Barrelling

Barreling, sometimes spelled barrelling, is a deformation pattern observed during uniaxial compression tests and forming operations, in which a cylindrical or prismatic specimen develops a barrel-shaped profile. The midsection becomes the widest region, while sections near the ends experience less bulging because they are constrained by contact with platens or dies.

The phenomenon is mainly caused by friction between the specimen ends and the contacting surfaces, which hinders material flow at the ends and redirects it toward the midsection. Material properties such as strain hardening, temperature, and strain rate, along with specimen geometry and lubrication quality, influence the degree of barreling. High friction, rapid deformation, or temperature-sensitive materials tend to exhibit more pronounced barreling.

Barreling affects the interpretation of mechanical data obtained from compression and forming tests. It introduces nonuniform strain fields, complicating the extraction of true stress-strain curves and yield criteria. Measurements taken assuming uniform cross-section (for example, area-based stress calculations) can be biased. To quantify barreling, researchers compare diameters at the ends and in the central region, using a barreling ratio such as end diameter divided by central diameter.

Mitigation strategies focus on reducing friction and improving uniformity of material flow. These include using lubricated or low-friction end surfaces, selecting platen materials with appropriate hardness and surface finish, ensuring precise alignment, and controlling temperature and strain rate. In analysis, finite element modeling can account for barreling by incorporating friction coefficients and boundary conditions to better interpret experimental data.