Non-contact Laser Scanning Research Articles

Residual mechanical properties of corroded ultra-high-strength steels and weld metals

This paper presents an in-depth investigation into the residual mechanical properties of ultra-high-strength steels and weld metals after exposure to corrosive environment. The tensile specimens of weld metals were fabricated using ER100S-G, ER110S-G, ER120S-G feedstock wires by robotic gas metal arc welding, whilst ultra-high-strength steel tensile coupon specimens were machined from the Q890 and Q960 steel plates. The high-strength steel and weld metal tensile specimens were exposed to neutral salt spray accelerated corrosion conditions. Six exposure durations were designed to achieve different corrosion degrees of specimens. A total of 23 corroded ultra-high-strength steel tensile coupon specimens and 19 corroded high-strength weld metal specimens were included. The geometric profiles of corroded steel specimens were determined via non-contact 3D laser scanning. Monotonic tensile tests were conducted to determine the stress-strain responses and key mechanical properties of corroded steel and weld specimens. Mechanical properties deterioration of corroded ultra-high-strength steels and weld metals are reported and discussed. Prediction equations on the residual mechanical properties regarding the tensile loading capacity, yield stress and ultimate tensile stress of ultra-high-strength steels and weld metals after exposure to corrosive environment were established.

Behavior of wire arc additively manufactured 316L austenitic stainless steel single shear bolted connections

This paper aims to investigate the behavior of single shear bolted connections made of wire arc additively manufactured 316L austenitic stainless steel. A set of 44 wire arc additive manufacturing (WAAM) 316L austenitic stainless steel single shear bolted connections were included with consideration of various bolt positions, surface conditions and loading orientations respective to the printing layer direction. The geometric dimensions of the WAAM austenitic stainless steel plates were measured with the assistance of non-contact 3D laser scanning prior to tensile testing. Monotonic tensile tests were carried out to investigate the load-deformation responses, failure patterns and resistances determined by both the deformation and strength criteria of the single shear bolted connections. The effects of geometric and printing parameters on the single shear bolted connections were analyzed. Due to the absence of codified design provisions for WAAM austenitic stainless steel bolted connections, the suitability of the existing design rules originally developed for traditionally manufactured carbon steel and stainless steel bolted connections was examined. Design resistances calculated by the Eurocode 3 (prEN 1993-1-8 and prEN 1993-1-4), the American Specification (ANSI/AISC 370-21) as well as the prevalent design recommendations proposed in existing literature were compared with the obtained experimental results. It is shown that the abovementioned design methods offer conservative predictions for the resistances of WAAM 316L austenitic stainless steel single shear bolted connections. Further study is needed to improve the accuracy of design resistance predictions.

Numerical Analysis of Water–Sediment Flow Fields within the Intake Structure of Pumping Station under Different Hydraulic Conditions

The vortices, backflow, and siltation caused by sediment-laden flow are detrimental to the safe and efficient operation of pumping stations. To explore the effects of water–sediment two-phase flow on the velocity field, vorticity field, and sediment distribution within intake structures, field tests and numerical simulations were conducted in this study with consideration for the sediment concentration, flow rate, and start-up combination. We applied a non-contact laser scanner and ultrasonic Doppler velocimetry to obtain the field data and reverse modeling of the three-dimensional model of the intake structure under siltation. A multiphase flow model based on the Euler–Euler approach combined with the k-ε turbulence model was adopted for numerical simulation under 10 working conditions, and the reliability was verified with field data. The results indicate that sediment promotes the evolution of coaxial vortices into larger-scale spiral vortices along the water depth, and the process of sediment deposition is controlled by the range, intensity, and flow velocity of the backflow zone. Furthermore, the maximum volume fraction of the near-bottom sediment increased by 202.01% compared to the initial state. The increase in flow rate exacerbates the turbulence of the flow field. Although the increase in sediment concentration benefits the flow diffusion, it further promotes sediment deposition. This study provides a new idea for modeling complex surfaces and considers different operating conditions. It can serve as a scientific reference for the structural optimization and anti-siltation design of similar water-conservancy projects.

Research on rapid detection of characteristic parameters of aeroengine blade surface based on laser scanning

How to detect and evaluate the profile quality of aeroengine blades and provide technical support for blade manufacturing has become one of the key technical problems in the field of aviation manufacturing quickly and effectively. This paper studies the evaluation criteria of medium surface quality in the processing and manufacturing process of aeroengine blades, optimizes and innovates the fast extraction algorithms of various geometric parameters such as aeroengine blade section line, middle arc, front/rear edge center, front/rear edge radius, blade chord length, and chord angle, and establishes the evaluation criteria of aeroengine blade surface. According to the geometric relationship of blade chord length and front/rear edge radius in the blade section profile, the parameters are solved one by one through an optimization algorithm, combined with non-contact laser scanning measurement, and the blade detection efficiency is improved by more than 40%.

Experimental investigation of fixed-ended hot-rolled austenitic stainless-steel unequal-leg angles under compression

Structural stainless steel is gaining traction in the structural engineering field, however, there is currently limited published data on the performance of stainless steel unequal-leg single-angle compression members. This limitation of published data is reflected in the recently released AISC 370: Specification for Structural Stainless Steel Buildings which is limited in scope to equal-leg cross sections. Furthermore, the Specification requires the consideration of flexural–torsional buckling for single angles which is in contrast to the original design guidelines from AISC published in 2013, which mirrored the carbon steel specifications and did not required checking for flexural–torsional buckling for single angles. This paper reports a comprehensive experimental study on the behavior of hot-rolled austenitic stainless steel unequal-leg angle columns. A series of unequal-leg angles with cross-sectional dimensions of 76.2 × 50.8 × 6.35 mm (3″× 2″× 1/4″) and lengths ranging from 250 mm (10″) to 3760 mm (148″) were tested in compression. The ultimate loads were recorded in addition to displacements, twists, and failure modes through the use of strain gauges and an optical tracking system. The material properties were obtained through a series of tensile coupon tests, and the member geometric imperfections were measured through a non-contact 3D laser scanning technique. In addition, residual stress distributions were measured by the sectioning method. The results obtained from this experimental investigation indicated: (1) that torsional buckling is dominant in the shorter lengths and minor-axis flexural buckling in the longer lengths, with a transition occurring gradually in the middle lengths; (2) that the measured material properties are significantly higher than nominal values, and that this had a significant effect on the capacity predicted by the design provisions; (3) flexural buckling design provisions provide a better estimation than flexural–torsional buckling design provisions, although both are conservative.

Delamination imaging in composites using cross-correlation method by non-contact air-coupled Lamb waves

This paper presents a cross-correlation damage detection technique using damage scattered waves of all directions cross-correlate with the incident waves for delamination imaging in carbon fiber reinforced polymer (CFRP) composite plate. The presented imaging can not only detect the delamination but also precisely quantify the damage with locations and sizes. First, a CFRP composite sample with interlaminar delamination by inserting the Teflon layer is designed and manufactured in house using the hot-press machine. And a three-dimensional model of composite sample is simulated using the finite element method. Next, the cross-correlation imaging algorithm is introduced in detail, and the cross-correlation imaging proof-of-concept study is conducted with the simulated Lamb waves in the composite sample. Finally, a fully non-contact air-coupled transducer and scanning laser Doppler vibrometer system with a single-mode Lamb wave method is established to actuate and sense the interrogating Lamb waves in the structure. The imaging method is experimentally implemented for the one delamination and two delaminations imaging and quantification.

Characterization of the Nozzle Ablation Rate Based on 3D Laser Scanning System

The nozzle of solid rocket motor (SRM) is easily ablated by high temperature, high pressure, high speed, and corrosive particles, which affects the stability of rocket flight. Therefore, the measurement and characterization of the nozzle ablation rate are helpful in providing some guidance for the design of nozzle material and structure. However, due to the high surface roughness of the composite nozzle after ablation, it is difficult to obtain an accurate ablation rate by contact measurement methods. The 3D laser scanning system is a 3D non-contact measurement technology using structured light technology, phase measurement technology, and computer vision technology. It has the advantages of non-contact, large scanning size, flexibility, and portability. In this paper, a 3D reconstruction of the ablation nozzle is carried out based on the 3D laser scanning system. Additionally, the ablation rate of the nozzle is measured without cutting the actual specimen. Furthermore, the pressure, temperature, and surface convective heat transfer coefficient trends are numerically calculated and compared with the ablation rate. Additionally, the empirical formula between ablation rate and pressure, temperature, convective heat transfer coefficient is obtained empirically by the inversion analysis method. The empirical formula can provide theoretical guidance for nozzle size design and optimization. The results show that the non-contact 3D laser scanning system is a valuable method for reconstructing the model of the ablated nozzle, and the empirical formula of ablation rate can accurately predict the ablation rate of the nozzle.

REKONSTRUKSI SUDU PRIMARY AIR FAN PLTU MENGGUNAKAN STANDAR NACA

This PA Fan is one of the vital components in the generating system that functions to drain air and carry fuel (coal) from the pulverizer to the boiler burner. The research has a focus on designing methods to reconstruct the blades in order to increase independence to maintain the reliability of turbo engine equipment. Damage to axial turbo engine equipment generally occurs as a defect in the blades. The method of self-constructing blades needs to be carried out to increase the speed of the repair process. The limitation in this study is that the blade airfoil profile is adjusted to the standards of the National Advisory Committee for Aeronautics (NACA). The benefit of the PA Fan blade reconstruction process is to find the technology of the PA Fan blade product and the basic concepts of the product design process as desired by the initial maker (design intent). The research methods used include: Measurement and geometric modeling of the PA Fan blade using the Mitutoyo Cyrsta-Apex S9106 Coordinate Measuring Machine which is connected to a non-contact laser scanner Mitutoyo Surface Measure 606 to obtain a collection of many coordinates of the measurement results (point clouds), then process point clouds processing to obtain a 3D model of the measurement results, after that identify the airfoil with the NACA standard, and the final stage is to process machine drawings of complete components with geometry specifications.

A novel general-purpose three-dimensional continuously scanning laser Doppler vibrometer system for full-field vibration measurement of a structure with a curved surface

Three-dimensional (3D) full-field vibration measurement is significant to structures, especially those with curved surfaces. A triaxial accelerometer and a commercial non-contact 3D scanning laser Doppler vibrometer (SLDV) system are usually used in 3D vibration measurement of a structure. However, the triaxial accelerometer can lead to the mass-loading problem for a light-weight structure, and the 3D SLDV system can take a long time to complete scanning of a structure with a large surface in a step-wise scanning mode. This study proposes a novel general-purpose 3D continuously scanning laser Doppler vibrometer (CSLDV) system to measure 3D full-field vibration of a structure with a curved surface in a non-contact and fast way. The proposed 3D CSLDV system consists of three CSLDVs, a profile scanner, and an external controller, and is experimentally validated by measuring 3D full-field vibration of a turbine blade with a curved surface under sinusoidal excitation and identifying its operating deflection shapes (ODSs). A 3D zig-zag scan path is proposed for scanning the curved surface of the blade based on results from the profile scanner, and scan angles of mirrors in CSLDVs are adjusted based on relations among their laser beams to focus three laser spots at one location, and direct them to continuously and synchronously scan the proposed 3D scan path. A signal processing method that is referred to as the demodulation method is used to identify 3D ODSs of the blade. The first six ODSs from 3D CSLDV measurement have good agreement with those from a commercial 3D SLDV system with modal assurance criterion values larger than 95%. In the experiment, it took the 3D SLDV system about 900 s to scan 85 measurement points, and the 3D CSLDV system 115.5 s to scan 132,000 points, indicating that the 3D CSLDV system proposed in this study is much more efficient than the 3D SLDV system for measuring 3D full-field vibration of a structure with a curved surface.

Modeling Full-Field Transient Flexural Waves on Damaged Plates with Arbitrary Excitations Using Temporal Vibration Characteristics.

We propose an efficient semi-analytical method capable of modeling the propagation of flexural waves on cracked plate structures with any forms of excitations, based on the same group of vibration characteristics and validated by a non-contact scanning Laser Doppler Vibrometer (LDV) system. The proposed modeling method is based on the superposition of the vibrational normal modes of the detected structure, which can be applied to analyze long-time and full-field transient wave propagations. By connecting the vibration-based transient model to a power flow analysis technique, we further analyze the transient waves on a cracked plate subjected to different excitation sources and show the influence of the damage event on the path of the propagating waves. The experimental results indicate that the proposed semi-analytical method can model the flexural waves, and through that, the crack information can be revealed.

Effects of surface treatment and shade on the color, translucency, and surface roughness of high-translucency self-glazed zirconia materials

Statement of problemThe impact of different surface treatments and shades on the color, translucency, and surface roughness of high-translucency self-glazed zirconia materials is unclear. PurposeThe purpose of this in vitro study was to investigate the effects of different external surface treatments (self-glazed, milled, polished, and glazed), intaglio surface treatments (milled and airborne-particle abraded), and shades (A1 and A3 shades) on the color, translucency, and surface roughness of high-translucency self-glazed zirconia materials, as well as the correlations among optical parameters, translucency, and surface roughness. Material and methodsEighty shade A1 and 80 shade A3 disks were fabricated with a thickness of 0.80 ±0.02 mm and divided into 16 groups (n=10). Different external and intaglio surface treatments were applied to the specimens. CIELab values were measured with a spectrophotometer, and color differences (ΔE00) and relative translucency parameter (RTP) were calculated. Total transmittance (Tt%) and reflectance (R%) were tested with a spectrophotometer equipped with an integrating sphere. Surface roughness (Ra and Rz) (μm) was measured with a noncontact 3-dimensional laser scanning microscope. One specimen from each group was subjected to scanning electron microscope (SEM) examination. Data were analyzed with ANOVA and the Tukey post hoc test. The correlation among optical parameters, translucency, and surface roughness was investigated by using Pearson correlation analysis (α=.05). ResultsThe effects of external surface treatments, intaglio airborne-particle abrasion, and shades on ΔE00, RTP, and Ra values of the disks were significantly different (P<.001). The smoothest external polishing surface had the greatest RTP and color difference (P<.001). Shade A3 disks had lower RTP and Tt% values than shade A1 disks (P<.001). ΔE00 had a highly positive relationship with the RTP (A1: r=0.884, P<.001; A3: r=0.859, P<.001). SEM images demonstrated that surface treatments affected the surface texture of monolithic zirconia ceramics. ConclusionsDifferent surface treatments affected the surface roughness, translucency, and final color of zirconia materials. The smoothest external polishing surface had the greatest RTP and color difference. Different shades influenced the translucency, as the darker the disk shade, the lower the translucency. The RTP was appropriate as an auxiliary indicator for evaluating the color of a dental ceramic.

Large-scale additive manufacturing tooling for extrusion-compression molds

Carbon fiber reinforced polymer composites (CFPC) have been used in additive manufacturing (AM) due to both the high-strength-to-weight and superior-stiffness-to-weight ratios. CF AM is being considered for tooling applications. In AM, CFPCs are usually aligned along the deposition direction; however, it results in anisotropic thermal properties which affect the heat transfer and warpage of the final part. In this study, three male molds with different infill patterns were produced via the material extrusion additive manufacturing (EDF-AM) process. These include (a) 0°: infill pattern along the printing direction; (b) 90°: infill pattern perpendicular to the printing direction; and (c) 0°/90°: alternate layers along and perpendicular directions. The effect of the infill pattern on thermal conductivity was analyzed and observed that 0° infill (surface temperature: 79.2°C) had the highest conductivity; and 90° infill (surface temperature: 66.4°C) had the least. In Additive manufacturing, carbon fibers are usually aligned along the deposition direction; however, it results in anisotropic thermal properties which affect the heat transfer and warpage of the final part. In this study, three molds with different infill patterns were produced via the extrusion deposition fabrication-additive manufacturing (EDF-AM) process. These include (a) 0°: infill pattern along the printing direction; (b) 90°: infill pattern perpendicular to the printing direction; and (c) 0°/90°: alternate layers along and perpendicular directions. Mold was used for extrusion compression molding and degradation of the mold was analyzed using non-contact laser scanning device.

A combined global-local approach for delamination assessment of composites using vibrational frequencies and FBGs

In this paper, a combined global-local strategy was developed for structural health monitoring (SHM) of fiber reinforced polymer (FRP) composites to assess the internal delamination damage, which has combined vibrational frequency shifts as the global index and the fiber Bragg grating (FBG) wavelength shifts as the local index. The delamination detection was carried out in two steps. The first step was based on the global damage index, which is the changes in multiple modes of frequencies measured by a non-contact scanning laser Doppler vibrometer (SLDV) system. Machine learning (ML) algorithms including support vector machine (SVM) and extreme learning machine (ELM) algorithms were used to initially predict the delamination interface, location, and size through frequency shifts. Numerical and experimental verification results show that SVM has a higher prediction accuracy than ELM when only a small number of samples exist, and the classification of SVM is better than its regression function to be used in the prediction of discrete delamination interfaces. To verify the damaged area predicted by frequency changes and further update the delamination edges with better accuracy, the second step has taken the changes in the wavelength of multiple FBG sensors as the local damage index. Multistage loads were applied at equidistant positions of the FRP specimens to induce deformations and the wavelength shifts in FBGs were used to determine the boundary of delamination. The results showed that delamination in FRP composites can be assessed more precisely using the global-local two-step SHM strategy, which can compensate for the shortcomings of only using vibration-based or FBG-based monitoring techniques. Besides, the SVM algorithm showed excellent predictive performance in both steps and had great potential in delamination damage monitoring.

Evaluation of Maraging Steel Produced Using Hybrid Additive/Subtractive Manufacturing

Hybrid manufacturing is often used to describe a combination of additive and subtractive processes in the same build envelope. In this research study, hybrid manufacturing of 18Ni-300 maraging steel was investigated using a Matsuura LUMEX Avance-25 system that integrates metal additive manufacturing using laser powder bed fusion (LPBF) processing with high-speed machining. A series of benchmarking coupons were additively printed at four different power levels (160 W, 240 W, 320 W, 380 W) and with the integration of sequential machining passes after every 10 deposited layers, as well as final finishing of selected surfaces. Using non-contact three-dimensional laser scanning, inspection of the final geometry of the 18Ni-300 maraging steel coupons against the computer-aided design (CAD) model indicated the good capability of the Matsuura LUMEX Avance-25 system for net-shape manufacturing. Linear and areal roughness measurements of the surfaces showed average Ra/Sa values of 8.02–14.64 µm for the as-printed walls versus 0.32–0.80 µm for the machined walls/faces. Using Archimedes and helium (He) gas pycnometry methods, the part density was measured to be lowest for coupons produced at 160 W (relative density of 93.3–98.5%) relative to those at high power levels of 240 W to 380 W (relative density of 99.0–99.8%). This finding agreed well with the results of the porosity size distribution determined through X-ray micro-computed tomography (µCT). Evaluation of the static tensile properties indicated that the coupons manufactured at the lowest power of 160 W were ~30% lower in strength, 24% lower in stiffness, and more than 80% lower in ductility relative to higher power conditions (240 W to 380 W) due to the lower density at 160 W.

Review Article Recent Advances in Preventing Dental Erosion

Dental erosion is defined as an irreversible loss of dental hard tissue due to exposure to chelating agents or non-bacterial acids. The occurrence of this condition was noted and the incidence and prevalence of dental erosion has been increasingly documented.The Ant erosive agents such as Anacardic acid in which the key component is the cashewnut shell liquid is phenolic lipids. It is a mixture of molecules which are saturated and unsaturated. It is also considered to have an anti-microbial effect and has been studied for the treatment of cancer, oxidative damage, inflammation and obesity disorders. Other anti-erosive agent like Fluoride helps in tooth remineralization. Fluorapatite, rather than hydroxyapatite, forms during the process of remineralization when fluoride is found in oral fluids. In apatite crystal lattice formation, fluoride ions replace hydroxy ions. Fluorapatite, even under acidic conditions, is less soluble than hydroxyapatite, which helps to regenerate tooth enamel. Fluoride is therefore a stronger anti-erosive agent. Various Recent advances in anti-erosive agents are Calcium and phosphate, Casein phosphopeptide amorphous calcium phosphate (CPP-ACP), Protease inhibitors, Oils, Chitosan chitosan and Multivalent metal ions Various techniques to evaluate dental erosion are in vitro techniques and in vivo techniques. In vitro techniques are Scanning electron microscope, Surface Profilometry, Polarized Light Microscopyand Non-Contact Confocal Laser Scanning Microscopy (CLSM). And iv vivo techniques are Photographs Clinical review and indices. The most important point of treatment is identifying and removing the erosion factor, above all current materials and methods. Therefore, early identification of the lesions, evaluation and removal of the etiological variables are relevant topics.

Online detection of part size based on laser contour scanner

In aerospace die manufacturing, the processing quality of the processed workpiece is an important guarantee for the quality of the final product. Traditional detection methods have high labor intensity and low efficiency. Visual detection can only detect width, not depth information. Based on this, this paper proposes a non-contact laser scanning point cloud processing quality online detection method, through the laser contour scanner to obtain the actual machining parts of the surface point cloud information, and then in the Geomagic Control environment of the actual manufacturing parts point cloud information and Solid Works theoretical design model comparison analysis. Thus, the manufacturing error of the actual manufacturing parts can be obtained, which provides a fast and accurate judgment method for the quality control of the product manufacturing.

Experimental and numerical study of high-order complex curvature mode shape and mode coupling on a three-bladed wind turbine assembly

Experimental and numerical modal analysis on wind turbine blades has been previously studied, considering mainly low order bending modes. However, high-order modes are also critical modes for understanding blade dynamics. The mode coupling is essential because a better understanding of the high-frequency blade dynamics can support advances in model validation, blade aeroelastic simulations, blade design, and structural health monitoring. However, these high-order modes and the associated mode couplings of wind turbine blades have not been studied. This work presents a comprehensive experimental and numerical study based on three modal tests and a correlated finite element simulation to study the complex curvature mode shapes and mode coupling dynamics for a three-bladed wind turbine assembly. Three tests are conducted: Test 1, ten accelerometers are deployed on the whole assembly under impact excitation; Test 2, nine accelerometers are deployed on a single blade under impact excitation; and Test 3, a non-contact 3D Scanning Laser Doppler Vibrometer (SLDV) test is performed on a single blade under shaker excitation. This is the first work to use a 3D SLDV for an experimental modal test on the wind turbine blade. With 300–400 points measured with the 3D SLDV, experimental mode shapes having a high spatial resolution with 3D response are used to characterize the coupling for the low-order and high-order modes with complex curvatures. A reliable finite element model of the three-bladed assembly, including the composite blade modeling, is also developed and is well correlated with Test 2 and Test 3. With the high-fidelity 3D SLDV test and well-correlated finite element model, this is also the first work of using experimental and numerical approaches to investigate the high-order mode shape with complex curvatures and mode coupling of bending and torsional behavior that is present in the wind turbine blade for these high-order modes.

Forensic Recreation and Visual Representation of Greek Orthodox Church Saint Eftychios of Crete.

Facial reconstruction is employed in medical science and archaeology. Though quite popular as anthropological method, it has not so far been used in the orthodox ecclesiastical tradition. This work presents the facial reconstruction of St Eftychios of Crete, who lived between the ninth and tenth centuries. Computed tomography and reverse engineering methods were employed to complete the task. Reconstruction of the mandible and the missing left zygomatic arch was implemented following the Sassouni method. The American method was followed for the soft tissues, with clay deposition of appropriate thickness, on the surface of the skull model. The eyes, nose, and lips were added based on the dimensions of the underlying bone structures. Long hair and beard were added, according to the classic Byzantine tradition pattern of the time period. The final bust developed was then digitized, using a 3D non-contact laser scanner. The 3D geometry produced was employed to produce a mold with vacuum casting techniques. This mold provides the ability to produce copies of the bust, if needed. At the same time, a realistic 3D representation of the Saint's bust was developed, with the aid of special software, in order to compare the traditional forensic reconstruction to the pure digital one. This work is the first case of a Saint's facial reconstruction in the Orthodox Church. The facial reconstruction process, with all the limitations considered, offers the ability to present a realistic aspect of a Greek Orthodox Church Saint, in a form that is easily accessible. Both physical and digital facial reconstruction processes were based on scientific data, so they were as accurate as possible, considering that the mandible was missing in the skull. The facial reconstruction was entirely implemented in Greece creating the basis for similar work in the future. The final bust developed was donated to the Odigitria Monastery, to be exhibited to its visitors.

Dispersion curve regression – assisted wideband local wavenumber analysis for characterizing three-dimensional (3D) profile of hidden corrosion damage

Corrosion as common damage in civil, petrochemical, nuclear, and aerospace structures affects the integrity and safety of the structures and may lead to catastrophic failures. This paper presents dispersion curve regression-assisted local wavenumber analysis method, which can analyze the time–space wavefield containing wideband information of wave-damage interaction and further extract the structural information carried by such wavefield for characterizing hidden corrosion damage in an isotropic plate. To acquire the time–space wavefield, a noncontact scanning laser Doppler vibrometer is used. In our analysis method, the acquired time–space wavefield is firstly processed to generate a local wavenumber function. The derived wavenumber function is further analyzed with a dispersion curve regression step, which searches in a set of theoretical frequency-wavenumber dispersion curves for different plate thicknesses and identifies the optimal plate thickness whose theoretical curve best matches the frequency-wavenumber relation contained in the local wavenumber function. By this means, a 3D profile including both in plane and thickness dimensions of the structure can be constructed for corrosion visualization and quantification. The experimental study demonstrates that our method can quantify the profile of hidden uniform corrosion in metal plates in terms of its in-plane shape and size as well as its out-of-plane depth in the subwavelength scale. Moreover, compared to previous Lamb wave-based corrosion inspection methods, our technique allows for noncontact 3D characterization of hidden corrosion from a far distance to the structure. We believe this work will inspire new 3D damage quantification methods that are based on wavefield analysis as well as enable potential applications for the quantification of hidden corrosion in civil, petrochemical, nuclear, and aerospace structures.

Non-destructive Consolidation Assessment of Historical Camorcanna Ceilings by Scanning Laser Doppler Vibrometry

This paper presents a procedure for the evaluation of the conservation state and restoration efficiency of nineteenth century camorcanna vaults based on the analysis of objective features extrapolated from non-destructive vibration testing data. The camorcanna vault in “Salone Grande” of the ninteenth century Villa Greppi in Monticello Brianza, near Milan, Italy, was chosen as an application example. Non-contact scanning Laser Doppler Vibrometry was exploited for the evaluation of the dynamic behaviour of the vault before and after rehabilitation. In the first section, the frescoed structure in question, a reed ceiling spread with mortar, is described and possible related aging problems, e.g painting detachment, are highlighted. In Sects. 1 and 2, traditional and innovative non-invasive diagnostic techniques are illustrated, with particular attention to Laser Doppler Vibrometry. In Sect.3, the case study of Villa Greppi is illustrated, reporting on the restoration intervention, the equipment used on site and how the measurements were taken. While in Sect.4 the results are shown, objective feature indices are defined and conclusions are drawn.