Glued laminated timber (GLT) is an engineered wood product widely used in structural applications. The mechanical properties of the GLT beams significantly depend on the mechanical properties of ...local weak sections such as knots and finger joints (FJs). Conventionally, the mechanical behavior of the local weak sections has been mainly investigated in the individual lamellae. In the present study, their mechanical behaviors within the GLT beams are investigated. 22 GLT beams with well-known beam setups in four-point bending tests were studied. Digital image correlation was used to measure displacements and strains in the region of the beams with the constant bending moment. This paper presents the strain distributions in the GLT beams and discusses the influence of the timber board arrangements and, accordingly, the knots and the FJs. As expected, the strain distributions of the GLT beams vary significantly. Depending on the arrangement of the knots, they can cause strain concentrations in the beams, which can be distributed to the adjacent lamellae. FJs do not cause significant strain concentrations; however, they can influence the strain distribution along the lamellae. Furthermore, a reduced stiffness of the FJs, compared to the connected timber boards, is identified.
•22 glulam beams with well-known beam setups were investigated in four-point bending.•Local strains due to growth irregularities were measured using digital image correlation.•Stiffness of finger joints and connected boards in glulam beams was studied.•Finger joint stiffness is reduced compared to those of the connected boards.
Digital image correlation is a widely used technique in the field of experimental mechanics. In fracture mechanics, determining the precise location of the crack tip is crucial. In this paper, we ...introduce a novel crack tip detection algorithm based on displacement and strain fields obtained by digital image correlation. Iterative crack tip correction formulas are discovered by applying deep symbolic regression guided by physical unit constraints to a dataset of simulated cracks under mode I, II and mixed-mode conditions with variable T-stress. For the training dataset, we fit the Williams series expansion with super-singular terms to the simulated displacement fields at randomly chosen origins around the actual crack tip. We analyse the discovered formulas and apply the most promising one to digital image correlation data obtained from uniaxial and biaxial fatigue crack growth experiments of AA2024-T3 sheet material. Throughout the experiments, the crack tip positions are reliably detected leading to improved stability of the crack propagation curves.
•Crack tip correction formulas learned from FE simulations with physical deep symbolic regression.•Distinct correction formulas based on Williams coefficients for mode I, mode II, and mixed mode load cases.•Application to uniaxial and biaxial fatigue crack growth experiments accompanied by full-field and high-resolution DIC.
•Multiple cracking from SCC on a 600 Alloy in a tetrathionate solution is evaluated.•A setup coupling Digital Image Correlation, Acoustic Emission and Electrochemical Noise techniques is ...developed.•Crack population is classified into initiation, active and dormant cracks.•Correlations between DIC, AE and EN allow the identification of three stages for the crack colony growth.•The emergence and intensification of interactions are associated to the different stages of the colony growth.
Digital Image Correlation (DIC), Acoustic Emission and Electrochemical Noise measurements were applied to study the growth of multiple intergranular cracks as a colony on an Alloy 600 in a tetrathionate solution. Cracks exceeding 55μm in length and 0.45μm in opening were successfully detected by DIC. Moreover, crack population was classified into initiating, active and dormant cracks, active population being the larger one. The emergence and intensification of interactions produced a modification on the colony growth behavior. They range from a mostly surface crack propagation (in the absence of interactions), to in depth propagation predominantly governed by crack shielding.
Background
The association of advanced digital image correlation (DIC) and numerical simulation has been widely used for inverse parameter identification.
Objective
It is attractive to develop an ...accurate DIC method sharing the common features with numerical simulation, which can lead to better synergy between experiments and simulations.
Methods
A new meshfree digital image correlation (MF-DIC) using element free Galerkin method (EFGM) is proposed for deformation measurement. The EFGM is a classical meshfree method in numerical studies, and it is directly used to construct the shape function in MF-DIC from a set of scattered nodes for image matching. The MF-DIC is principally different from the classical local DIC and global DIC since it does not rely on the concept of a subset or an element.
Results
In MF-DIC, the
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-continuous displacement for every point is constructed based on a group of scattered nodes in a small support domain surrounding it. The continuous strain map can then be directly derived from the displacement, instead of using an additional smoothing technique as required in classical local DIC or post-processing used in global DIC. A performance assessment based on the Metrological Efficiency Indicator (MEI), as defined in DIC Challenge 2.0, shows that the proposed MF-DIC yields an excellent balance between spatial resolution and measurement resolution for both displacement and strain measurements.
Conclusions
Given that the proposed MF-DIC shares common features with the classical meshfree method in computational mechanics, it paves the way for an enhanced synergy between experiments and simulations required for robust inverse parameter identification methods.
A simple and efficient non-destructive testing method is presented to quantify translaminar fracture properties in quasi-isotropic 90/45/0/-453s T800SC/3900-2B carbon fibre-reinforced polymer ...laminates subjected to Over-height Compact Tension (OCT) and Compact Compression (CC) fracture tests. The combination of Digital Image Correlation (DIC) with phased-array ultrasonics enables the consistent measurement of the fibre-dominant translaminar crack length, damage height and hence damage resistance curves as well as the continuous monitoring of the Fracture Process Zone (FPZ). The length of the FPZ is determined by overlaying regions of saturated (fully developed) fibre damage obtained from DIC and ultrasonic C-scans. The analysis of the progressive fracture tests reveals average laminate fracture energies of 161 kJ/m2 and 68 kJ/m2 and FPZ lengths of up to 8–12 mm and 10 mm in tension and compression, respectively. It is shown that the proposed method works best when fibre-dominated damage is confined to a narrow band normal to the loading direction as observed in CC tests. In contrast, OCT test results show that delamination and the corresponding isolated ply behaviour can alter the DIC analyses and hence complicate the measurement of translaminar fracture properties.
Kink band formation is a common deformation mode for anisotropic materials and has been observed in polymer matrix fiber composites, single crystals, geological formations, and recently in metallic ...nanolaminates. While numerous studies have been devoted to kink band formation, the majority do not consider the often rapid and unstable process of kink band propagation. Here we take advantage of stable kink band formation in Cu-Nb nanolaminates to quantitatively map the local strain fields surrounding a propagating kink band during uniaxial compression. Kink bands are observed to initiate at specimen edges, propagate across the sample during a rising global stress, and induce extended strain fields in the non-kinked material surrounding the propagating kink band. It is proposed that these stress/strain fields significantly contribute to the total energy dissipated during kinking and, analogous to crack tip stress/strain fields, influence the direction of kink propagation and therefore the kink band inclination angle.
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Digital image correlation (DIC) techniques have been widely used for experimentally characterizing the mechanical behavior of polymer materials. However, practical applications of DIC for tensile ...testing of polymers often face serious image decorrelation caused by crazing and excessive deformation. In this work, a fluorescent three-dimensional digital image correlation (3D-DIC) with an adaptive incremental calculation strategy is proposed to realize reliable large deformation measurement of polymers by eliminating or mitigating the image decorrelation caused by these issues. The proposed technique first utilizes fluorescent 3D-DIC to eliminate image decorrelation caused by the crazing effect. Then, an adaptive incremental calculation strategy that can automatically update reference images is adopted to mitigate image decorrelation due to excessive deformation. The effectiveness and practicality of the proposed technique were demonstrated by measuring the full-field deformation in chloroprene rubber samples subjected to large tensile deformation. Also, the proposed method was applied to investigate the mechanical behavior of a specific waterproof coating material. Experimental results indicate that the combination of fluorescent 3D-DIC and adaptive incremental calculation strategy can effectively address image decorrelation problems in large deformations of polymers, yielding high-accuracy displacement and strain measurements. This technique holds potential for broader applications in studying the mechanical behavior of other materials or structures undergoing large or super-large deformations.
•Propose a fluorescent 3D-DIC with an adaptive incremental calculation strategy to measure large deformations in polymers.•Fluorescent stereovision imaging effectively avoids decorrelation problem caused by "crazing" in strained polymers.•Adaptive incremental calculation strategy mitigates image decorrelation problem caused by large deformation.
•Fracture characteristics in concrete members have been investigated using DIC technique.•Both monotonic and fatigue loading have been considered.•A systematic approach has been proposed to determine ...the size of fracture process zone in concrete.•DIC measurements has been used to predict fracture parameters accurately.
In this work, an attempt has been made to understand the evolution of fracture process zone in plain concrete member utilizing Digital Image Correlation (DIC) technique. Series of experiments have been performed in centre point bending under the action of monotonic and repetitive loadings and DIC technique is used during the entire test process. A systematic procedure has been developed to monitor the evolution and propagation of the fracture process zone and traction free crack. Size of fully developed FPZ has been found to be approximately equal in both static and fatigue loading cases. It has been also seen that traction free crack propagation has occurred only in medium and large size beams. DIC analysis results have been compared with the measured CMOD values through validation study and both are found to be in good agreement. An analysis has been performed for evaluating the resolution and standard uncertainty in the DIC measured displacements and strains.
This paper presents a mixed numerical–experimental method for the identification of the four in-plane orthotropic engineering constants of composite plate materials. A biaxial tensile test is ...performed on a cruciform test specimen. The heterogeneous displacement field is observed by a CCD camera and measured by a digital image correlation (DIC) technique. The measured displacement field and the subsequently computed strain field are compared with a finite element simulation of the same experiment. The four independent engineering constants are unknown parameters in the finite element model. Starting from an initial value, these parameters are updated till the computed strain field matches the experimental strain field. Two specimen geometries are used: one with a centered hole to increase the strain heterogeneity and one without a hole. It is found that the non-perforated specimen yields the most accurate results.
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