Induced Anisotropy in the Fracturing Behavior of 3D Printed Parts Analyzed by the Size Effect Method

Overview

This paper presents a detailed analysis of the fracturing behavior of 3D printed parts made from Acrylonitrile Butadiene Styrene (ABS) using the size effect method. The study investigates the induced anisotropy in strength, fracture toughness, fracture process zone (FPZ) size, and the degree of quasibrittleness. It demonstrates that 3D printed parts exhibit significant anisotropy in fracturing behavior compared to their monolithic counterparts, influenced by the orientation of the pre-crack and the printed layers.

Key Contributions

  1. Anisotropic Fracture Behavior:

    • Demonstrates significant anisotropy in strength, toughness, and FPZ size caused by the relative crack path and 3D printed layer orientations.

  2. Quasibrittle Behavior:

    • Reveals a transition between brittle and quasibrittle behavior depending on the size and orientation of specimens.

  3. Validation of Size Effect Laws:

    • Confirms the size effect laws for strength and fracture toughness, enabling extrapolation of lab-scale results to real-world applications.

  4. Fracture Process Zone Analysis:

    • Estimates the FPZ size for various orientations, providing insights into the anisotropic quasibrittleness of 3D printed parts.

Experimental Methodology

  1. Material and Specimen Geometry:
    • ABS was selected due to its widespread use in 3D printing.
    • Single edge notch bending (SENB) specimens were tested at three scales (small, medium, large) with consistent geometry.
SENB specimen geometry and dimensions used for testing.

  1. 3D Printing:

    • Specimens were printed in three orientations (A, B, C), varying the alignment of macrolayers and microlayers relative to the pre-crack.

  2. Testing Protocol:

    • Conducted 27 SENB tests across all orientations and sizes.
    • Used the size effect method to analyze fracture properties, including strength and toughness.

Results and Insights

  1. Anisotropic Fracture Toughness:
    • Orientation C exhibited the highest toughness and largest FPZ size, indicating quasibrittleness.
    • Orientation B showed the lowest toughness and brittle behavior.
Fracture toughness comparison for different orientations.
  1. Quasibrittleness Analysis:
    • FPZ sizes for orientations A and C were 2.85 mm and 18.38 mm, respectively.
    • For orientation B, the FPZ was negligible, resulting in conformance with Linear Elastic Fracture Mechanics (LEFM).
Fracture process zone (FPZ) sizes for different orientations.
  1. Size Effect Validation:
    • Observed a strong size dependence in nominal strength and fracture toughness for orientations A and C.
    • Validated Bazant’s size effect law for quasibrittle materials.
Validation of Bazant's size effect law for different specimen sizes.

Applications

  • Design of 3D Printed Components:
    • Highlights the importance of considering anisotropic fracture behavior for reliable designs.
  • Additive Manufacturing:
    • Provides insights into tailoring layer orientations for desired mechanical properties.

Conclusion

This work demonstrates that 3D printing induces significant anisotropy and quasibrittleness in the fracture behavior of ABS parts. The findings underscore the importance of accounting for these effects in design processes to ensure reliability and performance.