Finite element modeling and validation of thermomechanical behavior of Ti-6Al-4V in directed energy deposition additive manufacturing

Invited review article: Metal-additive manufacturing—Modeling strategies for application-optimized designs

“…Among different approaches, energy absorption can be fully accounted for in the efficiency term 𝜂, where the material absorbance and laser efficiency are lumped together. E. Yang et al (2016) set this value to 45% for DED of Ti6A14V [64]. Mukherjee et al (2017) incorporated a second absorptivity term to represent the absorption of laser energy by the previously deposited layer, adding an additional level of detail that is typically ignored within most models [57].…”

“…[1,80], which fundamentally shows that plastic strain plays a significant role in the metal-AM process, and indicates why authors typically choose to incorporate elastic-plastic theory into their thermomechanical models for residual stress prediction. Heigel et al (2015) and Yang et al (2016) both used a perfect plasticity model for DED, and Heigel et al also incorporated effects from annealing due to reaching the annealing temperature for Ti6Al4V [64,70]. Vastola et al (2016) used an isotropic hardening model related to the absolute stress in the material developed during the EBM process [81].…”

“…To quantify the model error for temperature, a node in the thermal model that is nearest to the actual thermocouple location is chosen, and the temperatures at each time point for the model are compared to the actual thermocouple reading. Within experimental investigations, Yang et al (2016) measured as high as 1.2mm of deflection at the furthest point from the constrained substrate end when printing Ti6Al4V [64]. Using a similar setup, Heigel et al (2015) demonstrated that the deflection direction is dependent on which direction the energy source is traveling (towards the free end or away from the free end) [70].…”

Short review on modeling approaches for metal additive manufacturing process

“…Then, the nodal temperatures are applied as a thermal load to the structural analysis. The mechanical modeling is based on the equilibrium mechanics of a continuum body and implementing a constitutive model for elastic (Hook's law) and plastic (isotropic/kinematic hardening rules) behavior of the built material as: in which σ is Cauchy stress; C is fourth‐order elastic stiffness matrix; and ϵ , ϵ p , and ϵ T are total, plastic, and thermal strain tensors, respectively. By applying the boundary conditions on the mechanical FE model, the residual stresses as well as distortions are computed.…”

“…Therefore, research studies have recently focused on developing numerical‐based models that could outline the thermophysical phenomena of the AM process. Finite element (FE)‐based thermomechanical models were developed to assess thermal cycles of AM parts as the result of the heat source and obtain the mechanical response of the AM parts by enforcing the temperature history into the built part . The aforementioned models commonly make some simplifying assumptions or employ certain techniques to investigate the material deposition onto the substrate and formation of residual stresses and geometrical distortions in AM parts.…”