An official website of the United States government
Hydrogels are a class of soft, highly deformable materials formed by swelling a network of polymer chains in water. With mechanical properties that mimic biological materials, hydrogels are often proposed for load bearing biomedical or other applications in which their deformation and failure properties will be important. To study the failure of such materials a means for the measurement of deformation fields beyond simple uniaxial tension tests is required. As a non-contact, full-field deformation measurement method, Digital Image Correlation (DIC) is a good candidate for such studies. The application of DIC to hydrogels is studied here with the goal of establishing the accuracy of DIC when applied to hydrogels in the presence of large strains and large strain gradients. Experimental details such as how to form a durable speckle pattern on a material that is 90% water are discussed. DIC is used to measure the strain field in tension loaded samples containing a central hole, a circular edge notch and a sharp crack. Using a nonlinear, large deformation constitutive model, these experiments are modeled using the finite element method (FEM). Excellent agreement between FEM and DIC results for all three geometries shows that the DIC measurements are accurate up to strains of over 10, even in the presence of very high strain gradients near a crack tip. The method is then applied to verify a theoretical prediction that the deformation field in a cracked sample under relaxation loading, i.e. constant applied boundary displacement, is stationary in time even as the stress relaxes by a factor of three.
more »
« less
In-situ tensile test scanning electron microscopy dataset for solutionized Inconel 718
High-resolution Digital Image Correlation (HR-DIC) was performed on an Inconel 718 specimen, which was subjected to a heat treatment to form a fully solutionized system. In-situ measurements in the small strain regime were made through SEM imaging, followed by HR-DIC to extract quantitative representations of the strain and in-plane displacement induced by deformation events during plastic deformation.
more »
« less
- Award ID(s):
- 2234892
- PAR ID:
- 10577386
- Publisher / Repository:
- Dryad
- Date Published:
- Subject(s) / Keyword(s):
- FOS: Materials engineering FOS: Materials engineering Plastic deformation High-resolution digital image correlation In-situ tensile testing
- Format(s):
- Medium: X Size: 5496277740 bytes
- Size(s):
- 5496277740 bytes
- Right(s):
- Creative Commons Zero v1.0 Universal
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Solid‐state welding of Al 1043 sheets is achieved via high‐pressure torsion (HPT) processing to produce bulk nanostructured Al disks. A homogeneous nanostructure without segregation is observed, with grain sizes of ≈430–470 nm. Miniature tensile testing, coupled with the digital image correlation (DIC) technique, is employed to determine the room‐temperature tensile deformation behavior, particularly the nonuniform behavior with necking, of the HPT‐bonded ultrafine‐grained (UFG) aluminum, comparing it with annealed coarse‐grained counterpart. The HPT‐bonded UFG Al exhibits a large fraction of post‐necking strain, which is supported by the estimated high strain rate sensitivity value ofm = 0.085, suggesting the delay of local necking leading to tensile fracture. Detailed DIC analysis reveals 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 nonuniform deformation. Moreover, the DIC data illustrate that local necking predominantly occurred at a limited neck zone, maintaining a plateau strain distribution at the out‐of‐neck zone throughout necking deformation toward 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.more » « less
-
Abstract Carbon and glass fiber-reinforced plastic (CFRP and GFRP) composites have gained popularity in various industries and settings owing to their exceptional strength-to-weight ratio, corrosion resistance, fatigue resistance, and design flexibility. Adhesives are commonly utilized to bond carbon fiber reinforced plastics to other materials or to themselves. Bonded joints have been found to enhance the mechanical characteristics of materials, while also reducing additional costs for practical applications. The bonding region’s strength can be influenced by different material combinations and substrate thicknesses. The present investigation employed a double-sided multi-digital image correlation (DS-Multi-DIC) system to quantify the deformation and fracture mechanisms of adherends during tensile testing. The primary objective was to assess the static impact on the strength of the bonded zone under tensile loading. The system comprises of two stereo vision DIC measurement systems, wherein each system comprises of two GigE cameras. These cameras are positioned at the front and back of the sample, respectively the process of system calibration involves the utilization of the double-sided calibration technique to integrate the coordinate systems of the two DIC measurement subsystems with the global coordinate system. This enables the direct measurement of deformation and strain in three dimensions. This paper examines the impact of adhesive thickness and type on the strength of the bonded area and fracture mechanism by analyzing the alteration in strain distribution and maximum strain during static stretching. The study yielded a conclusion that the magnitude of the bonded region’s strength is positively correlated with the thickness of the bonding material. The cohesive force of the bonded region is positively correlated with the malleability of the adhesive bond. Furthermore, an examination was conducted on the impact of adhesive thickness and type on peeling strain. As the bond’s bending stiffness diminishes, there is a corresponding increase in the peel strain it undergoes. Furthermore, a succinct description is provided regarding the unequal allocation of auditory alterations that occur during stationary stretching.more » « less
-
Density‐graded elastomeric foams are emerging as effective protective structures to guard humans against mechanical loading. This research investigates the deformation of ungraded and graded foams under quasistatic and impact scenarios using digital image correlation (DIC). The graded samples are assembled using two interfacing strategies (seamless and adhered), leveraging the adhesiveness of the foam slurry and bulk polyurea, respectively. Deformation mechanisms, including the effect of the interface type on strain transduction and localization in density‐graded structures, are imperative for improving the impact efficacy of protective paddings. Cuboid foam plugs are subjected to quasistatic and impact loading while recording the corresponding deformation for DIC analysis. The DIC results are separated into three case studies based on the number of layers (1, 2, and 3). The interface effect on the overall mechanical performance of polyurea foam is revealed from the bilayer, monodensity samples, showing drastic differences between the deformations within each layer. Seamless interface samples exhibit greater compliance than their adhered counterparts in the bilayer density‐graded configurations. Trilayer‐graded foams broaden strain–time history, extend the impact duration, and reduce strains. This research substantiates the importance of interfacing and gradation strategies on the mechanical response of elastomeric foams as a function of strain rate.more » « less
-
This study addresses the limitations of cross weld tensile testing (CWTT) in quantifying local mechanical properties across microstructural and compositional gradients in dissimilar– and matching–filler metal welds. A digital image correlation (DIC) methodology was validated for application in CWTT by direct comparison of stress-strain curves generated using conventional and virtual DIC extensometers in tensile testing of homogeneous steel samples. DIC-instrumented CWTT of dissimilar weld metal Alloy 625 filler metal on F65 steel demonstrated capability in quantifying the local yield strength, strain-hardening kinetics, and strain at failure in the base metal, heat-affected zone (HAZ), fusion boundary (FB) region, and weld metal in dissimilar and matching filler metal welds. It was shown that the high strain-hardening capacity in Alloy 625 weld metal led to base metal failure in CWTT despite the lower Alloy 625 weld metal yield strength. It was also shown that DIC-instrumented CWTT can be used for determining weld metal undermatching and overmatching conditions in compositionally matching- and dissimilar-metal welds. Furthermore, by quantifying local strain distribution (both elastic and plastic) in the HAZ, FB region, and weld metal, DIC-instrumented CWTT provides an additional method for evaluating hydrogen-assisted cracking susceptibility in dissimilar-metal welds.more » « less
