Key Concepts¶

Understanding how XdTd is organized will help you work with it efficiently.

Case Studies¶

Everything in XdTd revolves around case studies. A case study is a self-contained unit that stores:

The structural configuration — panel geometry (external and internal boundaries), material properties, and thickness
Reinforcements — stiffeners and/or patches, each with their own geometry, properties, and attachments
Cracks — edge cracks or embedded cracks
Boundary condition sets — loading and constraint scenarios
Result sets — analysis outputs

Case studies are saved as .xdtd files. Multiple case studies can be open simultaneously, and their results can be compared side by side or overlaid in the same chart.

The Panel¶

Each case study contains a panel — a 2D structure made up of a sheet and, optionally, reinforcements.

Sheet¶

The sheet is the base structure, defined by its boundaries, material properties, and thickness.

External Boundary — the outer contour of the panel. Always present, one per panel.

Internal Boundaries — holes, cutouts, or other openings within the sheet.

Cracks — edge cracks (originating from boundaries) or embedded cracks (within the sheet).

Reinforcements¶

Reinforcements are structural elements attached to the sheet that redistribute loads and slow crack growth. They are central to damage tolerance design — a well-placed reinforcement can significantly extend the life of a cracked structure.

XdTd supports two types:

Stiffeners¶

Linear reinforcing elements such as stringers and frames. Each stiffener is defined by:

Geometry — a line with position, orientation, and length
Material properties — from the material database
Cross-section properties — area and moment of inertia, from the cross-section database
Attachment — how the stiffener is connected to the sheet (see below)
Boundary conditions — loads at the stiffener start and end points

Stiffeners can be oriented in the X or Y direction. For stiffened panels, XdTd can automatically generate symmetric stiffener configurations, including broken central stiffeners.

Patches¶

2D reinforcements overlaid on the sheet surface. Each patch is defined by:

Geometry — a closed polygon
Material properties — from the material database
Thickness
Attachment — how the patch is connected to the sheet (see below)
Configuration — single-sided (one face) or double-sided (both faces)

Patches are commonly used to model repairs on cracked structures.

Attachments¶

Every reinforcement is connected to the sheet through an attachment, which determines how load is transferred between the two. XdTd supports two attachment types:

Fastened (rivets, bolts) — discrete mechanical fasteners with properties from the fastener database:

Fastener diameter, modulus, and strength
Pitch (spacing between fasteners)
Joint flexibility calculated using industry-standard formulas (Grumman, Huth, or Douglas)

Bonded (adhesive) — continuous adhesive layer with properties from the bond database:

Adhesive thickness, shear modulus, and shear strength
Yield and ultimate strain limits

The attachment type can be switched at any time through the component's context menu.

Automated Panel Creation¶

Building a panel component by component gives full control, but for common structural configurations XdTd offers automated creation driven by high-level parameters.

Stiffened Panels¶

The stiffened panel creator takes a compact set of parameters and automatically generates a complete panel:

Sheet — material and thickness
Y-direction stiffeners (stringers) — number, spacing, material, cross-section, attachment type
X-direction stiffeners (frames) — same parameters, independent from Y
Crack — growth direction, initial length, centered in the panel
Loading — applied traction and constraint conditions
Central stiffener — intact or broken (per direction)

From these inputs, XdTd automatically calculates the panel dimensions, generates a symmetric grid of stiffeners, creates the crack, and applies boundary conditions — all in one step. The external boundary is sized to fit the stiffener layout, and stiffener lengths are adjusted to align with the fastener pitch.

Configuration Files¶

All parameters can be saved to a configuration file (.xdstfpn / .json). These files can be:

Reused — load a saved configuration to recreate the same panel instantly
Shared — distribute standard configurations across a team
Edited externally — modify parameters in a text editor or generate them programmatically for parametric studies (e.g., sweeping stiffener spacing or crack length across a range of values)

Future Scope¶

The stiffened panel configuration is the first implementation of a broader concept. Future development aims to:

Extend to other configurations — multi-site damage scenarios (multiple holes with cracks of varying sizes), lap joints, and other common structural details.
Enable parametric studies — instead of a single value for a design variable like stiffener spacing, define a range (initial, final, step). XdTd would then generate multiple panels in a single case study, one per parameter value, making it straightforward to compare results and find the optimal design.

Selection Model¶

XdTd uses two levels of selection:

Single click — selects individual edges and vertices. Click directly on or near the edge or vertex you want to select.

Double click — selects entire components. For boundaries and patches, double-click within the enclosed geometry. For stiffeners, double-click on or near the stiffener line.

The selection determines what operations are available through context menus.

Context Menus¶

Right-click on a selected element to access its context menu. The available options depend on what is selected:

Edges and vertices:

Boundary condition operations (create, change, delete)
Edge splitting (at a point or into N segments)
Edge crack definition

Components (boundaries, patches, stiffeners):

Browse and change geometry
Change material properties
Change cross-section properties (stiffeners)
Change attachment type (fastened or bonded, for patches and stiffeners)
View results (when available)

External boundary has the richest context menu — from here you can also add internal boundaries, stiffeners, patches, and embedded cracks to the panel.

Boundary Condition Sets¶

Boundary conditions are organized into sets. A case study can have multiple BC sets, but only one is active at a time. This lets you define different loading scenarios for the same geometry and compare their results.

Boundary conditions can be applied to individual edges and vertices, or to all edges/vertices of a component at once.

Result Sets¶

Each analysis run produces a result set. A case study can accumulate multiple result sets — for example, from different BC sets, mesh refinements, or material variations.

Results include stress intensity factors, residual strength, crack growth data, sheet and stiffener stresses, and attachment forces. They are accessed through the context menu of the relevant component.

Clipboard¶

Internal boundaries, patches, and stiffeners can be cut, copied, and pasted (Ctrl+X, Ctrl+C, Ctrl+V). When pasting, all properties (material, cross-section, attachment) carry over, but the geometry must be redefined for the new location.

Mesh¶

Before running an analysis, the panel must be meshed. Use the Generate Mesh button on the panel toolbar.

Once a mesh exists, geometry modifications are locked — you must delete the mesh first to make structural changes.

Tips¶

Tooltips everywhere

Most dialog fields have tooltips — hover your mouse over them for quick explanations.

Context menus are your main tool

Right-click is how you access most operations. Select an element, then right-click to see what you can do with it.

See it in action

The home page has video walkthroughs of complete analyses.

Ready to learn the interface in detail? Continue to the Interface Guide.