Article

Polymers and Polymer Composites

1–10
Mechanical behavior simulation: NCF/ ª The Author(s) 2018
Article reuse guidelines:

epoxy composite processed by RTM sagepub.com/journals-permissions

DOI: 10.1177/0967391118817174
journals.sagepub.com/home/ppc

Francisco Maciel Monticeli1, David Daou2, Mirko Dinulović2,

Herman Jacobus Cornelis Voorwald1 and
Maria Odila Hilário Cioffi1

Abstract
Considering aeronautics requirements, academies and industries are developing matrixes and reinforcements with
higher mechanical performance. The same occurs with the process where new studies focus on obtaining composites
with suitable matrix/reinforcement interface. The use of epoxy resin and carbon fiber with high mechanical perfor-
mance does not guarantee a composite with high mechanical properties, considering imperfections and void formation
along the laminate in case of inappropriate processing parameters. The aim of this article was to analyze and quantify the
mechanical behavior of polymer composite reinforced with continuous fibers using finite element methodology and
postprocessing software simulation. In addition, the classical laminate theory and finite elements were used to simulate
flexural and tensile tests of composite specimens. Simulation results were compared with experimental test results
using a carbon fiber noncrimp fabric quadriaxial/epoxy resin composite processed by resin transfer molding. Although
void volume fraction for structural materials presenting results under aeronautics requirements regarding of 2%,
imperfections like lack of resin and impregnation discontinuity showed an influence in tensile and flexural experimental
results. Experimental mechanical behavior decreased 10% of strength, in comparison with simulation results due to
imperfection on impregnation measured by C-Scan map. Improvement in processing procedures could able to provide
greater impregnation continuity, reducing defect formation and ensuring better matrix/reinforcement interface. As a
final conclusion, the process plays a role as important as the characteristics of reinforcement and matrix and, con-
sequently, the mechanical properties.

Keywords
Polymer composite, finite element analysis (FEA), mechanical behavior, porosity

Introduction
To produce quadriaxial laminate, laying up unidirectional fibers in different orientation is a waste of time and can make
errors when fibers are stacked in distinct angles. In order to optimize the stacked fiber direction and save time in laying up
process getting higher characteristics of composite reinforcement, a stitched fabric has been introduced in resin transfer
molding (RTM) manufacturing process. This type of fabric is known as noncrimp fabric (NCF).1–5
In composite, matrix is responsible for the reinforcement union as well as the distribution of applied tension through the
interface. Epoxy resin has great prominence for aeronautics application due to its higher elasticity modulus and tensile
strength compared with several polymeric matrices. It has yet the ability to get low viscosity with an increase in
temperature, which is an advantage for process in the RTM, for example.3–10
In aerospace industry, RTM is one among many new processing developments, but at the same time, it is one of the
most promising. The cost advantage can enable the aircraft industries to use some specific features of advanced compo-
sites such as weight saving potential, corrosion resistance, and high fatigue strength. The technique is based on resin

1
Department of Materials and Technology, Fatigue and Aeronautic Materials Research Group, School of Engineering, São Paulo State University
(Unesp), Guaratinguetá, Brazil
2
Department of Aerospace Engineering, Faculty of Mechanical Engineering (FEM), University of Belgrade, Beograd, Serbia

Corresponding author:
Francisco Maciel Monticeli, Department of Materials and Technology, Fatigue and Aeronautic Materials Research Group, School of Engineering,
São Paulo State University (Unesp), No. 333, Guaratinguetá 12516-410, Brazil.
Email: francisco_monticelli@hotmail.com
2 Polymers and Polymer Composites XX(X)

Figure 1. Porosity in carbon fiber composites.

injection which has shown a significant increase to produce light and efficient structures with a very high level of
mechanical performance and safety in aeronautical field.2,8,11,12
The preform complete impregnation must be guaranteed by the process. Inappropriate impregnation of fibers can
produce, as a consequence, dry spot areas with missing fiber/matrix adhesion between layers. The imperfections like dry
spots make the surface rough and irregular and decrease the mechanical resistance.13–15
Low fraction of voids and defects that eventually are formed in polymer composites during the process are important
factors to obtain a material with high performance. Porosity occurs during processing, which is a consequence of
entrapping bubbles, humidity, or inappropriate parameter processing, such as high viscosity, cure temperature, and cure
time out of adjustment. This fact evidences the importance of an adjusted processing to obtain a composite with a high
quality of interaction between reinforcement and matrix without defects. Figure 1 shows a superficial porosity present in a
carbon fiber composite.13,16–18
Together with experimental tests, mechanical and thermal behavior studies by numerical modeling are an ally to
extend the experimental comprehension of the materials. A three-dimensional simulation can predict material proper-
ties, allowing for the composite processing evaluation and the necessity of improvement modifications, for product
suitability. For a composite simulation close to reality, an accurate representation of the reinforcement and matrix
structure is required; only then, it will be possible to represent the complexity behavior of these materials. To contribute
to the use of complex three-dimensional simulations, industry and researchers have been using software in base of finite
element methodology (FEM).19–21
FEM is a numerical procedure determined to troubleshooters, subdivided geometrically into small portions in order to
evaluate the outline and to represent the continued dominance of the problem.22,23 The use of the FEM and postprocessing
(FEMAP™) software became feasible to simulate polymer composites reinforced with fibrous material, since it contem-
plates the classical laminate theory (CLT) used for geometry formulation and representation, which simplifies the
implementation of outline calculations.22–24
Even using high-quality materials, problems occurring during the process can damage the composite mechanical
properties, which prevents its uses in structural application. In composites with defects like voids, dry, wide, and twisted
fibers act as stress concentrators. Therefore, if partial impregnation occurs in the vicinity of a connecting zone among
elements, it can cause a discontinuity in integration with a consequent strength loss.15,25–27
The objective of this article was to quantify the absolute mechanical behavior of a composite (NCF carbon fiber/epoxy
resin) using the CLT and FEMAP software to simulate flexural and tensile tests. In addition, simulation results were
compared with experimental flexural and tensile test results of the composite processed by RTM. To verify its processing
effectiveness, porosity and impregnation measurements were taken along the composites’ specimen.

Materials and methods

CLT
The CLT was used to evaluate the elastic behavior of the quadriaxial orthotropic carbon NCF in order to describe the
mechanical behavior of each single layer, using the following parameters: Ef1, Ef2, Gf12, n 12, Em, Gm, n m, and t, which is
the total thickness of the used laminate. The Hooke’s law defines the stress/strain relation that is given by Equation (1)28
Monticeli et al. 3

Table 1. Mechanical properties of the reinforcement and the matrix.

Matrix type Prism EP2400

Modulus, Em (GPa) 3.4

Shear modulus, Gm (GPa) 1.6
Poisson’s ratio, n m 0.0625

Fiber type NCF IM7 (12 k) GP

Longitudinal modulus, Ef1 (GPa) 276

Transverse modulus, Ef2 (GPa) 23
In plane shear modulus, Gf12 (GPa) 27
Major Poisson’s ratio, n 12 0.35
Transverse shear modulus, Gf23 —

NCF: noncrimp fabric.

½R11  ¼ ½Qr   ½e or ½e ¼ ½Sr   ½R ð1Þ

whereby [R] is the stress tensor, and [Qr] and [Sr] are reduced stiffness matrixes (equation (2))
2R 3 2 3 2 3 2 3 2 3 2R 3
1 Q 11 Q12 0 e1 e1 S11 S 12 0 1
4 R2 5 ¼ 4 Q 21 Q22 0 5  4 e 1 5; 4 e 1 5 ¼ 4 S21 S 22 0 5  4 R2 5 ð2Þ
t6 0 0 Q66 g6 g6 0 0 S66 t6

Equation (3) is a matrix or an equation of transformation that connects the stress in the coordinate system of material
with the strain in a particular coordinate system that matches with the direction of the load, and Y is the angle that
determines the layer’s orientation relative to the main coordinate (equation (4))29–31
2 3 2 3
2R 3 2R 3 e1 ex
1 x 6 e 7 6 e 7
4 R2 5 ¼ ½T   4 Ry 5 or 6 1 1 7 ¼ ½T  6 1 y 7 ð3Þ
4 g 5 4 5
t6 ts 6 gs
2 2
2 3
m2 n2 2mn
½T  ¼ 4 n2 m2 2mn 5; m ¼ cos Y ; n ¼ sin Y ; h 22 ¼ 0:5; h12 ¼ 0:4 ð4Þ
mn mn m2  n2

Process via RTM

The laminate was processed using eight layers of carbon NCF (IM7-12 k) stitched by polyester yarn in the following
symmetrical sequence: [90 /45 /0 /45 ] with a total thickness of 3 mm. The approximate fiber fraction volume used was
61% to produce a material for structural application.
Epoxy resin PRISM® EP2400 from Cytec (Wrexham, UK) was used, injected at 120 m C for a suitable viscosity of
resin (90 mPas). The pressure of 2.5 bar (0.25 MPa) and vacuum of 500 mbar (0.05 MPa) were applied. The cure process
was performed at 180 C for 120 min; after cooling process, the laminate was extracted from the mold. The epoxy resin and
NCF data, presented in Table 1, were important to use in the laminate theory calculation.32

Programming via FEMAP

In FEMAP software, a three-dimensional structure was designed to simulate a plate shape of composite in each single test
dimension, illustrated in Figure 2. The distance between interaction points was 1 mm for the three directions. The load
applied, load direction, and support points were submitted according to each test and each American Society for Testing
and Materials (ASTM) standard. CLT results were uploaded to the software, in particular, the young’s modulus E1 and E2,
shear modulus G12, and the major Poisson’s ratio n 12, calculated for this specific composite. The final step was to insert the
load and simulate the flexural and tensile tests.32
The steering coordinates indicate the following arrangement: x – sample length; y – sample width; and z – sample
thickness, which in this case was 3 mm.
4 Polymers and Polymer Composites XX(X)

Figure 2. Composite (NCF/epoxy resin) designed by FEMAP. NCF: noncrimp fabric; FEMAP: finite element methodology and
postprocessing.

Figure 3. Specimen dimensions for the tensile test.

Ultrasonic inspection microscopy

Scanning acoustic microscopy (SAM) test for NCF composite was used to evaluate impregnation and to measure
imperfections along the experimental specimen, generated by composite processing. The test was performed using the
ultrasonic wave pulse-echo mode by SAM system, model PSS-600, from MATEC® obtaining an A-Scan graphic and
C-Scan map. A concave transducer with a frequency of 10 MHz was used, and the data were analyzed by using I-View
software, developed by MATEC®. Ultrasonic inspection resulted in a two-dimensional image of wave return, C-Scan
map. Each image was interpolated in an interactive three-dimensional surface construction, by using ImageJ software, for
impregnation discontinuity analysis along the laminate.

Void fraction analysis

To determine void volume fraction, matrix was digested by sulfuric acid, according to ASTM 3171 (Proceed B).33
Resulted fibers from the digestion process were removed from the acid solution using hydrogen peroxide and, finally,
washed with distilled water. For this test, it was possible to know the resin and fibers volume fraction, through Equation
(5). Void volume fraction was obtained by the difference between the fiber and resin fraction.
     
m f rc mi  mf rc
Vv ¼ 100  100 þ 100 ð5Þ
mi rr mi rm
where, Vv, void volume fraction (%); mf, final mass of the fiber (g); mi, initial composite mass (g); rc, composite specific
mass (g cm3); rr, reinforcement specific mass (g cm3); and rm, matrix specific mass (g cm3).

Tensile and flexural tests

Specimen for tensile test was prepared according to ASTM D 3039/D 3039M34 (Figure 3). The same dimension and
specifications of standard were used for the FEMAP tensile simulation. The tests were performed at Shimadzu AG-X, with
a load of 10 kN.
The three-point bending model was prepared according to the specification from ASTM D790,35 with a length of 48
mm (using the reason 16:1 between the length and the thickness). The test forward speed was 1.30 mm min1.

Results and discussion

The CLT results, presented in Table 2, were important to upload the reinforcement and matrix data in FEMAP software to
simulate the composite with real mechanical properties. FEMAP software uses unit in MPa for input and output data;
therefore, all units used were in MPa.
Monticeli et al. 5

Table 2. Laminate theory results.

Laminate data Result

Young’s modulus E1 1,696,860 MPa

Young’s modulus E2 11,118 MPa
Shear modulus G12 6378 MPa
Poisson’s ratio, n 12 0.24

Figure 4. Tensile simulation in FEMAP: (a) specimen; (b) stress level scale along the specimen (MPa). FEMAP: finite element meth-
odology and postprocessing.

Figure 5. Three-point bending simulated in FEMAP: (a) specimen; (b) stress level scale along the specimen (MPa). FEMAP: finite
element methodology and postprocessing.

A three-dimensional model designed in FEMAP was used to upload the composite behavior. Both composite design
specimens were done according to the ASTM. Figure 4 shows the tensile test in which the specimens were fixed on one
side and the load was applied on the other side, simulating the real test. The ultimate tensile strength was equal to 859
MPa, detected in the net area of specimen according to the scale presented in Figure 4(b).
6 Polymers and Polymer Composites XX(X)

Figure 6. C-Scan surface map.

Figure 7. C-Scan result for tensile specimens.

Figure 5 shows flexural strength simulation resulted from FEMAP software, test based on ASTM D790. The strength
value of 842 MPa was indicated by the specimen net area of fracture. Figure 5(b) represents the stress level scale along the
specimen, revealing the stress behavior, where maximum stress was found in net area. In specimen edges, it was observed
a negative value of the applied load, which is associated with the opposite load applied in the net area due to the three-
point flexural test configuration.
Ultrasonic inspection resulted in an attenuation image, called C-Scan map. The resulting image of ultrasonic inspection
indicates the variation in attenuation levels over the material, as a consequence of processing procedures.
From the C-Scan map, it was possible to assemble an interactive 3D surface image for better visual evaluation of
attenuation, shown in Figure 6. Black arrow indicates resin injection direction (Figure 6). It was detected discontinuities
referring to small difference during resin impregnation along the laminate. Higher return of wave generated bright colors
and represents better impregnation continuity. In contrast, lower wave return, represented by dark color, is the result of
voids or other defects.
According to Shiino et al.36 and Pelivanov et al.,37 resin has faster wave return than fiber; consequently, the white
coloration indicates resin accumulation. Resin-rich zone was found at composite injection region, which is related to
lower attenuation. On the other hand, higher attenuation was observed from the middle of the laminate, where it was
harder to resin impregnate the reinforcement.
For a precise evaluation of experimental tests, it was highlighted ultrasonic results for each specimen, presented in
Figures 7 and 8. The subscript T represents specimens for tensile tests, and F represents specimens for flexural tests.
Visually, it was difficult to observe variation in wave attenuation of specimens T1, T2, and T3, due to dispersion
between image results.
Meanwhile, specimen F1 showed the greater visual discontinuity than other specimens for flexural specimens. This
discontinuity could influence directly the material mechanical properties, the result of an inadequate fiber/matrix inter-
face. If discontinuity presented in specimen F1 presents sections with lack of resin, it would result in a stress concen-
tration, decreasing it mechanical strength.
C-Scan results showed a variation between specimen attenuation, observed by visual difference in wave return.
Numerical result of ultrasonic inspection provided the average of wave return (%) and standard deviation (SD) for each
specimen, as shown in Table 3.
Monticeli et al. 7

Figure 8. C-Scan result for flexural specimens.

Table 3. Average and standard deviation of acoustic inspection signal return.

Specimens Average wave (%) Standard deviation

T1 39.05 3.08
T2 38.25 3.32
T3 37.59 2.98
F1 22.26 10.75
F2 27.75 5.25
F3 28.56 4.70
T: tensile test; F: flexural test.

Table 4. Void fraction volume of the composite.

Identification Void fraction volume (%) Void average (%)

1 1.95 1.95 + 0.15

2 2.09
3 1.89
4 1.73
5 1.52

Table 5. Tensile test results.

Identification Tensile strength (MPa) Tensile average (MPa)

T1 770 771 + 7
T2 779
T3 764

Values of wave return normally found in literature have high disparity, between 20% and 50%, due to the intrinsic
anisotropy of this material.36–39 SD is associated with materials’ homogeneity. In other words, high SD values mean
heterogeneity in impregnation. T1, T2, and T3 values presented a considerably low SD and average wave return close to
each other, confirming visual analysis.
Wave return values for F specimens were lower, and there was a high discrepancy between SDs, especially for
specimen F1, which presented higher deviation. With this statement, it is possible to conclude that F1 presented higher
discontinuity in impregnation compared with other specimens and also certify previous visual analysis.
One concern for composites with structural application is to have less than 2% of void volume fraction. Table 4 shows
porosity fraction result of the laminate. Void volume fraction results were very close to each other. Even with the dis-
continuity found in ultrasonic inspection result, it can be considered that this composite is within aeronautical requirements.
Experimental test results, with average value and SD, were represented in Tables 5 and 6, for tensile and flexural tests,
respectively.
SD values exhibited in mechanical test results were a consequence of the discontinuity in resin impregnation during
processing. Figure 9 shows the relation between the discontinuity degree and mechanical properties, evidencing the
influence of impregnation discontinuity on the material mechanical properties.
8 Polymers and Polymer Composites XX(X)

Table 6. Flexural test results.

Identification Flexural strength (MPa) Flexural average (MPa)

F1 727 759 + 28
F2 771
F3 781

Figure 9. Comparative relation between mechanical behavior and discontinuity degree.

Divergence between the results of experimental tensile test was only 1%, evidencing the same mechanical
characteristic between specimens. The proximity between wave return values guaranteed greater continuity and
homogeneity in the tensile specimens’ impregnation. These factors promoted the low divergence found in the tensile
test results. In contrast, the discrepancy between wave return SD for flexural specimens increased the divergence
between experimental results for 4%. Divergence was evidenced by F1 specimen, which had higher heterogeneity
and lower flexural strength.
In FEMAP simulation, there was no variation in results, for being a material without any discontinuity or
defects. Experimental results for tensile and flexural tests decreased 10% (approximately 100 MPa) of strength
than those provided by simulation, which are associated with imperfections occurred during the processing for
experimental tests.
Another important point to be considered is the influence of defects on mechanical behavior, as void volume
fraction and impregnation discontinuity had same influence on tensile and flexural behaviors. As a result
of heterogeneity in impregnation, experimental mechanical strength results decreased in comparison with simula-
tion values.

Conclusions
The use of FEMAP software allows the composite mechanical behavior simulation with a high performance, considering
that simulation results presented mechanical behavior very similar to experimental results. Uploading the CLT results, it
was feasible to set comparison parameters with experimental results, in which it was possible to quantify the absolute
tensile and flexural strength. In addition, the simulation of mechanical behavior allowed the visual analysis of the stress
along the specimens, evidencing the FEMAP simulation advantage. As a matter of fact, it is possible to simulate the
mechanical behavior for different composites prior to the material process.
The RTM process is feasible for aeronautic requirements with a good cost benefit. At the same time, even with void
fraction less than 2%, as aeronautic request for dry fabrics, the tensile and the flexural strength decreased 10% (100 MPa),
due to residual stress caused by impregnation defects exhibited in C-Scan analysis. Therefore, even a composite with
appropriate materials for structural application, problems in the process may result in a weak fiber/matrix adhesion.
Processing improvement is able to provide greater impregnation continuity, reducing defect formation and avoiding loss
of mechanical properties. As a conclusion, process plays a role as important as the characteristics of reinforcement and
matrix and, consequently, the composite properties.
Monticeli et al. 9

Acknowledgments
The authors acknowledge the financial support from the Fundação de Amparo à Pesquisa do Estado de São Paulo (process numbers:
2015/19967-4 and 2016/07245-7), Coordenação de Aperfeiçoamento de Pessoal de Nı́vel Superior – Brasil, and International Asso-
ciation for the Exchange of Students.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The
author(s) received financial support for the research from FAPESP (process numbers: 2015/19967-4 and 2016/07245-7), CAPES –
Brasil, and International Association for the Exchange of Students.

References
1. Drapiera S, Monattea J, Elbouazzaouia O, et al. Characterization of transient through-thickness permeabilities of Non Crimp New
Concept (NC2) multiaxial fabrics. Compos A 2005; 36: 877–892.
2. Brocks T, Shiino MY, Cioffi MOH, et al. Experimental RTM manufacturing analysis of carbon/epoxy composites for aerospace
application: non-crimp and woven fabric differences. Mater Res 2013; 16(5): 1175–1182.
3. Bel S, Boisse P and Dumont F. Analyses of the deformation mechanisms of non-crimp fabric composite reinforcements during
preforming. Appl Compos Mater 2011; 19(3): 513–528.
4. Dell’anno G, Treiber JWG and Partridge IK. Manufacturing of composite parts reinforced through-thickness by tufting. Robot Cim
Int Manuf 2016; 37: 262–272.
5. Margossian A, Bel S and Hinterhoelzl R. Bending characterisation of a molten unidirectional carbon fibre reinforced thermoplastic
composite using a dynamic mechanical analysis system. Compos A 2015; 77: 154–163.
6. Tsanzalis S, Karapappas P, Vavouliotis A, et al. Enhancement of the mechanical performance of an epoxy resin and fiber reinforced
epoxy resin composites by the introduction of CNF and PZT particles at the microscale. Compos A 2007; 38: 1076–1081.
7. Cheng QF, Wang JP, Wen JJ, et al. Carbon nanotube/epoxy composites fabricated by resin transfer molding. Carbon 2010; 48(1):
260–266.
8. Reia da Costa EF, Skordos AA, Partridge IK, et al. RTM processing and electrical performance of carbon nanotube modified
epoxy/fibre composites. Compos A 2012; 43(4): 593–602.
9. Umer R, Rao S, Zhou J, et al. The low velocity impact response of nano modified composites manufactured using automated dry
fibre placement. Polym Polym Compos 2016; 24(4): 233–240.
10. Fiore V, Di Bella G and Valenza A. The effect of alkaline treatment on mechanical properties of kenaf fibers and their epoxy
composites. Compos B 2015; 68: 14–21.
11. Bodaghi M, Cristóvãob C, Gomeset R, et al. Experimental characterization of voids in high fibre volume fraction composites
processed by high injection pressure RTM. Compos A 2016; 82: 88–99.
12. Lyu MY and Choi TG. Research trends in polymer materials for use in lightweight vehicles. Int J Precis Eng Man 2015; 16:
213–220.
13. Park CH, Lebel A, Saouab A, et al. Modeling and simulation of voids and saturation in liquid composite molding processes.
Composites: Part A 2011; 42(6): 658–668.
14. Little J, Yuan X and Jones M. Characterisation of voids in fibre reinforced composite materials. NDT E International 2012; 46:
122–127.
15. Hernandez S, Sket F, Molina-Aldareguı́ JM, et al. Effect of curing cycle on void distribution and interlaminar shear strength in
polymer-matrix composites. Compos Sci Technol 2011; 71: 1331–1341.
16. Dong C. Effects of process-induced voids on the properties of fibre reinforced composites. J Mater Sci Technol 2016; 32(7):
597–604.
17. Oliveira A, Becker CM and Amico SC. Efeito de aditivos desaerantes nas caracterı́sticas de compósitos de epóxi/fibras de vidro.
Polı́m Ciência e Tecnol 2014; 24: 117–122.
18. Costa ML, Almeida SFM and Rezende MC. Resistência ao cisalhamento interlaminar de compósitos com resina epóxi com
diferentes arranjos das fibras na presença de vazios. Polı́m Ciência e Tecnol 2001; 11(4): 182–189.
19. Phadnis VA, Makhdum F, Roy A, et al. Silberschmidt, drilling in carbon/epoxy composites: experimental investigations and finite
element implementation. Compos A 2013; 47: 41–51.
20. Drach A, Drach B and Tsukrov I. Processing of fiber architecture data for finite element modeling of 3D woven composites. Adv
Eng Softw 2014; 72: 18–27.
21. Figueiredo RB, Pereira PHR, Aguilar MTP, et al. Using finite element modeling to examine the temperature distribution in quasi-
constrained high-pressure torsion. Acta Mater 2012; 60: 3190–3198.
22. Kołakowski Z and Mania RJ. Semi-analytical method versus the FEM for analysis of the local post-buckling of thin-walled
composite structures. Compos Struct 2013; 97: 99–106.
10 Polymers and Polymer Composites XX(X)

23. Ramji M, Srilakshmi R and Prakash MB. Towards optimization of patch shape on the performance of bonded composite repair
using FEM. Compos B 2013; 45: 710–720.
24. Doubrava R. Effect of mechanical properties of fasteners on stress state and fatigue behaviour of aircraft structures as determined
by damage tolerance analyses. Proc Eng 2015; 101: 135–142.
25. Shiino MY, Pelosi TS, Cioffi MOH, et al. The role of stitch yarn on the delamination resistance in non-crimp fabric: chemical and
physical interpretation. J Mater Eng Perform 2017; 26(3): 978–986.
26. Matsuzaki R, Ueda M, Namiki M, et al. Three-dimensional printing of continuous-fiber composites by in-nozzle impregnation. Sci
Rep 2016; 6: 23058.
27. Tian X, Liu T, Yang C, et al. Interface and performance of 3D printed continuous carbon fiber reinforced PLA composites. Compos
A 2016; 88: 198–205.
28. Mantari J, Oktem A and Soares CG. A new higher order shear deformation theory for sandwich and composite laminated plates.
Compos B Eng 2012; 43(3): 1489–1499.
29. Xiong J, Ma L, Wu L, et al. Mechanical behavior and failure of composite pyramidal truss core sandwich columns. Compos B Eng
2011; 42(4): 938–945.
30. Brunbauer J and Pinter G. Fatigue life prediction of carbon fibre reinforced laminates by using cycle-dependent classical laminate
theory. Compos B Eng 2015; 70: 167–174.
31. Jiang L, Zeng T, Yan S, et al. Theoretical prediction on the mechanical properties of 3D braided composites using a helix geometry
model. Compos Struct 2013; 100: 511–516.
32. Bayraktar H, Tsukrov I, Giovinazzo M, et al. Development of realistic simulation techniques to predict cure-induced microcracking
in 3D woven composites. SIMULA Commun Conf 2012; 1: 1–10.
33. American Society for Testing and Materials. ASTM D 3039/D 3039M: standard test method for tensile properties of polymer matrix
composite materials. West Conshohocken, USA: American Society for Testing and Materials, 2000.
34. American Society for Testing and Materials. ASTM D790: standard test methods for flexural properties of unreinforced and
reinforced plastics and electrical insulating materials. West Conshohocken, USA: American Society for Testing and Materials,
2003.
35. American Society for Testing and Materials. ASTM 3171 proceed B: standard test methods for void content of reinforcement
plastic. West Conshohocken, USA: American Society for Testing and Materials, 2009.
36. Shiino MY, Faria MCM, Botelho EC, et al. Effect of mechanical properties of fasteners on stress state and fatigue behaviour of
aircraft structures as determined by damage tolerance analyses. Proc Eng 2015; 101: 135–142.
37. Pelivanov I, Ambrozinski Ł and O’Donnell M. Heat damage evaluation in carbon fiber-reinforced composites with a kHz A-scan
rate fiber-optic pump-probe laser-ultrasound system. Compos A 2016; 84: 417–427.
38. Shiino MY, Cioffi MOH, Voorwald HCJ, et al. Tricot stitched carbon fiber reinforced polymer composite laminates manufactured
by resin transfer molding process: C-scan and flexural analysis. J Compos Mater 2012; 47(14): 1695–1703.
39. Bickerton S, Stadtfeld HC, Stainer KV, et al. Design and application of actively controlled injection schemes for resin-transfer
molding. Compos Sci Technol 2001; 61: 1625–1637.