Advanced Engineering Materials最新文献

The objective of this research is to develop and characterize polyethylene composites with randomly and partially oriented hybrid filler (HF) based on multiwalled carbon nanotubes (MWCNTs) decorated with gamma iron (III) oxide (γ-Fe₂O₃) nanoparticles (Fe₂O₃/MWCNTs). The structure of Fe₂O₃/MWCNTs hybrid is determined by X-ray diffraction (XRD), Raman spectroscopy, and microscopy techniques (scanning electron microscopy–energy-dispersive X-ray spectroscopy, transmission electron microscopy). A low-density polyethylene (LDPE) matrix is filled with 5 and 10 vol% HF. The effect of external magnetic field on the distribution of Fe₂O₃/MWCNTs in LDPE composites comparing to filler distribution without magnetic field is studied. The XRD and differential scanning calorimetry results confirm an increasing trend in the degree of crystallinity of LDPE matrix with increasing HF content and as an additional result of magnetic field application. The presence of more ordered Fe₂O₃/MWCNT particles in the matrix has enhanced the nucleation effect for LDPE crystallization process in composites under magnetic field. The effect of magnetic treatment on thermal, electrical, and thermoresistive properties of HF-LDPE composites is studied. The highest thermoresistive response (723%) and fastest recovery are detected for the HF-LDPE composite with 10 vol% magnetically oriented filler with the perspective to be applied as a critical temperature resistor.

Prealloyed powders present a promising alternative to traditional ball milling processes in powder metallurgy, addressing challenges such as uneven powder mixing and incomplete reinforcement reactions. This study investigates the preparation of Ti–TiBw composites using spark plasma sintering (SPS) at temperatures ranging from 950 to 1050 °C, utilizing Ti–TiBw prealloyed composite powders. The effects of sintering temperature on the microstructure and mechanical properties of Ti–TiBw composites are studied, comparing prealloyed composite powders with ball-milled premixed powders. As a result, the composites exhibit excellent strength and ductility, with an ultimate tensile strength of 676 MPa at 1000 °C and an elongation of 20.42% at 1050 °C. Comparatively, Ti–TiBw composites prepared from premixed powders achieve densification at 1050 °C, 50 °C higher than those prepared from prealloyed powders.

To enhance the mechanical properties of bioceramic composite bone scaffolds, a composite paste of polyethylene glycol diacrylate (PEGDA) and hexagonal boron nitride (h-BN) with a solid content of up to 42 wt% was developed in this study. The part was produced using stereolithography (SLA). The SLA printing parameters and material ratios of the paste were optimized through a homogeneous design and mechanical property tests. The results indicate that the single-line curing width of the PEGDA/h-BN paste in the XY plane ranged from 172 to 209 μm, while the curing depth of a single layer along the Z-axis ranged from 99 to 154 μm. Laser power was identified as the primary factor influencing both the width and depth of curing. The compressive strength of the printed sample of PEGDA/h-BN ceramic composite paste was measured at 222.4 ± 5.6 MPa, which is 61 times greater than the compressive strength of a pure PEGDA structure and comparable to that of cortical bone (100-230 MPa). Finally, the superior biocompatibility of PEGDA/h-BN ceramics was confirmed through cytotoxicity experiments. Consequently, PEGDA/h-BN ceramic composites meet the mechanical properties and biocompatibility requirements necessary for bone tissue applications, indicating promising potential in the field of bone tissue engineering.

The clinical diagnosis of diabetes mellitus typically depends on blood glucose measurements. Many laboratory studies have focused on enzyme–electrode biosensors that require an external power source. In this study, the potential of triboelectric nanogenerators (TENGs) as self-driven sensors for glucose detection is investigated by utilizing the glucose specificity of glucose oxidase. When immersed in glucose solutions with concentrations ranging from 3.9 to 13.1 mmol L⁻¹, the TENGs exhibit a linear relationship between the glucose concentration and current and voltage changes. These findings suggest that the TENGs developed in this study can effectively function as glucose sensors, providing a foundation for future human blood glucose monitoring applications and demonstrating a promising new approach for biomedical sensor technology.

Self-Healing Waterborne Polyurethanes

In article number 2400993, Jong S. Park and co-workers develop waterborne polyurethanes (WPUs) with dynamic disulfide bonds, offering exceptional self-healing capabilities without compromising adhesive strength. Additionally, flexible electrochromic devices with WPU-based sustainable ion gels show impressive switching performance, featuring high coloration efficiency and enduring stability.

A finite-element (FE) analysis of the active bistability of an antagonistic shape memory alloy (SMA) beam actuator of TiNiCu is presented. The actuator comprises two coupled SMA beams that are clamped at both ends and coupled in their center by a spacer having different memory shapes being deflected in opposite out-of-plane directions. The actuator is characterized by two equilibrium positions. To determine bistable behavior as a function of geometrical parameters, a force criterion is defined by the coupling force of the beams in austenitic and martensitic states. Bistable behavior is achieved, if the coupling force does not change sign in the entire displacement range. This implies that the austenitic beam dominates the opposing martensitic beam. Thus, selective heating of the SMA beams results in a snap-through motion of the coupled SMA beams. Depending on which of the two beams is in austenitic state, either of the two equilibrium positions is reached without the need for an external force. It is demonstrated that geometrical parameters like initial predeflection and spacer length have a crucial effect on the bistable performance. Bistable regions as well as critical limits characterized by geometry-dependent stability ratios, beyond which the actuator's performance becomes monostable, are identified.

4D printing technology offers the potential to create smart structures that respond to external stimuli. This study focuses on a novel magnetic hydrogel with promising applications in 4D printing, particularly for medical devices such as guidewire robots, drug delivery systems, and vascular stents. Magnetic-responsive hydrogels suitable for 4D printing are scarce, and their complex rheological properties pose challenges for printing. The study investigates these properties and optimizes them through adjustments in ink composition and the application of an external magnetic field, improving printability. Using the direct writing (DLP) method, which allows magnetic programming of individual strands, the study achieves greater flexibility compared to the traditional SLA method. Optimized printing parameters and material ratios produced high-quality single strands, grids, and sheet-like structures, demonstrating responsiveness to varying magnetic fields. Results confirm that DLP can be effectively applied to hydrogel 4D printing, achieving flexible structures with tunable mechanical properties. Additionally, magnetic-responsive, self-folding hydrogel structures were created, with a response speed of 180 ms under a magnetic field. This research establishes a foundation for magnetic hydrogel 4D printing and offers insights for the development of future smart medical devices.

A series of uniform porous structures and radial stepwise and radial linear gradient structures are designed based on sheet-gyroid to explore the influence mechanism of porosity and gradient parameters on forming quality and compressive mechanical properties. On this basis, mathematical models for predicting mechanical properties of porous structures based on uniform, discrete gradient, and linear gradient porosity distribution are established. The volume fraction deviation of uniform porous structures increases gradually with the increase of porosity. The relative density of porous structures ranges from 96.78 to 98.79%. The influence of porosity on compressive mechanical properties is investigated, and a prediction model of the equivalent elastic modulus and yield strength of porous structures is constructed based on the generalized G-A model. The elastic modulus of the radial stepwise gradient porous structures is predicted by combining the rule of mixing. The deviation between the predicted results and the experimental results ranges from 0.21 to 2.61%. At the same time, a prediction model of the compressive mechanical properties of the radial linear gradient porous structure is constructed, and it is found that the predicted value is somewhat different from the experimental value, which is related to the synergistic strengthening effect of the gradient porous structure.

Understanding hydrogen–grain boundary (GB) interactions is critical to the analysis of hydrogen embrittlement in metals. This work presents a mesoscale fully kinetic model to investigate the effect of GB misorientation on hydrogen diffusion and trapping using phase-field-based representative volume elements (RVEs). The flux equation consists of three terms: a diffusive term and two terms for high and low angle grain boundary (H/LAGB) trapping. Uptake simulations show that decreasing the grain size results in higher hydrogen content due to increasing the GB density. Permeation simulations show that GBs are high-flux paths due to their higher enrichment with hydrogen. Since HAGBs have higher enrichment than LAGBs, due to their higher trap-binding energy, they generally have the highest hydrogen flux. Nevertheless, the flux shows a convoluted behavior as it depends on the local concentration, alignment of GB with external concentration gradient as well as the GB network connectivity. Finally, decreasing the grain size resulted in a larger break-through time and a larger steady-state exit flux.

Tungsten Fiber-Reinforced Tungsten

In article number 2301929, Alexander Lau and co-workers explore potential synergies between CVD and SPS for the production of W_f/W. A key finding involves the strategic application of thin CVD-W layers to the ceramic interface. This technique significantly improves the stability of yttria and W-fibers during SPS, substantially reducing the interaction with the surrounding matrix.