Experimental Study on the Effect of Medium in Optical Path on Digital Image Correlation Measurement

To study the influence of glass spacing on digital image correlation measurement in the optical path, an experimental method of displacement stepping for digital image correlation measurement was designed under nine working conditions (without glass, single glass, and double glass with different spacings of 20 mm, 70 mm, 120 mm, 170 mm, 220 mm, 270 mm, 320 mm respectively). The results of digital image correlation method and dial gauge method were compared, and the measurement error and standard deviation of digital image correlation measurement under different working conditions were analyzed. The experimental results show that the variation trend of displacement measured by DIC under nine working conditions is consistent with the step change of the specimen displacement, but there exist obvious errors between the nine conditions. Based on the results of dial gauge measurement, DIC measurement results are larger, and the maximum deviation is less than 3 μm. Under the condition of without glass, the relative error of displacement measured by DIC was the smallest, with an average error of 2.92%. Under the condition of double glass spacing of 170 mm, the relative error was the largest, with an average error of 11.37%. The standard deviation of double glass condition with a certain spacing was less than that of single glass condition. In general, when the double glass spacing is within a certain range, the measurement results are more accurate and less discrete than those of single glass, and the thermal protection performance is also better.

The use of 2D ultrasound elastography for measuring tendon motion and strain

Flange bulging test of zinc alloy: comparison of analyses with analytical models and with stereo-correlation technique

Comparison of specimen-specific vertebral body finite element models with experimental digital image correlation measurements

Applying a homogeneous pressure distribution to the upper vertebral endplate: Validation of a new loading system, pilot application to human vertebral bodies, and finite element predictions of DIC measured displacements and strains

In this study, carbon epoxy cruciform type specimens with a cross‐ply layup were biaxially and uniaxially in‐plane loaded using four independent servo‐hydraulic actuators. Four different biaxial loading ratios were investigated when the applied load was quasi‐static. A comparison between experimental observations (for the damage and strain evolution of the biaxially loaded central section of the specimen) coming from digital image correlation measurements and a 3D finite element damage model will be shown. The symmetry and the uniformity of the strain field on the biaxially loaded zone were by the use of digital image correlation measurements investigated. Furthermore, the failure loads coming from the load cells of the machine were straightforward compared with the output of the finite element damage model. POLYM. COMPOS., 31:1554–1561, 2010. © 2009 Society of Plastics Engineers

High-speed digital image correlation is a camera-based displacement measurement technique that has experienced increasing popularity for modal analysis. It is due to a high spatial density of measurement that provides an outstanding interpretation of mode shapes or operational deflection shapes. However, its sensitivity is typically lower than other techniques and transducers such as accelerometers or laser vibrometry. With these measurements, the estimation of any transfer function in the frequency domain is noisier in valley regions of the response, including anti-resonances. Therefore, an accurate analytical model of the response should be used for modal identification. Modal analysis algorithms perform an identification of the modal parameters and a reconstruction of the response based on the transfer function between force excitation and displacement response. This is called the frequency response function. However, force measurements are not available in many experiments, where the motion excitation is recorded instead. This is the case when the vibration is applied to the specimen through a motion in its base. This transfer function, also known as the transmissibility function, relates the motion of excitation and response, whose shape differs from the frequency response function. This difference in the response function is relevant in a relatively noisy measurement like using digital image correlation. Hence, in this work, a transformation of the transmissibility function into equivalent frequency response function, based on theoretical models, is performed prior to modal identification in base motion tests. More suitable experimental response functions are obtained, increasing the accurateness of the modal parameter estimation.KeywordsModal analysisTransmissibility functionsFull-field measurement

How heterogeneous microstructure determines mechanical behavior of laser powder bed fusion AlSi10Mg

This report describes the use of three-dimensional (3D) digital image correlation to mea sure the shape, displacement, and in-plane strain fields, during testing of gusset plate struc tural connections.Twelve full-scale bridge gusset plate connections of various geometries and boundary conditions were tested at the the Federal Highway Administration (FHWA) Turner-Fairbank Highway Research Center (Ocel et al., 2012).These experiments are part of the ver ification of numerical models as part of the National Cooperative Highway Research Program (NCHRP) Project 12-84 "Guidelines for the Load and Resistance Factor Design and Rating of Riveted and Bolted Gusset Plate Connections for Steel Bridges".The measurements described here are in regards to the tests performed to failure (i.e., maximum load carrying capacity of the connection).During each of the twelve tests to failure, a series (typically about 150) of image pairs were taken for subsequent digital image correlation analysis.Although all of the image pairs were processed, only a very small portion of the results are explicitly presented here.General access to the overall data set will be given to other researchers.Overall, the measurements showed reasonable uncertainties on the order of ± 175 µm/m of maximum inplane shear strain, and the measured out of plane initial shapes of the plates typically matched qualitative inspections of the connections.In this report, the layout, calibration, and measurement procedure associated with the dig ital image correlation system are described in detail to aid in understanding of the results.The results shown here include a sample of the measured and derived variables for one experiment at two conditions, to inform the reader of the type of data that is available.The results also include an abbreviated set of results that show the evolution of the out of plane shape and max imum shear strain field at four points in loading from the initial condition to failure.These are very useful in visualizing the mechanisms (buckling and/or shear failure of the plate) that lead to eventual failure of the connection.The evolution of strain bands of maximum in-plane shear is seen quite clearly in many of the plates.These localized bands of deformation frequently extended from the bolt lines of one member to another member through the large open areas of the plate.Comparison between all of the plates at failure, in terms of the maximum in-plane strain fields, is also presented.This comparison helps delineate plates that failed after signif icant shearing versus the ones that failed with minimal or no shearing.The comparison also shows very clearly the effect of reduced thickness, which was used as an analog to section loss due to corrosion.

The ability to measure strains quasi‐continuously with high spatial resolution makes distributed fiber optic sensing a promising technology for structural health monitoring as it allows to locate and measure damages in concrete structures, such as cracks. Depending on whether the distributed fiber optic sensor (DFOS) is embedded into the concrete matrix or bonded to the reinforcement, different approaches for crack width calculation exist. The high spatial resolution of DFOS quickly leads to a large amount of data, especially with time continuous monitoring. Scalable, automated analysis approaches are required to handle such big data and to derive a gain in knowledge from the measurements. Thus, in a first step, the Python framework fosanalysis is presented and made available to other researchers or monitoring specialists as free software. The most important input parameters for crack width calculation are discussed for concrete strain and steel strain DFOS. Accurate crack monitoring for a 4 m long reinforced concrete beam is demonstrated by using fosanalysis. The calculated crack widths are in good agreement with digital image correlation measurements.

Local stress/strain field analysis of die-casting Al alloys via 3D model simulation with realistic defect distribution and RVE modelling

Prediction of macro-mechanical properties of 3D braided composites based on fiber embedded matrix method

Wire arc additive manufacturing (WAAM) is a method of metal three-dimensional (3D) printing that has the potential for a significant impact on the construction industry due to its ability to produce large parts with reasonable printing times and costs. However, there is currently a lack of fundamental data on the performance of structural elements produced using this method of manufacturing. Seeking to bridge this gap, the compressive behavior and resistance of WAAM square hollow sections (SHS) are investigated in this paper. In a previous study by the authors, testing reported of sheet material produced in the same manner as the studied SHS is first summarized. The production, measurement, and testing of a series of stainless steel SHS stub columns are then described. Regular cross-section profiles were chosen to isolate the influence of 3D printing and enable direct comparisons to be made against equivalent sections produced using traditional methods of manufacturing. A range of cross-section sizes and thicknesses were considered to achieve variations in the local cross-sectional slenderness of the tested specimens, allowing the influence of local buckling to be assessed. Repeat tests enabled the variability in response between specimens to be evaluated; a total of 14 SHS stub columns of seven different local slendernesses was tested, covering all cross-section classes of AISC 370 and Eurocode 3. Advanced noncontact measurement techniques were employed to determine the as-built geometric properties, while digital image correlation measurements were used to provide detailed insight into the deformation characteristics of the test specimens. Owing to the higher geometric variability of WAAM relative to conventional forming processes, the tested 3D printed stub columns were found to exhibit more variable capacities between repeat specimens than is generally displayed by stainless steel SHS. Comparisons of the stub column test results with existing structural design rules highlight the need to allow for the weakening effect of the geometric undulations that are inherent to the WAAM process in order to achieve safe-sided strength predictions.

Cracks generated by a wire electric discharge machining on compact tension specimens are first repaired by high powered laser beam with different weight fractions of nano‐WC added at the crack tip. Digital image correlation method combined with J‐integral theory is used to measure and calculate J‐integrals of the repaired specimens. Fracture properties of the repaired specimens are compared and studied. The residual stress of specimens after being repaired by laser was also studied to analyze the feasibility of J‐integral to evaluate the fracture properties of the repaired parts. It is found that the influence of residual stress can be neglected when calculating J‐integral in a certain region in case of when the residual stress is small. The J‐integral obtained by the digital image correlation measurement is accurate and can effectively evaluate repairing effects. The paper provides guidance for laser repaired cracks with nanomaterial addition and an effective method for the evaluation of repairing effect.

Deformation during the flapping cycle can be used as a determinant of hover-mode performance. The wing used here is a small hummingbird sized wing constructed from carbon fiber and machined acetal plastic. Digital image correlation measurements while the wing was flapped at 25 Hz is compared with aerodynamic thrust performance to reveal characteristics that might translate to favorable or poor wing performance. This is aimed to provide flapping micro air vehicle designers with knowledge of how to tailor their wings for desired aerodynamic performance. Three different wing designs were tested; all of which were the same planform area and tested using a single active degree of freedom flapping mechanism. Tip deflection and twist angle at 50 % and 75 % are extracted from the full-field deformation and used as metrics. The twist measurements showed advanced rotation in all the wings tested, though to different extents. The wing which had the most advanced rotation was also found to have produced the most thrust at 25 Hz, while the wing with the least tip deflection and was most efficient. This suggests that the larger tip deflection seen with the other wings may be detrimental to the efficiency of the wing.