Residual Stress

Theory

Residual stresses arise from non-uniform plastic deformation, thermal gradients during solidification, phase transformations, or mechanical working. They are self-equilibrating: tensile residual stress in one region must be balanced by compression elsewhere. Measured by X-ray diffraction, neutron diffraction, or hole-drilling. Compressive residual stress at surfaces retards crack initiation (shot peening); tensile residual stress promotes cracking.

Application

In FDM, residual stress is a primary driver of warping and delamination. The extruded bead cools and contracts while constrained by the layer below, inducing tensile stress in the print direction and compressive stress through thickness. Heated build plates, enclosures, and slow cooling reduce residual stress. Annealing FDM parts at 10°C below Tg for 1-2 hours can significantly reduce residual stress and improve dimensional stability.

Common mistakes

Residual stresses add algebraically to service stresses: a part designed to 80% of yield may be already at yield before any load is applied. Warping occurs when residual stress overcomes part adhesion to the build plate. Measuring residual stress in FDM parts is difficult; predictions require thermal FEA of the deposition process. Painting or coating a stressed part can trigger cracking at the interface.

Related terms: Stress, Fatigue, Creep, Anisotropy