•Introducing comprehensive literature review about deformation measurement technique in the presence of discontinuities.•The techniques are grouped together as per their relevance.•Discussing DIC ...based techniques for measuring discontinuous deformation.•Future research areas for discontinuous deformation measurement are discussed.
Digital Image Correlation (DIC) is the heart of the remote deformation measurement techniques using images. It is applied to many different applications from medical imaging to engineering problems for measuring deformation remotely with high accuracy. Whereas it is highly successful in measuring continuous deformation, it has severe limitation of failure in measuring discontinuous deformation. Most of the real world problems contains discontinuous deformation and this makes the DIC application restricted to lab environment only. This study presents the first comprehensive literature review on remote deformation measurement in the presence of discontinuities using images. Different methodologies to overcome the limitation of DIC are analysed and categorized systematically. Finally, based on the reviewed literature, a broader outlook and possible future research directions in this area of research are presented.
For the determination of the shear properties such as strength, strain and modulus of unidirectionally reinforced composites, nearly a dozen measurement techniques exist, several of which have found ...their way into standards. One non-standardized method for sheet materials is the 10° off-axis tensile test of unidirectional coupons. The current work focuses on the experimental investigation of tensile testing of CFRP-UD coupon specimens using the 10° off-axis test and DIC strain mapping to measure the full-field deformation response. A sensitivity analysis on the measured stresses, strains and moduli is performed by varying the aspect ratio of the specimens and the location of strain measurement. Test related uncertainties such as the loading angle and specimen preparation details are investigated and quantified with the help of these full-field DIC measurements.
A nickel-based superalloy is examined during monotonic deformation from ambient to cryogenic temperatures, reaching as low as liquid helium temperature. A detailed multimodal analysis of the ...microstructure and plasticity is conducted to discern changes in deformation mechanisms and plastic deformation localization under cryogenic conditions. This study employs high-resolution digital image correlation and transmission electron microscopy to identify the deformation mechanisms and understand their influence on plastic deformation localization as the temperature varies. At cryogenic temperatures, unusual plastic deformation localization processes are observed, attributed to the competing activation of a range of deformation processes. Furthermore, a mechanism of slip delocalization, i.e., local plastic deformation homogenization through closely spaced slip, is noted at these extreme temperatures. Ultimately, the impact of the microstructure is identified across the temperature range, from room to cryogenic temperatures.
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This study reviews the recent progress in the application of digital image correlation (DIC) to testing composite structures with an order of size magnitude of meters. The DIC technique has gained ...wide popularity in materials and structural testing due to the merit of being full-field and non-contact compared to conventional point-wise measurement techniques. This study focuses on the DIC application to large-scale composite structure testing. Experimental setup requirements, measurement capabilities, and the associated challenges are thoroughly reviewed and analyzed. Typical applications found in the literature are from wind energy and aerospace sectors for displacement and strain measurements under static loading and operational modal analysis in dynamic structural tests. The remaining challenges along with their possible solutions are discussed and summarized in this work to shed light on future research needs on testing large-scale composite structures using the DIC technique.
The effect of aging on the accumulation of microscale plasticity, and the resulting macroscopic mechanical behavior, were examined in the magnesium alloy WE43 under uniaxial tension. Full-field ...strains on the length scale of the microstructure, and their relation to the underlying crystallography, were captured using a combination of electron backscatter diffraction, custom nanoparticle patterning processes for corrosion-susceptible alloys, scanning electron microscopy (SEM), in-SEM uniaxial tensile and compressive loading, and distortion-corrected digital image correlation. The as-received material exhibited an average grain size of 12 µm. The strain incurred on individual slip traces in magnesium was resolved for the first time. Insights into slip activation across the microstructure revealed that using Schmid's Law with the nominal Schmid Factor appeared to be predictive for basal and non-basal slip. The DIC results were compared with simulation using an advanced open-source crystal plasticity finite element (CPFE) code, PRISMS-Plasticity. The PRISMS-Plasticity model is a more precise determination of the local Schmid Factor and was used to simulate variations in slip and twin activity within each grain. Such simulations provide an avenue for physically interpreting the various slip traces observed in the dense DIC data and an improved understanding of the critical resolved shear stress of the various slip systems.
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Laser powder bed fusion (L-PBF) is an additive manufacturing technology widely applied to the manufacture of metallic parts. The L-PBF processed aluminum-silicon (Al–Si) cast-type alloy components ...exhibit an anisotropic tensile ductility. In this study, we investigated the influence of heat treatments on the microstructural features of an Al–12%Si binary alloy fabricated via L-PBF and the associated inhomogeneous deformation of its melt-pool structure, which contributes to the resulting anisotropic tensile ductility. The mechanical inhomogeneity of the melt-pool structure and the change induced by annealing at various temperatures (300 and 530 °C) were characterized using microscale digital-image correlation analyses of scanning electron microscopy images obtained in situ during tensile deformation and nanoindentation hardness mapping. In the specimen fabricated via L-PBF, the high strain was concentrated at the locally coarsened microstructure (the soft region) along the boundaries of the melt pools rather than at the refined solidification microstructure (the hard region) within the melt pools. The localized strain varied depending on the geometrical relation between the orientation of the melt-pool boundary and the tensile direction, thus contributing to the anisotropic tensile ductility. This tendency appeared less pronounced in the specimen annealed at 300 °C, which exhibited a slightly homogenized melt-pool structure. The reduced strain localization is associated with a reduced difference in local strength between the melt-pool boundary (soft region) and the melt-pool interior (hard region). The slight homogenization of the melt-pool structure emphasized the effect of grain morphologies in the α-Al matrix on the inhomogeneous deformation within melt pools. In the specimen annealed at 530 °C, which exhibited a homogenized α-Al/Si two-phase microstructure, the uniformly distributed Si phase would be responsible for the homogenous deformation, resulting in an isotropic tensile ductility. This study advances our understanding of the correlation between the melt-pool structure and the deformation behavior of Al–Si alloys processed using L-PBF, which provides new insights for controlling the ductility by post-processing.
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•Microstructures of L-PBF Al–12Si alloy after annealing at 300/500 °C were studied.•Nanoindentation revealed that melt-pool boundary was locally softer than interior.•Micro-DIC analysis captured inhomogeneous deformation on the melt-pool structure.•Strain localization behavior at melt-pool boundary depended on tensile direction.•Strain distribution in melt-pool interior can be affected by α-Al grain structure.
•Average stress versus local axial strain yields reasonable estimate of post-necking hardening response.•Demonstrated validity of stress–strain curve estimate through numerical simulations.•Performed ...uniaxial tension and bulge tests for experimental validation.•Stress–strain curve obtained from uniaxial tension experiments of DP780 steel for strains as high as 0.5.
The exact stress–strain curve can be directly identified from uniaxial tension experiments up to the point of onset of diffuse necking. To gain insight into the post-necking hardening response of metals, other experimental methods such as the bulge, compression or torsion experiments are typically employed. Here, we introduce the idea of using surround DIC to obtain accurate specimen shape measurements of tensile specimens with rectangular gage section. Based on the results from a series of detailed three-dimensional finite element simulations of ASTM E8 type of uniaxial tension experiments on a wide spectrum of steel and aluminum behaviors, it is proposed to combine the history of the axial strain on the surface at the specimen center with the average axial stress to extract the stress–strain curve for strains of up to axial true strain of 1. The estimation uncertainty of this stress–strain curve estimation procedure is of the same order as that of the associated experimental uncertainties. This result is validated through an additional computational study for more than 100 distinct hardening behaviors. Furthermore, a surround DIC system composed of four stereo DIC systems is built and used to determine the stress–strain curve for a 1.5 mm thick DP780 steel. In addition, bulge experiments are performed on the same material revealing a good agreement of the post-necking hardening behavior determined through uniaxial and bulge testing.
The use of recycled aggregates in the manufacturing of asphalt concrete is becoming increasingly widespread. This requires special attention to characterize their performance in terms of durability ...to reduce major maintenance and rehabilitation expenditures. To achieve this, it is necessary to use effective and easy-to-implement test procedures to observe and estimate the various damage and cracking processes that often lead to the structural failure of materials. Many studies have shown that the estimation of cracking energy depends on the extent of damage and cracking processes. In this context, the method of estimating the crack propagation path and the accompanying damage strongly influence the calculated value of the fracture energy. This can lead to an overestimation or underestimation of the material’s performance. Based on these considerations, our aim is to introduce a new approach for improving the estimation of cracking processes to assess resistance to crack propagation. A three-point bending test was conducted on recycled bituminous concrete samples with a single notch at two distinct temperatures, −5 °C and 10 °C. The extent of the cracking process and damage was estimated using 2PDIC, a two-part digital image correlation method. The parametric analysis of the measurements obtained by 2PDIC reveals that defining the pseudo-strain threshold enables the observation of different amplitudes and levels of strain associated with the various processes that accompany the cracking test. The results obtained for the two temperatures considered demonstrate a significant change in cracking energy, which is often overestimated and depends on the crack propagation path and the granular arrangement of the material through which the crack passes. The measurements obtained using 2PDIC also demonstrate the greater tortuosity of the crack propagation path at higher temperatures, which results in a reduction of the estimated cracking energy derived from more simplistic approaches.
Here, we investigate the tensile deformation behavior in a Ni42Fe30Cr12Mn8Al5Ti3 complex-concentrated alloy with heterogeneously-grained structure consisting of fine and ultrafine grains containing ...nano-sized L12 precipitates. It is found that Lüders band initiation and propagation account for the early stage of deformation. High-resolution digital image correlation investigation reveals that there is strong strain partitioning between fine and ultrafine-grained domains upon plastic deformation. Significant strain gradient across the domain-interfaces is thus established. Strain partitioning promoted dense microshear bands are observed in the deformed alloy. They are uniformly distributed and interacted with each other, resulting in the formation of strain concentration zones, which are mostly evolved in fine-grained domains and some of them extend into ultrafine-grained domains at high strain levels. Thus, the global plastic deformation of the alloy is synergistically accommodated. Finally, local high stress in strain concentration zones in ultrafine-grained domains promotes the formation of voids at triple junctions of grain boundaries.
The process of formation and subsequent propagation of transverse cracks in 90° plies of carbon-fiber laminated composites was studied using modal acoustic emission approach and digital image ...correlation techniques. The results from modal acoustic emission approach, which included a newly developed processing tool for acoustic emission waveforms, provided information for identification and subsequent characterization or localization of signals originating from transverse cracking by analysis of the separated flexural and extensional Lamb wave modes in terms of their modal parameters. The digital image correlation method served as a verification tool of the acoustic emission data outputs in the terms of activity of significant localized events originating from the formation of the transverse crack in the 90oply. This made it possible to specify more locally the accompanying activity belonging to the formation or propagation of the magistral transverse crack. The manuscript also presents results related to the evolution of flexural/extensional wave modal parameters as the function of loading force for both 0/0/0/90S and 90/0/0/0S panels. It can be concluded that the detection of transverse cracks requires the need for applying a more complex acoustic emission data analysis methodology, while the standard parametric analysis, including the waveform peak frequency, is not sufficient. The presented methodology may serve as a basis for development of robust analysis tool capable of detecting the investigated phenomena.
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