MIT studies micro-impacts at 100 million frames per second

Engineers know that tiny, high-speed objects can cause damage to the spacecraft, but it's hard to understand how this damage occurs because the moment of impact is extremely brief. A new study by MIT seeks to reveal the processes at work that produce microscopic craters and holes in materials. The hope is that by understanding how the impacts work, we might be able to make more durable materials.

Accidental space impacts are not the only place where these mechanisms come into play. There are also industrial applications on Earth such as the application of coatings, the reinforcement of metal surfaces and the cutting of materials. A better understanding of micro-impacts could also make these processes more efficient. Observing such impacts has not been easy, however.

For experiments, the MIT team used tin particles of a diameter of about 10 microns, accelerated to 1 kilometer per second. To launch the projectile, they used a laser system that instantly evaporates a surface material and ejects the particles, thus ensuring a constant timing. This is important because the high speed camera directed to the test surface (also in tin) required specific lighting conditions. At the agreed time, a second laser illuminated the particle, allowing the camera to track the impact at a speed of up to 100 million frames per second.

In previous studies on micro-impacts, researchers had to rely entirely on a "post-mortem" badysis of the damage caused by the impact. Looking at it in real time and comparing it to the final product revealed several important factors. At speeds above a certain threshold, the team discovered a melting hinge period when the particle hit the surface. This plays a crucial role in the erosion of the material.

The moment of impact when a particle of 10 micrometers strikes a metal surface. Credit: MIT

Using high speed camera data, the team developed a model to predict how a particle will interact with the surface. This could bounce, stick or loosen material and leave a crater that would weaken the surface. This is important, especially in industrial applications, since it has long been thought that higher speeds are more efficient. We now know that this is not always the case.

Until now, research has focused on pure metals, but most industrial and space applications rely on alloys. The extension of the test to more materials is next on the agenda. Similarly, researchers plan to project particles on surfaces from different angles. These initial tests were only direct impacts.

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