Beneficial Compressive Residual Stresses
Fatigue strength improvements are proportional to the magnitude and depth of induced compressive residual stresses present in a component. Deeper compressive residual stresses provide superior resistance to crack propagation and fatigue failure. Laser peening typically produces compressive residual stresses up to 10X deeper than competing surface enhancement processes.
So how does laser peening produce effective compressive residual stress profiles? LSPT engineers control the depth and magnitude of compressive residual stresses by increasing the power density and coverage of the laser pulse.
Compared to shot peening, laser peened parts retain deeper compressive residual stress profiles in high-temperature environments. Laser peening’s superior heat resistance results from the lower percentage of cold work involved, producing deep compressive residual stresses that remain stable at elevated temperatures.
Surface enhancement techniques like shot peening and laser peening rely upon plastic strain to produce beneficial compressive residual stresses within a material. Laser peening is a mechanical process that utilizes a high-energy, pulsed laser to generate a compressive stress wave at the surface of a part. The compressive stress wave induces plastic deformation as it propagates into the material, causing dislocations in the microstructure that enhance the strength and fatigue resistance of the part. Compressive residual stresses inhibit the initiation and propagation of fatigue cracks.
Metal Fatigue Prevention
Metal fatigue failure typically results from microscopic crack formation at the surface of the material. Cracks may initiate due to cyclic loading, foreign object damage, or corrosive environments, and cracks will propagate with successive loads or continued exposure until failure occurs.
Enhancing materials through the introduction of compressive residual stresses inhibits the initiation and propagation of fatigue cracks. Compressive residual stresses provide a counterbalance to the tensile stresses present at the part surface, and the compressive environment slows the propagation of microcracks. Deep compressive residual stresses provide enhanced fatigue resistance, and can significantly extend the fatigue life of a metal part.