Residual Strength and Fatigue Lifetime of ... - Solid Mechanics

(2.2)
where and for plane stress and plane strain, respectively. E and are
Young’s modulus and Poisson’s ratio, respectively. Normal force and moment in the TSD
specimen can be determined from the vertical force P and the tilt angle by
(2.3)
(2.4)
For the reduced formulation where ==0
Finally, the energy release rate can be calculated by
Regarding the mode-mixity it was revealed that the mode-mixity for a conventional TSD
specimen remains quite unaffected by the tilt angle (Li and Carlsson, 2001). Furthermore, it was
discovered that the unreinforced TSD specimens display positive mode-mixity phase angles for
tilt angles up to around 80 for all analysed PVC core materials, thus provoking the crack to kink
into the core (Berggreen and Carlsson, 2010). To increase the range of achieved mode-mixities
by the TSD specimen, two modified designs of the TSD specimen were proposed by Berggreen
and Carlsson (2010). In the first modified design the upper face sheet of the TSD specimen is
reinforced by a thick stiff steel plate to increase the stiffness of the loaded face sheet as shown in
Figure 2.10. It was shown that by reinforcing the upper face sheet with a stiff steel plate the
range of phase angles is expanded because of increasing shear loading and crack tip root rotation
in the specimen.
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(2.5)
(2.6)
(2.7)