Fiber-matrix composites with negative Poisson's ratio

1 . A composite material, comprising:

a stratified material,

wherein the stratified material comprises:

(i) a first hard phase and a second hard phase, optionally wherein the first hard phase and the second hard phase are not parallel;

wherein each of the first hard phase and the second hard phase comprises a fiber material with an effective stiffness (E f ); and

(ii) a soft phase, wherein the soft phase comprises a matrix material with an effective stiffness (E m );

wherein the ratio of E f to E m (E f /E m ) is a stiffness ratio greater than about 10;

in a representative volume element of the composite material, the angle of the first hard phase with respect to a central y-axis of the representative volume element is represented by α;

the angle of first hard phase with respect to the second hard phase is represented by β;

α is about 0° to about 75°; and

β is about 0° to about 65° or about 110° to about 180°.

2 . The composite material of claim 1 , wherein the composite material exhibits auxetic behavior.

3 . The composite material of claim 1 , wherein the volume fraction of the composite material is less than about 10%.

4 . The composite material of claim 1 , wherein the composite material has no pores or voids.

5 . The composite material of claim 1 , wherein the fiber material is selected from carbon fibers, glass fibers, aramid fibers, natural fibers, basalt fibers, polymer fibers, and metallic fibers.

6 . The composite material of claim 1 , wherein the matrix material is selected from polymer matrix, metal matrix, ceramic matrix, carbon matrix, and hybrid polymer/ceramic matrix.

7 . The composite material of claim 1 , wherein the composite material is patterned.

8 . The composite material of claim 1 , wherein the stiffness ratio is greater than 10.

9 . The composite material of claim 1 , wherein the stiffness ratio is about 100.

10 . The composite material of claim 1 , wherein the stiffness ratio is about 1000.

11 . The composite material of claim 1 , wherein the stiffness ratio is about 10000.

12 . The composite material of claim 9 , wherein α is about 45° and β is about 20° to about 45° or about 145° to about 155°.

13 . The composite material of claim 10 , wherein α is about 45° and β is about 15° to about 45° or about 145° to about 155°.

14 . The composite material of claim 11 , wherein α is about 45° and β is about 10° to about 45° or about 140° to about 165°.

15 . The composite material of claim 1 , wherein the composite material exhibits auxeticity.

16 . The composite material of claim 15 , wherein α is about 45° and β is about 15° to about 45° or about 140° to about 165°.

17 . An aerospace structural component, comprising a composite material of claim 1 .

18 . A sports or body armor material or a wearable material, comprising a composite material of claim 1 .

19 . The composite material of claim 9 , wherein α is about 60° and β is about 30° to about 60°.

20 . The composite material of claim 10 , wherein α is about 60° and β is about 15° to about 60° or about 150° to about 160°.

21 . The composite material of claim 11 , wherein α is about 60° and β is about 15° to about 60° or about 155° to about 165°.

22 . The composite material of claim 10 , wherein α is about 60° and β is about 25° to about 40°.

23 . The composite material of claim 7 , wherein the composite material is patterned with a chevron pattern.

24 . The composite material of claim 1 , wherein β is about 0° to about 65°.

25 . The composite material of claim 1 , wherein β is about 110° to about 180°.