Parts used in aircraft engines, power plants, and other high-temperature machines must survive extreme stress for long periods of time.
Many of these parts are made from tough materials called superalloys, such as Inconel 718.
These materials are designed to handle heat and pressure, but they still face a common problem: tiny cracks often begin around holes used for bolts and fasteners.
Over time, repeated stress can cause these cracks to grow, eventually leading to failure.
Engineers have been trying for years to find better ways to strengthen these weak points.
Traditional methods, like peening or cold expansion, work by pressing or deforming the material around the hole to create what is known as compressive residual stress.
This type of stress helps stop cracks from forming or spreading.
However, these methods are not perfect. Some can roughen the surface, while others create uneven changes in the material, which can reduce their overall benefit.
A new study published in Materials Science and Engineering: A offers a promising solution.
Led by Run-Zi Wang and his team, the research introduces a new technique called Hertz contact rotation expansion processing, or HCR-EP. This method uses a rotating tool that presses gently but precisely against the inside of a hole, expanding it in a controlled way.
The key advantage of this method is that it creates a more uniform change in the material. It forms a deep layer of compressive stress without causing much surface damage or unwanted buildup of material around the hole. In simple terms, it strengthens the hole more evenly and cleanly than older methods.
To test how well this works, the researchers carried out high-temperature fatigue experiments. These tests simulate the repeated stress that parts experience during real use. The results showed that parts treated with HCR-EP lasted much longer before failing, especially under conditions where stress cycles happen many times.
The team also wanted to understand why this improvement happens. They paused their tests at different stages to examine changes in the material. They found that some properties, like hardness and plastic deformation, stayed mostly the same over time. However, the compressive residual stress gradually decreased as the material was repeatedly stressed. This showed that this type of stress plays the most important role in extending the life of the material.
Interestingly, the researchers also discovered that the benefits of this method depend on how the part is used. Under moderate conditions, the improvement in fatigue life is clear. But under more extreme stress, the advantage becomes smaller. This means the method needs to be matched carefully to the real working conditions of each part.
This study suggests a new way of thinking about material design. Instead of simply predicting when a part might fail, engineers can now actively shape the material to prevent damage from starting. In the future, the team hopes to combine this approach with artificial intelligence to better connect manufacturing methods, material properties, and real-world performance.
By focusing on stopping cracks before they begin, this new technique could help create safer, longer-lasting components in many industries.
