In this research, a design method for triply periodic minimal surface (TPMS) structures with a high specific strength for broadband sound absorption is proposed. The graded TPMS structures are controlled by linear, quadratic, and sine functions. Homogeneous TPMSs and graded TPMSs were manufactured by laser powder bed fusion (LPBF) with AlSi7Mg powder, and acoustic impedance tube, compression, and digital image correlation (DIC) tests were applied to obtain the sound absorption and compression properties. The sound absorption coefficient of a homogeneous gyroid increases as the height and offset thickness of the surface increase, and it increases as element size decreases. The sound absorption peak shifts to low frequencies as the height of the structure increases. The average sound absorption coefficient at 1/3 octave from 500 to 6300 Hz of the graded TPMS with a porosity from 60.51 to 77.59% (surface of incident sound wave to rigid backing) is superior to that of the graded TPMS with a porosity from 77.59 to 60.51%, but the latter has a broadband sound absorption coefficient. The compression and DIC results of graded TPMS also show excellent mechanical properties and energy absorption characteristics.

Because their topological structures have certain crystallographic symmetry, there is anisotropy in triply periodic minimal surface (TPMS) porous structures. Anisotropy can affect the mechanical properties of porous structures; thus, it is necessary to research the anisotropy of TPMS structures. In this study, based on quaternionic three-dimensional rotation, TPMS structures were rotated around three crystal directions: [100], [110], and [111]. The mechanical anisotropy behaviors of TPMS porous structures, including gyroid, diamond, primitive, and I-graph-wrapped package (IWP) graph surfaces, were studied through finite element analysis (FEA). The FEA results show that the anisotropy of the IWP structure with rotation in the [110] direction was the most significant, and its relative elastic modulus increased by 275.33% when the IWP was rotated 60° in the [110] direction. These results indicate that the uniaxial compression performance of TPMS structures can be significantly improved by using structural anisotropy. However, it should be noted that due to this significant anisotropy, the performance of such structures will significantly decrease in specific directions. For example, after the primitive structure was rotated 60° in the [111] and [110] directions, its relative elastic modulus decreased by 72.66% and 77.6%, respectively. Therefore, it was necessary to reasonably consider the bearing capacity in fragile directions under complex working conditions. Based on the anisotropy of TPMS, gradient TPMS structures with three rotation angles were designed and manufactured using selective laser melting technology. The compressive results show that multi-peaks appeared in the primitive structure with gradient rotation in the [111] direction from 0° to 40°, and step-by-step behaviors were observed in the IWP structure with gradient rotation in the [110] direction from 0° to 60°. This result shows that the yielding platform can be enhanced using gradient rotation designation based on the anisotropy of TPMS porous structures.

In this research, a design method for the graded triply periodic minimal surface (TPMS) structures with lightweight, high-strength, and high sound absorption properties is proposed. The graded TPMS structures are controlled by linear, quadratic, and sine functions. Uniform TPMS and graded TPMS were manufactured by laser powder bed fusion (LPBF) with AlSi7Mg powder, and an acoustic impedance tube test, compression test, and digital image correlation (DIC) test were ap-plied to obtain the sound absorption and compression properties. The sound absorption coefficient of a uniform Gyroid increases as the number of layers and surface thickness increase, and it in-creases as element size decreases. The sound absorption peak shifts to low frequencies as the number of layers increases. The sound absorption property of Type-Ⅰ graded TPMS is superior to the Type-Ⅱ, and the G-LinearⅠ has the highest sound absorption properties among the three functions. It reveals that the graded TPMS has superior sound absorption performance at low and medium frequencies. The compression and DIC results of graded TPMS also show excellent mechanical properties and energy absorption characteristics.

This study investigated the impact of aging heat treatment time on the mechanical properties of NiTi triply periodic minimal surface structures fabricated through laser powder bed fusion. X-ray diffraction analysis results indicate that with increasing aging time, the NiTi2 phase precipitates while the content of the B19’ phase decreases. At 10 h of aging time, the Ni4Ti3 phase becomes evident in the sample. The differential scanning calorimeter results show that R phase transformation occurs, and the phase transformation temperature increases when the aging time reaches 6 h. Microhardness increases with aging time, peaking at 477.8 HV after 10 h. Compression experiment results reveal a maximum elastic modulus of 1262.82 MPa for the gyroid sheet-shaped structure achieved after 2 h. In addition, the superelasticity test indicates the highest recoverable strains at 2%, 4%, and 6% compressive strain for the gyroid rod-shaped structure after aging for 10 h. In cyclic compression experiments, the ratio of shape memory recovery increases from 40% at 0 h to 97% at 6 h. Fracture analysis results show that the transition in the fracture mechanism from brittle fracture to quasi-cleavage fracture occurs after aging heat treatment.