PSI - Issue 60

Amardeepa KCS et al. / Procedia Structural Integrity 60 (2024) 60–74 Amardeepa KCS/ StructuralIntegrity Procedia 00 (2023) 000–000

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the application of internal fuel pressure. This FE modelling approach was validated by experiments using the test results of composite co-cured T-joints and adhesively bonded composite joints. Assessing the failure load of this L angle flange in a global wing or wing box requires an enormous amount of composite materials for fabrication, workforce, and time. With or without expensing all these resources, it still poses technical challenges to the structural designer to understand the failure load and location of failure of the wing or wing box when subjected to internal fuel pressure. The present modelling approach and novel failure criterion helped overcome such technical challenges in understanding the stress distribution, failure load, and failure location. Initially, extensive time has been spent on creating the FE model. The sectional properties of each 1D CBAR element became different from other elements due to dimensional changes in each zone. Thereby the size of the FE model became large. Subsequently, the mesh pattern is revised to have the same sectional properties of 1D elements over a large area in the web and flange regions. The radial element pattern shown in Figure 11(b) helped to have a minimum number of sectional properties for 1D elements, which drastically reduced the size of the FE model, as shown in Figure 10. The other challenge is enforcing boundary conditions in the standalone FE model of the L angle flange. After many iterations, it is decided to apply an enforced global displacement on the standalone FE model. Estimating failure load with the enforced displacements is possible only through analytical study; an experimental test is impossible to carry out with the enforced displacement. Conducting the experimental study until the failure of the L angle does not validate the design. The failure of the L angle with differently randomly applied displacements does not truly represent the actual failure load in the global wing structure. Therefore, the present study gained importance over the mechanical tests as the stress and strain distributions in the web of the L angle around the cut-out region are closely correlated with that of values obtained from the global wing/wing box. 5. Analysis The linear static analysis provides three force components of 1D CBAR elements in the output data file F06, which is the crucial input data for computing the various stress values using Eq. (1) to (3). The axial force and shear force components are acting along the plane 1 and 2 of 1D CBAR elements as shown in Figure 11. The force values are exported to an Excel spreadsheet for carrying out simple engineering and mathematical calculations/operations outside the FE analysis domain. The failure criterion given in Sec. 5.1 is applied for estimating the failure load and its location identification between layers (Figure 10(b)) of composite laminate.

5.1. Failure Criteria used for checking the strength of L angle against out-of-plane stresses at the radius region:

σ � = � �� + �� + �� +� � − 2 � � +� � − 2 � � + � � − 2 � � τ � =�P � � +P � �

Eq-(1)

Eq-(2)

τ = τ r /a n ≤ tt No failure n > tt Failure

Eq-(3)

τ ≤ ss No failure τ > ss Failure

Where, σ X = stress due to Axial force (along the element axis)

σ Y = stress due to P1 (along the tangent of the curve)

σ Z = Stress due to P2 (along the span) A F = Axial force of a CBAR element

σ n = Normal stress

P 1 = Tangential force component of a CBAR element tt = Transverse tensile strength of composite laminate, which is equivalent to resin tensile strength ss = Shear strength of composite laminate, which is equivalent to resin shear strength τ = Shear stress τ r = Resultant shear

P 2 = Longitudinal force component of a CBAR element