Fracture Benchmark
All CFRAC participants are invited to contribute to a special fracture benchmark organized by Julien Réthoré. They are encouraged to present the results of their simulations in the benchmark session, which supplements the minisymposia. This presentation is not counted when the policy of one presentation per registered participant is applied.
The proposed benchmark focuses on quasi-brittle failure of a Plexiglas plate. In total, four experiments have been performed and documented using high resolution imaging and full-field displacement measurement based on Digital Image Correlation (DIC). Two experiments will be used for calibration of model parameters, and the other two experiments should then be predicted.
Calibration
The samples are subjected to quasi-static loading. An extensive data set is provided for calibration purposes in the data repository (password cfrac2023). Our estimate of the nonzero coefficients of the linear elastic stiffness matrix for two-dimensional simulations is D12 = D21 = 1.17 GPa, D33 = 1.33 GPa (shear modulus), and D11 = D22 = D12 + 2*D33 = 3.83 GPa, assuming isotropy. If the simulation is performed under plane stress, this corresponds to Young’s modulus E=3.47 GPa and Poisson’s ratio nu=0.306.
 | CLOVER is a plate with 4 holes inducing strain concentration and leading to crack initiation. The load-displacement curve and data from DIC (mesh, displacement fields, etc.) are provided. Experimentally, a misalignment is intentionally applied to force failure initiation to occur on one side of the specimen. To avoid any bias due to this misalignment, the participants may use the measured displacement along the boundaries of the DIC mesh as boundary conditions. More details can be found in the repository. |
 | TDCB (Tapered Double Cantilever Beam) is a crack propagation experiment in which the crack propagates smoothly. The initiation takes place at the tip of a notch obtained by a laser cutting process. This means that its contour is not perfect. Some information is provided for the participants to make their model as realistic as possible. If the model needs a real pre-crack (not a pre-notch), the comparison with the experimental data should focus on the propagation phase of the experiment, not on the initiation. Fracture mechanics parameters are obtained through the analysis of the DIC displacement field, they are provided synchronized with the load measurements. |
Prediction
After calibration of their model using the provided experimental results, the participants can proceed to predictive simulation of the other two tests.
 | TRIANGLE: The loading is similar to the TDCB experiment, but the sample geometry is different. |
 | SCDC (Single Crack Drilled Compression): This is a kind of DCDC (Double Crack Drilled Compression) sample but the circle is shifted from the sample center and a notch is cut to initiate a crack in a way that is easier to control. The left and right edges of the specimen can be considered to have their vertical displacement fixed. The horizontal displacement of the right edge is fixed and for the left edge, it is controlled by the loading device. The loading is in compression and the applied displacement rate is 0.005 mm/s. |
Reporting
The results should be collected and sent to the organizer (julien.rethore@ec-nantes.fr) in the form of csv files containing at least the evolution of the reaction force versus the prescribed displacement and, if available, also the crack length evolution. The force should be specified in N/m (to make the result independent of the specimen thickness) and the displacement and the crack length in mm. For TRIANGLE, the crack length should be measured from the left edge of the sample and for SCDC from the center of the hole.
The final results can be submitted until 15 June 2023. However, it would be very helpful if you can send us your results before 15 May 2023. If you cannot meet this first deadline, please let us know by email that you are planning a later submission, so that we have at least an idea about the expected number of benchmark presentations. This is important for preparation of the detailed conference program.