KR20040047837A - Three-dimensional knit spacer fabric sandwich composite - Google Patents

Abstract

The present invention relates generally to the use of three-dimensional knit spacer fabric components in the manufacture of sandwich core interface composites. More specifically, the present invention uses such spacer fabrics as skin-to-core laminate interfaces to enhance laminate bonding, in particular to improve interfacial flatness of monolithic core grid cuts to rough bends and to eliminate discontinuities in composite structures. It is about.

Description

THREE-DIMENSIONAL KNIT SPACER FABRIC SANDWICH COMPOSITE}

This application is partly filed in US Provisional Application No. 60 / 307,109, filed on June 17, 2002 and filed on July 23, 2001, which is incorporated herein by reference. The contents are incorporated herein by reference. This application enjoys the benefit of priority to US Provisional Application No. 60 / 322,602, filed September 17, 2001, the entire disclosure of which is also incorporated herein by reference.

Fiber reinforced plastic (FRP) composite structures are generally known and take many shapes and forms, ranging from simple forms to complex forms, for end uses ranging from marine vessels to bathtubs and aircraft. Typically, this type of manufacture involves providing a reinforcing fiber structure, woven, or non-woven that is laminated into an open mold of the desired form, commonly referred to as a preform. Also, a core structure is typically inserted between the inner and outer laminas of the composite. Such dry fiber reinforcements are then curable, generally thermoset resins, which must generally be fully wetted using manual techniques. After wetting the preform, the resin is cured to form a composite of the desired form. The resulting composite structure can be finally removed from the mold and used after appropriate post-treatment.

Despite the many advantages these FRP composites exhibit over other materials, laminate stiffness (bending resistance) was not one of its strengths. With the exception of using expensive high modulus fibers, i.e. carbon fibers and / or advanced, i.e., an uneconomical manufacturing process technology, FRP laminates are generally resistant to bending moments in which panels of some weight are resistant to bending moments. Considering the capacity, the general result was inferior to other low density materials such as wood.

The stiffness of panels, especially FRP composite panels, depends largely not only on the flexural modulus, which is a measure of material stiffness, but also largely on the function of the cube of panel thickness. Thus, a relatively small increase in this panel thickness to substantially increase the composite stiffness also has drawbacks in terms of weight and cost.

In other words, it is clear that one approach to strengthening FRP panels is to make it thicker, but unnecessarily very heavy laminates probably result in unnecessary strength properties, unnecessarily expensive, and provide substantial manufacturing problems for the final intended structure. Can cause disadvantages.

Essentially, problems of inadequate strength and modulus can also arise from inadequate uniformity in the fabrication of FRP composites. For example, the resin component may be improperly distributed through the fiber matrix before the resin is completely distributed in the fiber matrix and may have voids or irregularly cured (eg, resulting in surface discontinuities that degrade the strength). Reaching the gel point in advance).

A preferred technique for increasing the stiffness of FRP panels is to use sandwich structures. The sandwich structure of the laminate offers comparable advantages in the form of I-beams, but a light-weight core facing one or both sides by the skin of the FRP instead of the web and flange of a typical I-beam. Use a substance. The role of such skins in composite structures is to withstand bending moments on panels or beams by resisting the compressive and tensile loads set at opposite skins when the panels are subjected to bending loads.

In order for the skins to be able to withstand the bending moments, they must be firmly fixed away from the central axis of the sandwich (centerline) to prevent movement against each other. The task of the selected core material and the bond line strength between the core and the skin is to provide and meet these conditions. For certain industrial applications, the integrity of the sandwich structure, regardless of the skin and core material chosen, depends in particular on the interfacial bond strength between the skin and the core material.

The physical or mechanical use of the core in the laminate also depends very much on the manufacturing technique used for the given structure. Those skilled in the art have generally recognized that the vacuum bag technique is useful for achieving complete and intimate contact between the core member and the outer skin (in contrast, the inner skin when using a female mold, or the inner skin when using a hydraulic mold). In vacuum bag technology, the skin is laminated and wetted, the core member is attached thereto with or without a bonding adhesive, and the vacuum bag is attached to the assembly. As the air is removed, the external ambient air pressure tends to pressurize the core member evenly on the skin surface, but the contact between the lamina and the core member is limited by the dimensional shape of the core member. The vacuum bag is often held in place until the outer skin (eg in a female mold) cures with the core attached to it. Often, the production of (ultimately) inner fiberglass lamina presents little or no problem in achieving a reasonably uniform lamination result, when a laminator visually shows the core surface when a relatively transparent wet glass fiber laminate is produced. Because it can observe. However, if the core member obstructs or obstructs visual observation, serious problems can be raised by the FRP skin adjacent to the mold tool.

Vacuum injection techniques can be used to simultaneously produce the skin while applying ambient pressure to the core member. If the material for the core member is relatively hard and the molded part is designed to provide a concave or convex surface, the core material may be drawn in small compartments, and in some cases a scratch may be applied to one side The small compartments can be held together in a flat x, y fashion.

However, a common problem encountered is that the lateral dimension of one or more lined, often straight, enclosed core sections is much larger than the radius of the mold surface desired for the intended structure. This results in voids at the interface of the fiber stack and the core member. In this case, the ultimately desired close contact between the skin and the core can often be achieved only by using excess adhesive or other filler that occupies the resulting dimensional spacing.

This technique is not practical for vacuum injection methodologies, and usually skin or core voids must be filled with resin. In either case, the skin to core spacing is filled with a medium having mechanical and strength properties that are significantly different from the skin to core, resulting in areas with branching stress properties. In addition, in applying vacuum injection, severe voids at the interfaces described above can result from incomplete resin wetting. The resulting interface can then be damaged for optimal desired properties. As a result, there will be discontinuities that adversely affect the strength of the desired purpose.

The present invention generally relates to novel uses and applications of core materials that increase the stiffness and other properties of sandwich composites and improve the injection of resins. Specifically, the present invention relates to the interfacial planarity of a monolithic grid core member that has been cut and placed in an attempt to follow the curvature in a desired structure, in particular as a laminate interface to enhance laminate bonding of three-dimensional knit spacer fabrics. It relates to a use as a laminate interface to calibrate.

1 schematically shows a cross section of a FRP laminate structure according to the prior art,

Figure 2 schematically shows a cross section of the FRP laminate structure according to the present invention,

Figure 3 schematically shows the three-dimensional spacer fabric used in the present invention in an uncompressed state,

Figure 4 schematically shows the three-dimensional spacer fabric used in the present invention in a compressed state,

5 is an enlarged schematic view of the three-dimensional spacer fabric used in the present invention in an uncompressed state,

6 is an enlarged schematic view of the three-dimensional spacer fabric used in the present invention in a compressed state,

7 is a schematic plan view of a further aspect of the present invention.

In view of the above-mentioned drawbacks inherent in known types of FRP cores and vacuum injection application techniques used in the prior art, the present invention is directed to the use of three-dimensional knit spacer fabrics as bonding interfaces in laminates to greatly improve bondability. It provides a new technique for skin-to-core bonding.

In particular, the novel use of three-dimensional knit spacers as skin to core lamina interfaces, or as intermediate laminas of the present invention improves interfacial flatness of cut monolithic core member grids and deviates from conventional concepts and prior art designs. In so doing, the present invention provides techniques, materials and products developed for the purpose of improving the integrity of FRP skin to core bond lines.

The general objects and results of the present invention, which will be described in more detail below, provide a novel skin-to-core member bonding interface with improved advantages over the composite sandwich structures used to date. To achieve this, the present invention generally involves the use of three-dimensional knit spacer fabrics with elastic Z-directional fibers used as one lamina in a laminae between the skin and the core. This technique not only provides improved skin to core bonding but is also a component of the laminate.

Accordingly, one object of the present invention is to provide a three-dimensional knit spacer fabric as a bonding medium between the skin and core of a sandwich composite, overcoming the drawbacks of conventional devices.

It is a further object of the present invention to provide a three-dimensional knit spacer fabric as a bonding medium between the skin and the core of the sandwich composite for use in all processes for manufacturing the composite.

Other objects and advantages of the invention will be apparent to those skilled in the art, and these objects and advantages are intended to be within the scope of the invention.

To the accomplishment of the foregoing and other related objects, the present invention is embodied in the form of descriptions in the accompanying drawings, and attention is to be paid to them, although these drawings are presented for illustrative purposes only and modifications within the illustrated specific structures have been made. Can be done.

As shown in FIG. 1, a woven or nonwoven fibre-reinforced preform layer 12 (finally, the outer skin here) is applied to a mold 10 of the desired shape. In this embodiment, the core material 14 member is placed between the inner 12 and outer 16 layers of the fiber reinforcement or lamina to construct the structure in the lamina. The curvature of the mold form 10 in this embodiment is such that a void 18 is formed between the outer skin 12 and the core member 14. Next, it is required to fill this space 18 with a selected resin to join the various elements of the composite.

However, the voids 18 between the core members and between these core members 14 and the lamina 12 are difficult to completely fill during manufacture such that air spaces or voids are created there and adversely affect the bonding of the composite. Experience.

2, a similar mold tool 20 is shown and an outer skin lamina 22, a core member 24 and an inner skin lamina 26 are shown. In this figure, the invention is carried out with the use of an additional lamina 28 of spacer fabric as shown.

3 is a further schematic view of the spacer fabric structure 30. It will be appreciated that this consists of two spatially separated fabrics and / or stitched outer layers 32 and 34. There is a transverse fiber 36 made to extend between these two layers and connect these two layers. These transverse fibers are made to be relatively elastic.

4 shows a schematic view of the spacer fabric of FIG. 3, but in a compressed state 40 by application of external pressure. The outer layers 42 and 44 maintain their uncompressed orientation and shape relatively well, but the transverse fibers 46 are angularly displaced as a result of the reduction in lamina thickness. Pressing and displacement of the transverse fibers 46 nevertheless leaves elastic fibers with spring back tendencies and strain resistance. Of course, the overall spacer fabric is flexible and therefore conforms to the irregularities of the shape of the core member and the mold surface itself, thereby reducing voids therebetween.

As described below, and as also described in the applicant's parent application, such spacer fabrics, commonly referred to by the applicant as trade name "Polybeam ^™ ", allow the flow of liquid resin across fiber / fabric preforms during the manufacture of composite structures. And a great advantage of promoting dispersion, allowing the filling of voids between the core members even before the gelation point of the resin.

Thus, as shown in FIG. 2 and associated figures, the voids are replaced by structural FRP reinforcements by using the three-dimensional spacer fabric 28 of the present invention located between the outer skin 22 and the core member 24. do.

For example, the three-dimensional knit spacer fabric 50 of FIG. 5 itself may be a first fabric layer 52, a second fabric layer 54, and monofilament polyester, fiberglass, and the like, and the two layers 52 and 54 is composed of intermediate elastic spacer yarns 56 that connect each other. The fibers of the fabric layers 52, 54 generally extend in the X and Y directions as indicated in the figure. An elastic yarn 56 extending generally in the Z direction (although angled) separates the two fabric layers in a free form, at a pressure-free thickness ranging from about 0.0625 "to 1". A wide range of woven and yarn fibers can be used in spacer yarns, for example polyesters, glass fibers, Kevlar, carbon and composites thereof. In addition, traditional materials such as fiberglass mats and rovings can also be bonded or stitched on one or both sides of the three-dimensional knit spacer fabric and also stitched around other materials. As shown in FIG. 5, there is virtually free, open space between the layers 52, 54.

As shown in FIG. 6, the three-dimensional knit spacer fabric 60 is applied in a Z-direction when a vacuum (ie, under ambient pressure) is applied to press the core member against the skin as shown in FIG. 2. It is elastically compressed. This spacer fabric is somewhat flattened by this, but nevertheless conforms to the core-skin interface to achieve a more uniform reinforcing structure throughout the interface.

The planarized interface may then be infused with an adhesive or a resin, depending on the manufacturing technique used, but is preferably filled with a resin for the duration of the process. Even when compressed as shown in this figure, there is still considerable free open space between the outer layers in that the fiber density continues to be significantly smaller than that of the outer surface. Although difficult to measure, current calculations show that uncompressed spacer fabrics have about 88-90% free volume, while compressed spacer fabrics have about 65-75% free volume or open space for resin injection. Shows.

Fig. 7 is a plan view of one embodiment of the present invention, in which the " Tool " In this example, "Vaccum" means vacuum at the top end of the figure and the Resin Input is shown at the bottom. Of course, the exact point of resin injection may be elsewhere, but it is most useful to be at a position relatively far from the point that usually leads the vacuum pump. A spiral cut tube portion is shown in FIG. 7, which simply functions as a large amount of resin infusion device. Laminae A and Laminae B shown in this figure, which in each case comprise a three-dimensional spacer fabric, are described in more detail later.

One dramatic feature of the use of three-dimensional spacer fabrics according to the present invention is that, even when compressed under vacuum application, virtually no open space remains for injection of uncured resin throughout the composite structure elements. This can be observed, in particular, in uncored sample composites by the forward flow of the liquid resin as the liquid resin is introduced through one or more of the structures in the assembly. As mentioned in the applicant's parent application, an increase of 200-400% in the rate of movement of this forward flow can be observed. This important feature has many advantages in the present invention. For example, it is possible to use a wider range of viscosities for the resins used. In addition, in this technique, there is always some "race" to achieve wetting or complete resin injection of the fiber preform before the resin reaches the gel point, resulting in rejection of the manufactured product. By realizing a higher rate for the forward flow of the resin composition, complete injection and wetting can easily be achieved under a wide range of ambient conditions and resin / catalyst mixtures.

The implementation of the invention will now be described in detail by the following several examples, but it should not be understood that the invention is limited to the specific conditions described herein.

It is common to use balsa wood core members in an FRP composite, where the final particles are arranged normal to the flat surface of the resulting structure. Here, four test panels were made of the final particle firing core member as indicated. Laminate schedules for each panel are described below. Each panel was made of Hetron 922 vinyl ester resin and injected and cured under a 25 inch vacuum of mercury (Hg).

Panel 1 : 18 oz. 3Tex Glass Panel 2 : 18oz. 3Tex Glass

18 oz. 3Tex Glass 18oz. 3Tex Glass

18 oz. 3Tex Glass 18oz. 3Tex Glass

¾ "CK-89 LamPrep Balsa ¾" CK-89 LamPrep Balsa

Polybeam ^TM 730 ¹ Polybeam ^TM 703 ¹

18 oz. 3Tex Glass 18oz. 3Tex Glass

18 oz. 3Tex Glass 18oz. 3Tex Glass

Panel 3: 18 oz. 3Tex Glass Panel 4 : 18oz. Glass

18 oz. 3Tex Glass 18oz. Glass

Polybeam ^TM 703 ¹ 18 oz. Glass

¾ "CK-89 LamPrep Balsa ¾" CK-89 LamPrep Balsa

Polybeam ^TM 703 ¹ 18 oz. Glass

18 oz. 3Tex Glass 18oz. Glass

18 oz. 3Tex Glass 18oz. Glass

18 oz. 3Tex Glass

¹ Footnote: Polybeam ^™ is the trade name for the spacer fabric used in these panels.

Polybeam ^™ 730 fabric is a three bar Raschel knitted spacer fabric made from a double bed machine having the following properties:

The wale / meter is 590 and the course / meter is 530 (the wale is the vertical line of the stitch and the course is the horizontal line of the stitch). Yarn is understood to be 100% monofilament polyester of about 0.2 mm diameter. The wrapping for this structure is as follows:

Bar 1 02, 22, 20, 00, 02, 66, 810, 1010, 108, 88, 810, 66,

Bar 2 (20, 46, 810, 64) × 3

Bar 3 66, 810, 1010, 108, 88, 810, 66, 20, 00, 02, 22, 02,

0-2 is one needle shog (displacement). The trick plate gap is 10 mm.

Polybeam ^™ 703 is a similar Raschel knit spacer fabric with similar properties.

The inner and outer "skin" is made of orthogonal woven glass fiber material, supplied from 3Tex.

After curing, two tests were performed on the panel.

Test 1: ASTM C-393 "Flexure Test" is an evaluation of the stiffness and strength of sandwich panel specimens subjected to bending loads.

Test 2: The ASTM C-297 "Flat-wise Tension Test" is an evaluation of the tensile strength and tensile modulus of a structural core in a direction perpendicular to the sandwich exterior.

Edgewise loading along the edge of the sandwich panel can cause buckling on the face of the sandwich panel. This outward deflection is representative of these flat stresses.

result:

TABLE 1

exam ASTM C-297 Tensile Strength and Tensile Modulus ASTM C-393 Flexural Stiffness and Flexural Modulus Strength (psi) Modulus (psi) Rigid (in * lbf) mold surface / rear Coefficient (psi) Mold Face / Rear Deflection @ 100 lbs (in) Mold Face / Rear Panel 1 1164 30356.3 53642.4 / 53888.4 20700.2 / 21049.1 0.045 / 0.045 Panel 2 1083 27506.1 45069.3 / 43350.0 19350.9 / 18681.1 0.054 / 0.056 Panel 3 877.2 25944.7 51947.5 / 51592.7 21128.7 / 20435.9 0.047 / 0.047 Panel 4 1205.4 28016.2 50772.9 / 49408.1 22361.4 / 21922.7 0.046 / 0.049

These test results show that although the structure with the fabric layers positioned apart apart clearly includes internal regions of greatly reduced fiber density in both uncompressed and compressed forms, the use of spacer Polybeam ^™ fabrics is responsible for the composite strength properties. It does not indicate any adverse effect.

A striking observation of this experiment was that tensile failure always occurred between the core (the launch member) and the skin. No destruction was observed at the face of the firing core member bonded to contact the spacer fabric. In fact, panel 3 with Polybeam ^™ 703 was observed on both sides of the core. 3Tex outer fiberglass skins and the core member has been destroyed, Polybeam ^TM for the core interface remained not always damage.

Test panel production :

Additional flat test panels were made to evaluate the mechanical properties of the Polybeam ^™ containing laminates. Dimensional considerations were specified by the requirements of the selected ASTM test. Laminates were chosen on this basis to produce composites of appropriate thickness. The schedule on the selected lamina is as listed in the table below (see also FIG. 7 for explanation).

TABLE 2

ASTM D3039 Tensile Test of Fiber-Resin Composites

ASTM D790 Three-Point Flexural Test

Lamina A:

Lamina material Warp orientation Ply orientation ¹ One E-LTM 2415-7 0 ° - 2 Polybeam ^TM 730 0 ° NA 3 E-LTM 2415-7 0 ° -

TABLE 3

ASTM D790 Three-Point Flexural Test

Lamina B:

Lamina material Warp orientation Ply orientation One E-LTM 2415-7 0 ° - 2 Polybeam ^TM 730 0 ° NA 3 E-LTM 2415-7 0 ° - 4 E-LTM 2415-7 0 ° - 5 Polybeam ^TM 730 0 ° NA 6 E-LTM 2415-7 0 ° -

¹ 2415 is a ²⁴ oz / yd ² biaxial stitched roving having 1.5 oz / ft ² . CSM stitches on one side. Here, (-) represents a mat with roving for Polybeam ^™ .

Laminae A is designed to have a thickness of 0.157 "(4mm) according to ASTM standard conditions and Laminae B is designed to have a thickness of 0.354" (9mm).

Reinforcing lamina consists of stitch bonded glass fibers, supplied from Johnson Industries, and has the following properties:

Johnson's confirmation number: E-LTM 2415-7

Fiber Type: Fiberglass (E)

Structure: 0 ° / 90 ° Biaxial "LT" Series

Dry Thickness: 0.066in./1.6764mm

Total Weight: 39.08oz / yd ² /1291.41g/m ²

Fiber structure data

0 °: 12.03oz / yd ² / 304.64g / m ²

90 °: 11.95oz / yd ² / 405.06g / m ²

Matt / Vale: 13.5oz / yd ² / 1.5oz / ft ²

Manufacture process:

To meet sample conditions as described above, one 24 "x 24" panel was made. The tool consisted of wax release treated 48 "x 48" flat formica plates. Lamina A (Table 2) was completed by cutting the lamina into 24 "x 24" dimensions and placing them on the tool surface in a specific order. Laminae B (Table 3) was completed by repeating the ply lamination sequence of A to lamina with 6 "x 24" lamina with the correct orientation on top of group A aligned along one edge. As shown in FIG. 7, a single vacuum port was mounted near B to lamina and a spiral cut tube wrap for resin injection was mounted to the opposite edge of A to lamina. The flexible vacuum bag was then mounted and sealed in the laminate, the resin infusion tube was clamped and the vacuum drawn in.

The vacuum scale was read with a gauge attached to a standard resin trap. When the vacuum reached 26 "Hg, the clamp was removed from the resin injection tube and the tube was placed in vinyl ester resin (-230 cps). A uniform forward flow across this part was observed. The front of the resin was directed to the vacuum port. When reached, the resin clamps were reattached to the injection tube. Sufficient vacuum (26 "Hg) was maintained during this process. At this point, excess resin in the laminate was removed by vacuum to the point at which time the resin gelled and no longer flows. Sufficient vacuum was maintained until this time. After the resin had completed its exotherm and cooled to room temperature, the panel was removed for post cure and testing. The following conditions were observed during this test:

Room temperature: up to 68 ° F

Resin temperature: ～ 68 ℉

Tooling temperature: ～ 68 ℉

The viscosity was specified at 230 cps at 77 ° F.

Fiber Volume: The typical fiber / resin ratio range for vacuum injection (without injection medium) into the laminate is 40:60 to 75:35. These ranges are based on weight and are therefore very dependent on the components used in terms of both resins and fibers. It will therefore be understood that the invention is in no way limited to these specific proportions.

It will be apparent to those skilled in the art that the advantages and utility provided by the present invention can be realized with the use of a wide range of fiber sizes and fiber compositions. Glass fibers are often the most widely used, but other fibers such as carbon fibers or Kevlar polyaromatic fibers may also be used. Similarly, a wide range of thermosetting resins (epoxy, vinyl and other crosslinkable materials) are also suitable for this use. What is essentially found in the present invention, in contrast to the conventional use of three-dimensional spacer fabrics, is that they have the special ability to allow more rapid, improved introduction and flow of resin into and through the composite stacks. Surprisingly, this feature exists even under vacuum applied to the spacer fabric. In addition, the structure or Z-direction fibers (shown in FIGS. 6 and 7) retain their tendency to bounce back because they retain elasticity, which would otherwise be undesirable voids and pores or comparable in the final cured composite. Fill in the discontinuities. This spring back is actually aided by lubrication introduced by resin injection, which otherwise reduces the fiber-to-fiber mutual friction present in the anhydrous material. The resulting composites thus exhibit higher grades of completeness and uniformity not only in this structure but also in terms of final strength properties. Significant economics in the manufacturing process are a further advantage of the use of the present invention in that it can reduce consumption and reduce substandard products.

The advantage of the present invention is that at least one monolithic core member disposed between the outermost preform laminated to the mold surface using vacuum bag means to induce subsequent curable resin flow of negative pressure in communication with the three-dimensional spacer fabric. Is currently considered to be the most fully realized. A feature of the present invention is that the resulting relatively high velocity flow of the curable resin provides full lateral wetting of adjacent fiber fabric layers even when the fiber fabric layer itself does not have a three-dimensional spacer fabric structure, so that uniform resin injection results in composite laminates. Can be achieved in the whole. Of course, the present invention can also be used with many different molds and is likewise suitable for use in the closed mold technique as well as the open mold technique described above.

Accordingly, the invention is limited only by the scope and spirit of the appended claims.

Claims (3)

A product consisting of a fiber-reinforced composite laminate consisting of at least one woven or nonwoven fiber-containing cotton and a facing woven or nonwoven fiber-containing cotton, with one or more interlaminar three-dimensional spacer fabric structures disposed therebetween. A first fabric layer having fibers generally lying in a first X and Y plane, a second fabric layer having fibers generally lying in a second X and Y plane, and between the first and second fabrics A plurality of spacer fibers connecting the layers to one another and generally extending in the Z direction, providing a substantially lateral glass path for injecting resin through and between the first and second fabric layers, wherein the composite laminate as a whole Products that are substantially saturated with curable resins. One or more first preforms of woven or nonwoven fibrous structures are placed on the mold surface and thereon the first fabric layer with the fibers generally lying in the first X and Y planes, the fibers generally lying in the second X and Y planes. A three dimensional spacer fabric consisting of a second fabric layer having a plurality of spacer fibers, and a plurality of spacer fibers connecting the first and second fabric layers to each other and extending generally in the Z direction; Applying thereon a second preform made of a woven or nonwoven fibrous structure; Encapsulating the resulting stack in a vacuum bag; Providing means for applying a vacuum to the enclosure of the vacuum bag; Providing means for introducing a curable resin composition along at least one side of the vacuum bag while in communication with at least the three-dimensional spacer fabric; And Introducing the resin to flow through and wet the entire fiber structure. The method of claim 2, further comprising providing at least one monolithic core member between at least a portion of the first or second fiber stack and the three-dimensional spacer fabric.