Periodic Surface Structures Research Articles

Mechanical properties and failure analysis of 3D-printing micron-scale ceramic-based triply periodic minimal surface scaffolds under quasi-static-compression and low-speed impact loads

Numerous developments in additive manufacturing have endowed triply periodic minimal surface (TPMS) structures with excellent mechanical properties, providing possibilities for the wide application prospects of such scaffolds in repairing bone defects. However, current studies mainly focus on the basic mechanical and biomedical properties of TMPS with relatively large scale and low precision made from conventional materials such as stainless powder. Therefore, challenges exist in manufacturing ceramic-based TPMS bone scaffolds that stratify the precision requirements for human bones at the micron scale and further investigating their dynamic mechanical properties. Herein, we successfully design and fabricate two TPMS scaffolds named TPMS-B and TPMS-C with microstructures similar to that of human bone utilizing advanced 3D-printing technology. The experiments reveal that TPMS-C outperforms conventional porous scaffold (Normal-A) and TPMS-B for certain parameters such as specific strength and specific energy absorption. Moreover, the numerical simulation analysis illustrates that structural asymmetry and discontinuous boundaries are the main causes of completely destructive disparities in TPMS-C when exposed to given loads. Meanwhile, the cytocompatibility and osteogenic differentiation of the three scaffolds are verified. The objective of this work is to reveal the mechanical properties and failure analysis of novel 3D-printing materials that can be used to fabricate advanced TPMS bone scaffolds for bone defects treatment.

UV Resistance of Super-Hydrophobic Stainless Steel Surfaces Textured by Femtosecond Laser Pulses

The loss of spontaneous liquid repellency on the surface of AISI 304 stainless steel under UV irradiation has been investigated depending on the textures formed by femtosecond laser pulses using Owens–Wendt plot analysis. Laser-induced periodic surface structures (LIPSS) have shown less liquid repellency compared to microgrooves. The polarity of the super-hydrophobic non-polar layer increased under UV irradiation to a super-hydrophilic state. The rate of this transition is determined by the surface topography and was faster for LIPSS compared to the bihierarchical textures formed by LIPSS in combination with microgrooves. The applicability of the Owens–Wendt approach for the numerical comparison of the achievable liquid repellency of textured surfaces in the Cassie state and the degree of polarity reversal of the hydrophobic layer was shown.

Increasing Heat Transfer from Metal Surfaces through Laser-Interference-Induced Microscopic Heat Sinks.

With the increasing processing power of micro-electronic components and increasing spatial limitations, ensuring sufficient heat dissipation has become a crucial task. This work presents a microscopic approach to increasing the surface area through periodic surface structures. Microstructures with a periodic distance of 8.5 µm are fabricated via Direct Laser Interference Patterning (DLIP) on stainless steel plates with a nanosecond-pulsed infrared laser and are characterized by their developed interfacial area ratio. The optimal structuring parameters for increasing the surface area were investigated, reaching peak-to-valley depths up to 12.8 µm and increasing surface area by up to 394%. Heat dissipation in a natural convection environment was estimated by measuring the output voltage of a Peltier element mounted between a hot plate and a textured sample. The resulting increase in output voltage compared to an unstructured sample was correlated to the structure depth and developed interfacial area ratio, finding a maximum increase of 51.4%. Moreover, it was shown that the output voltage correlated well with the structure depth and surface area.

Method for fabrication of laser-induced periodic surface structures on vascular stents

Abstract Laser-induced periodic surface structures (LIPSS) provide the possibility to functionalize the surface of various materials, which can be used to control the wettability of metal surfaces or influence cell adhesion. LIPSS thus offer great potential for application on implant surfaces if their fabrication process is compatible with standard implant fabrication techniques. Here we demonstrate an easy-to-use two-step fabrication method for stents with different types of LIPSS. The separation between the fabrication of the stent structure and the surface structuring process allows the implementation of any stent structure finishing technique without affecting the LIPSS. The suggested fabrication method may be a step further in implementing laser machining-based surface functionalization in commercial implants.

Finite element analysis of the mechanical properties of sheet- and skeleton-gyroid Ti6Al4V structures produced by laser powder bed fusion

Additive manufacturing, and laser powder bed fusion (L-PBF) in particular, can produce complex geometric components with high resolution, and is very suitable for manufacturing lightweight triple periodic minimal surface (TPMS) structures to achieve lightweight. With regard to the two forms of the same structure, most of the previous studies focused on sheet-TPMS, but lacked the understanding of the difference between skeleton-TPMS and sheet-TPMS structures. In order to explore the characteristics of these two structures and provide theoretical support for the development of lightweight structure design, this paper compares the manufacturing performance and defect distribution of skeleton-gyroid (GSK) and sheet-gyroid structures (GSH). It employs high-precision finite element analysis (FEA) prediction and experimental verification to compare comprehensively the mechanical properties, failure behavior and energy absorption characteristics of the two structures. The results show that, compared to GSK, the larger specific surface area of GSH leads to more unmelted powder and draping adhesion, without affecting its higher stiffness and strength. Moreover, the more stable failure mode of GSH leads to more gentle stress platform stage and superior energy absorption performance. The results predicted by simulation are highly consistent with the experimental results. This improved understanding allows better prediction of the mechanical properties of the specimens using the Gibson–Ashby theory, which can reduce the experimental cost and time, and improve the resource consumption of TPMS structural performance research. This study can open new possibilities for the design and application of TPMS structures.

INFLUENCE OF STRAIN RATE ON THE ASHBY-GIBSON PARAMETERS OF SHEET DIAMOND LATTICE STRUCTURES

Triply periodic minimal surface structures (TPMSs) can be used as a substitute for polymeric foams in applications where is necessary to absorb a large amount of energy with high structural deformation. Diamond TPMS offers higher energy absorption per unit weight. This structure is based on the Ashby-Gibson material model that establishes the main mechanical material properties as functions of the relative density and material properties. However, since TPMSs are used in dynamic applications, it is essential to analyse them under dynamic loads. In this study, we investigate the influence of the strain rate on the Ashby-Gibson parameters of sheet diamond Keywords: Triple periodic minimal surface; strain rate; additive manufacturing; diamond; Ashby-Gibson

Laser machining of free-standing silicon nitride membranes

Patterning free-standing Silicon Nitride membranes has enabled the development of various SiN-based devices such as quantum resonators, biosensors, temperature detectors, and plasmonic devices. Patterning SiN membranes usually involves expensive and time-consuming cleanroom techniques that limit flexibility in the development of new SiN membrane designs. While ultrafast laser machining has been proposed to create micron to submicron features in these membranes, laser machining of large area features has not been reported as it often results in membrane failure due to stress concentration during laser machining. We show that continuous laser machining can be used to create a crack and to extract the fracture toughness of the membrane (1.9 ± 0.3 MPa.m1/2). To successfully patterned SiN membranes without failure, a low stress laser machining method is developed, where stress concentration can be minimized by adjusting the laser drilling sequence, a result confirmed by finite element simulations. Complex shapes can thus be machined over a large area with a very high success rate. Laser parameters are optimized to improve the quality of the laser-cut edges without the formation of laser-induced periodic surface structure. Transmission Electron Microscopy and Electron Energy Loss Spectroscopy indicate a modification of the Si/N ratio over a small region next to the laser machined features. These results demonstrate that low stress ultrafast laser machining can be used to create patterns in SiN membranes quickly and economically, enabling the rapid development of new membrane designs.

Effect of heat treatment on mechanical properties, failure modes and energy absorption characteristics of lattice skeleton and sheet structures fabricated by SLM

Triply periodical minimal surface (TPMS) structures have attracted much attention in the biomaterials, aerospace, and automotive industries because they are lightweight, have high strength, and can absorb energy and shocks. In this study, uniform skeletal (USK), uniform sheet (USH), grade skeletal (GSK), and grade sheet (GSH) diamond lattice structures with the same 20% volume fraction were fabricated by selective laser melting (SLM) using AlSi10Mg metal powder. Their mechanical properties, deformation behavior, and energy absorption performance were systematically investigated by compression tests and finite element analysis (FEA). The skeleton structures had a higher elastic modulus, yield strength, and more severe stress fluctuation than the sheet structures. In addition, comparing the 45° shear deformation for as-built uniform structures accompanied by a mixture of ductile and brittle fracture modes, both gradient structures fractured by a sub-layer pattern from the layer with a lower volume fraction. Furthermore, the numerical simulation results illustrated that the stress of the skeleton structures was mainly concentrated at the skeleton joint, while the sheet structures were distributed evenly on the thin wall, without being concentrated in the interconnection region. For skeleton structures, heat treatment controlled the failure degree by improving the microstructure of the material, while for GSH structures at 300 °C, the fracture mode changed from the previous layer-by-layer fracture to a 45° shear failure. The accumulated energy absorption of gradient structures was more than that of the uniform structure, especially the GSH structures and the energy absorption efficiency of the skeleton structures was higher.

Experimental investigations into nonlinear dynamic behaviours of triply periodical minimal surface structures

Natural frequency, damping ratio and dynamic stiffness are fundamental to the performance of structures subjected to dynamic loads. Triply Periodic Minimal Surface (TPMS) composite structures, celebrated for their superior energy absorption capacity and specific strength, represent some of the most promising meta-structures. However, their dynamic properties are yet to be fully understood, thereby hindering their practical applications within civil engineering domains. Damping properties, crucial to vibration reduction, remain particularly elusive; previous studies have not successfully established a connection between these properties and the force excitation amplitude in TPMS structures. This study aims to compare the damping properties of different TPMS structures and to investigate their potential for adoption within civil engineering fields. Three types of TPMSs, including Schoen I-graph-wrapped package surface (IWP), Schwarz primitive (Primitive) and Schoen Gyroid (Gyroid), have been adopted to design solid and sheetal TPMS composite structures with identical relative density (50%) to compare their damping properties under varying excitation amplitudes. These TPMS structures are manufactured from photosensitive resin (UV resin) using stereolithography 3D printing technology. Owing to the lack of previous research into the damping properties and dynamic stiffness of TPMS structures as support structures, we have conducted single-freedom modal tests to determine the modal parameters, including natural frequency and damping ratios. Our novel results indicate that the natural frequency and damping ratio of the TPMS structures vary with the excitation amplitude. Additionally, the dynamic stiffness of TPMS structures reveals a similar decreasing trend to frequency when load amplitude escalates. As the excitation amplitude increases, the TPMS structures demonstrate softening and are capable of offering a higher vibration damping coefficient. Notably, the SS-Gyroid structure exhibits higher stiffness and damping ratio compared to other TPMS structures. These fresh insights pave the way for the integration of 3D printed smart TPMS structures within civil engineering, particularly for vibration reduction and efficient material usage. A judicious TPMS structure design can provide relatively high stiffness and damping ratio without excessive material use.

Formation and modulation of multi-pulse femtosecond laser-induced periodic surface structures by electromagnetic and partial differential equation simulations.

In order to demonstrate the formation of laser-induced periodic surface structures (LIPSS), simulations were performed to investigate the effect of multiple femtosecond laser pulses with different laser energy densities on a Ti6Al4V surface. In this work, a set of partial differential equations calculating the electron and lattice temperature variations, followed by coupling with an electric field, is used to analyze the evolution of the periodic surface structure induced by the interaction of the femtosecond laser with the material. As the number of pulses increases, the surface structure of the material changes from none to produce LIPSS structure and from low spatial frequency LIPSS (LSFL) structure to high spatial frequency LIPSS (HSFL) structure. In order to compare the results, single-point laser scanning ablation experiments were carried out at femtosecond laser energy. The experimental results are consistent with the simulation results.

Formation of laser-induced periodic surface structures on Zr-based bulk metallic glasses with different chemical composition

Bulk metallic glasses (BMG) are amorphous metal alloys known for their unique physical and mechanical properties. In the present study, the formation of femtosecond (fs) laser-induced periodic surface structures (LIPSS) on the Zr-based BMGs Zr46Cu46Al8, Zr61Cu25Al12Ti2, Zr52.5Cu17.9Al10Ni14.6Ti5 (Vit105) and Zr57Cu15.4Al10Ni12.6Nb5 (Vit106) was investigated as a function of their different chemical composition. For this purpose, LIPSS were generated on the sample surfaces in an air environment by fs-laser irradiation (λ = 1025 nm, τ = 300 fs, frep = 100 kHz). The surface topography was characterized by scanning electron microscopy and atomic force microscopy. Moreover, the impact of LIPSS formation on the structure and chemical surface composition was analyzed before and after fs-laser irradiation by X-ray diffraction and X-ray photoelectron spectroscopy as well as by transmission electron microscopy in combination with energy dispersive X-ray spectroscopy. Despite the different chemical composition of the investigated BMGs, the fs-laser irradiation resulted in almost similar properties of the generated LIPSS patterns. In the case of Zr61Cu25Al12Ti2, Vit105 and Vit106, the surface analysis revealed the preservation of the amorphous state of the materials during fs-laser irradiation. The study demonstrated the presence of a native oxide layer on all pristine BMGs. In addition, fs-laser irradiation results in the formation of laser-induced oxide layers of larger thickness consisting of an amorphous ZrAlCu-oxide. The precise laser-structuring of BMG surfaces on the nanoscale provides a versatile alternative to thermoplastic forming of BMG surfaces and is of particular interest for the engineering of functional material surfaces.

Performance optimization of Si/SiC ceramic triply periodic minimal surface structures via laser powder bed fusion

AbstractSiC ceramic lattice structures (CLSs) via additive manufacturing (AM) have been recognized as potential candidates in engineering fields owing to their various merits. Compared with traditional SiC CLSs, SiC triply periodic minimal surface (TPMS) CLSs could possess more outstanding properties, making them more promising for wider applications. Since SiC CLSs are hard to be fabricated through stereolithography techniques because of inferior light performance, the laser powder bed fusion (LPBF) process via selective sintering is an effective method to prepare near‐net‐shaped SiC TPMS lattices. As the mechanical performances of lattice structures are the foundation for future practical applications, it is of great significance to optimize the preparation process, thus improving the mechanical properties of SiC TPMS structures. In this work, the optimal printing parameters of the LPBF and liquid silicon infiltration process for SiC ceramic TPMS CLSs with three different volume fractions were systematically illustrated and analyzed. The effects of the printing parameters and carbon densities on the fabrication accuracy, microstructure, and mechanical performance of SiC TPMS CLSs were defined. The mechanism of the reactive sintering process for the SiC TPMS lattice structure was revealed. The results reveal that Si/SiC TPMS CLSs with optimum preparation have superior manufacturing accuracy (most less than 6%), relatively high bulk densities (about 2.75 g/cm3), low residual Si content (6.01%), and excellent mechanical properties (5.67, 15.4, and 44.0 MPa for Si/SiC TPMS CLSs with 25%, 40%, and 55% volume fractions, respectively).

Field-driven design and performance evaluation of dual functionally graded triply periodic minimal surface structures for additive manufacturing

Triply periodic minimal surface (TPMS) structures prepared by additive manufacturing (AM) have been widely used in aerospace and thermal management systems due to their functional advantages such as high specific strength and excellent heat transfer coefficient. However, lattices with uniform or simple gradients cannot match the regional diversity needs of functional advantages in service. This study proposed a field-driven AM data processing framework for dual functionally graded TPMS lattices. For unified data processing, mathematical functions, simulated outcomes, and geometric models were transformed into fields. I-WP and Diamond units were selected as the primitive and filling structures of Ti-6Al-4V lattices, respectively. According to the functional requirements, the gradient distribution design guided by the simulated stress field is completed through the proposed framework. The results illustrate that the field-driven dual graded lattices present superior compressive mechanical response. At almost equal volume fractions, their compressive strength is approximately 100% more than that of primitive lattices and 69% greater than that of dual uniform lattices. Furthermore, the dual lattices have larger specific surface areas than the primitive lattices, making them better at heat insulation and heat dissipation. This field-driven digital framework will show enormous potential in the matching design of functionally graded lattices.

Assessment of flow and heat transfer of triply periodic minimal surface based heat exchangers

An efficient intermediate heat exchanger is crucial for ensuring the safe operation, lifespan and energy efficiency of the advanced nuclear systems. Benefiting from the development of additive manufacturing technology, it is possible to design and optimize heat exchangers by introducing triply periodic minimal surface (TPMS) structures. With the excellent mechanical and thermal performance of TPMS, further improvements in the energy efficiency of advanced nuclear systems are achievable. In this study, I-WP surface, Primitive surface based heat exchangers and a printed circuit heat exchanger for accelerator driven subcritical systems are constructed in three dimensions. In order to obtain the potential enhancement of thermal performance of TPMS-based heat exchangers, the fluid flow and conjugate heat transfer characteristics in TPMS heat exchangers, especially for the specific working medium of lead-bismuth eutectic (LBE) are investigated. A parametric analysis is conducted on the key design variables including the solid volume fraction and hydraulic diameter. The results indicate that TPMS-based heat exchangers could achieve about 2–3 times the total heat transfer rate with half the volume of a printed circuit heat exchanger. The TPMS topologies contribute greater heat transfer enhancement on the Helium side than the LBE side, which helps to optimize the thermal resistance allocation in Helium-LBE heat exchangers. An increase of solid volume fraction enhances the convective heat transfer of Helium in I-WP heat exchanger, while homogenizing the local thermal performance. This study provides a database for the design and optimization of TPMS-based heat exchangers, which contributes to the sustainable future target.

Self-organized submicron structures in photoresist films by UV-laser irradiation at water-confined conditions

A new kind of self-organized pattern formation process has been found during laser irradiation of polymer films in water confinement just below the laser ablation threshold, resulting in a randomly oriented pattern with a period of about 475 nm. The morphology, orientation, period, and amplitude of these patterns are inconsistent with both laser-induced periodic surface structures that typically consist of linear grooves with periods smaller the laser wavelength and wrinkling patterns that feature a much larger period and appear at layered systems. Excimer laser (λ = 248 nm, tp = 25 ns) exposure of 650 nm thick photoresist films on silicon wafers cause the growth of irregular submicron patterns. The pattern morphology that is examined with imaging techniques is correlated to processing parameters. The amplitude of these laser-induced self-organized (LISE) submicron structures are strengthened with pulse number and laser fluence. The experimental results are discussed together with simulations of laser heating the photoresist film in water confinement. The proposed pattern formation mechanism of such laser-induced self-organized submicron structures at temporal excitation of a confined polymer surface comprises the formation of an oriented roughness based on LIPSS that are developed to wrinkled structures due to the transient formation of a soft subsurface area that provides conditions for wrinkling of the water cooled, stiff polymer surface by laser-induced stress fields. Size, amplitude, and morphology of the LISE pattern provide good properties for applications in such fields as wetting, friction, optics, and bioactivity.

Novel modified triply periodic minimal surfaces (MTPMS) developed using genetic algorithm

The desirable properties of natural porous materials have inspired humans to design cellular materials with remarkable properties such as high energy absorption, acoustic and thermal insulation, and high specific strength structures. Triply Periodic Minimal Surface (TPMS) structures are particularly important among the architected materials. In this research, we have developed a novel approach based on a genetic algorithm for geometry modification of TPMS structures. The approach is exploited to enhance the effective thermal and mechanical properties of TPMS structures, namely Primitive, IWP, Gyroid, and GPrime. New modified TMPS structures (MTPMS) have much higher Young's modulus and thermal conductivity than their base structures, and some of them have properties very close to the upper Hashin-Shtrikman bounds. Unlike previous studies conducted to improve the properties of TPMS structures, MTPMS can be expressed by simple equations. Although MTPMS are not generally considered minimal surfaces, they nonetheless possess the desirable geometric qualities of TPMS structures, such as being smooth and splitting space into two non-intersecting and continuous domains, etc.

3D-Printed PEEK/Silicon Nitride Scaffolds with a Triply Periodic Minimal Surface Structure for Spinal Fusion Implants.

The issue of spine-related disorders is a global healthcare concern that requires effective solutions to restore normal spine functioning. Spinal fusion implants have become a standard approach for this purpose, making it crucial to develop biomaterials and structures that possess high osteogenic capacities and exhibit mechanical properties and dynamic responses similar to those of the host bone. This study focused on the fabrication of 3D-printed polyether ether ketone/silicon nitride (PEEK/SiN) scaffolds with a triply periodic minimal surface (TPMS) structure, which offers several advantages, such as a large surface area and uniform stress distribution under load. The mechanical properties and dynamic response of PEEK/SiN scaffolds with varying porosities were evaluated through mechanical testing and finite element analysis. The scaffold with 30% porosity exhibited a compressive strength (34.56 ± 1.91 MPa) and elastic modulus (734 ± 64 MPa) similar to those of trabecular bone. In addition, the scaffold demonstrated favorable damping properties. The biological data revealed that incorporating silicon nitride into the PEEK scaffold stimulated osteogenic differentiation. In light of these findings, it can be inferred that PEEK/SiN TPMS scaffolds exhibit significant potential for use in bone tissue engineering and represent a promising option as candidates for spinal fusion implants.

3D-Printed Graphene Nanoplatelets/Polymer Foams for Low/Medium-Pressure Sensors.

The increasing interest in wearable devices for health monitoring, illness prevention, and human motion detection has driven research towards developing novel and cost-effective solutions for highly sensitive flexible sensors. The objective of this work is to develop innovative piezoresistive pressure sensors utilizing two types of 3D porous flexible open-cell foams: Grid and triply periodic minimal surface structures. These foams will be produced through a procedure involving the 3D printing of sacrificial templates, followed by infiltration with various low-viscosity polymers, leaching, and ultimately coating the pores with graphene nanoplatelets (GNPs). Additive manufacturing enables precise control over the shape and dimensions of the structure by manipulating geometric parameters during the design phase. This control extends to the piezoresistive response of the sensors, which is achieved by infiltrating the foams with varying concentrations of a colloidal suspension of GNPs. To examine the morphology of the produced materials, field emission scanning electron microscopy (FE-SEM) is employed, while mechanical and piezoresistive behavior are investigated through quasi-static uniaxial compression tests. The results obtained indicate that the optimized grid-based structure sensors, manufactured using the commercial polymer Solaris, exhibit the highest sensitivity compared to other tested samples. These sensors demonstrate a maximum sensitivity of 0.088 kPa-1 for pressures below 10 kPa, increasing to 0.24 kPa-1 for pressures of 80 kPa. Furthermore, the developed sensors are successfully applied to measure heartbeats both before and after aerobic activity, showcasing their excellent sensitivity within the typical pressure range exerted by the heartbeat, which typically falls between 10 and 20 kPa.

Energy-Absorbing Characteristics of an ABS-M30i-based 3D-Printed Periodic Surface and Strut-Based Lattice Structure

Energy-Absorbing Characteristics of an ABS-M30i-based 3D-Printed Periodic Surface and Strut-Based Lattice Structure

High-Resolution Laser Interference Ablation and Amorphization of Silicon.

The laser interference patterning of a silicon surface via UV femtosecond pulse irradiation, resulting in 350 nm periodic structures, is demonstrated. The structuring process was performed using a laser with a 450 fs pulse duration at a wavelength of 248 nm in combination with a mask projection setup. Depending on the laser fluence, single-pulse irradiation leads to amorphization, structure formation via lateral melt flow or the formation of voids via peculiar melt coalescence. Through multipulse irradiation, combined patterns of interference structures and laser-induced periodic surface structures (LIPSS) are observed.