Coulomb’s constructions

Charles de Coulomb carried out some of the earliest published research on brittle materials. His work led to him travelling widely.

Coulomb’s family left Paris after his father lost money in unwise investments. Coulomb enrolled to study as a military engineer and one of his first roles on graduating in 1761 was the construction of fortifications on the island of Martinique. Although he became seriously ill a number of times during the posting, the determined young engineering officer carried out experiments on the shear and tensile strength of rocks and devised an expression for the bending of a rectangular beam.

Whilst working on Fort Bourbon in Martinique, he contributed to the development of a model of how brittle materials respond to stresses, known as the Mohr-Coulomb theory.

Subsequently, Coulomb was posted to Rochefort in western France to supervise the construction of new kind of fort. In charge of the project was the military engineer, the Marquis de Montalembert, described by a modern historian as “a clever, well-connected, very persistent, insufferable dilettante, wishful thinker and, to put it bluntly, fraud”.

The project did not proceed smoothly — the Marquis neglected the work and Coulomb suffered from seasickness, having to travel to the Île-d’Aix three times a week to inspect the slow progress. Despite his difficulties with sea travel, Coulomb was named ‘the king’s intendant for waters and fountains’ and worked on a project to build canals in Brittany for which he was awarded a jewelled gold watch complete with a second hand, which he used in experiments.

In addition to the science of materials, Coulomb was interested in friction and devised what has been called the third law of friction, namely that frictional force is independent of the velocity of an object for ordinary sliding speeds.