Some authors have observed that the frequency of ToF stimulation has an effect on the measured velocity. Haines et al.  observed that dynamic bending tests overestimate the MoE of boards compared to static bending. They hypothesised that this was because the wood was acting viscoelastically. This causes the effective stiffness to increase with the frequency of stimulation. Ouis  explained that the viscoelasticity of wood leads to an acoustic wave speed which is frequency dependent. This is known as dispersion. O’Donnell et al.  explained that a Kramers-Kronig relationship may be used to show that a medium which exhibits attenuation is also dispersive. The dispersive and attenuative qualities of generalised solids are explored in more detail by Kolsky . Divos et al.  analysed the speeds of resonant modes in a spruce specimen. They found that the speed of the modes tends to increase with frequency. Bucur and Feeney  measured the attenuation and stress wave velocity in horse chestnut wood using a continuous transmission technique. They found that the longitudinal velocity increased significantly with frequency. Salmi et al.  measured the dynamic MoE in Norway spruce samples at several ultrasonic frequencies. They found a general trend of increasing MoE as frequency increases. Chiu et al.  measured acousic velocity in Taiwan incense cedar using both ultrasonic ToF and hammer-excited ToF methods. They found that in general the ultrasonic velocity was greater than the lower-frequency hammer-hit excited velocity. These results are consistent with the behaviour of viscoelastic models of solids, which predict that MoE and acoustic velocity increase as frequency increases.
Divós et al. (2001) investigated the change in velocity and amplitude of a constant impact when introducing sawn notches halfway between the transmitter and the receiver which were placed 60 cm apart. The tests were conducted on Norway spruce (Picea abies) and beech (Fagus sylvatica) boards of a length between 80 – 200 cm and a cross-section of 2x4 cm through to 10x12 cm respectively (11-13% moisture content). Preliminary tests showed that within the first 60 cm the acoustic wave was not travelling as a plane wave front as significant differences within the cross-section of the boards were evident (near-field conditions). Beyond the initial so called near- field area a planar wave front takes over creating far-field conditions. According to Divós et al. (2001) the amplitude of the first received signal (TOF) decreases exponentially with distance once the signal is travelling in far-field conditions. Where 2mm wide saw cuts were introduced in 5-6 consecutive steps perpendicular to the longitudinal axis of the boards, the amplitude of the received signal was significantly more sensitive to the artificially created defect than was the velocity. Thus, Divós et al. (2001) concluded that measuring the signal amplitude is highly effective in terms of defect detection in wood, but this would require further research to be related to mechanical properties of wood.
The principal of using airborne ultrasound for nondestructive testing seems, in the first instance, to be ideal for a variety of non-contacting applications. This technique has, however one major flaw, namely that of transmitting ultrasound across the interface between the air and the sample under test. Because of the very large acoustic impedance mismatch between most solids and air, only a very small proportion of the ultrasonic energy is transmitted across this boundary. This is compounded when testing materials with the transducer acting as both transmitter and receiver, as the ultrasonic signal needs to cross the boundary between air and the sample twice, introducing significant losses, often prohibitively, into the received signal. Because of these massive losses, most samples cannot currently be tested in such a way. However, experiments have shown that nondestructive testing with airborne ultrasound can now be usefully employed in three situations; Firstly if another method (for example a laser) is used to generate the ultrasound (removing the losses encountered at one interface)13. Secondly, when materials with low acoustic impedances (such as paper and wood) are tested. Thirdly where the air is under high pressure
NDT have wide application in areas where there is doubt about the structural integrity of a part, sometimes inaccessible, such as dams, bridges, churches, roofs, etc. The advantage to perform NDT in a structural element is that it is not necessary to take it to the lab and destroy it to know its mechanical properties; the estimation of these properties is made in loco. When dealing with wood it is also possible, with NDT, to verify the integrity in living trees, which brings greater security to society and also avoids unnecessary felling of perfectly healthy trees in parks and urban areas. A combination of several NDT methods for monitoring is generally required to provide reliable results for the characterization of a material, failure detection and determination of geometric parameters. This can lead to the need of information of different scales that are combined, Kurz, J. et al., (2012). Among the various sorts of NDT the following local non-destructivetesting and global nondestructive testing can be cited: resistance to penetration testing and resistance to perforation testing (local NDT) and ultrasound, acoustic emission, microwave tomography, thermography and x-rays (global NDT), among others. Thermographic analysis is a diagnostic technique based on a NDT, which uses cameras and infrared sensors to measure temperature and heat distribution, in order to detect problems
plantation species in the UK, but is being assessed for possible greater planting. The key wood properties are similar to those of the UK’s major species: Sitka spruce (Picea sitchensis PCST) and Norway spruce (Picea abies PCAB). The diametric cutting pattern is not a normal industrial sawing pattern, and was done for scientific reasons (to investigate radial trends in wood properties). This has some consequences on the distribution of knots in this dataset, and, importantly, the direction of grain with respect to the width and depth (see 3.4).
This thesis concentrates on research into pulse compression and metamaterials. Each has the potential for improving the quality of measurements in various materials. Chapter 2 reports the mathematical background of several kind of coded excitations, as well as algorithms to perform pulse compression technique and filtering. Moreover, numerical simulations results are shown with the aim to give a guideline on the optimal choice of a coded excitation for a specific purpose. Chapter 3 is focused on the historical and theoretical background to acoustic metamaterial and phononic crystals. Chapter 4 shows the finite element simulation results for several exotic acoustic metamaterial structures. Numerical results on the use of acoustic metamaterial for sub-wavelength acoustic imaging are also shown. Experimental results on the use of acoustic metamaterials for sub-wavelength imaging purpose are given in Chapter 5, together with a path toward the realization of a broad-band acoustic metamaterial device. Chapter 6 reports the use of coded signals and advanced signal processing techniques for the non-destructivetesting of several highly attenuating materials. Furthermore, it also shows the realization of a portable device for real time pulse compression, as well as its application on the investigation of concrete structure. An advanced application of the combined use of coded signals and pulse compression for thermography is shown in Chapter 7. Finally, Chapter 8 gives overall conclusions and ideas for further work.
structure's in-situ strength. In this paper author gave guideline related to visual inspection. Dhananjay Mangrulkar et. al. (4), In this research paper author did a case study of various Non-Destructive Test (NDT) done on a building whose age was 20 years and was located far away from any industrial or chemical plants. Various NDT methods like ultrasonic pulse velocity test, carbonation test, rebound hammer test and half-cell potential test were used to access the quality of structure. These tests were done to find the voids and cracks in the structural elements. The depth of carbonation was checked whether it is less than the cover concrete or not to make sure the reinforcements does not corrode. Finally, based on the results, the structural elements requiring repairs were identified. D. Breysse (5), In this paper has been analyzes why and how nondestructive testing (NDT) measurements can be used in order to assess on site strength of concrete. It is based on (a) an in-depth critical review of existing models; (b) an analysis of experimental data gathered by many authors in laboratory studies as well as on site, (c) the development and analysis of synthetic simulations designed in order to reproduce the main patterns exhibited with real data while better controlling influencing parameters. The key factors influencing the quality of strength estimate are identified. Two NDT techniques (UPV and rebound) are prioritized and many empirical strength-NDT models are analyzed. It is shown that the measurement error has a much larger influence on the quality of estimate than the model error. The key issue of calibration is addressed and a proposal is made in the case of the SonReb combined approach. Jibin Babu and Akhilchandran Bs et. al. (6), In this paper concrete slabs of different dimensions and characteristics are taken and subjected to destructive test by compressive strength testing and non- destructivetesting
defects in aluminium friction stir welds. However, there is no published literature on non-destructivetesting on friction stir welds of dissimilar materials. In view of the foregoing, research into the effect of rotational speed and feed rate on defect formation in dissimilar aluminium and copper joints has been published by Akinlabi et al . Non-destructivetesting for defects is the most effective method of determining the integrity of a friction stir weld, hence research studies into non-destructive techniques of dissimilar joints between aluminium and copper will ultimately lead to achieving optimised setting to produce quality welds and increase material performance in this regard. The successful technique reported in this paper can also be extrapolated to conducting non-destructive tests on other dissimilar FSW joints. The aim of this paper therefore, is to present results of non-destructivetesting techniques on dissimilar friction stir welds of aluminium and copper.
Chapter 3 Ultrasonic Field Measurement using Miniature Piezoelectric Probe A schematic representation showing the structure of the miniature probe is given in Figure 3.3. In creating it, a PMN disc of around 0.5 mm in diameter and thickness 0.2mm was bonded to the tip of a stainless steel needle of similar diameter and length around 50mm, using electrically conducting epoxy. The needle acts as a heavily damping backing material as well as a means to provide electrical connection to the back face of the element. Then the needle and element were abraded using fine polish paper to reduce the diameter of the tip assembly to around 0.3mm. The needle was bonded to the inner terminal of a BNC coaxial plug, which provides a convenient means to support the probe and allows direct connection to a head amplifier. The front face of the element was abraded to reduce the thickness of the element to around 0.15mm. The half-wave resonant frequency of such a PMN disc is around 14MHz, but the heavily damping, needle-like backing greatly damps this and other unwanted modes of reverberation with the probe element. To electrically isolate the needle and back face of the element from the front face, they were together coated with an electrically insulating layer that also provides further acoustic damping. Again the tip was abraded to expose the front face of the PMN element and the whole assembly is coated with a conducting layer to provide connection of the front face to the BNC outer “earth” electrode. Finally, the probe was encapsulated in a further coat to protect it and provide further acoustic damping, care being taken to keep the thickness over the front face small enough to avoid unwanted loss of sensitivity due to destructive interference.
INTERNATIONAL JOURNAL OF ADVANCES IN ENGINEERING RESEARCH With a preselected limit reading, the probe can be moved at a maximum search speed of 0.25 m/s without having any interruption to measure the thickness continuously. If the current cover displayed is less than the limit ranges, an acoustic alarm sounds. If the probe is over the bar is indicated in the current concrete cover in the display field. If the rebars of the 1 st layer run in a vertical direction, the travel paths must be positioned horizontally with the selected grid spacing in vertical direction. Move the mobile probe along these paths. The smallest concrete cover measured in a grid field is displayed and stored automatically as grey scale.
Non-destructivetesting methods and applications have become of increasing interest due to the worldwide aging and deteriorating infrastructure network. In the field of Civil Engineering, bridges and bridge components as well as non-structural elements such as roadway pavements for example, are affected. In particular, the Acoustic Emission (AE) technique offers the unique opportunity to monitor infrastructure components in real-time and detect sudden changes in the integrity of the monitored element. The principle is that dynamic input sources cause a stress wave to form, travel through the body, and create a transient surface displacement that can be recorded by piezo-electric sensors located on the surface.
Abstract— In this paper, we present the design and the implementation of a digital Application Specific Integrated Circuit (ASIC) for Acoustic Emission (AE) non-destructivetesting. The AE non-destructivetesting method is a diagnostic method used to detect faults in mechanically loaded structures and components. If a structure is subjected to mechanical load or stress, the presence of structural discontinuities releases energy in the form of acoustic emissions through the constituting material. The analysis of these acoustic emissions can be used to determine the presence of faults in several structures. The proposed circuit has been designed for IoT (Internet of Things) applications, and it can be used to simplify the existing procedures adopted for structural integrity verifications of pressurized metal tanks that, in some countries, they are based on periodic checks. The proposed ASIC is provided of Digital Signal Processing (DSP) capabilities for the extraction of the main four parameters used in the AE analysis that are the energy of the signal, the duration of the event, the number of the crossing of a certain threshold and finally the maximum value reached by the AE signal. The circuit is provided of an SPI interface capable of sending and receiving data to/from wireless transceivers to share information on the web. The DSP circuit has been coded in VHDL and synthesized in 90 nm technology using Synopsys. The circuit has been characterized in terms of area, speed, and power consumption. Experimental results show that the proposed circuit presents very low power consumption properties and low area requirements.
Several methods have realistic potential for non-destructive inspection of adhesive joints, as example, ultrasonic waves, electromechanical impedance, and acoustic emission. Ultrasonic wave pitch-catch techniques have proven to be an effective method for inspection of adhesive bonds integrity of isotropic materials. Corrosion detection at locations with limited access gives rise to many inspection problems in daily practice. Hidden corrosion at inaccessible locations such as pipes on sleepers or supports, insulated pipe work, tank floor, clamping and complex joints made the inspection difficult to be done. For the solution, a new ultrasonic pulse echo method, the Long Range Ultrasonic System (LORUS) has been optimized for inspection over considerable distance (typically one meter) which can overcome most of the access problem. The technique utilizes optimized bulk wave transducers with a dedicated data recording system .
Acoustic waves are longitudinal waves, the molecules move back and forth in the direction of wave propagation, causing adjacent regions of compression and refraction. As a result, the pressure change that occurs is the only restoring force capable of propagating a wave . On Solids, the propagating waves, in addition to longitudinal waves, can also be transmitted shear waves and combinations of these with the longitudinal. Neglecting the transverse components which propagate in the solid, the wave propagation in the solid can be described with a model of longitudinal pressure wave, which depends on the density and velocity of phase , Eq (1).
Colombo and Felicetti  proposed new technique based on ultrasonic pulse velocity and drilling resistance to estimate fire damage caused to reinforced concrete structures. They applied the technique on two full scale reinforced concrete structures surviving from real fire to plot fire damage profile. The authors compared their results with laboratory testing to validate their proposed technique. The authors also discussed pros and corns of the proposed technique.
Abstract Pulsed eddy current (PEC) non-destructive test- ing and evaluation (NDT&E) has been around for some time and it is still attracting extensive attention from researchers around the globe, which can be witnessed through the reports reviewed in this paper. Thanks to its richness of spectral components, various applications of this technique have been proposed and reported in the lit- erature covering both structural integrity inspection and material characterization in various industrial sectors. To support its development and for better understanding of the phenomena around the transient induced eddy currents, attempts for its modelling both analytically and numeri- cally have been made by researchers around the world. This review is an attempt to capture the state-of-the-art development and applications of PEC, especially in the last 15 years and it is not intended to be exhaustive. Future challenges and opportunities for PEC NDT&E are also presented.
However, the idea of measuring a certain layer of the solid propellant material which has developed different (mechanical) properties than the original material with ul- trasound is not new. Applications in the field of inspecting a layer of deteriorating concrete have been proven to be suitable. In this case ultrasonic waves are used to reflect on the surface of the deteriorated material layer. This way three different re- flections can be distinguished in the received signal as shown in figure 1.6 . The purple wave is passed on through the interfaces, while the blue arrows indicate the part of the signal energy that is reflected from each interface. The same technique may work for inspecting a deteriorating layer in solid propellants. Assuming there is a sharp enough interface between non-aged and aged solid propellant material, ultra- sonic waves that propagate inside the material and reach the interface of the pristine and the aged material give a reflection visible in a pulse-echo measurement.
In the other hand, Destructive tests are usually carried out either on test specimens made for that purpose or may be made on one specimen taken as representative of several similar items. They are done in laboratories, workshops or training centre and can be chemical or mechanical in nature (Rangaraju, 2003). Destructive tests are usually quantitative measurements of load for failure, significant distortion or damage, or life to failure under given load and environmental conditions. They are carried out to the specimen’s failure, in order to understand behaves under different loads which consequently yield numerical data useful for design purposes or for establishing standards or specifications.
Due to beam divergence, in traditional synthetic aperture imaging the lateral resolution degrades with depth. Considering a focal point positioned some distance from the transducer, as the depth from the transducer to the focal point increases, so the ultrasonic beam widens. As the imaging algorithm selects the appropriate sample point from each raw signal in relation to the image focal position, transducer geometry and received signal, sample points that are in-phase provide constructive interference during the image reconstruction process. This corresponds to high spatial coherence across the received synthetic aperture acquired signals, as shown in Figure 12(a). This constructive interference is desirable with the synthetic aperture imaging process. However, in the case that the synthetic focus is steered away from the high intensity sample points produced by an indication, out-of-phase data is selected, producing destructive interference within the image reconstruction algorithm corresponding to low spatial coherence, as shown in Figure 12(b).