Additively Manufactured Aerospace Parts: Why Fracture Testing Matters
Fracture testing and certification are critical for understanding the impact of defects and anisotropy that arise from additive manufacturing
Written By: Rebecca Reiff-Musgrove
Aerospace components rarely fail through simple overload. Instead, cracks initiate at small defects and propagate under service loads until fracture occurs. As metal additive manufacturing (AM) continues its transition from development into flight-critical aerospace applications, understanding how additively manufactured materials behave in the presence of flaws is essential for safe adoption.
Why Fracture Behavior Matters in Aerospace Additive Manufacturing
Metal additive manufacturing introduces characteristics that strongly influence fracture toughness:
- Internal porosity and lack-of-fusion defects that act as crack initiators
- Residual stresses from steep thermal gradients during the build
- Heterogeneous microstructures driven by rapid solidification
- Anisotropy, with properties differing by build orientation
Even when static strength is comparable to wrought material, fracture toughness can be lower or highly directional. Fracture toughness and crack growth testing provides the data needed to quantify damage tolerance and define safe operating limits.
Testing Challenges Unique to Additive Manufacturing
Fracture testing of additively manufactured materials presents several challenges. Specimens are often sub-size due to material cost and limited build volumes. Crack resistance can vary significantly with orientation, making alignment and load control critical. In addition, 3D-printed materials typically exhibit greater data scatter, driven by variability in defect size, location, and morphology.
Testing to stringent international standards can also be challenging when using novel manufacturing methods. High-stiffness, comparatively “brittle” materials such as aluminum and titanium alloys may show slightly reduced linear-elastic behavior with additive manufacturing, which can challenge the validity of traditional ASTM E399 fracture toughness evaluations. This is compounded when considering that small specimens often push the boundaries of size requirements.
Conversely, materials such as high-strength steel alloys may exhibit lower ductility compared to conventionally manufactured equivalents. This reduction is likely to be detrimental in basic critical crack tip opening displacement (CTOD) testing such as ISO 12135, although its effect is less clear in methods that assess crack initiation or tearing resistance, such as JIc measurements typically using ASTM E1820.
Fatigue crack growth is another significant area of interest, but it is inherently more complex to assess. Differences relative to conventionally produced materials can be more pronounced, and the results are consistently sensitive to residual stresses introduced during the manufacturing process.
These factors demand fracture testing systems with excellent force and displacement resolution, precise alignment control, and high repeatability to ensure measured behavior reflects the material, not the test setup.
How Instron Supports Fracture Testing
Instron® has decades of experience supporting fracture and damage tolerance testing for aerospace applications. Our testing systems, combined with Bluehill® Fracture software, are designed to meet the precision, stability, and data-analysis requirements of fracture mechanics testing from early material screening to certification-driven programs.
Instron systems enable aerospace engineers to:
- Perform reliable fracture toughness and crack growth tests on additively manufactured metals using integrated, standards-aligned workflows
- Accurately test sub-size specimens and complex geometries with automated compliance, crack length, and data reduction tools provided by Bluehill Fracture
- Maintain precise alignment and measurement fidelity for highly anisotropic materials
- Generate repeatable, defensible fracture data and reports with integrated validity checks suitable for regulatory and certification submission
Conclusion
Additive manufacturing offers significant advantages for aerospace, but fracture behavior remains a key challenge. By combining carefully designed fracture tests with precise, repeatable testing systems, aerospace organizations can confidently qualify additively manufactured components for safety-critical use. With Instron, engineers gain fracture data they can trust to bring innovative designs from build platform to flight.
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About the Author
Rebecca Reiff-Musgrove
Rebecca Reiff-Musgrove is Business Development Manager for ElectroPuls® at Instron. Her background includes an MSci from the University of Cambridge with a focus on the surface properties of additively manufactured parts, as well as previous roles in materials testing for the additive manufacturing industry. At Instron, she has held a range of technical and commercial roles, giving her a grounded understanding of both the technology and the customer challenges it addresses.