Application: Optical Crack Detection

Small Defect – Big Risk: How to Reliably Detect Invisible Microcracks

A microcrack in a material often marks the beginning of the end, especially in safety-critical or high-stress applications. But how can these tiny weak points be detected before they lead to costly or dangerous failures?

In this post, you’ll learn why microcracks are so treacherous and what limitations conventional testing methods have. You'll also learn how TENTA makes the invisible visible.

What is a crack – and why is it critical?

A crack is the result of locally broken atomic bonds in a material. This occurs where mechanical stresses concentrate, such as at sharp edges, holes, or transitions. Microdamage can form during manufacturing, such as shaping or assembly, or during operation and can then develop into cracks.

The relevance of a crack depends on the respective application — often, a difference in crack length of a few micrometer determines whether a component has a long life or fails completely.

Metal ring with superficial hairline crack ( seen from the photographed end face). There is a high risk of breakage as it is a rotating component. This could damage the surrounding components and turn it into a projectile.

Microcracks: The invisible threat

Cracks are only visible to the naked eye if they are at least 100 µm long. Modern microscopes and camera systems improve visibility, and computed tomography can reveal deeper crack structures, though this method is time-consuming and costly.

The problem is that traditional inspection methods rely on optical visibility. Microcracks, which are extremely fine and closed, remain invisible. Even long, deep cracks can go undetected if they do not open up. The consequence is unrecognized weakening of structural components.

There is a long hairline crack in the structured ceramic tile. The tile is 5 mm thick, and the crack is continuous and completely invisible. There is severe structural weakening and a risk of breakage.

Is there a way to detect microcracks?

Yes, and most people are familiar with this method of inspection: when suspecting a crack, they instinctively bend or pull the part slightly to expose it. However, this intuitive method is neither digitizable nor objective and damages the part further.

The solution? TENTA applies this physical principle with high precision, contactlessly, and without causing damage.

How it works: With minimal, targeted excitation, the component is stressed. The highly sensitive TENTA sensor detects the resulting deformation with nanometer accuracy. Even the slightest crack creates local stress peaks, which are measurable as distinct expansions at that precise location.

There are cracks in the rubber ring on the front side at approximately 5 o'clock. There is also a crack running radially on the shell surface at approximately 8 o'clock. The latter is invisible from the camera's point of view because it is under the surface. There is a risk of leakage.

It's more than just "crack or no crack." TENTA goes beyond that.

Our technology goes beyond simple crack detection.

We provide:

• Exact crack dimensions (depth, length)

• Assessment of the structural relevance of the damage

• Distinction between real cracks and minor surface defects e.g. scratches, grooves, or dirt

• Reduction of pseudo-rejects – for more accurate decisions in quality control and production