Damage Detection in a Polymer Matrix Composite from 4D Displacement Field Measurements

Standard Digital Volume Correlation (DVC) approaches enable quantitative analyses of specimen deformation to be performed by measuring displacement fields between discrete states. Such frameworks are thus limited by the number of scans (due to acquisition duration). Considering only one projection per loading step, Projection-based Digital Volume Correlation (P-DVC) allows 4D (i.e., space and time) full-field measurements to be carried out over entire loading histories. The sought displacement field is decomposed over a basis of separated variables, namely, temporal and spatial modes. In the present work, the spatial modes are constructed via scan-wise DVC, and only the temporal amplitudes are sought via P-DVC. The proposed method is applied to a glass fiber mat reinforced polymer specimen containing a machined notch, subjected to in situ cyclic tension and imaged via X-ray Computed Tomography. The P-DVC enhanced DVC method employed herein enables for the quantification of damage growth over the entire loading history up to failure

Characterization of glass fiber reinforced polymer via Digital Volume Correlation: Quantification of strain activity and damage growth

International audienceStrain and damage distributions within a dogbone specimen containing a rectangular notch were assessed in-situ via X-Ray Computer Tomography coupled with Digital Volume Correlation. The specimen cut from a continuous glass fiber mat reinforced polyester resin composite plate was subjected to cyclic tensile loading. The strain-damage interplay wasevaluated by analyzing major eigen strain and correlation residual fields. The horizontal strained band emanating from the notch root was present from the beginning of loading. The final failure proceeded along this strained band. The first cracks did not initiate in the notched region, despite high strain gradients. Strain activity and damage growth were quantified by analyzing the cumulative probabilities of major eigen strains. The comparison was made between the notched region and the remaining part of the inspected specimen. It is shown that, although the mean levels were higher in the notched region, the standard deviations of the major eigen strain distributions were higher in the remaining part of the specimen

De l’utilisation de la tomographie en mécanique des matériaux

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De l’utilisation de la tomographie en mécanique des matériaux

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Characterization of glass fiber reinforced polymer via Digital Volume Correlation: Investigation of notch sensitivity

International audienceThe results of in-situ cyclic tensile experiments performed on two dogbone specimens made of glass fiber mat reinforced polyester resin are presented (the second specimen contains a machined rectangular notch). The experimental data were obtained by using X-Ray Computed Tomography. The reconstructed volumes were analyzed via Digital Volume Correlation. The investigated material was notch-insensitive since both specimens failed at equal stress levels. To further confirm this hypothesis, and to study strain-damage interactions, the major eigen strain and correlation residual maps of both specimens were analyzed. Even in the first loading cycle, an inner strained band extending through the whole ligament area developed within both specimens, already indicating the path to final fracture. It is shown that the final failure of the studied material was primarily driven by the yarn mesostructure, i.e., the influence of the underlying heterogeneities prevailed over the effects due to specimen machining and/or geometric singularity

Tensile deformation and failure of AlSi10Mg random cellular metamaterials

International audienceCellular metamaterials are an emerging class of porous materials, in which the topology of the solid is precisely-engineered to achieve attractive combinations of properties. This work specifically examines the tensile response of a novel type of cellular metamaterials, in which pores of arbitrary elliptical shape are randomly-dispersed into an aluminum alloy matrix. Their porous mesostructure is generated numerically via a random sequential absorption algorithm, and is fabricated by laser powder bed fusion from AlSi10Mg powders. The results – obtained by means of digital image correlation combined with X-Ray tomography - highlight the advantages offered by a random cellular topology. These are notably a low sensitivity to geometric imperfections (which result inevitably from manufacturing), coupled with the ability to delay long-wavelength strain localization (which is in turn responsible for failure). Structural disorder also leads to highly heterogeneous deformation patterns, which result from the interaction between geometric pores and promote void growth and coalescence during plastic straining. The presence of manufacturing defects, moreover, exacerbates void interaction and in turn promotes early plastic flow localization. Interestingly, experiments reveal that this class of porous solids effectively display features of the ductile fracture of metals, albeit at the mesoscale. For example, void-sheeting is observed with increasing pore aspect ratio and is accompanied by large geometric distortions of the voids upon coalescence. Measured data for the pore strains are, moreover, highly scattered and show a departure from McClintock’s model predictions for the voids within the fracture band. Collectively, this study highlights the potential offered by random porous metamaterials, which can be harnessed to revisit the complex mechanisms of ductile fracture at the mesoscale

Calibration of cohesive parameters for a castable refractory using 4D tomographic data and realistic crack path from in-situ wedge splitting test

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DVC Analyses to Study Deformation and Damage mechanisms of Teak in Torsion

International audienceWood is a material with anisotropic elastic properties at the macroscale. In the present work, a sample made of Beninise teak was subjected to in situ torsion. DVC analyses were run at the mesoscale to measure displacement fields. The corresponding strain fields were obtained at the same scale in addition to the gray level residuals at the voxel scale. The out-of-plane shear modulus could be calibrated at the macroscale and was in good agreement with earlier coauthors' results. The ultimate shear strength was also assessed at the same scale. Last, damage was detected and quantified at the mesoscale thanks to strain fields and at the microscale via gray level residual fields