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INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING–GREEN TECHNOLOGY Vol. X, No. X, pp. X-XX XXXX 201X / 1

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1. Introduction

Over millions of years of evolution, nature provides an opportunity for us to benefit from considerable diversity of solutions. It shapes limited building blocks into delicate natural materials that own the incomparable properties by modulating its microstructures. Many natural materials such as stomatopod dactyl club seemingly circumvent the trade-off faced by conventional synthetic materials, achieving its dual proficiency in satisfying high strength and toughness.1-9

Despite those tempting advantages, manufacturing biomimetic materials with analogous microstructures remains extremely difficult. The complete biomimetic process can be divided into three steps: (1) Extract the relevant design motifs based on the desired biological properties; (2) Devise approaches for translating design motifs found in natural materials to a wider range of material combinations; (3) Develop a suitable manufacturing process using the extracted design motifs to make bioinspired structural materials in practical form and in bulk.1

However, none of the problems mentioned above have been

perfectly solved, especially the last step. Some recent researches indicate, besides fabrication of objects with complex three dimensional geometry, additive manufacturing technologies (3D printing) also have great potentiality to fabricate intricate microstructural materials that are not accessible by conventional processing routes. Such techniques would unleash the true power of additive manufacturing, in that the printing process could directly couple spatial variations in composition with structural features of components. In the past few years, several specifically modified 3D printing processes were developed to fabricate reinforced composites with designed microstructures.

Lewis has aligned carbon fiber reinforced inks by flowing it through the extrusion head and printed bioinspired cellular composites.10 Joshua J. Martin has designed bioinspired composite reinforcement bone architectures via 3D magnetic printing.11 Yang has printed bouligand architectures by electrically assisted nanocomposite 3D printing.12 Yunus has taken Digital Light Procession (DLP) 3D printing process to align the fibers with lateral oscillation.13

Except for the field-assisted deposition methods, M. Mirkhalaf

DOI: XXX-XXX-XXXXISSN 2288-6206 (Print) / 2198-0810 (Online)

3D Printing of Bioinspired Structure Materials by Shear Induced Alignment of Fibers Using Doctor Blading Spread Process

Luquan Ren1, Bingqian Li1, Zhengyi Song1, Qingping Liu1,#, Lei Ren1,2,# and Xueli Zhou1

1 Key Laboratory of Bionic Engineering (Ministry of Education), Jilin University, Changchun 130022, China2 School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester M13 9PL, UK

# Corresponding Author / E-mail: [email protected], [email protected], TEL: +86-0431-85095760

KEYWORDS: 3D printing, Bio-inspired structure materials, Stereolithography, Fiber arrangement, Doctor blading

Fiber is a crucial element in biological micro-structural materials. Replication of fiber-reinforced composites with analogous architectures of their natural counterparts has caused widespread academic concern. Recent researches indicate 3D printing technology has the potential to produce biomimetic structural materials. The aim of this study is to develop a process to fabricate fiber-reinforced composites with ordered yet spatially tunable fiber arrangement. Specifically, we present a method to align fibers during the 3D printing of fiber-reinforced composites. A modified slurry-based stereolithography process was developed, and the fibers of the fiber-resin mixture were aligned by shear-induced effect during the spreading of slurry. We investigated the influence of relative factors on fiber orientation, and two models were used to uncover the inner mechanism. By controlling the speed and the direction of the moving blade, the patterns that fibers were arranged in can be freely programmed. Therefore, we have extracted bioinspired sinusoidal and zigzag design motifs to analyze the influence of some parameters on its mechanical properties. The proposed method is relatively material agnostic, more efficient and more economical. It thus provides a promising route to fabricate fiber-reinforced composites, and has potential to be adopted in broad research and industrial applicability.

Manuscript received: March XX, 201X / Revised: August XX, 201X / Accepted: December XX, 201X

2 / XXXX 201X INTERNATIONAL JOURNAL OF PRECISION ENGINEERING AND MANUFACTURING–GREEN TECHNOLOGY Vol. X, No. X

and Christ both used the non-field-assisted deposition method which exploited the friction between the blade and the fibers to align the fibers in the liquid and powdery matrix respectively.14-16 However, the doctor blading technique has not combined with 3D printing, thus the fibers or particles can only be assembled in a single direction which lacks of bioinspired design. Therefore, the influence of processing parameters and material properties on fiber orientation and the orientation mechanism was not fully understood.

Compared to field-assisted method of fiber arrangement, non-field-assisted method used by M. Mirkhalaf and Christ is relatively material agnostic, requiring no specific material properties and pretreatment. More importantly, it can assemble materials with high solid content and high viscosity. Although it may have limited resolution and control degree of phase ordering, its process is more efficient and economical, which is suitable for building bulk materials. However, the influence of the processing parameters and material properties on the orientation and the orientation mechanism has rarely been reported.

In this paper, based on the shear-induced fiber orientation process and the slurry-based stereolithography 3D printing technique, we proposed a manufacturing method which can programme fibers' orientation and distribution during 3d printing of fiber-reinforced composites. In the process, fibers in the slurry (fiber-resin mixture) were shear-induced and oriented with the direction of spreading. By controlling the velocity (direction and magnitude) of the moving blade, the intended orientation and distribution of fibers could be realized. This investigation examined the influence of (1) fiber aspect ratio γ, (2) fiber volume fraction Ø and (3) layer thickness t on fiber orientation. Two models (fiber-wall model and fiber-fiber model) were utilized to analyze the orientation mechanism. Besides, based on the herringbone structure of the outer layer (impact region) of the mantis shrimp dactyl club,17-18 we designed and printed fiber-reinforced materials with bioinspired sinusoidal and zigzag microstructures. Simultaneously, we analyzed the strength and impact toughness of composites with and without bioinspired microstructures. Two mathematical models were cited to analyze the enhancement mechanism at last. Taken together, we demonstrated this material agnostic, more efficient and more economical induced non-field-assisted fiber-assembly method have potential in mesoscale fiber motifs design, which has great prospects in producing bioinspired structure materials.

2. Experimental

2.1 Materials and ProcessCarbon fibers and photo-resin were used to prepare slurry for 3D

printing. Two kinds of carbon fibers were selected in our experiment. The diameters of the fibers are both 7μm, and the aspect ratio are 150 and 15 respectively. Photo-resin (Clear FLGPCL04 - from Formlabs, America) was purchased as matrix of the slurry. The viscosity of the fiber-resin mixture can be tuned by fumed silica, and rheology of the slurry was characterized by viscometer (NDJ-8S - from TOOLSO, China). These materials were homogenized in a specific fraction with

a mechanical stirrer (FSH-2A, China) for 20 minutes, and ultrasonic treatment was implemented next to remove air bubbles for 0.5h. The diagram of doctor-blading 3D printing platform is showed in Fig. 1a. Compared to traditional powder bed 3D printing platform, our devices increased the DOF of the blade and building unit. The blade can move in both x and y-axis simultaneously, and the building unit can rotate around the z-axis (Fig. 1a). The 3D printing process is illustrated in Fig. 1b. Firstly, the slurry was poured into the resin container. Then the base of resin container moved up for 1.2 times layer thickness and the building unit moved down for one layer. The blade moved along the pre-programmed path during which the slurry was spread across the building unit to form a thin layer on the building unit and the fibers were oriented along the spreading direction of the blade. Then the photo-resin was cured by a customized DLP projector system. When the first layer was cured, the building unit rotated a specific angle and the blade returned its initial position. Subsequently, the printing process of the next layer would be repeated.

Fig. 1 Diagram of 3D printing platform using doctor-blading spread-ing process and its printing process. (a) The 3D printing platform, (b) process of aligning carbon fibers in photo curable resin with the assis-tance of shear-induced spreading.

2.2 Process characterization of shear-induced fiber orienta-tion

To figure out the influence of factors (motifs) and its parameters on fiber orientation, we considered the effect of fiber aspect ratio, fiber mass fraction, layer thickness and programmed design motifs on the degree of fiber orientation and the mechanical properties, as shown in Table 1.

Table 1 Factors affecting orientation of fibers

Fiberaspect ratio

Fiber mass fraction

Layerthickness

Designmotifs

1 150 1wt.% 0.1mm Line2 15 2wt.% 0.2mm Sinusoidal3 0.3mm Zigzag

Micrographia and Two Dimensional (2D) Fast Fourier Transform (FFT) were used to measure the degree of fiber orientation and evaluate the usability of fiber alignment process. To discover the mechanism underlying the shear-induced alignment of fibers, fluid mechanics models were cited to analyze the interplay between fibers and resin.


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2.3 Multilayer 3D models and mechanical testingIn order to compare the effects of different patterns on mechanical

properties, we have printed samples with the bioinspired sinusoidal, zigzag patterns and the line, random patterns of 1wt.% fiber A as illustrated in Fig. 2. Besides, for comparison of the effects of fiber content, we juxtaposed the line design motifs of 1wt.% and 2wt.%. Meanwhile, the fiber B with smaller aspect ratio was utilized to investigate the influence of aspect ratio. The samples were fabricated with the dimensions of 70 mm×10 mm×3 mm and three samples for each pattern. In order to test their impact resistance, the pendulum impact test (JB-300B - from ZHONGLITE, China) was conducted. The span selected is 40 mm and the impact speed is 5.2 m/s. Simultaneously, a compression test (HS-3001C - from HESON, China) was done to analyze the strength of the samples.

Fig. 2 Schematic of different patterns of fiber arrangement. (a) Line designs, (b) sinusoidal designs, (c) zigzag designs, (d) random distribution designs.

3. Results and discussion

3.1 The results of influencing parameters on fiber orientationAs shown in Fig. 3, the rheological behavior of the slurry with 1%

wt. fiber A and 0.1% wt. fumed silica addition has a pronounced shear thinning behavior, which will be beneficial to the shear-induced process.

Fig. 3 The rheological behavior of the slurry. (a) Schematic of the shear-induced process of the slurry, (b) the shear thinning behavior of the slurry (1% wt. fiber A and 0.1% wt. fumed silica addition).

To preprogramme the design motifs, we need to plan the travel

path of the blade by controlling its speed in both x axis and y axis, as shown in Fig. 4.

Fig. 4 Pre-programme the travel path by synthesizing the speed of blade in both x axis and y axis. (a) Line pattern with angle of 45°, (b) line pattern with angle of 30°, (c) curve pattern.

By programming the spreading speed and direction of the blading, line (Fig. 5a), sinusoidal (Fig. 5b) and zigzag design motifs (Fig. 5c) can be obtained. With the increase of the carbon fiber A, the aggregation of all the three designs is more pronounced (Fig. 5d).

To further evaluate the degree of fiber orientation, two Dimensional (2D) Fast Fourier Transform (FFT) was used to measure the fiber alignment. Pictures were randomly picked from line design monolayer samples using microscope. Then each image was cropped to the same pixel size and saved as a grayscale image in the TIFF graphics file format. Image J software supported by an oval profile plug-in was utilized to conduct the 2D-FFT analysis. The plug-in took the image bounded by an oval region and sampled the oval at equal angle.19-20

The FFT Frequency image with long stripes radiated from the center point represents the high frequency of the fibers arranged at the angle. In contrast, the FFT graph showing the circular white circle at the center is more a random alignment. In the normalized intensity values plot, the peak shape and height determine the degree of alignment, and the peak position indicates the principle axis of orientation of the fibers. The frequency plots were rotated 90°to correct the rotation induced by the 2D FFT analysis.

We compared the influences of layer thickness t (Fig. 6a, c, e), the fiber contentΦV (Fig. 6c, g) and fiber aspect ratio γ (Fig. 6c, i) on alignment. By comparing the FFT Frequency images and the normalized image pixel intensity values, we can get the conclusion that the degree of orientation is negatively related to the layer thickness t and fiber contentΦV but positively related to the fiber aspect ratio γ. In the next section, we will uncover the mechanism under the trends influencing the degree of orientation.



Fig. 5 Optical images of different aligning design motifs. (a) Line design, (b) sinusoidal design, (c) zigzag design of 1wt.% carbon fiber A,(d) line designs of 2wt.% carbon fiber A (Layer thickness of the four samples above are 0.2mm).

Fig. 6 FFT frequency images and angle 2D FFT analysis of different layer thicknesses, fiber contents and fiber aspect ratios. 1wt.% carbon fiber A with 0.1 (a, b), 0.2 (c, d) and 0.3mm (e, f) layer thickness. 2wt.% carbon fiber A with 0.2mm layer thickness (g, h) and 1wt% carbon fiber B with 0.2mm layer thickness (i, j). Images (a, c, e, g, i) are frequency plots. Images (b, d, f, h, i) are 2D FFT alignment plots for corresponding plot (a, c, e, g, i).

3.2 The mechanism under the aligning behavior of fibers in shear flow

Fiber motion and orientation in a simple shear flow without a solid boundary will tend to align in the shear direction with periodic rotations. Such periodic tumbling motion in simple shear flow was described by Jeffery's orbit.21 Different from Jeffery's orbit, the characteristics of fiber motion are affected by the existence of a solid wall and the fiber-fiber interactions.22-25

In our research, the flow of the slurry is managed by the moving blade. The blade has been regarded as the solid wall, and the degree of fiber orientation varies across the thickness of the sample. Therefore, the skin-core structure common to injection molded parts is observed.26 The skin part near the wall has a greater degree of alignment than the core far away from the wall. With the increasing concentration of the fiber, the experimental value deviates further from Jeffery's prediction value. Thus, a translation model and slender body theory-based solution was utilized to explain fiber-wall interactions and fiber-fiber interactions.

The translation model provides a theoretical support to the results that were obtained experimentally.22

Fig. 7 Schematic of the translation model for a fiber oriented parallel (a) and normal (b) to the wall.

When the fiber oriented parallel to the wall, as in Fig. 7a, the total

drag on the rod is given by

F1=2π η υ χ ε l [2+ε (−0.614+W Ι )+Ο(ε2 , ε rL )]

(1)

where W Ι, is defined by W Ι=2 Arcsinh l

L−3√1+ L2

l2 + 7 L2l

− L2

2 l2√1+ L2

l2

(2)

and r is the radius of the fiber and 2l is the length of the fiber. ε=¿¿is a small parameter. L is the distance from the centroid of the fiber to the wall, η is the viscosity of the fluid and υ χ is the translation velocity.

The angular velocity is calculated by

ω1=ε 3υ χ L2

l3 〔1+ l2

2L2

√1+ l2

L2

−1〕+Ο(ε2) (3)

When the fiber is moving parallel to the wall but is oriented normal to it (Fig. 7b), the total drag on the rod is given as

F2=4 π η υ χ ε l [2+ε (−1.386+WⅡ )+Ο ( ε2 )] (4)

where WⅡ, is defined by

WⅡ=(Ll+1) ln (1+ L

l )+( Ll−1) ln(1−L

l )+ l2 L (5)

If the rod is free to rotate, its angular velocity is

ω2=3

8 π l3 ηεL2 (6)

where L2 is the couple needed to maintain the orientation of the fiber normal to the wall.

L2=−2 π ηυ χ ε2 l2〔1+( L2

l2 −1) ln(1− l2

L2 )〕+Ο(ε 3) (7)

This model explained the following phenomenon: (1) The initial orientation of the fiber determines the angular velocity it experienced as it is placed close to the wall. A fiber perpendicular to the wall rotates faster than the fiber parallel to it. It explains that the fibers with the same aspect ratio and the same induced force have varying degree of orientation. (2) Increasing the length of the fiber will increase the fiber angular velocity and the effective shear rate. It means that the wall effect is higher for larger aspect ratio fibers and the larger aspect ratio fibers will get a greater degree of orientation. (3) When the center of the fiber is a fiber length away from the wall, the wall effect is small for a fiber moving parallel to the wall at any orientation, thus leading to the emergence of the core layer.


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Fig. 8 Superposition of the force and the torque exerted on the two fibers by each other and the imposed flow field.

With the increase of fiber concentration, the fiber-fiber interaction becomes more crucial for truly understanding the orientation and the motion of fibers. The Jeffery's model indicates that the fiber tends to rotate along its orbits in simple shear flow. However, in our experiment, the interaction between fibers changed their orbit such that the energy dissipation was minimized or the volume swept by the fiber was minimized. Ranganathan superposed the lubrication solution and the slender theory solution to determine the motion of two fibers interaction with each other.23-25 The lubrication solution is used to explain the force and torque exerted on two surfaces separated by small gaps and the slender theory solution is for the force and torque exerted by the fluid on the fibers as shown in Fig. 8. Ranganathan demonstrated that the fiber-fiber interaction would change its angular and linear velocity and thus would affect the orientation state, leading to non-homogeneity of fiber suspension. The deviation in the angular velocity from that predicted by Jeffery's theory and the experiment was found to increase as the distance of spacing between the fibers decreased. It is noteworthy that the spacing is positively related to the aspect ratio and the orientation degree but negatively related to the fiber concentration.

Based on the above two theories and data analysis, it indicates that when the layer thickness increases, the peak value of the normalized intensity values plot increases first and declines once over the thickness of the skin part as shown in Fig. 6a, c, e. In other words, when the thickness of the layer increases before getting to the 0.2mm thickness (the skin part), there is no core layer and the fibers are all well-aligned. Once over the thickness, for example 0.3 mm, the core layer will appear and the fibers in the core layer can not be aligned. The reason for the lower peak value of the normalized intensity values plot for the 0.1mm layer thickness sample is that the amount for the fibers of a thinner layer is small but the degree of orientation of thinner layer is greater. Therefore, the degree of orientation is negatively related to the layer thickness.

There are three concentration regions according to the fiber volume fraction ΦV and fiber aspect ratioγ: dilute, semi-concentrated and concentrated.24 The carbon fiber A (the aspect ratio of 150) of 1wt.% fraction and above belong to concentrated (the density of the fibers is 1.6g/cm3). The carbon fiber B (the aspect ratio

of 15) of 1wt.% fraction and below belong to semi-concentrated. When the concentration of the fibers is so high that over the lower limit of the concentrated regions (in our experiment, the lower limit is 0.67% for carbon fiber A), the steric interactions between fibers arise which can prevent the fibers from rotating freely into aligned orientations, causing the fiber to form an entangled mass instead. In addition, with the rising of fiber content, fiber agglomeration will also appear during blending the slurry. Both factors will lead to the decreased degree of alignment. As observed from the Fig. 6d, h, the peak value of the normalized intensity values plot falls from 0.189 to 0.155.

ΦV <1/γ ² dilute (8)1/γ ²<ΦV <1/γ semi-concentrated (9)

1/γ <ΦV concentrated (10)Considering the aspect ratio, the fiber with higher aspect ratio has

higher angular velocity and more effective shear rate, thus a large aspect ratio fiber is slow to leave an aligned orientation and quick to realign itself once it is out of alignment. So higher the aspect ratio is, easier it is to get the fibers well-aligned. It indicates that the peak value of the normalized intensity values plot falls from 0.189 to 0.109 with the decrease of aspect ratio in Fig. 6d, j.

3.3 Results of mechanical testingThe average impact energy and compression modulus of the

samples with the force exerted on the y-axis are shown in Fig. 9a and Fig. 9b. They indicate that the bioinspired designs own the highest impact energy and compression modulus by comparing zigzag and sinusoidal patterns with other designs. The samples with fibers of smaller aspect ratio has lower Young's modulus and lower impact energy value. The compression modulus and the impact energy value increase first and then decrease as the fiber content exceeds a critical value.

Fig. 9 Mechanical testing of multilayer 3D models. Impact energy (a) and compression modulus (b) of the different designs, fiber contents and fiber aspect ratios were compared (zigzag, sinusoidal, line and random represent different design motifs. A and B mean fiber A and fiber B. 1% and 2% mean the fiber content of 1wt.% fraction and 2wt.% fraction. Pure is matrix without fibers).

3.4 The influence of related factor on mechanical propertiesMost engineered materials are hard to satisfy high strength and

remain good toughness at the same time. To maintain strength and toughness, some nature materials feature based complex designs



frequently incorporate nanofibers and other build blocks.27-30 To understand the strengthening and toughening mechanism of fiber reinforced composites, many researches have been investigated in previous studies.

A cox model with Carman-Reifsnider correction was exploited to study the relationship between tensile modulus and some critical parameters.31-34

EC=(η0 η1 ECF−EM )ΦV +EM (11)

a=√ −3 EM

2 ECF ln ΦV, η1=1−tan ¿¿ (12)

where EC ,ECF,and EMrepresents the tensile modulus of composite, carbon fibers and the matrix, respectively. l is the length and d is the diameter of the carbon fibers. ΦV is the volume fraction of embedded carbon fibers. η0=1/5 for randomly oriented fibers and η0=1 for the aligned carbon fibers.

Besides, variation of elastic modulus with fiber orientation angle θ was modeled by using the theory of linear elasticity for orthotropic materials and Tsai–Hill criterion,35 respectively, and it was expressed as：

E (θ )=( cos4θEL

+ sin4 θET

+ 14( 1

G¿−2 υ¿

ET)sin22θ)

−1

(13)

where EL, ET , and G¿ are axial and shear elastic moduli, and υ¿ is Poisson ratio which is approximated 0.34 because of linear rule of mixture.θ is the angle between fiber orientation and loading direction.

However, the predicted results are higher than the experimental values. We assume the difference between the predicted results and experimental values is due to the fact that the compression force we exerted was not parallel to the fiber direction and the modulus parallel to the fiber is about 1000 times of the modulus perpendicular to the carbon fibers. Therefore, the elastic modulus we calculated is not exactly the compression modulus but less than the compression strength. What’s more, the discrepancy is also caused by ignoring the influence of aggregation while calculating the predicted results. Besides, in the mathematical model, we assume a perfect boundary condition between the fibers and the matrix.

However, in the actual living environment of mantis shrimp, it suffers more from impact than from compression. According to the mean work of fracture model proposed by the IR. E. ALLRED in 1973, impact toughness was related to the following factors.36-37

W =4 ΦV

rl ∫x=0

l /2

( l2−x)τ ( x ) xdx , for l ≤lc(14)

W =4 ΦV

rlc( rl c

l )∫x=0

lc

2

( lc

2−x )τ (x ) xdx , for l>¿ lc¿

(15)lc=

r σ f

τ(16)

Equations 14 and 15 were examined to determine the sensitivity of toughness to various material parameters: the fiber length l, the fiber radius r, the fiber volume fraction ΦV and the distance away from the end of the fiber x . As the fiber length l decreases to the critical length lc, fracture increasingly occurs by fiber pull-out rather than by fiber fracture. When the fiber length was just slightly less

than lc, fracture occurs exclusively by pullout and the toughness reaches maximum.

Equation 14 and 15 demonstrate such a way that the increase in fiber content will not only increase the amount of pull-out, but also reducing the fiber spacing cause higher shear stress concentrations. Equation 16 indicates that the critical fiber length is determined by the fiber radius r, the fiber stress in 1/2lc and the tangential stress τ exerted on the fiber through the yielding matrix.

Based on the above mathematical models of elastic modulus and impact toughness of composites and data analysis of Fig. 9, we can get the following conclusions:

(1) The bioinspired zigzag designs and bioinspired sinusoidal-architected designs own the highest impact energy and Young's modulus compared to other patterns with the same fiber aspect ratio and fiber volume fraction. We assume that the sinusoidal-arranged and zigzag-arranged fibers within the 3D printed samples mimics straighten upon compression, thus the bioinspired pattern is tougher and will absorb more impact energy.12

(2) The samples with fibers of smaller aspect ratio have lower degree of orientation, lower Young's modulus and lower impact energy value. Both the smaller aspect ratio and lower degree of orientation will lead to lower Young's modulus based on the equations 11 and 12. Since the work of fracture is controlled by the interfacial strength and there is a greater contact area exists in the slender fibers and the matrix, the fiber with smaller aspect ratio will have lower impact energy value.36

(3) When the fiber content exceeds the lower limit of concentrated regions (about 0.67%), the higher the fiber factions is, the lower the Young’s Modulus and the impact energy value are.24 Because of the low density of carbon fiber and the limitation of the process, a relatively small mass fraction will lead to the emergence of aggregation and thus leading to failure of the sample. The samples of 1wt.% and 2wt.% both exceed the lower limit. Thus, the Young's modulus and impact toughness of 2wt.% fraction are lower than the 1wt.% fraction. The result is consistent with previous reports of experimental work on fiber reinforcement during 3D printing.16

4. Conclusions

We devised a modified slurry-based stereolithography process which could easily tune the local microstructure through changing the speed of the blade and the building unit by the shear-induced effect during the spreading of slurry. The experimental results revealed that the de-gree of fiber orientation is negatively related to the layer thickness t and fiber contentΦV , but positively related to the fiber aspect ratio γ. The translation model and the slender theory solution (the lubrication solution) were exploited to analyze the fiber-wall effect and the fiber-fiber effect to clarify the underlying mechanism. By fabricating the multilayer 3D models, we demonstrated the bioinspired designs own the highest impact energy and compression modulus by comparing zigzag and sinusoidal architectures with other designs. The samples with fibers of smaller aspect ratio have lower modulus and lower im-pact energy. The compression modulus and the impact energy value


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increase first and then decrease as the fiber content exceed a critical value. A cox model and a fracture model were utilized to study the modulus and impact toughness of the composites. We demonstrate the relatively material agnostic, more efficient and more economical method could provide a promising route to fabricate fiber-reinforced composites, and has potential to produce biomimetic materials and other engineering materials.

ACKNOWLEDGEMENT

The authors thank the funding of Key Scientific and Technologi-cal Project of Jilin Province (No. 20170204061GX).

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