Process for the manufacture of curved objects
The invention relates to a process for the manufacture of an object, curved in one or more directions, from a package of at least one stacked ply containing polymeric fibers by the deforming thereof at elevated temperature, the process comprising imposing on the fibres a tensile stress at a temperature lying between the melting point of the fibers at the imposed tensile stress and 20° C. below the melting point, which tensile stress is high enough for the fibers to be drawn. This process allows objects, curved in one or more directions, to be produced from flat fiber plies without appreciable wrinkling using even fiber plies with low internal and/or mutual deformability and without material being drawn into the die in a controlled manner. The invention also relates to an object, curved in one or more directions, obtainable by the process according to the invention.
1. A wrinkle-free object, curved in one or more directions, comprising at least one ply containing drawn polymeric fibres, which object exhibits in different locations a different mean fibre diameter which is a diameter common to a majority of fibres, with a difference between greatest and smallest mean values of the different mean fibre diameters being at least 7%, wherein the object is made by a process comprising deforming at elevated temperature the at least one ply containing polymeric fibres, wherein the step of deforming includes imposing a tensile stress on the fibres at a temperature lying between the melting point of the fibres at the imposed tensile stress and 20° C. below the melting point, which tensile stress is high enough for the fibres to be drawn to achieve the difference between the greatest and smallest mean values of the different mean fibre diameters.
2. The object of claim 1 , wherein the difference between the greatest and the smallest mean value of the mean fibre diameter is at least 10%.
3. The object of claim 1 , wherein the polymeric fibres are chosen from the group consisting of polyolefin fibers, polyvinyl alcohol fibers, polyamide fibers and polyester fibers.
4. The object of claim 1 , wherein the fibres have a tensile strength of at least 2 GPa and a tensile modulus of at least 50 GPa as measured according to ASTM D885M.
5. The object of claim 1 , wherein the fibres are ultrahigh molecular weight polyethylene fibres.
6. The object of claim 1 , further comprising multiple plies containing drawn polymeric fibres, wherein the plies are unidirectional plies containing continuous fibres which are unidirectionally aligned.
7. The object of claim 1 , further comprising multiple plies containing drawn polymeric fibres, wherein the plies are unidirectional plies and the fibre direction in each ply is preferably at an angle with the fibre direction in adjacent plies.
8. The object of claim 1 , wherein the at least one ply consists of polymeric fibres and up to 50% by mass of a binder.
9. The object of claim 1 , wherein the at least one ply is thinner than 0.1 mm.
10. The object of claim 1 , wherein the object is chosen from the group consisting of radomes, helmets, ballistic protection panels for shoulders and armour panels for automobiles or for military helicopters.
11. A wrinkle-free object comprising at least one ply which is deformed so as to provide a curve in at least one or more directions, the at least one ply containing polymeric fibres which are drawn in response to deformation of the at least one ply so that the object exhibits in different locations a different mean fibre diameter which is a diameter common to a majority of fibres, with a difference between greatest and smallest mean values of the different mean fibre diameters being at least 7%.
12. The object of claim 11 , wherein the difference between the greatest and the smallest mean value of the mean fibre diameter is at least 10%.
13. The object of claim 11 , wherein the polymeric fibres are chosen from the group consisting of polyolefin fibers, polyvinyl alcohol fibers, polyamide fibers and polyester fibers.
14. The object of claim 11 , wherein the fibres have a tensile strength of at least 2 GPa and a tensile modulus of at least 50 GPa as measured according to ASTM D885M.
15. The object of claim 11 , wherein the fibres are ultrahigh molecular weight polyethylene fibres.
16. The object of claim 11 , further comprising multiple plies containing polymeric fibres, wherein the plies are unidirectional plies containing continuous fibres which are unidirectionally aligned.
17. The object of claim 11 , further comprising multiple plies containing polymeric fibres, wherein the plies are unidirectional plies and the fibre direction in each ply is preferably at an angle with the fibre direction in adjacent plies.
18. The object of claim 11 , wherein the at least one ply consists of polymeric fibres and up to 50% by mass of a binder.
19. The object of claim 11 , wherein the at least one ply is thinner than 0.1 mm.
20. The object of claim 1 , wherein the object is chosen from the group consisting of radomes, helmets, ballistic protection panels for shoulders and armour panels for automobiles or for military helicopters.