December 2024
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19 Reads
Experimental Mechanics
Fused filament fabrication delivers composites with incomplete interface bonding prone to delaminate under loading due to the non-isothermal molecular entanglement during deposition. We aim to localize the mesoscale porosity in 3D-printed composites and quantify its volumetric growth under loading to investigate whether incomplete filament adhesion can lead to delamination. We measured the porosity volumic content by X-ray tomography testing. To distinguish between damage nucleated at the crack tip and mesoscale interface delamination, we quantified the local, 3D strain concentration region size at the crack tip by 2D digital image correlation of slice images over orthogonal planes. Through image segmentation, we observed that the mesoscale porosity resulting from the deposition process clustered at the filament interfaces and doubled from roughly 7% to 14% from an applied opening load of 700 N to 1400 N due to the stress concentration at the filament interfaces. Digital image correlation emphasized the strain concentration over a reduced area at the notch, up to the damage nucleation for an applied load of 1400 N, before the sudden brittle failure. The presented contactless characterization technique emphasizes that mesoscale porosity concentrates at the filament interface, which is a critical delamination nucleation site under loading. This fracture mechanism is even more severe for high-performance composites such as carbon fiber reinforced PEEK.
![Schematic overview of the automated shot peen forming workflow. The numerical model of the target shape (a) is input into the simulation software (b). The latter computes an optimal peening pattern (c), that must be applied to form the plate into the target shape. The peening pattern is input into the translation software (d), which generates the peening program (e). The peening program includes the nozzle paths and a set of peening parameters that allow the peening robot (f) to reproduce the peening pattern. The peening program is loaded into the peening robot in the form of a programming code. When the treatment is finished, we characterize the curved shape of the plate using a 3D scanner (g) and trace an error map (h), which shows discrepancy between the target and the scanned shapes. The simulation and the translation softwares require experimental calibration, which consists in characterizations of the shot stream (i), of the eigenstrain (j) induced by the peening treatment, and of the eigenstrain anisotropy (k). The shot stream is characterized with flat dummy specimens, the eigenstrain is measured using 76×19\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$76 \times 19$$\end{document} mm aluminum coupons, and the anisotropy is quantified with the help of square aluminum plates. Art by IMPAKT Scientifik](https://www.researchgate.net/publication/379570561/figure/fig1/AS:11431281246927739@1716517851411/Schematic-overview-of-the-automated-shot-peen-forming-workflow-The-numerical-model-of_Q320.jpg)
![A triangular mesh element and the vectors serving for computation of the local fundamental forms. The vectors v0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\textbf{v}_{0}$$\end{document}, v1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\textbf{v}_{1}$$\end{document}, v2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\textbf{v}_{2}$$\end{document} define positions of the element vertices in the global coordinate system. The edge vectors e0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\textbf{e}_{0}$$\end{document}, e1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\textbf{e}_{1}$$\end{document}, e2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\textbf{e}_{2}$$\end{document} are computed as the difference between the corresponding vertex vectors. The vectors n0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\textbf{n}_{0}$$\end{document}, n1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\textbf{n}_{1}$$\end{document}, n2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\textbf{n}_{2}$$\end{document} are traced in the center of the corresponding edges and define the local curvature of the mesh. They are normal to the edges, but their angle of inclination with respect to the element constitutes a degree of freedom](https://www.researchgate.net/publication/379570561/figure/fig2/AS:11431281246871185@1716517851646/A-triangular-mesh-element-and-the-vectors-serving-for-computation-of-the-local_Q320.jpg)
![Determination of the dimensionless error Ωz=dH/Δz\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Omega _z = d_H/\Delta z$$\end{document} between the simulated shape and the shape of the treated plate. a) The simulated shape and its bounding box. The deflection Δz\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta z$$\end{document} is computed as the smallest dimension of the bounding box. b) A photo of the plate treated following the computed pattern that leads to the simulated shape. The non-reflective surface is the treated part. c) The meshed shape scanned with a 3D scanner. d) Map of the local distances d between the simulated and the scanned shapes that were optimally aligned. The map is traced on the simulated shape. The Hausdorff distance dH\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$d_H$$\end{document} is the maximal value of local distances d](https://www.researchgate.net/publication/379570561/figure/fig5/AS:11431281246927740@1716517852339/Determination-of-the-dimensionless-error-OzdH-Dzdocumentclass12ptminimal_Q320.jpg)
![Figure 1: Schematic of a body Ω containing (a) a sharp crack Γ c , and (b) the phase-field approximation of the crack through the continuous damage field d(x). Adapted from [44].](https://www.researchgate.net/profile/Olivier-Lampron/publication/374538642/figure/fig1/AS:11431281229105425@1710335016073/Schematic-of-a-body-O-containing-a-a-sharp-crack-G-c-and-b-the-phase-field_Q320.jpg)
