3D Printed Fracture Mechanics Stress Fields Mode I, II, III

Summary
Visualizing the exact stress distribution ahead of a crack tip is one of the greatest hurdles in university-level materials science and engineering. This educational kit provides physical, multi-color 3D printable models of the three fundamental fracture mechanics loading modes, alongside a standard Compact Tension (CT75) specimen geometry.

The primary models in this collection are not just arbitrary shapes. They are multipart assemblies derived from actual Finite Element Analysis (FEA) data. The separate bodies represent discrete von Mises stress contours. When printed with a multi-color system (e.g., Bambu Lab AMS or Prusa MMU), the resulting physical parts accurately display the stress concentrations and plastic zones surrounding the crack tip.

This kit is designed specifically for university lectures, laboratory demonstrations, and independent study to help students literally grasp the physics of fracture mechanics.

What is Included?

• Mode I (Opening Mode): Represents a tensile stress applied normal to the plane of the crack. This is the most common loading mode encountered in engineering design. The color gradients perfectly illustrate the classic "butterfly" yield zone shape ahead of the crack tip.
• Mode II (In-Plane Shear Mode): Represents a shear stress acting parallel to the plane of the crack and perpendicular to the crack front. The model highlights the distinct, skewed stress distribution causing the crack surfaces to slide over one another.
• Mode III (Out-of-Plane Shear Mode): Represents a shear stress acting parallel to the plane of the crack and parallel to the crack front (tearing).
• CT75 Specimen (ASTM E647): A standardized Compact Tension specimen scaled to W = 75 mm. This model serves as a practical reference for the standard geometry used worldwide for fatigue crack growth.

Educational Application
These models serve as a bridge between theoretical equations and physical reality. Instructors can use them to physically demonstrate:

• The relationship between the stress intensity factors (KI, KII, KIII) and the spatial stress distribution.
• The difference between plane stress (surface edges) and plane strain (interior) conditions.
• How the superposition of these three basic modes can describe any complex macroscopic fracture event.

Printing Instructions
To achieve the stress-contour effect, you must use a multi-extruder or material-switching 3D printer.

1. Import the provided .3mf files into your slicer.
2. Ensure your slicer imports the file as a single "Multipart" or "Multi-body" object, not as separate individual models.
3. Assign your filament colors sequentially to the different bodies. It is highly recommended to use a standard thermal colormap (e.g., Blue for the lowest stress/background material, transitioning through Green and Yellow, to Red for the maximum stress concentration directly at the notch root).
4. Standard PLA or PETG works perfectly. A layer height of 0.2 mm provides a good balance between print time and contour resolution.
5. Infill can be kept low (10% to 15%) to save material, as these are educational display pieces.