In structural dynamics a structure’s dynamic properties are often determined from its frequency-response functions (FRFs). Commonly, FRFs are determined by measuring a structure’s response while it is subjected to controlled excitation. Impact excitation performed by hand is a popular way to perform this step, as it enables rapid FRF acquisition for each individual excitation location. On the other hand, the precise location of impacts performed by hand is difficult to estimate and relies mainly on the experimentalist’s skills. Furthermore, deviations in the impact’s location and direction affect the FRFs across the entire frequency range. This paper proposes the use of ArUco markers for an impact-pose estimation for the use in FRF acquisition campaign. The approach relies on two dodecahedrons with markers on each face, one mounted on the impact hammer and another at a known location on the structure. An experimental setup with an analog trigger is suggested, recording an image at the exact time of the impact. A camera with a fixed aperture is used to capture the images, from which the impact pose is estimated in the structure’s coordinate system. Finally, a procedure to compensate for the location error is presented. This relies on the linear dependency of the FRFs in relation to the impact offset.

Usually, only one surface or one side of 3D structures is measured in Scanning Laser Doppler Vibrometer (SLDV) tests due to test setup and instrumentation limitations. However, in this work, we demonstrate an approach to overcome these limitations while also using an SLDV that provides high spatial resolution measurement. In the case of a wind turbine blade, only one surface is typically measured. In most scenarios, only focusing on one surface of the blade is sufficient to characterize the dynamics of the global blade modes. However, as we show measurement of both surfaces offers valuable insights to explore both the global blade modes and the relative motions of the two surfaces of the blade. This work proposes and applies a new method of experimental modal testing on both surfaces of the wind turbine blade using a high spatial resolution 3D SLDV. The two surfaces of the wind turbine blade are scanned by the 3D SLDV respectively under the same global test coordinate system defined by several alignment objects. Then the two surfaces are stitched together to build the blade mode shapes of both surfaces. In the current testing, a total of over 1,500 points (4,500 response degrees of freedom for the 3D measurement) are scanned from both surfaces of the blade in a non-contact fashion to obtain the flap-wise, edge-wise, and torsional mode shapes of the blade. The orthogonality of the measured mode shapes, either one surface or both surfaces, is validated by the correlation tool, Modal Assurance Criterion (MAC). The effectiveness of the two-surface measurement is demonstrated by comparing the drive point Frequency Response Function and by correlating the mode shapes from the two surfaces. With the high spatial resolution 3D SLDV measurement, local panel modes of the wind turbine blade are observed from the mode shapes. Especially the panel breathing mode can only be revealed due to the two-surface measurement. This work also provides a useful reference for the wind turbine blade designers and researchers for design, structural analysis, and reliability study on the wind turbine blade. The two-surface measurement technique proposed in this work is demonstrated on a wind turbine blade, and it will also be applicable for other types of two-surface shell-type structures.

As a maraging steel, Corrax, is used in many engineering applications in the manufacturing, aerospace, and medical industries thanks to its properties such as high strength, hardness and corrosion resistance. However, these high specifications can cause some issues for manufacturing operations such as forging, machining, grinding. In addition to that, using heat treatment applications changes materials' mechanical specifications, affecting the material's behavior during machining. Therefore, it is important to characterize the influences of different heat treatment conditions on the material's property and behavior. In this study, the effects of heat treatment process on the mechanical properties, drilling machinability and corrosion resistance of Corrax steel were experimentally investigated with the samples of solution heat treated and aged at 400 °C, 525 °C, 600 °C, and 700 °C. The machinability was evaluated based on thrust force, chip morphology, hole quality, and tool wear. The results showed that the thrust force, torque and hole quality depend on feed rate, cutting speed, and mechanical properties affected by aging treatment. The highest hardness (47.4 HRC), ultimate tensile strength (1720 MPa), maximum elongation (33%), and toughness (198 jm-3) were obtained for the sample which aged at 525 °C for four hours, consequently the highest cutting force and surface roughness results were measured for this sample. Better hole surface quality and less burr formation were observed in the samples aged at 600 °C and 700 °C, and not-aged. On the other hand, while the highest value of corrosion potential were measured in the sample aged at 400 °C, the lowest corrosion potential value were measured in the sample aged at 700 °C.Graphical abstract

This paper proposes a solution to the need for appropriate methods to control the health of the final product which is among the challenges of applying three-dimensional (3D) printers in mass production. Sheared laser interferometry so-called shearography is considered a proper option for this aim. The main objective of this paper is to inspect defective 3D-printed polymer parts. In addition, this study explores the influence of the infill percentage of the samples on the defect detectability as well as the shearography setup parameters. To this aim, three samples of Polylactic-acid (PLA) with different infill percentages were printed by the fused deposition modeling (FDM) method. Burnt filament defects were deliberately created inside the samples during printing. Shearography tests were carried out applying thermal excitation. Based on the results, the infill percentage directly affects the defect detectability as well as the shearography parameters. Accordingly, an increase in infill percentage enhanced the quality of shearography resultant fringe patterns. Additionally, it significantly leads to an increase in the detectable range of loading size and shear distance. Therefore, shearography was regarded as appropriate for detecting burnt filament defects, especially in high infill percentages.

This study investigated the influence of the number of nucleation sites on the evolution of the dissolved CO2 concentration of beer contained in an etched glass comprising 0 to 70 etchings. Four identically shaped glasses were studied, three etched and one non-etched. We followed the temporal evolution of the liquid (i.e., beer) and gaseous (i.e., CO2) phases of the beer for each of them. The gaseous phase is monitored by measuring the evolution of the dissolved CO2 concentration in the beer once poured into the glass. Particle image velocimetry (PIV) techniques are used to quantify the mixing dynamics of the beer during the tasting. The results show that the CO2 concentration decreases approximately 3.7 times faster in the glass with 70 etchings than in the unetched glass. This study suggests a close link between the number of nucleation sites and the release of dissolved CO2 by different mechanisms: bubble bursting, molecular diffusion, and mass convection-diffusion, the latter being increased by liquid mixing mechanisms. On the one hand, too many bubbles will bother the consumer by causing a chemical sting and will quickly deplete the beer in dissolved gas. On the other hand, too few bubbles will not allow conveying the aromas to the surface and the consumer will judge the beer as too bland and not visually flattering, hence the need to find a compromise.

Composite sandwich structures are widely used for their mechanical properties combined to lightweight. However, damage area quantification caused by low velocity impacts represents generally a crucial task in sandwich composites. In the last years, recent advantages of thermographic devices offer new promising and different real-time industrial and engineering applications where lower computation time, accuracy of results and convenient cost are required. The present research deals with the comparison of standard or latest image-processing methods proposed for pulsed thermography regarding their suitability for determining the impact damage area in sandwich materials made of Aluminium core an a GFRP laminated skins. The Infra-Red processed results are compared with the advanced ultrasonic Phased array method commonly employed in the industrial Non-Destructive Testing. Specifically, the damage area quantification is performed by means of an appropriate MATLAB binarization algorithm for the post-processing of acquired thermal and ultrasonic maps. The data results verify the effectiveness of the image-processing thermographic technique combined to advanced processing approaches for the quantitative assessment of impact damage in sandwich component.

The proper representation of friction contact conditions between each wheel and the rail is necessary to accurately model the behaviour of a heavy haul locomotive since friction conditions at the wheel-rail interface affect the locomotive’s dynamic performance under traction and braking conditions. In normal operations, a phenomenon commonly known as rail cleaning effect occurs. The rail cleaning effect causes increased friction coefficients between the following wheel treads and the rail head. The wheel-rail interaction causes the third body layer to be partly or wholly eliminated from the surfaces in contact and generates new layer. An experimental analysis of the changes in friction coefficients under simulated locomotive wheel-rail contact conditions, in terms of contact pressure and slip, is presented in this paper. For this study, data processing equations are presented to obtain the experimental traction coefficient and slip. Furthermore, the rail cleaning effect is examined under different slip conditions. The experiment shows the traction coefficient increases for a given number of cycles until reaching a steady value, demonstrating that the rail cleaning effect is measurable in various slip conditions on a twin disc machine.

In this work, an off-axis 2D Particle Image Velocimetry system is used to obtain the 3D flow field at the outlet of a tubular reactor equipped with Kenics static mixers. The 3D flow fields are obtained exploiting the out-of-plane velocity component and considering the symmetrical features of the flow generated by the static mixers. The raw results show that the velocity vectors, measured on a cross section perpendicular to the tube axis by 2D-PIV with the camera located at 24° from the measurement plane, are affected by the axial component of the flow. However, taking into account the symmetry of the flow field with respect to the tubular reactor axis and evaluating the effect of the out of plane velocity component, the correct 2D velocity vectors on the plane and also the velocity component in the axial direction can be calculated from the raw 2D PIV data. The consistency of the methodology is demonstrated by comparison of the results with the flow field measured in a smaller tubular reactor of similar geometry and Reynolds number with a symmetrical 2D-PIV system, with the camera located perpendicularly to the laser plane. Then, the 3D features of the flow are analyzed to characterize the effects of the different combinations of static mixer configurations on the fluid dynamics of the system in turbulent conditions. The results show that, as the pressure drop increases, a more uniform velocity distribution is achieved.Graphical Abstract

There is a gap between mechanical measurement methods under laboratory conditions and those under real conditions of structural monitoring. This paper proposes a method that applies well-established computer vision developments to photomechanics in difficult conditions. It is therefore a technique that is flexible and versatile while maintaining satisfying accuracy. It consists in marker tracking using ArUco fiducial markers as measurement points. It allows locating markers in non-optimal conditions of camera orientation and position. A homography process was used to analyse pictures taken with a view angle. The accuracy of the method was estimated, especially in case of out-of-plane motions, and the impact of the view angle and of the distance between camera and markers on the location error was studied. The method was applied in creep tests to measure crack parameters as well as the transverse expansion of wooden beams. In the application example presented, it enabled to compute distances between markers with only 0.28% of relative error and hence to measure the crack parameters and the long-term shrinkage-swelling of the wooden beams. However, the impacts of brightness variations and camera parameters have not been estimated. This method is very promising when experimental conditions are variable and when multiple measurements are necessary.

In real collision conditions, axial crushing rarely occurs. Generally, lateral collapse occurs in thin-walled beams under collision conditions. The bending displacement of thin-walled beams is one of the most important deformation mechanisms to dissipate the kinetic energy generated by the collision. Bending displacement deformation occurs in pure bending and three-point bending modes. However, pure bending is rarely encountered in real collision events. The three-point bending analysis is more complex as it involves variable bending moment and shear forces at different cross-sections. In this study, it is aimed to investigate the behavior of thin-walled s235 structural steel under three-point bending in three different section geometries as square, rectangular and, tube. Experiments were performed using three different punch geometries and three different span distances for each section. It is concluded that the influence of section geometries of thin-walled structures, span distance, and punch radius has a significant effect on the deformation pattern and force/bending moment response of thin-walled structures.

A camera exposure time control method that can automatically determine the optimal camera exposure time has been proposed for high-quality digital image correlation (DIC) measurement recently. However, due to the relatively long optimization time required by the adaptive algorithm, this method cannot rapidly find the optimal exposure time during certain high-temperature tests. To improve the efficiency of the camera exposure time control method, we adopted a more efficient adaptive exposure (AE) algorithm and compared its performance with the existing method. The previously used false-position algorithm and the improved average grayscale algorithm are first compared in a static test with changing ambient light. Results reveal that the improved average grayscale algorithm is more efficient in recording high-quality images, thus is recommended for the real high-temperature DIC measurement. The rapid adaptive optimal exposure time control method was then applied at the mid-test of the practical high-temperature DIC measurement to examine the effectiveness of the proposed method. Compared to the conventional fixed exposure mode, the rapid adaptive exposure time control method will enhance the robustness of the DIC system against the changing thermal radiation.

The interaction integral is commonly utilized in numerical methods for evaluating the fracture parameter—stress intensity factor—and it can also be used in experiments. The purpose of this paper is to examine the effect of mesh density on the accuracy and convergence of the stress intensity factors evaluated in experiments using the interaction integral. The interaction integral is applied to the numerical displacement fields obtained by ABAQUS, and then the experimental displacement fields measured by digital image correlation are used to investigate the influence of mesh density on the stress intensity factor. The stress intensity factors estimated using the numerical displacement field and the experimental displacement field were compared at four mesh densities. The numerical results indicate that the higher the mesh density, the more accurate the stress intensity factor. However, there is a discrepancy between the experimental and numerical displacement fields. When using the interaction integration method to evaluate the stress intensity factor in experiments, too high a mesh density will reduce the accuracy and convergence of the stress intensity factor. This paper can provide a basic understanding for evaluating stress intensity factors using the interaction integral in experiments.

Compacted specimens prepared from four clayey soils were subjected to drying in order to monitor the volumetric shrinkage period. Specimen volumes were recorded with manual caliper readings and the proposed image-based method as the shrinkage continues. For the image-based method, a photogrammetry technique known as Structure from Motion was applied. This technique offers a complete three-dimensional solid model of objects from two dimensional images. In this technique, the object is photographed from different perspectives to construct a digital point cloud. Once a proper calibration is made, these points represent the real-world coordinates and comprehensive analyses can be made using surface data. To that end, an imaging setup was established and a parametric study was conducted on a solid calibration object for the accuracy assessment of the method. The volumes of the compacted specimens obtained with the image-based technique and conventional Vernier caliper readings were compared to each other and evaluations were made by means of volumetric strain graphs and soil shrinkage curves. The proposed shrinkage monitoring technique offered accurate, nondestructive and operator independent results.

Fundamental lateral mode frequency of a spacecraft is determined experimentally by performing a base excited vibration testing. For the above vibration testing, the spacecraft is mounted on the slip table of the shaker system. It is shown in this work that even if the test fixture is quite stiff, the fundamental lateral mode of the spacecraft can be influenced by the slip table system. The frequency obtained in the test is lower than the base fixed frequency. In this mode, even though the test fixture does not undergo bending, the slip table undergoes bending resulting in rotation of the test fixture. The stiffness of the bearing and the bending stiffness of the slip table are the causes of reduction in stiffness. A mathematical model that represents this behavior is developed for two typical shaker-slip table systems, one having a capacity of about 150 kN force and the other about 300 kN force. It is seen that the test system can cause a drop of about 3 Hz for a 3000 kg class of spacecraft, while using 150 kN shaker system. This is quite significant as their frequencies are in the range of 12–15 Hz.

Storage tanks are placed in group arrangements in refinery plants. Furthermore, winds may be treated as a critical lateral load for such structures. The present study explores the effects of storage tank adjacency on wind pressure variations. The wind tunnel test was employed to obtain the wind pressure coefficients on corrugated-plate tanks with rise-to-span ratios of 0.25, 0.5, 1.0, and 1.5. These coefficients were also calculated numerically through a computational fluid dynamics (CFD) approach and compared to the experimental data. To evaluate the adjacency effect, two adjacent tanks in the transverse and longitudinal directions and the base tank with longitudinal and transverse adjacency were studied. The wind pressure coefficients were compared to the non-adjacency scenario. It was found that the adjacency effect was below 10% in transverse and longitudinal adjacency scenarios at distances three and four times as large as the diameter, respectively. The corrugated-plate tanks were found to have smaller negative (suction) pressure coefficients than simple-plate ones.

In this research, to investigate the impact of the guide vanes on the flow analysis in the axial pump, unsteady numerical turbulence field simulations with and without guide vanes are simulated using the model of standard κ–ε turbulence with the technique of sliding mesh (SM). The numerical results are firstly validated and compared with experimental outcomes. Different detailed information data regarding flow analysis, for instance, static, dynamic, total pressures, turbulent kinetic energy, shear stress, and velocity magnitude are qualitatively analysed. Then pressure at varying regions in the pump is qualitatively investigated under different operating conditions. The results have shown that the flow field and performance of the pump are highly affected by adding the guide vane to the axial impeller. The impeller with guide vane can lead to enhance the pump performance. Moreover, results show that the pressure, kinetic energy, shear stress, and velocity are increased by adding a guide vane to the axial impeller. This study will provide good information and guidance to enhance and improve the axial flow pump design operation.

The paper presents the design, fabrication, and experimental validation of a new non-contact resonance-based measurement system to measure the thickness of ferromagnetic sheets and their alloys. The measurement system consists of a cantilever beam as a resonating structure with electromagnetic excitation and piezoelectric detection. The system measures the unknown thickness of a ferromagnetic sheet by measuring the resonance frequency of the cantilever beam resonator. The resonator vibrates at different resonance frequencies depending on the thickness of the ferromagnetic sheet. The electromagnet and the piezoelectric patch are connected with appropriate electronic circuitry for resonance excitation and detection of the resonator. The electronic circuitry will automatically track the resonance frequency of the measurement system for a variation in the ferromagnetic sheet thickness. A complete analytical model of the measurement system was developed and evaluated through experimentation. The analytical and experimental results are found to be in good agreement. The proposed measurement system is simple in design, compact, low cost, and its frequency output decrease linearly with an increase in thickness of the ferromagnetic sheets.

Machining of complex components with high added value requires the development and implementation of technologies for monitoring the processes outputs and to ensure the performance and reliability of the manufactured part. Cutting tool wear is one of the most relevant variables in machining due to its effect on both the machining cost and quality of the manufactured component. Although tool wear has been extensively investigated for more than a century, the advent of Industry 4.0 has required more accurate and reliable monitoring systems. This work investigates the feasibility of using a low-cost vibration sensor, based on a micro-electromechanical system (MEMS), connected to a wireless data transmission system attached to a rotary tool (milling cutter) for tool wear monitoring when milling annealed AISI H13 hot work die with coated tungsten carbide inserts. A microcontroller with an integrated internet connection connected to a local server through the Wi-Fi network was employed. In order to validate the proposed system, tests were performed comparing its behavior with a conventional piezoelectric sensor in terms of sensitivity to changes in the cutting conditions and tool wear evolution. The results indicated that the proposed system responds satisfactorily to changes in the cutting conditions, with approximately a four-fold increase in the acceleration amplitude when either cutting speed or axial depth of cut were doubled. Although neither the MEMS nor the piezoelectric accelerometer was capable to detect tool wear evolution (considering a tool life criterion VBB = 0.3 mm), the RMS value of the signal generated by the vibration sensor based on MEMS is approximately four times higher than that provided by the piezoelectric accelerometer, thus indicating a better representation of the vibration phenomenon resulting from fixing the MEMS on the tool (in contrast to the piezoelectric accelerometer attached to the workpiece).