Silica Volume Fraction Research Articles

Predicting mechanical heterogeneity in glassy polymer nanocomposites via an inverse computational approach based on atomistic molecular simulations and homogenization methods

Probing the mechanical behavior of the region formed between a nanoparticle reinforcement and a polymer matrix in a polymer nanocomposite structure, denoted as the “interphase”, is a main challenge as such regions are difficult to investigate by experimental methods. Here, we accurately characterize the heterogeneous mechanical behavior of polymer nanocomposites, focusing on polymer/nanofiller interphases via a combination of nanomechanical simulations and numerical homogenization techniques. Initially, the global mechanical performance of a glassy poly(ethylene oxide) polymer nanocomposite reinforced with silica nanoparticles is studied using detailed atomistic molecular dynamics simulations for 1.9% and 12.7% silica volume fractions. Next, the polymer/silica interphase thickness is identified by probing the polymer atom-based density distribution profile in the vicinity of the nanofiller at equilibrium. On the basis of this thickness, the interphase is subdivided to check the position-dependent change in mechanical properties. Then, using continuum mechanics and atomistic simulations, we proceed to compute the effective Young’s modulus and Poisson’s ratio of the polymer/nanoparticle interphase as function of the distance from the nanoparticle. In the last step, an inverse numerical homogenization model is proposed to predict the mechanical properties of the interphase on the basis of a comparison criteria with the data from MD. The results were found to be acceptable, raising the possibility of accurately and efficiently predicting interfacial properties in nanostructured materials.

Percolation to jamming in polymethylvinylsiloxane/silica nanocomposites

Researchers have conducted extensive experimental and theoretical studies on the jamming transition of colloidal and granular suspensions, but the existence and characteristics of jamming transition in nanoparticle-filled polymers remain elusive. In this work, two kinds of polymethylvinylsiloxane/silica nanocomposites were studied. A liquid-solid transition was found at the silica volume fraction of about 5 vol%, corresponding to the percolation of particle agglomerates. At higher silica content (about 10 vol%), a solid-solid transition was found in yield stress, equilibrium modulus, and the contact stress between agglomerates. The characteristic length of the particle network and inter-molecular distance also showed a transition at this transition. This transition corresponds to the simultaneous jamming of particles inside agglomerates and between agglomerates. This bi-level jamming behavior is distinct from the well-known jamming behavior in soft or hard particulate suspensions. Moreover, the dependence of the yield stress and equilibrium modulus on the distance to the jamming concentration differs from the simulations using simple interaction models like harmonic and Hertzian models. It implies that the interfacial viscoelastic layer may offer additional attractive and adhesive interactions between nanoparticles, which is critical in the jamming of polymer nanocomposites.

Colloidal Photonic Composites with a Long-Range Order by Hot-Pressing Polymer Brush-Grafted Silica Colloids.

Colloidal photonic composites (CPCs) are unique optical materials that combine flexible and responsive polymers with colloidal photonic crystals, and they have promising applications in colorful displays, optical anticounterfeiting, and visual sensors. However, conventional self-assembly strategies for constructing CPCs via solvent evaporation have faced limitations due to the meticulous regulation required during the evaporation process and typically long preparation durations. Here, we present an external force method to achieve a long-range ordered arrangement in CPCs by hot-pressing poly(2-[[(butylamino)carbonyl]oxy]ethyl acrylate (PBCOE)) brush-grafted silica colloidal particles (SiO2-g-PBCOE). We show that the hot-pressing conditions (i.e., temperature and pressure) and the silica volume fraction (φsilica) of the SiO2-g-PBCOE colloidal particles play crucial roles in determining their ordering and optical properties. By optimization of the hot-pressing temperature up to 100 °C and pressure of 5 MPa, a long-range ordered arrangement of SiO2-g-PBCOE colloidal particles with a φsilica of 20.3% can be achieved. For the effect of structural features, our findings reveal that SiO2-g-PBCOE colloidal particles featuring a higher φsilica are more prone to obtain a long-range ordered arrangement compared to a lower φsilica under hot-pressing conditions at relatively low temperature and pressure (50 °C and 5 MPa), which is mainly attributed to the chain entanglement and hydrogen bonding interactions induced by grafted longer polymer brushes, leading to additional energy inputs and weakening the ordering. Significantly, the critical φsilica (φc) of SiO2-g-PBCOE colloidal particles is discerned, strongly influencing the optical properties of the hot-pressed films. Specifically, a hot-pressed SiO2-g-PBCOE film with a critical φsilica of 29.3% displays enhanced optical properties characterized by intensified reflection peaks, narrowed full width at half-maximum (FWHM), and brilliant structural colors. Notably, in this work, we reveal the mechanism of hot-pressing-driven core-shell colloidal particle ordering and the key factors affecting the ordering of colloidal particles, i.e., chain entanglement and hydrogen-bonding interactions, which play a crucial role in obtaining CPCs with controllable structures. Moreover, angle-dependent structural color is observed in the hot-pressed SiO2-g-PBCOE film with a φsilica content of 29.3% due to the unique attributes of the highly ordered arrangement, while the films exhibit mechanochromic properties due to chain entanglement and hydrogen bonding interactions. This work provides valuable insights into the rapid construction of highly ordered CPCs and establishes a solid foundation for external force-assisted ordering of colloidal particles.

Modeling the rheological behavior of silica filled rubber compounds

The rheological behavior of styrene–butadiene rubber (SBR) compounds filled with silica is investigated as a function of silica volume fraction. To predict the mechanical response, a continuum model for entangled polymer melts filled with nanoparticles is herein introduced. This model is capable of describing the rheological response in both the linear and nonlinear viscoelastic regimes in the context of non-equilibrium thermodynamics to guarantee its thermodynamic admissibility. The constitutive model describes the polymer nanocomposite melts at a mesoscopic level of description by considering the conformation tensor between successive entanglement points, and the orientation tensor for the, in general, spheroidal nanoparticles that describes their average orientation. Evolution equations are developed for nanoparticles with an arbitrary shape but are eventually specified to the case of spherical ones. The multimode version of the new constitutive model provides a very accurate prediction of the rheological behavior of the processability range of SBR/silica nanocomposites. Thus, the new model is a tool able to provide answers to the several difficulties that rubber-producing manufacturers face when processing rubber compounds.

Hard-Templated Porous Niobia Films for Optical Sensing Applications

Porous Nb2O5 films obtained by a modified hard-template method were studied and their optical and sensing properties were optimized in order to find applications in chemo-optical sensing. Porous films were prepared by following three steps: liquid mixing of niobium sol and SiO2 colloids in different volume fractions, thermal annealing of spin-coated films for formation of a rigid niobia matrix, and selective removal of silica phase by wet etching thus generating free volume in the films. The morphology and structure of the films were studied using transmission electron microscopy and selected area electron diffraction, while their optical and sensing properties were estimated using UV-VIS-NIR reflectance measurements in different ambiences such as air, argon and acetone vapors and nonlinear curve fitting of the measured reflectance spectra. Bruggeman effective medium approximation was applied for determination of the volume fraction of silica and air in the films, thus revealing the formation of porosity inside the films. For further characterization of composite films, their water contact angles were measured and finally conclusions about the impact of initial chemical composition and etching duration on properties of the films were drawn.

Ultra‐low loss polyphenylene oxide‐based composites with negative thermal expansion fillers

AbstractThe mismatch of coefficient of thermal expansion (CTE) of components has created numerous reliability issues in electronic packages. Incorporating inorganic fillers into polymer matrices has been proven to be an effective way to reduce the CTE, but properly balancing CTE with other key properties of the composites is still a challenge. In the current work, negative thermal expansion Zr2WP2O12 (ZWP) particles were prepared by a high‐temperature solid‐phase synthesis method. Polyphenylene oxide (PPO)‐based composites with different volume fractions (0, 10, 20, 30 vol%) of ZWP particles were prepared and their thermal expansion and dielectric properties were characterized. PPO/silica composites with the same volume fractions of silica were also prepared and characterized for comparison. With the content of filler increased from 0 to 30 vol%, the CTE of the PPO/ZWP composites reduced from 74.2 to 45.4 ppm/°C, which is more significant than that of the PPO/silica composites (48.0 ppm/°C with 30 vol% silica). Meanwhile, the dielectric loss of PPO/ZWP composites decreased significantly from 0.0024 (0 vol% ZWP) to 0.0018 (30 vol% ZWP) at 10 GHz, which is better than PPO/silica composites (0.0019 with 30 vol% Silica). The PPO/ZWP composites exhibit excellent comprehensive properties, which may be promising materials for high‐frequency applications in electronic packaging fields.

Recycled soda lime silica glass inclusion in polytetrafluoroethylene matrix as reinforcement for microwave substrate application

AbstractRecycled soda lime silica glass‐filled polytetrafluoroethylene composites were prepared for substrate application at microwave frequencies. Various volume fractions (0.05–0.25) of the filler were dispersed in the polytetrafluoroethylene matrix. The composites’ dielectric, mechanical, and thermal properties were examined with respect to the filler content. X‐ray diffraction data established the phase structure of the polytetrafluoroethylene matrix and recycled soda lime silica glass. Scanning electron microscope micrographs revealed uniform filler distribution at lower recycled soda lime silica contents, while energy dispersive x‐ray analysis showed the purity of the composites. The tensile strength of the composites reduced from 13.5 MPa to 4.26 MPa, while the moisture absorption and density raised from 0.07 % and 2.195 g/cm3 to 0.19 % and 2.228 g/cm3 when the recycled soda lime silica filler volume fraction was adjusted from 0.05–0.25. The lowest coefficient of thermal expansion values was recorded at 0.25 % recycled soda lime silica volume fraction, which increased from 31.12 ppm/°C to 68.32 ppm/°C at 40 °C to 200 °C. At 0.05 filler volume fraction, the respective values of , and of the composites decreased from 2.20, 0.0017, and 29.69 ps to 2.15, 0.0015, and 29.35 ps in the 8.2 GHz–12.4 GHz range.

Unusual High-Frequency Mechanical Properties of Polymer-Grafted Nanoparticle Melts.

Brillouin light spectroscopy is used to measure the elastic moduli of spherical polymer-grafted nanoparticle (GNP) melts as a function of chain length at fixed grafting density (0.47 chains/nm^{2}) and nanoparticle radius (8nm). While the moduli follow a rule of mixtures (Wood's law) for long chains, they display enhanced elasticity and anomalous dissipation for graft chains <100 kDa. GNP melts with long polymers at high σ have a dry zone near the GNP core, surrounded by a region where the grafts can interpenetrate with chain fragments from adjacent GNPs. We propose that the departures from Wood's law for short chains are due to the effectively larger silica volume fraction in the region where sound propagates-this is caused by the short, interpenetrated chain fragments being pushed out of the way. We thus conclude that transport mechanisms (of gas, ions, sound, thermal phonons) in GNP melts are radically different if interpenetrated chain segments can be "pushed out of the way" or not. This provides a facile new means for manipulating the properties of these materials.

Experimental analyzing the static puncture resistance performance of shear thickening fluid impregnated polypropylene hybrid composite target structures for armour application

The challenges of today’s protective material developers' requirements for body armour target structure design, strength, stiffness, and light weight structures have historically come from composite structures having high cost, complex manufacturing, and time-consuming process. Hence, there is a need to identify suitable alternate materials with reliable composites and essential design requirements for high impact armour structures. At present, hybrid composite structures are increasingly utilized in armour structure developments because they offer quick adoption to produce low cost, high impact strength, and a methodology for easy and quick manufacturing process without compromising the performance of traditional composite structures. This experimental analysis reports that the prepared hybrid composite target structures are composed of woven polypropylene fabric impregnated with single, double, and triple layers with a prepared shear thickening fluid (STF) concentration (50 vol% silica dispersed in polyethylene glycol 600 g/mol) used as a core layer in this structure and a neat/silica gel coated aluminum face sheet is used as the skin material. The prepared STF is characterized through rheological analysis exhibits shear thickening behavior reveals that extensively depends on silica particle morphology, volume fraction, and particle size distribution. The prepared hybrid composite target structure test results demonstrate a significant enhancement in tensile strength, modulus, better peel resistance properties, and puncture resistance evaluated in different geometry of projectiles like flat, hemispherical, elliptical, and conical indentor penetration velocity at 500 mm/min have been performed to demonstrate the improvements in the target structure. It enhances the performance layer thickness increases with increasing puncture resistance for all indentors sequently identified and penetration damage of target structures varied with respect to indentor nose head surface area of contacts.

Static puncture resistance characteristics with various indenter nose shape geometry perforation of shear thickening fluid impregnated polypropylene fabric for soft armour application

At present, puncture resistance and rheological performance of shear thickening fluid (STF) is an essential design requirement for a soft armour material (target sample). The target sample is prepared with a dip and dry process of STF impregnated woven polypropylene (PP) fabric. These samples were tested and compared with neat PP fabric. The penetration depth of target samples is highly sensitive to the coefficient of friction between the indenter’s nose shape geometry and the target sample. The STF is prepared by mechanical dispersion of synthesized microsphere silica microparticles at a volume fraction of 57% in polyethylene glycol (400 g/mol). The rheological response indicates that the prepared concentration of silica microparticles in the STF suspension is observed to have a better shear thickening effect. The viscosity of suspension is highly sensitive to silica aspect ratio, volume fraction and particle size distribution in this work. Tensile tests along with puncture resistance with different indenter nose shapes geometry (hemispherical, elliptical, flat and conical) have been performed in the present study. Results indicate that the energy absorption is more with the hemispherical indenter and less with that of the conical indenter, which is attributed to the minimum surface area of contact as compared to all other indenters. A total of 16 number of fabricated target samples with various coating thicknesses of STF impregnated fabrics achieved the desired tensile strength, modulus and puncture resistance.

Effects of fillers on the hydrogen uptake and volume expansion of acrylonitrile butadiene rubber composites exposed to high pressure hydrogen: -Property of polymeric materials for high pressure hydrogen devices (3)-

To develop sealing materials for high-pressure hydrogen devices, the effects of filler type and amount on the hydrogen uptake and volume expansion of rubber composites were evaluated up to 90 MPa. The amount of hydrogen in the rubber matrix and carbon black was elucidated using nuclear magnetic resonance, and the hydrogen elimination behavior of the composites was analyzed by thermal desorption analyses. As hydrogen physically adsorbed on carbon black, the hydrogen uptake of carbon black-filled composites increased. The hydrogen uptake of the composites filled with nonabsorbent silica was smaller, depending on the weight fraction of silica. The ratio of volume expansion to the amount of hydrogen in the matrix of carbon black-filled composites was suppressed by the reinforcement effect of carbon black, which did not expand with hydrogen uptake. The suppression of silica-filled composites was limited by the volume fraction of silica.

Concerted effect of boron and porosity on shear thickening behavior of hybrid mesoporous silica dispersions

In the present work, the influence of porosity and boron on shear thickening behavior of hybrid mesoporous silica has been studied. Three different levels of boron modification were performed by varying the molar composition of boric acid viz., 1.5 mmol, 2.5 mmol, and 3.5 mmol in a co-condensation approach. The incorporation of boron in mesoporous silica network was confirmed by various techniques such as Fourier transform infra-red (FTIR), and 11B solid- state nuclear magnetic resonance (NMR) spectroscopy. The morphology and particle size were confirmed by using scanning and transmission electron microscopy. To evaluate the effect of boron and porosity on the shear thickening behavior, dispersions were prepared from mesoporous boron- modified silica (MSiB), control mesoporous silica (MSi), non-porous boron-modified silica (SiB), and control non-porous silica (Si) in polyethylene glycol. The shear thickening behavior was studied using steady shear rheology. The dispersion prepared from different loadings of synthesized MSiB containing 1.5 mmol boron showed more than 16 times increase in viscosity (657.7 Pa.s) compared to that of MSi (39.2 Pa.s) at a fairly low volume fraction (φ = 0.15) of silica. It is expected that the highly ordered mesoporous architecture of hybrid silica has improved the interaction between the particle and the dispersing medium through hydrogen bonding. The porous morphology of the hybrid mesoporous silica as well as the incorporation of boron in the silica network favors the formation of a frictional contact network, and a transition from continuous shear thickening (CST) to discontinuous shear thickening (DST) behavior was observed. Therefore, silica prepared via incorporation of boron as well as porosity can be material of interest in variety of applications, for example, soft body armors, sporting goods, and shear thickening electrolytes for high impact resistant batteries.

Silica Fouling in Reverse Osmosis Systems-Operando Small-Angle Neutron Scattering Studies.

We present operando small-angle neutron scattering (SANS) experiments on silica fouling at two reverse osmose (RO) membranes under almost realistic conditions of practiced RO desalination technique. To its realization, two cells were designed for pressure fields and tangential feed cross-flows up to 50 bar and 36 L/h, one cell equipped with the membrane and the other one as an empty cell to measure the feed solution in parallel far from the membrane. We studied several aqueous silica dispersions combining the parameters of colloidal radius, volume fraction, and ionic strength. A relevant result is the observation of Bragg diffraction as part of the SANS scattering pattern, representing a crystalline cake layer of simple cubic lattice structure. Other relevant parameters are silica colloidal size and volume fraction far from and above the membrane, as well as the lattice parameter of the silica cake layer, its volume fraction, thickness, and porosity in comparison with the corresponding permeate flux. The experiments show that the formation of cake layer depends to a large extent on colloidal size, ionic strength and cross-flow. Cake layer formation proved to be a reversible process, which could be dissolved at larger cross-flow. Only in one case we observed an irreversible cake layer formation showing the characteristics of an unstable phase transition. We likewise observed enhanced silica concentration and/or cake formation above the membrane, giving indication of a first order liquid–solid phase transformation.

Rheological and Mechanical Properties of Silica/Nitrile Butadiene Rubber Vulcanizates with Eco-Friendly Ionic Liquid.

In this paper we designed greener rubber nanocomposites exhibiting high crosslinking density, and excellent mechanical and thermal properties, with a potential application in technical fields including high-strength and heat-resistance products. Herein 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc) ionic liquid was combined with silane coupling agent to formulate the nanocomposites. The impact of [EMIM]OAc on silica dispersion in a nitrile rubber (NBR) matrix was investigated by a transmission electron microscope and scanning electron microscopy. The combined use of the ionic liquid and silane in an NBR/silica system facilitates the homogeneous dispersion of the silica volume fraction (φ) from 0.041 to 0.177 and enhances crosslinking density of the matrix up to three-fold in comparison with neat NBR, and also it is beneficial for solving the risks of alcohol emission and ignition during the rubber manufacturing. The introduction of ionic liquid greatly improves the mechanical strength (9.7 MPa) with respect to neat NBR vulcanizate, especially at high temperatures e.g., 100 °C. Furthermore, it impacts on rheological behaviors of the nanocomposites and tends to reduce energy dissipation for the vulcanizates under large amplitude dynamic shear deformation.

Evaporation-driven self-assembly of binary and ternary colloidal polymer nanocomposites for abrasion resistant applications

We harness the self-assembly of aqueous binary latex/silica particle blends during drying to fabricate films segregated by size in the vertical direction. We report for the first time the experimental drying of ternary colloidal dispersions and demonstrate how a ternary film containing additional small latex particles results in improved surface stability and abrasion resistance compared with a binary film. Through atomic force microscopy (AFM) and energy-dispersive X-ray spectroscopy (EDX), we show that the vertical distribution of filler particles and the surface morphologies of the films can be controlled by altering the evaporation rate and silica volume fraction. We report the formation of various silica superstructures at the film surface, which we attribute to a combination of diffusiophoresis and electrostatic interactions between particles. Brownian dynamics simulations of the final stages of solvent evaporation provide further evidence for this formation mechanism. We show how an additional small latex particle population results in an increased abrasion resistance of the film without altering its morphology or hardness. Our work provides a method to produce water-based coatings with enhanced abrasion resistance as well as valuable insights into the mechanisms behind the formation of colloidal superstructures.

Use of silica particles to improve dispersion of -COOH CNTs/carbon fibers to produce HyFRCC

The development of hybrid fiber reinforced cement composite that has high strength, scope to be used as cement-based sensors has been investigated in this study by using a combination of carbon fibers and carbon nanotubes (CNT) at low volume fraction. The dispersion of CNTs was enhanced by using polycarboxylate based superplasticizer that resulted in a homogeneous aqueous stable solution, and profoundly improved dispersion when integrated with the cementitious matrix. Different siliceous additives were also incorporated into the mixes to improve the dispersion of CNTs in the matrix, where micro-silica outperformed as compared to nano-silica, confirmed morphologically. On the other hand, nano-silica enhanced dispersion of milled carbon fibers in the aqueous state. The sensing behavior was determined by the measurement of bulk resistance of mixes and the samples were subjected to compressive loading to study the strength improvement with the incorporation of fibers. The experimental results reveal that hybrid combination of chopped carbon fibers, micro silica, and low volume fraction of CNTs in a cementitious matrix results in a stronger and durable concrete that holds the potential for sensing applications. Thus, laying a strong foundation for the future of low cost smart cement based materials.

Effect of residue formed during the AC and DC dry-band arcing on silicone rubber filled with natural silica

This paper investigates the residue formed on silicone rubber filled with natural silica in the inclined plane tracking and erosion test under AC and DC voltages. Simultaneous thermogravimetric and differential thermal analyses reveal residue formation dependent on volatilization and crosslinking in silicone rubber. Thermo-oxidation of volatiles yields silica-based residue protecting the surface during dry-band arcing; whereas, crosslinking leaves carbonaceous residue leading to more severe dry-band arcing. Volume fraction of natural silica replacing silicone rubber is shown to be a main source of silica residue suppressing carbonaceous residue, thus preventing failure in the inclined plane test. More severe erosion under the equivalent +DC voltages as compared to standard AC and equivalent — DC voltages of the inclined plane test is attributed to more severe dry-band arcing heat promoted by carbonaceous residue. Silicone rubber filled with lower particle sizes of natural silica is demonstrated to deteriorate erosion performance, possibly as result of filler-polymer interactions or lower particle size reducing the integrity of the protective silica residue. The following paper highlights the importance of using critical AC and DC voltages during the inclined plane tracking and erosion tests.

Evaluating the internal structure of monodispersed mesoporous silica spheres by small-angle X-ray scattering

Although the spherical morphology and mesoporous structure of monodispersed mesoporous silica spheres (MMSS) have been extensively investigated by scanning electron microscopy and transmission electron microscopy, the statistical distribution of mesopores from the surface to the center of a particle, average density of the spheres, and volume fraction of silica have not been investigated. Herein, small-angle X-ray scattering (SAXS) was performed on aqueous dispersions of MMSS with diverse sphere diameter, mesopore radius, and nanoparticle inclusion. The SAXS spectra fitted by a spherical model showed that the mesopores were homogeneously distributed in each particle. The mass density of the MMSS was obtained from the zero scattering intensity, and the volume fraction of silica was calculated considering the absorbed water in the pores. While the sphere diameter and mesopore radius had little influence, nanoparticle inclusion induced an increase in the volume fraction of silica.

Influence of Ionic Liquids on Structure and Rheological Behaviors of Silica-Filled Butadiene Rubber

Nanoparticle dispersion is important for the performance of rubber compounds. Herein, ionic liquids (ILs) and silane are used to prepare silica-filled butadiene rubber vulcanizates. The results show that replacement of a half of silane by ILs could greatly improve the dispersions of silica and zinc oxide, restrain the migration of sulfur and other additives inside the composite, and maintain the cross-linking degree of the matrix possibly by suppressing the adsorption of sulfur and other additives by silica. The regulated filler dispersity and matrix cross-linking strongly influence the dynamic rheological behaviors of the vulcanizates as a function of silica volume fraction. In comparison with silane, the introduction of ILs could improve the reinforcement effect, reduce energy dissipation, and lower the frequency dependences of loss modulus and loss tangent in the linear region.

Solid State Additive Manufacturing of Acrylonitrile Butadiene Styrene with Silica Augmentative: Application of Friction Stir Processing

The additive manufacturing processes are increasing their importance in fabrication of composite like structures. Friction stir processing is classified as a solid state additive manufacturing technique that is used for lamination or powder deposition in a matrix substrate. In the present work an attempt was made to add the silica as secondary phase into the acrylonitrile butadiene styrene (ABS) surface for enhancing the mechanical and surface properties of fabricated composite. The parameters such as amount of silica fraction, pass number, tool rotational speed and linear speed were considered to be involved in the study. The responses surface method (RSM) was used here to assess relationship between aforementioned inputs and outputs vs bending strength and deflection before fracture. Optimal setting of process parameters was determined by maximizing bending strength and deflection. The obtained optimal results showed that maximum strength and deflection can be achieved by selecting of 100% silica volume fraction, 1 pass number, 1400 rpm tool rotation and 80 mm/min travel speed. The optimum results were further verified through confirmatory experiment and the result showed that the values of prediction error for bending strength and deflection are 6.1% and 8.5%, respectively. This proves the validity of the proposed approach for empirical modeling and optimization of friction stir additive manufacturing process.