Metal additive manufacturing promises to revolutionize aerospace: design freedom, part consolidation, rapid iteration, and supply chain resilience all sound transformative. And in many ways, they are. But here's the reality that every design lead and program manager needs to understand: aerospace doesn't start with manufacturing capability—it starts with requirements.
To leverage AM effectively in our industry, we must fundamentally understand how structural, durability, and certification requirements shape what AM can (and cannot) do. This isn't about constraining innovation—it's about channeling it productively.
Aerospace operates under a "no surprises" culture for good reason. Our parts don't just need to work—they need to work predictably across thousands of flight cycles, temperature extremes, and loading scenarios we can anticipate in advance. Redundancy expectations and damage tolerance philosophies aren't negotiable luxuries; they're the foundation of safe flight.
AM must slot into a system built around predictable, mature processes like forging, casting, and machining. This means AM parts face the same scrutiny—and often more, given their relative novelty.
Regulatory pathways require stable processes, validated material data, and demonstrated repeatability. For design teams, this translates directly into tighter process windows, more constraints, and significantly more required analysis compared to non-critical applications.
Every parameter variation, every machine difference, every feedstock batch change potentially expands your qualification test matrix. Understanding this upfront changes how you approach AM from day one.
Here's a truth that catches many teams off guard: static tensile properties of AM parts often look excellent. Ti-6Al-4V produced via powder bed fusion routinely shows ultimate tensile strengths exceeding wrought material. But that's not the performance that matters most.
Aerospace structure must survive fatigue cycling, thermal stress variations, and damage accumulation over years of service. Fatigue crack growth behavior and fracture toughness—not yield strength—ultimately govern whether an AM part is viable for flight-critical applications.
When you select an AM material for aerospace, you're not just choosing an alloy—you're choosing a process + material system, and each combination has profound implications for how you'll design, analyze, and certify the part.
Selective laser melting (SLM) and electron beam melting (EBM) produce parts with fine resolution and excellent surface quality. They're ideal for complex geometries with tight tolerances. But they're also slow, expensive, and highly sensitive to parameter changes.
For aerospace requirements, this means:
Laser engineered net shaping (LENS) and similar DED processes offer advantages for large structures and repair applications. They're faster than PBF and excel at adding material to existing parts—a game-changer for sustainment programs.
The tradeoff: rougher surfaces, lower dimensional accuracy, and typically coarser microstructures. This makes DED excellent for non-critical structure and repair operations, but challenging for fracture-critical designs where surface finish and defect control are paramount.
Aerospace demands strict control of powder morphology, chemistry, and oxygen content. Gas-atomized spherical powders pack more densely than irregular particles, directly impacting consolidation quality and defect formation.
But here's what matters for your program: every controlled variable increases your qualification test matrix. Switching powder suppliers, adjusting particle size distribution, or changing storage conditions can all require re-substantiation. This isn't a procurement detail—it's a design constraint that affects timeline and cost.
If there's one issue that dominates aerospace AM's structural viability, it's porosity. Porosity equals uncertainty, and uncertainty is fundamentally unacceptable in flight-critical applications.
Not all pores are created equal:
Gas-induced spherical pores form when process gases or volatile alloying elements get trapped during solidification. These nearly spherical defects significantly reduce fatigue life, with larger pores having increasingly detrimental effects.
Lack-of-fusion defects occur when powder particles don't fully melt and bond together. These irregular voids act like pre-existing microcracks and dominate fracture risk.
The structural implications are profound. A part might pass static testing with flying colors but fail catastrophically under cyclic loading if porosity isn't controlled.
Different typed of defects: (a) nearly spherical pore due to entrapped gas (b) lack of fusion void (Molaei & Fatemi, 2018)
Here's a counterintuitive reality: porosity increases at both extremes—relatively slow velocities and relatively fast velocities, relatively low power and relatively high power.
At low power or high speed, insufficient melting creates lack-of-fusion voids. At high power or low speed, keyhole instabilities and gas entrapment create spherical pores. The "sweet spot" exists, but it's narrow and material-dependent.
For program managers, this means: The "process recipe" isn't a commodity setting you can outsource and forget. It's an integral part of the design that requires careful development, validation, and control throughout production.
Research has shown that porosity characteristics can vary systematically throughout a build. Defect density, size distribution, and spatial location can differ between the start, middle, and end of the build process.
This nonuniformity complicates structural analysis and part acceptance criteria. You can't simply qualify "the part"—you need to qualify the part as a function of build location, or demonstrate that variation is acceptably bounded.
Traditional aerospace design often relies on handbook allowables—proven material properties established through extensive testing of conventionally manufactured materials. For AM, this approach is insufficient.
AM parts must be sized not for generic "design allowables" but for defect-informed performance. The distribution of porosity in your specific process, with your specific parameters, on your specific machine becomes part of the structural substantiation.
This fundamentally changes the design workflow. Durability and damage tolerance can't be afterthoughts verified late in development—they must inform initial design decisions.
Let me be direct: AM static properties often look great, but fatigue properties vary widely based on defects. Ti-6Al-4V produced via LENS shows ultimate tensile strength comparable to mill-annealed material, but ductility can be significantly reduced due to microstructural features. Post-processing heat treatments can improve performance, but they add cost and complexity.
The critical insight: defects drive crack initiation, and crack behavior ultimately drives certification. Understanding fatigue crack growth in the presence of porosity isn't an advanced analysis exercise—it's a fundamental design requirement.
Traditional finite element analysis assumes homogeneous materials and explicitly defined crack geometries. But AM presents a different challenge: materials with statistically distributed defects that may interact with growing cracks in complex ways.
Extended finite element method (XFEM) and multiscale modeling approaches offer a path forward. These techniques can model crack propagation through materials containing realistic defect populations without requiring prohibitively fine meshes throughout the entire structure.
Recent research demonstrates that micro-defects near a propagating macro-crack significantly influence crack path and growth rate. The orientation, size, and proximity of pores relative to the crack front all matter. For spherical pores, the ratio of pore radius to distance from the crack path determines whether the pore shields or amplifies crack growth.
For program managers: These analysis capabilities aren't yet commodity tools, but they represent where the industry is heading. Investments in computational capability and analyst training will increasingly differentiate programs that can efficiently qualify AM parts from those that struggle.
Here's where aerospace fundamentally inverts the typical AM innovation mindset: You don't design freely and then see if AM can build it. You start with structural requirements and design to the process constraints.
This isn't limiting creativity—it's directing it toward solutions that can actually be certified and produced.
Let's trace a single structural requirement through the system:
Your damage tolerance requirement dictates an allowable pore size distribution → which dictates process parameters (power, speed, scan strategy) → which dictates machine selection and in-process monitoring requirements → which constrains achievable part geometry and build orientation → which determines required non-destructive inspection strategy → which establishes your production throughput and cost
Each link in this chain is coupled to the others. Change one, and you potentially impact all downstream decisions. This is why "designing for AM" in aerospace isn't just about lattice structures and organic shapes—it's about understanding the entire requirement-to-production pathway.
Not all defects can be eliminated economically. Process optimization can minimize porosity, but achieving zero defects is neither practical nor necessary if you can demonstrate that remaining defects are structurally acceptable.
This means structural analysis must incorporate realistic defect populations. Rather than assuming perfect material, design and analysis teams need to work with statistically characterized defect distributions from actual production data.
This approach—sometimes called defect-tolerant design—requires more sophisticated analysis but can dramatically expand the design space and reduce production costs by relaxing unnecessarily tight process controls.
AM qualification resembles engine-level certification more than typical structure qualification. Why? Because the number of coupled parameters is enormous.
Feedstock supplier, particle size distribution, machine manufacturer, laser/beam parameters, scan strategy, build orientation, post-processing heat treatment, surface finishing—each variable potentially requires substantiation testing.
The hidden cost: Each change in any of these parameters may require re-qualification work. Switching powder suppliers isn't a simple procurement decision—it's a design change that could trigger months of testing.
Smart programs establish process specifications early, lock them down with supplier agreements, and resist the temptation to "optimize" during production without understanding qualification implications.
Ensuring defect consistency across multiple machines, vendors, and production sites requires unprecedented configuration management discipline.
You need:
This isn't just paperwork—it's the mechanism that ensures the part produced in Year 5 has the same structural integrity as the part you qualified in Year 1.
The appropriate role for AM varies dramatically based on program phase and application:
Clean-sheet aircraft programs: Maximum opportunity for AM integration, but also highest qualification burden. You're building the requirements and design together, which allows optimization but requires substantial upfront investment.
Incremental improvements to existing platforms: More constrained design space, but lower qualification risk if you're replacing non-critical components or using AM for secondary structure first.
Sustainment and repair: Often the lowest-risk, highest-value entry point for AM. DED processes excel at repairing damaged components, and the comparison case is scrapping the part entirely rather than competing with pristine new material.
Aerospace's stringent requirements aren't barriers to AM adoption—they're the framework that will make AM reliable, certifiable, and ultimately trusted for flight-critical applications.
The transformation won't come from printing radically organic shapes that ignore structural requirements. It will come from design teams who understand how requirements shape AM processes, who can navigate the coupled decisions between design and manufacturing, and who leverage advanced analysis to efficiently substantiate designs that incorporate realistic defect populations.
The opportunity is real: Part consolidation, lead time reduction, supply chain resilience, and design optimization are all achievable. But achieving them requires a process-driven design approach from the start.
For design leads and program managers, success with AM is less about printing parts and more about designing with process-driven insight. Understand the requirement chain. Control the process variables. Invest in the analysis capability. Lock down configuration management.
Do this, and AM becomes a competitive advantage. Skip these steps, and AM becomes a program risk.
The choice is yours—but the requirements aren't negotiable.
🔗 Download my full 2018 Master's Literature Review & Research Proposal: Structural Analysis of Porosity Effects in Aerospace Metal AM
This article draws from the literature review and research proposal I developed during my master's degree on porosity effects in aerospace metal additive manufacturing, with particular focus on the structural analysis methods required to predict performance in the presence of process-induced defects. The intersection of advanced manufacturing and structural integrity represents one of the most challenging and rewarding frontiers in aerospace engineering.
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