This research, recently carried out by Prof. Jay Feinberg and Neri Berman from the Rekh Institute of Physics, was published in the prestigious journal Physical Review Letters. The study revealed, for the first time, the behavior in the immediate vicinity of the crack tip. In fact, this is the first time in the world that this tiny region, where material breaking occurs, has been observed in a laboratory experiment
Cracks weaken a broken material, many know that, but their existence is what determines the strength of a material in general. Cracks concentrate an enormous amount of energy in their tip region, where the stresses in this microscopic region can mathematically reach infinity. In nature, contrary to the theoretical predictions, the effort focusing mechanism activated at the moment of creating a crack in the material varies from material to material, and of course there is a limit to any energetic effort that manifests at the end of the process in a fracture of the material. For example, glass is a material that puts a relatively weak limit to the infinite efforts that a crack centers on its edge - and therefore it breaks easily when it is formed. On the other hand, in aluminum or steel, a different mechanism occurs at the edge of the crack, which prevents the crack's efforts from breaking the material.
In a recently published study, researchers proactively performed small "earthquakes" in a perspex material (perspex, a type of transparent acrylic glass) and turned the "spotlights" on the mysterious behavior that occurs at the edges of cracks during breakage. This research, recently carried out by Prof. Jay Feinberg and Neri Berman from the Rekh Institute of Physics, was published in the prestigious journal Physical Review Letters. The study revealed, for the first time, the behavior in the immediate vicinity of the crack tip. In fact, this is the first time in the world that this tiny region, where material breaking occurs, has been observed in a laboratory experiment.
One of the important findings in the study is that the crack tip goes through a phase at a critical speed of progress, in which it completely changes its character. The phase transition is analogous to the phase transition that characterizes the transition of water to ice. "The main difficulty Looking at the edge of the crack is the microscopic size of the area, capable of moving at the speed of sound (about km/second)," explains Prof. Feinberg. "Despite the challenging measurement, for the first time we were able to simulate the cracks running at the speed of sound, and through it we discovered the The form in which the material itself is organized In order to avoid the large pressures at the edge of the crack. That is, the material is affected by the process of creating the crack. The form that was discovered turned out to be completely different from the expectations described in the scientific literature in the last decades".
This is not Prof. Feinberg's first work regarding the infinity of crack efforts. In a previous publication in the prestigious journal Nature, Prof. Feinberg explained Because "When we studied the phenomenon of friction in the laboratory, we discovered that the beginning of the sliding process is, in fact, described by the progress of earthquakes that break the contacts between any two bodies that rub against each other. These 'earthquakes' that start at a weak point and progress at a speed approaching the speed of sound. In order to understand their behavior, we invented a method that allows us to follow the movements of these earthquakes by means of rapid photography (about a million pictures per second) of the contact area at each point of contact between two plates sliding on each other.. These measurements showed that the earthquakes constitute the mechanism through which friction takes place. This was the first time anyone had measured such a thing. Beyond that, we have shown that earthquakes have properties that are completely parallel to the properties of moving cracks. In the current study, we used this knowledge to decipher the behavior of materials under the influence of the tremendous efforts created at the edge of a crack when materials break."
The research may have many consequences, since its results undermine the basic concept regarding the properties and stability of materials. The traditional view assumes that at the time of breaking the material is quite passive, i.e. it is affected by the tremendous pressures exerted on it - but it does not affect these efforts, and certainly should not have affected the form of organization of the efforts exerted on it. "In light of the surprising results of the study, we must take this reciprocity into account," clarifies Prof. Feinberg. Moreover, the new models that will be developed will have to include the 'phase transition' processes that occur when a material succumbs to the pressures exerted on it - and perhaps this will be the key to understanding the great difference in the strength of materials - especially regarding materials that are very similar in all other mechanical properties that characterize them.
Future research by Prof. Feinberg will try to examine how the microscopic area of the crack can be influenced in order to change the behavior and strength of materials in the different layers. The characterization of this critical region is the first step towards changing its properties proactively, a fascinating possibility with the help of which it may be possible to intelligently engineer the properties of new materials, and create stronger materials for human benefit.
Prof. Guy Feinberg concludes: "In many cases, gaining new understanding leads to new ways to 'direct' and change natural behavior. We expect (and hope) that achieving this new understanding of the behavior of the material at the edge of a crack will lead to the development of new materials whose strength can be 'tuned'.
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