PSI - Issue 28

D.A. Bondarchuk et al. / Procedia Structural Integrity 28 (2020) 743–751 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2. Problem statement The study was conducted by means of general-purpose FE package ABAQUS and special constitutive material model that was implemented in special user subroutine-UMAT. As mentioned before, the AS4/8552-1 carbon-epoxy composite with [0°/90°] 12 lay-up was considered for analysis. The sample and its geometrical dimensions are shown in Fig. 1.

Fig. 1. A specimen of carbon-epoxy composite AS4/8552-1 with [0°/90°] 12 layup.

The problem of free edge stress analysis (zone of delamination) consists of two stages. On the first stage of analysis the modeling of the curing process of composite sample with initial delamination defect and formation of residual stresses is provided. On the next stage the ideal free edge cut (modeling of composite machining) of the sample is modeled. To describe the behavior of the material during polymerization, well-established constitutive material model, which takes into account changes in the physical and mechanical properties over time and dependence on temperature was used. The cure cycle presented in Hexply AS4/8552 data sheet (2020) was used for temperature initial and boundary conditions. 3. Finite element model Considering the layup symmetry, the model was analyzed in 2D plane strain formulation. In the present work, it was decided to exclude the mold from the analysis as it is insignificant for such sample. Sample considered free to move during all calculation steps. The FE model is constructed in such way that the most elements have a rectangular shape and retain this shape during mesh sensitivity analysis, changing only the dimensions of elements. The model is built up using both 3-node linear displacement and temperature and 4-node bilinear displacement and temperature, reduced integration with enhanced hourglass control elements (CPE3T, CPE4RT in Abaqus notation). Two materials were used to model composite AS4/8552 –Material-1 for layers with orientation 0° and Material-2 for layers with orientation 90°. The modelling procedure is described in details in research work, conducted by Bondarchuk D.A. et al. (2019). The mesh near the initial crack zone and the zone of cut is more detailed in order to see the emerging effects in this area. The FE model with Local (123) and Global (XYZ) coordinate system is shown in Fig.2. Since the singularity expected at the delamination front, the fine mesh is done only in this zone and larger elements used in the vicinity. Each lamina was presented 8 elements per layer. The initial crack was placed between 0° and 90° ply as shown in Fig.2.