Thermal dynamics during DLD
Residual stress is defined as the “stress in a body which is at rest and in equilibrium and at uniform temperature in the absence of external and mass forces” .
Factors influencing residual stress formation in DLD metal parts [3-8]
- The magnitude of local residual stresses can be up to 75% of nominal yield strength .
- The material stress–strain relationship and strain mismatch during the cooling phase affect the amplitude of resultant residual stresses.
- residual stresses with higher magnitude usually occur in materials with higher Young’s modulus (modulus of elasticity) and yield stress
- Residual stresses of In718 (yield strength=1100MPa) >> 316SS (yield strength=450MPa) .
- The yield stress–temperature curve of a material system is an important factor. As the yield stress decreases rapidly with increasing temperature, the strain mismatch is low at high temperatures.
- As these volume changes can be accommodated by plastic flow , materials with high yield strength at high temperatures (ex: In718) produce greater residual stresses .
- The highest residual stress value tend to be compressive and occur along the build direction (normal to the build plate) .
- Generally, increasing the build height increases the level of residual stresses .
- Within the building plane, residual stresses are typically aligned with the laser scanning direction. They are compressive at the center and tensile at the edges of the part [3,7,8].
- residual stresses are lower at the starting location of laser scanning and reach their maximum value at the end of the laser scanning path .
- Compressive residual stresses are larger near the substrate and transit to tensile stresses with lower magnitudes toward the top of parts as the number of layers increases .
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