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A method to produce a unidirectional reinforcement for fiber reinforced composites by a resin transfer or vacuum infusion molding process include: laying continuous rovings unidirectionally side by side in one layer for forming a unidirectional web, applying thermoplastic or thermoset binder on the

A method to produce a unidirectional reinforcement for fiber reinforced composites by a resin transfer or vacuum infusion molding process include: laying continuous rovings unidirectionally side by side in one layer for forming a unidirectional web, applying thermoplastic or thermoset binder on the web, activating the binder for bonding the rovings together to form a unidirectional reinforcement, and forming flow passages for resin in a direction transverse to the direction of the unidirectional rovings by laying thin discrete flow passage having, under compression, an aspect ratio of equal or less than 2 on the continuous unidirectional rovings.

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1. A unidirectional reinforcement assembly for the manufacture of fiber reinforced composites by one of resin transfer molding process and vacuum infusion molding process, the unidirectional reinforcement assembly comprising: a reinforcement layer having continuous unidirectional fiber rovings arran

1. A unidirectional reinforcement assembly for the manufacture of fiber reinforced composites by one of resin transfer molding process and vacuum infusion molding process, the unidirectional reinforcement assembly comprising: a reinforcement layer having continuous unidirectional fiber rovings arranged in a longitudinal direction of the reinforcement layer, and fiber rovings in the reinforcement layer are bonded to each other by a thermoplastic or thermoset binder,the reinforcement layer having a top surface and a bottom surface, andan impregnation facilitator that facilitates, when wetting-out a stack of reinforcement layers, impregnation of the reinforcement layers with resin in a direction transverse to the direction of the fiber rovings,wherein the impregnation facilitator includes a monofilament fiber arranged transverse to the fiber rovings on at least one of the top surface and the bottom surface of the reinforcement, and wherein the monofilament fiber has, under compression, an aspect ratio of equal or less than two, a diameter or Z-direction thickness of 100 μm to 300 μm, and a flow passage formed to a side of the monofilament fiber, wherein the flow passage extends from one longitudinal edge of the unidirectional reinforcement assembly to the opposite longitudinal edge thereof. 2. The unidirectional reinforcement assembly as recited in claim 1, wherein the monofilament fiber is arranged within 45 degrees of a right angle to the longitudinal direction of the unidirectional fiber rovings. 3. The unidirectional reinforcement assembly as recited in claim 1, wherein the reinforcement layer is formed of two or more layers of fiber rovings and that the monofilament fiber is arranged between at least two of the two or more layers of fiber rovings or only on at least one of the top surface and the bottom surface of the reinforcement layer. 4. The unidirectional reinforcement assembly as recited in claim 1, wherein the monofilament fiber is bonded to the fiber rovings by the thermoplastic or thermoset binder, or that the monofilament fiber has a bicomponent that binds the monofilament fiber to the fiber rovings, or the monofilament fiber includes another outer layer comprising a binder that binds the monofilament fiber to the fiber rovings, or an additional binder is applied on the fiber rovings or on the monofilament fiber to bind the monofilament fiber to the fiber rovings. 5. The unidirectional reinforcement assembly as recited in claim 1, further comprising a plurality of monofilaments including the monofilament fiber, and the monofilaments are arranged in parallel and positioned at a spacing of 2 mm to 50 mm along the longitudinal direction on the reinforcement layer. 6. The unidirectional reinforcement assembly as recited in claim 1, wherein the monofilament fiber has an elongation at break higher than that of a surrounding matrix in a final product formed with the reinforcement layer. 7. The unidirectional reinforcement assembly as recited in claim 1, wherein the monofilament fiber has a diameter or Z-direction thickness in a range of 100 μm to 200 μm. 8. The unidirectional reinforcement assembly as recited in claim 1, wherein the fiber rovings include man-made or natural fibers formed of at least one of glass, carbon, aramid, basalt, kenaf, sisal, flax, hemp, jute and linen. 9. The unidirectional reinforcement assembly as recited in claim 1, wherein the thermoplastic or thermoset binder is in the form of a dry powder, dispersion, or solution. 10. The unidirectional reinforcement assembly as recited in claim 1, wherein the monofilament fiber has, under compression, an aspect ratio of less than 1.5. 11. A preform comprising at least two of the unidirectional reinforcement assembly of claim 1. 12. A unidirectional reinforcement assembly for the manufacture of fiber reinforced composites by one of resin transfer molding process and vacuum infusion molding process, the unidirectional reinforcement assembly comprising: at least two reinforcements having continuous unidirectional and overlapping fiber rovings arranged in a longitudinal direction of each of the reinforcements, and the fiber rovings of each of the reinforcements are bonded to each other by a thermoplastic or thermoset binder with the fiber rovings in the respective reinforcement,the reinforcement having a top surface and a bottom surface, and provided with an impregnation facilitator configured to, when wetting-out a stack of reinforcements, facilitate the impregnation of the reinforcement with resin in a direction transverse to the direction of the fiber rovings,wherein the impregnation facilitator includes monofilament fibers arranged on at least one of the top surface and the bottom surface of each of the reinforcements, and the monofilament fibers are transverse to the unidirectional fiber rovings, the monofilament fibers have, under compression, an aspect ratio of no greater than two, a diameter or Z-direction thickness of 100 μm to 300 μm, and transverse flow passages adjacent sides of the monofilament fibers, wherein the transverse flow passages extend from one longitudinal edge of the unidirectional reinforcement assembly to an opposite longitudinal edge of the unidirectional reinforcement assembly. 13. The unidirectional reinforcement assembly as recited in claim 12, wherein the monofilament fibers are arranged within 45 degrees of a right angles to the longitudinal direction of the unidirectional reinforcement assembly. 14. The unidirectional reinforcement assembly as recited in claim 12, wherein the reinforcement is formed of layers of the fiber rovings and the monofilament fibers are arranged between the layers of the fiber rovings or on a top surface of the reinforcement and or a bottom surface of the reinforcement. 15. The unidirectional reinforcement assembly as recited in claim 12, wherein at least some of the monofilament fibers are bonded together. 16. The unidirectional reinforcement assembly as recited in claim 12, wherein the at least some of the monofilament fibers are bonded together by a binder material that includes at least one of: the thermoplastic or thermoset binder that binds the fiber rovings, a bicomponent included with the monofilament fibers, a binder in an outer layer of the monofilament fibers, and an additional binder applied on the fiber rovings or on the monofilament fibers. 17. The unidirectional reinforcement assembly as recited in claim 12, wherein at least some of the monofilament fibers are parallel to each other, and are spaced 2 mm to 50 mm along the longitudinal direction from each other. 18. The unidirectional reinforcement assembly as recited in claim 12, wherein at least some of the monofilament fibers have an elongation at break characteristic which is higher than an elongation at break characteristic of a surrounding matrix formed with the reinforcement. 19. The unidirectional reinforcement assembly as recited in claim 12, wherein at least some of the monofilament fibers have, under compression, a diameter or Z-direction thickness of 100 μm to 200 μm. 20. The unidirectional reinforcement assembly as recited in claim 12, wherein the fiber rovings include man-made or natural fibers formed of at least one of glass, carbon, aramid, basalt, kenaf, sisal, flax, hemp, jute and linen. 21. The unidirectional reinforcement assembly as recited in claim 12, wherein the thermoplastic or thermoset binder is in the form of a dry powder, dispersion, or solution or is heated for making it low-viscous. 22. The unidirectional reinforcement assembly as recited in claim 12, wherein the monofilament fibers have, under compression, an aspect ratio of less than 1.5. 23. A preform comprising at least two of the reinforcements of claim 12. 24. A unidirectional reinforcement comprising: fiber rovings extending continuously in a longitudinal direction of the reinforcement and aligned parallel to each other and to the longitudinal direction;a binder bonding the fiber rovings together, andmonofilament fibers arranged transverse to the longitudinal direction on at least one of the top surface and the bottom surface of the unidirectional reinforcement, wherein the monofilament fibers, while under compression, have an aspect ratio of two or less, a diameter or Z-direction thickness of 100 μm to 300 μm, and form transverse flow passages extending from one longitudinal edge of the unidirectional reinforcement to an opposite longitudinal edge of the unidirectional reinforcement. 25. A non-woven unidirectional reinforcement assembly for the manufacture of fiber reinforced composites by one of resin transfer molding process and vacuum infusion molding process, the unidirectional reinforcement assembly comprising: a first reinforcement layer having unidirectional non-woven fiber rovings bonded together by a thermoplastic or thermoset binder;a second reinforcement layer having unidirectional non-woven fiber rovings bonded together by a thermoplastic or thermoset binder, the fiber rovings in the second reinforcement layer are bonded separately from the first reinforcement layer;at least one monofilament fiber provided in between a bottom surface of the first reinforcement layer and a top surface of the second reinforcement layer, the monofilament fiber extends in a direction that is transverse to the direction of the fiber rovings, wherein the monofilament fiber, while under compression, has an aspect ratio of two or less, and a diameter or Z-direction thickness of 100 μm to 300 μm; andat least one flow passage defined by the bottom surface of the first reinforcement layer, the top surface of the second reinforcement layer, and a lengthwise portion of the surface of the monofilament fiber, the flow passage abuts and extends along the length of the monofilament fiber in between the first reinforcement layer and the second reinforcement layer. 26. The unidirectional reinforcement of claim 24, wherein the monofilaments are laid in a straight and parallel formation, and the monofilaments are arranged to have a lateral distance of between about 2 mm to 50 mm from one another. 27. The non-woven unidirectional reinforcement assembly of claim 25, wherein more than one monofilament fibers are provided, and the monofilament fibers are laid in a parallel formation with a lateral distance of between about 2 mm to 50 mm from one another.