Uniaxial tensile tests of basalt fiber/epoxy (BF/EP) composite material with four different fiber orientations were conducted under four different fiber volume fractions, and the variations of BF/EP composite material failure modes and tensile mechanical properties were analyzed. The results show that when the fiber volume fraction is constant, the tensile strength, elastic modulus, and limiting strain of BF/EP composite material all decrease with increasing fiber orientation angle. When the fiber orientation angle is constant, the tensile strength, elastic modulus, and limiting strain of BF/EP composite material all increase with increasing fiber volume fraction. A certain degree of fiber clustering appears in the epoxy resin when the basalt fiber volume fraction is >1.2%. The fiber equidistribution coefficient and clustering fiber content were used to characterize the basalt fiber clustering effect. With the increase of fiber volume fraction, the clustering fiber content gradually increased, but the fiber equidistribution coefficient decreased. Meanwhile, based on Tsai theory, a geometric model and a tensile mechanical model of the clustering fiber are established. By considering the fiber clustering effect, the BF/EP composite material tensile strength is calculated, and the calculated values are close to the experimental results.
Basalt fiber is a new type of mineral fiber made from the melting of natural basalt at high temperature (1400–1500°C) [
Because of the high tensile strength, light weight, and convenient construction, BF/EP composite material can be used as a new type of reinforcement material and applied to repair and strengthening of concrete structure and steel structure in civil engineering [
To sum up, the intensive research of the manufacturing process and mechanical property of BF/EP composite material provides powerful help for its application in civil engineering. At present, research on BF/EP composite material focuses on the influence of fiber surface modification on mechanical properties [
In this paper, with the use of a handmade chute device, 16 kinds of BF/EP composite materials (with different volume fractions and different fiber orientations) were produced. Uniaxial tensile testing of these BF/EP composite materials was then conducted. The goal is to understand the influence of fiber orientation and fiber volume fraction on the tensile properties of the BF/EP composite material and to provide some experimental bases for the design and engineering application of BF/EP composite material.
The curing agent used was polyamide, and the diluent was acetone. The matrix was compounded according to a mass ratio of
Physical and mechanical indexes of basalt fiber.
Density (g/cm^{3})  Tensile strength (MPa)  Limit elongation (%)  Tensile modulus (GPa)  Diameter (mm)  Length (mm) 

2.65  3300  3.2  100  0.01  12 
First, we designed the basic parameters of the BF/EP composite material. The volume fractions
Second, we used a handmade device to fabricate the oriented basalt fiber/epoxy composite material. For the epoxy resin, a curing agent and diluent were mixed according to a predetermined proportion, thus forming a liquid epoxy resin matrix. Basalt fiber was then added, and the mixture was stirred for two minutes. The resulting mixture was then poured into the hopper of the chute stretch device (Figure
The chute stretch device.
Molding effect of oriented basalt fiber/epoxy composite material (
Third, we fabricated BF/EP composite materials with different fiber orientations. After the completion of matrix solidification (about 48 h at 20°C ± 2°C), along the fiber direction, we cut the samples at included angles of 0°, 15°, 30°, and 45°, thus obtaining BF/EP composite material with four different fiber orientations.
Uniaxial tensile tests were conducted using a WAW1000 universal testing machine and stressstrain curves were collected at a loading rate of 5 N/s. Figure
The tensile test machine (WAW1000).
Figure
Tensile stressstrain curves of BF/EP composite materials with different orientations and different volume fractions of fibers.
Tensile property parameters of BF/EP composite material.
Sample number  Fiber orientation angle, 
Fiber volume fraction (%)  Tensile strength (MPa)  Limiting strain (mm/mm)  Elastic modulus (MPa) 

00  0  0  16.13  0.00210  8576 
11  0  0.6  18.54  0.00257  13638 
12  15  0.6  17.35  0.00220  11530 
13  30  0.6  16.12  0.00213  10918 
14  45  0.6  15.85  0.00205  9730 
21  0  0.9  23.56  0.00273  14741 
22  15  0.9  21.78  0.00255  11868 
23  30  0.9  19.62  0.00228  11257 
24  45  0.9  17.90  0.00218  10315 
31  0  1.2  30.37  0.00323  16568 
32  15  1.2  29.05  0.00303  13320 
33  30  1.2  25.13  0.00256  11360 
34  45  1.2  21.54  0.00241  10428 
41  0  1.5  33.26  0.00354  19226 
42  15  1.5  32.01  0.00339  15302 
43  30  1.5  28.60  0.00333  11675 
44  45  1.5  25.27  0.00313  10911 
The elastic modulus of the matrix and BF/EP composite material can be obtained by calculating the slope of the elastic section of the stressstrain curve (Figures
It can also be seen from Table
In conclusion, the tensile strength, limiting strain, and elastic modulus of the BF/EP composite material are related to the orientation and volume fraction of fiber. To further analyze the influence of the orientation and volume fraction of fiber on tensile properties of the BF/EP composite material, the following enhancement coefficient
The correlation coefficients for (
Esports scan results of the BF/EP composite material sample fracture surface.
We analyzed the tensile failure mode of samples by observing the fracture surface of samples through scanning electron microscopy. It was found that there is a certain degree of agglomeration occurring in the epoxy resin when the basalt fiber volume fraction is >1.2%. Figure
This kind of fiber agglomeration can be called “fiber clustering.” Because of the fiber clustering effect, there are only small gaps in between fibers, which make it hard for the matrix to enter the fiber agglomerates, and there are crevices in the fiber agglomerates (Figure
However, the matrix is destroyed before the pullout fiber reaches its yield limit, and the bonding strength of the fiber and matrix is smaller than the tensile strength of the fiber, so the fibers do not play an enhanced role in the matrix. Similarly, a crevice in a fiber cluster leads to matrix cracking in advance to some degree, and the tensile strength of the composite decreases (Figure
Consider an agglomerate of oriented fibers and matrix material in their adjacent area as a mesocharacteristic unit, as shown in Figure
Micromechanics model of clusterfiberreinforced epoxy matrix composites.
Figure
If
Equation (
Substituting (
All edges of
Based on Tsai theory [
According to (
Representative sections of BF/EP composite material samples with the volume fractions of 0.6%, 0.9%, 1.2%, and 1.5% were magnified for observation after cutting and polishing so that the number of clustering fibers and inside arrangement can be obtained, as shown in Figure
Graph division and calculation of
Calculated values of




 










1  1.6873  0.1297  2.2260  0.2516  1.7707  0.1216  1.9107  0.1247  
2  2.1040  0.2116  2.0927  0.1159  1.4033  0.0869  1.3867  0.0752  
3  1.0007  0.0566  1.5520  0.0903  1.8380  0.1683  1.3893  0.1380  
4  0.8187  0.0493  1.6253  0.0956  1.1933  0.0966  1.5607  0.1260  
5  1.6520  0.0930  1.7587  0.1676  1.3293  0.0992  1.6360  0.1342  
6  1.7920  0.1739  1.7880  0.1684  1.4427  0.1413  1.3000  0.1041  
7  —  —  1.6073  0.1047  1.6980  0.1489  1.5373  0.1346  
8  —  —  1.6093  0.0887  1.4333  0.1111  1.4927  0.1354  
9  —  —  1.3620  0.0674  1.4267  0.1195  1.4587  0.1337  
10  —  —  —  —  1.1420  0.0857  1.2833  0.0870  
11  —  —  —  —  1.5180  0.1199  1.4673  0.1136  
12  —  —  —  —  1.5467  0.1460  1.3733  0.1151  
13  —  —  —  —  1.5067  0.1380  1.6620  0.1601  
14  —  —  —  —  —  —  1.2527  0.0982  
15  —  —  —  —  —  —  1.3993  0.1104  
16  —  —  —  —  —  —  1.3820  0.1068  
17  —  —  —  —  —  —  1.4807  0.1082  
18  —  —  —  —  —  —  1.8280  0.1551  
19  —  —  —  —  —  —  1.6640  0.1220 
By taking a section from the oriented basalt fiber/epoxy composite material samples with different volume fractions (0.6%, 0.9%, 1.2%, and 1.5%), the length of each being 12 mm, as a representative volume unit, the effective coefficient of fiber (
Fiber equidistribution coefficient and content of fiber clustering as a function of fiber volume fraction.
By substituting the fiber equidistribution coefficient
Calculated and experimental values of the tensile strength of the BF/EP composite material as a function of fiber volume fraction change.
From Figure
Different fiber orientations and BF/EP composite material tensile strength experiments were analyzed, and research on failure modes of different fiber volume fractions was conducted. The following can be concluded:
With a certain amount of basalt fiber, the tensile strength, elastic modulus, and limiting strain of epoxy resin composite material significantly improve. When the fiber volume fraction is constant, the tensile strength, elastic modulus, and limiting strain of BF/EP composite material all decrease with increasing fiber orientation angle. When the fiber orientation angle is constant, the tensile strength, elastic modulus, and limiting strain of BF/EP composite material all increase with increasing fiber volume fraction.
The fibers play an enhanced role in the matrix when the bonding strength of the fiber and matrix is greater than the yield strength of the fiber. However, the matrix is destroyed before the pullout fiber reaches its yield limit, and the bonding strength of the fiber and matrix is smaller than the tensile strength of the fiber, so the fibers do not play an enhanced role in the matrix.
The calculated values of the BF/EP composite material tensile strength with fiber clustering effect taken into account and the test values exhibit a strong linear correlation (with a correlation coefficient of 0.991). This conclusion can provide a theoretical basis and reference value for predicting the tensile strength of BF/EP composite material.
The data used to support the findings of this study are available from the corresponding author upon request.
This work was presented in the form of abstract in “The 8th International Conference on Computational Methods (ICCM2017).”
The authors declare that they have no conflicts of interest.
The authors would like to thank the opportunity offered by the ICCM2017 on the exchange of “tensile mechanical properties and its failure modes of the basalt fiber/epoxy resin composite material.” The authors gratefully acknowledge the support of the National Natural Science Foundation of China (no. 11572244) and NSAF (no. U1630144).