breaking point

How will a glass surface, plastic material or concrete layer break under pressure? This question is of great economic importance, and affects many areas - from the integrity of airplane wings to the design of new strong materials

How will a glass surface, plastic material or concrete layer break under pressure? This question is of great economic importance, and affects many areas - from the integrity of airplane wings to the design of new strong materials. In fact, the principles of this basic process - fast cracking - still remain a mystery, partly because it is very difficult to observe: a fast crack can cross the material at a rate close to the speed of sound, while the forces that drive the crack are increased to an extraordinary degree, and are concentrated in a tiny area near the moving tip His.

Dr. Eran Buchbinder, who recently joined the Department of Chemical Physics in the Faculty of Chemistry at the Weizmann Institute of Science, is interested in the physics of solid materials out of equilibrium. In other words, he studies how they warp, slip and break under mechanical forces. In joint research with Prof. J. Feinberg's research group from the Hebrew University of Jerusalem, where he conducted post-doctoral research, Dr. Buchbinder developed a new theory, which may give scientists and engineers a new tool for investigating the cracking process. The research, the findings of which were recently published in the scientific journal Science, was based on a breakthrough in Prof. Feinberg's laboratory: a gel that breaks like glass, but at a speed 500 times slower, and has an edge area much larger than usual - that is, the edge of the crack is large and slow enough that it can be followed with a high-speed camera. When Dr. Ariel Livna and Ilya Svetlitsky - members of Prof. Feinberg's team - began to measure the dynamics of the progress of the cracks in the gel, they discovered that the numbers did not match the accepted theory. The deviation even increased as the measurements approached the edge of the crack. The scientists concluded that the existing theory does explain quite well what happens away from the edge of the crack, but does not fit the physics of the area close to the point where the cracking process takes place. These experiments made it possible to establish the differences between the experimental data and the theory; At this point, Dr. Buchbinder entered the picture, with the aim of finding an explanation for the discrepancy.

The mathematics of the conventional theory of dynamic cracking is based on a relationship formulated by Robert Hooke in the 17th century, which describes elastic deformation (ie without breaking) of a material in response to an external force. The relationship established by Hooke is linear: the material bends in direct proportion to the force applied to it. It turns out that this linear relationship goes wrong near the edge of the crack, which led Dr. Buchbinder to the understanding that the main physical process taking place is actually non-linear elasticity. The analytical solution he developed, and tested in an experiment carried out by Dr. Livna, explains the measurements for the entire length of the crack in great detail, even very close to the edge of the crack. In addition, it provides an answer to several mysteries that remain unexplained in the accepted theory, including, among other things, why very fast cracking does not usually develop in straight lines: the crack often becomes unstable, thus creating a branched or wavy pattern.

Dr. Buchbinder's new theory defines a new length scale in the area of ​​the crack tip - which does not exist in the accepted theory - which may explain the observed instabilities. It also explains the directionality of the main forces acting on the crack tip region, in a way that corrects controversial predictions in the old theory. More importantly, the new theory shows that in any cracked material there is a non-linear elastic transition zone, which bridges the more distant linear processes and the cracking processes closer to the crack tip. More than 300 years after Hooke's Law was formulated, scientists and engineers have a new approach to solving the mysteries of dynamic cracking.

Today, at the Weizmann Institute of Science, Dr. Buchbinder, the theoretician, plans to continue his collaboration with research groups of experimental scientists, with the aim of investigating phenomena far from equilibrium in real systems. These include the development of mathematical tools for understanding processes such as deformations and instabilities in crystalline and polycrystalline solids, plastic deformation of disordered solids, and sliding under frictional conditions: a process in which two surfaces in contact break while moving. In addition, he plans to research natural materials resistant to the formation of cracks, with the aim of imitating nature and designing particularly strong artificial materials.

personal

Dr. Eran Bochbinder grew up in Kfar Saba. As a student in high school he was interested in physics and literature, and in his undergraduate studies at Tel Aviv University, he focused on physics and philosophy. After two years in which he worked as a physicist in industry, he came to the Weizmann Institute of Science to continue his studies in the group of Prof. Itamar Procacia from the Department of Chemical Physics. He completed his third degree in 2007, and after two years of post-doctoral research at the Hebrew University, he joined the Weizmann Institute of Science as a senior researcher.

Dr. Buchbinder is married to Miki, a PhD student in neuroscience at Bar Ilan University, and they have two children, Yonatan, five years old, and Shira, two years old. Although his path led to science, he is still passionate about books and reads in every free moment.