STRAND PROFILE AND PROCESS FOR PRODUCING A STRAND PROFILE

Abstract

A strand profile (10) is proposed. The strand profile (10) extends in a longitudinal extent direction (22), the strand profile (10) having a first layer structure (24) arranged around the longitudinal extent direction (22) and a second layer structure (32) surrounding the first layer structure (24), the first layer structure (24) comprising a first multiplicity of layers (26), each layer (26) of the first layer structure (24) having multiple fibers (28), the second layer structure (32) comprising a second multiplicity of layers (34), each layer (34) of the second layer structure (32) having multiple fibers (36), the fibers (28) of the first multiplicity of layers (28) and the fibers (36) of the second multiplicity of layers (34) each extending in longitudinal extent directions (30, 38), the longitudinal extent directions (30) of the fibers (28) of the first multiplicity of layers (26) and the fibers (36) of the second multiplicity of layers (34) each being oriented at an angle with a magnitude in a range from 30 to 60, and preferably in a range from 40 to 50, with respect to the longitudinal extent direction (22) of the strand profile (10), the fibers (28) of the first multiplicity of layers (26) extending relative to the longitudinal extent direction (22) of the strand profile (10) in such a way that, in the presence of setpoint torsional loading of the strand profile (10), said fibers are subjected to longitudinal compressive loading in their longitudinal extent directions (30), the fibers (36) of the second multiplicity of layers (34) extending relative to the longitudinal extent direction (22) of the strand profile (10) in such a way that, in the presence of setpoint torsional loading of the strand profile (10), said fibers are subjected to longitudinal tensile loading in their longitudinal extent directions (38), the longitudinal extent directions (30) of the fibers (28) of adjacent layers (26) of the first multiplicity of layers (26) differing from one another by an angle with a magnitude in a range from 0 to 10, preferably 2 to 10 and even more preferably 2 to 6, the longitudinal extent directions (38) of the fibers (36) of adjacent layers (34) of the second multiplicity of layers (34) differing from one another by an angle with a magnitude in a range from 0 to 10, preferably 2 to 10 and even more preferably 2 to 6. A process for producing a strand profile (10) is also proposed.

Claims

1. A strand profile, the strand profile extending in a longitudinal extent direction, the strand profile having a first layer structure arranged around the longitudinal extent direction and a second layer structure surrounding the first layer structure, the first layer structure comprising a first multiplicity of layers, each layer of the first layer structure having multiple fibers, the second layer structure comprising a second multiplicity of layers, each layer of the second layer structure having multiple fibers, the fibers of the first multiplicity of layers and the fibers of the second multiplicity of layers each extending in longitudinal extent directions, the longitudinal extent directions of the fibers of the first multiplicity of layers and the fibers of the second multiplicity of layers each being oriented at an angle with a magnitude in a range from 30 to 60 with respect to the longitudinal extent direction of the strand profile, the fibers of the first multiplicity of layers extending relative to the longitudinal extent direction of the strand profile in such a way that, in the presence of setpoint torsional loading of the strand profile, said fibers are subjected to longitudinal compressive loading in their longitudinal extent directions, the fibers of the second multiplicity of layers extending relative to the longitudinal extent direction of the strand profile in such a way that, in the presence of setpoint torsional loading of the strand profile, said fibers are subjected to longitudinal tensile loading in their longitudinal extent directions, the longitudinal extent directions of the fibers of adjacent layers of the first multiplicity of layers differing from one another by an angle with a magnitude in a range from 0 to 10, the longitudinal extent directions of the fibers of adjacent layers of the second multiplicity of layers differing from one another by an angle with a magnitude in a range from 0 to 10.

2. The strand profile according to claim 1, the second layer structure comprising more fibers than the first layer structure.

3. The strand profile according to claim 1, the fibers of the first multiplicity of layers being impregnated with a first impregnating agent and the fibers of the second multiplicity of layers being impregnated with a second impregnating agent, the first layer structure being separated from the second layer structure by a layer which is impermeable to the first impregnating agent and the second impregnating agent, the first impregnating agent differing from the second impregnating agent.

4. The strand profile according to claim 1, the strand profile having a core on which the first layer structure is arranged, the core being an arrangement of twisted fibers, a solid core, an encased solid core, a hollow core or an encased hollow core.

5. The strand profile according to claim 1, the strand profile being bent into the form of a helical spring, the helical spring having a pitch H, a spring diameter D and a pitch angle , a ratio tan =H/(*D) being not greater than 0.22.

6. The strand profile according to claim 5, the strand profile being in the form of a right-handed compression spring or a left-handed tension spring, the longitudinal extent directions of the fibers of the first multiplicity of layers being in a right-handed orientation with respect to the longitudinal extent direction of the strand profile at an angle with a magnitude in a range from 40 to 50, the longitudinal extent directions of the fibers of the second multiplicity of layers being in a left-handed orientation with respect to the longitudinal extent direction of the strand profile at an angle with a magnitude in a range from 40 to 50, or the strand profile being in the form of a left-handed compression spring or a right-handed tension spring, the longitudinal extent directions of the fibers of the first multiplicity of layers being in a left-handed orientation with respect to the longitudinal extent direction of the strand profile at an angle with a magnitude in a range from 40 to 50, the longitudinal extent directions of the fibers of the second multiplicity of layers being in a right-handed orientation with respect to the longitudinal extent direction of the strand profile at an angle with a magnitude in a range from 40 to 50.

7. The strand profile according to claim 1, the fibers of the first multiplicity of layers and the fibers of the second multiplicity of layers being glass fibers.

8. A process for producing the strand profile according to claim 1, comprising: (i) providing a core which, in order to define a longitudinal extent direction of the strand profile, extends in a longitudinal extent direction, (ii) arranging a first layer structure around the core, the first layer structure being formed from a first multiplicity of layers, each layer of the first layer structure having multiple fibers, (iii) arranging a second layer structure around the first layer structure, the second layer structure being formed from a second multiplicity of layers, each layer of the second layer structure having multiple fibers, the fibers of the first multiplicity of layers and the fibers of the second multiplicity of layers each extending in longitudinal extent directions, the longitudinal extent directions of the fibers of the first multiplicity of layers and the fibers of the second multiplicity of layers each being oriented at an angle with a magnitude in a range from 30 to 60 with respect to the longitudinal extent direction of the strand profile, the fibers of the first multiplicity of layers extending relative to the longitudinal extent direction of the strand profile in such a way that, in the presence of setpoint torsional loading of the strand profile, said fibers are subjected to longitudinal compressive loading in their longitudinal extent directions, the fibers of the second multiplicity of layers extending relative to the longitudinal extent direction of the strand profile in such a way that, in the presence of setpoint torsional loading of the strand profile, said fibers are subjected to longitudinal tensile loading in their longitudinal extent directions, the longitudinal extent directions of the fibers of adjacent layers of the first multiplicity of layers differing from one another by an angle with a magnitude in a range from 0 to 10, the longitudinal extent directions of the fibers of adjacent layers of the second multiplicity of layers differing from one another by an angle with a magnitude in a range from 0 to 10, and (iv) removing the core or leaving the core in the first layer structure.

9. The process according to claim 8, the second layer structure being formed with more fibers than the first layer structure.

10. The process according to claim 8, the fibers of the first multiplicity of layers being impregnated with a first impregnating agent and the fibers of the second multiplicity of layers being impregnated with a second impregnating agent, the first layer structure being separated from the second layer structure by a layer which is impermeable to the first impregnating agent and the second impregnating agent, the first impregnating agent differing from the second impregnating agent.

11. The process according to claim 8, further comprising bending the strand profile into the form of a helical spring, the helical spring in particular having a pitch H, a spring diameter D and a pitch angle , a ratio tan =H/(*D) being not greater than 0.22.

12. The process according to claim 11, the strand profile being in the form of a right-handed compression spring or a left-handed tension spring, the longitudinal extent directions of the fibers of the first multiplicity of layers being in a right-handed orientation with respect to the longitudinal extent direction of the strand profile at an angle with a magnitude in a range from 40 to 50, the longitudinal extent directions of the fibers of the second multiplicity of layers being in a left-handed orientation with respect to the longitudinal extent direction of the strand profile at an angle with a magnitude in a range from 40 to 50, or the strand profile being in the form of a left-handed compression spring or a right-handed tension spring, the longitudinal extent directions of the fibers of the first multiplicity of layers being in a left-handed orientation with respect to the longitudinal extent direction of the strand profile at an angle with a magnitude in a range from 40 to 50, the longitudinal extent directions of the fibers of the second multiplicity of layers being in a right-handed orientation with respect to the longitudinal extent direction of the strand profile at an angle with a magnitude in a range from 40 to 50.

13. The process according to claim 8, the fibers of the first multiplicity of layers and the fibers of the second multiplicity of layers being glass fibers.

14. A strand profile obtained by the process according to claim 8.

15. A spring comprising the strand profile according to claim 1.

Description

[0075] The invention will be discussed in more detail below with reference to the drawings. The drawings are to be understood as diagrammatic illustrations. They do not constitute a limitation of the invention, for example with regard to specific dimensions or design versions.

[0076] In the drawings:

[0077] FIG. 1 shows a side view of a strand profile,

[0078] FIG. 2 shows a side view of a strand profile according to a first embodiment,

[0079] FIGS. 3A to 3E each show a plan view of the first layer structure and examples of possible orientations of the fibers of the first layer structure,

[0080] FIG. 4 shows a side view of a strand profile according to a second embodiment,

[0081] FIG. 5 shows a side view of a strand profile according to a third embodiment,

[0082] FIG. 6 shows a side view of a strand profile according to a fourth embodiment,

[0083] FIGS. 7A to 7D show different steps of a process for producing a strand profile,

[0084] FIG. 8 shows results for the shear modulus, the shear strength and the ratio of shear modulus to the square of the shear strength,

[0085] FIG. 9 shows the endurable shear stress .sub.max as a function of tan and

[0086] FIG. 10 shows the endurable shear stress .sub.max for two laminate types in springs with similar profile and different chemistry for the materials used.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0087] FIG. 1 shows a side view of a strand profile 10 which is bent into the form of a right-handed helical spring 12. Correspondingly, the strand profile 10 is wound in right-handed fashion about an axis of symmetry 14. For the purposes of explanation, certain parameters of the helical spring 12 are indicated in FIG. 1. The helical spring 12 has an outer diameter d.sub.e of the strand profile 10. The strand profile 10 may be of tubular form and may thus have an inner diameter d.sub.i. The helical spring 12 furthermore has a pitch H, a spring diameter D and a pitch angle . Here, the pitch H is defined as the spacing of central points of adjacent windings in a direction parallel to the axis of symmetry 14. Here, spring diameter D is defined as the spacing of central points of adjacent windings in a direction perpendicular to the axis of symmetry 14. The pitch angle is defined as the angle between a centerline 16 of the strand profile 10 and a plane 18 perpendicular to the axis of symmetry 14.

[0088] FIG. 2 shows a side view of a strand profile 10 according to a first embodiment of the present invention. The strand profile 10 is bent into the form of a right-handed helical spring 12. The helical spring 12 has a pitch H, a spring diameter D and a pitch angle , a ratio tan =H/(*D) being not greater than 0.22 and preferably not greater than 0.21. The helical spring 12 is a right-handed compression spring, as indicated by arrows 20. The strand profile 10 extends in a longitudinal extent direction 22. The strand profile 10 has a first layer structure 24 arranged around the longitudinal extent direction 22. The first layer structure 24 has a first multiplicity of layers 26, of which only one is indicated in FIG. 2. The first layer structure 24 is preferably composed of the first multiplicity of layers 26. Each layer 26 of the first layer structure 24 has multiple fibers 28. The fibers 28 of the first multiplicity of layers 26 extend in each case in longitudinal extent directions 30. The longitudinal extent directions 30 of the fibers 28 of the first multiplicity of layers 26 are each oriented at an angle with a magnitude in a range from 30 to 60, and preferably in a range from 40 to 50, with respect to the longitudinal extent direction 22 of the strand profile 10. The fibers 28 of the first multiplicity of layers 26 extend relative to the longitudinal extent direction 22 of the strand profile 10 in such a way that, in the presence of setpoint torsional loading of the strand profile 10, said fibers are subjected to longitudinal compressive loading in their longitudinal extent directions 30. In the first embodiment, the longitudinal extent directions 30 of the fibers 28 of the first multiplicity of layers 26 are oriented in right-handed fashion at an angle with a magnitude in a range from 40 to 50 with respect to the longitudinal extent direction 22 of the strand profile 10.

[0089] The strand profile 10 furthermore has a second layer structure 32 surrounding the first layer structure 24. The second layer structure 32 has a second multiplicity of layers 34, of which only one is indicated in FIG. 2. The second layer structure 32 is preferably composed of the second multiplicity of layers 34. Each layer 34 of the second layer structure 32 has multiple fibers 36. The fibers 36 of the second multiplicity of layers 34 extend in each case in longitudinal extent directions 38. The longitudinal extent directions 38 of the fibers 36 of the second multiplicity of layers 34 are each oriented at an angle with a magnitude in a range from 30 to 60, and preferably in a range from 40 to 50, with respect to the longitudinal extent direction 22 of the strand profile 10. The fibers 36 of the second multiplicity of layers 34 extend relative to the longitudinal extent direction 22 of the strand profile 10 in such a way that, in the presence of setpoint torsional loading of the strand profile 10, said fibers are subjected to longitudinal tensile loading in their longitudinal extent directions 38. In the first embodiment, the longitudinal extent directions 38 of the fibers 36 of the second multiplicity of layers 34 are oriented in left-handed fashion at an angle with a magnitude in a range from 40 to 50 with respect to the longitudinal extent direction 22 of the strand profile 22.

[0090] The fibers 28 of the first multiplicity of layers 26 and the fibers 36 of the second multiplicity of layers 34 are glass fibers. The second layer structure 32 comprises more fibers 36 than the first layer structure 24. For example, the number of fibers 36 of the second multiplicity of layers 34 is greater by a factor of 1.5 to 9, preferably 1.5 to 4, particularly preferably 2 to 3, than the number of fibers 28 of the first multiplicity of layers 26. The first multiplicity of layers 26 and the second multiplicity of layers 34 may have different fiber volume fractions. For example, the first multiplicity of layers 34 has a fiber volume fraction of 50% to 70% in relation to the volume of the first layer structure 24, and the second multiplicity of layers 34 has a fiber volume fraction of 35% to 60% in relation to the volume of the second layer structure 32. The fibers 28 of the first multiplicity of layers 26 may be embedded into a first matrix material. The fibers 36 of the second multiplicity of layers 34 may be embedded into a second matrix material. The second matrix material optionally differs from the first matrix material. In the case of different matrix material, the first matrix material has a high strength with a tensile modulus of preferably greater than 2.9 GPa, and the second matrix material exhibits high ductility. The fibers 28 of the first multiplicity of layers 26 are impregnated with a first impregnating agent, and the fibers 36 of the second multiplicity of layers 34 are impregnated with a second impregnating agent. The first layer structure 24 is optionally separated from the second layer structure 32 by a layer which is impermeable to the first impregnating agent and the second impregnating agent. The first impregnating agent differs from the second impregnating agent. The fibers 36 of the second layer structure 32 are formed as rovings with a filament diameter which is optionally smaller than a filament diameter of the fibers 28 of the first layer structure 24. The strand profile 10 may optionally have a core on which the first layer structure 24 is arranged. The core may be an arrangement of twisted fibers, a solid core, an encased solid core, a hollow core or an encased hollow core. The core may remain in the finished workpiece or else may be removed.

[0091] In the strand profile 10, the longitudinal extent directions 30 of the fibers 28 of adjacent layers 26 of the first multiplicity of layers 26 differ from one another by an angle with a magnitude in a range from 0 to 10, preferably 2 to 10 and even more preferably 2 to 6. Furthermore, the longitudinal extent directions 38 of the fibers 36 of adjacent layers 34 of the second multiplicity of layers 34 differ from one another by an angle with a magnitude in a range from 0 to 10, preferably 2 to 10 and even more preferably 2 to 6. This will be discussed in more detail below on the basis of the first layer structure 24, wherein the explanations apply analogously to the second layer structure 32.

[0092] FIGS. 3A to 3E each show a plan view of the first layer structure 24 and examples of possible orientations of the fibers 28 of the first layer structure 24. Merely by way of example, a first layer 26a, a second layer 26b and a third layer 26c of the first layer structure 24 are shown, which are arranged one on top of the other in the stated sequence. The first layer 26a has a first multiplicity of fibers 28a. The second layer 26b has a second multiplicity of fibers 28b. The third layer 26c has a third multiplicity of fibers 28c. Of the fibers 28a, 28b, 28c, in each case only one is illustrated for the sake of clarity. Alternatively, in the case of only two layers, the fibers 28a and 28c may vary about an imaginary line of symmetry which has the profile of the fiber 28b.

[0093] In FIG. 3A, the second multiplicity of fibers 28b extends at an angle of 0 to 10, preferably 2 to 10 and more preferably 2 to 6 clockwise as viewed in relation to the first multiplicity of fibers 28a. Furthermore, the third multiplicity of fibers 28c extends at an angle of 0 to 10, preferably 2 to 10 and more preferably 2 to 6 clockwise as viewed in relation to the second multiplicity of fibers 28b.

[0094] In FIG. 3B, the second multiplicity of fibers 28b extends at an angle of 0 to 10, preferably 2 to 10 and more preferably 2 to 6 counterclockwise as viewed in relation to the first multiplicity of fibers 28a. Furthermore, the third multiplicity of fibers 28c extends at an angle of 0 to 10, preferably 2 to 10 and more preferably 2 to 6 counterclockwise as viewed in relation to the second multiplicity of fibers 28b.

[0095] In FIG. 3C, the second multiplicity of fibers 28b extends at an angle of 0 to 10, preferably 2 to 10 and more preferably 2 to 6 clockwise as viewed in relation to the first multiplicity of fibers 28a. Furthermore, the third multiplicity of fibers 28c extends at an angle of 0 to 10, preferably 2 to 10 and more preferably 2 to 6 counterclockwise as viewed in relation to the first multiplicity of fibers 28a.

[0096] In FIG. 3D, the second multiplicity of fibers 28b extends at an angle of 0 to 10, preferably 2 to 10 and more preferably 2 to 6 counterclockwise as viewed in relation to the first multiplicity of fibers 28a. Furthermore, the third multiplicity of fibers 28c extends at an angle of 0 to 10, preferably 2 to 10 and more preferably 2 to 6 clockwise as viewed in relation to the first multiplicity of fibers 28a.

[0097] It is self-evident that the respective angles need not be identical in magnitude.

[0098] FIG. 3E shows an arrangement in which, in each case, the fibers 28a, 28c of every second layer 26a, 26c of the same layer structure 24 extend parallel to one another. Correspondingly, the fibers 28a, 28c overlap in the plan view of FIG. 3E.

[0099] FIG. 4 shows a side view of a strand profile 10 according to a second embodiment of the present invention. Only the differences in relation to the first embodiment will be described below, and identical components are denoted by the same reference designations. The strand profile 10 is bent into the form of a left-handed helical spring 12. The helical spring 12 is a left-handed compression spring, as indicated by arrows 20. In the second embodiment, the longitudinal extent directions 30 of the fibers 28 of the first multiplicity of layers 26 are oriented in left-handed fashion at an angle with a magnitude in a range from 40 to 50 with respect to the longitudinal extent direction 22 of the strand profile 10. Furthermore, in the second embodiment, the longitudinal extent directions 38 of the fibers 36 of the second multiplicity of layers 34 are oriented in right-handed fashion at an angle with a magnitude in a range from 40 to 50 with respect to the longitudinal extent direction 22 of the strand profile 22.

[0100] FIG. 5 shows a side view of a strand profile 10 according to a third embodiment of the present invention. Only the differences in relation to the first embodiment will be described below, and identical components are denoted by the same reference designations. The strand profile 10 is bent into the form of a right-handed helical spring 12. The helical spring 12 is a right-handed tension spring, as indicated by arrows 20. In the third embodiment, the longitudinal extent directions 30 of the fibers 28 of the first multiplicity of layers 26 are oriented in left-handed fashion at an angle with a magnitude in a range from 40 to 50 with respect to the longitudinal extent direction 22 of the strand profile 10. Furthermore, in the third embodiment, the longitudinal extent directions 38 of the fibers 36 of the second multiplicity of layers 34 are oriented in right-handed fashion at an angle with a magnitude in a range from 40 to 50 with respect to the longitudinal extent direction 22 of the strand profile 22.

[0101] FIG. 6 shows a side view of a strand profile 10 according to a fourth embodiment of the present invention. Only the differences in relation to the first embodiment will be described below, and identical components are denoted by the same reference designations. The strand profile 10 is bent into the form of a left-handed helical spring 12. The helical spring 12 is a left-handed tension spring, as indicated by arrows 20. In the fourth embodiment, the longitudinal extent directions 30 of the fibers 28 of the first multiplicity of layers 26 are oriented in right-handed fashion at an angle with a magnitude in a range from 40 to 50 with respect to the longitudinal extent direction 22 of the strand profile 10. Furthermore, in the fourth embodiment, the longitudinal extent directions 38 of the fibers 36 of the second multiplicity of layers 34 are oriented in left-handed fashion at an angle with a magnitude in a range from 40 to 50 with respect to the longitudinal extent direction 22 of the strand profile 22.

[0102] A process for producing a strand profile 10 will be described below. Here, the process will be described with reference to production of a strand profile 10 according to the first embodiment. The process is however likewise suitable for the production of a strand profile according to the second to fourth embodiments.

[0103] Here, FIGS. 7A to 7D show different steps of the process. As shown in FIG. 7A, a core 40 is firstly provided. In order to define the longitudinal extent direction 22 of the strand profile 10, the core 40 extends in a longitudinal extent direction. The core 40 extends for example in straight fashion. The core 40 may be an arrangement of twisted fibers, a solid core, an encased solid core, a hollow core or an encased hollow core. As shown in FIG. 7B, the first layer structure 24 is arranged on the core 40 around the longitudinal extent direction 22. The first layer structure 24 has the first multiplicity of layers 26. The first layer structure 24 is preferably composed of the first multiplicity of layers 26. Each layer 26 of the first layer structure 24 has multiple fibers 28, of which only one is illustrated in FIG. 7B. The fibers 28 may for example be arranged on the core 40 by means of filament winding. The fibers 28 of the first multiplicity of layers 26 extend in each case in longitudinal extent directions 30. The longitudinal extent directions 30 of the fibers 28 of the first multiplicity of layers 26 are each oriented at an angle with a magnitude in a range from 30 to 60, and preferably in a range from 40 to 50, with respect to the longitudinal extent direction 22 of the strand profile 10. The fibers 28 of the first multiplicity of layers 26 extend relative to the longitudinal extent direction 22 of the strand profile 10 in such a way that, in the presence of setpoint torsional loading of the strand profile 10, said fibers are subjected to longitudinal compressive loading in their longitudinal extent directions 30. In the embodiment shown, the longitudinal extent directions 30 of the fibers 28 of the first multiplicity of layers 26 are oriented in right-handed fashion at an angle with a magnitude in a range from 40 to 50 with respect to the longitudinal extent direction 22 of the strand profile 10.

[0104] As shown in FIG. 7C, the second layer structure 32 is arranged on the first layer structure 24 so as to surround the latter. The second layer structure 32 has the second multiplicity of layers 34. The second layer structure 32 is preferably composed of the second multiplicity of layers 34. Each layer 34 of the second layer structure 32 has multiple fibers 36, of which only one is illustrated in FIG. 7C. The fibers 36 may for example be arranged on the first layer structure 24 by means of filament winding or pull winding. The fibers 36 of the second multiplicity of layers 34 extend in each case in longitudinal extent directions 38. The longitudinal extent directions 38 of the fibers 36 of the second multiplicity of layers 34 are each oriented at an angle with a magnitude in a range from 30 to 60, and preferably in a range from 40 to 50, with respect to the longitudinal extent direction 22 of the strand profile 10. The fibers 36 of the second multiplicity of layers 34 extend relative to the longitudinal extent direction 22 of the strand profile 10 in such a way that, in the presence of setpoint torsional loading of the strand profile 10, said fibers are subjected to longitudinal tensile loading in their longitudinal extent directions 38. In the first embodiment, the longitudinal extent directions 38 of the fibers 36 of the second multiplicity of layers 34 are oriented in left-handed fashion at an angle with a magnitude in a range from 40 to 50 with respect to the longitudinal extent direction 22 of the strand profile 22.

[0105] The fibers 28 of the first multiplicity of layers 26 and the fibers 36 of the second multiplicity of layers 34 are glass fibers. The second layer structure 32 comprises more fibers 36 than the first layer structure 24. For example, the number of fibers 36 of the second multiplicity of layers 34 is greater by a factor of 1.5 to 9, preferably 1.5 to 4, particularly preferably 2 to 3, than the number of fibers 28 of the first multiplicity of layers 26. The first multiplicity of layers 26 and the second multiplicity of layers 34 may have different fiber volume fractions. For example, the first multiplicity of layers 34 has a fiber volume fraction of 40% to 70% in relation to the volume of the first layer structure 24, and the second multiplicity of layers 34 has a fiber volume fraction of 35% to 60% in relation to the volume of the second layer structure 32. The fibers 28 of the first multiplicity of layers 26 are embedded into a first matrix material. The fibers 36 of the second multiplicity of layers 34 are embedded into a second matrix material. The second matrix material may differ from the first matrix material. For example, the first matrix material may have a high stiffness, and the second matrix material may exhibit high ductility. The fibers 28 of the first multiplicity of layers 26 and the fibers 36 of the second multiplicity of layers 34 are each impregnated with an impregnating agent. The first layer structure 24 may be separated from the second layer structure 32 by a layer which is impermeable to the impregnating agents. The impregnating agents may differ from one another. The fibers 36 of the second layer structure 32 are formed as rovings with a filament diameter which may be smaller than a filament diameter of the fibers 28 of the first layer structure 24.

[0106] In the strand profile 10, the longitudinal extent directions 30 of the fibers 28 of adjacent layers 26 of the first multiplicity of layers 26 differ from one another by an angle with a magnitude in a range from 0 to 10, preferably 2 to 10 and even more preferably 2 to 6. Furthermore, the longitudinal extent directions 38 of the fibers 36 of adjacent layers 34 of the second multiplicity of layers 34 differ from one another by an angle with a magnitude in a range from 0 to 10, preferably 2 to 10 and even more preferably 2 to 6, as described above. The core 40 may subsequently be removed or may remain in the first layer structure 24. A removal of the core 40 is for example possible if the core 40 is produced from PTFE, because this material does not adhesively bond to the matrix system of the fiber composite material.

[0107] As shown in FIG. 7D, the strand profile 10 is subsequently bent. The strand profile 10 is for example bent into the form of a right-handed helical spring 12, for example by means of a free-form tool. The helical spring 12 is formed with a pitch H, a spring diameter D and a pitch angle , a ratio tan =H/(*D) being not greater than 0.22 and preferably not greater than 0.21. The helical spring 12 is subsequently cured, which may be performed with a supply of heat.

EXAMPLES

[0108] The present invention will be discussed in more detail on the basis of the following examples.

[0109] For the examples below, the following nomenclature will be used, which was used in the determination of the test results. [0110] B Exponent fatigue strength [0111] C Ratio D/d.sub.e [0112] d.sub.e Strand profile outer diameter [0113] d.sub.i Strand profile inner diameter [0114] D Spring diameter [0115] F Force [0116] G Shear modulus, averaged [0117] H Pitch of the spring winding [0118] k Ratio d.sub.i/d.sub.e [0119] K Spring constant [0120] n Number of oscillations until failure [0121] N Number of spring windings [0122] Pitch angle of the spring winding [0123] Deflection of the spring from the unloaded position [0124] .sub.B,max Bending stress at the horizontal outer edge of the strand profile cross section [0125] T.sub.S Shear stress resulting from shear [0126] T.sub.T Shear stress resulting from torsion at the strand profile circumference in the case of radially increasing stress [0127] .sub.max Increased shear stress at the inner circumference of a thick spring owing to torsion and shear, calculated in accordance with Waals [0128] Density

[0129] For the geometry of the helical spring, the following ratio applies between pitch H, spring diameter D and pitch angle :

[00001]$\tan \left(\right)=\frac{H}{.Math..Math.D}$

[0130] As can be gathered from the standard literature relating to the design of helical springs, stresses resulting from torsion, bending and shear act on the cross section of a hollow helical spring when an axial force is introduced.

[0131] Shear stress:

[00002]${}_S=\frac{4.Math.F}{\left(d_e^2-d_i^2\right)}$

[0132] Bending stress about the spring axis:

[00003]${}_{B,\max }=\frac{16.Math.\mathrm{FD}.Math..Math.\sin \left(\right)}{.Math..Math.d_e^3\left(1-k^4\right)}$

[0133] Shear stress resulting from torsion at the outer edge in the case of a radial stress profile:

[00004]${}_T=\frac{8.Math.\mathrm{FD}}{.Math..Math.d_e^3\left(1-k^4\right)}$

[0134] In the case of springs composed of thick bars or strand profiles, there is a resulting increased shear stress at the inner circumference of the spring winding owing to torsion and shear, which, according to Waals, is approximated by:

[00005]${}_{\max }=\frac{8.Math.\mathrm{FD}}{.Math..Math.d_e^3\left(1-k^4\right)}.Math.\left(\frac{4.Math.C-1}{4.Math.C-4}+\frac{0.615}{C}\right)$

[0135] Tests relating to fatigue strength are often depicted as Whler curves in accordance with the following equation:

[00006]$\left({10}^6\right)=\left(n\right).Math.{\left(\frac{n}{{10}^6}\right)}^B$

[0136] The deflection of the spring is calculated as

[00007]$=\frac{8.Math.{\mathrm{FD}}^3.Math.N}{{\mathrm{Gd}}_e^4\left(1-k^4\right)}$

[0137] The spring constant is the local gradient of the force as a function of the deflection:

[00008]$K=\frac{.Math..Math.F}{}$

[0138] Conversely, the required shear modulus can be determined from the gradient:

[00009]$G=K.Math.\frac{8.Math.D^3.Math.N}{d_e^4\left(1-k^4\right)}$

[0139] The mass of a helical spring is determined from the demands on the admissible force and desired deflection in the presence of said force as a function of the three material parameters of shear modulus, density and shear strength:

[00010]$m=2.Math.\frac{1}{1+k^2}.Math.\frac{.Math..Math.G}{{}_T^2}.Math.F.Math..Math.$

[0140] In order, to minimize the mass m in the case of a spring, it is necessary to develop laminates, that is to say layer structures, with a low shear modulus G and a high shear strength .sub.T.

[0141] Tests were performed on right-handed helical springs under compression with the dimensions D=99.5 mm, d.sub.e=19.5 mm, d.sub.i=10.0 mm. The pitch was generally shallower at the two ends, as is conventional in the case of helical springs for the field of automotive engineering. Table 1 shows the pitch of the windings during the forming. The pitch of the spring seats is also listed. The pitch H is stated in mm in table 1. In the first row, the numerical values denote winding portions, wherein the numeral 1 indicates one complete winding, or 360.

TABLE-US-00001 TABLE 1 Winding tan() = (1 360) 0- 0.75- 1- 3.5- 3.75- H.sub.max/ Pitch H Seat 0.75 1 3.5 3.75 4.5 ( *D) Profile I 20 40 40-65 65 65-40 40 0.21 Profile II 20 40 40-75 75 75-40 40 0.24 Profile III 20 20 20-90 90 90-20 40 0.29 Profile IV 45 64 0.21

[0142] Laminate: The laminate structure of the individual samples was of fine-layered (F) or coarse-layered (G) configuration with different ratios of the fibers subjected to compressive loading in their longitudinal direction to the fibers subjected to tensile loading in their longitudinal direction. Here, fine-layered means an alternating arrangement of the layers of different direction of rotation, and coarse-layered means that firstly a multiplicity of layers with fibers of the same direction of rotation and then a multiplicity of layers with fibers of an opposite or different direction of rotation are applied. In table 2, in the first column, sample variants are specified which have different laminate or layer structures, wherein the laminate or layer structures are specified in the second column. Here, in the first column, between the parentheses, firstly the number of layers subjected to compressive loading and then the number of layers subjected to tensile loading are specified. For example, F(3/7) signifies a fine-layered structure with three layers subjected to compressive loading and seven layers subjected to tensile loading. The exact structure of the layers is specified in the second column, wherein () denotes an orientation or an angle relative to the longitudinal extent direction of the strand profile for layers subjected to compressive loading, and (+) denotes an orientation or an angle relative to the longitudinal extent direction of the strand profile for layers subjected to tensile loading.

TABLE-US-00002 TABLE 2 Sample Laminate structure F(5/5) [45, +45, 45, +45, 45, +45, 45, +45, 45, +45] F(3/7) [48, +42, +48, 42, +48, +42, 48, +42, +48, +42] G(5/5) [48, 42, 48, 42, 48], [+42, +48, +42, +48, +42] G(4/6) [48, 42, 48, 42], [+48, +42, +48, +42, +48, +42] G(3/7) [48, 42,48], [+42, +48, +42, +48, +42, +48, +42] G(2/8) [48, 42], [+48, +42, +48, +42, +48, +42, +48, +42] G(1/9) [48], [+42, +48, +42, +48, +42, +48, +42, +48, +42]

[0143] The following materials were used for the tested strand profiles. The glass fiber was a roving with a weight of 2400 g/km (2400 tex). System A was composed of the resin bisphenol-A-diglycidyl ether with 22 wt. % butanediol-diglycidyl ether and the curing agent diethylmethylbenzenediamine in the mixing ratio 100:26. System B was composed of the resin bisphenol-A-diglycidyl ether with 22 wt. % butanediol-diglycidyl ether and the curing agent dicyanamide (56 wt. %)+methylcyclohexyl diamine (26 wt. %)+3,3-(4-methyl-1,3-phenylene)bis(1,1-dimethylurea), obtainable under the trade name Uron Dyhard UR500, (18 wt. %) in the mixing ratio 100:11. The fiber mass fraction was determined by calculation, from the used quantity of glass material, core material, auxiliary materials and the total weight of the profiles, as 67%+/2% for system A and as 65%+/2% for system B.

[0144] The spring rods were produced with a filament winding with 8 filaments per layer with a multiple filament eyelet ring. Winding was performed onto a 7-mm steel core, encased by a polyethylene hose with a 10 mm outer diameter and 1 mm wall thickness, which has no significant influence on the strength and stiffness of the springs. The steel core was drawn after the filament winding. The steel bars were wound onto a tube with 80 mm outer diameter. The pitch in the forming process was set by means of spacers. The curing of system A was performed for 2 h at 120 C. and for 5 h at 150 C. The curing of system B was performed for 3 h at 90 C. and for 1 h at 140 C.

[0145] The laminates not only had different load capacities but also exhibited different torsional stiffnesses. Therefore, the tests relating to fatigue strength were run from a minimum holding force of 1000 N up to a highest possible force to a point shortly before the spring assumed a block state, which was 3-5 kN depending on the laminate. The frequency was 3.5 1/s. Thus, in the presence of a force F, a number of cycles n until failure was determined.

[0146] The parameters for the comparison of the laminates were calculated as follows: From the spring characteristic curve F(), the pitch K was determined at a mean deflection of 55 mm. The shear modulus G was determined from this pitch under the assumption that, at this spring deflection, 4 free windings were able to twist.

[0147] The highest torsional stress and maximum shear stress at the number of cycles n was determined as:

[00011]${}_T\left(n\right)=\frac{8.Math.\mathrm{FD}}{.Math..Math.d_e^3\left(1-k^4\right)}$${}_{\max }\left(n\right)=\frac{8.Math.\mathrm{FD}}{.Math..Math.d_e^3\left(1-k^4\right)}.Math.\left(\frac{4.Math.C-1}{4.Math.C-4}+\frac{0.615}{C}\right)$

[0148] With an experimentally determined exponent B=0.05, for the comparison of the laminates, the admissible torsional stress and maximum shear stress at 1 million cycles was determined:

[00012]${}_T\left({10}^6\right)={}_T\left(n\right).Math.{\left(\frac{n}{{10}^6}\right)}^B$${}_{\max }\left({10}^6\right)={}_{\max }\left(n\right).Math.{\left(\frac{n}{{10}^6}\right)}^B$

[0149] FIG. 8 shows the thus determined results for the shear modulus, the endurable shear stress at 1 million cycles and the ratio of shear modulus to the square of the endurable shear stress.

[0150] The results in FIG. 8 show the superiority of these laminates under torsional loading. In particular the ratio G/.sub.T.sub.2, which is proportional to the required spring mass, decreases from the value of the fine-layered standard laminate F(5/5) to 55%, which permits a weight saving in relation to said standard laminate of 45%.

[0151] With increasing pitch H or increasing pitch angle , however, the bending stress in the strand profile also increases. The strand profile can no longer be optimized exclusively for torsion. FIG. 9 shows the endurable shear stress .sub.max as a function of tan . FIG. 9 shows that, in the case of a spring design with a large pitch H, owing to the higher bending stresses, the torsion-optimized laminate performs less effectively.

[0152] Table 3 shows the comparison of shear strength and, in part, shear modulus for different laminates for two different epoxy systems.

TABLE-US-00003 TABLE 3 Spring n T.sub.T(n) T.sub.max(n) T.sub.T(10.sup.6) T.sub.max(10.sup.6) K G G/T.sub.T.sup.2(10.sup.6) profile Chemistry Laminate [] [MPa] MPa] [MPa] [MPa] [N/mm] [GPa] [1/MPa] IV B F(5/5) 5.66E+03 183 240 142 186 IV B G(3/7) 2.46E+06* >158 >165 >208 >218 III A F(5/5) 1.28E+05 148 192 133 174 III A G(3/7) 1.00E+00 155 202 78 101 II A G(3/7) 5.00E+00 167 218 91 118 1 A F(5/5) 3.50E+04 166 217 141 183 45.0 10.6 0.54 II A F(5/5) 2.73E+03 171 222 127 165 I A G(3/7) 5.70E+06* >161 >210 >175 >229 40.0 9.1 <0.30 I A G(2/8) 9.30E+05 145 189 144 188 34.0 7.8 0.38 I A G(5/5) 1.05E+06 141 184 141 184 40.0 8.9 0.45 I A G(4/6) 5.87E+05 175 228 171 222 39.0 9.8 0.34 I A G(1/9) 2.00E+06* >110 >143 >113 >148 30.5 7.1 <0.55 I A F(3/7) 8.94E+04 152 197 135 175 38.8 9.5 0.52 *Test ended without spring failure

[0153] FIG. 10 shows the endurable shear stress .sub.max for two laminate types in springs with similar profile and different chemistry for the materials used. More specifically, FIG. 10 illustrates the endurable shear stress .sub.max for a strand profile in the form of standard laminate F(5/5) produced with the chemistry in accordance with the above-described systems A and B and for a strand profile with a structure G(3/7) according to the invention produced with the chemistry in accordance with the above-described systems A and B. It can be seen from FIG. 10 that the endurable shear stress .sub.max for the strand profile with a structure G(3/7) according to the invention is higher than that for the strand profile in the form of standard laminate F(5/5), wherein the chemistry used has a negligible influence on the endurable shear stress .sub.max. From FIG. 10, it is possible to clearly see the advantageous effect on the endurable shear stress .sub.max owing to the present invention.