Experimental database of mixed-mode crack propagation tests performed on mortar specimens with a hexapod and full-field measurements. Part II: interactive loading

International audienceThis second paper presents a series of 4 crack propagation tests with the same experimental protocol as in a companion paper, but with some significant loading modifications. The first difference is that the loading is composed of in-plane rotation in addition to tension and shear translations. The second difference is that the loading is manually changed during the tests, depending on the crack tip location. This leads to tests with several bifurcations, and/or different loading ratios during the same test. One of them leads to mode I+II, and then mode I+III crack propagation. Some tests end with instabilities while others are controlled to be stable up to the complete failure of the specimen. In some cases, crack closure and friction between the crack faces occur

Comparison between experimental and numerical results of mixed-mode crack propagation in concrete: Influence of boundary conditions choice

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Phase-field simulation of interactive mixed-mode fracture tests on cement mortar with full-field displacement boundary conditions

International audiencePhase-field modeling is an elegant approach to simulate complicated fracture processes, including crack initiation, propagation, merging and branching in a unified framework without the need for ad-hoc criteria and on a fixed mesh. These capabilities can only be fully validated through the comparison with experiments featuring crack development histories and patterns of sufficient complexity. As opposed to conventional mixed-mode fracture tests with predefined loading, interactive tests with multiaxial loading which are controlled during the propagation of the cracks can create more complex and stable crack propagation patterns. Moreover, the development of measurement techniques such as digital image correlation (DIC) provides the possibility to quantitatively characterize the full-field kinematics during the tests. In this work, full-field displacements measured by DIC during interactive mixed-mode fracture tests on cement mortar specimens are adopted as boundary conditions for phase-field numerical simulations. Qualitative and quantitative comparisons are illustrated, demonstrating the capability of the phase-field approach to predict complex mixed-mode fracture phenomena in cement mortar and suggesting possible further developments

Digital image correlation & Fracture mechanics: Brittle Fracture of Ceramics and Refractories

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A complex mixed-mode crack propagation test performed with a 6-axis testing machine and full-field measurements propagation

International audienceA new type of mixed mode crack propagation test is proposed. A single crack is initiated and propagates in a stable way up to complete failure. A combination of tensile, shear and in-plane rotation performed by a 6-axis testing machine is prescribed. The rotation creates a tension/compression gradient in the sample ensuring the stability, while the shear direction is closely related to the orientation of the crack and the tensile load is responsible for the actual propagation. The experiment is performed in an interactive manner, namely, depending on the crack tip position estimated by Digital Image Correlation (DIC) during the test, the loading is changed to bifurcate the crack. The displacements of the sample surfaces are assessed using multiple DIC measurements and displacement sensors. The displacement fields on each face of the sample give access to the crack pattern, and also to the actual boundary conditions that are crucial for a faithful numerical analysis of the test. Last, the 6 load components are recorded enabling for a complete description of the 3D mechanical behavior of the specimen

A virtual hybrid test to control mixed-mode crack propagation in concrete

International audienceThe minimization of the number of experimental tests to characterize the material behavior continues to be an important challenge. The main aim of this work is to set up a relevant and discriminating concrete fracture test, able to fully investigate its complex mechanical behavior within a single run. Therefore a hybrid cracking test on a concrete sample with controlled stress intensity factors (SIFs) is currently developed. Prior to the real test, a virtual one is conceived to validate the principle of the proposed hybrid test.La minimisation du nombre d'essais nécessaires pour caractériser le comportement de matériaux reste encore un enjeu majeur. Le but de ce travail est de développer un test de fissuration de béton, riche et discriminant, capable de révéler l'ensemble du comportement mécanique en un seul essai. Un essai hybride de fissuration du béton piloté en facteur d'intensité des contraintes (FIC) est développé dans ce but. Préalablement au test réel, un test virtuel est conçu pour valider le principe de l'essai hybride proposé