Interlaced Z-pin sandwich structure

• US 5,935,680 A
• Filed: 08/22/1997
• Issued: 08/10/1999
• Est. Priority Date: 11/01/1995
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Childress, James J.
• Primary Examiner(s): PEZZUTO, HELEN LEE
• Application Number:
  US08/916,623
• Time in Patent Office: 718 Days
• Field of Search: 428/119
• US Class Current: 428/119
• CPC Class Codes: B29C 31/08 of preforms to be moulded, e.g. tablets, fibre reinforced preforms, extruded ribbons, tubes or profiles; Manipulating means specially adapted for feeding preforms, e.g. supports conveyors B29C31/066, B29C37/001, B29C43/085 take precedence
• CPC Class Codes: B29C 70/086 and with one or more layers of pure plastics material, e.g. foam layers applying a non-preformed coating, e.g. a gel-coat, B29C37/0025; with foam blocks B29C70/86
• CPC Class Codes: B29C 70/24 oriented in at least three directions forming a three dimensional structure
• CPC Class Codes: B29K 2105/04 cellular or porous
• CPC Class Codes: B32B 2305/022 Foam
• CPC Class Codes: B32B 5/00 Layered products characterised by the non- homogeneity or physical structure , i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
• CPC Class Codes: B32B 5/18 characterised by features of a layer of foamed material
• CPC Class Codes: B32B 5/32 at least two layers being foamed and next to each other
• CPC Class Codes: B64C 1/12 Construction or attachment of skin panels
• CPC Class Codes: B64C 2001/0072 from composite materials
• CPC Class Codes: E04C 2/296 composed of insulating material and non-metallic or unspecified sheet-material E04C2/288 takes precedence
• CPC Class Codes: Y02T 50/40 Weight reduction
• CPC Class Codes: Y10T 428/233 Foamed or expanded material encased
• CPC Class Codes: Y10T 428/23914 Interlaminar
• CPC Class Codes: Y10T 428/24008 including fastener for attaching to external surface
• CPC Class Codes: Y10T 428/24033 including stitching and discrete fastener[s], coating or bond
• CPC Class Codes: Y10T 428/24099 On each side of strands or strand-portions
• CPC Class Codes: Y10T 428/24107 including mechanically interengaged strands, strand-portions or strand-like strips
• CPC Class Codes: Y10T 428/24149 Honeycomb-like
• CPC Class Codes: Y10T 428/24174 including sheet or component perpendicular to plane of web or sheet
• CPC Class Codes: Y10T 428/24182 : Inward from edge of web or sheet
• CPC Class Codes: Y10T 428/249923 : Including interlaminar mechanical fastener
• CPC Class Codes: Y10T 428/249953 : Composite having voids in a component [e.g., porous, cellular, etc.]
• CPC Class Codes: Y10T 428/24996 : With internal element bridging layers, nonplanar interface between layers, or intermediate layer of commingled adjacent foam layers
• CPC Class Codes: Y10T 428/249961 : With gradual property change within a component
• CPC Class Codes: Y10T 428/249981 : Plural void-containing components
• CPC Class Codes: Y10T 428/249987 : With nonvoid component of specified composition
• CPC Class Codes: Y10T 428/249991 : Synthetic resin or natural rubbers

Abstract

Improved pin-reinforced sandwich structure ties the face sheets (typically on opposite sides of a foam core) together with a plurality of Z-pins that extend into each face sheet (through the core). The pins are arranged in a an interlaced configuration off-normal to provide crack resistance around fasteners for connecting the composite structure to other structural elements in aerospace applications.

Claims

1. A reinforced sandwich structure comprising:

(a) a core having opposed first and second surfaces defining a reference plane and a normal plane;

(b) a first face sheet adjacent the first surface;

(c) a second face sheet adjacent the second surface;

(d) rigid reinforcement inserted into and extending between the first and second face sheets and extending through the core to form a reinforced sandwich structure, wherein the reinforcement forms an interlaced, ordered configuration with at least a portion of the reinforcement off-normal to the reference plane to provide crack growth resistance in the face sheets;

(e) a bore through the core and face sheets in the region having the interlaced reinforcement; and

(f) a fastener in the bore.

2. The structure of claim 1 wherein the reinforcement is carbon.

3. A pin-reinforced sandwich structure, comprising:

(a) first and second, substantially planar, fiber-reinforced composite sheets spaced to define a sandwich structure;

(b) a plurality of pins inserted into and terminating in a Z-pin region of the sheets to interconnect the sheets, at least a portion of the pins being off-normal to a reference plane of the sheets, the pins being present in sufficient amount to provide an areal density sufficient for the pins to increase crack growth resistance in the sheets.

4. The structure of claim 3 further comprising a bore through both sheets in the Z-pin region.

5. The structure of claim 3 further comprising a core adhered between the sheets to form a three layer sandwich, the pins extending completely through the core.

6. The structure of claim 3 wherein the sheets include carbon-fiber reinforced thermoplastics.

7. The structure of claim 3 wherein the pins have a Young'"'"'s modulus of at least about 10⁷, and wherein the areal density of pins is about 0.75-1.50%.

8. Reinforced composite structure, comprising:

(a) a plurality of plies of a fiber-reinforced resin matrix composite having fiber reinforcement defining a reference plane; and

(b) Z-direction rigid reinforcement in a regular pattern within the composite for reinforcing the composite and being in sufficient areal density to increase crack growth resistance in the composite, at least a portion of the Z-direction reinforcement being off-normal to the reference plane.

9. The structure of claim 8 wherein the fiber reinforcement includes discrete, individual pins present at an areal density of at least 0.375%.

10. The structure of claim 8 wherein the composite includes at least two separate and discrete laminates that are interconnected by the reinforcement to define a sandwich structure.

11. The structure of claim 10 further comprising a core between the laminates wherein at least a portion of the reinforcement extends entirely through the core.

12. The structure of claim 11 wherein the core is foam.

13. The structure of claim 8 wherein the reinforcement surrounds a bore in the composite.

14. The structure of claim 8 wherein the reinforcement is at both plus and minus angles to the reference plane.

15. The structure of claim 8 wherein the reinforcement increases pull-off strength in both X-direction and Y-direction shear, and wherein the reference plane includes the X and Y directions.