Deformation Measurement Research Articles

Asynchronous event stream noise filtering for high-frequency structure deformation measurement

Large-scale structures suffer high-frequency deformations due to complex loads. However, harsh lighting conditions and high equipment costs limit measurement methods based on traditional high-speed cameras. This paper proposes a method to measure high-frequency deformations by exploiting an event camera and LED markers. First, observation noise is filtered based on the characteristics of the event stream generated by LED markers blinking and spatiotemporal correlation. Then, LED markers are extracted from the event stream after differentiating between motion-induced events and events from LED blinking, which enables extracting high-speed moving LED markers. Ultimately, high-frequency planar deformations are measured by a monocular event camera. Experimental results confirm the accuracy of our method in measuring high-frequency planar deformations.

Flow and Deformation in Earth's Deepest Mantle: Insights From Geodynamic Modeling and Comparisons With Seismic Observations

AbstractThe dynamics of Earth's D″ layer at the base of the mantle plays an essential role in Earth's thermal and chemical evolution. Mantle convection in D″ is thought to result in seismic anisotropy; therefore, observations of anisotropy may be used to infer lowermost mantle flow. However, the connections between mantle flow and seismic anisotropy in D″ remain ambiguous. Here, we calculate the present‐day mantle flow field in D″ using 3D global geodynamic models. We then compute strain, a measure of deformation, outside the two large‐low velocity provinces (LLVPs) and compare the distribution of strain with previous observations of anisotropy. We find that, on a global scale, D″ materials are advected toward the LLVPs. The strains of D″ materials generally increase with time along their paths toward the LLVPs and toward deeper depths, but regions far from LLVPs may develop relative high strain as well. Materials in D″ outside the LLVPs mostly undergo lateral stretching, with the stretching direction often aligning with mantle flow direction, especially in fast flow regions. In most models, the depth‐averaged strain in D″ is >0.5 outside the LLVPs, consistent with widespread observations of seismic anisotropy. Flow directions inferred from anisotropy observations often (but not always) align with predictions from geodynamic modeling calculations.

Quantitative analysis of fetal cardiac structure and function in gestational diabetes mellitus using fetal HQ technology

BackgroundGestational diabetes mellitus (GDM) can contribute to changes in fetal cardiac structure and function, with potential implications for long-term cardiovascular health. This study focuses on assessing these cardiac adaptations in fetuses from GDM pregnancies by using the innovative Fetal Heart Quantification (Fetal HQ) technology to provide a detailed evaluation of structural and functional parameters. MethodsA prospective study was conducted from March 2023 to October 2024 at Xiangyang No.1 People's Hospital, involving 382 pregnant women in their second and third trimesters, including 167 with GDM and 215 healthy controls. Fetal cardiac assessments were performed using Fetal HQ, which allows for direct measurement of cardiac deformation and function. Key parameters such as left ventricular (LV) and right ventricular (RV) dimensions, global longitudinal strain (GLS), and fractional area change (FAC) were analyzed. Maternal clinical data, including blood glucose levels and body mass index (BMI), were also collected. Statistical analyses were performed to compare the cardiac parameters between the two groups. ResultsSignificant differences were observed in fetal cardiac dimensions, with the GDM group exhibiting larger LV end-diastolic area (2.04 ± 0.73 cm2 vs. 1.81 ± 0.69 cm2, p = 0.002) and lower RV GLS (−20.1 ± 5.3 % vs. -22.6 ± 4.6 %, p = 0.000). Other functional parameters, including LV GLS and FAC, did not show significant differences between groups. Correlation analysis revealed a significant positive relationship between maternal HbA1c levels and RV FAC (r = 0.348, p = 0.036), indicating that maternal glycemic control may influence fetal cardiac function. ConclusionsThe findings suggest that GDM is associated with altered fetal cardiac morphology, particularly in the left ventricle, and impaired right ventricular function, as evidenced by reduced GLS. These results highlight the potential impact of maternal hyperglycemia on fetal cardiac development and underscore the importance of monitoring fetal cardiac health in pregnancies complicated by GDM. The use of Fetal HQ technology provides a valuable tool for early detection of cardiac dysfunction in this high-risk population.

A robust feature-based full-field initial value estimation in path-independent digital image correlation for large deformation measurement

The feature-based path-independent digital image correlation (DIC) method has been shown to be a formidable tool for non-contact, full-field measurement of large deformation, but its effectiveness hinges crucially on acquiring sufficient matched features to perform a reliable full-field initial value estimation (IVE) for all points of interest (POIs), thus ensuring their successful and rapid convergence in the succeeding path-independent iterative DIC refinement. This prerequisite is a challenging task particularly when confronted with large deformation. Moreover, in many real-world measurement scenarios, the accuracy of IVE is also influenced by image noise, such as Gaussian noise and shot noise, further compounding the challenge. To mitigate these issues, we propose a robust feature-based full-field IVE method. The core of this method consists of two main components: (i) For feature detection, we leverage the strengths of nonlinear multiscale representations on speckle images using an Accelerated-KAZE (A-KAZE) detector, which extracts features in a nonlinear scale space via nonlinear diffusion filtering. Noise is suppressed and edges are preserved. Compared to existing state-of-the-art feature detectors used in DIC, such as Scale Invariant Feature Transform (SIFT) and Speeded-Up Robust Feature (SURF) detectors, which rely on the use of Gaussian linear scale spaces, the A-KAZE-based nonlinear scale space detector identifies more salient features with higher localization accuracy. (ii) For feature description, considering the need for robustness against large deformation and the computational burden of descriptor matching for considerable salient features that may be detected in speckle images, we introduce a robust Gradient Location and Orientation Histogram (GLOH) descriptor and propose an improved version of it. The GLOH's improved version incorporates a restricted adaptive binning (RAB) strategy to optimize the descriptor’s structure parameters, which is able to reduce the computational cost of descriptor matching through restricting its dimensionality while without sacrificing its robustness and discriminability. These two components are designed to provide sufficient matched features for a full-field IVE. The initial deformation for each POI is estimated independently by fitting a local affine transformation model, which is refined to subpixel accuracy through iterative path-independent DIC analysis. To handle complex large deformation, the inverse compositional Gauss-Newton (IC-GN) algorithm with a second-order shape function is employed. Extensive experimental results demonstrate that our method has improved IVE accuracy as well as behaves more robustness against local geometric transformations and image noise including Gaussian noise and shot noise, as compared to existing state-of-the-art feature-based full-field IVE methods.

Tube deformation measurement with camera and laser

Underwater tubes are critical infrastructure components for city transportation. The installation and connection of immersed tubes in underwater environments require accurate localization technologies. Currently, many immersed tube localization methods rely on Global Navigation Satellite System (GNSS) based satellite towers. However, various forces such as the tube’s own weight, water pressure, etc. inevitably cause tube deformations and satellite tower to tilt, then affecting tube posture estimation. Targeting this challenge, this paper develops a novel underwater immersed tube deformation measurement algorithm, which detects tube geometric deformation based on cameras and lasers. The cameras and lasers are used to measure horizontal and vertical deformations respectively. Then, the overall geometric deformation can be obtained from the two deformations accurately. Extensive real-world experiments demonstrate that, compared to the GNSS-based satellite towers method, our proposed method significantly reduces localization errors and has been applied to the construction program of the Shenzhen-Zhongshan underwater tube tunnel.

An essay on deformation measures in isotropic thin shell theories: Bending versus curvature

It has become commonplace for the stored energy function of any realistic shell model to align “within first order” with the classical Koiter membrane-bending (flexural) shell model. In this paper, we assess whether certain extended Cosserat shell models are consistent with the classical linear Koiter model. In doing this, we observe that there are numerous reasons why a modified version of the classical Koiter model should be considered, a consensus reached not only by Koiter himself but also by Sanders and Budiansky, who independently developed the same theory during the same period. To provide a comprehensive overview of the strain measures employed in our Cosserat shell models, this paper presents them in a unified manner and compares them with the strain measures previously utilized in the literature. We show that all our new strain tensors either generalize (in the case of nonlinear constrained or unconstrained models) or coincide (in the case of the linear constrained model) with the strain tensors recognized as the “best" or those possessing a well-defined geometric interpretation connected to bending or curvature.

Directional DIC method with automatic feature selection

Using displacement identification via high-speed cameras is a non-contact, full-field technique for characterizing the dynamic properties of engineered structures. Achieving reliable measurements of structural deformation through conventional Digital Image Correlation (DIC) requires a well-defined spatial gradient in two orthogonal directions within an image subset of pixels. However, DIC is susceptible to the aperture problem, which leads to an ill-conditioned optimization problem. An example of such a case is cable systems on which no speckle patterns can be applied. This study proposes Directional DIC (D-DIC) as an alternative technique to overcome the limitations posed by the aperture problem in conventional DIC methods. Directional DIC assumes the local direction of motion, which is often a valid assumption in structural vibration tests, as individual vibration shapes are often unidirectional at localized parts of the structure. This alleviates some restrictions on trackable image subsets, enabling more trackable locations. A parameter for quantifying expected tracking performance for D-DIC is introduced. The parameter enables automatic feature selection for D-DIC, making optical methods more accessible for displacement identification on structures where no speckle patterns can be applied. Experimental modal tests are conducted using a flexible spider web-like structure to validate the D-DIC method and compare it to conventional DIC. The experimental findings show that the Directional DIC method allows for measuring displacements at significantly more locations than conventional DIC. Additionally, D-DIC provided less noisy frequency response functions, more retrieved stable poles, and more fitted vibrational modes. Lastly, the findings show that D-DIC is especially superior to DIC when using small subsets since D-DIC is less inhibited by the aperture problem.

UHPC girder multi-modal deformation measurements: Photogrammetry, physical sensing, and FEA

Ultra-high performance concrete (UHPC) has become increasingly popular in flexural design of structural members that require high performance. Although numerous experimental studies on passively reinforced UHPC flexural members exist, studies on monolithic members with larger cross sections are limited, and no information exists on full-field deformation measurements of such specimens. An experimental program consisting of 8 large-scale UHPC doubly-reinforced specimens with continuous longitudinal rebars was conducted under 4-point monotonic loading. The experimental objectives were to investigate rebar slip from one side of the specimens (longitudinal rebar with hooks only on one side), track crack propagation, and capture the full-field displacement and strain measurements during the loading. The noncontact measurements from the multi-camera computer vision system using 3D digital image correlation (3D-DIC) and AprilTag-based photogrammetry were compared with the physical (contact) displacement measurement system. Strain fields were obtained using dual-camera 3D-DIC and finite element (FE) analysis. Results showed a close agreement of the point-wise displacements obtained from the physical and computer vision monitoring systems. The asymmetric structural design caused slip that delayed rebar fracture and reduced the peak load below that predicted by sectional analysis. The measured global force-deflection curve was predicted by the FE model when using a calibrated bond-slip model between rebar and UHPC. Comparison between the full-field measurements using 3D-DIC and FE numerical models showed that the evolution of principal strains and cracking were consistent. 3D-DIC proved to be a promising measurement method for monitoring strain/displacement and calibrating/confirming FE model that conventional methods without full-field measurements cannot provide.

A Novel non-invasive optical framework for simultaneous analysis of contractility and calcium in single-cell cardiomyocytes

The use of a video method based on the Digital Image Correlation (DIC) algorithm from experimental mechanics to estimate the displacements, strain field, and sarcolemma length in a beating single-cell cardiomyocyte is proposed in this work. The obtained deformation is then correlated with the calcium signal, from calcium imaging where fluorescent dyes sensitive to calcium Ca2+ are used. Our proposed video-based method for simultaneous contraction and intracellular calcium analysis results in a low-cost, non-invasive, and label-free method. This technique has shown great advantages in long-term observations because this type of intervention-free measurement neutralizes the possible alteration in the beating cardiomyocyte introduced by other techniques for measuring cell contractility (e.g., Traction Force Microscopy, Atomic Force Microscopy, Microfabrication or Optical tweezers). Three tests were performed with synthetically augmented data from cardiomyocyte images to validate the robustness of the algorithm. First, a simulated rigid translation of a referenced image is applied, then a rotation, and finally a controlled longitudinal deformation of the referenced image, thus simulating a native realistic deformation. Finally, the proposed framework is evaluated with real experimental data. To validate contraction induced by intracellular calcium concentration, this signal is correlated with a new deformation measure proposed in this article, which is independent of cell orientation in the imaging setup. Finally, based on the displacements obtained by the DIC algorithm, the change in sarcolemma length in a contracting cardiomyocyte is calculated and its temporal correlation with the calcium signal is obtained.

Electrochemical cutting with flexible electrode of controlled online deformation

Abstract Improvements in aero-engine performance have made the structures of the aero-engine components increasingly complex. To better adapt to the processing requirements of narrow twisted channels such as an integral shrouded blisk, this study proposes an innovative method of electrochemical cutting in which a flexible tube electrode is controlled by online deformation during processing. In this study, the processing principle of electrochemical cutting with a flexible electrode for controlled online deformation (FECC) was revealed for the first time. The online deformation process of flexible electrodes and the machining process of profiles were analysed in depth, and the corresponding theoretical models were established. Conventional electrochemical machining (ECM) is a multi-physical field-coupled process involving electric and flow fields. In FECC, classical mechanics are introduced into the tool cathode, which must be loaded at all times during the machining process. Therefore, in this study, before and after the deformation of the flexible electrode, a corresponding simulation study was conducted to understand the influence of the online deformation of the flexible electrode on the flow and electric fields. The feasibility of flexible electrodes for online deformation and the validity of the theoretical model were verified by deformation measurements and in situ observation experiments. Finally, the method was successfully applied to the machining of nickel-based high-temperature alloys, and different specifications of flexible electrodes were used to complete the machining of the corresponding complex profiles, thereby verifying the feasibility and versatility of the method. The method proposed in this study breaks the tradition of using a non-deformable cathode for ECM and adopts a flexible electrode that can be deformed during the machining process as the tool cathode, which improves machining flexibility and provides a valuable reference to promote the ECM of complex profiles.

Measurement of dynamic deformation during shock loading using a fiber-optic loop-sensor

Abstract Characterizing materials under shock loading has been of interest in fields such as protective material development, biomechanics to study the injury mechanics and high-speed aerodynamic structures. However, shock loading of material is a very short duration phenomenon and it is extremely challenging to develop sensors for dynamic measurements under such loading conditions. Optical fiber sensors that present the possibilities to allow high resolution measurement of force or displacement in such high strain rate loading conditions. This work studies the possibility of developing a single mode optical fiber sensor based on the principle of power losses from the curved section for dynamic measurements under shock loading conditions. The strain measurement results obtained from the optical sensors are validated with the controlled digital image correlation measurements are found to be in close correlation. The sensor was able to provide time sensitivity of better than 1 ms. The results show that the fiber sensor has the characteristics of high sensitivity and high precision, which can be used to measure fine vibration in real-time.

GMDIC: a digital image correlation measurement method based on global matching for large deformation displacement fields

The digital image correlation method is a non-contact optical measurement method, which has the advantages of full-field measurement, simple operation, and high measurement accuracy. The traditional DIC method can accurately measure displacement and strain fields, but there are still many limitations. (i) In the measurement of large displacement deformations, the calculation accuracy of the displacement field and strain field needs to be improved due to the unreasonable setting of parameters such as subset size and step size. (ii) It is difficult to avoid under-matching or over-matching when reconstructing smooth displacement or strain fields. (iii) When processing large-scale image data, the computational complexity will be very high, resulting in slow processing speeds. In recent years, deep-learning-based DIC has shown promising capabilities in addressing the aforementioned issues. We propose a new, to the best of our knowledge, DIC method based on deep learning, which is designed for measuring displacement fields of speckle images in complex large deformations. The network combines the multi-head attention Swin-Transformer and the high-efficient channel attention module ECA and adds positional information to the features to enhance feature representation capabilities. To train the model, we constructed a displacement field dataset that conformed to the real situation and contained various types of speckle images and complex deformations. The measurement results indicate that our model achieves consistent displacement prediction accuracy with traditional DIC methods in practical experiments. Moreover, our model outperforms traditional DIC methods in cases of large displacement scenarios.

Method for luminescent digital image correlation deformation measurement in non-illuminated environments

This study presents a luminescent digital image correlation (DIC) method that utilizes long afterglow materials to prepare speckle patterns, overcoming the limitations of classical DIC in achieving high-precision deformation measurements, such as the issues of specular reflections from specimens and insufficient contrast of speckle patterns. While fluorescent DIC has some advantages in overcoming these limitations, it relies on active ultraviolet light sources, making it challenging for luminescent measurements. Long afterglow materials, capable of maintaining brightness for extended periods, serve as a viable alternative. Through sphere reconstruction experiments, the accuracy of this method was validated, demonstrating a relative error of 0.04% under well-illuminated conditions and 0.025% under non-illuminated conditions. Finite element simulations and a comparison with DIC experimental results showcased excellent consistency, suggesting the potential for this method to further replace fluorescent DIC measurements. Furthermore, the study revealed that speckle patterns prepared using this approach ensure measurement validity in both well-illuminated and non-illuminated scenarios. This luminescent DIC method holds promising potential for broader applications in non-illuminated measurement environments.

Strain and Deformation Analysis Using 3D Geological Finite Element Modeling with Comparison to Extensometer and Tiltmeter Observations

This study verifies the practicality of using finite element analysis for strain and deformation analysis in regions with sparse GNSS stations. A digital 3D terrain model is constructed using DEM data, and regional rock mass properties are integrated to simulate geological structures, resulting in the development of a 3D geological finite element model (FEM) using the ANSYS Workbench module. Gravity load and thermal constraints are applied to derive directional strain and deformation solutions, and the model results are compared to actual strain and tilt measurements from the Jiujiang Seismic Station (JSS). The results show that temperature variations significantly affect strain and deformation, particularly due to the elevation difference between the mountain base and summit. Higher temperatures increase thermal strain, causing tensile effects, while lower temperatures reduce thermal strain, leading to compressive effects. Strain and deformation patterns are strongly influenced by geological structures, gravity, and topography, with valleys experiencing tensile strain and ridges undergoing compression. The deformation trend indicates a southwestward movement across the study area. A comparison of FEM results with ten years of strain and tiltmeter data from JSS reveals a strong correlation between the model predictions and actual measurements, with correlation coefficients of 0.6 and 0.75 for strain in the NS and EW directions, and 0.8 and 0.9 for deformation in the NS and EW directions, respectively. These findings confirm that the 3D geological FEM is applicable for regional strain and deformation analysis, providing a feasible alternative in areas with limited GNSS monitoring. This method provides valuable insights into crustal deformation in regions with sparse strain and deformation measurement data.

High-Speed Three-Dimensional-Digital Image Correlation and Schlieren Imaging Integrated With Shock Tube Loading for Investigating Dynamic Response of Human Tympanic Membrane Exposed to Blasts.

Investigating the dynamic response of human tympanic membranes (TMs) exposed to blasts requires full-field-of-view and three-dimensional (3D) methodologies. Our paper introduces a system that combines high-speed 3D digital image correlation (HS 3D-DIC) and Schlieren imaging (HS-SI) with a custom-designed shock tube for generating blast waves. This integrated system allows us to measure TM surface motions under intense transient loading, capturing full-field-of-view shape deformations exceeding 100 μm with a temporal resolution of 10 μs. System characterization encompasses (i) measuring the shock tube's output levels and repeatability, (ii) assessment of the spatial and temporal resolutions of the imaging techniques, and (iii) identification of overall system limitations. Optimizing these factors is crucial for improving the reliability of our system to ensure the accurate measurement of deformations. To assess our shock tube's reliability in generating repeated blast waves, we instrumented it with high-pressure (HP) and high-frequency (HF) pressure sensors along the blast wave pathway to record overpressure waveforms and compared them with Schlieren imaging visualized blast waves. We validate our HS 3D-DIC measured deformations by comparing them with deformations measured using single-point laser Doppler vibrometry (LDV), establishing a comprehensive assessment of the TM's dynamic response and potential fracture mechanics under blast. Finally, we test our approach with 3D-printed TM-like samples and a real cadaveric human TM. This methodology lays the groundwork for further investigations of blast-related auditory damage and the invention of more effective protective and medical solutions.

Experimental method for internal deformation measurement of 3D solids with embedded cracks based on 3D printing and digital speckle techniques

Quantification of the internal deformation of fractured solids such as rock masses under external loads, especially the deformation around internal fractures, is crucial for understanding and predicting the failure of fractured solids. However, it is very difficult to achieve the goal using conventional experimental methods. In this study, we proposed a novel internal deformation measurement method based on three-dimensional (3D) printing and digital speckle techniques. The 3D printing technology was applied to fabricate a 3D transparent model with an embedded elliptical crack and to set a speckle pattern on the internal section of the transparent model. The digital image correlation (DIC) method was used to determine the internal deformation field of the 3D fractured model. The measured displacements and strains of the internal sections in the fractured model were compared with the numerical simulation results. The comparison indicates that the proposed experimental method can well determine the deformation inside the 3D model. This built-in speckle method can realize real-time observation of the internal deformation of a 3D solid model in a non-contact and non-destructive manner.

Tunnel full-space deformation measurement based on improved downsampling and registration approach by point clouds

To fully leverage the volume measurement advantage of three-dimensional laser scanning technology in tunnel deformation monitoring, a full-space deformation analysis is proposed. A Box Improved Moving Average (BIMA) method featured by the adaptive window size downsampling is proposed which aims to achieve varying levels of downsampling in different densities regions. The combination of Maximal Cliques (MAC) and Iterative Closest Point (ICP) is utilized to achieve accurate registration. Point normal information is utilized to determine the correspondence to calculate deformation which shows an average accuracy of 7 % higher than the ICP by a convergence measurement test. The deformation convergence accuracy can go beyond 76 % when the point cloud reserved rate is approximately 10 %. Comparison between the method proposed in this study and the traditional point cloud cross sectional fitting method shows that the discrepancy between these two methods is approximately within 5 mm, with a minimum value of only 0.15 mm.

Light-tracing based surface deformation measurement strategy for large radio telescopes

Light-tracing based surface deformation measurement strategy for large radio telescopes

Development of a multibody model for go-karts considering frame flexibility

AbstractThis study focuses on the optimization dynamics of racing go-karts, which is heavily influenced by the frame's stiffness. Lacking suspensions and differentials, go-karts rely on the frame stiffness for wheel balancing and skid prevention by lifting the inner rear wheel during turns. Utilizing a rigid-flexible model in MSC Software ADAMS View, validated by frame deformation measurements, this research integrates finite element analysis with multibody techniques. The model, leverages computer aided design files for frame geometry and employs finite element analysis for frame validation. It facilitates evaluating go-kart dynamics through simulations, aiding in maneuver testing and design optimization. This approach provides a comprehensive framework for advancing go-kart designs.

Ultrasensitive Ultrasoft Buckled Crack‐Based Sensor for Respiration Measurement and Enhanced Human–Machine Interface

Wearable strain sensors have transformed the real‐time monitoring of health conditions and human–machine interactions. However, recently developed wearable strain sensors exhibit several limitations. For example, when a sensor is designed with high sensitivity to detect strain, it struggles to accurately measuring the deformation of low‐stiffness materials like skin. Additionally, finding the optimal balance between sensitivity, durability, hysteresis, and strain range in sensor design is challenging. To address these challenges, a Buckled, Ultrasoft, Crack‐based, Large strain, EpiDermal (BUCKLED) sensor is developed. This sensor integrates the benefits of soft structure engineering with high sensitivity of crack‐based sensing mechanisms to ensure optimal skin deformation measurements. The BUCKLED sensor exhibits significant improvements in compliance (18 500 mm N−1), stretchability (100%), hysteresis (2%), durability (10 000 cycles with 100% strain), and force sensitivity () owing to its buckled shape, confirming its ability to detect subtle movements with enhanced accuracy. The sensor's high compliance allows it to accurately measure low‐stiffness objects, ensuring reliable performance. Furthermore, the sensor's tunability is demonstrating its effectiveness in applications such as respiratory monitoring, facial expression recognition, and silent speech interfaces. Consequently, the proposed sensor is versatile and holds great potential for a wide range of sensing applications.