A new method of controlling the residual stress in laser directed energy deposition additive manufacturing (DED AM) products proposed based on constraints used in manufacturing and the substrate design. The simulation results of the residual stress, which were validated with the experimental measured data, showed that weaker constraints on the substrate could greatly decrease the residual stress in the laser DED AM products. In addition, by designing local reduced thickness regions into the substrate, such as long strip holes or support legs, the residual stress in DED AM products could be further decreased. In this study, when long strip holes were designed in the substrate, the tensile residual stress was decreased by 28%. An even smaller amount of residual stress was achieved when the design structure was changed to support legs. The tensile residual stress decreased by more than 30%. The fewer support legs, the smaller the residual stress. The residual stress in DED AM products could be well-controlled by design, while the stiffness can be weakened with fewer constraints.

Phase change material (PCM) is particularly advantageous in developing low-carbon buildings. However, its melting efficiency is severely determined by the dynamics of the molten phase, which is greatly associated with the applied heating orientation. This work aims to describe the dynamic character in the melting process of paraffin under different heating modes. A total of four heating modes are considered for the paraffin enclosed in a square cavity, including side heating, top heating, bottom heating, and around heating. The around heating can be regarded as the combination of the first three heating modes along a single wall. A comparative study of numerical and experimental results of temperature is firstly performed for the side heating case to verify the computational model, which is then extended to study the dynamic state during the melting process of paraffin. The evolutions of the solid/liquid interface and the internal flow field show that the bottom heating can maximally activate the involvement of natural convection of the liquid paraffin and thus has the highest efficiency than the side and top heating. The contribution rate of the bottom heating is about 1.55 times over that of the top heating. This observation is useful to identify the contribution of each heating mode to the heat transfer in the paraffin and guide its practical application.

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