## Introduction

In many applications, beams are complex build-up structures with thin- and thick-walled cross-sections and the increasing use of laminated composite materials leads to heterogeneous, highly anisotropic structures. Based on linear, three dimensional elasticity theory, it can be shown that the analysis of complex beam structures splits into two simpler problems.

1. A linear, two-dimensional problem over the beam's cross-section. This two-dimensional analysis is carried out via the finite element method and is implemented in SectionBuilder.
2. A nonlinear, one-dimensional problem over the beam's span. These equations are the so called “Geometrically Exact Beam Equations,” which are implemented in the beam element of Dymore.

SectionBuilder and Dymore interact through the SectionBuilder-Dymore interface that allows information to be exchanged seamlessly between these two pieces of software.

The definition of the cross-section of as beam is a complex task that requires the definition of the topology of the section and of its geometric and material properties. When advanced composite materials are used, which is the case for many aerospace applications, this task becomes even more complex. Indeed the geometry of each layer of composite material must be defined and their properties are highly anisotropic.

The cross-section can be defined in a CAD program. Typically, the geometry of the entire beam is defined in the three-dimensional CAD system, and the two-dimensional geometry of a cross-section can be extracted using tools built into the CAD program. Next, mesh generation tools are used to obtain a two-dimensional mesh representing the cross-section. This mesh can be imported to SectionBuilder.

In many cases, the configuration of cross-sections is defined in a company proprietary code. For instance, the airfoil sections used for helicopter or wind turbine blades are first designed in company proprietary codes. Typically, the outer shape of the airfoil is dictated by aerodynamics considerations, while the detailed, layer-by-layer definition of the composite material lay-up stems from strength, fatigue, and dynamics performance requirements. Although CAD systems are often used to describe the blades' final design to ease the development of the manufacturing process, the company proprietary codes are used during the design process.

## SectionBuilder input options

##### Figure 1. The three input options for SectionBuilder.

The input to SectionBuilder must define the two-dimensional geometry of the beam's cross-section along with the corresponding material properties. The following three options are available, as illustrated in fig. 1.

1. ShapeBuilder, a preprocessor to SectionBuilder, enables the parametric definition of simple cross-sectional shapes that are used in mechanical and aerospace engineering. Typical sections include solid sections such as rectangular or circular sections, thin- or thick-walled sections such as C- or I-sections, or airfoil sections. ShapeBuilder is fully integrated with SectionBuilder.
2. Most CAD software packages provide two-dimensional mesh generation capabilities. SectionBuilder is capable of reading and interpreting these mesh files. To exercise this option, the name of the “mesh file” must be provided to SectionBuilder, which reads it, translates it, and constructs the corresponding two-dimensional model. Three types of mesh files can be read by SectionBuilder.
1. PATRAN style mesh file,
2. CUBIT style mesh file, and
3. HYPERMESH style mesh file, and
3. Finally, high-level sectional shape definition codes have been developed for specialized applications. For instance, rotorcraft or wind turbine blades can be defined using dedicated tools, which typically, are company proprietary codes. If the shape definition files are available, it could be possible to allow SectionBuilder to interpret them directly.

Although it is possible to create the SectionBuilder (The file denoted file.seb in fig. 1.) input file directly, this is not a recommended option because this file is very lengthy for all but the simplest cross-sectional configurations.