The question of the strongest object in the world is not a simple one, as the answer depends entirely on how “strength” is defined. In materials science, strength is not a single, unified property but a collection of distinct mechanical characteristics. The material that resists being scratched, for example, is often not the same material that excels at resisting being pulled apart. To find the true contenders for the title of “strongest,” one must look at materials that dominate different categories of mechanical performance. The world’s strongest materials are typically found in rare minerals or in the cutting-edge of engineered materials at the nano-scale.
Defining Physical Strength Categories
Materials scientists categorize strength into several distinct properties, three of which are most relevant to the common understanding of “strongest.” The first is hardness, which is a material’s resistance to localized plastic deformation, such as scratching or indentation. Hardness is commonly measured using scales like the Mohs scale or the Vickers test.
The second category is tensile strength, which measures the maximum stress a material can endure while being stretched or pulled before it breaks. This property is measured in pressure units like Pascals (Pa) or GigaPascals (GPa). A material with high tensile strength can bear a heavy load along its length without snapping.
Finally, fracture toughness describes a material’s ability to absorb energy before fracturing, especially when a crack or flaw is already present. This is often described as the resistance to crack propagation. A material can exhibit high hardness and tensile strength but still have low toughness, meaning it will shatter catastrophically upon impact, like a diamond.
Materials with Extreme Hardness and Stiffness
Hardness, the resistance to scratching and compression, is the most common measure of strength in the public imagination, largely due to the fame of diamond. Diamond, a carbon allotrope, remains the benchmark for hardness because of its dense crystalline structure and the strong covalent bonds between its atoms. Its exceptional stiffness and ability to resist indentation have made it the material of choice for cutting and abrasive tools.
However, diamond’s title as the hardest material is being challenged by other carbon and boron compounds. Theoretical and simulation studies suggest that Wurtzite Boron Nitride (w-BN) and Lonsdaleite, or hexagonal diamond, exceed diamond’s hardness. Wurtzite Boron Nitride is calculated to withstand 18% more stress than diamond, while Lonsdaleite is potentially 58% harder.
These materials achieve their superior hardness through structural mechanisms that allow them to resist compression. In Wurtzite Boron Nitride, the bonds between atoms are thought to reorient themselves when subjected to extreme pressure, enhancing the material’s strength. While these newer contenders are difficult to synthesize in large, pure forms, their existence points to the limits of what a highly-ordered, covalently-bonded structure can achieve.
Contenders for Ultimate Tensile Strength
When the definition of strength focuses on resistance to being pulled apart, the strongest materials are found at the nanoscale. Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, holds the record for the highest intrinsic tensile strength ever measured. Its two-dimensional structure is stabilized by powerful sp² covalent bonds, giving it a theoretical tensile strength of approximately 130 GigaPascals (GPa).
Graphene’s strength is often discussed in terms of its specific strength, which is its tensile strength divided by its density, making it extremely strong for its weight. Carbon Nanotubes (CNTs) also excel, as they are essentially graphene sheets rolled into cylinders. Individual CNT shells have shown tensile strengths approaching 100 GPa and a specific strength value that is orders of magnitude greater than high-carbon steel.
In the natural world, a similar principle of high specific strength is seen in Spider Silk, particularly dragline silk. While its absolute tensile strength is around 1.1 GPa, comparable to some high-grade steel alloys, its density is much lower. This low density means that on a weight-for-weight basis, spider silk is far stronger than steel, making it the strongest known naturally occurring fiber in terms of specific strength.
The Concept of Fracture Toughness
The final, and perhaps most practical, measure of strength is fracture toughness, the ability to absorb energy and resist failure when a crack begins to propagate. Materials that are exceptionally hard or have high tensile strength are often brittle and lack this property, which is why a diamond can be shattered with a hammer. Tough materials manage this failure by deflecting or arresting cracks, often through a disorganized or layered internal structure.
Bulk Metallic Glasses (BMGs), also known as amorphous metals, are a class of materials known for their high strength and unique toughness properties. Unlike traditional metals, their atomic structure is random, similar to glass, which allows them to deform by localizing stress into narrow bands. The strongest BMGs, such as certain zirconium-based alloys, have demonstrated fracture toughness values comparable to some high-strength steels.
Nature provides the strongest examples of combining strength and toughness in bio-composites like Nacre, the iridescent material found in the inner shell of mollusks. Nacre achieves its durability through a “brick-and-mortar” structure, where microscopic ceramic platelets are cemented together by a soft, organic polymer. This layered architecture forces cracks to dissipate their energy by following a tortuous path, preventing catastrophic failure. Scientists are now mimicking this structure to create new synthetic materials with superior impact resistance. The strongest object in the world is therefore a subjective title, depending on whether one requires a material that resists scratching (Wurtzite Boron Nitride), being pulled apart (Graphene), or breaking from impact (Nacre-inspired composites).