The question of what constitutes the strongest material on Earth does not have a single, simple answer because “strength” is not a singular, definable property in material science. Instead, a material’s strength is a collection of distinct metrics that measure its resistance to different types of forces. The material considered the “strongest” depends entirely on the specific mechanical stress being applied, whether that stress is a sharp indentation, a steady pull, or a sudden impact. Understanding how scientists categorize and measure a material’s capacity to withstand failure is necessary for an accurate answer.
Defining Material Strength: Hardness, Tensile, and Toughness
The field of materials science uses three primary properties to describe how a substance resists different mechanical loads.
Hardness
Hardness measures a material’s resistance to localized surface deformation, such as scratching, abrasion, or indentation. Tests like the Mohs scale or Vickers test determine how difficult it is to cause a permanent mark on a material’s surface.
Tensile Strength
Tensile strength refers to the maximum pulling or stretching stress a material can withstand before it breaks or fractures. This property is important in applications subjected to stretching forces, such as cables or suspension bridges. Yield strength, a related concept, is the point at which the material begins to deform permanently (plastically) and will not return to its original shape once the load is removed.
Toughness
Toughness describes a material’s ability to absorb energy and plastically deform without fracturing. A tough material resists the propagation of cracks and shattering, providing resilience under sudden stress or impact. Toughness is a combination of both strength and ductility; therefore, a very hard, brittle material may be strong but possess low toughness.
Materials Excelling in Pure Hardness and Rigidity
Materials that excel in pure hardness possess a dense, rigid crystal lattice structure with extremely strong atomic bonds. Diamond, the most commonly known super-hard material, consists of carbon atoms arranged in a tetrahedral lattice, where each atom is covalently bonded to four neighbors. This uniform structure and short bond lengths make diamond highly resistant to scratching, registering a Vickers hardness in the range of 70–150 GPa.
Several other materials theoretically surpass the hardness of standard diamond. Lonsdaleite, sometimes called hexagonal diamond, is a rare form of carbon found at meteorite impact sites. Computational models suggest that its different crystal structure could make it approximately 58% harder than diamond if synthesized without impurities.
Wurtzite Boron Nitride is another compound predicted to be 18% harder than diamond. This material forms a crystal lattice using boron and nitrogen atoms. Like diamond, it forms a tetrahedral structure, but its unique arrangement results in a highly incompressible solid with a theoretical hardness exceeding that of its carbon counterpart.
Materials Excelling in Tensile Strength and Strain Resistance
When measuring resistance to pulling forces, the champions of tensile strength are carbon-based nanomaterials. Graphene, a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice, has the highest intrinsic tensile strength ever measured. It is approximately 200 times stronger than structural steel by mass, yet it is flexible and nearly transparent.
The strength of graphene comes from the perfection of its atomic structure and the strength of the carbon-carbon bonds within the sheet. Carbon nanotubes, which are graphene sheets rolled into seamless cylinders, also exhibit extraordinary tensile strength. An aggregation of these structures can be formed into a macroscopic sheet called buckypaper, which is hundreds of times stronger than steel while weighing only 10% as much.
In terms of natural materials, spider silk stands out as the biological champion of toughness and strength-to-weight ratio. Certain types of spider silk possess a tensile strength comparable to high-grade steel, but its density is far lower. The silk’s remarkable toughness, or ability to absorb kinetic energy before failing, arises from a combination of crystalline protein regions that provide strength and amorphous regions that allow for extensibility. This balance allows it to stretch significantly, up to 35% of its length, without breaking, making it highly resilient to sudden forces.
Real-World Applications of Ultra-Strong Materials
These ultra-strong materials are transforming industrial and technological applications that require exceptional performance under stress. Super-hard materials like diamond and tungsten carbide are routinely used to manufacture durable cutting tools, drill bits, and wear-resistant coatings for machinery. Tungsten carbide, a composite of ceramic and metal, is valued for its high hardness combined with the toughness of a metallic binder.
Materials with high tensile strength and low density, such as graphene and carbon fiber, are cornerstones of advanced engineering. Carbon fiber is widely used in high-performance automotive parts, sporting goods, and aerospace components where minimizing weight is paramount. The unique properties of graphene and carbon nanotubes are leading to advancements in flexible electronics, ultra-fast charging batteries, and high-performance composites for lighter, more durable structures. Ongoing research focuses on utilizing high-strength alloys and advanced composites in applications ranging from cryogenic environments to the development of next-generation armor and protective gear.