Mechanical Properties Of Materials Research Articles

Insights into the fracture properties of recycled ceramic and rubber composite cement-based materials: Fracture mechanics, acoustic emission, and digital image correlation

Recycling plays a pivotal role in construction waste management, offering a path toward sustainability for the industry. Although waste ceramics can compensate for the mechanical properties of rubberized cement-based materials, the smooth glaze surface of waste ceramics increases the risk of brittle failure. This study investigated the effect of ceramic waste aggregate (CWA) on the fracture properties of rubberized mortar through the three-point bending experiment. The fracture parameters were calculated using the Double-K fracture criterion. Simultaneously, acoustic emission (AE) and digital image correlation (DIC) technologies were used to explore the fracture damage mechanism and the crack evolution process. The results indicate that the integration of 15 % and 45 % CWA significantly enhances both initiation (KICini) and unstable (KICun) fracture toughness, whereas incorporating 90 % CWA leads to a 16.8 % and 8.2 % decrease in (KICini)and (KICun), respectively. The fracture energy (GF) of rubberized mortar exhibits a continuous decline as a function of increasing CWA substitution rates. Furthermore, GMM-based RA-AF analysis elucidates a positive correlation between CWA content and tensile crack proportion in specimens. When the CWA content reaches 90 %, the proportion of tensile cracks is quantified at 29.83 %, surpassing that in standard mortar. Crack tip opening displacement (CTOD) at 0.5post-Pmax for specimens with 15 %, 45 %, and 90 % CWA substitution reveal improvements of 49.1 % and 17.2 %, and a decrease of 23.3 %, respectively, compared to standard mortar, indicating that 15 % and 45 % CWA effectively preserve the ductility of rubberized mortar. Elevated CWA substitution leads to an amplified strain localization phenomenon around the crack tip, heightening the propensity for brittle failure.

Fast prediction of concrete equivalent modulus based on the random aggregate model and image quadtree SBFEM

Abstract To evaluate the mechanical property of concrete materials rapidly, a fast prediction model of the concrete equivalent modulus is proposed based on the random aggregate model and scaled boundary finite element method (SBFEM). First, a random aggregate model of meso-concrete is employed to construct the representative volume element (RVE) according to the aggregate content, gradation, shape, etc. Second, the RVE model is transformed to be a grayscale image and stored as a digital matrix. The quadtree mesh is partitioned automatically for simulation by SBFEM. There are only six types of unique subdomains, and the hanging node does not affect the simulation accuracy. The global stiffness matrix can be assembled directly according to the six subdomain stiffness matrices. Finally, the equivalent modulus is predicted by using the numerical homogenization method. Several numerical examples are employed to verify this model, and the results are compared with that of other methods. The result indicates that the proposed model can efficiently determine the equivalent modulus. Furthermore, the effect of the aggregate gradation, shape, porosity, and pore water are studied and analysed in this work. The proposed model is potential and helpful in predicting the mechanical properties of concrete or other composite materials.

Conglomerate rock interface debonding characteristics and damage evolution based on cohesive phase-field method

Rock failure often occurs due to uneven mechanical strength and discontinuous strain at the interface. However, due to the complex interaction mechanism between different phases of conglomerate, it is necessary to improve the crack growth model at the conglomerates' interface. In view of the physical structure and mechanical properties of conglomerate materials, this paper innovatively adopts the cohesive phase field model to study the material deformation and crack growth of conglomerate materials. Different from the traditional phase field model, this model characterises the real structure of the interface by adding an interface phase field, which is used to simulate the debonding of the interface during crack propagation and damage evolution. The regularization of the phase field is carried out to ensure the smoothness of the interface. The transition state of the interface region is determined by the element and the additional phase field. The energy equation is coupled with the crack propagation process using the crack surface density function. The evolution of the damaged phase field and displacement field is driven by the principle of energy minimization. The innovative assumption is that there is a virtual crack at the crack tip, and the interface related elements show a certain cohesive softening form during the damage evolution, which is the main way to realize the particularity of interface mechanics. By controlling the crack dispersion state and stiffness degradation of the material, several ideal softening models are innovatively assumed according to the cohesive force change law to satisfy the mechanical properties and stress function constraints. When cutting blocks n=2.5×104, the errors of the linear model, exponential model, and compound inverse model are 1.76%, 7.48%, and 5.19%, respectively. The results of the exponential model agree well with the stress strength (the error is 2%) and interface crack kinking angle (68.89°). The simulation results indicate that the deformation process of the conglomerate can be divided into three stages: elastic deformation stage, crack propagation stage, and stable load stage. The tensile strength of conglomerate is positively correlated with interface's fracture toughness and proportion of gravel area, respectively.

Experimental investigation on microstructure, hardness and corrosion resistance of an electromagnetic welded titanium-stainless steel dissimilar materials

The electromagnetic welding (EMW), often known as magnetic pulse welding, is a solid-state welding technology that is used to join two different materials using high-velocity impact. In this study an attempt was made to join the Titanium(Ti)- Stainless Steel(SS 304) materials with the help of multi turn disc coil along with the field shaper. A comparative investigation was conducted on the joint’s microstructure, as well as its mechanical and corrosion properties. Inverted optical microscopy (OM) and x-ray diffraction (XRD) were used to do the microstructural characterization of the joint. The micro-Vickers hardness test was used to analyse the material’s mechanical properties. In addition, electrochemical experiments were run on the Ti-SS 304 EMW junction as well as the component materials to establish how resistant they were to corrosion. Using an electrochemical impedance analyzer, the levels of corrosion that were caused by the structures were measured while they were submerged in a solution of nitric acid at room temperature. The microstructural pictures revealed a wave-like pattern at the material’s interface, which is evidence of strong adhesion between the components. The micro vickers hardness of the joints was within the permitted range, as was the corrosion rate.

Tuning generalized planar fault energies to enable deformation twinning in nanocrystalline aluminum alloys

As deformation twins have a profound impact on the plastic flow and mechanical properties of metallic materials, enhancing deformation twinning in face-centered cubic (FCC) metallic materials has long served as a unique microstructure design strategy to attain an extraordinary strength-ductility synergy. Deformation twinning, however, rarely occurs in pure FCC Al and its alloys since its generalized planar fault energies (GPFEs) are almost unaffected by most soluble alloying elements such as Mg, Zn and Cu. Here we successfully tune the GPFEs of a nanocrystalline Al-Mg alloy by alloying with Zr, Fe or Y element, and enable deformation twinning in the Zr-, Fe- and Y-containing alloys. Based on a combined analysis of microscopic observations, modeling and ab initio calculations, we find a strong grain-size-dependent twinning (i.e., twinning occurs in preferable grains having sizes in the range ∼20–40 nm), as well as only one single twinning plane (i.e., twinning occurs in single, parallel atomic planes) for twin formation rather than intersecting twinning planes (i.e., twinning occurs in multiple, unparallel atomic planes) usually observed in coarse-grained FCC materials. This interesting twinning behavior is further observed to be accompanied by grain rotations, producing defective twin boundaries. Our experimental results extend the current understanding of the plastic deformation mechanisms in nanograined metallic materials, and will guide microstructure design of twinnable nanograined Al alloys with an improved strength-ductility synergy.

Effect of the incorporation of plastic waste on the mechanical properties of composite materials

Through this scientific research, we have tried to study the effect of the incorporation of plastic waste on the mechanical properties of concrete, in order to obtain good concrete with high resistance at a lower cost. To carry out this work, we adopted the following steps: Knowledge of the properties of concrete, which contains plastic waste of High Density Polyethylene (HDPE). Thus, the natural aggregate was replaced by concrete formulated with plastic waste in partial substitution varying between 0%, 10% and 20%. In all the concrete mixtures, the components, water, cement, gravel 3/8 and 8/15 and sand 0/3, remained constant while the HDPE waste varied according to the substitution rate. Through this process, the mechanical properties of concrete in fresh and hardened states were determined. The analysis of the results of the study allowed us to know the incorporation of plastic waste and its effect on the behaviour of the manufactured concrete. The results showed that the density of concrete made from plastic waste is lighter than the reference concrete without waste (C0), which contains only natural aggregates, in a fresh state. In the case of hardening, the results showed a decrease in the compressive strength of composite concrete produced from plastic waste compared to (C0) the reference concrete. In the study's second part, a numerical model for precision and effectiveness is constructed using the finite element (FE) method. Furthermore, manufacturing experiments are scheduled to use computer simulations that account for labour, materials, tests, and time. The nonlinear stress-strain relationship for time-dependent concrete deformations and tension cracks presents a challenge for concrete modelling. ANSYS software is used to use three-dimensional nonlinear finite elements in order to determine this kind of complex mechanical behavior.

Crystal plasticity framework related to size effect: From single crystal parameters to polycrystalline mechanical properties

Size effect has a significant influence on the accuracy of two key factors of parameters and models in crystal plasticity simulation. This study introduces a parameter identification method that considers the indentation size effect, determining the initial slip resistance of IN625 alloy. Based on the identified parameters and utilizing the integral point traversal method, a grain boundary affected zone (GBAZ), whose strength field related to the distance to the grain boundary (GB) is introduced into the polycrystalline microstructure to represent the hindering effect of GBs on dislocations. This method effectively predicts the Hall-Petch effect and strain hardening behavior of IN625 alloy. The research reveals that dislocation pile-ups primarily concentrate in small grain clusters within the material. In fine-grained microstructures, a large volume fraction of GBs promotes dislocation pile-ups, reducing the mean free path of dislocations, leading to an increase in dislocation multiplication rate, and consequently, enhancing the strain hardening rate. An increase in GBAZ thickness results in a large stress level within the material, accompanied by a decrease in the homogeneity of stress distribution. However, the sensitivity of strain to GBAZ thickness is found to be low. The method proposed in this work holds significant applicative relevance in parameter calibration and prediction the mechanical properties of polycrystalline materials.

Determination of Poisson’s ratio of coal gangue-based shotcrete materials using a non-contact test method

ABSTRACT Preparing shotcrete materials using coal gangue is an effective method of disposal and use of gangue solid waste, while testing the Poisson’s ratio of coal gangue-based shotcrete materials (CGSM) is an important step in evaluating the mechanical properties of such materials. Therefore, to study the evolution of the Poisson’s ratio of CGSM under different influencing factors, detailed test schemes and procedures were designed based on the non-contact test method of Poisson’s ratio. The accuracy of the non-contact test method is verified. In addition, changes in the Poisson’s ratio of CGSM under different factors were studied. Results show that the Poisson’s ratio of CGSM tends to reduce with prolonged curing. When the particle sizes of coal gangue are 0 ~ 2.5 and 2.5 ~ 5 mm, fine particles can fill interstitial voids in shotcrete materials. As the mass concentration and cement content increase, the Poisson’s ratio of CGSM gradually decreases; as the sand content rises, the Poisson’s ratio gradually increases.

Investigating the grinding characteristics of vanadium-titanium iron ore tailings for sustainable utilization in cementitious material preparation

The study of the cementitious material activity of industrial solid wastes is a key issue in the comprehensive utilization of its green building materials. In this study, mechanical activation was used to prepare cementitious materials from vanadium-titanium iron ore tailings (VTIOT) as the main raw materials, and the effects of grinding time, the key parameter, on the grinding characteristics of VTIOT, the mechanical properties of the VTIOT cementitious material, and the hydration mechanism were investigated by means of surface area analysis, particle size analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), alkali leaching, mechanical testing, hydration heat analysis, and thermogravimetric analysis (TGA). The results show that: the grinding time and specific surface area of VTIOT exhibit a linear correlation. Prolonging the grinding time, the fractal dimension of the particles gradually increases. The activity of Si4+ and Al3+ elements increases rapidly, reaching a Si4+ and Al3+ content of 96 mg·L−1 at 90 min of grinding. With a VTIOT mixing amount of 30 %, a mortar paste ratio of 1:3, and a water cement ratio of 0.5, the 50 min ground VTIOT mortar demonstrates 7 d and 28 d compressive strengths of 29 MPa and 38.7 MPa, corresponding to the highest values of the activity index, measured at 71.4 % and 75.2 %, respectively. Under standard curing conditions, the hydration products of cementitious materials at 7 d are ettringite (AFt), calcium silicate hydrate (C-S-H), alumina, ferric oxide, monsulfate (AFm), calcium hydroxide (Ca(OH)2), and calcium silica (CS). In the hydration process of 7 d, the exothermic peak and exothermic amount of the 50 min VTIOT cementitious materials are greater than those observed for other grinding times, but lower than those of pure reference cement.

From theory to application: Innovative ice-phobic polyurethane coatings by studying material parameters, mechanical insights, and additives

This investigation introduces new insights into the influence of material parameters on the anti-icing properties of polyurethane (PU) coatings, encompassing chemical characteristics, cross-link densities, mechanical analysis, and additive diversity. To comprehensively address these aspects, a meticulous exploration was conducted to delve into the effects of these parameters on wettability and icephobicity. To fabricate the PU coatings, three distinct acrylic polyols with various hydroxyl content along with two widely employed aliphatic isocyanates boasting diverse %NCO values were utilized. By employing stoichiometric and non-stoichiometric ratios, an array of coatings with different crosslink densities and mechanical properties was fabricated. The principal influence of crosslink density alterations in PU coatings on ice nucleation temperature and ice adhesion strength emerged distinctly, underpinned by the establishment of hydrogen bonds between water molecules and polar functional groups within the coating, coupled with the appearance of a quasi-liquid layer (QLL). The mechanical properties, wettability characteristics, and surface roughness of the coatings were examined and it was clearly demonstrated that Young's modulus and physicochemical properties play significant roles in the characteristics of ice adhesion strength. In particular, lower Young's modulus in the samples was associated with reduced ice adhesion, albeit with compromised durability. In the next step of this investigation, the matrix demonstrating optimal mechanical properties and icephobicity was subjected to surface energy adjustment. This was accomplished by introducing various concentrations of both fluorinated and non-fluorinated additives. This adjustment led to a significant reduction of ice adhesion strength, measuring less than 100 Kpa as an icephobic PU coating. Nevertheless, it was observed that the effectiveness of the fluorinated additives diminished after repetitive icing-deicing cycles, while the non-fluorinated additive maintained its influence on ice adhesion strength even after numerous cycles. The interplay between material attributes, mechanical properties, and additive influences has been meticulously unraveled, charting a course for further advancements in the pursuit of robust icephobic coating.

Peridynamic differential operator for stress analysis of imperfect functionally graded porous sandwich beams based on refined zigzag theory

This study focuses on the stress analysis of imperfect functionally graded porous (FGP) sandwich beams using the Peridynamic Differential Operator (PDDO) and Refined Zigzag Theory (RZT). Functionally graded materials (FGMs) can be found in diverse engineering applications since they offer smooth transitions in the mechanical properties of distinct materials, unlike traditional composite materials. Micro-voids and porosities may appear inside the FGMs due to technical challenges during the manufacturing process of such materials. Therefore, understanding the stress variations of the FG sandwich beams with porosities/micro-voids, which are called imperfect FGMs, under loads is of vital importance. In order to achieve the porous configuration in the FG structures, the modified rule of mixtures is applied to calculate the effective material properties of FGMs. The RZT is very suitable for stress analysis of laminated composites, especially for thick and moderately thick beams. It contains only four kinematic variables and eliminates the use of the shear correction factors. In this study, the equilibrium equations of the RZT are solved by means of the PDDO for the stress analysis of imperfect FG sandwich beams having uniform and non-uniform porosity distributions. The PDDO transforms the differential equations into their nonlocal form, namely integral form, providing highly accurate approximations of the derivatives. A comprehensive PDDO analysis is performed for the investigation of the influence of the material variation, and even and uneven porosity distributions on the stress variations of the imperfect FG sandwich beams. It is noted that when the FG core exhibits soft material distributions, the effect of porosity is evident. The even type porosity distribution pattern is more influential on the axial displacement and stress variations in comparison with those of the uneven type porosity distribution pattern.

Non-local Maxwell model for ultraslow relaxation of concrete under different normal stress levels

Stress relaxation is widely present in concrete structures and has a significant impact on the long-term mechanical properties of materials and structural safety. The previous stress relaxation models for concrete follow exponential or power-law law, which cannot accurately describe the ultraslow relaxation phenomenon with a logarithmic law. Thus, this paper proposes a non-local Maxwell model, i.e. Hadamard fractional derivative Maxwell (HFM) model with a normalized logarithmic kernel, and derives the constitution and relaxation modulus. A set of relaxation experimental data of cement concrete under different normal stresses is used to test the HFM model. Compared with the power-law fractional Maxwell model, the HFM model shows reasonable accuracy and can effectively capture the ultraslow relaxation in concrete. The fitting results indicate that the larger derivative order in the HFM model represents faster relaxation. Interestingly, the results also show that the normal stress in the concrete specimen is positively correlated with the derivative order in the HFM model.

The origin of the straight propagation of the σ phase in a Ni-based single crystal superalloy at elevated temperature

Topologically close-packed (TCP) phases, although inherently hard, are commonly perceived as detrimental in various alloys. In Ni-based single crystal superalloys (Ni-SXs), the primary adverse impact of TCP phases on material mechanical properties stems from their direct propagation, disrupting the original γ/γ′ dual-phase structure and leading to cleavage along the TCP phases under applied stress. Understanding the specific reasons for the straight propagation of TCP phases through the complex phase structure is essential for mitigating or potentially reversing their detrimental effects on material performance, a challenge that remains elusive. This study addressed this challenge by employing ultra-high spatial and energy resolution transmission electron microscopy (TEM) characterization, coupled with in situ scanning transmission electron microscopy (STEM) heating experiments in a fourth-generation Ni-based single crystal superalloy. Our research unveiled a significant phase-separation process during the incubation stage preceding σ phase formation at elevated temperatures, driven by the diffusion of atoms. Notably, domains of the γ′ phase, characterized by a scale of tens of nanometers, emerged within preexisting γ phases, and vice versa. This phenomenon reconstructed the original γ/γ′ dual-phase structure, leading to a finely refined dual-phase structure. The refined structure effectively reduced the diffusion distance of alloy elements necessary for forming σ phases. Consequently, the σ phases nucleated randomly and propagated directly through the newly refined γ/γ′ dual-phase structure. Throughout the thickening process, the notable difference in the diffusivity of alloying elements eventually resulted in the growth of a highly defective σ phase structure.

A comprehensive investigation of the process and atmospheric coupling corrosion on corroded and mechanical properties of the SPA-H weathering steel

Weathering steel has recently become popular in engineering due to its corrosion resistance, but its mechanical characteristics must alter during double corrosion, process chemical solution corrosion (CSC), and atmospheric corrosion (AC). However, no studies have been published on the coupling effect of process and atmospheric corrosion. The durability and safety of weathering steel structures can be challenging to assess. As a result, we used SPA-H weathering steel as the object, ran process corrosion and double corrosion simulations (process corrosion plus atmospheric corrosion simulation), and created three corrosion conditions: non-corrosion, single-side corrosion, and double-side corrosion. CSC was the corrosion process. Following CSC, the second (120, 360, 720, and 1200 hour) Copper-Accelerated Acetic Acid-Salt Spray Testing (CASS) was performed to simulate atmospheric corrosion. A correlation analysis was conducted using the grey correlation method between indoor and atmospheric corrosion. After corrosion testing, these specimens were subjected to White Light Interferometry (WLI) and tensile coupon tests (TCT) to evaluate the corrosion characteristics and the deterioration of material mechanical properties. Finally, linear fitting was used to produce the calculation formula between the mechanical properties and the mass loss ratio of single-side and double-side corrosion.

In-situ synchrotron diffraction analysis of deformation mechanisms in an AA5083 sheet metal processed by modified equal-channel angular pressing

Severe plastic deformation (SPD) is a process to significantly improve the mechanical properties of materials by grain refinement. For forming at room temperature (RT), higher strengths can thus be achieved; for increased temperatures (HT), greater elongations can be achieved. This great potential has been chiefly applied only on laboratory scale due to a lack of industrial process design. Equal-channel angular pressing (ECAP) offers the possibility to integrate these advantages in industrial processes. This paper investigates a modified ECAP process for aluminum AA5083 sheet metal. Two passes of ECAP for sheet metal and an additional heat treatment were used. To study the material deformation on a micro-scale, in-situ synchrotron measurements at DESY (Hamburg) were performed to analyze the evolution of lattice strains and dislocation densities during tensile testing. The mechanical properties of the ECAP-processed sheet material reveal an increase in yield strength and a decrease in elongation at RT. Higher strains can be measured for the processed material at elevated test temperatures. In-situ diffraction results show a changed behavior of the ECAP sheet material compared to the reference material for both temperature regimes. These changes are based on the increased defect density in the material, which leads to increased strength at RT. At HT, dynamic recrystallization occurs during tensile testing, and the prevailing deformation mechanisms reconfigure. Electron backscatter diffraction (EBSD) and micrographs are used to interpret and supplement the observations. The findings provide the basis for the in-depth understanding of the deformation behavior of the material and help to apply the ECAP process on an industrial scale.

In situ growth and shrinkage of coated voids in aluminium

Voids can be detrimental to the mechanical and electrical properties of materials but may also find applications in catalysis and plasmonics. Key to the performance of materials containing voids are the sizes and morphologies of the voids, which can be tuned by heat treatment. The present work investigates the morphological evolution of voids, with solute segregation at their surfaces, in an aluminium‑copper‑tin alloy during in situ heating in a transmission electron microscope (TEM). These voids exhibited complex morphological changes that included growth or shrinkage, in contrast to voids in pure Al, which all shrank and disappeared (as reported in an earlier study). Without electron irradiation, the voids never grew. Nearly one fourth of the voids grew under certain heating and electron irradiation conditions, showing distinct growth stages. Growth and shrinkage of the voids both occurred primarily along the surface of the Sn particles to which they were attached. The voids exhibited faceting as they grew and gained morphological isotropy while they shrank. The growth and shrinkage fronts were both found to be primarily the curved surfaces and not the facets at the void surfaces. Growth followed by shrinkage led to a well-defined rounded triangular shape, in projection, with smooth boundaries. This work is, to the best of our knowledge, the first to characterise the growth of nanoscale voids in aluminium using in situ heating TEM. The dual effect of heating and electron irradiation could be utilised to switch the voids between growth and shrinkage to manipulate the void size and shape. This work provides useful insights into tuning void morphologies in the development of advanced materials such as for applications in engineering, catalysis and plasmonics.

Static and dynamic buckling analysis of two-layer shells include auxetic honeycomb core combined with laminated three-phase polymer/GNP/fiber surface resting on Kerr elastic medium in hygro-thermal environments

This article investigates the static and dynamic buckling behavior of a double-curved sandwich shell composed of two layers via improved first-order shear deformation theory without using the shear correction is utilized to model the sandwich shell. The sandwich two-layer shell are held together by elastic pins, each layer made from an ultra-light auxetic honeycomb core layer (negative Poisson’s ratio) and is reinforced by a layer of tri-phase polymer, graphene nanoplatelets (GNP), and fiber. The double-curved sandwich shell is supported by a Kerr elastic medium in hygro-thermal environment assuming that temperature and humidity only cause forces to be applied tangentially to the shell and do not change the mechanical properties of the shell material. The motion equations of sandwich two-layer shell are derived by Hamilton’s principle, then the finite element method and Bolotin method are used to derive the dynamic instability region of sandwich two-layer shell. The accuracy of these results is confirmed by a comparison with established statements within the specific conditions of the problem model. The influence of inputs on the static and dynamic stability of sandwich two-layer shell is fully explored and discussed. Additionally, this serves as a crucial foundation for the calculation and design of structures that can integrate a variety of materials with different properties with low cost and simplification.

Determination of selective laser melting process parameters of tungsten carbide powders coated with nickel via electroless plating for improved interface properties

Tungsten carbide powders are commonly used at various industrial applications due to their high hardness. However, these powders may exhibit low binding and processing challenges without a binder. Therefore, various binding methods such as electroless Ni coating are used to hold WC powders together, increase their processability and improve the mechanical properties of the final product. Electroless Ni plating plays an important role in the use of WC powders, especially in processes such as selective laser melting. The structural, tribological, and mechanical properties of parts manufactured by SLM method are significantly influenced by the parameters employed in the process. Hence, optimizing process variables is essential to unlock the full potential of this advanced manufacturing technique. The main objective of this study was to identify the optimum process parameters for the SLM method of WC-Ni composite powders, which were prepared by coating WC powder materials with electroless Ni. Experimental investigations focused on analyzing the laser power, scanning speed, and hatch spacing parameters. The effects of these parameters on the mechanical and tribological properties of WC-Ni composite material were investigated using microhardness tester, tribometer device, optical microscope, 3D optical profilometer and scanning electron microscope. Eventually, it was determined that the manufacturing parameters employed in the SLM method had a significant impact on relative density, microstructure, surface roughness, hardness, and tribological properties. Samples exhibited a relative density of nearly 99%, and the highest observed hardness value was 1962 HV. This article supports a specialized SLM manufacturing process developed specifically to enhance durability and performance across a broad spectrum of industrial applications through interface improvement and the optimization of manufacturing parameters.

Significantly improved mechanical properties of mullite ceramics by adding AlOOH with different sizes and morphologies

AbstractMullite ceramics with high purity and toughness were prepared by hot‐press sintering of pyrophyllite at 1300°C using AlOOH nanomaterials with different sizes and morphologies (nanoparticles, nanorods, nanoflakes, and micro‐sized sea urchin–like) as additives. Among the four types of AOOH additives, the incorporation of nanoflakes and sea urchins resulted in the formation of a relatively uniformly distributed and tightly packed microstructure within the ceramics, which significantly improved the density and mechanical properties of the ceramic materials. Compared to nano‐sized AlOOH, the addition of micron‐sized sea urchin–like AlOOH could produce mullite ceramics with best purity and flexural strength. The flexural strength and fracture toughness of ceramics prepared from micro‐sized sea urchin–like AlOOH and pyrophyllite reach 427.34 ± 1.99 MPa and 4.68 ± .31 MPa m1/2, respectively. During the ball milling process, the originally micron‐sized sea urchin–like AlOOH particles were broken down into micro‐ and nano‐sized AlOOH particles. The resulted micron and nanoscale AlOOH particles exhibited synergistic and multi‐scale effects with pyrophyllite, which contributed to the formation of uniformly sized and densely arranged mullite crystals within the ceramics. Additionally, the bridging between the mullite crystals further improved the mechanical properties of the mullite ceramic material.

Formation of Stable Vascular Networks by 3D Coaxial Printing and Schiff-Based Reaction.

Vascularized organs hold potential for various applications, such as organ transplantation, drug screening, and pathological model establishment. Nevertheless, the in vitro construction of such organs encounters many challenges, including the incorporation of intricate vascular networks, the regulation of blood vessel connectivity, and the degree of endothelialization within the inner cavities. Natural polymeric hydrogels, such as gelatin and alginate, have been widely used in three-dimensional (3D) bioprinting since 2005. However, a significant disparity exists between the mechanical properties of the hydrogel materials and those of human soft tissues, necessitating the enhancement of their mechanical properties through modifications or crosslinking. In this study, we aim to enhance the structural stability of gelatin-alginate hydrogels by crosslinking gelatin molecules with oxidized pullulan (i.e., a polysaccharide) and alginate molecules with calcium chloride (CaCl2). A continuous small-diameter vascular network with an average outer diameter of 1 mm and an endothelialized inner surface is constructed by printing the cell-laden hydrogels as bioinks using a coaxial 3D bioprinter. The findings demonstrate that the single oxidized pullulan crosslinked gelatin and oxidized pullulan/CaCl2 double-crosslinked gelatin-alginate hydrogels both exhibit a superior structural stability compared to their origins and CaCl2 solely crosslinked gelatin-alginate hydrogels. Moreover, the innovative gelatin and gelatin-alginate hydrogels, which have excellent biocompatibilities and very low prices compared with other hydrogels, can be used directly for tissue/organ construction, tissue/organ repairment, and cell/drug transportation.