Wave springs are a novel type of axial compression spring that offer complete axial load transmission and a significant free height reduction when compared to coil springs. In this paper, it is shown that direct 4D printing using bilayers on a fused filament fabrication system can be used to create deployable, polymer wave springs that do not suffer from layering effects, as is common in other cyclically loaded additively manufactured parts. Bilayer actuators enable a flat print configuration and subsequent deployment by a thermal stimulus that then aligns the layers in the direction of the wave in the spring. Due to this, the springs exhibit exceptional performance under cyclic loading, reaching 104 cycles without failure. After plastic deformation caused by extended cyclic loading, the springs can be redeployed to recover their original mechanical properties using cold programming. These findings show the great potential of direct 4D printing in fused filament fabrication to create functional, 4D printed components with complex geometry and greatly increased lifespan compared to conventional 3D printed parts. The presented approach to compression spring fabrication further provides a standard component that enables the design of highly integrated, monolithically printed, and tunable mechanical systems.

Styrene-butadiene-styrene (SBS)/crumb rubber (CR) blend-modified asphalt is a desirable binder for pavement engineering with both environmental and economic benefits. However, the inherent incompatibility of SBS and CR in asphalt is still a critical issue. Herein, 3D porous graphene (3DPG) with high surface area and rich micropores as reinforced additive was investigated in SBS/CR blend-modified asphalt for the first time. The experimental results demonstrate that incorporating 3DPG can effectively improve the compatibility of SBS and CR in asphalt and thus significantly enhance the high and low temperature performance and fatigue resistance of the modified asphalt, compared with that without 3DPG. Theoretical calculations further reveal that the nanopores in graphene can endow graphene with electrophilic property, providing a capability of absorbing nonpolar molecules in asphalt while the non-pore part in graphene can interact with polar molecules by conventional π − π stacking. The two forces within graphene can break the original colloidal structures of asphalt, which is conductive to the homogenous formation of SBS network and swelling of CR in asphalt, significantly promoting the pavement performance of the modified asphalt. This work presents the great potential of 3DPG as new additive to solve the inherent incompatibility of SBS/CR blend-modified asphalt for high-grade pavement engineering.

We compare microstructure formation during laser powder bed fusion (LPBF) of a Ti-22Al-25Nb alloy applying low and high pre-heating build plate temperatures. Fast cooling rates during low-temperature LPBF lead to metastable weakly ordered β phase, i.e., bcc–(Ti,Al,Nb) with pronounced 〈1 0 0〉 texture in build direction and nanosized segregations within grains elongated in the build direction. For high-temperature LPBF a Widmanstätten microstructure was observed with lenticular O phase precipitates within the β matrix. Microscopical and in situ high-energy synchrotron diffraction investigations demonstrate that the microstructure formation can be widely explained by the precipitation of O phase from supersaturated β rather than by a sequence of solid-state phase transformations, as it would be expected under thermodynamic equilibrium conditions. A detailed analysis of the microstructural gradient in the subsurface region, however, demonstrates that precipitation from metastable β cannot fully explain the observed microstructures, and that the process energy density, i.e., the intensity of the intrinsic heat treatment of LPBF, plays a relevant role. The investigation of the graded area near the surface of the LPBF materials produced with high pre-heating temperature is particularly interesting as it reveals preferred nucleation of the O phase at subgrain boundaries and dislocations.

A wide range of mechanical properties are vital in structures, from macro (e.g., load-bearing) down to atomistic (nanomaterial) level. To design structures with the target mechanical properties, it is crucial to understand the correlation between the mechanical characteristics and structural information. To this end, we explored the similarity in the mechanical behavior between atomistic structures and actual 3D-printed zeolite structures. The zeolite structure was chosen because of its various structural parameters such as pore size, distribution, and geometry. Molecular dynamics (MD) simulations confirmed that similar behavior was observed in the mechanical responses at an atomic scale and with a 3D-printed macro-scale structure. 3D printing with ductile thermoplastic polyurethane (TPU) filaments showed a high degree of agreement with microstructure-level simulations. The mechanical response of zeolite structures is classified depending on their linearity and the characteristics with respect to the applied strain, to anticipate the potential applications of mechanical metamaterials. Further comparative analysis was conducted between the structural characteristics and mechanical properties, linking the changes in the stress to factors, such as density, porosity, angle, and bond length. This study demonstrates that metamaterial design with a mechanical response can be achieved using atomic-level structural design degrees of freedom.

Customizable stress plateau of lattice structures is sought-after for various engineering applications. In this study, we present a new design strategy to achieve customizable plateau, by introducing the concept of embedding self-similar structure in a face-centered cubic (FCC) lattice, which thereby constitutes a novel FCC hierarchical lattice (FCCH). These FCCH specimens were experimentally validated through quasi-static compression tests, on samples 3D-printed through selective laser melting using SS316L. These deformation characteristics were clarified by finite element analysis. The experimental and numerical results consistently show the serrated, dual, and upward plateaus were experienced for the 0th-order FCC, 1st-order FCCH, and 2nd-order FCCH structures, respectively. The mechanical reinforcements are based on the stronger interactions between unit cells induced by the embedded sub-structures. The deformation mechanisms dominated by hierarchical order are determined by horizontal layer-by-layer interaction as well as longitudinal buckling and collapse. The effect of geometric configuration show that stress plateau can be customized via optimizing different slave-cell sizes, connecting face-centers of lattice components, and arranging row layered gradient strategy.

Visualization techniques are effective tools in diagnosis and therapy for biomedical applications. Due to the unavoidable shortcomings of single optical or magnetic resonance imaging, the introduction of dual functional imaging system is of great significance. Herein a new Gd1-xNdx(CO3)OH@SiO2 core–shell nanostructure were developed to fulfill the corresponding demands. Uniform nanospheres were acquired with surface modification and coated with thickness tunable silica shells. The samples presented strong luminescence penetrating biological tissue, due to the wide spectral region covering NIR I & II window of Nd3+ under 808 nm laser excitation. On the other hand, distinct contrast enhancement could be viewed for in vitro and in vivo MRI trials, which generates from high paramagnetic relaxation of Gd3+ and well dispersibility caused by silica shells. Along with the non-toxicity proved by the low concentration of leaching Gd3+ and nice biocompatibility of silica coated nanospheres, it is a superior candidate for NIR and MRI dual functional imaging platform in biological applications.

Low-cost perovskite solar cells (PSCs) have experienced unprecedented gains in power conversion efficiency (PCE) of up to 25% of lab-scale devices. To be realized in the market, however, PSCs are not only required to be efficient but also scalable in production. While spray coating has viability as an industrial manufacturing process for perovskite photovoltaics scaling, optimizing the spray conditions is often seen as a challenging and time-consuming process due to its complex and multidimensional parameters. Herein, we use a machine learning (ML) approach to capture the relationship between spray parameter settings to the resultant photoconversion efficiency (PCE) of PSCs from experimental collected data points. This data-driven approach has the potential to accurately predict PCE values given the manufacturing parameters, enabling optimization and resulting in an increased experimentally recorded PCE. Furthermore, we also used a Convolutional Neural Network (CNN) to predict defect size distributions in the PSC structures to improve the understanding of defect formation mechanism at given spray parameters. The implications of the results are discussed for optimizing spray manufacturing process of efficient perovskite photovoltaics.

Flexible graphite (FG) with ρ = 1 g/cm3 density is a type of highly porous and anisotropic graphite, mainly used for gaskets and sealing applications, but also suitable for energy absorption, such as in the beam dumping devices of the Large Hadron Collider (see Heredia 2021 [1]). Knowledge of its microstructure and mechanical properties needs to be developed for the selection of an adequate material model able accurately predict stresses and failure in FG components. Here, the FG microstructure properties available in literature are reviewed, followed by Focused Ion Beam - Scanning Electron Microscopy investigation and compression tests. Specifically, a single 100 μm × 150 μm cross section was obtained, and the 2D pore sizes and shapes were quantified using image segmentation. Monotonic and cyclic out-of-plane compression tests were performed in single and stacked configuration. Stress-strain curves showed three domains: the initial toe, the transition and the densification domain. The cyclic tangent modulus was also calculated from the cyclic tests. Many observations suggested that FG behaves similarly to crushable foams, crumpled materials and compacted powders, and that both crystalline microstructure and crumpled mesostructure play a predominant role in the deformation mechanism.

Mechanical metamaterials such as origami or ordered 3D printed structures have shown tremendous applications in science and technology. However, the main disadvantage of these systems is their dependency on a perfectly ordered structure, making them sensitive to defects. Disordered metamaterials offer a way to circumvent this sensitivity. Within disordered metamaterials, crumpled systems have recently received increased attention due to their intriguing properties such as negative Poisson’s ratio, low density, high mechanical shock absorption, and easy manufacturing process. Mechanical relaxation of these systems was successfully explained by stretched exponential and logarithmic models, typically used for complex relaxation in amorphous systems. This drove researchers to study crumpled systems as amorphous systems with a complex energy landscape. Further research remarked similarities between crumpled structures and other metastable systems such as glasses, by studying the mechanical memory effect. Edward’s statistical mechanics was also applied to crumpled systems to unravel their statistical properties. In this review, we summarize different aspects of crumpled materials and their potential to be exploited for designing new robust disordered metamaterials. Finally, we build on the current knowledge and introduce a design principle to make crumpled origami-like structures with robust mechanical responses.

The selection of optimal process conditions is very important for the production of large pultruded thermoplastic profiles. This study investigates the influence of pulling speed on the temperature distribution and consolidation of glass fiber/polypropylene (GF/PP) preconsolidated tapes during thermoplastic pultrusion. For this purpose, several pultruded thermoplastic profiles with a cross-section of 75 mm × 3.5 mm were produced at various pulling speeds, and their cross-sections were studied under a microscope. In addition, a 3D numerical model was developed to analyze the influence of the pulling speed on the temperature distribution and to predict the consolidation of the tapes. Full consolidation of the tapes was observed in the profiles produced at a pulling speed of 0.2 m/min. The profiles produced at a pulling speed of 0.4 m/min contained unconsolidated tape, which resulted in reduced flexural, tensile, and compressive strengths by as much as 43%, 15%, and 23%, respectively. The results of the simulations and microscopic investigations show that the GF/PP tapes consolidate at temperatures above the Vicat softening temperature. Finally, a GF/PP tube with dimensions of 50 mm × 40 mm × 5 mm was produced using the optimum pulling speed and temperature determined using the developed 3D model. These results provide valuable insight into the design of thermoplastic pultrusion regimes.

Carbon fiber epoxy resin (CFRP) is gradually used as the space satellite antenna material, thermal control coatings (TCCs) are prepared on the surface to ensure the stable operation. However, the traditional TCCs have no wave transmission capability. The hollow glass microspheres (HGMs) were used to prepare the coating in our work, and ZrO2 was coated on its surface (Zr-HGM) to improve the solar reflectivity. The Zr-HGM powders were obtained by a homogeneous precipitation method with an appropriate reaction time of 4 h. By investigating the optical and dielectric properties, we found that the solar absorption of the coating with Zr-HGM was reduced by half compared to the coating with the original HGM. The microwave transmittances were all above 96.5% from 2 to 18 GHz. Our findings have proposed a preparation method for a new CFRP-based TCC, which will ensure the stable operation of the satellite antenna.

Ultrasonic polar scan (UPS) records the amplitude in transmission for a wide range of incidence angles, providing a UPS image with characteristic contours reflecting the acoustic parameters of the material. This study focused on a newly developed wave velocity measurement of the DD6 single-crystal material plate by analyzing the UPS image to realize the ultrasonic thickness measurement of the DD6 single-crystal material plate accordingly. Firstly, considering transducer contour size compensation, the UPS images are obtained by numerical simulation on the DD6 single-crystal material plates with different crystal orientations. Secondly, the fitting equations are obtained by analyzing the UPS images to calculate wave velocity in the thickness direction. Finally, a 5-joint UPS scanner is designed to validate the accuracy of wave velocity simulation results experimentally, and it indicates a good agreement with conventional ultrasonic velocity measurement. The measurement results demonstrated that the UPS method could evaluate the wave velocity in the through-thickness direction of the DD6 single-crystal material plate with high precision.

The kinetics of solid-state reactions involving non-metallic inclusions (NMIs) in steel is a topic of growing interest due to the need to understand the effects of heat treatments on NMI composition and stability. In this study, a High Temperature Environmental Scanning Electron Microscope (HT-ESEM) is utilized to conduct in-situ observations of various types of NMIs, including calcium aluminate complex, CaS, MgAl2O4-CaS, MnS, and TiN, in steels at temperatures of 800 °C and 900 °C for different holding times. The observed morphological variations in the NMIs indicate a decrease in the fractions of CaS and MnS, promoting void formation and ferrite–austenite phase transformation. To estimate the NMI reactions with the residual atmosphere in the sample chamber during experiments, HT-ESEM-driven thermodynamic calculations have been performed using FactSage 8.2 software. These calculations provide valuable insights into the interpretation of the experimental data, facilitating a better understanding of the complex NMI reactions in steel.

In view of the importance of alkaline phosphatase (ALP) as a clinical diagnostic indicator of related diseases and physiological research, developing a reliable measurement assay with high efficiency and accuracy is of tremendous value. In this study, bifunctional carbon dots (CDs) with peroxidase-like and fluorescence properties were synthesized through a readily available solvothermal method. Peroxidase-like CDs could oxidaze colorless 1,4-phenylenediamine (PPD) to the colored oxidized product (oxPPD), which quenched the CDs' fluorescence. A multi-signal sensing system was strategically fabricated for detecting ALP for the first time, taking advantage of CDs' remarkable peroxidase-mimic activity and fluorescence properties. The limits of detection (LOD) and linear ranges for ALP was 0.034 and 0.027 U/L, 0.1 to 1.8 and 0.05 to 1.8 U/L by the colorimetric and fluorescent method, respectively. Besides, the results of hydrogel devices processed by smartphones also exhibited satisfactory results. The multi-signal strategy developed in this study provides a new impetus for designing different biosensors with bifunctional nanomaterials.

Solute segregation in the carbon-depleted (CDZ) heat-affected zone of dissimilar metal welds (DMW) designed for nuclear power plant EPRTM reactors has been investigated by atom probe tomography (APT) and related to the mechanical properties (toughness test). The analysis of grain boundaries (GBs) by APT allowed the quantification of the P segregation and other solute elements, in all the analyzed samples, before and after long-term ageing heat treatments. The post-weld stress-relief heat treatment applied to the samples before the ageing heat treatments leads to important GBs segregation levels. Following thermal ageing treatments allow a relative increase of GB segregation. P segregation increases with the various thermal ageing conditions. The experimental data were used to model P segregation in high-angle GBs. The simulations show that P segregation is kinetically limited by bulk diffusion, explaining the observed P segregation increase with temperature. P segregation in GBs in the CDZ of the DMW should remain low compared to the expected equilibrium segregation level during the entire reactor service. In addition to solute segregation in extended defects, APT measurements revealed the presence of Cu-rich clusters in GBs, dislocations, and grains in all the aged samples. These clusters were not observed in the sample before ageing.

This research was focused on innovative design of lattice metamaterials that can exhibit tunable double-negative mechanical properties and elastic isotropy simultaneously. A discrete topology optimization method using a multi-material ground structure was developed to create microlattices exhibiting both negative thermal expansion coefficient and negative Poisson’s ratio in a single integrated design, while maintaining elastic isotropy. First, the numerical homogenization method with beam elements was used to estimate the effective thermal and elastic properties of a microlattice. Second, the topological design, subject to required geometric constraints, was formulated as a mixed integer programming problem to discover a series of multi-material microlattices that present customized isotropic values of negative thermal expansion coefficient and negative Poisson’s ratio. Finally, several three-dimensional multi-material microstructures were produced by altering either the cross-sections or constituent materials of struts to demonstrate their tunable mechanical properties.

The role of a ∑3{1 1 2} incoherent twin boundary (ITB) on the shear stress of Cu at the micron scale has been investigated through microcompression of bi-crystalline pillars containing ITB, as well as single-crystalline pillars, in two different compression directions. The Cu sample containing ITBs was synthesized using magnetron sputtering on a sapphire substrate. Firstly, pillars along [1 1 1] compression direction were milled on the film surface. As multiple slip systems were activated upon loading, the dislocation-ITB interaction in this direction was dominated by the dislocation–dislocation interactions. Another set of pillars was milled from the side of the film (in the thickness of the film) in a nominally [134¯] compression direction. Compression in this direction activated a single slip in each grain, which facilitated the investigation of the interaction between dislocations and ITBs. Post-mortem images showed that slip traces were not distinctly connected at the boundary unlike ideal slip transmission in pillars containing a coherent twin boundary. Moreover, bi-crystalline pillars in the single slip direction are stronger than single-crystalline pillars. The observations indicate that ITBs are not impenetrable for dislocations, but the boundary demonstrates some resistance to transmission.

Nanodiamond (ND) is becoming the core center of interest for many researchers due to its immense utilization in different fields of science. The extraordinarily unique attributes provided by NDs include biocompatibility, easy production, chemical inertness, rich surface chemistry, small size, and fluorescence resistance. In biomedical sciences, all these characteristics uplift the standards of ND particles. Recent studies on the biomedical side have been found to strengthen its significance ever since ND tested positive for utilization in diagnostics and drug delivery. In addition, NDs have been proven beneficial in the manufacturing of biodegradable surgical instruments, scaffolds for tissue engineering, and drugs to eliminate resistant microbes and viruses. Genetic materials are also delivered to the center of the nucleus with the aid of ND particles. In this review, we have discussed in detail all the benefits of NDs, their applications in sensors, ND-blood interactions, blood-contacting, orthopedics, anti-cancer agents, antimicrobial agents, and drug/gene delivery. The importance and significance of the purification, synthesis, processing, and surface functionalization of NDs have been discussed. Recent advances in modern technologies in the field of biomedical and biological sciences also have been covered in this manuscript.

Transplanted cells rarely survive because of the inflammatory cytokines after spinal cord injury. To increase the survival, we synthesized a hydrophilic and aligned nanofibrous mat. We electrospun thiolate (SH)/aligned (A) poly(lactic-co-glycolic acid) (PLGA) nanofibrous mats. The PLGA-SH (A) nanofibrous mats were conjugated with gold nanoparticles (GNPs) to increase the hydrophilicity. The contact angle is decreased from 105.3° ± 5.2 (for randomly directional PLGA mats) to 28.1° ± 2.8 (for PLGA-GNP (A) mats). Green fluorescent protein (GFP)-expressing neural progenitor cells (NPCs) were dissociated from the embryonic spinal cords of Fisher 344 rats. We embedded the embryonic spinal-cord-derived NPCs in glycol chitosan (gC)-oxidized hyaluronate (oHA) hydrogels (=NPC graft). The NPC graft was transplanted into spinal-cord-injured Sprague-Dawley rats. Afterwards, the aligned PLGA-GNP nanofibrous mat was positioned onto the NPC-grafted region (=Injury + NPC graft + PLGA-GNP (A) nanofibrous mat (INP) group). We also added Injury (=I) and Injury + NPC graft (=IN) groups as control groups. The survival outcomes of transplanted NPCs were noticeably increased in the INP group compared to those in the IN group. We suggest a separate implanting therapy of NPCs and a hydrophilic PLGA-GNP (A) nanofibrous mat for spinal cord injuries.

To obtain the low-cost titanium alloys with simultaneously improved strength and ductility by thermomechanical processing, 0.1 wt% of boron was added to the Ti-4Al-2.5V-1.5Fe alloy using titanium diboride (TiB2) as a boron source. The deformation mechanisms and microstructure evolution were systematically studied by comparative investigation of Ti-4Al-2.5V-1.5Fe alloys with and without boron. The results indicated that the addition of boride had a significant effect on the material parameters. Furthermore, TiB greatly improved the spheroidization and recrystallization of the alloy, and it can effectively limit grain growth during thermal exposure. Consequently, both high-temperature forging and further thermal deformation facilitated the generation and retention of the fine grain structure, dramatically improving the processibility of Ti alloys. For bare alloys, severe plastic deformation often leads to inhomogeneous microstructures and flow instability, which is harmful to mechanical integrity. In contrast, the addition of borides can significantly mitigate flow localization. In this study, boron-modified titanium alloys exhibited improved processibility and beneficial mechanical properties attributed to beneficial effects due to the addition of borides, which may enable new strategies for manufacturing high-strength titanium alloys in a more cost-effective way.