Laser Powder Bed Fusion (LPBF) additively manufactured superstructures are highly promising for aerospace vehicles due to their excellent weight reduction performance and design flexibility, fulfilling the demand for high-performance, lightweight, and integrated components. However, surface roughness and internal porosity introduced by additive manufacturing tend to serve as initiation sites for fatigue cracks, potentially leading to premature failure of the lattice structures. To investigate effects of surface roughness and porosity on fatigue performance, Body Centered Cubic (BCC) lattice specimens were designed and fabricated by additive manufacturing. Fatigue tests under five different loading levels were conducted to obtain the corresponding Stress-Number of cycles (S-N) curves. A semiempirical formula was used to calculate the stress concentration factor introduced by surface roughness. Additionally, the concept of effective load-bearing area was applied to account for the influence of both porosity and surface roughness. The accuracy of this method was verified through finite element simulations based on 3D reconstructed models, and the Neuber-Kuhn formula was used to estimate the fatigue limit. Based on the effective area correction, a fatigue S-N curve for a single strut was established, then a mapping method from the single-strut S-N curve to the lattice S-N curve was developed, and a corrected S-N curve was proposed. It is shown that the model incorporating effective load-bearing area correction more accurately reflects the coupled effect of surface roughness and internal porosity, and thereby it can improve the predictive accuracy of the fatigue limit and fatigue life of the lattice structures. The periodic boundary conditions in one unit lattice can be built and effectively simulate stress concentration in the whole structure. The corrected S-N curve is used to predict the fatigue life of the lattice, and its results fall within a scatter band of factor 3.

In the deposition process of Cold Spraying (CS), the bonding strength between particles is small, and defectsas pores and interparticle boundaries are common in the coatings. In order to study the formation mechanism of these defects, three kinds of Ti coatings with different particle sizes distributions were prepared at different airflow temperatures. According to the experimental parameters, the Coupled Euler-Lagrange (CEL) model of random multi-particle deposition was established, and the deformation of particles after deposition and the pores distribution law inside the coatings were calculated. The results showed that the numerical simulation and experimental results were in good agreement. The collision action causes the accumulation of particles to be directional, and with the increase of velocities, the deformation of particles increases, and the inner particles are more affected by the velocities than the outer particles. Under the same parameters, the deposits with large particles have larger pores and higher porosities. At low velocities, the pores inside the coatings communicate with each other to form pore clusters, and as the velocities increase, the pore sizes decrease and the porosities decrease.

Carbon Fiber Reinforced Polymer (CFRP) composites are widely used in aircraft structures, because of their superior mechanical and lightweight properties. CFRP composites are often exposed to hygrothermal environments in service. Temperature and moisture can affect the material properties of composites. In order to make clear the moisture diffusion behavior and the properties degradation of composites, the TG800/E207 composite laminates with four stacking sequences [0]₁₆, [90]₁₆, [±45]_4s, and [(+45/0/0/–45)_s]_s are designed and manufactured. Moisture absorption tests are carried out at 80 ℃, 90 %RH. It is shown that the moisture absorption curves of composite laminates present a three-stage. A modified Fickian model was proposed to capture the diffusion behavior of TG800/E207 composite laminates. The relationships among the non-Fickian parameters, the environmental parameters and the stacking sequences of CFRP were correlated and compared. Results showed that the modified Fickian curve is sensitive to the diffusivity of Stage Ⅰ and Stage Ⅱ. Compared with unaged specimens, the maximum tensile stress for [0]₁₆, [90]₁₆, [±45]_4s, and [(+45/0/0/–45)_s]_s decreased by 14.94 %, 28.15 %, 11.96 %, and 26.36 %, respectively. The strains at failure for [0]₁₆, [90]₁₆, [±45]_4s, and [(+45/0/0/–45)_s]_s decreased by 55.38 %, 62.65 %, 46.41 %, and 31.71 %, respectively. The elastic modulus for [0]₁₆, [90]₁₆, [±45]_4s, and [(+45/0/0/–45)_s]_s increased by 90.93 %, 94.57 %, 49.22 %, and 8.22 %, respectively. [90]₁₆ sample has the minimum saturated moisture content and the maximum strength degeneration.