When a steel bridge girder develops fatigue cracks, the standard playbook is brutal: shut things down, cut out the damaged component, and replace it. That's expensive, disruptive, and sometimes physically impossible when the part is welded into a structure that can't come apart. Researchers at Empa, the Swiss Federal Laboratories for Materials Science and Technology, just showed there's another way. Instead of replacing cracked steel, they're 3D printing custom metal reinforcements directly onto the damage, and in testing with ETH Zurich, the approach extended the fatigue life of cracked steel plates by up to four times.
For anyone who has ever stared at a cracked bracket, a worn housing, or a fatigued weldment and thought "there has to be a better option than scrapping this," this research is worth your attention.
What Empa actually did
The Empa team used wire arc additive manufacturing (WAAM), a metal 3D printing process where a robotic arm feeds welding wire through an electric arc and deposits metal layer by layer. Conventional welding joins two components. WAAM builds full three-dimensional shapes, which means the reinforcement printed over a crack can be engineered as a structure in its own right, with geometry tailored to the specific stress pattern of each defect.
In Empa's construction hall, researchers took cracked steel plates, printed different reinforcement designs onto them, and then hammered the plates with repeated loading cycles to simulate years of service. Every reinforced sample outlasted the unrepaired control plates. The best performer was a two-layer, stepped reinforcement geometry, and in the collaboration with ETH Zurich, damaged plates survived up to four times longer than their unrepaired counterparts.
The headline finding is counterintuitive: piling on more metal is not the answer. "The key isn't to apply as much material as possible," says Hossein Heydarinouri of Empa's Structural Engineering laboratory. "The shape is much more important: an optimized geometry distributes stresses in such a way that the propagation of existing cracks is stopped or significantly slowed down." Get the geometry wrong, and you can actually create new stress concentrations where the printed metal meets the original part.
I have a cracked metal bracket on equipment we still use. Can 3D printing actually fix it?
Yes, in many cases a cracked or broken metal part can be repaired or reproduced with 3D printing, and for parts that are hard to source, printing a replacement is often faster and cheaper than hunting one down or paying for one-off machining. Empa's research targets the repair side: printing reinforcement onto the damaged component itself. For most small businesses and makers, though, the practical route is reproduction, where the part is 3D scanned, modeled, and printed fresh in a material that matches or exceeds the original's demands. That's exactly the kind of work we do every week at our 3D scanning and reverse engineering service in Rockville, MD.
Why shape beats volume, and why that matters beyond bridges
The Empa result echoes something every experienced engineer eventually learns: material placement wins over material quantity. A fatigue crack grows because stress concentrates at its tip. A well-designed reinforcement reroutes load around the crack so it stops growing. A badly designed one just moves the problem somewhere else.
This is where additive manufacturing has a structural advantage over traditional repair. A welder can lay a bead; a machinist can bolt on a doubler plate. But a 3D printed reinforcement can be shaped precisely to the stress field, with thickness that varies exactly where the analysis says it should. Empa develops these geometries through numerical simulation and validates them experimentally before any real-world use.
The same logic applies at the scale of everyday parts. When we reprint a discontinued bracket or redesign a failed housing for a customer, we're not just copying the original. We can thicken the region that cracked, add a fillet where stress concentrated, or switch to a tougher material entirely. The replacement is frequently better than the part it replaces.
I need a replacement part for a machine the manufacturer discontinued. Can someone 3D print one?
Yes. If the physical part still exists, even broken, it can be 3D scanned, reverse engineered into a CAD model, and 3D printed as a functional replacement, with no drawings from the original manufacturer required. We handle this workflow start to finish: scan the old part, rebuild the geometry, fix whatever weakness caused the failure, and print it in anything from tough nylon to carbon fiber blends to high-temperature materials like PEEK and ULTEM. One-offs are welcome, and there are no minimum order quantities. If you'd rather skip the phone tag, you can upload your model for an instant quote and we'll ship the finished part to your door.
What still stands between the lab and the bridge
Empa is candid about the limits. WAAM currently runs on large industrial robotic systems that don't travel well, and most damaged structural components are embedded in the structures they support. "Damaged components are usually installed within the structure," Heydarinouri notes. "Today, they would have to be taken to a workshop for repair, which isn't always realistic in practice." Mobile robotic systems are in early development, so near-term applications will focus on accessible components or parts removed during scheduled maintenance.
The team is also pushing past repair into adaptive structures: printed metallic elements that deliberately deform to absorb energy during extreme events like earthquakes, then recover most of their shape. Empa materials scientist Maryam Mohri is investigating shape memory alloys for exactly this purpose. Keep an eye on that thread; energy-absorbing printed steel could end up in bridges, buildings, and industrial equipment.
The takeaway for makers and engineering buyers
The repair-versus-replace math is changing. When a printed reinforcement can quadruple the life of cracked steel, and a scanned-and-reprinted part can outperform the discontinued original, throwing hardware away starts to look like the expensive option. Whether it's a bridge girder in Switzerland or a vintage car bracket in your garage, the pattern is the same: scan it, model it, print it smarter than it was before.
By the way, if your company makes tools, materials, or hardware relevant to this kind of work and you'd like us to put a product through its paces in a future article, we're open to review units. Reach us at info@dcadditivepros.com.
Frequently asked questions
My part cracked. Can 3D printing repair it instead of replacing the whole thing?
Often, yes. Research like Empa's shows metal can be printed directly onto damaged steel to stop crack growth, and for smaller parts the practical fix is usually scanning and reprinting a stronger replacement.
I only need one replacement part. Is 3D printing worth it for a single piece?
Yes. 3D printing has no tooling costs, so a single part is economical. One-offs are a core use case, and shops like ours run them daily with no minimum order.
The manufacturer discontinued my part and there are no drawings. What do I do?
Have the physical part 3D scanned and reverse engineered. A scan captures the geometry, a CAD model is rebuilt from it, and a new part is printed, often in a better material than the original.
How strong are 3D printed metal repairs compared to the original part?
With the right geometry, a printed repair can dramatically outperform the unrepaired part. In Empa and ETH Zurich testing, optimized printed reinforcements extended the fatigue life of cracked steel plates by up to four times.