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- 实验方案
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Error estimation of 3D reconstruction in 3D digital image correlation
摘要： Three-dimensional digital image correlation (3D-DIC) is widely used in various measurement fields. Once a DIC setup is established, different parameters, such as lens focal length, pixel size, stereo angle, and working distance, are easy to know or measure; the range of the matching error is generally 0.01–0.02 pixels. It would be very convenient if the measurement error could be estimated based on the parameters above without performing the entire DIC calculation process. In this study, a numerical simulation was conducted to study the variation of the 3D reconstruction error with the stereo angle in different measurement areas. It was found that the error of the center point was closely related to the error of the full field. Therefore, using simple parameters to describe the 3D reconstruction error of the center point is of great significance for estimating the overall error of a DIC system. The general solution of the 3D reconstruction equation was simplified on the premise that high order terms of pixel coordinates could be omitted. The derived error estimation formulas had a simple form and described the 3D reconstruction error of the center point in three directions. Through a set of static experiments, the 3D reconstruction error of a planar object under different stereo angles (from 10° to 120°) was studied. The matching error was calculated by a 2D-DIC software and inserted into the proposed formulas to obtain the estimated error. The estimated error was compared with the results of a 3D-DIC software, and the effectiveness of the proposed method was verified.
关键词： digital image correlation,error estimation,3D reconstruction
更新于2025-09-19 17:15:36
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Low-frame-rate single camera system for 3D full-field high-frequency vibration measurements
摘要： A single-camera stereo-digital image correlation (stereo-DIC) system to obtain 3D full-field vibration measurements is proposed. The optical setup is composed of two planar mirrors and a single low frame rate camera, thus resulting in a compact and low-cost equipment. The two mirrors are used to create pseudo-stereo images of a target surface on the camera sensor, which are then correlated by using stereo-DIC. The image acquisition process is carried out at low frame rates and the Nyquist-Shannon frequency limitation is overcome by adopting a down-sampling approach under the hypothesis that the vibration signal is characterized by a single known frequency component. The developed pseudo-stereo DIC system allows to obtain 3D full-field vibration measurements in a frequency range up to 4 kHz even with an available frame rate (at full resolution) of 178 fps. The effectiveness of the described approach has been verified by performing vibration measurements on a cantilever plate and a turbine blade.
关键词： Single low-speed camera,Vibration measurement,Down-sampling approach,Digital image correlation
更新于2025-09-19 17:15:36
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Development of a non-contact and non-destructive laser speckle imaging system for remote sensing of anisotropic deformation around fastener holes
摘要： Strain sensing around the fastener holes is fundamentally significant in structural health monitoring and failure detections. Conventional non-destructive testing (NDT) techniques typically have limitations in performing reliable and efficient inspections. Here, a laser speckle imaging system (LSIS) has been developed to achieve non-contact, non-destructive and remote strain sensing. Methods for determining optimal laser speckle patterns have been investigated to achieve remote sensing of strain up to a working distance of 5 m. This LSIS was applied to study the anisotropic properties of un-notched and circular notched specimens in cold-rolled aluminium sheet, an important material for the construction of lightweight aircraft structures. The results showed that strain distributions determined by LSIS are consistent with finite element (FE) predictions in which the evolution of strain concentrations not only depends on the notch size but also on material anisotropy. This study demonstrates the potential application of LSIS as an effective NDT technique for full-field, non-contact and remote sensing of anisotropic deformation around fastener holes.
关键词： Non-destructive testing,Digital image correlation,Laser speckle imaging,Remote strain sensing
更新于2025-09-19 17:13:59
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Performance of Distributed Optical Fiber Sensors (DOFS) and Digital Image Correlation (DIC) in the monitoring of RC structures
摘要： Distributed Optical Fiber Sensors (DOFS) are strain measuring tools whose potential related to the civil engineering field has been discovered in the latest years only. A unique utility lies in the possibility of bonding these extremely thin sensors to steel reinforcement bars which will later be embedded in concrete elements (RC) in order to monitor its mechanical strains. The present paper presents the results of an experimental campaign that saw the tensing of two RC tensile members (ties) with DOFS-instrumented steel rebars providing strain readings every 7.5mm. Their cracking behavior allows to gain insight on the steel rebar’s strain profile when surrounded by cracking concrete. The described results are novel as measurements that are accurate, completely distributed, experimentally extracted, both before and after concrete cracking, have been impossible up until now. The internal strain measurements are additionally integrated with an external Digital Image Correlation (DIC) monitoring which provides data on the displacements and strains of the members’ surfaces. The present research represents the beginning of an in-depth experimental campaign aimed at providing reinforcement strain data for multiple loaded RC ties encompassing different geometrical features (concrete cover, reinforcement ratio, bar diameter).
关键词： strain monitoring,concrete cracking,Digital Image Correlation (DIC),Distributed Optical Fiber Sensors (DOFS),RC structures
更新于2025-09-16 10:30:52
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Wholea??field strain analysis and strength prediction of fiber laser machined CFRP laminate at elevated temperature
摘要： High power fiber laser was proved to be feasible to cut carbon fiber reinforced plastic (CFRP) laminate with high efficiency, while the machined quality on mechanical performance was not fully understood. This paper studied the effect of high temperature up to 220°C on tensile strength degradation and strain distribution of unidirectional CFRP laminate with open hole machined with fiber laser. Differential scanning calorimetry (DSC) was firstly employed to determine the glass transition temperature (Tg) of polymer-matrix composite. Digital image correlation technique was applied to evaluate whole-field strain distribution and crack propagation/evolution of CFRP laminate featured with open hole under tensile loading. Results showed that the tensile strength of laser machined CFRP laminate degraded significantly during working in high temperature above 100°C. The value of strains distributed around center hole was highly related to the elevated temperature and applied load levels. Splitting was the prevalent failure mode of CFRP laminate under elevated temperature up to 180°C. Finally, semi-empirical model was developed for evaluating tensile performance of laser machined CFRP laminate at elevated temperature based on regression analysis.
关键词： digital image correlation,laser cutting,mechanical behavior,strain distribution,CFRP
更新于2025-09-16 10:30:52
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Quality assessment of laser speckle patterns for digital image correlation by a Multi-Factor Fusion Index
摘要： Digital image correlation based on laser speckle has its unique advantages in ultra-high temperature deformation measurement. The traditional quality assessment criteria of arti?cial speckle which consider only the contrast of the speckle pattern or the morphology of the speckle particles are not suitable for laser speckle. Here, a new index, called Multi-Factor Fusion Index (MFFI), which takes the inhomogeneity of gray distribution, the mean square deviation of gray and the standard deviation of speckle particles size into consideration, is proposed to evaluate the quality of laser speckle patterns. Multi-Factor Fusion Index was compared with three commonly used criteria, the mean intensity gradient, the mean intensity of the second derivative, and the pattern quality metric combining the sum of square of subset intensity gradients (SSSIG) and the secondary auto-correlation peak height. The results showed that the proposed index had better capability of assessing the quality of laser speckle patterns. And the in?uence by external factors such as apertures, laser powers and temperatures and material factors such as roughness and light re?ectance were analyzed by MFFI. Experiments on arti?cial speckle showed that MFFI was also suitable for arti?cial speckle patterns in most cases.
关键词： Quality assessment criteria,Laser speckle characteristics,Multi-Factor Fusion Index (MFFI),Digital image correlation (DIC)
更新于2025-09-12 10:27:22
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In-situ measurement of near-tip fatigue crack displacement variation in laser melting deposited Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy
摘要： Laser melting deposition (LMD) is an attractive additive manufacturing technique for fabricating titanium alloy components. A variety of distinct layer bands, heat affected bands (HABs), were found in the LMDed sample, which lead to a periodic fluctuation in the fatigue crack growth rate. In this paper, an in-situ fatigue testing was performed to investigate the crack tip opening displacement (CTOD) variation within a full loading cycle. Digital image correlation (DIC) technique was implemented for obtaining the displacement fields at the vicinity of the crack tip. The crack closure phenomenon is observed from the CTOD variation and the crack opening stress level is different between HAB and non-HAB zone. Another key difference between HAB and non-HAB zone is the value of CTOD when the crack is opening. Besides, the variation of the CTOD loop and its influence on fatigue crack growth rate were also discussed in detail.
关键词： Digital image correlation,In-situ,Crack tip opening displacement,Laser melting deposition
更新于2025-09-12 10:27:22
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Development of LED-based illumination system for high-speed digital image correlation
摘要： The present work describes the design and development of a dedicated illumination system for application to high-speed digital image correlation. This type of application requires image acquisition to be performed with very short shutter times. This means that there is less time to integrate the incoming light and, as such, it is necessary to have significant light flux to acquire quality images. As such, illumination is usually the major concern in such high-speed imaging applications. The developed system uses a strobing high-power LED light source to tackle this issue, and illuminate the specimen with a large light flux during a very short period. This reduces the amount of heat that the specimen receives from the lighting source and has the advantage of enabling the use of cameras that would otherwise be unable to use such short shutter times effectively. In this paper, the whole design of the device is described. From the control electronics to the mechanical design, including the optical design of an appropriate reflector.
关键词： Structural Integrity,LED light source,Digital Image Correlation
更新于2025-09-12 10:27:22
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A sensor detecting kissing bonds in adhesively bonded joints using electric time domain reflectometry
摘要： The joining technology with the highest potential in lightweight construction is the adhesive bonding. In an adhesively bonded joint different defects can occur. Alongside gross defects like areas of uncured adhesive and voids, adhesion defects like kissing bonds pose a serious problem to the confidence in these kind of joints in the aircraft industry and other industries. Since kissing bonds are small interfacial defects of as few as nanometers in thickness, the detection by conventional nondestructive testing methods is not possible in most applications. In this paper a novel adhesive sensor based on the electric time domain reflectometry is proposed detecting differences in the deformation of the adherents in an adhesively bonded joint to infer that a kissing bond is taking affect. Numerical calculations are used to show that the proposed sensor principle poses a productive approach. For the numerical calculations a finite difference time domain model is used. The sensor is then validated experimentally by shear tension testing of single lap shear specimens with the adhesive sensor integrated into the joint.
关键词： Kissing bond,Fiber reinforced plastics,Digital image correlation,Non-destructive testing,Adhesively bonded joint,Electric time domain reflectometry
更新于2025-09-10 09:29:36
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Vibration and modal analysis of a rotating disc using high-speed 3D digital image correlation
摘要： Rotating structures are of interest in many engineering fields, where knowing their dynamic behaviour is important to prevent undesired operating states. However, the experimental measurement of vibrations in rotating structures is still a relatively demanding task that requires the use of special measurement technique or method. The paper deals with the application of high-speed digital image correlation in vibration analysis of rotating structures. The method introduced in this research is based on the elimination of rigid body motion components contained in the primary responses measured by cameras. The process of separation and subsequent elimination of these components is given by numerical post-processing of three-dimensional displacement fields. The basis is to determine rotation matrix and translation vector that optimally describe rigid transformation between two positions of an analysed object. The proposed method is applicable for measuring under both constant and variable speed of rotation. Practical application is presented by three experiments in which vibrations of a flat rotating disc were analysed. The first experiment is focused on determine the operating deflection shapes of the disc rotating at 4700 rpm. The second one is a run-up analysis under variable rotational speed that ranges from 0 to 4700 rpm. The aim of the third measurement is to obtain natural frequencies and modal shapes of the disc rotating at 4800 rpm. The results of the experiments show that the elimination of rigid body motions leads to a higher accuracy of measurement and provides more pronounced frequency response spectra.
关键词： Vibration analysis,Rotating disc,Rigid body motion elimination,Digital image correlation,Modal analysis
更新于2025-09-09 09:28:46