3D Crack Complexity Linked to Material Toughness, Study Finds Swiss Army Knife and Confocal Microscope Reveal Secret to Stronger Materials . Credit: techxplore.com

Have you ever accidentally broken your favorite mug or sat on your glasses, too distracted to notice the intricate pattern of cracks that formed? For John Kolinski and his team at the Laboratory of Engineering Mechanics of Soft Interfaces (EMSI) in EPFL's School of Engineering, studying these patterns is their specialty.

Their research focuses on understanding how cracks spread in brittle solids, which is crucial for developing safe and cost-effective composite materials used in construction, sports, and aerospace engineering. However, traditional methods of analyzing crack formation assume that cracks are flat on the surface of a material. In reality, most cracks, like those in everyday objects such as glass, form complex three-dimensional networks of ridges and other features.

Observing this complexity in real time is challenging due to the opacity of materials and the speed at which cracks form. But Kolinski and his team have found a way to do so using a Swiss Army knife and a confocal microscope. Through their observations, they have discovered a positive relationship between crack complexity and material toughness.

According to Kolinski, the amount of energy needed to drive cracks has been considered a material property, but their research reveals the key role of geometry. By increasing the complexity of geometric features at the crack tip, a material can become tougher, as more strain energy is required to advance a complex crack compared to a simple one. This highlights a gap in the current theory of 3D cracks.

The team's findings have been published in Nature Physics. Their method involved creating thin slices of four different hydrogels and an elastomer. These transparent and brittle materials, easy to deform and measure without shattering, served as proxies for understanding how cracks form in glass and brittle plastics, while the elastomer represented materials like rubber and silicone polymers.

Using a custom apparatus to control sample alignment and loading, the team induced cracks in the samples using a standard Swiss Army knife. They then used a confocal microscope to capture a series of fluorescent images and stack them to create a 3D map of each fracture surface.

According to Kolinski, people have known about the complex nature of cracks by examining fracture surfaces, but they lose information about the loading conditions and forces applied during the crack's formation. However, their imaging method allows for a rigorous characterization of this relationship in real-time.

In short, the team's experiments showed that the strain energy required to drive cracks was directly related to the length of the crack tip. This suggests that the increased geometric complexity of a 3D crack requires more energy to advance as it creates more fracture surface. Additionally, their research showed how a smoother crack approaching a rigid obstacle embedded in the sample can break its planar symmetry, increasing both the crack tip length and the energy needed to drive the crack forward.

Kolinski believes that their research could inspire new design approaches and highlights the importance of careful materials testing. Any deviation from a planar crack front can lead to mis-measurements and potentially dangerous overestimations of material toughness.

David Lamy
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David Lamy owns the Bachelor in Atmospheric Science Degree. He is associated with Industry News USA from last 2 years. With proficiency in his work, David obtained a strong position at Industry News USA and heads the Science section. “Weather forecasting” is the field of his interest. He bags total 5 years of experience in this field. Apart from his routine work, David loves to explore his cooking skills. He has participated in various cookery shows.