Reinforcing material comprising twisted carbon threads for the manufacture of composite parts, and corresponding methods and use
The invention relates to a reinforcing material ( 1 ) consisting of a unidirectional reinforcing web ( 2 ) formed of one or more carbon reinforcing yarns ( 3 ), associated on each of its faces with a veil of polymeric fibers ( 4, 5 ) chosen from among nonwoven materials, the polymeric portion of the reinforcing material representing from 0.5% to 10% of the total weight of the reinforcing material ( 1 ), and preferably from 2% to 6% of its total weight, said unidirectional reinforcing web ( 2 ) comprising one or a series of reinforcing yarns ( 3 ) individually twisted having a twist of 3 turns/m to 15 turns/m, preferably from 6 turns/m to 12 turns/m.
1 . A reinforcing material comprising:
(a) a unidirectional reinforcing web formed of a plurality of carbon reinforcing yarns;
(b) a layer of nonwoven material, comprising polymeric fibers affixed to each to each side of said unidirectional reinforcing web, said layers of nonwoven material comprising from 2 to 6% of the total weight of the reinforcing material;
(c) wherein said reinforcing yarns each have a twist of 3 turns/m to 15 turns/m; and
wherein all the carbon reinforcing yarns forming the unidirectional reinforcing web are individually twisted, the two possible directions of twist being denominated as either S-twist or Z-twist, and having a twist of 3 turns/m to 15 turns/m, the unidirectional reinforcing web comprising at least 3 carbon reinforcing yarns thus twisted with at least one S-twist reinforcing yarn and at least one Z-twist reinforcing yarn:
wherein, when the total number of twisted carbon reinforcing yarns forming the unidirectional reinforcing web is even, the number of twisted carbon reinforcing S-twist yarns on one side of a plane Δ and the number of twisted carbon reinforcing S-twist yarns on the other side of the plane Δ, each of which is, independently, an integer in the range {[(total number of yarns)/4]−35%; [(total number of yarns)/4]+35%}, each endpoint of the range being rounded to the nearest integer if the formula defining it result in an integer, the other twisted carbon reinforcing yarns being Z-twist yarns;
wherein, when the total number of twisted carbon reinforcing yarns forming the unidirectional reinforcing web is odd, the number of twisted carbon reinforcing S-twist yarns on one side of the plane Δ and the number of twisted carbon reinforcing S-twist yarns on the other side of the plane Δ, which are either two integers or two and a half integers, and are, each independently, in the range {[(total number of yarns)/4]−35%; [(total number of yarns)/4]+35%}, each endpoint of the range being rounded to the nearest integer or integer and a half if the formula defining it results in an integer or integer and a half, the other twisted carbon reinforcing yarns being Z-twist yarns;
the plane Δ being the plane parallel to the general direction of extension of said unidirectional web and which divides said unidirectional web into two equal parts, being perpendicular to its surface.
2 . The reinforcing material according to claim 1 , characterized in that the unidirectional reinforcing web has a weight within the range from 126 g/m2 to 280 g/m2.
3 . The reinforcing material according to claim 1 , wherein the reinforcing yarns of having a titer of 3 to 24 K.
4 . The reinforcing material according to claim 1 , characterized in that it has a width greater than 12 mm.
5 . The reinforcing material according to claim 4 , characterized in that the polymeric fiber layers comprise fibers made of a thermoplastic polymer, a partially crosslinked thermoplastic polymer, a mixture of such polymers, or a mixture of thermoplastic and thermosetting polymers.
6 . The reinforcing material according to claim 5 , characterized in that said nonwoven materials have a basis weight within the range from 0.2 g/m2 to 20 g/m2 and a thickness of 0.5 microns to 50 microns.
7 . The reinforcing material according to claim 6 , characterized in that it is neither perforated, nor sewn, nor knitted, nor woven.
8 . A method for preparing a reinforcing material comprising the following successive steps:
a1) providing a unidirectional reinforcing web formed of one or more reinforcing yarns, each of said yarns being individually twisted and having a twist of 3 turns/m to 15 turns/m,
a2) providing at least two layers of polymeric fibers in the form of nonwoven materials,
a3) associating each of the polymeric fiber layers with each of the faces of the unidirectional reinforcing web.
9 . The method according to claim 8 , characterized in that it comprises, upstream of step a1), a step for the production of the unidirectional reinforcing web comprising the application of a twist of 3 turns/m to 15 turns/m to a reinforcing yarn or to a series of yarns, said twist being applied to each yarn individually.
10 . The method according to claim 9 , characterized in that the unidirectional reinforcing web is formed of a plurality of reinforcing yarns and in that the method comprises, upstream of step a1): i) applying a twist of 3 to 15 turns/m to a series of reinforcing yarns, said twist being applied to each yarn individually, ii) aligning the twisted yarns thereby obtained, with other reinforcing yarns, and arranging said yarns side by side, so as to form a unidirectional reinforcing web.
11 . A reinforcement material for use as an infusion preform comprising:
(a) at least one layer of fibrous reinforcing material comprising a plurality of unidirectional carbon fiber yarns, said yarns being coplanar and arranged next to each other in a parallel direction;
(b) each of said carbon fiber yarns having been subjected to rotational twisting along its longitudinal axis, said twisting being denominated as either S-twist or Z-twist, said carbon fiber yarns being subjected to twisting of between 3 turns/meter and 15 turns/meter;
(c) the carbon fiber yarns of a given layer of said fibrous reinforcing material being subjected to S-twist or Z-twist in equal numbers, whereby half of said carbon fiber yarns will have S-twist and half will have Z-twist; and
(d) a layer of non-woven polymeric thermoplastic material in the form of a veil or mesh being affixed to both the top and bottom of said reinforcement material, said layers of non-woven polymeric thermoplastic material comprising between 2 and 6% by weight of the reinforcement material.
12 . The reinforcement material of claim 11 , wherein the twists utilized for the carbon fiber yarns within a layer of fibrous reinforcing material are chosen from the following sequences: SZ, SZS, ZSZ, SZZS, SZSZ, SZSZS, SSZZSS, SZSSZS, SZSZSZ, and SSZZSSZZ.