Fiber-reinforced films
An apparatus includes a first layer including unidirectional first fibers oriented in a first direction and embedded within the first layer, where the first layer has a thickness of less than 25 μm and a second layer bound to the first layer, the second layer including unidirectional second fibers oriented in a second direction and embedded within the second layer, where the first layer has a thickness of less than 25 μm and where the first direction is nonparallel to the second direction.
1. A computing device comprising:
a foldable display;
a bend limit layer coupled to the foldable display, the bend limit layer configured to increase its stiffness non-linearly when the foldable display is bent to a radius of curvature less than a limit radius, the limit radius being less than 10 mm; and
a backing film coupled to the foldable display, the backing film including:
a first layer including a monolayer of unidirectional first fibers oriented in a first direction and embedded within the first layer, wherein the first layer has a thickness of less than 25 μm; and
a second layer bound to the first layer, the second layer including a monolayer of unidirectional second fibers oriented in a second direction and embedded within the second layer, wherein the first layer has a thickness of less than 25 μm, wherein the first direction is nonparallel to the second direction.
2. The computing device of claim 1 , wherein the bend limit layer includes a plurality of segments that are attached to a film and that are physically separated from each other when the radius of curvature of the foldable display is greater than the limit radius and that are in physical contact with neighboring segments when the radius of curvature of the foldable display less than or equal to the limit radius.
3. The computing device of claim 1 , wherein the bend limit layer includes a plurality low stretch fibers, wherein the fibers are arranged in the bend limit layer, such that when the radius of curvature of the foldable display is greater than the limit radius, the distance between ends of each fiber in a plane of the bend limit layer is less than the length of the fiber, and such that when the radius of curvature of the foldable display is less than or equal to the limit radius, the distance between ends of each fiber in a plane of the bend limit layer is approximately equal to the length of the fiber.
4. The computing device of claim 1 , wherein the bend limit layer includes a material whose stiffness changes non-linearly in response to a strain in the material exceeding a threshold value.
5. The computing device of claim 1 , wherein the unidirectional first fibers include a ceramic material.
6. The computing device of claim 1 ,
wherein the foldable display includes an OLED layer, the OLED layer having a first coefficient of thermal expansion,
wherein a weighted average coefficient of thermal expansion of the unidirectional first fibers in the first layer is within 25% of the first coefficient of thermal expansion.
7. The computing device of claim 6 , wherein the unidirectional first fibers in the first layer include fibers of different materials, the different materials having different coefficients of thermal expansion.
8. The computing device of claim 7 , wherein the first fibers in the first layer include ceramic fibers and include carbon fibers.
9. The computing device of claim 6 , wherein the weighted average coefficient of thermal expansion of the unidirectional first fibers in the first layer is greater than 7 ppm per Kelvin.
10. The computing device of claim 1 , wherein the direction of the first fibers is substantially perpendicular to the direction of the second fibers.
11. The computing device of claim 1 , wherein the first fibers and the second fibers have cross-sections that are substantially circular, wherein diameters of the first fibers and of the second fibers are less than about 12 μm.
12. The computing device of claim 11 , wherein an average spacing between adjacent unidirectional first fibers is greater than two times the diameter of the first fibers.
13. The computing device of claim 11 , wherein an average spacing between adjacent unidirectional first fibers is greater than five times the diameter of the first fibers.
14. The computing device of claim 1 , further comprising:
a third layer bound to the second layer, wherein the second layer is located between the first and third layers, the third layer including unidirectional third fibers embedded within the third layer, wherein the third layer has a thickness of less than 25 μm and wherein a direction of the third fibers is nonparallel to a direction of the second fibers.
15. The computing device of claim 14 , wherein the direction of the third fibers is substantially parallel to the direction of the first fibers.