The Wuhan University research team discovered the “strongest” substance to date

The reporter of “China Science News” learned from Wuhan University that recently, “Advanced Science” and “Physical Review Application” published the research results of Gao Enlai’s research group, associate professor of the School of Civil Engineering and Architecture of the university, on the limits of mechanical properties. Related studies have revealed the upper limit of material stiffness and strength theory, and found the strongest and toughest substance to date. The titles of the two papers are “Predicting the Toughest and Strongest Materials: Chains of Carbon Nitride Atoms Approaching the Theoretical Limit” and “Exploring the Boundary between Young’s Modulus and Specific Young’s Modulus”.

The relevant principle is schematic. Photo courtesy of interviewee

Young’s modulus and tensile strength are measures of a material’s stiffness and strength. However, in the two hundred years since the proposal of mechanical measures such as Young’s modulus, the upper limit of the theory has been unresolved, causing long-term controversy and confusion. Faced with this dilemma, Gao Enlai’s research group first established a microphysical model of the extreme Young’s modulus from the theoretical limits of chemical bond stiffness, orientation and density, theoretically derived the theoretical expressions of the extreme Young’s modulus and the specific Young’s modulus, and determined that the theoretical upper limits of the Young’s modulus and the specific Young’s modulus were 3074 GPa and 1036 GPa·g-1·cm3, respectively. Young’s modulus is closely related to sound velocity and tensile strength. According to the theoretical upper limit of Young’s modulus, the research group further theoretically determined the upper limit of sound velocity (37 km/s) and the upper limit of tensile strength (tensile strength 384GPa and specific tensile strength 130 GPa·g-1·cm3).

The above studies determine the theoretical limit of mechanical properties such as Young’s modulus, and there is still a huge gap between some mechanical property records of existing materials and their theoretical limits, which indicates that there is still huge room for innovation in the improvement of mechanical properties. To this end, the research group further developed the theoretical design of solid mechanics based on the structural component characteristics of extreme Young’s modulus substances (Chem. Mater., 2021, 33: 1276) discovered by the previous data. Based on the combination of boron, carbon, nitrogen and other light elements, they designed a large number of material structures, from which they screened a variety of crystal structures with stable chemical properties and mechanical properties breaking existing records, among which the Young’s modulus of confined linear carbon crystals was as high as 2973 GPa, which was close to the theoretical limit of Young’s modulus (3074 GPa), and the linear carbon nitride crystal had a specific tensile strength of 1032 GPa·g-1·cm3 and 108 GPa·g-1·cm3, which greatly exceeded that of diamond, Graphene and other known high-modulus high-strength materials, and close to the theoretical limits of specific Young’s modulus and specific tensile strength (1036 GPa·g-1·cm3 and 130 GPa·g-1·cm3).

The relevant achievements have expanded human understanding of material stiffness and strength, and the discovered extreme performance substances have important application prospects in cutting-edge fields such as national defense industry. (Source: China Science News, Li Sihui, Liao Xin)

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