eddy current method over other techniques is that inspection can be implemented without any direct physical contact between the sensor and the inspected piece.
(a) Normalized impedance plane. Lift-off curves and crack displacement at impedance plane for two values of conductivity P1 and P2 (adapted from [12]). (b) Altered eddy current flow by a crack on the surface.
When a crack is present in the test piece, it obstructs the eddy current flow, as Figure 2(b) illustrates. There is a displacement from P1 or P2. This causes the eddy current path to become longer, and the secondary magnetic field from the eddy currents is reduced. In conclusion, the real part of impedance Rcn+crack, which is related to eddy current dissipation, decreases Rcn > Rcn+crack, In addition to that, the sum of the primary magnetic field and secondary magnetic field increases, which means that the inductive part of impedance Xcn+crack increases Xcn
Highly conductive materials such as cooper and aluminum create intense eddy currents and have two advantages over less conductive materials. First, cracks generate higher signal levels, as the impedance plane in Figure 2(a) illustrates. In addition to that, the phase lag between the flaws and lift-off line is larger when highly conductive materials are tested, that is φ1 > φ2 as Figure 2(a) shows. The disadvantage of highly conductive materials is that the standard penetration depth is lower at a fixed frequency than in lower conductive materials such as steel and stainless steel. Factors that exert an influence in conductivity are the temperature of the test piece, the alloy composition and the residual stress, which is related to the atomic structure.
The disadvantage of inspecting magnetic materials is that permeability changes generally have a much greater effect on eddy current response than conductivity variations. This heterogeneity means that crack detection is not possible when permeability changes randomly. The equalization of the permeability is often related to how the test piece was manufactured [28]. The heterogeneity of permeability for cast iron is stronger than that of carbon steel [28].
There are methods for lift-off compensation when eddy currents are used in order to detect cracks and lift-off becomes an undesired variable. For instance, Yin et al. researched dual excitation frequencies and coil design to minimize the lift-off effect [32]. Research into processing data is also conducted, with a view to minimizing the lift-off effect. Lopez et al. proposed the use of wavelets to remove eddy current probe wobble noise from steam generator tubes [35]. Reduction of the lift-off effect has also been attempted by optimizing the coil design [36] and sensor array.
In contrast to the conventional eddy-current instrument, pulsed instruments generate square, triangular or a saw tooth waveform [44]. These waveforms have a broad spectrum of frequencies; hence, pulsed eddy current testing techniques provide more information than traditional eddy current testing methods that can be used for the detection and characterization of hidden corrosion and cracking [45]. The data at different frequencies can be correlated to obtain the defect depth.
Pulsed eddy current is useful for more than just crack detection. Haan et al. have used pulsed eddy current to accurately characterize the permeability and the conductivity [48, 49]. Taking a reference measurement of an object with a known thickness, they also determined the thickness of several types of carbon steel materials, which was proportional to the product of conductivity and magnetic permeability.
Some authors have conducted research into pulsed eddy-current techniques. Many years ago, in 1969, Waidelich et al. researched the attenuation of a pulsed field by a conducting sheet [52]. They investigated how to increase the spatial resolution by putting the coil probe in a copper enclosure with a small aperture. Other authors such as Guang et al. presented a system for the inspection of aircraft structures [43]. The system generated pulse excitation that energized a planar multi-line coil of Figure 15(a). The transient field was detected via a giant magnetoresistive GMR field sensor placed on the line of symmetry at the center of the source coil. In the absence of discontinuities, the normal component of the magnetic field was zero at the center of the source coil. When the uniform distribution of the induced currents was distorted by a rivet and/or crack as sketched qualitatively in Figure 15(b) the zero field on the line of symmetry was destroyed and a nonzero transient signal of the normal component was measured by the GMR sensor.
(a) Schematic of the multi-line coil for inducing linear eddy currents (adapted from [43]). (b) Induced eddy current flow in the absence and presence of rivet and cracked rivet (adapted from [43]). 2ff7e9595c
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