Ultrasonic Immersion Technique Research Articles

Automatic image alignment and stitching for ultrasound-based robotic inspection of complex geometry components

Robotic inspection of complex geometry components using immersion ultrasonic techniques is relevant for many ultrasonic Non-Destructive Testing (NDT) applications in different industries. To image large component, ultrasonic probe is manipulated around the component immersed in water using a robotic guided system to create a tiled image of the entire component. Due to the mechanical vibrations of the high-speed robotic arm, the probe position coordinates provided by the robotic system are not precise enough to ensure an accurate reconstruction (stitching) of a composite image from all individual images. In this work, we propose a stitching method specifically designed to create a single 2D image of the surface of an inspected component from a stack of Total Focusing Method (TFM) images. This stitching method uses Iterative Closest Point (ICP) registration to estimate a 2D rigid transformation between two consecutive 2D images, by maximizing the overlap between the surface geometries extracted from each image. The capabilities of this imaging technique are illustrated by various simulated and experimental results carried out in a water tank. Significant improvements in surface image quality, leading to accurate surface reconstruction, are shown for vertical vibrations with displacements of more than two operating wavelengths and for rotational vibrations with deviation angles of less than 1°. The results also show that the resolving power of the ICP algorithm decreases for strong rotational vibrations.

Green perspective of N-CDs towards energy crisis and photodegradation of toxic dyes

Here we have presented a general overview of an environmental friendly, one-step, cost-effective, and efficient microwave irradiation method for the preparation of self heteroatom doped Nitrogen doped carbon dots (N-CDs) which demonstrated an average size of less than 10 nm and an interplaner distance of 0.334 nm. These N-CDs possess 2.35 eV energy gap with 65.5% fluorescence quantum yield. The surfaces of these graphitic-like structures are doped with (S, P, K, Mg, Zn) = 1% along with the extra passivating agent nitrogen (N). They have demonstrated wider absorption (between 300 and 550 nm) and emission (between 400 and 600 nm) bands and also managed enormous active surface sites and defects, that further extend its usage in energy harvesting, storage and photo catalysis owing to their unique property of electron transport and collection system. In addition, we have prepared, tested, and optimised new TiO2/N-CDs composite as photo anode and N-CDs/CB composite as photo cathode for application in dye-sensitized solar cells (DSSC). The achieved power conversion efficiency of the DSSC employed photoanode N-CDs/TiO2 and counter electrode carbon black/N-CDs, demonstrated a substantial improvement, in photo current and photo voltage owing to their multiple factor visible light absorption, effective electron separation, and longer recombination time resulted a Jsc. of 22.90 mA cm2, Voc. of 0.780 V, FF. of 74% and an overall PCE of about 13.22% approximating 2.5-fold increase in power conversion efficiency as compared to that of pure TiO2 and platinum based DSSC, where Jsc. (= 10 mA cm2), Voc. (= 0.750 V) and a total of 5.42% power efficiency. Furthermore, TiO2 was modified with Heteroatom-doped N-CDs using a novel ultrasonic immersion technique, and demonstrated greater photocatalytic activity for the degradation of methylene blue (85%) with a rate constant of 0.1068 in accordance with the pure TiO2 film and N-CDs which have showed only 20% and 30% photodegradation with lower rate constants under short UV irradiation, demonstrating the formation of reactive oxygen species and H+ ions in the sample solution resulting enhanced effective mobility of electrons and holes between TiO2/N-CDs composite nanomaterial, resulted greater photo degradation.

Experimental studies of CFRP laminates under repetitive low-velocity impact loading

Due to their exceptional properties such as high strength-to-weight ratio and fatigue tolerance, laminated composites are widely used in aircraft structures. When subjected to impact loading, composite structures experience intra/inter-laminar damages, and it is crucial to investigate the effect of damages on the strength of the laminate. Single and multiple impact tests are performed on CFRP laminates with different stacking sequences. Cross-ply [0/90]4S and quasi-isotropic [45/90/-45/0]2S laminates are fabricated and tested. Damage size as a function of the number of impacts and impact energy for different stacking sequences are studied. The damage configuration of impacted specimens is studied using the immersion ultrasonic technique. Damage size and shape of multiple impacted specimens are compared with single impacted specimens.

Ultrasonic non-destructive evaluation of selectively laser-sintered polymeric nanocomposites

Ultrasonic testing as a non-destructive evaluation (NDE) technique is newly introduced to characterize additively manufactured composite materials to identify their anisotropic mechanical properties, being especially facile, useful and accurate approach for dimensional dependent measurement. In this study, the immersion ultrasonic technique is employed to measure the energy loss of ultrasonic elastic waves, and wave propagation speed in the laser-sintered nanocomposite of carbon nanotube reinforced polyamine 12. The relationship of process-structure-property is revealed to establish the correlations between process parameters and energy loss of ultrasound, as well as mechanical moduli. The orientation-dependent wave attenuation and mechanical moduli of nanocomposites along three orthogonal directions are strongly associated with the layer-by-layer fusion induced microstructures and internal imperfections. This technique is capable of quantifying orientation-dependent mechanical properties such as moduli and attenuation without compromising additively manufactured parts, showing a high potential of quality control and safety inspection in end-use applications.

The Detectability of Welding Defects in MIAB Welded Thin-Walled Tubular Components by Immersion Ultrasonic Technique

The article demonstrates an effective solution for ultrasonic quality monitoring of transmission and drive components of motor vehicles, joined using an innovative method called magnetically impelled arc butt welding (MIAB). The major challenge was the application of ultrasonic technology for quick and reliable testing of thin-walled components with complex geometry. To solve this problem the idea of using ultrasonic subsurface waves was investigated. By using finite elements method (FEM) the angle of the ultrasonic beam incident on the tested element and the frequency of the ultrasonic transducer were verified. Then, scanning acoustic microscopy (SAM) and X-ray computed tomography (CT), both nondestructive tests on thin-walled welded tubular components were performed. The research have shown that it is possible to detect defects with diameter of 0.3 mm with the angle of incidence of wave 31.5°. The results of the numerical analysis were compared with the experimental approach and confirmed the usefulness of proposed method. Finally, the potential of using immersion ultrasonic technique for quick and reliable validation of thin-walled tubular components was proven, as the test duration for a one elements was around 3 s.

Development of tungsten armored high heat flux plasma facing components for ITER like divertor application

The dome and reflector plate are the parts of divertor plasma facing components (PFCs) of ITER tokamak which are mainly aimed for the removal of heat load of maximum 5 MW/m2 in steady state condition. The dome is a curved tungsten armoured component and the reflector plate is a straight component. These components have multi-layered joints made of various materials such as tungsten (W), OFHC copper (Cu), copper alloy (CuCrZr) and stainless steel (SS316LN). Joining of such multi-layered joints is known to be problematic due to joining of several dissimilar materials. In this paper, we report the indigenous development of medium size dome and reflector plate via vacuum brazing route for ITER like tokamak application. In order to evaluate the performance of the dome against ITER-like scenarios (maximum heat flux removal of 5MW/m2), the dome has been successfully tested for 1000 number of steady-state thermal cycles at incident heat fluxes of 3.87 MW/m2 in the High Heat Flux Test Facility (HHFTF) at IPR. Subsequent testing of additional 200 thermal cycles was also done at incident heat flux of 6 MW/m2. During the High heat flux (HHF) tests, surface temperature of W tiles reached 640oC and the beam power was restricted at 6MW/m2 to limit the temperature below 450oC at the CuCrZr heat sink. Total 1200 steady-state thermal cycles have been completed. At 6 MW/m2, the absorbed heat flux was 4 MW/m2. Engineering analysis on the HHFT of the dome has been performed using Finite element method (FEM) and Computational Fluid Dynamics (CFD) to simulate and to correlate with the experimental data. Ultrasonic immersion technique – Non destructive testing (NDT) was used to inspect the brazed joint quality of the dome before and after the HHFT. The results of the experimental details, engineering analysis and methodology adopted to fabricate the medium size dome and reflector plate are presented here.

A non-destructive material characterization framework for retrieving a stiffness matrix using bulk waves

The accuracy of the stiffness matrix used as input in dispersion curve algorithm determine the accuracy of the predicted wave speeds. Common practice is to use standard mechanical testing procedures to determining the E11,E22,G12 and ν12. The other engineering constants are then based on assumptions such as: E33=E22. The engineering constants are converted to the stiffness matrix and used as input. Due to this approach the dispersion curves can vary significantly from those obtained experimentally.In this research the stiffness matrix components are determined non-destructively using a newly introduced ultrasonic immersion technique, the LAMSS approach. The LAMSS approach utilizes the symmetry planes within an orthotropic transversely isotropic material and the critical angle approach to divide the stiffness matrix retrieval process into several steps to reduce the complexity of the process and increase the accuracy of the solution.As last, the predicted group velocity dispersion curves obtained using a stiffness matrix based on mechanical testing and the ultrasonic immersion technique are compared to experimentally obtained velocities.

Preparation of W/CuCrZr mono-block test mock-up using vacuum brazing technique

Development of the joining for W/CuCrZr mono-block PFC test mock-up is an interesting area in Fusion R&D. W/Cu bimetallic material has been prepared using OFHC Copper casting approach on the radial surface of W mono-block tile surface. The W/Cu bimetallic material has been joined with CuCrZr tube (heat sink) material with the vacuum brazing route. Vacuum brazing of W/Cu-CuCrZr has been performed @ 970°C for 10 min using NiCuMn-37 filler material under deep vacuum environment (10-6 mbar). Graphite fixture was used for OFHC Copper casting and vacuum brazing experiments. The joint integrity of W/Cu-CuCrZr mono-block mock-up of W/Cu and Cu-CuCrZr interface has been checked using ultrasonic immersion technique. The result of the experimental work is presented in the paper.

Determination of the elastic properties in CFRP composites: comparison of different approaches based on tensile tests and ultrasonic characterization

The mechanical characterization of composite materials is nowadays a major interest due to their increasing use in the aeronautic industry. The design of most of these materials is based on their stiffness, which is mainly obtained by means of tensile tests with strain gauge measurement. For thin laminated composites, this classical method requires adequate samples with specific orientation and does not provide all the independent elastic constants. Regarding ultrasonic characterization, especially immersion technique, only one specimen is needed and the entire determination of the stiffness tensor is possible. This paper presents a study of different methods to determine the mechanical properties of transversely isotropic carbon fibre composite materials (gauge and correlation strain measurement during tensile tests, ultrasonic immersion technique). Results are compared to ISO standards and manufacturer data to evaluate the accuracy of these techniques.

Polymer self-heals in seconds

mously restoring themselves have attracted more and more research interests. Many approaches that impart remendability to polymeric materials by either incorporation of healing agent into the matrices or making use of reversible inter/intra-macromolecular bonding have been proposed. Comparatively, however, most of the research concerns are focused on the extent of properties recovery rather than the speed. In fact, rapid healing of cracks is highly desired for practical applications. On the one hand, crack propagates very fast; on the other hand, the damaged materials should be healed immediately to prevent occurrence of catastrophic failure. By reviewing the available literature, we find that the reported time taken for reaching steady state or maximum healing used to be on the level of hour or dozens of minutes. Evidently, it needs to be greatly shortened. To tackle the problem, SbF5 (ACS Appl. Mater. Interfaces, DOI: 10.1021/am405989b), a strong Lewis acid, and trifluoromethanesulfonic acid (Compos Sci. Technol., DOI: 10.1016/j.compscitech.2014.08.028), a strong Bronsted acid, were employed for formulating fast healing systems, respectively. In actual operation, the acids were encapsulated by silica, and then embedded in epoxy matrix together with encapsulated epoxy monomer. Upon cracking of the composite, the fluidic chemicals released from the broken microcapsules flowed to the damage sites due to capillary effect and curing of the epoxy monomer occurred, re-connecting the cracked faces. Both impact and fatigue tests demonstrated that mechanical strength of the epoxy filled with the healing agent can be recovered within seconds at room temperature without manual intervention. Moreover, the healing system consisting of trifluoromethanesulfonic acidepoxy pair turned out to possess significant thermal stability. It can survive the rigorous processing of high Tg epoxy (>240°C) during composite fabrication and provide the composite that was pre-treated at 180°C for 5 h with the same healing efficiency as the untreated one. The above investigations also indicate that the healing speed of fast self-healing materials is difficult to be precisely evaluated by the existing destructive tests because of the time consuming recombination of the broken specimens. Fast in-situ measurement protocol like ultrasonic immersion technique that allows for determining elastic constants (Angew. Makromol. Chem., DOI: 10.1002/apmc.1992.051980104) within short time should be introduced. Although the healing systems based on the encapsulated strong Lewis or Bronsted acids and epoxy monomer have shown their ultrafast healability, much milder substitute with comparable healing speed is still worth being developed in view of easy handling. Besides, the balance between the rate of curing and speed of healing agent delivery should be considered when large damage sites are dealt.

Curved Small Tungsten Macro-Brush Test Mock-Up Fabrication Using Vacuum Brazing for Divertor Target Elements

The aim of the work is to develop the fabrication technology of a small curved tungsten (W) macro-brush–type geometry using a vacuum brazing technique. Taking the design concept of the ITER divertor dome, the present mock-up has scaled down more than ten times in size. A feasibility study of the curved brazing was done, and design and fabrication of the special fixture for the curved profile brazing were carried out. The vacuum brazing technique was used to develop the joining of tungsten tiles in the curved profile of a CuCrZr block (heat sink) using silver-free brazing alloy (NiCuMn-37) with a specially designed custom-made fixture (Type 304 stainless steel). Nondestructive testing, particularly the ultrasonic immersion technique, was incorporated to inspect the quality of the brazed joint in the mock-up. The hardness value (HV) measured on the copper alloy was found to degrade from 143 to 46 HV (before and after brazing). The results of the experimental activity and methodology adopted to fabricate the small-sized trial W mock-up are presented and discussed in the paper.

Isothermal epoxy-cure monitoring using nonlinear ultrasonics

Isothermal curing of LY 1564SP resin in an aluminium-adhesive-aluminium laminate is investigated, using a nonlinear ultrasonic immersion technique, to prove its applicability for this type of dynamic material transformation. For verification and comparison, epoxy-cure kinetics and rheological behavior are measured using differential scanning calorimetery (DSC) and dynamic mechanical analysis (DMA). Results reveal that the nonlinear ultrasonics, based on noncollinear wave mixing, can successfully be applied to in situ epoxy-cure monitoring—for example, to adhesive bonds—with reliable detection of gelation and vitrification time instants.

On the validity and improvement of the ultrasonic pulse-echo immersion technique to measure real attenuation

A fundamental assumption embraced in conventional use of the ultrasonic pulse-echo immersion technique to measure attenuation in solid materials is revisited. The cited assumption relies on perfect and immutable adhesion at the water to sample interface, a necessary condition that allows calculating the reflection coefficient at any interface from elastic wave propagation theory. This parameter is then used to correct the measured signal and obtain the real attenuation coefficient of the sample under scrutiny. In this paper, cases in which the perfectly cohesive interfacial condition is not satisfied are presented. It is shown also that in those cases, the repeatability of the conditions at the interface is always uncertain. This implies that the reflection coefficients are unknown, even when density is known. A new method of simultaneously measuring the reflection coefficients for both exposed interfaces that are normal to the transducer, and the attenuation coefficient of the specimen is developed and is presented here. The robustness of the new method is proven, as we demonstrate that the proper value of attenuation is achieved independently of the continuously varying interfacial conditions of these non-ideal cases.

Ultrasonic characterization of polymeric composites containing auxetic inclusions

Composite materials are often used as damping treatments or structural materials to mitigate the effects of unwanted vibration and sound. Recent work on materials displaying a negative Poisson’s ratio, known as auxetic materials, indicate that composite materials consisting of a lossy matrix containing auxetic inclusions may lead to improved vibro-acoustic absorption capacity compared to composites containing positive Poisson’s ratio inclusions. This work presents ultrasonic measurements of an epoxy matrix material (Epon E828/D400) containing volume fractions of α-cristobalite inclusions ranging from 5% to 25% by volume. The effective frequency dependent speed of sound and attenuation coefficient of each sample is measured from 1 to 10 MHz using ultrasonic immersion techniques. Ultrasonic test results are compared with Dynamic Mechanical Thermal Analysis and modal damping measurements of stiffness and loss behavior. This material is based upon work supported by the U. S. Army Research Office under grant number W911NF-11-1-0032.

Characterization of Grain Size and Yield Strength in AISI 301 Stainless Steel Using Ultrasonic Attenuation Measurements

AISI 301 stainless steel samples were annealed over the temperature range of 800–1200°C for 60 minutes to produce different grain sizes. These samples were characterized by ultrasonic immersion technique, tensile test, and optical microscopy. The attenuation of ultrasonic waves measured at a frequency of 20 MHz showed a good correlation with average grain size, hardness, and yield strength of AISI 301 stainless steel samples. A new equation was derived for calculation of yield strength on the basis of ultrasonic wave attenuation and Hall-Petch relation.

Correlation between ultrasonic velocity and solutionising time in Rene 80 superalloy

Ultrasonic measurements have been used to characterise the solutionising phenomenon in Rene 80, a Ni based superalloy. Starting material was solutionised at 1204°C for 30–120 min on identical samples. The microstructures of these samples were evaluated by ultrasonic immersion technique, X-ray diffraction and scanning electron microscopy. It was observed that the area fractions and, consequently, the γ′ volume fractions were decreased by increasing the solutionising time. A direct correlation was observed between ultrasonic wave velocity and solutionising time at 1204°C. The ultrasonic compression wave velocity followed a descending pattern similar to that of γ′ area fraction with the increase in solutionising time. The observed variation in ultrasonic velocity has been attributed to the effect of the γ′ dissolution on the elastic constants of the material.

Immersion ultrasonic technique for investigation of total welding residual stress

Objective of this study is the prediction of total residual stress and fusion boundary in three pass welded stainless steel plates. In this work, immersion ultrasonic technique is used to measure residual stress through the thickness of the material. Two 316L stainless steel plates with the same material properties are examined. Three weld passes are applied to one of these plates and the other one is used as zero stress state reference plate. As it is well known, ultrasonic wave speed is constant for a material unless deformations such as residual stress occur. The main source of residual stress is the heat effect of welding. The relation between thermal stress and ultrasonic wave velocity variations are investigated by using ultrasonic wave velocity measurements which were done at approximately 1200 points for each plate. The differences in the ultrasonic wave velocity discriminations of two plates gave the final total residual stress distribution throughout the welded plate. Therefore the total residual stress which is the sum of longitudinal, transversal, and vertical stresses through the thickness of the plates were measured. Residual stresses are dense around weld zone due to the heat affected zone. Residual stress distribution around the weld zone also provides information about the fusion boundary. Comparison of these results with the previous studies on residual stress measurement showed that the ultrasonic immersion technique allowed more precious measurements than the measurements with couplingmaterials. This method provides a practical and accurate approach for residual stress measurements showed that fusion boundary reaches up to 20mm from weld zone center

Processing and characterization of textured mullite ceramics from phyllosilicates

Ceramics are obtained from a kaolinite aqueous suspension and are shaped by centrifugation. It favors preferred orientations of particles in the powder compact. Sintered samples at 1410 °C were analyzed by QTA and SEM to determine mullite orientation and the important role of process parameters in the organization degree is evidenced. The c-axes of mullite are mainly aligned parallel, but randomly in the sample plane to form a planar texture. A second texture component is seen with b-axes oriented parallel to the centrifugation direction. Mechanical properties are closely related to the organization degree of mullite crystals that is consistent with the development of an interconnected mullite network within the microstructure. At the microscopic scale, Young's modulus values determined by nano-indentation and by ultrasonic immersion techniques in directions parallel and perpendicular to layers evidence an anisotropic behavior of samples. The specific and important role of residual porosity is also shown with the comparison of mechanical behavior of different centrifuged samples.

Application of ultrasonic iterative deconvolution technique to the case of internal defect detection in multi-layered PCB components

Possibilities of improvement in detection and characterisation accuracy concerning internal defects in multi-layered printed circuit boards (PCB) and electronic components by applying the ultrasonic immersion technique have been investigated. The experiments have been carried out on a real PCB with a mounted defective microchip. Defect-free and defective high-voltage semiconductor components have also been investigated. The investigations have been performed using the acoustic microscope produced by Ultrasonic Science Ltd and ultrasonic measurement system developed at the Ultrasound Institute of Kaunas University of Technology. The novel signal processing method based on the adaptive numerical model of ultrasonic wave propagation through a multi-layered electronic component and respective selection of signal components in time and frequency domains have been proposed. Two different signal processing techniques have been used to increase the contrast of defective regions and so improve reliability of ultrasonic inspection.

Great improvement over electrochemical performance of zinc electrodes from sonochemical growth of cerium conversion films on zinc powder

The corrosion and dendritic growth of zinc electrodes are main reasons why zinc-based batteries have not been commercialized extensively. This work focuses upon the growth of cerium conversion films on modified zinc powder using ultrasonic immersion technique to obtain novel electrode materials for reducing the issues of zinc electrodes. Simultaneously, the surface state of conversion films and trace yields of Ce element imposing various concentrations of immersion solutions are evaluated. It is found that the yields of Ce element can be controlled by varying the concentrations of initial Ce(NO 3) 3 solutions due to the dependence of conversion rate on the concentration of Ce(NO 3) 3 solution. Moreover, the cerium conversion layers formed on zinc powder make significant contributions to suppress corrosion and dendritic formation of zinc electrodes. In particular, the cerium conversion films obtained with 0.0306 mol L −1 Ce(NO 3) 3 solution provide the strongest inhibition capability in corrosion and dentritic growth. This is attributed to the surface characteristics of conversion layers with the effective formation of Ce-rich particles on the defect sites of zinc powder.