PSI - Issue 12

Venanzio Giannella et al. / Procedia Structural Integrity 12 (2018) 479–491 V. Giannella Structural Integrity Procedia 00 (2018) 000 – 000

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3. DBEM analyses

3.1. Introduction

A DBEM submodel (Fig. 6) is extracted from the FEM submodel (Fig. 1b). The DBEM submodel is obtained by means of a spherical cut from the FEM domain (Fig. 1b), considering a sphere centered on the crack insertion point (Fig. 4d) with a radius of 0.5 inches. The uncracked DBEM model is built with 2086 quadratic elements. SIFs along the crack front are calculated by the J -integral approach (Rigby et al. 1993, 1998; Dell’Erba et al. 2000) whereas the crack path assessment is based on the Minimum Strain Energy Density (MSED) criterion (Sih et al. 1974).

Figure 6. DBEM submodel.

Table 1. DBEM thermal, mechanical and fatigue properties, evaluated at 375 °F.

Young’s mod. [psi]

Poisson ’s ratio Exp. coeff. [in/(in*°F)]

Reference temp. [°F]

C [psi^(1 n)/inch^(n/2)]

n

K th [psi*in^0.5]

K c [psi*in^0.5]

28.9 E6

0.315

6.93 E-6

77

2.04E-20

3.32

7000

40000

Different approaches have been proposed in the past to perform thermomechanical fracture assessments by a coupled usage of FEM and DBEM: • Fixed Displacement (FD), where the displacement field calculated by a FEM analysis on the global domain is applied on the DBEM submodel cut surfaces, in addition to the FEM temperatures that are applied on all the DBEM boundaries; • Fixed Load (FL), where the stress field calculated by a FEM global analysis is applied on the DBEM submodel cut surfaces, in addition to the FEM temperatures that are applied on all the DBEM boundaries; • Loaded Crack (LC), where the stresses calculated by a FEM analysis on the uncracked global model are extracted along the virtual surface traced by the propagating crack (as provided by the DBEM simulation) and applied on the crack faces.