Advanced Nanostructure-Controlled Functionally Graded Materials Employing Carbon Nanotubes

9 - Metal-ceramic functionally graded materials (FGMs)

Carbon nanotubes (CNTs) embedded in carbon/epoxy (c/ep) composites offer a lightweight, stiff solution with high damping for structural components. To manufacture CNT/c/ep hybrid composites with high concentrations of CNTs, a CNT yarn interlayer concept is used. Through a mechanism known as stick-slip, the interface between CNTs and c/ep laminates dissipate energy during dynamic cycling. It is predicted that altering the interfacial bond strength can enhance dynamic properties: loss factor, loss modulus, and storage modulus. In this research, the effect of surface treatments on CNT yarns prior to inserting the CNTs into the laminate was explored to determine if the dynamic properties of the composite were enhanced. It was determined that 2,3-dibromo-1,4-butanediol (23D14B), Triton X-100 (TX) and a solution of sulfuric and nitric (S/N Acid) were the best treatments of 12 tested based on the increased dynamic properties. For a composite with 5 vol% CNT yarn interlayers, 23D14B, TX, and S/N Acid increased Loss Factor by 230%, 130%, and 160%, respectively. Elevated temperature, moisture-saturated/elevated temperature, and cyclic loading frequency were investigated on 5vol. % CNT interlayers to determine their effects on dynamic properties of the CNT hybrid composites.

Carbon nanotubes reinforce polymer composites providing nanotube-based nanohybrids with potentially outstanding properties. The dispersion quality, however, influences the performances of the resulting materials. Therefore, new preparation procedures and efficient dispersion strategies are needed. A new method encapsulating single-walled carbon nanotubes in a nematic phase of double stranded DNA–water–NaCl is reported here. The procedure relies on osmotic compression and on its role in compacting DNA–nanotube composites. An anionic polymer (sodium dextransulfate) was added to the above dispersions and segregative phase separation was induced. DNA–nanotube composites were concentrated and phase-separated from the coexisting polymer solution. In this way, high concentrations of carbon nanotubes can be incorporated in the DNA-rich phase, inducing a transition from liquid- to solid-like behavior. The resulting nematic fluids are homogeneous and orient when shear stresses are applied. The kinetics of re-alignment was determined by rheological and spectroscopic methods. The effect of the nanotubes on the resulting behavior was accounted for. A slowing down of DNA motion observed in such composite matrices suggests interactions with nanotubes.

The interphase thickness in polymer carbon nanotube (CNT) nanocomposites (PCNT) is expressed by CNT characteristics and interfacial conductivity between CNT and polymer matrix. Also, the effective length and concentration of CNT are defined supposing interfacial conductivity to suggest the percolation threshold and the fraction of networked CNT. Furthermore, a simple model is developed to predict the conductivity of PCNT assuming tunneling effect, interphase region and interfacial conductivity. The influences of all parameters on the interphase thickness, percolation threshold, the fraction of networked CNT and the conductivity of PCNT are studied. In addition, some experimental results are provided to compare the predictions of developed model to the experimental measurements. The high levels of CNT radius, CNT length, CNT conductivity, interfacial conductivity and conductivity transferring can produce a thick interphase, but the waviness cannot change it. Moreover, the developed model can properly calculate the conductivity of studied samples. A desirable conductivity is obtained by thin and long CNT, medium CNT conductivity, poor waviness, high interfacial conductivity and good conductivity transferring, because they provide high effective CNT concentration and low percolation threshold in nanocomposites.

Mechanical properties of CNT reinforced hybrid functionally graded materials for bioimplants

Four-component barium titanate stannate (BaTi1−x Sn x O3, BTS) functionally graded materials (FGMs) were designed, processed and examined. BTS powders with different tin content (x = 0.025, 0.05, 0.07 and 0.10, abbreviated as BTS2.5, BTS5, BTS7 and BTS10, respectively) were used as ingredient materials. Four-layered samples, produced by powder-stacking method and uniaxial pressing, were consolidated in BTS2.5/BTS5/BTS7/BTS10 FGMs by sintering at 1420 °C with dwell time of 2 h. To achieve high-quality FGMs, without structural or microstructural damages, the master sintering curve (MSC) approach were used. In this study, the MSC was constructed for four-layered FGMs using shrinkage data obtained by a heating microscope during non-isothermal part of the sintering up to 1420 °C with heating rates of 2, 5, 10 and 30°/min. To prepare FGMs with desired final density the corresponding Θ value was estimated from the abscissa of the master sintering curve. Estimated Θ value was used in Φ(ρ) = logΘ(t,T(t)) equation, which correlate density (ρ) and the time and temperature dependent parameter Θ(t,T(t)). This calculation allowed us to determine experimental parameters which should be applied in sintering procedure to obtain FGMs with projected density. According to constructed MSC, four different sintering schedules were designed and applied where four BTS2.5/BTS5/BTS7/BTS10 FGMs were prepared. To validate the constructed MSC, the microstructure and chemical (Ti/Sn) gradient in the prepared FGMs were examined by SEM–EDS methods.

Insights into the mechanism of multi-walled carbon nanotubes phytotoxicity in Arabidopsis through transcriptome and m6A methylome analysis

Functionally Graded Material (FGM) is a material with engineered gradients of composition, structure and/or specific properties aiming to become superior over homogeneous material composed of same or similar constituents. In the recent years, research has been undertaken on manufacturing of functionally graded materials (FGM) using numerous techniques like powder metallurgy, melt processes, centrifugal casting, electrophoretic deposition, spark plasma sintering, physical vapor deposition, chemical vapor deposition etc. Most of these techniques may be well suited for a specific application yet they suffer from one or more limitations like lower graded thickness, low deposition rate, complexity in process requirement, or high processing cost. To circumvent these limitations innovative technique called laser assisted manufacturing technique is applied for manufacturing functionally graded materials. Three methods that employ Laser for synthesis of FGM is elaborated in this work (i) 3-D Laser Cladding, (ii) LENS and (iii) Selective laser sintering. Laser Cladding is used for obtaining coatings of FGM by direct powder injection into the laser beam. 3-D Laser-engineered net shaping (LENS) is used to fabricate FGM directly from CAD solid models and thus further reduce the lead times for metal art fabrication. Selective laser sintering (SLS) is a layered manufacturing based freeform fabrication approach for constructing three dimensional structures in functionally graded composites. All these methods are used to manufacture FGMs in a short interval of time and the process can be controlled digitally, thus all these methods come in the heading of rapid manufacturing (RM). These methods have a huge industrial potential and can be commercialized for manufacturing bulk FGM.

Functionally Graded Materials (FGMs) can outperform their homogeneous counterparts. Advances in digitalization technologies, mainly additive manufacturing, have enabled the synthesis of materials with tailored properties and functionalities. Joining dissimilar metals to attain compositional grading is a relatively unexplored research area and holds great promise for engineering applications. Metallurgical challenges may arise; thus, a theoretical critical analysis is presented in this paper. A multidisciplinary methodology is proposed here to unify optimal design, multi-feed Wire-Arc Additive Manufacturing (WAAM), and image-based characterization methods to create structure-specific oriented FGM parts. Topology optimization is used to design FGMs. A beam under pure bending is used to explore the layer-wise FGM concept, which is also analytically validated. The challenges, limitations, and role of WAAM in creating FGM parts are discussed, along with the importance of numerical validation using full-field deformation data. As a result, a conceptual FGM engineering workflow is proposed at this stage, enabling digital data conversion regarding geometry and compositional grading. This is a step forward in processing in silico data, with a view to experimentally producing parts in future. An optimized FGM beam, revealing an optimal layout and a property gradient from iron to copper along the build direction (bottom-up) that significantly reduces the normal pure bending stresses (by 26%), is used as a case study to validate the proposed digital workflow.

Strong and tough bioinspired nacre-like B4C/Al functionally graded materials with eliminated abrupt interfaces

Bio-printing on the thermoplastic substrate for functionally graded materials with improved dielectric properties

In industrial machines and machine elements, it is quite common to find contact between surfaces under various loading conditions. Interaction between such contacting surfaces during loading and subsequent unloading and the responses of the contact system are important in terms of the longevity and sustainability of the components. The present work studies flattening contact of a carbon nanotube (CNT) reinforced functionally graded material (FGM) matrix nanocomposite (CNTR-FGMMC) using a finite element-based cylindrical contact model. It focuses on the effect of gradation parameter or index of the functionally graded matrix material. The FGM is treated as an elastically-graded material, where both the modulus of elasticity and tangent modulus vary while the yield strength remains constant. The finite element model has been tested for convergence and validity by comparison with established results from systems with lesser complexity. The flattening analysis is conducted by varying elastic inhomogeneity/gradation parameters while maintaining a constant wall thickness of CNTs. Stress and deformation behaviours, including contact force and contact area, throughout the loading and unloading phases as gradation parameters vary. Additionally, the analysis encompasses an examination of energy losses attributed to plasticity. The study reveals that the gradation parameter plays a significant role in contact behaviour.

The effect of gradients in hardness, microstructure and composition in the surface layers on magnetic Barkhausen noise (MBN) was investigated in two widely used gear steels. In the experiment one material was through hardened in two ways: (i) A set of Ovako 667 was hardened according to the standard process of this type and, (ii) Another set was deliberately decarburized. The other material, EN36 was gas case carburized according to the standard procedure. It was found that, the inhomogeneity in the decarburized and the case-carburized materials showed up clearly in the MBN measurements. This took the form of a two-peak MBN profiles whereas, a single peak profile was seen with the homogenous martensitic microstructure specimen. It is found that the shape of the MBN profile is significantly affected when a gradient in microstructure is induced by a gradient in carbon content. This was confirmed by metallographic examination and the microhardness tests. The result concludes that the MBN as an effective non-destructive testing technique which may replace the used destructive techniques.

Actuators and materials play a key role in developing advanced precision engineering. The breakthroughs in this field are closely related to the development of various types of actuators and related materials. The successes of piezoelectric ceramics and ceramic actuators have. For instance, the propagating‐wave type ultrasonic motor that produces precise rotational displacements has been used in autofocusing movie cameras and VCRs. Multimorph ceramic actuators prepared from electrostricitive Pb(Mg1/3Nb2/3)O3(PMN) ceramics are used as deformable mirrors to correct image distortions from atmospheric effects. The likelihood that the range of applications and demand for actuators will grow actively and has stimulated intensive research on piezoelectric ceramics. Functionally graded materials (FGMs) are a new class of composites that contain a continuous, or discontinuous, gradient in composition and microstructure. Such gradients can be tailored to meet specific needs while providing the best use of composite components. Furthermore, FGM technology is also a novel interfacial technology for solving the problems of the sharp interface between two dissimilar materials. In recent years, significant advances in developing FGMs have been achieved. In this article, we introduce and summarize the recent progress in piezoelectric ceramic actuators and review recent applications of FGMs in piezoelectric ceramic devices.

Nonlinear vibration of sandwich plate with functionally graded material (FGM) core and carbon nano tubes reinforced (CNTs) nano-composite layers by considering temperature-dependent material properties are studied in this paper. Base on Classical plate theory (CPT), the governing partial differential equations of motion for sandwich plate are derived using Hamilton principle. The Galerkin procedure and multiple scales perturbation method are used to find relation between nonlinear frequency and amplitude of vibration response. The dynamic responses of the sandwich plate are also investigated in both time and frequency domains. Then, the effects of nonlinearity, excitation, power law index of FG core, volume fraction of carbon nanotube, the function of material variations of FG core, temperature changes, scale transformation parameter and damping factor on the frequency responses are investigated.