Terms Of Material Properties Research Articles

4D Printing of Hydrogels: A Review

Abstract3D printing permits the construction of objects by layer‐by‐layer deposition of material, resulting in precise control of the dimensions and properties of complex printed structures. Although 3D printing fabricates inanimate objects, the emerging technology of 4D printing allows for animated structures that change their shape, function, or properties over time when exposed to specific external stimuli after fabrication. Among the materials used in 4D printing, hydrogels have attracted growing interest due to the availability of various smart hydrogels. The reversible shape‐morphing in 4D printed hydrogel structures is driven by a stress mismatch arising from the different swelling degrees in the parts of the structure upon application of a stimulus. This review provides the state‐of‐the‐art of 4D printing of hydrogels from the materials perspective. First, the main 3D printing technologies employed are briefly depicted, and, for each one, the required physico‐chemical properties of the precursor material. Then, the hydrogels that have been printed are described, including stimuli‐responsive hydrogels, non‐responsive hydrogels that are sensitive to solvent absorption/desorption, and multimaterial structures that are totally hydrogel‐based. Finally, the current and future applications of this technology are presented, and the requisites and avenues of improvement in terms of material properties are discussed.

Numerical microstructure model of NiTi wire reconstructed from 3D-XRD data

In this paper, the grain microstructure and strain partitioning in a polycrystalline NiTi wire subjected to tensile loading was reconstructed from an experimental 3D-XRD dataset. The reconstruction of a volume containing more than 8000 stressed grains involved optimization with respect to both the geometrical features and material elastic properties. The geometrical features of the microstructure were reconstructed using Laguerre tessellations based on the experimental 3D-XRD dataset. Two different algorithms fitting Laguerre tessellations were applied in order to assess the sensitivity of the reconstruction to the choice of the algorithm. The material properties in terms of elastic anisotropy were refined from an initial published value to minimize the mismatch between experiment and simulation using an optimization algorithm based on linear elasticity simulations. As a result of this, we constructed a numerical microstructure model that statistically matches the experimentally probed material in terms of positions and sizes of grains as well as partitioning of elastic strain and stress in the microstructure (average elastic properties and standard deviations of piecewise constant components of elastic strain and stress tensors in grains).

Questioning a fundamental assumption of rheology: Observation of noninteger power expansions

We report the most complete experimental evidence to date of noninteger power-law expansions for nonlinear viscoelastic properties. Our observations, made with a capillary suspension of spherical poly(methyl methacrylate) (PMMA) particles, falsify the universality of the standard assumption where shear stress nonlinearities arise as the amplitude cubed, e.g., σ ∼ O ( γ 0 3 ) in an oscillatory shear test at small amplitudes. In terms of material properties, our measurements require noninteger Taylor expansions about a linear reference state. Furthermore, distinct power-law exponents are found for the storage and loss signals. In this work, we conclusively demonstrate that the noninteger scaling is real and not an experimental artifact. Our experimental and data analysis methods ensure that we report the most complete result to date. While the noninteger scaling remains to be associated with underlying microstructural physics, the thorough experimental data reported herein demonstrate that such theoretical studies are worth pursuing.

Glass-Ceramics Processed by Spark Plasma Sintering (SPS) for Optical Applications

This paper presents a review on the preparation of glass-ceramics (GCs) and, in particular, transparent GCs by the advanced processing technique of spark plasma sintering (SPS). SPS is an important approach to obtain from simple to complex nanostructured transparent GCs, full densification in a short time, and highly homogeneous materials for optical applications. The influence of the different processing parameters, such as temperature, pressure, sintering dwell time on the shrinkage rate, and final densification and transparency, are discussed and how this affects the glass material properties. Normally, transparent glass-ceramics are obtained by conventional melt-quenching, followed by thermal treatment. Additionally, the GC scan is produced by sintering and crystallization from glass powders. Hot pressing techniques (HP) in which the source of heating is high-frequency induction can be also applied to enhance this process. In the case of transparent ceramics and glass-ceramics, spark plasma sintering is a promising processing tool. It is possible to enhance the material properties in terms of its compactness, porosities, crystallization, keeping the size of the crystals in the nanometric scale. Moreover, the introduction of a high concentration of active gain media into the host matrix provides functional glass-ceramics systems with enhanced luminescence intensity through reducing non-radiative transitions like multi phonon relaxation (MPR) and cross relaxations (CR), thus providing longer lifetimes. More effort is needed to better understand the sintering mechanisms by SPS in transparent GC systems and optimize their final optical performance.

ON THE TRIBOLOGICAL PROPERTIES OF POLYLACTIDE (PLA) APPLIED IN 3D PRINTING TECHNOLOGY

The article presents the results of basic tribological research of polylactide enriched with MoS2 powder. The research was conducted on a pin-on-disc station. Samples dimensions: 8 mm height, 8 mm diameter, printed in FFF/FDM method. Two mass percentages of addition were created: 1% and 2.5%. As counter-specimen steel (C45) disc was used. Ra roughness of counter-specimen was in the range of 0.3–0.4. The main purpose is to determine optimal, in the light of tribological properties, mass percentage values of additions in polylactide in the 3D printing application. The research has shown that materials with more MoS2 addition would not be a good material for use in the production of prototype bearings, due to increased linear wear. It is also worth noting that the MoS2 addition improves material properties in terms of the 3D printing process. Thanks to the addition, even up to 1%, the required temperature of the printing nozzle has been significantly reduced, as well as flow resistance in the nozzle.

Integrated Taguchi cum grey relational experimental analysis technique (GREAT) for optimization and material characterization of FSP surface composites on AA6061 aluminium alloys

This work focuses on the optimization of process parameters for friction stir processed (FSP) AA 6061 for superior mechanical properties. The distinctive work is to integrate the Taguchi Method with the Grey Relational Experimental Analysis Technique (GREAT) for a hybrid portfolio. Eight experimental investigations were carried out with varying process parameters of two levels of tool speed (25 and 28 mm/s), processing speed (1000 and 1500 rpm) and pin profiles (cylinder and square) with reinforcements such as Silicon carbide (SiC), Titanium Carbide (TiC), Titanium DiBromide (TiB2) and Zirconium DiBromide (ZrB2) to uncover the influence that it holds to the process. Surface composites quality of all the samples was evaluated for tensile strength. After a single pass of FSP. TiC reinforcement showed a promising optimized welding quality at 1500 rpm, 25 mm/s with a square pin profile by GREAT. when TiC reinforcement was used along with the rotational speed of 1500 RPM, the processing speed of 25 mm/s with a square pin profile as a process parameter and significant improvement of 37.85% and 46.6% for tensile strength and yield strength respectively due to the grain refinement of added reinforcement particle dispersoids, processed AA6061 composites showed significant improvement in terms of material property.

Effective structural chirality of beetle cuticle determined from transmission Mueller matrices using the Tellegen constitutive relations

Several beetle species in the Scarabaeoidea superfamily reflect left-handed polarized light due to a circular Bragg structure in their cuticle. The right-handed polarized light is transmitted. The objective here is to evaluate cuticle chiral properties in an effective medium approach using transmission Mueller matrices assuming the cuticle to be a bianisotropic continuum. Both differential decomposition and nonlinear regression were used in the spectral range of 500–1690 nm. The former method provides the sample cumulated birefringence and dichroic optical properties and is model-free but requires a homogeneous sample. The materials chirality is deduced from the circular birefringence and circular dichroic spectra obtained. The regression method requires dispersion models for the optical functions but can also be used in more complex structures including multilayered and graded media. It delivers the material properties in terms of model functions of materials’ permittivity and chirality. The two methods show excellent agreement for the complex-valued chirality spectrum of the cuticle.

A probabilistic framework to define the design stress and acceptable defects under combined-cycle fatigue conditions

Probabilistic routines are necessary to determine the permissible design stress when the operational conditions of traditional gas turbines are further challenged to reach higher performances in terms of flexibility. This paper focuses on the definition of a probabilistic tool aimed to simulate the damage development under combined high and low cycle fatigue conditions considering the stochastic nature of some of the variables introduced in the model. The variables considered in the present study are the long crack threshold ΔKth,LC and the slope of the crack growth law C in the so-called Paris region, the endurance limit Δσw0 and the variability of the applied stress as it cannot be considered a fixed variable in the complex loading scenario of gas turbines. A broad experimental campaign was performed to characterize the material properties in terms of short and long crack resistance under constant and combined cyclic conditions. The data were used to define the average and variance of the materials parameters to feed Montecarlo simulations and, at a target probability of failure, establish the design stress. This work points to determine safety margins which strictly depend on the natural variability of the variables that govern the damage accumulation in the mechanical component.

System Identification and Seismic Performance Assessment of a Stone Arch Bridge

ABSTRACT This paper presents system identification and seismic performance assessment of a masonry arch bridge located on the railway route which is on the northeastern part of Turkey. Forty-one masonry arch bridges were registered as historical and needed to be preserved on the route. On the other hand, the railway line passes through North Anatolian Fault, resulting in high seismic demand on bridges. Therefore, seismic assessment of the bridges was carried out by finite element analysis; however, masonry structures such as stone arch bridges have significant uncertainties in terms of material properties, boundary conditions, and modeling assumptions. As a result, it becomes almost unavoidable to perform dynamic identification tests to validate finite element models (FEM). Modal properties of 12 bridges such as modal frequencies, mode shapes, and modal damping ratios were identified through vibration measurements collected under ambient conditions, impact loading, and train passage. Based on identified modal parameters, FEM of the bridges were updated to obtain actual values of Young’s modulus of masonry and soil. FEM updating procedure was performed by minimizing the difference between experimental and analytical modal properties. Afterwards, seismic performance assessment of a representative bridge was carried out using ANSYS software. Two different nonlinear approaches were considered, namely, pushover and nonlinear time history (NLTH) analyses. In the analyses, macro-modeling approach was followed to develop homogenized behavior of stone and mortar. It was found that mass proportional pushover analysis gave similar results to NLTH in terms of seismic performance. The other significant point was that modeling soil medium reflects the actual behavior of the bridge in the sense that artificial stress concentrations do not occur at the pier base. It was also observed that tensile strength capacity was reached on spandrel walls which may result in a probable failure.

Analysis of PLA Geometric Properties Processed by FFF Additive Manufacturing: Effects of Process Parameters and Plate-Extruder Precision Motion.

The evolution of fused filament fabrication (FFF) technology, initially restricted to the manufacturing of prototypes, has led to its application in the manufacture of finished functional products with excellent mechanical properties. However, FFF technology entails drawbacks in aspects, such as dimensional and geometric precision, and surface finish. These aspects are crucial for the assembly and service life of functional parts, with geometric qualities lagging far behind the optimum levels obtained by conventional manufacturing processes. A further shortcoming is the proliferation of low cost FFF 3D printers with low quality mechanical components, and malfunctions that have a critical impact on the quality of finished products. FFF product quality is directly influenced by printer settings, material properties in terms of cured layers, and the functional mechanical efficiency of the 3D printer. This paper analyzes the effect of the build orientation (Bo), layer thickness (Lt), feed rate (Fr) parameters, and plate-extruder movements on the dimensional accuracy, flatness error, and surface texture of polylactic acid (PLA) using a low cost open-source FFF 3D printer. The mathematical modelling of geometric properties was performed using artificial neural networks (ANN). The results showed that thinner layer thickness generated lower dimensional deviations, and feed rate had a minor influence on dimensional accuracy. The flatness error and surface texture showed a quasi-linear behavior correlated to layer thickness and feed rate, with alterations produced by 3D printer malfunctions. The mathematical models provide a comprehensive analysis of the geometric behavior of PLA processing by FFF, in order to identify optimum print settings for the processing of functional components.

Effective design space exploration of gradient nanostructured materials using active learning based surrogate models

Inspired by gradient structures in the nature, Gradient Nanostructured (GNS) metals have emerged as a new class of materials with tunable microstructures. GNS metals can exhibit unique combinations of material properties in terms of ultrahigh strength, good tensile ductility and enhanced strain hardening, superior fatigue and wear resistance. However, it is still challenging to fully understand the fundamental gradient structure-property relationship, which hinders the rational design of GNS metals with optimized target properties. In this paper, we developed an adaptive design framework based on surrogate modeling to investigate how the grain size gradient and twin thickness gradient affect the strength of GNS metals. The Gaussian Process (GP) based surrogate modeling technique with adaptive sequential sampling is employed to develop the surrogate models for the gradient structure-property relationship. The proposed adaptive design integrates physics-based simulation, surrogate modeling, uncertainty quantification and optimization, which can efficiently explore the design space and identify the optimized design of GNS metals with maximum strength using limited sampling data generated from high fidelity but computational expensive physics-based simulations.

Modeling resilient modulus of fine-grained materials using different statistical techniques

For the realistic prediction of pavement performance, it is very important to accurately characterize the mechanical behavior of unbound material layers and subgrade soils. In pavement analysis using the elastic layered theory, material properties in terms of dynamic elastic modulus and Poisson’s ratio are the major input parameters. The dynamic elastic modulus of pavement materials or resilient modulus (MR) is measured by conducting repeated load triaxial compression tests typically not available to highway authorities due to the high costs involved in acquiring such high-performance equipment and/or lack of knowledge on how to operate this specialized equipment. Therefore, pavement engineers are obligated to use pavement design methodologies based on empirical tests. The main objective of this study is to use multiple linear regression (MLR), nonlinear regression and backpropagation artificial neural network algorithms to develop models to predict the resilient modulus of fine-grained materials based on 3709 soil samples collected from the Long-Term Pavement Performance (LTPP) website. The key input parameters selected for this study are: the confining pressure (σ3), nominal maximum axial stress (σ1), percent of silt (S), Liquid Limit (LL), Plasticity Index (PI), percent passing number 200 sieve (P#200), maximum dry density (ρmax-dry), percent of clay (C), optimum moisture content (wopt), and laboratory-determined resilient modulus. Results revealed that the change of wopt has a higher effect on MR compared with the change in density, the percent fines, percent of silt, percent of clay, confining pressure, PI and LL but less than the effect of changing axial stress. In addition, the best modeling technique to predict the resilient modulus of fine-grained soil was found to be the Artificial Neural Network (ANN) followed by the nonlinear regression and finally the MLR.

Order-disorder transition in Nano-Cu2ZnSnS4: A Raman spectroscopic study

Quaternary compound Cu2ZnSnS4 (CZTS) is a highly promising photo absorbing material, due to its suitability in terms of material properties, relative abundance and non-toxicity of its constituents. We report Raman spectroscopic investigation of temperature induced changes in nano-crystalline kesterite structured CZTS synthesized by microwave method. High-temperature Raman spectroscopic studies of nano-crystalline CZTS revealed relative intensity changes in the Raman spectra around the temperatures at which transition from ambient kesterite phase to disordered kesterite phase is reported by earlier neutron diffraction studies in bulk CZTS. This was also confirmed by a laser heating experiment with estimation of temperatures carried out using the Stokes/Anti-Stokes intensity ratio. The changes observed are reversible. The present results indicate a reversible transition to disordered kesterite phase at 550 K which is also achieved by laser heating.

Multi-directional functionally graded materials for enhancing the durability of shell structures

Uni-directional functionally graded materials (FGMs) providing a relative change in terms of material properties have been implemented in many high-tech engineering applications, including shells and plates. As a new concept, multi-directional FGMs highlight the emergence of modern materials design in the development of multi-functional materials. Pressure vessels made of materials varying in the radial direction have been comprehensively studied. In some practical instances, however, tailored grading of material properties is required in other directions. Shells with bi-dimensional FGM properties can present practical problems arising from excessive temperature gradients and extreme deflections. In this work, asymmetric deformations of two-directional FG pressure vessels under the effect of thermo-mechanical loads are studied numerically, taking advantage of Fourier and polynomial quadrature methods. Unlike most published research on this topic, we assume that the material properties of the shell are graded in the radial and axial directions obeying an exponential formulation, leading to a more accurate simulation of the real work condition. Governing equations are formulated based on three-dimensional elasticity theory, discretised into the series form, and then the resulting equations are solved. To evaluate the accuracy and superiority of this approach, numerical results are obtained and compared with exact solutions for material properties defined by the power law and are found to be in good agreement. In the results section, it is shown that variations of the grading parameter, temperature shock, geometry profile and boundary conditions play important roles in the distribution of stress, displacement and temperature fields. In the context of the thermoelastic theory of shells and plates, the results of this work will provide a reliable database for design engineers to choose a desirable material property function, changing throughout different directions of the geometry, to mitigate thermal stresses, which should be as small and uniform as possible.

Functional Skin Grafts: Where Biomaterials Meet Stem Cells.

Skin tissue engineering has attained several clinical milestones making remarkable progress over the past decades. Skin is inhabited by a plethora of cells spatiotemporally arranged in a 3-dimensional (3D) matrix, creating a complex microenvironment of cell-matrix interactions. This complexity makes it difficult to mimic the native skin structure using conventional tissue engineering approaches. With the advent of newer fabrication strategies, the field is evolving rapidly. However, there is still a long way before an artificial skin substitute can fully mimic the functions and anatomical hierarchy of native human skin. The current focus of skin tissue engineers is primarily to develop a 3D construct that maintains the functionality of cultured cells in a guided manner over a period of time. While several natural and synthetic biopolymers have been translated, only partial clinical success is attained so far. Key challenges include the hierarchical complexity of skin anatomy; compositional mismatch in terms of material properties (stiffness, roughness, wettability) and degradation rate; biological complications like varied cell numbers, cell types, matrix gradients in each layer, varied immune responses, and varied methods of fabrication. In addition, with newer biomaterials being adopted for fabricating patient-specific skin substitutes, issues related to escalating processing costs, scalability, and stability of the constructs under in vivo conditions have raised some concerns. This review provides an overview of the field of skin regenerative medicine, existing clinical therapies, and limitations of the current techniques. We have further elaborated on the upcoming tissue engineering strategies that may serve as promising alternatives for generating functional skin substitutes, the pros and cons associated with each technique, and scope of their translational potential in the treatment of chronic skin ailments.

Experimental investigation of phase change materials fabricated using selective laser sintering additive manufacturing

The increased demand for phase-change-materials-enabled energy storage systems exposed the limitations of established manufacturing methods in terms of material properties, fabrication speed, material waste, and shape-form flexibility. Phase change materials have unique merits in latent heat thermal energy storage, due to its capability of providing high-energy density storage by solidifying/melting at a constant temperature. In this research, a phase change composite was developed by mixing paraffin wax with a thermal conductive expanded graphite. Using a layer-by-layer laser sintering method, these two materials were combined at a micro-scale, forming a phase change composite that possesses good thermal conductivity, superior latent heat, and good mechanical strength. This work investigated the key parameters for successful production of paraffin wax/expanded graphite composite using laser sintering technique. In particular, the paraffin wax is melted and then impregnated into the inter-particle pores of expanded graphite through capillaries. It serves as a binder that bonds the expanded graphite molecules together into a solid form-stable object during the laser sintering process. To validate the developed sintering process, samples with a various number of layers were fabricated and tested. Results showed good structural integrity and functionality of the printed samples. The thermal conductivity was in the range of 0.83–0.92 W m−1 K−1. The latent heat was in the range of 150–156 kJ kg−1. Modulus of elasticity was between 808–880 MPa while the tensile strength in the range of 2.2–3.3 MPa. The electrical resistivity ranged between 8 and 28 Ohm m. These experimental results verified that the developed laser sintering process could be used as an effective nontraditional manufacturing technique for fabricating phase change materials for thermal energy storage applications.

Radio-Frequency Polymer Field-Effect Transistors Characterized by S-Parameters

Thanks to recent progress in terms of materials properties, polymer field-effect transistors (FETs) operating in the MHz range can be achieved. However, further development towards challenging frequency ranges, for a field accustomed to slow electronic devices, has to be addressed with suitable device design and measurements methodologies. In this work, we report n-type FETs based on a solution-processed polymer semiconductor where the critical features have been realized by a large-area compatible direct-writing technique, allowing to obtain a maximum frequency of transition of 19 MHz, as measured by means of Scattering Parameters (S-Parameters). This is the first report of solution-processed organic FETs characterized with S-Parameters.

Ionic silver functionalized ovine forestomach matrix \u2013 a non-cytotoxic antimicrobial biomaterial for tissue regeneration applications

BackgroundAntimicrobial technologies, including silver-containing medical devices, are increasingly utilized in clinical regimens to mitigate risks of microbial colonization. Silver-functionalized resorbable biomaterials for use in wound management and tissue regeneration applications have a narrow therapeutic index where antimicrobial effectiveness may be outweighed by adverse cytotoxicity. We examined the effects of ionic silver functionalization of an extracellular matrix (ECM) biomaterial derived from ovine forestomach (OFM-Ag) in terms of material properties, antimicrobial effectiveness and cytotoxicity profile.MethodsMaterial properties of OFM-Ag were assessed by via biochemical analysis, microscopy, atomic absorption spectroscopy (AAS) and differential scanning calorimetry. The silver release profile of OFM-Ag was profiled by AAS and antimicrobial effectiveness testing utilized to determine the minimum effective concentration of silver in OFM-Ag in addition to the antimicrobial spectrum and wear time. Biofilm prevention properties of OFM-Ag in comparison to silver containing collagen dressing materials was quantified via in vitro crystal violet assay using a polymicrobial model. Toxicity of ionic silver, OFM-Ag and silver containing collagen dressing materials was assessed toward mammalian fibroblasts using elution cytoxicity testing.ResultsOFM-Ag retained the native ECM compositional and structural characteristic of non-silver functionalized ECM material while imparting broad spectrum antimicrobial effectiveness toward 11 clinically relevant microbial species including fungi and drug resistant strains, maintaining effectiveness over a wear time duration of 7-days. OFM-Ag demonstrated significant prevention of polymicrobial biofilm formation compared to non-antimicrobial and silver-containing collagen dressing materials. Where silver-containing collagen dressing materials exhibited cytotoxic effects toward mammalian fibroblasts, OFM-Ag was determined to be non-cytotoxic, silver elution studies indicated sustained retention of silver in OFM-Ag as a possible mechanism for the attenuated cytotoxicity.ConclusionsThis work demonstrates ECM biomaterials may be functionalized with silver to favourably shift the balance between detrimental cytotoxic potential and beneficial antimicrobial effects, while preserving the ECM structure and function of utility in tissue regeneration applications.

A finite-element technique for flows in the single screw extruder using a partial periodic unit

It is of great importance to understand and predict screw characteristics (SC) during the single screw extrusion process for the extruder design and the operation optimization. In order to simulate SC effectively, we introduce the concept of a partial rotational fraction for a partial periodic unit of helical geometry in the metering section of the single screw extruder. In this work, the partial rotational fraction has been implemented with the finite element. We report that simple and accurate computation can be achieved at low computational cost in obtaining the three-dimensional flow field and three-dimensional screw characteristics in terms of material properties with the proposed partial period unit concept in the single screw extruder.

Energetic ions during plasma-enhanced atomic layer deposition and their role in tailoring material properties

Plasma-enhanced atomic layer deposition (PEALD) has obtained a prominent position in the synthesis of nanoscale films with precise growth control. Apart from the well-established contribution of highly reactive neutral radicals towards film growth in PEALD, the ions generated by the plasma can also play a significant role. In this work, we report on the measurements of ion energy and flux characteristics on grounded and biased substrates during plasma exposure to investigate their role in tailoring material properties. Insights from such measurements are essential toward understanding how a given PEALD process at different operating conditions can be influenced by energetic ions. Ion flux-energy distribution functions (IFEDFs) of reactive plasmas typically used for PEALD (O2, H2, N2) were measured in a commercial 200 mm remote inductively coupled plasma ALD system equipped with RF substrate biasing. IFEDFs were obtained using a gridded retarding field energy analyzer and the effect of varying ICP power, pressure and bias conditions on the ion energy and flux characteristics of the three reactive plasmas were investigated. The properties of three material examples—TiOx, HfNx and SiNx—deposited using these plasmas were investigated on the basis of the energy and flux parameters derived from IFEDFs. Material properties were analyzed in terms of the total ion energy dose delivered to a growing film in every ALD cycle, which is a product of the mean ion energy, total ion flux and plasma exposure time. The properties responded differently to the ion energy dose depending on whether it was controlled with RF substrate biasing where ion energy was enhanced, or without any biasing where plasma exposure time was increased. This indicated that material properties were influenced by whether or not ion energies exceeded energy barriers related to physical atom displacement or activation of ion-induced chemical reactions during PEALD. Furthermore, once ion energies were enhanced beyond these threshold barriers with RF substrate biasing, material properties became a function of both the enhanced ion energy and the duration for which the ion energy was enhanced during plasma exposure. These results have led to a better insight into the relation between energetic ions and the ensuing material properties, e.g. by providing energy maps of material properties in terms of the ion energy dose during PEALD. It serves to demonstrate how the measurement and control of ion energy and flux characteristics during PEALD can provide a platform for synthesizing nanoscale films with the desired material properties.