13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Figure 2 Specimen geometry (dimensions in mm) 2.2. Testing methods The SENT specimens were tested using a tensile test machine in the displacement control at rate of 0.5mm/min. Load and crosshead displacement were recorded throughout the test. The self-healing FRP specimens were loaded until large load drops occurred, indicating damage progression. Before the specimens fractured completely, the specimens were unloaded and removed from the tensile test machine. Then, the specimens were clamped in a vise and allowed to heal for 10 days at room temperature. After healing, the specimens were tested again. For the reference FRP specimens, the specimens were immediately unloaded and reloaded to fracture after virgin tests, and the critical fracture load of the damaged specimen was evaluated. Healing efficiency η was defined as the ability of a healed specimen to recover critical fracture load healed residual virgin residual c c P P P P η − = − (1) where virgin cP is the critical fracture load of the virgin specimen, healed cP is the critical fracture load of the healed specimen and residual P is the load value that was established at the end of the virgin test. To investigate the microstructure and damage behavior of the specimens, optical microscope observations were also performed. 2.3. Finite element analysis The 3D finite element model was developed using ANSYS finite element code. A schematic diagram of the SENT specimen model is shown in Fig. 3. In this figure, R and h denote the radius of the fiber strand and the thickness of the coating layer, respectively. The geometric parameters of coated fiber strands as measured in the optical microscope were used. A rectangular Cartesian coordinate system ( 1x , 2x , 3x ) is used and 1x , 2x and 3x axes are assumed to lie along the longitudinal direction (fiber direction), transverse direction and thickness direction, respectively. Due to symmetry in both geometry and loading configurations, only one-quarter of the SENT specimens were modeled. Let the displacement and stress components be denoted by iu δ and ij δσ ( , 1,2,3, , , ) i j f m c δ = = , respectively. The subscripts 1, 2 and 3 are related to the three axes of the coordinate system and the superscripts f , m and c indicate the fiber strand, matrix and coating layer, respectively. The boundary conditions can be written as 11 2 3 2 0 3 (0, , ) 0 (0 ,0 / 2) x x x a x t δσ = ≤ < ≤ ≤ (2) 1 2 3 0 2 3 (0, , ) 0 ( ,0 / 2) u x x a x W x t δ = ≤ ≤ ≤ ≤ (3) 12 2 3 2 3 (0, , ) 0 ( ,0 / 2) 0 x x x W x t δσ = ≤ ≤ ≤ ≤ (4) t =2 or 3 Coated fiber strands W=20 70 a0=5 Aluminum tabs L=40 Initial notch
RkJQdWJsaXNoZXIy MjM0NDE=