Analysis of Mechanical Properties of Unidirectional Flax Roving and Sateen Weave Woven Fabric-Reinforced Composites


 Natural fiber-reinforced composites are getting more attention from researchers and manufacturing companies to replace metals and synthetic materials that have dominated the manufacturing industries. In this study, the mechanical properties of unidirectional (UD) flax roving-reinforced composites and woven fabric-reinforced composites were investigated. Three different composites were prepared from flax rovings, which have the same linear density and epoxy resin matrix, with different reinforcement and composite preparation methods. The samples were subjected to experimental tests of flexural rigidity and tensile strength in a parallel and perpendicular direction to fiber orientation. The test results showed that flexural rigidity and tensile strength of flax fiber-reinforced composites are highly dependent on the direction of fiber orientation. The results also reveal that in a parallel direction to fiber orientation, UD composites have higher flexural rigidity and tensile strength than woven fabric-reinforced composite.


Introduction
A composite material is defi ned as a material consisting of two or more constituent materials (reinforcement and matrix) with different chemical and physical properties in which the property of the fi nal composite is intended to be better than the component materials [1][2][3]. Depending on the ideas and concepts that need to be identifi ed, composite materials are classifi ed into different groups [2]. Natural fi ber-reinforced composite (NFRC) is one of the composite classifi cations based on their reinforcement type [4]. Textile composites are formed to use textile fi bers, yarns, and fabrics as a composite reinforcement to achieve high-strength and lowdensity composites with reasonable manufacturing cost [4,5,6]. Nowadays, fl ax fi ber-reinforced composite is one from natural fi ber textile-reinforced composites, which is getting more attention from manufacturing industries and researchers due to its unique properties, including cost-effectiveness, low density, good specifi c strength, good bio-degradability, and environment-friendly material [3,5,[7][8][9][10]. These properties widely spread the usage of fl ax fi ber-reinforced composites in the aerospace, civil engineering, automotive, and many other industries [8,10,11].
The fl ax fi ber-reinforced composite materials are produced by incorporating fl ax fi bers with polymeric materials to fulfi ll the mechanical properties of the materials needed for different applications. The method of fabricating composite materials also depends on the intended end use of the composite and specifi c features of the materials looked-for the application.
Unidirectional (UD) composites are arranged in one direction with all fi bers in a matrix; they are distinguished by their reinforcement angle [12]. The fabric structure/reinforcement type, constituent fi ber, a resin matrix, composite preparation method, and their interface are the essential things to determine the strength of composite material [13,14]. Omrani et al. [15] showed the impact of the weaving process and the waviness of weft yarns on the mechanical properties of the composites. Yukseloglu et al. [16] presented the modulus of UD fl ax fi berreinforced composites increases with the increase of fi ber volume fraction percentage in the reinforcement. Prasad et al. [17] showed the infl uence of composite preparation methods on the mechanical strength of composite material. Many researchers investigated and revealed that UD composites provide the greatest strength in the fi ber direction [7,9,12].
The crucial characteristics of textile fi ber-reinforced composites are their anisotropic property, which means their mechanical property is in-line with the direction of fi ber orientation in the composite structure [18]. In this study, samples were tested in the parallel and perpendicular direction to the fi ber orientations in the composite structure to determine and analyze the anisotropic mechanical properties of sateen weave fabric-reinforced composites and UD fl ax roving-reinforced composites.

Materials and methods
The low twist fl ax roving supplied by the Safi lin company, which has a linear density of 190 tex, was used to produce the reinforcements. Based on the experimental test performed in the laboratory of the Institute of Architecture of Textiles at the Lodz University of Technology, fl ax rovings are characterized by breaking strength of 6.82 cN/tex and 1.32% elongation at the break.
An epoxy resin LH145 from Havel composites company was used as a matrix. Based on the supplier recommendation, epoxy resin LH145 was mixed with H135 hardener in the ratio of 100:35 parts by weight, respectively. Also, three different reinforcement materials were prepared from the same count of fl ax roving (190 tex) with varying roving densities per centimeter and employing different ways of preparation, as described below. The fi rst type of reinforcement was prepared from 3/10 sateen weave fabric, which was woven from 190 tex fl ax yarn (weft) and 40 tex cotton yarn (warp) on a MAV rapier loom. The weft (fl ax yarn) was the prevailing yarn in the fabric structure with a density of 14 yarns/cm and the cotton yarn with a density of 10 yarns/cm ( Figure 1a). The second type of reinforcement was unidirectionally arranged fl ax roving prepared by removing warp yarn (cotton) from woven fabric ( Figure 1b); this UD reinforcement has a density of 14 rovings/cm. The third type of reinforcement was prepared on a rectangular frame, which has been made from the sheet of metals and wooden materials fi xed with the reeds. Each single roving strand was drawn through reeds to form a parallelly arranged UD fl ax roving reinforcement ( Figure 1c). The UD fl ax reinforcement made by this method has a density of 10 rovings/cm.

Composite preparation methods
Flax roving-reinforced composites were prepared by vacuum bagging (Figure 2a) and resin infusion (Figure 2b) [19] methods of composite formation. In both methods, the mold was sealed using a vacuum bag, and atmospheric pressure was applied to hold laminate plies together. The pressure between the outside and inside of the sealed envelope must be equal to 0 to fabricate composite material with better quality. The pressure difference was measured using the gauge bar mounted on a vacuum pump motor. The main difference between the vacuum bagging method (Figure 2a) and the resin infusion method (Figure 2b) is the way of applying the resin to the reinforcement. In case of vacuum bagging method (Figure 2a), each ply of reinforcement has to be wetted manually using epoxy resin before the mold is sealed; in contrast to this, in the resin infusion method ( Figure  2b), fi rst, the dry plies of reinforcement have to be placed on the mold and sealed, as shown in Figure 2b, and then epoxy resin is slowly drawn to the envelope through a resin inlet valve, and by using a resin distribution medium, the resins are equally distributed over the surface of reinforcement plies. In both methods, a vacuum outlet valve is used to suck the air in the envelope and excess resin residues.
The vacuum bagging method of composite formation was used to produce woven fabric-reinforced composites, and the resin infusion method was used to produce UD composites. Also, the formation of UD composites was tried using a vacuum bagging method, but due to the diffi culties of removing air from the gaps between parallelly arranged rovings, the produced composite was not good enough to be used for further experimental tests. In both methods, two layers of reinforcements were stacked together to produce the composite.

Experiments
The tensile strength and fl exural rigidity experimental tests were performed at the Lodz University of Technology in the Faculty of Mechanical Engineering by using the Shimadzu AG-X plus testing machine (Figure 4a), which has a maximum testing load of 50 KN. For the tensile strength experimental test, 10 specimens have been tested for each sample type both in perpendicular and parallel direction to fi ber orientation in the composite structure. These specimens' dimensions were prepared based on the American Standard of Test Method (ASTM) D3039 ( Figure 3a) with a testing condition of 2 mm/ min speed.  Flexural rigidity test was performed to know the force required to bend the fl ax fi ber-reinforced composites and determine the stiffness of the material. To do so, 10 specimens were prepared from each sample, both in perpendicular and parallel direction to fi ber orientation in the composite structure with the dimension of the specimens(fi g.3b) were prepared based on the ASTM D7264/ D 7264-M standard. The specimens were tested using

Results and discussion
Experimental test results conducted for flexural rigidity and tensile strength experimental tests of composites are presented in Tables 1 and 2.

Analysis of the influence of fiber orientation and reinforcement types on the flexural rigidity of composites
The composite sample reinforced with sateen weave fabric has 28.47% and 13.07% lower ability to withstand flexural stress in comparison to UD composite reinforced by 14 rovings/cm and 10 rovings/cm respectively in the direction of fiber orientation ( Figure 5), this illustrates UD reinforced flax composites have higher bendable property than woven-reinforced composites. Also, in a perpendicular direction to fiber orientation, 14 rovings/ cm reinforced UD composite has 28.81% and 39.21% higher flexural stress than woven fabric-reinforced composite and 10 rovings/cm reinforced UD composites, respectively ( Figure  5). During the flexural rigidity experimental test, when the load applied to specimens in the direction of fiber orientation (0°), the specimens were bent to their maximum deflection point in all types of composites made; after the removal of applied load, each specimen is almost returned to their original position. Also, when experimental tests were carried out on specimens in perpendicular to the fiber orientation, both unidirectionally reinforced composites were cracked. In contrast to this, woven fabric-reinforced composites were almost returned to their original position after the removal of applied force.

Analysis of the influence of fiber orientation and reinforcement types on the tensile strength of composites
The influence of reinforcement type and density of roving on the tensile strength of composites are shown in Figure 6. The study of tensile test result reveals that when a tensile force is applied to the specimen on a parallel direction to fiber orientation (0°), UD composite reinforced with 10 roving/cm has 18.73% and 34.90% higher tensile strength than woven fabricreinforced composite and UD flax composite reinforced with 14 rovings/cm, respectively. As a result of the weaving process, the tensile strength of yarns is degraded, and this affects the composite material reinforced either by using woven fabric or UD composite made from yarns/rovings removed from woven fabric, this discloses the influence of single yarn/roving tensile properties on the composite material tensile strength. Summing up the analysis of fl exural rigidity and tensile strength of the composites shows that mechanical properties of fl ax fi berreinforced composites are highly dependent on the direction of fi ber orientation in the composite structure with signifi cantly showing higher fl exural rigidity and tensile strength in the direction of fi ber orientation, signifying that textile materialreinforced composites have anisotropic properties. Besides, unidirectionally reinforced fl ax fi ber exhibits higher tensile strength and fl exural rigidity than woven fabric-reinforced composites. In contrast, woven fabric-reinforced composites have higher tensile strength than unidirectionally reinforced composites when the test was carried out in a perpendicular direction. Woven fabric-reinforced composite has exhibited excellent elongation in comparison with UD fl ax rovingreinforced composites during the tensile strength test because of the crimpage of yarns in the structure of the woven fabric.

Conclusion
In this study, the mechanical properties of woven and UD fl ax roving-reinforced epoxy composites were investigated. The experimental result obtained shows that woven fabric and UD fl ax roving-reinforced composites have higher tensile strength and fl exural rigidity in the fi ber direction (0°) compared with the experimental test carried out in the perpendicular direction (90°). Also, the experimental result reveals that the density of rovings in the composite structure infl uences the mechanical properties of UD fl ax fi ber-reinforced composites, the higher density, the higher fl exural rigidity property, and the vice-versa is true. The fl exural rigidity and tensile strength of UD composites are higher than woven fabric-reinforced composites in the direction of fi ber orientation. However, the woven fabric-reinforced composites have excellent tensile strength properties in the perpendicular direction to the fi ber orientation, compared with UD composites.