Full-field Displacement Research Articles

Exploratory Full-Field Mechanical Analysis across the Osteochondral Tissue-Biomaterial Interface in an Ovine Model.

Osteochondral injuries are increasingly prevalent, yet success in articular cartilage regeneration remains elusive, necessitating the development of new surgical interventions and novel medical devices. As part of device development, animal models are an important milestone in illustrating functionality of novel implants. Inspection of the tissue-biomaterial system is vital to understand and predict load-sharing capacity, fixation mechanics and micromotion, none of which are directly captured by traditional post-mortem techniques. This study aims to characterize the localised mechanics of an ex vivo ovine osteochondral tissue–biomaterial system extracted following six weeks in vivo testing, utilising laboratory micro-computed tomography, in situ loading and digital volume correlation. Herein, the full-field displacement and strain distributions were visualised across the interface of the system components, including newly formed tissue. The results from this exploratory study suggest that implant micromotion in respect to the surrounding tissue could be visualised in 3D across multiple loading steps. The methodology provides a non-destructive means to assess device performance holistically, informing device design to improve osteochondral regeneration strategies.

Identification of full-field dynamic modes using continuous displacement response estimated from vibrating edge video

The video of vibrating structure provides dense quantitative continuous spatial information that is harnessed using various computer vision algorithms in the past decade. Computer vision algorithms that implement sparse optical flow, have been successful in acquiring the Lagrangian representation of motion. Such vision-based measurement already proved its potential in replacing the need for a contact based vibration measurement sensors. In order to obtain full-field, spatially dense, vibrational modes, a large number of discrete sensors would be necessary throughout the specimen’s length, making it impractical. The phase-based video processing method is found to be successful in visualizing full-field operational mode shapes of a vibrating structure. However, the phase-based optical flow provides an Eulerian representation of the motion at every pixel of the image space, which does not acquire the full-field spatiotemporal Lagrangian displacement trajectory of the structure. Hence, there is a need to design a target-free, noncontact vision-based framework that can directly extract and quantify full-field dynamic modes of a real-life vibrating structural member from its video, by acquiring the trajectory of every particle on the structure at each frame of the video using optical flow. The continuous edge of a moving object is a rich optical feature whose motion perpendicular to its orientation can be tracked in Lagrangian coordinates using optical flow. In a recent paper by authors, the method of measuring full-field displacement response of a vibrating continuous edge of a structural member has been reported. In this paper, the full-field displacement response is acquired using the recently presented method and subsequently, its spatially dense dynamic modes are extracted from its video using the acquired full-field spatiotemporal displacement response of the vibrating structure. The full-field dynamic modes and modal parameters are extracted using the Hankel dynamic mode decomposition method, which is applicable both for linear, as well as nonlinear dynamical systems. Further, experimental validation of the proposed method is presented for two kinds of structures (1) a three-story steel frame, and (2) an aluminum cantilever beam, both undergoing free vibration. The results obtained using the proposed method is validated with the displacement measured using Laser Doppler Vibrometer at a particular point of the edge. The extracted modal properties using the proposed methodology compares satisfactorily with the results of the eigensystem realization algorithm applied to the discrete point accelerometer measurements attached at all three floors of the frame. Also, the numerically obtained mode shapes from the analytical model of the cantilever beam validate the estimated modal parameters and the full-field mode shapes. To validate the efficacy of the proposed method in real-world structures, part of the vibrating cable of Tacoma Narrows bridge is tracked from its video, moments before its collapse. The proposed method does successfully extract the dominating vibrational modes of the cables of the Tacoma Narrows bridge.

Deformation Reconstruction for a Heavy-Duty Machine Column Through the Inverse Finite Element Method

The processing errors for columns of heavy-duty machine tools are affected by deformation induced by a variety of force loads and thermal loads. In general, error reduction usually uses method of error compensation. However, the precondition of error compensation is to accurately obtain the machine full-field displacement. The inverse finite element method (iFEM) is an efficient tool for the real-time reconstruction of deformation. It obtains nodal degree of freedoms (DOFs) by solving the minimum value of the error least-squares function, which constitutes the relationship between the DOFs and analytical strain. Although double-sided strain rosettes are widely used in the iFEM to obtain strain information, the strain rosettes have some shortcomings, including the internal installation being difficult and measurement size being large. Fiber Bragg grating (FBG) sensors have the advantages of being lightweight, small geometric profile and being easy to installation. Therefore, this study utilizes distributed single-sided and unidirectional strain data obtained from FBG sensors. To further improve the possibility of this practical application, cubic spline interpolation is used to reduce the number of sensors and further extend the practical usefulness. Considering coordinate transformation and boundary conditions, the total deformation of the column is determined. The superior accuracy and practical applicability of the improved formulation is demonstrated after comparing the results of analytic solutions and that of the FEM. Therefore, new direction method for supporting the machining precision of heavy-duty machine tools is proposed.

Augmented Lagrangian Digital Volume Correlation (ALDVC)

Digital volume correlation (DVC), the volumetric extension of the popular digital image correlation (DIC) technique, is a powerful experimental tool for measuring 3D volumetric full-field displacements and strains. Most current DVC algorithms can be categorized into either local or finite-element-based global methods. As with most experimental approaches, there are drawbacks with each of these methods. In the local method the subvolume deformations are estimated independently and the computed displacement field may not necessarily be kinematically compatible. Thus, the deformation gradients can be noisy, especially when using small volumetric subsets. Although the global method often enforces kinematic compatibility, it generally incurs substantially greater computational costs than its local counterpart, which is especially significant for large volumetric data sets. To address these shortcomings, we present a new hybrid DVC algorithm, called augmented Lagrangian digital volume correlation (ALDVC), which combines the advantages of both the local (fast computation time) and global (compatible displacement field) methods. This new algorithm builds on our recent work on the augmented Lagrangian digital image correlation (2D-ALDIC) technique and solves the general motion optimization problem by using the alternating direction method of multipliers (ADMM). We demonstrate that our ALDVC algorithm has high accuracy and precision while maintaining low computational cost, and is a significant improvement compared to current local and global DVC methods. ALDVC is a computationally efficient algorithm to measure 3D volumetric displacements and strains. An open-source Matlab implementation is freely available.

Compression Properties of 3d Printed Honeycomb and Re-Entrant Sandwich Core Materials

In the presented paper, honeycomb (cellular) and re-entrant (auxetic) structures were produced with different thermoplastic filaments on FDM type 3D printer and their compression properties were tested. Samples were prepared from PP, ABS, PLA and PA thermoplastic polymers. The samples were subjected to quasi-static compression in edgewise and flatwise direction and their stress-strain relationships were established. For a proper strain evaluation, digital-image correlation was applied to measure full-field displacements on the sample surfaces and their and their compressive-deformation behaviour in both elastic and plastic regime up to the densification were evaluated. It was shown through compression tests in flatwise and edgewise directions re-entrant type of auxetic cores components exhibit higher compression failure stresses compared to those of cellular honeycomb core components. The stress strain curves of the re-entrant core failure show a higher energy absorbance of the honeycomb cores for the same polymer types

Lamine kompozit ve sandviç plakaların şekil ve gerilme algılaması için yeni bir dört-düğüm noktalı ters-plaka elemanı

Kompozit malzemeler, çeşitli mühendislik yapılarının birincil yük taşıyıcı bileşenlerinin imalat sürecinde yaygın olarak kullanılmaktadır. Ancak, kompozitlerin yapısal bütünlüğünün, yapının hizmet ömrü boyunca meydana gelen hasarlardan dolayı azalması muhtemeldir. Duruma dayalı bakım programlaması için kompozit yapılara gerçek zamanlı şekil ve gerilme algılaması gerçekleştirebilen bir yapısal sağlık izleme sistemi entegre edilebilir. Bu çalışmada, Rafine Zikzak Teorisinin (RZT) temel olarak kullanıldığı ters sonlu elemanlar yöntemine (iFEM) dayanan yeni bir dört düğümlü ters plaka elemanı önerilmiştir. Buradaki iFEM-RZT formülasyonu, membran, eğilme, enine kayma ve zikzak kesit gerinimlerini içeren RZT'nin bütün gerinim ölçüleri kümesini kullanan ağırlıklı en küçük kareler fonksiyonunu en aza indirgemektedir. Mevcut elemanın temel faydası, herhangi bir yükleme bilgisi gerektirmemesi ve şekil algılaması için yalnızca yerleşik sensörlerden alınan gerinim ölçer ölçümlerini kullanmasıdır. Diğer bir avantajı, aynı zamanda genel bir lamine kompozit ve sandviç yapı sınıfının tam alan ve üç boyutlu yer değiştirmelerini ve gerilmelerini tahmin etmek içinde uygulanabilir olmasıdır. Mevcut elemanın potansiyel yeteneklerini göstermek için, farklı laminasyon tiplerine sahip olan bir lamine kompozit plaka üzerinde çeşitli vaka çalışmaları yapılmıştır. İFEM-RZT sonuçları ve son derece hassas sonlu elemanlar çözümleri arasındaki karşılaştırmaya göre, mevcut yaklaşımın üstün doğruluğu ortaya konmuştur.

Reconstruction of full-field complex deformed shapes of thin-walled special-section beam structures based on in situ strain measurement

This study proposed a method capable of reconstructing complex deformations of thin-walled special-section beam structures subjected to highly coupled loading cases, in terms of the combination of tension/compression, biaxial bending, and warping torsion. The complex beam deformation was decoupled, depending on axial strain measurement strategy on beam surface, and leads to reconstructed full-field displacements (deformed shapes) as the linear superposition of deformations subject to individual loading types. Full-filed strain/stress distributions can then be derived based on the reconstructed displacements. Particular efforts were focused on reconstructing beam deformation subject to warping torsion, where both rotations angles and warping displacements across the beam cross-section and along the beam length were identified precisely. As a proof-of-concept validation, the effectiveness of the method was examined using finite element analysis, where the deformed shape of a thin-walled hat-section beam under the coupling between uniaxial bending and warping torsion was reconstructed., Experiments were conducted subsequently to reconstruct deformation of an aluminum hat-section beam using distributed optical fiber sensors for the measurement of axial strains on the beam surface. The reconstructed full-field deformed shapes of the beam were compared with the three-dimensional displacement signals captured using a non-contact digital image correlation system. The effectiveness of the proposed methodology for complex deformation reconstruction is possible to be extended to a variety of thin-walled beam-type structures which are typical in civil and aerospace engineering, showing potential contributions in fields such as on-line structural health monitoring and active structural control.

Osmo-inelastic response of the intervertebral disc annulus fibrosus tissue.

The aim of this article is to provide some insights on the osmo-inelastic response under stretching of annulus fibrosus of the intervertebral disc. Circumferentially oriented specimens of square cross section, extracted from different regions of bovine cervical discs (ventral-lateral and dorsal-lateral), are tested under different strain-rates and saline concentrations within normal range of strains. An accurate optical strain measuring technique, based upon digital image correlation, is used in order to determine the full-field displacements in the lamellae and fibers planes of the layered soft tissue. Annulus stress-stretch relationships are measured along with full-field transversal strains in the two planes. The mechanical response is found hysteretic, rate-dependent and osmolarity-dependent with a Poisson's ratio higher than 0.5 in the fibers plane and negative (auxeticity) in the lamellae plane. While the stiffness presents a regional-dependency due to variations in collagen fibers content/orientation, the strain-rate sensitivity of the response is found independent on the region. A significant osmotic effect is found on both the auxetic response in the lamellae plane and the stiffness rate-sensitivity. These local experimental observations will result in more accurate chemo-mechanical modeling of the disc annulus and a clearer multi-scale understanding of the disc intervertebral function.

Experimental study on the vertical interface of thin-tile masonry

This article presents the results of an experimental study on the structural behaviour of the vertical mortar thin-tile interface in thin-tile masonry. Four compression tests involving two- and three-leaf prisms made of two different types of mortar were carried out. The Digital Image Correlation (DIC) technique was used to capture the full-field displacement of the mortar thin-tile interface. The experimental results revealed that, while all the leaves presented a similar deformation in the longitudinal direction, transversally, the deformations tended to separate the mortar and tile leaf. Thus, it could be concluded that the failure mode of the thin-tile masonry was due to tensile stress perpendicular to the vertical thin-tile mortar interface (mode I), which seemed to be associated with the transverse deformation of the horizontal mortar joints. An analytical approach for the compressive strength of thin-tile masonry based on the usual equation available in the literature for unreinforced multi-leaf masonry walls has been presented. This model seems suitable for determining the compressive strength of thin-tile masonry, but has a more relevant role for mortar leaf.

Flexural deformation characterization of glass panel in curtain walls based on digital image correlation technique

In architectural engineering, full-field mechanical characterization for the outer surface of buildings has been increasingly an essential part of the building safety evaluation, especially for high-rise buildings. However, due to the inherent nature of local and contact measurements of some traditional methods, both measurement accuracy and detected regions are generally quite limited. In this paper, the non-contact digital image correlation (DIC) technique was employed to implement full-field surface flexural deformation characterization for the glass panel of curtain wall system. Firstly, a set of experimental apparatus was designed to obtain the digital speckle image sequences of the tested glass panel under wind load conditions. Secondly, full-field deformation of the glass panel was quantitatively calculated and compared with those data resulted from finite element analysis (FEA) and some traditional measurement devices including strain gauges and digital indicators, which demonstrated that the introduced DIC method not only was capable of achieving full-field flexural deformation measurement for the glass panel, but also could obtain comparable measurement results in comparison with the conventional methods. Consequently, full-field displacement and strain of the glass panel were evaluated, so that surface deflections and curvatures of the panel under wind load conditions were carefully analyzed, by which the wind resistance performance for the glass panel of curtain wall system could be readily characterized.

Centrifuge modeling of the geogrid-reinforced slope subjected to differential settlement

A series of centrifuge model tests of geogrid-reinforced slopes with superstructure was conducted under differential settlement condition. The influence of reinforcement placement on the deformation and failure behavior of the slope and superstructure is investigated by considering different numbers of geogrid layers. The response of the slope and superstructure is analyzed based on a full-field displacement measurement via image analysis. The differential settlement induces distinguishable superstructure movement and slope deformation above the subsidence zone. The slope displacement, close to the vertical direction, appears only in a limited zone. An integrated analysis scheme of deformation and failure processes is adopted to reveal the failure mechanism of both the unreinforced and reinforced slopes: a certain level of deformation localization induced by differential settlement results in the local failure, and adversely, the local failure aggravates the deformation localization near it. The geogrid reinforcement mechanism is further clarified as the reduction on the deformation localization of the slope due to geogrid placement. The geogrid reinforcement effect can be comprehensively described with two respects: hooping effect and shielding effect, which illustrates the influence sphere and degree of geogrid reinforcement on restraining the slope deformation. The geogrid reinforcement is proven effective to improve the safety of the slope and superstructure.

Calibrating stereo-digital image correlation system using synthetic speckle-pattern calibration target

We describe an alternative stereo calibration method for stereo-digital image correlation (stereo-DIC) using computer-simulated speckle-pattern calibration targets and a DIC-based control points matching technique. The present work refines and extends the recently proposed camera calibration method to stereo calibration, which is an essential part of stereo-DIC measurement. In the proposed calibration method, the calibration target is generated by displaying a synthetic speckle pattern on a commercial tablet. On the simulated speckle pattern, a group of control points is specified with flexible location and number, which is further precisely matched to the captured calibration images using the well-developed subset-based DIC algorithm. These precisely matched control points are subsequently used to calibrate the intrinsic and extrinsic parameters of the stereo-DIC system with stereo calibration algorithm. For better accuracy, the error in the manufacture of the calibration target is also considered and compensated. As a flexible number of control point matches are registered with high accuracy and strong robustness, the presented stereo calibration method using synthetic speckle pattern calibration target offers higher calibration accuracy than that based on a calibration target with a limited number of designated features, such as checkerboard target and circular point target. After being demonstrated by a set of simulated calibration tests, the proposed stereo calibration method was applied to calibrate a real stereo-DIC system, which was then used to measure 3D full-field shapes and displacements. The results confirm the effectiveness and accuracy of the proposed stereo calibration method for stereo-DIC applications.

Evaluating the displacement field of paperboard packages subjected to compression loading using digital image correlation (DIC)

Digital image correlation (DIC) is a full-field non-contact optical technique for measuring displacements in experimental testing based on correlating several digital images taken during the test, particularly images before and after deformation. Application of DIC cuts across several fields, particularly in experimental solid mechanics; however, its potential application to paperboard packaging has not been fully explored. To preserve fresh horticultural produce during postharvest handling, it is crucial to understand how the packages deform under mechanical loading. In this study, 3D digital image correlation with two cameras and stereovision was used to determine the full-field displacement of corrugated paperboard packaging subjected to compression loading. Strain fields were derived from the displacement fields. Results obtained from the displacement fields showed the initiation and development of the buckling behaviour of the carton panels. The displacement was observed to be largely heterogeneous. The displacement field in the horizontal direction was smaller compared to that of vertical and out-of-plane directions. In addition, the strain variation increased as load increased, which could be a precursor to material failure. The technique proved to be efficient in providing relevant information on the displacement and strain fields at the surface panels of corrugated paperboard packages used for handling horticultural produce. In addition, it offers prospects for improved mechanical design of fresh produce packaging.

Evaluation of Fracture Toughness of Sandstone and Shale Using Digital Image Correlation

Success of a hydraulic fracturing operation depends on the height and width of the induced fractures. One of the critical components controlling fracture size is fracture toughness of the formation. In this work, mode I fracture toughness of Berea Sandstone and Mancos Shale is measured by combining semi-circular bend test (SCB) and digital image correlation (DIC). Experiments were carried out in different notch orientations with respect to bedding. DIC is used to measure full-field displacements and to visualize and quantify fracture process zone (FPZ). Full-field displacements from DIC are utilized in Williams’ series solution to extract critical stress intensity factor, or fracture toughness. Accuracy of measuring fracture toughness using DIC displacements depends on area of interest (AOI), field of view (FOV), and the number of terms of solution (N). A parametric study is conducted, allowing to choose an optimal set of these parameters for evaluation of fracture toughness in rock specimens. It is known that fracture toughness values obtained directly from the SCB test, using conventional maximum load method, are underestimated due to the effect of nonlinear behavior caused by the fracture process zone. FPZ length is considered as an increase in the effective crack length. Irwin’s correction for effective crack length is utilized to measure fracture toughness values obtained directly from the SCB test that account for the fracture process zone. Fracture toughness values measured using DIC method and Irwin’s correction method are in a good match for both Berea Sandstone and Mancos Shale. Both methods show higher fracture toughness for samples in arrester orientation. In addition, the results show that FPZ length in Berea Sandstone is much larger than in Mancos Shale.

MR-u: Material Characterization Using 3D Displacement-Encoded Magnetic Resonance and the Virtual Fields Method

Experimental, fully three-dimensional mechanical characterization of opaque materials with arbitrary geometries undergoing finite deformations is generally challenging. We present a promising experimental method and processing pipeline for acquiring and processing full-field displacements and using them toward inverse characterization using the Virtual Fields Method (VFM), a combination we term MR-u. Silicone of varying crosslinker concentrations and geometries is used as the sample platform. Samples are stretched cyclically to finite deformations inside a 7T MRI machine. Synchronously, a custom MRI pulse sequence encodes the local displacement in the phase of the MR image. Numerical differentiation of phase maps yields strains. We present a custom image processing scheme for this numerical differentiation of MRI phase-fields akin to convolution kernels, as well as considerations for gradient set calibration for data fidelity. The VFM is used to successfully determine hyperelastic material properties, and we establish best practice regarding virtual field selection via equalization.

Underwater implosion pressure pulse interactions with submerged plates

An experimental and analytical investigation is conducted to study the underwater interaction of implosion pressure pulses with large plates. Two plates with stiffnesses significantly apart are investigated experimentally in a large-diameter pressure vessel for their Fluid-Structure Interaction (FSI) phenomena during proximal implosions of thin metallic shells. High-speed photography, in conjunction with 3D Digital Image Correlation (DIC) measurements, is employed to obtain full-field displacements of the plates. Local dynamic pressure histories are also simultaneously recorded to investigate the incident, reflected and transmitted fluid pressures across the plates during dynamic loading. The lesser stiffness plate showed higher deflection, allowed a weaker reflected pressure pulse and allowed a stronger transmitted pressure pulse as compared to the higher stiffness plate. The peak deflections of the plates occurred during the underpressure phase of the implosion event. Four analytical modeling iterations with increasing complexities starting from Taylor's FSI model are considered to assess the response of water backed plates to dynamic pressure pulse loadings. Each iteration is analyzed individually in an experimental context to understand its role as a building block in a final analytical model. The final model developed is based on the classical plate-bending equation and fluid velocity corrected for ‘afterflow’ effects and performed better than Taylor's original model in predicting pressure-time history of the plates’ reflected pressure and transmitted pressure. The plates’ mid-point deflection profiles are also better predicted using this model. Furthermore, the model showed that the response of a plate during a dynamic implosion pressure pulse interaction is weakly dependent on its bending stiffness. Instead, it is observed that for a large plate, its areal mass density is the dominant factor in determining the reflected pressure, the transmitted pressure and the plate mid-point deflection profiles.

Experimental analysis of progressive failure behavior of rock tunnel with a fault zone using non-contact DIC technique

Geological discontinuities govern the strength and deformation of rock mass and play an important role in the stability of geotechnical excavations, such as tunnels, caverns, slopes, and mines. In this paper, the failure mechanism of a tunnel in the vicinity of a fault zone is investigated by physical model tests with dimensions of 3 m × 2.4 m × 0.4 m, in which the non-contact Digital Image Correlation (DIC) technique is employed to provide full-field displacement measurements. Results show that the fault zone near the tunnel shoulder has a significant influence on the stability of the surrounding rock, in terms of strain localization and failure initiation. With the increase of surcharge loading, cracks initiate at the two sidewalls, following by the initiation of cracks at the left shoulder and the crown. Cracks propagate to the fault zone eventually, leading to asymmetrical collapse. The stress loosening zone (SLZ) in the surrounding rock after tunnel excavation is significantly influenced by the fault zone near the left shoulder of the tunnel, showing the occurrence of stress redistribution. It is recommended to implement reinforcement in the rock mass between the tunnel and the fault to improve the stability.

Analytical Solution for a Deep Circular Tunnel in Anisotropic Ground and Anisotropic Geostatic Stresses

Rock masses that have a well-defined structure may also present a remarked in situ stress anisotropy; thus, the misalignment of a tunnel with the geostatic principal stresses and/or with the principal axes of material anisotropy is very likely. Analytical solutions for tunnels in transversely anisotropic rock available in the literature assume alignment of the tunnel with the geostatic principal stresses and with one of the principal directions of the material anisotropy (i.e. 2D plane strain condition). Such assumption is quite restrictive. In this paper, a new analytical formulation for circular deep tunnels in fully anisotropic rock is presented. It provides the full stress and displacement fields around a tunnel misaligned with the geostatic principal stresses or with the directions of material anisotropy. The analytical solution has been verified by comparing its predictions with results from 3D FEM modelling, for a number of scenarios with increasing complexity. A parametric analysis has been conducted to investigate the interplay that exists between the orientation of the axis of the tunnel and the directions of the principal geostatic stresses and/or the directions of material anisotropy.

Full-field measurement and fracture and fatigue characterizations of asphalt concrete based on the SCB test and stereo-DIC

This study investigated the full-field displacement and strain fields of asphalt concrete under semi-circular bending (SCB) through the stereo-digital image correlation (stereo-DIC) technique. Fracture and fatigue tests were conducted with two high-speed cameras at 500 frames per second (fps) with a pixel resolution of 1520 × 1160 and two medium-speed cameras at 50 fps with a pixel resolution of 2048 × 2048, respectively. The accuracy of the three kinds of speckle patterns was verified. Further, the out-of-plane displacements in both fracture and fatigue tests were measured. The results indicate that the effects of the out-of-plane displacement cannot be ignored in the SCB test, and stereo-DIC must be used instead of 2D-DIC. The fracture and fatigue characteristics of asphalt concrete were investigated quantitatively based on the full-field displacement and strain fields retrieved by stereo-DIC. The fracture test indicates that the size of the plastic zone at the crack tip is much smaller than the crack length; hence, the linear elastic theory can be used to analyze the crack propagation behavior of asphalt concrete. The fracture energy was further calculated to serve the numerical simulation and modeling of the actual pavement. The fatigue test indicates that many small secondary cracks occur along the area near the main crack during cyclic loading. Based on the average strain of the area of damage, the damage–fatigue cycle curve was finally obtained to assess the asphalt concrete damage.

Robust and precise identification of the hygro-expansion of single fibers: a full-field fiber topography correlation approach

Over the past decades, natural fibers have become an important constituent in multiple engineering- and biomaterials. Their high specific strength, biodegradability, low-cost production, recycle-ability, vast availability and easy processing make them interesting for many applications. However, fiber swelling due to moisture uptake poses a key challenge, as it significantly affects the geometric stability and mechanical properties. To characterize the hygro-mechanical behavior of fibers in detail, a novel micromechanical characterization method is proposed which allows continuous full-field fiber surface displacement measurements during wetting and drying. A single fiber is tested under an optical height microscope inside a climate chamber wherein the relative humidity is changed to capture the fiber swelling behavior. These fiber topographies are, subsequently, analyzed with an advanced Global Digital Height Correlation methodology dedicated to extract the full three-dimensional fiber surface displacement field. The proposed method is validated on four different fibers: flat viscose, trilobal viscose, 3D-printed hydrogel and eucalyptus, each having different challenges regarding their geometrical and hygroscopic properties. It is demonstrated that the proposed method is highly robust in capturing the full-field fiber kinematics. A precision analysis shows that, for eucalyptus, at 90% relative humidity, an absolute surface strain precision in the longitudinal and transverse directions of, respectively, 1.2 × 10-4 and 7 × 10-4 is achieved, which is significantly better than existing techniques in the literature. The maximum absolute precision in both directions for the other three tested fibers is even better, demonstrating that this method is versatile for precise measurements of the hygro-expansion of a wide range of fibers.Graphic abstract