Sandwich Panels

Useful for structures that have biaxial compression and/or shear loading causing buckling. A commonly used aerospace composite panel concept, but not for primary loaded commercial airframes.

Honeycomb and Foam

Sandwich panels are optimized by sizing each individual object – the top facesheet, the core, and the bottom facesheet – to its respective failure modes. Each object is prescribed dimensional bounds and material candidates.  

In addition to material strength and buckling stability, HyperX provides unique sandwich analyses such as core shear strength failures caused by out of plane loading, flatwise tension with interlaminar shear, as well as wrinkling and intracellur dimpling for thin facesheets overlaid on large-cell core. Sandwich concepts can be applied directly to 2D shell elements.

Stiffened Panels

Useful for structures that are mostly under uniaxial loading. Open sections such as ‘I” are often used for airframe wing skin and closed sections such as ‘Hat’ for fuselage skin.

Generally, wing skins are supported by relatively close rib spacing substructure, whereas the fuselage by closely spaced ringframes.

Each individual segment of a stiffened panel is represented as an object in the HyperX panel concept definition. Each object has its own unique sizing dimensions, material system candidates, and applicable failure modes. As an example, the skin thickness should be sized to account for local buckling between stiffener sections, whereas a stiffener web should be analyzed for its own local stability modes.  The stiffened panel is also analyzed as an entire system, meaning additional failure analyses combine all objects together to evaluate modes such as buckling of the entire panel and crippling of the entire cross-section. Failure modes can also vary based on the type of stiffener applied to the panel. For example, open cross section panels must analyze lateral torsional buckling. But, closed cross-section concepts, such as hat/omega panels, the torsional rigidity stiffness of the enclosed cell is computed for buckling stability evaluation.

HyperX supports several different strategies for modeling a stiffened panel. The simplest of which allows all objects to be ‘smeared’ into a single surface of 2D shell elements. This is accomplished by fully defining Aij, Bij, Dij stiffness terms for the shell elements.  Refer to the technical papers for more information. This modeling strategy opens up all geometric design variables, particularly useful in early optimization trade studies.

As the design matures, various geometric variables (like stiffener spacing and height) are going to become set – thereby allowing individual objects be discretely modeled into the FEM with bar/beam/shell elements.  All different modeling techniques are supported.

Bonded (Composite)

In addition to the sizing variables and failure analysis strategies outlined above, all bonded stiffener-to-panel concepts are optimized to account for the FAA requirement of a ¼” assumed crack in the bond line between the skin attached stiffener flange. This analysis is performed using the virtual crack closure (VCCT) energy method to quantify residual strength.

Fastened (Metal)

In addition to the bonded concepts above, HyperX stiffened-panel optimization can also account for stiffeners fastened to the skin. The thermoelastic Aij, Bij, Dij stiffness formulation for fastened panels is different than bonded panels due to the attached flange having its transverse strain being decoupled from the skin. There are also additional failure methods to analyze this case. If the stiffened panel is completely metal, traditional sheet metal NACA/NASA aerospace analyses are also performed.

Grid Stiffened Panels

As with other HyperX stiffened-panel concepts, Each individual segment of the grid is represented as an object in the HyperX panel concept definition. Each object has its own unique sizing dimensions, material system candidates, and applicable failure modes.

HyperX supports several different strategies for modeling a grid-stiffened panel. The simplest of which allows all objects to be ‘smeared’ into a single surface of 2D shell elements. This is accomplished by fully defining Aij, Bij, Dij stiffness terms for the shell elements.  Refer to technical paper for more information (https://collieraerospace.com/technical-papers/). This modeling strategy opens up all geometric design variables, particularly useful in early optimization trade studies.

As the design matures, various geometric variables (like stiffener spacing and height) are going to become set – thereby allowing individual objects be discretely modeled into the FEM with bar/beam/shell elements. All different modeling techniques are supported.

Orthogonal

The Orthogrid is the most commonly used grid stiffened panel concept. Applications include buckling critical, low to medium pressurized fuel tanks of rockets. These concepts are machined out from stock plate. Bumped forming is used to produce cylindrical curvature.

Angular

Beams

Beams can be analyzed and sized. Specific beam stiffness formulation and failure analyses are performed. Modeled with 1D elements.

1D elements allow for the analysis and sizing of each individual object within the beam. Much like stiffened-panel concepts, each object has its own sizing dimensions, material candidates, and applicable failure modes. The beam is also evaluated as a whole, particularly for stability criteria.

Open Cross Section

Most common for civil construction is the I beam.

Simple cap is the most commonly used beam for aerospace wings. It is used for spar caps and rib caps. It is supported from buckling by its attaching skin and rib.

Closed Cross Section

The closed cross sections are often used for unsupported span lengths – not attached to other structure. Typical applications include lunar landing legs, landing gear, and engine thrust supports.