Also, note that Sierra Adagio does not include a plane-strain element. Therefore, in order to approximate the plane-strain condition, the geometry shown in Fig. 16.12 was modeled with a depth of only 1 mm and appropriate boundary conditions were applied along the side surfaces of the simulated specimens. These approximations are discussed further in the following section. 16.5.5 Boundary Conditions Boundary conditions were applied to the DCB experiment simulations to approximate the plane-strain conditions as well as to emulate the formation of the thermal residual stresses and the application of the tensile, mode I loading. First, to approximate the plane-strain boundary conditions, the side surfaces of the specimen were translationally fixed in the depth, or y, direction, as shown by the red arrows in Fig. 16.13. Next, to model the formation of the thermal residual stresses before the application of the mode I loading, the process described in [16] was applied. Specifically, the DCB simulations were initiated will all components at a constant and uniform temperature equal to the experimentally measured stress-free temperature. Then, the modeled specimens were isothermally cooled to the appropriate testing temperature (71 C, ambient, or 54 C); and, since the material definitions for the composite and epoxy materials included the appropriate CTE values, residual stresses were formed due to thermal contractions within the bondline and adherends. Lastly, boundary conditions were defined to mimic the associated experimental loading after the simulated cooling process. In the DCB simulation, the bottom-front edge in the pre-cracked region was translationally fixed in the x and z directions (as shown by the blue triangles in Fig. 16.13), while the top-front edge was translationally fixed in the x direction with an applied velocity condition applied in the vertical, or z, direction (as shown by the green arrows in Fig. 16.13). For the ENF simulation, similar boundary Fig. 16.12 Representative geometry of four-point flexure simulations Fig. 16.13 Description of the DCB specimen’s applied boundary conditions 16 Effect of Process Induced Stresses on Measurement of FRP Strain Energy Release Rates 169
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