In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized by the material's ability to form a thin sheet by hammering or rolling. Both of these mechanical properties are aspects of plasticity, the extent to which a solid material can be plastically deformed without fracture. Also, these material properties are dependent on temperature and pressure (investigated by Percy Williams Bridgman as part of his Nobel Prize winning work on high pressures).

Ductility and malleability are not always coextensive – for instance, while gold is both ductile and malleable, lead is only malleable. The word ductility is sometimes used to embrace both types of plasticity.

Ductility is especially important in metalworking, as materials that crack or break under stress cannot be manipulated using metal forming processes, such as hammering, rolling, and drawing. Malleable materials can be formed using stamping or pressing, whereas brittle metals and plastics must be molded.

Tinius Olsen (December 7, 1845 – October 20, 1932) was a Norwegian born, American engineer and inventor. He was the founder of the Tinius Olsen Engineering Testing Machine Company. He was awarded the Elliott Cresson Medal of The Franklin Institute in 1891.

Tinius Olsen was born in Kongsberg, in the county of Buskerud, Norway. He was one of eight children of Ole Thorstensen (1821–1865) and Helene Marie Hansdatter (1818–1909). His father and grandfather were makers of wooden gun stocks. Olsen graduated from the Royal Norwegian Navy technical school at Horten in 1866.

Olsen emigrated to the United States during 1869. Starting in August 1869, Tinius worked as a designer for William Sellers & Co. He was later employed by the firm of Riehlé Brothers, scale and testing-machine manufacturers in Philadelphia. As the firm’s superintendent, Olsen was the principal designer of Riehl’s testing machines during the 1870s.

In 1880, he submitted a patent application for an improved testing machine and the patent was granted the same year, on June 1, 1880. Called the Little Giant it was presented to industrial expositions in Cincinnati and Atlanta during 1881, winning gold medals at both shows. In 1891, Olsen was awarded the Elliott Cresson Medal by the Franklin Institute for his invention.