Shear and foundation effects on crack root rotation and mode-mixity in moment- and force-loaded single cantilever beam sandwich specimen

Abstract

Foundation effects play a crucial role in sandwich fracture specimens with a soft core. Accurate estimation of deformation characteristics at the crack front is vital in understanding compliance, energy release rate and mode-mixity in fracture test specimens. Beam on elastic foundation analysis of moment- and force-loaded single cantilever beam sandwich fracture specimens is presented here. In addition, finite element analysis of the single cantilever beam specimen is conducted to determine displacements, rotations, energy release rate and mode-mixity. Based on finite element analysis, a foundation modulus is proposed that closely agrees with the numerical compliance and energy release rate results for all cases considered. An analytical expression for crack root rotation of the loaded upper face sheet provides consistent results for both loading configurations. For the force-loaded single cantilever beam specimen (in contrast to the moment-loaded case), it was found that the crack length normalized energy release rate and the mode-mixity phase angle increase strongly as the crack length decreases, a result of increased dominance of shear loading.

Finite element modeling of face/core interface fracture in homogenized honeycomb core sandwich SCB specimens

“…The results obtained for a SCB specimen with 6 mm thick face sheets are listed in Table 4. The normalized G values are higher than for the 3 mm thick face sheet case (Table 3) due to stronger foundation effects for the thicker face [19]. The results in Table 4 are qualitatively similar to the case for 3 mm face sheets Table 3.…”

“…For plane strain conditions, crack closure was not found, although a low core modulus ðE T ¼ 0:048 MPaÞ resulted in high deformation of the near tip core elements. The phase angle results for the 6 mm thick face are similar to those for the 3 mm face sheet Table 3, although the phase angles for the 6 mm face sheet (Table 4) are larger as results of increased shear dominance for thicker face [19].…”

“…This approach is overwhelmingly used in studies of face/core interface fracture of sandwich specimens and structures, e.g. Ural et al [16], Grau et al [17], Berggreen et al [18] and Saseendran et al [19]. It may be added that the energy release rate is not influenced by the details around the crack tip, since it is governed by the global response of the specimen or structure.…”

“…It is observed that the in-plane modulus of the core (E T ) does not influence the compliance strongly. This is expected because the most important core modulus for the compliance of the SCB specimen is the out-of-plane modulus (E L ) [19]. This modulus was kept constant (E L ¼ 140 MPa).…”

The effects of shear and near tip deformations on interface fracture of symmetric sandwich beams

“…The absolute values of the complex stress intensity factors associated to the elementary load systems, P and M, are defined using Eqs. (5) and (13) [3]. The values of  for symmetric sandwich beams, have been derived in [2] for a large range of elastic and geometrical properties.…”