Digital Image Correlation Analysis Research Articles

Notched Tensile Fracture of a Fe-15Mn-0.6C-2Al Twinning Induced Plasticity Steel at Room Temperature

The tensile fracture behavior of an Al-bearing TWIP steel was investigated by conducting a series of tensile tests on smooth and notched specimens with different notch geometries, focusing on the effects of evolution of the stress triaxiality and the effective strain during deformation. The flow curve and digital image correlation (DIC) analysis evidenced suppression of dynamic strain aging due to Al addition, and therefore, the effects of local inhomogeneous deformation associated with Portevin-Le Chatelier (PLC) band on fracture could be excluded. The smooth specimen fractured with negligible necking despite the absence of PLC bands. As a result, the effective strain was uniform through the gage section and the stress triaxiality (<i>η</i>) of ~0.33 was nearly unchanged over the entire cross-section up to the maximum load. This led to the fracture surface of the smooth specimen being entirely covered with fine equiaxed dimples. For notched specimens, the fracture strain was drastically reduced with decreasing notch radius, indicating the high notch susceptibility of the steel. The effective strain of the notched specimens was the highest at the edge of the notch root, regardless of the notch radius, so cracks first developed at the surface of the notch root. Although the <i>η</i> at the center of the notched specimens (0.40~0.48 depending on the notch radius) was higher than that of the smooth one, the center of the fracture surface of all notched specimens exhibited dimple features that were very similar to the smooth one, even in size. In contrast, in spite of the same <i>η</i> of ~0.33, fractography at the edge of the notched specimens revealed a fracture mode transition from dimple fracture to void sheet fracture to quasi-cleavage fracture as the notch radius decreased. The present results were rationalized in terms of the local evolution of stress triaxiality and effective strain during deformation, which were analyzed using the finite elemental method and DIC technique. It can be said that the fracture mode of TWIP steel, showing limited necking, was more influenced by the distribution and/or gradient of stress traiaxiality and effective strain rather than their local absolute values - that is, the severer their gradient is, the easier the quasi-cleavage fracture occurs.

Assessments of polymerization shrinkage by optical coherence tomography-based digital image correlation analysis—Part I: Parameter identification

ObjectiveTo investigate the feasibility of optical coherence tomography (OCT)-based digital image correlation (DIC) analysis and to identify the experimental parameters for measurements of polymerization shrinkage. MethodsClass I cavities were prepared on bovine incisors and filled with Filtek Z350XT Flowable (Z350F). One OCT image of the polymerized restoration was processed to generate virtually displaced images. In addition, the tooth specimen was physically moved under OCT scanning. A DIC software analyzed these virtual and physical transformation sets and assessed the effects of subset sizes on accuracy. The refractive index of unpolymerized and polymerized Z350F was measured via OCT images. Finally, different particles (70–80 µm glass beads, 150–212 µm glass beads, and 75–150 µm zirconia powder) were added to Z350F to inspect the analyzing quality. ResultsThe analyses revealed a high correlation (>99.99%) for virtual movements within 131 pixels (639 µm) and low errors (<5.21%) within a 10-µm physical movement. A subset size of 51 × 51 pixels demonstrated the convergence of correlation coefficients and calculation time. The refractive index of Z350F did not change significantly after polymerization. Adding glass beads or zirconia particles caused light reflection or shielding in OCT images, whereas blank Z350F produced the best DIC analysis results. SignificanceThe OCT-based DIC analysis with the experimental conditions is feasible in measuring polymerization shrinkage of RBC restorations. The subset size in the DIC analysis should be identified to optimize the analysis conditions and results. Uses of hyper- or hypo-reflective particles is not recommended in this method.

Digital Image Correlation Analysis of Uniform Deformation and Necking in Solid‐State Welded Nanocrystalline Aluminum via High‐Pressure Torsion

Solid‐state welding of Al 1043 sheets was achieved via high‐pressure torsion (HPT) processing to produce bulk nanostructured Al disks. A homogeneous nanostructure without segregation was observed, with grain sizes of ∽430‐470 nm. Miniature tensile testing, coupled with the digital image correlation (DIC) technique, was employed to determine the room‐temperature tensile deformation behavior, particularly the non‐uniform behavior with necking, of the HPT‐bonded ultrafine‐grained (UFG) aluminum, comparing it with annealed coarse‐grained counterpart. The HPT‐bonded UFG Al exhibited a large fraction of post‐necking strain, which is supported by the estimated high strain rate sensitivity value of m = 0.085, suggesting the delay of local necking leading to tensile fracture. Detailed DIC analysis revealed prolonged diffuse necking, thus delaying local necking, in the HPT‐bonded UFG Al, while the annealed samples show high fractions of local necking during the non‐uniform deformation. Moreover, the DIC data illustrated that local necking predominantly occurred at a limited neck zone, maintaining a plateau strain distribution at the out‐of‐neck zone throughout necking deformation towards tensile failure for both annealed and UFG aluminum. The DIC method offers an alternative means to demonstrate the transition in necking behaviors of materials by estimating the plastic lateral contraction exponent.This article is protected by copyright. All rights reserved.

Evaluation of crush performance of extruded aluminum alloy tubes based on finite element analysis with ductile fracture modeling

In this study, the crush performance of four aluminum extrusions are investigated through analysis based on finite element (FE) simulation incorporating experiment-numerical hybrid ductile fracture modeling. Tensile tests on standard and non-standard specimens, coupled with digital image correlation and FE analyses, are employed to establish constitutive models for the materials. The evaluation of crush performance is performed based on both axial crush test and corresponding 3-dimensional FE simulation, which could validate the employed plasticity and fracture laws and predict crush performance indicators with reliable accuracy. Additionally, FE modeling enables thorough analysis of highly non-proportional loading paths and potential crack initiation sites, with the crack formation mechanism elucidated through the evolution of a proposed damage variable. Furthermore, the modified crush performance indicators are newly suggested, which could explain the dependence on both the absorbed energy of tubular extrusion and properties of ductile fracture.

Low-temperature crack resistance of stone matrix asphalt mixtures under chloride salt dry-wet cycles

Given the current insufficient understanding of the low-temperature crack resistance performance and crack evolution patterns of asphalt mixtures under chlorinated salt wet-dry coupling environments, this study aims to fill this knowledge gap. We employed SMA-13 asphalt mixtures modified with different dosages of polyester fibers (0 %, 0.3 %, 0.35 %, 0.4 %, 0.45 %, 0.5 %) and tested their low-temperature crack resistance by conducting 0 to 8 wet-dry cycles in pure water and a 13.25 % chlorinated salt solution, to explore the improvement effect of polyester fibers on the performance of asphalt mixtures in such environments. The results indicate that an increase in the number of wet-dry cycles leads to a degradation of crack resistance performance across all fiber dosages, especially under the influence of chlorinated salt wet-dry coupling, where the adverse effects are more pronounced. Fracture energy analysis further confirms that 4 and 6 cycles of wet-dry cycling are effective indicators for evaluating the attenuation of low-temperature crack resistance under the long-term impact of wet-dry cycling. Through Digital Image Correlation (DIC) and Scanning Electron Microscopy (SEM) analyses, this study reveals the significant impact of wet-dry cycling on crack evolution and identifies 0.4 % as the optimal dosage of polyester fibers, significantly enhancing the low-temperature crack resistance performance of asphalt mixtures.

Thermomechanical behavior of textile-reinforced geopolymer concrete based on mineral-impregnated carbon-fibers (MCFs) composites

State-of-the-art textile reinforcements are well employed to strengthen, rehabilitate or build new structures, whilst polymeric impregnation degrades considerably in elevated temperatures or aggressive environments. Herein, mineral-based matrices are regarded as a viable and novel technique. This study introduces a methodology to manufacture 2D-textile reinforcements using mineral-impregnated carbon fiber (MCF) automatically via a pultrusion and robotic–based structuring process. The reinforcing ability of MCF textiles without and with surface modification in geopolymer (GP) concrete was compared to commercial epoxy-impregnated textiles. After thermally stimulated rapid solidification, the resulting grid-like structures were incorporated into the concrete matrix. The MCF-GP-concrete composites were evaluated regarding their load-bearing capacity from 20 °C to 200 °C. Digital Image Correlation (DIC) and μCT analysis were used to study damage processes and interphase adhesion. The results demonstrated that GP concrete components with MCF textiles exhibited superior thermal resistance and a bi-linear stress-strain behavior compared to polymer matrix composite. Dilatometry and TGA measurements provided shrinkage and dehydration evidence for the thermally induced strength decrease. The enhanced chemical compatibility achieved via GP impregnation facilitates the formation of finely distributed crack patterns with reduced crack widths, contributing to improved durability scenarios and failure behavior of textile-reinforced concrete (TRC).

High‐speed observation of dynamic delamination failure in tapered composite laminates under tensile loading

AbstractThis article presents high‐fidelity observations of the time evolution of unstable delamination growth in tapered composite beams under tensile loading via ultra‐high‐speed camera in conjunction with digital image correlation. Asymmetrically tapered GFRP laminates, with a thickness drop from 18 plies to 12 plies, are manufactured in three different layup configurations with grouped drop‐offs: [06/(02)3/06], [06/06/06], and [06/(±45)3/06]. Beam specimens are subjected to quasi‐static tensile loading in a servo‐hydraulic axial testing machine, and the damage evolution on one edge of the tapered beam is monitored in situ at 124,000 fps with a high‐speed camera (HSC). In selected tests, digital image correlation (DIC) analyses are conducted either on the edge or on the tapered surface to obtain the full‐field strain and elucidate failure mechanisms. Real‐time HSC observations of the damage sequence consistently affirm that the initial failure mechanism is a transverse crack at the nearest drop‐off to the thin section, which is followed by delaminations at interfaces of sublaminates. Unstable delamination growth is characterized by measurements of lower bounds of crack tip speeds. The unique crack speed data provide evidence for the existing effect of through‐the‐thickness stresses on delamination growth. The detailed sequence and patterns of dynamic failure presented in this paper can serve as a benchmark to validate damage models used in simulations of tapered laminates.Highlights The sequence of unstable delamination growth in tapered GFRP beams is investigated experimentally. Characterized unstable delamination growth based on crack tip speed measurements. Strain fields are evaluated along beam edges using DIC in real‐time. In‐situ observations of dynamic failure can serve as a benchmark to validate damage models.

The microstructure and precipitated phase dependence of plastic deformation and fracture mechanism in repaired IN718 alloy by directed energy deposition

This work studied microstructural evolution, precipitate behaviors, and micro-hardness distribution along the built direction of directed energy deposited IN718 alloy. In combination with digital image correlation and crystallographic orientation analysis, the plastic deformation and fracture mechanisms of coarse columnar grains were explored in detail. The columnar grains in the deposition zone (DZ) grow along the <001> direction in the crystallography and gradually widen with increasing built height. The misorientation angle per unit length within individual columnar grains first decreases and then slows down to ∼ 0.07 °/μm when the deposition height is ∼ 1.8 mm. The micro-hardness in the DZ is gradually decreased along the built direction, which may be due to the increasing average columnar grain width and primary dendrite arm spacing, as well as reducing the volume fraction of the γ'' + γ' phases. During the uniaxial tensile loading, most plastic deformation always occurs in the DZ irrespective of the lowest hardness in the heat-affected zone (HAZ). The nucleation of microvoids is ascribed to the granular Laves phase debonding from the γ matrix. The number of microvoids gradually decreases with increasing distance from the fracture surface, which may be attributed to the strain-controlled nucleation of microvoids. EBSD results substantiated that the columnar grains near the fracture surface occur to severe lattice rotation, leading to the Kernel misorientation angle distribution in each grain interior increasing to about 1° ∼ 4°.

Determination of the In-Plane Shear Behavior of and Process Influence on Uncured Unidirectional CF/Epoxy Prepreg Using Digital Image Correlation Analysis

The investigation of the in-plane shear behavior of prepreg is crucial for understanding the generation of wrinkles of preforms in advanced composite manufacturing processes, such as automated fiber placement and thermoforming. Despite this significance, there is currently no standardized test method for characterizing uncured unidirectional (UD) prepreg. This paper introduces a ±45° off-axis tensile test designed to assess the in-plane shear behavior of UD carbon fiber-reinforced epoxy prepreg (CF/epoxy). Digital image correlation (DIC) was employed to quantitatively track the strains in three dimensions and the shear angle evolution during the stretching process. The influences of the temperature and stretching rate on the in-plane shear behavior of the prepreg were further investigated. The results reveal that four shear characteristic zones and wrinkling behaviors are clearly distinguished. The actual in-plane shear angle is significantly lower than the theoretical value due to fiber constraints from both the in-plane and out-of-plane aspects. When the off-axis tensile displacement (d) is less than 15.6 mm, the ±45° specimens primarily exhibit macroscale in-plane shear behavior, induced by interlaminar interface shear between the +45° ply and −45° ply at the mesoscale. The shear angle increases linearly with the d. However, when d &gt; 15.6 mm, fiber squeezing and wrinkling begin to occur. When d &gt; 29 mm, the in-plane shear disappears in the completely sheared zone (A). The reduction in the resin viscosity of the CF/epoxy prepreg caused by increased temperature is identified as the primary factor in lowering the in-plane shear force resistance, followed by the effect of the increasing resin curing degree. Higher shear rates can lead to a substantial increase in shear forces, eventually causing cracking failure in the prepreg. The findings demonstrate the feasibility of the test method for predicting and extracting uncured prepreg in-plane shear behaviors and the strain-rate and temperature dependency of the material response.

The Tensile Behavior of Hybrid Bonded Bolted Composite Joints: 3D-Digital Image Correlation versus Finite Element Analysis.

This study examines the behavior of hybrid bolted/bonded (HBB) joints loaded in tensile shear comprising plain weave carbon/epoxy laminates in quasi-isotropic (QI) and cross-ply (CP) layups. It proposes a combined approach of 3D digital image correlation and finite element analysis (FEA) to assess their behavior. To apply the FEA simulation accurately, a single layer of plain fabric was replaced with [0/90]s lamination. Experimental standard open-hole tension test results, as well as only bolted (OB) and HBB, along with FEA predictions, confirmed the accuracy of the substitution method. The FEA, calibrated by experimental results, provides insight into the distinctive characteristics of HBB joints in comparison with bonded and bolted joints. Critical considerations include material properties, damage modeling, adhesive characteristics, and mass scaling. The FEA results underscored the pivotal role of adhesives in HBB joints, rendering them akin solely to bonded configurations. HBB joints retain their geometry better than OB joints with considerably less out-of-plane displacement, following a sinusoidal trend. Moreover, the overall behavior of the two layups demonstrates that CP benefits from having higher strength than QI, especially at the critical hole located closer to the grip side.

Laboratory Earthquake Ruptures Contained by Velocity Strengthening Fault Patches

Laboratory Earthquake Ruptures Contained by Velocity Strengthening Fault Patches

Experimental investigation on the load-bearing capacity and deformation behaviour of the composite lining with polyurethane compressible layer

Lining structures for tunnels in rheological rocks are susceptible to large deformations and damage. Installation of a polyurethane (PU) compressible layer between the primary and secondary lining provides a potential solution to mitigate large deformation hazards. Although the capability of PU-enhanced composite lining in adapting and absorbing large deformation has been found, its underlying load-bearing mechanism and deformation behaviour remain less understood. To fill the gap, large-scale model tests were conducted using a self-designed loading test setup, primarily focusing on the mechanical response of PU-enhanced composite lining. Ten lining specimens with varying thicknesses (25, 37.5, and 50 mm) and densities (50, 100, and 150 kg/m3) of the PU compressible layer were investigated. The digital image correlation (DIC) analysis technique was used to detect real-time deformation and strain fields under loading conditions. Results demonstrated that the PU compressible layer enhanced the ultimate load, toughness, and deformation capacity of the composite lining by an average of 17.6 %, 164.6 %, and 157.4 %, respectively. The load-displacement response of the specimens with PU compressible layer could be categorized into four stages: pre-cracking, post-cracking, strain-hardening, and failure. The primary lining experienced the largest vertical displacements among the specimens with the PU compressible layer, followed by the compressible layer and the secondary lining. Although the specimens exhibited similar progressive failure modes, there were variations in crack distribution and propagation. The analysis of rock-support interaction indicated that increasing the thickness of the PU compressible layer mainly affects the deformation capacity when the secondary lining reaches its elastic limit.

Behaviors of triaxial woven fabric composites reinforced concrete cylinders under eccentric compression

Concrete reinforced by textile composite materials has long been a focus of substantial interest in the engineering applications. In this paper, the compression performance of concrete cylinders confined by carbon fibers, glass fibers, and carbon–glass hybrid triaxial woven fabric composites under three different eccentricities were investigated. Moreover, the digital image correlation analysis method was introduced to observe the compression process and failure modes of reinforced concrete cylinders. Meanwhile, the strain process of yarns during the failure was also analyzed. The result showed that all of triaxial woven fabric composites can increase the strength of concrete cylinders, while the strength decreased with the increase of eccentricity and the mechanical performance converged gradually. In addition, using triaxial woven fabric composites made of glass fibers can promote the ductility of concrete cylinders. It also indicated that employing carbon–glass hybrid triaxial woven fabric composites can not only have the advantages of increasing the strength and ductility of concrete cylinders, and low cost, but also effectively reduces the eccentric sensitivity.

Strain partitioning in dual-phase eutectic high-entropy alloy: Dependence on phase boundary morphology

Strain partitioning in dual-phase eutectic high-entropy alloy, AlCoCrFeNi2.1, is investigated under uniaxial tension with in situ high-resolution digital image correlation (DIC) in a scanning electron microscope (SEM). Nanoscale speckles are fabricated on the sample surface. Three regions with different phase morphologies at different applied strains are characterized by SEM for DIC analysis. Strain localization tends to form at softer face-centered cubic (FCC) rather than body-centered cubic phase domains, and the degree of strain localization in a lamellar structure is much lower than in a bimodal structure. Transmission electron microscopy is conducted to characterize the phase interaction at the nanoscale. A straight phase boundary in a lamellar structure allows more geometrically necessary dislocations to pile up at the phase boundary and form a wide interface affected zone (IAZ) in the soft FCC domain. The IAZ strengthens the soft FCC and better accommodates the deformation of the two phases, resulting in a relatively uniform strain partitioning.

Cracking and failure mode behavior of hybrid FRP strengthened RC column members under flexural loading

AbstractStrengthening of reinforced concrete (RC) members in bridges and buildings is often required to improve flexural performance. Strengthening using fiber‐reinforced polymer (FRP) composites has become popular as FRPs offer multiple advantages compared with conventional strengthening practices like steel jacketing and concrete enlargement. External bonding (EB) using carbon FRP (CFRP) laminates/fabric has become a common strengthening practice. The effectiveness of the EB strengthened system is reduced due to possible debonding of FRP from concrete substrate. The near‐surface mounting (NSM) of FRP laminates is efficient in reducing the debonding failure, but it is not effective under dominant compression loading. Hybrid FRP (HYB) strengthening combines the advantages of both the NSM and EB techniques. HYB strengthening can enhance the performance of RC members under all loading combinations. The main objective of this study is to understand the flexural crack opening behavior of control and hybrid FRP strengthened RC column members under pure bending. The digital image correlation (DIC) analysis shows that the crack width and its propagation are significantly reduced due to hybrid FRP strengthening. The crack widths measured using the DIC are compared with the analytical predictions based on Eurocode 2 and fib bulletin 90. HYB FRP strengthening increased the strength and post‐cracking stiffness of RC elements under flexure without compromising the ductility. In addition, the HYB strengthening distributed the damage under flexural loading, unlike localized damage observed in control RC elements.

High temperature fracture behavior of 316L stainless steel-Inconel 718 functionally graded materials manufactured by directed energy deposition: Role of interface orientation and heat treatment

Investigation of functionally graded component consisting of stainless steel 316L (SS316L) and Inconel 718 superalloy (IN718) deposited by laser directed energy deposition (LDED) is presented here. Ambient as well as high temperature mechanical behavior is observed for as-deposited (AD) and for heat-treated (HT) states. The gradient sample was manufactured with the interface orientation parallel and perpendicular to the loading direction to understand the impact of this factor on the materials properties. The evolution of chemical composition, grain structure, phase transformations, and tensile properties at room and elevated temperatures, as well as creep behavior before and after heat treatment was determined. With use of digital image correlation (DIC) analysis, the effects of interface orientation and heat treatment on deformation and fracture mechanism was revealed. Results show that heat treatment smooths the chemical composition and mechanical deformation process, as characterized by the formation of an enhanced gradient diffusion zone in the IN718-rich region near the interface. Heat treatment impacts mechanical properties based on the orientation of the interface. Specimens with interfaces parallel to the load direction combine the strengths of both materials effectively. After HT, they exhibit enhanced mechanical performance, achieving an ultimate tensile strength of 973 MPa and 14% elongation at room temperature. Additionally, at elevated temperatures, the specimen demonstrates exceptional creep resistance, sustaining structural integrity for over 1700 h at 650 °C and 225 MPa. Sample orientation is shown a decisive effect on deformation and fracture mechanism, with the interface not consistently being the weakest point across various gradient samples.

Polymer-Infiltrated Ceramic Network Produced by Direct Ink Writing: The Effects of Manufacturing Design on Mechanical Properties

Polymer-infiltrated ceramic network (PICN) materials have gained considerable attention as tooth-restorative materials due to their mechanical compatibility with human teeth, especially with computer-aided design and computer-aided manufacturing (CAD/CAM) technologies. However, the designed geometry affects the mechanical properties of PICN materials. This study aims to study the relationship between manufacturing geometry and mechanical properties. In doing so, zirconia-based PICN materials with different geometries were fabricated using a direct ink-writing process, followed by copolymer infiltration. Comprehensive analyses of the microstructure and structural properties of zirconia scaffolds, as well as PICN materials, were performed. The mechanical properties were assessed through compression testing and digital image correlation analysis. The results revealed that the compression strength of PICN pieces was significantly higher than the respective zirconia scaffolds without polymer infiltration. In addition, two geometries (C-grid 0 and C-grid 45) have the highest mechanical performance.

Abstract 194: Single-cell mechanical analysis reveals that astrocytes and glioblastoma cells have similar viscoelastic properties

Abstract Despite recent advances in treatment, the survival rate of glioblastoma (GBM) patients remains low due to the cancer’s resistance to current treatment modalities. Solid tumors like GBM are known to harbor physical abnormalities at the tissue and cell level. An understanding of GBM cell mechanics may therefore lead to the identification of novel disease mechanisms, biomarkers, and therapeutic strategies to improve treatment outcomes. In this study, we aimed to compare the mechanics of human GBM cells and their normal counterpart, immortalized human astrocytes (IHAs). To accomplish this, we used a parallel-plate flow system to expose single cells to physiological fluid shear stress and recorded the resulting deformation using a camera-coupled microscope. We then utilized digital image correlation analysis to create strain-time profiles of individual cells and fit the profiles with a three-parameter generalized Maxwell model to characterize their nuclear and cytoplasmic viscoelastic properties. We also used fluorescence microscopy and atomic force microscopy to quantify actin density and alignment and adhesion energy in both cell types, respectively. Our results showed that, contrary to extracranial cancer cells, the viscoelastic properties of GBM cells are similar to their normal counterpart. This may explain why metastasis in GBM patients is rare and conventional treatment options are unsuccessful. We also found that actin organization and localization and adhesion energy is different between GBM cells and IHAs. Thus, future research which links the genetic and microenvironmental factors that modulate these unique mechanical features may lead to the development of rational and novel clinical strategies against GBM. Citation Format: Julian Najera, Killian Onwudiwe, Luke Holen, Alice A. Burchett, Dorielis Rodriguez, Maksym Zarodniuk, Saeed Siri, Meenal Datta. Single-cell mechanical analysis reveals that astrocytes and glioblastoma cells have similar viscoelastic properties [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 194.

Additive manufacturing of sensor prototype based on 3D-extrusion-printed zirconia ceramics

Additive manufacturing of ceramics has attracted large interest due to its unique ability to rapidly prototype, low cost, and increased geometric complexity. Material extrusion technique is often considered for processing and shaping fine and dense ceramic structures because of the high solid loading in ink. In this work, 8 mol.% yttria-stabilized zirconia ink with 70 wt% ceramic loadings was prepared to print zirconia samples in horizontal and vertical directions, following two different filament orientations: 0/90° and ±45°. The study's main objective was to evaluate printing design influences on mechanical properties. This was assessed through flexural testing and digital image correlation analysis. Experimental findings showed that samples printed horizontally with ±45° filament orientation displayed the highest strength. A detailed inspection of fracture surfaces revealed that printing defects were the critical failure location sites formed after sintering and intimately related to printing design issues. After that, a conductive sensor was integrated into the surfaces of 3D-printed specimens by screen-printing silver-based conductive ink to analyze the structural health of zirconia samples. The sensing capabilities of printed conductive patterns were investigated using the four-point bending tests. The results demonstrated that the electrical resistance of the printed silver patterns increased as the applied load on zirconia substrates rose. It indicates that hybrid material extrusion and screen printing techniques are favored ways to manufacture sensors for structural detection of advanced 3D-printed ceramics.

In-situ analysis of SCC initiation on Alloy 600 surface in primary water environment using digital image correlation with electron backscatter diffraction

This study examined the stress corrosion cracking (SCC) phenomenon of Alloy 600 in a high-temperature primary water environment. The investigation involved the observation of local plastic deformation and SCC initiation on the specimen surface using an observation apparatus, comprising a laser confocal microscope (LCM) and an autoclave equipped with a diamond window view-port. Prior to conducting the SCC initiation test, the crystalline structure of the specimen, including grain boundary (GB) characteristics, Schmid factor, and trace inclination angle, underwent examination using an electron backscatter diffraction (EBSD) technique. The local strain distribution was subsequently analyzed using a digital image correlation (DIC) method, employing LCM images obtained during the SCC experiments. The ex-situ EBSD analysis indicated that SCC mainly initiated at random high-angle grain boundaries (HAGB) with trace inclination angles close to 90° relative to the tensile axis. DIC analysis further revealed that most GBs in the vicinity of the highly strained area cracked among random HAGBs with a high trace inclination angle to the tensile axis. This confirms that the local strain gradient at GBs plays an important role in SCC initiation, serving as a more suitable indicator of an additional stress component to effective normal stress acting on GBs compared to the Schmid factor mismatch.