In this paper, investigation on the initial fracture behavior was carried out on roving glass woven fabric reinforced composites which were manufactured by hand lay-up method. Two kinds of roving glass woven fabrics of different FAW (Fabric Area Weight) and crimp ratio, Type A of 570 g/m2 and Type B of 800 g/m2, were adopted as reinforcement in this study. Tensile test was conducted and tensile properties w ere discussed on specimens of 6 degrees 0 ° /5 ° /10 ° /80 ° /85 ° /90 ° . The initial fracture behavior was observed on 0 degree and 90 degree and the fracture mechanism was compared and discussed among 5 ° /10 ° /80 ° /85 ° . The results showed that Type B has higher tensile modulus and tensile strength than that of Type A. And different initial fracture behaviors between two kinds of materials was observed and analyzed, which indicated that the crimp ratio plays an important role of woven fabric reinforced composites in fracture mechanism .
Recent decades, textile fabrics used as reinforcements for manufacturing composites are spreading in various fields, such as aerospace, automotive, construction and basic facilities industries [
Roving cloth, as one of the woven fabrics, is characterized with the cross section of the warp fiber bundles and weft fiber bundles, which are usually used as reinforcement for laminate molding [
In previous works, many researchers focused on the mechanical properties as well as the fracture mechanism of glass woven cloth reinforced composites. Demircan, O. carried out the investigation of the fracture process and mechanisms of glass roving and glass cloth composites [
Because of the complicated microstructure of woven fabric, it is of significance to understand of mechanical mechanism of textile fabric reinforced composite materials. There are references [
In this paper, investigation on the initial fracture behavior was carried out on roving glass woven fabric reinforced composites manufactured by the hand lay-up method. Two kinds of roving glass woven fabrics of different FAW (Fabric Area Weight) were adopted in this study. Tensile tests combined with AE (acoustic emission) measurements [
In this paper, two kinds of roving glass woven fabrics of different FAW (Fabric Area Weight), 570 g/m2 and 800 g/m2, were adopted. Unsaturated polyester resin (150 HRBQTNA, Showa Denko K.K.) was adopted as the matrix. The glass roving clothes manufactured by Hokuriku Fiberglass Co., Ltd are in plain structure as showing in
The glass roving cloth reinforced composites were manufactured by hand lay-up molding method for only 1 ply for the purpose of reveal the crack
Linear density (TEX) | Yarn density (N/25mm) | Crimp percentage (%) | Bundle area (mm2) | Bundle distance (mm) | ||
---|---|---|---|---|---|---|
Type A | Warp | 1150 | 6.5 | 14.4 | 1.22 | 4.90 |
Weft | 1150 | 5.8 | 11.2 | 1.08 | 5.12 | |
Type B | Warp | 2300 | 4.6 | 13.0 | 1.77 | 6.95 |
Weft | 2300 | 3.8 | 10.7 | 1.50 | 7.56 |
propagation and fracture mechanism. After the fabrication, the composite board was cut to the size of 200 mm × 20 mm (length × width) according to ASTM D3039 according to 6 orientations 0˚/5˚/10˚/80˚/85˚/90˚. The thickness of Type A is approximately 0.60 mm, while Type B is approximately 0.65 mm, a little thicker than Type A. Cross-sectional observation was carried out and the crimp percentage for both the 0 and 90 degree directions of Type A and Type B was calculated, and is showed in
Mechanical investigation of the tensile properties was carried out on specimens in 6 degrees 0˚/5˚/10˚/80˚/85˚/90˚. The tensile tests were carried out on an Instron universal testing machine at a speed of 1 mm/min and the test room temperature was 22˚C according to the ASTM D3039. (Specimen number N = 3). For 0˚ and 90˚, which are also defined as on-axis cases, the fracture progress during the tensile test has been observed by take video. During the tensile tests, an AE (acoustic emission) device was used in order to detect when the initial fracture occurred. A video was also shot in order to understand the fracture process. In the photographs collected from the video at different strain stages, three main periods can be identified to depict the fracture process. Combined with the AE data and the video footage, the initial fracture behavior has been discussed. For 5˚/10˚/80˚/85˚, which are defined as off-axis cases, tensile modulus, tensile strength were also tested and discussed. Besides, the difference of deferent degrees, and the comparison between Type A and B has been discussed and summarized.
The stress-stain curves are illustrated in
On the other hand, the tensile strength of Type B turned out to be much higher than that of Type A for both the 0 and 90 degree directions. The fiber bundle cross section area ratio of Type A and Type B was calculated and this value could be referred as an index similarly with Vf (volume fraction of reinforcing fibers). The result showed the value of Type A is slightly higher than that of Type B, which is revealing that Type A might get higher tensile strength. However, it does not agree with the tensile strength result.
When it comes to the elongation, it can be known from
Type | Degree | Tensile modulus (GPa) | Tensile strength (MPa) | Elongation rate (%) | Initial fracture stress (MPa) |
---|---|---|---|---|---|
A | 0 | 12.3 | 276.7 | 3.5 | 34.7 |
90 | 18.0 | 271.2 | 3.9 | 33.7 | |
B | 0 | 13.3 | 476.3 | 4.5 | 35.7 |
90 | 21.2 | 335.0 | 4.8 | 38.7 |
elongation rate for Type B is higher than Type A. This would be taken as one of the reasons for the high tensile strength of Type B. But the reason why Type B achieved higher elongation should be found out firstly because the crimp ratio of Type B is lower than that of Type A which indicated Type A should have got higher elongation.
Otherwise, the initial fracture results detected by acoustic emission showing in
In order to decide where exactly the initial fracture happened, specimens were under tensile testing and stretched to 1.3 times the initial fracture stress and stopped. Then observation was carried out on the longitudinal cross section by optical microscopy. From the photographs shown in
The fracture processes are illustrated by still images from the video in
There were several period before the final fracture can be summarized during the fracture period for both Type A and Type B involved with transverse cracks and wave shape cracks. Schemas are summarized and illustrated in
1) Firstly, for both Type A and Type B, transverse cracks occurred firstly in the transverse fiber bundles, and then the number of transverse cracks increases. During this period, the interface between the glass fibers and the resin is subjected to most of the load. White line of cracks can be observed in the cross section area of the warp and weft fiber bundles.
2) During this period, the interface between the glass fibers and the resin is still the main carrier of most of the load. White cracks increased gradually until the cracks went through the transverse fiber bundles. It can be seen that transverse cracks within Type B are much finer than those in Type A.
3) Because of the tendency of the fiber bundle in the crimp to be stretched, the cross section of the warp fiber bundle and weft fiber bundle is compressed and wave shape cracks began to show up both for Type A and Type B. During this period, the interface between the glass fiber and the resin still carried the most of the load but the longitudinal fiber bundles are beginning to take most of the load. More cracks in wave shapes appeared between the transvers fiber bundles were observed in Type A and then increased from
4) Fourthly, the longitudinal fiber bundles become carrying the most of the load and finally leading to the fracture of the specimen. It was obviously observed that much more wave shape cracks in Type A and propagated in transverse directions. However for Type B, wave shape cracks did not increase much, and plenty of fine transverse cracks were observed within the transverse fiber bundles.
When comparing Type A with Type B, the difference was observed from the second period. In the case of Type B, more and finer cracks were observed, while for Type A, more wave shape cracks propagated during the third and fourth period. AE results showed in
higher than that of Type B, the wave shape cracks led to fiber bundle breaking and specimen of Type A came to final fracture before it achieved a high elongation. On the contrast, the higher fiber bundle tex and lower crimp ratio of Type B makes it more tolerant with transverse cracks, and it is considered the specimen was stretched smoothly finally with a higher elongation than Type A.
Higher crimp ratio might lead a tendency to fierce wave shape cracks and result in a low tensile strength. But it is also predictable that the fabric reinforcement with a very low crimp ratio will also not achieve good tensile properties because of the low fiber volume fraction. It is considered that for woven fabric reinforced composites, there is a critical crimp ratio which contributes to better tensile properties.
Tensile test was also carried out on specimens of 5˚/10˚/80˚/85˚and the tensile results were summarized in
The summary of tensile modulus and strength of all 6 degrees of 0˚/5˚/10˚/80˚/85˚/90˚ are illustrated in
Tensile modulus (GPa) | Tensile strength (MPa) | Ultimate Fracture Elongation (%) | ||||
---|---|---|---|---|---|---|
Deg. | A | B | A | B | A | B |
5 | 2.0 | 2.7 | 32.4 | 54.9 | 3.1 | 2.8 |
10 | 1.9 | 2.5 | 19.0 | 20.0 | 1.9 | 2.6 |
80 | 1.9 | 2.4 | 15.4 | 21.0 | 1.5 | 1.7 |
85 | 2.3 | 2.6 | 38.4 | 46.5 | 2.9 | 3.1 |
The photographs of fractured specimens of Type A and Type B after the tensile test were shown in
that, in the case of 10 degree and 80 degree, especially for Type B, it can be observed that less fiber was pulled out and split, which revealed that the fiber bundle in the loading direction did not take most of the loading. And the shear stress played an important role during the tensile test, leading to the ultimate fracture of the specimen, which can be considered as the reason of the low strength in the case of the 10degree and 80 degree. Especially for Type B, there are very few fiber bundles pulled out and split in the case of the 10degree and 80 degree, and contacted with the tensile strength result which showing a decrease of more than 45% comparing with 5 degree and 85 degree.
In this paper, tensile properties, especially the initial fracture properties of two types of roving glass cloth reinforced composites were tested. Tensile test was conducted and tensile properties were discussed on 6 degrees 0˚/5˚/10˚/80˚/85˚/90˚. The tensile results of 0 degree and 90 degree showed that the Type B has higher tensile modulus and strength than Type A. As it is referred to the initial fracture behavior 4 stages have been observed, according to the main load carrier changed from the interface of glass fiber and the resin to the longitudinal fiber bundles. More cracks in wave shape were observed as the crack propagating, while more fine cracks in the transverse fiber bundles were observed in the case of Type B. The important role of crimp ratio was made clear, which can be considered of significance to obtain better tensile property. Among the cases of 5˚/10˚/80˚/85˚, dramatic decrease in tensile modulus and strength was made clear. And it seem that less fiber bundles pulled out from the specimen during the fracture in the cases of 10˚ and 80˚, revealing that less longitudinal fiber bundles carried the load.
Xu, Z. and Yokoyama, A. (2018) Influence of the Woven Structure on the Initial Fracture Behavior of Roving Glass Fabric Reinforced Composites. Open Journal of Composite Materials, 8, 54-67. https://doi.org/10.4236/ojcm.2018.82005