Unconstrained boundary condition

In Figure 5.23 the finite element model predictions based on with constraint and unconstrained boundary conditions for the modulus of a glass/epoxy resin composite for various filler volume fractions are shown. 

Figure 5.23 Composite modulus obtained using constrained and unconstrained boundary conditions...

The CTH approach is able to control the crack width, which can be closed by controlling the compression pre-strain level. A simple equation has been established by Li et al. [54] to correlate the crack width to be closed and the pre-strain level during compression programming. Cracks with different opening widths can be closed based on the level of compression programming (of course it is limited by the maximum allowed compression pre-strain level). In the unconstrained shape recovery approach such as the SMASH approach, it has not been demonstrated that it can close a wide-opened crack with constrained boundary. Also, it cannot control the crack width that can be closed because it depends on the external load to perform programming and relies on the shape recovery ratio and boundary condition of specimens to perform crack closing. 

The displacements shown in Table 9-31 have been compared to the hand calculations in Figure 10-18 of this document. According to both calculations, the piping will expand about 3 cm if unconstrained. This serves an independent confirmation of proper application of the material properties in ABACUS. Ryan Bechtel (KAPL) has performed an independent verification of the material properties used and the ASME B PV spreadsheet calculations. Jay Schuren (Bettis) has reviewed the application of material properties, section properties, beam element cross sections, load amplitudes, and boundary conditions in the ABACUS model. 

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