TORSION-LOADED ROD-SHAPED COMPONENT WITH DIFFERENT FIBRE REINFORCEMENTS FOR TENSILE AND COMPRESSIVE LOADING

Abstract

A torsion spring may be configured as a torsion bar or a helical spring made of a spring wire made of fiber-composite material. The torsion spring may have a plurality of layers of fiber reinforcement that have been saturated with a matrix material, wherein the layers may have fibers that are tension-loaded and fibers that are compression-loaded. The at least one compression-loaded group may have a lower group stiffness than the tension-loaded group with the highest group stiffness. Methods for designing or making torsion springs made of fiber-composite material are also disclosed.

Claims

1.-22. (canceled)

23. A torsion spring configured as a torsion bar or a helical spring comprised of a spring wire made of fiber-composite material and including a plurality of layers of fiber reinforcement that have been saturated with a matrix material, wherein each of the plurality of layers includes only fibers that are tension-loaded or only fibers that are compression-loaded, wherein the plurality of layers comprise tension-loaded groups of layers and compression-loaded groups of layers, wherein at least one compression-loaded group of layers has a lower group stiffness than a tension-loaded group of layers with a highest group stiffness.

24. The torsion spring of claim 23 wherein said lower group stiffness is at least 10% lower than said highest group stiffness of the tension-loaded group of layers.

25. The torsion spring of claim 23 wherein at least one internally-situated compression-loaded group of layers has a lower group stiffness than a tension-loaded group of layers that is situated further outward than the at least one internally-situated compression-loaded group of layers.

26. The torsion spring of claim 23 wherein said highest group stiffness of the tension-loaded group of layers is at least 60 GPa.

27. The torsion spring of claim 23 wherein the tension-loaded group of layers with the highest group stiffness is composed exclusively of carbon fibers.

28. The torsion spring of claim 23 wherein the tension-loaded groups of layers are comprised of at least 50% by mass carbon fibers.

29. The torsion spring of claim 23 wherein a proportion by mass of at least 50% of the tension-loaded groups of layers has a group stiffness differing by less than 50% from said highest group stiffness of the tension-loaded group of layers.

30. The torsion spring of claim 23 wherein all of the tension-loaded groups of layers have a group stiffness differing by less than 50% from said highest group stiffness of the tension-loaded group of layers.

31. The torsion spring of claim 23 wherein a proportion by mass of at least 20% of the compression-loaded groups of layers has a lower group stiffness than said highest group stiffness of the tension-loaded group of layers.

32. The torsion spring of claim 23 wherein a proportion by mass of at least 50% of the compression-loaded groups of layers has a group stiffness differing by less than 50% from that of a compression-loaded group of layers with a highest group stiffness classified as low.

33. The torsion spring of claim 23 wherein all of the compression-loaded groups of layers have a group stiffness differing by less than 50% from that of a compression-loaded group of layers with a highest group stiffness classified as low.

34. The torsion spring of claim 23 wherein the compression-loaded groups of layers are comprised of a proportion by mass of at least 30% glass fibers or basalt fibers.

35. The torsion spring of claim 23 wherein at most 6 different fiber types are used for the tension-loaded and compression-loaded groups of layers.

36. The torsion spring of claim 23 wherein at least one pair formed from two groups of layers has a group ratio in a range from 0.2 to 5.0.

37. The torsion spring of claim 23 wherein based on the spring wire and ignoring a mass of a core, a proportion by mass of the groups of layers that have formed pairs is at least 50%.

38. The torsion spring of claim 23 wherein for the layers that have a mixture of fiber types, a quantity of each fiber type present in each mixed-fiber layer is at least 10% by mass.

39. The torsion spring of claim 23 wherein a proportion by mass of layers classified as non-loadbearing in the spring wire, ignoring a mass of a core, is at most 25%.

40. The torsion spring of claim 23 wherein a cross section of the spring wire is circular, elliptical, or polygonal.

41. The torsion spring of claim 23 wherein a matrix of fiber-reinforced plastics plies is comprised of a filled or unfilled thermoset plastic.

42. The torsion spring of claim 23 wherein the spring wire has a core that is hollow, that is comprised of fiber-reinforced material with unidirectional fibers in an axial direction of the spring wire, or that is comprised of material without fiber reinforcement.

43. A method of making a torsion spring configured as a torsion bar or a helical spring made of a multiple-ply fiber-composite material, the method comprising: pre-designing the spring; forming groups of fibers made of layers in contact with one another and having an identical loading direction; determining computationally a group stiffness for each group of fibers; adjusting the group stiffnesses of compression-loaded groups such that the compression-loaded groups have a lower group stiffness than a tension-loaded group with a highest group stiffness; forming pairs from an inside towards an outside so that each pair comprises a tension-loaded group and a compression-loaded group that are radially adjacent; determining a group ratio as a quotient calculated as a relationship between the group extensional stiffness values of the tension-loaded group and the compression-loaded group of each pair; minimizing shear stresses between adjacent groups via variation of the stiffness ratios by at least one of varying a layer wall thickness, varying a type of material, or varying a fiber angle until the group ratio is in a range from 0.2 to 5; and repeating all steps except for pre-designing the spring until a desired loadbearing capability has been achieved with a given spring stiffness profile.

44. The method of claim 43 wherein the adjusting is achieved in that at least one of a fiber material is changed, mixtures of various fiber materials are changed, or a fiber angle is altered.

Description

FIGURES

[0101] FIGS. 1a and 1b are diagrams of two embodiments of the torsion spring of the invention. FIG. 1 a shows this as a helical spring with core, and FIG. 1b shows this as helical spring without core.

[0102] FIG. 2 is a diagram of the cross section A-A of a spring of FIG. 1a with solid core (1) and various layers (S.sub.1 to S.sub.J) with the associated layer wall thicknesses and layer materials.

[0103] FIG. 3 is a diagram of the cross section A-A of a spring of FIG. 1a with tubular core (1) and various layers (S.sub.1 to S.sub.J) with the associated layer wall thicknesses and layer materials.

[0104] FIG. 4 is a diagram of the cross section B-B of a spring of FIG. 1b without core and of various layers (S.sub.1 to S.sub.J) with the associated layer wall thicknesses and layer materials.

[0105] FIG. 5 is a diagram of the arrangement of the spring wire of the invention corresponding to inventive example 1 (tables 1 and 2) with a wound textile, where the layers are always arranged in alternation in the form of glassfiber ply (compression-loaded) and carbon-fiber ply (tension-loaded). There is a homogeneous external plastics ply arranged on the external side of the spring.

[0106] FIG. 6 is a diagram of the arrangement of the spring wire of the invention corresponding to inventive example 2 (tables 3 and 4) with a wound textile, where the compression-loaded layers take the form of basalt-fiber ply and the tension-loaded layers take the form of carbon-fiber ply. In the fourth ply, the spring has fibers oriented along the longitudinal axis.

TABLES

[0107] Table 1 shows the inventive example 1 of the design method of the invention with a wound textile, where the layers are always arranged in alternation in the form of glassfiber ply (compression-loaded) and carbon-fiber ply (tension-loaded). The table has two parts, and to improve legibility the first four columns containing characterizing information are repeated in the second part.

[0108] Table 2 shows the fiber materials used for the inventive example 1, with their properties. The properties are known from the prior art, and have merely been collated here.

[0109] Table 3 shows the inventive example 2 of the design method of the invention with a wound textile, where the arrangement has the compression-loaded layers as glassfiber ply or as basalt-fiber ply, and has the tension-loaded layers as carbon-fiber ply. In the fourth ply, the inventive example 2 has fibers oriented along the longitudinal axis. The table likewise has two parts, and to improve legibility the first four columns containing characterizing information are repeated in the second part.

[0110] Table 4 shows the fiber materials used for the inventive example 2, with their properties. The properties are known from the prior art, and have merely been collated here.

INVENTIVE EXAMPLE

[0111] In all of the inventive examples, the cross-sectional area is calculated by way of the formula for the cross section of a circular annulus. For each inventive example, the specific factual situation is described by using a sectional depiction of the spring wire, a table to describe the properties of the spring wire, and a table to show the relevant properties of the materials.

[0112] The inventive example 1 shows a spring wire arrangement of the invention composed of wound textile plies and of a hollow core (FIG. 5). Tables 1 and 2 show the properties of the arrangement of the spring wire and the properties of the materials used. The spring wire is characterized in that it uses, always in alternation, a glassfiber ply for pressure loading and a carbon-fiber ply for tensile loading. The large difference in fiber stiffness values between glass fiber and carbon fiber requires mutual adjustment of group extensional stiffness by way of the cross-sectional area. In this example this is achieved by way of the significantly lower layer wall thickness of the carbon-fiber layer at 0.4 mm in comparison with the glassfiber layer at 1.1 mm. The ply 9 is a non-loadbearing layer because, as a homogeneous plastics ply, it does not have any preferential fiber reinforcement in tension-oriented or compression-oriented loading direction. Instead, the ply 9 represents the external termination of the spring wire in relation to the environment. Possible functions here are shielding from effects of surrounding media, protection from possible impact (for example stone impacts), protection from abrasion (for example friction-resistant protective layer in the spring plates) or prevention of contact corrosion. The proportion by mass of the non-loadbearing layers is about 7%, based on the total mass of the spring wire cross section (ignoring the mass of any spring wire core that may possibly be present).

[0113] The glassfiber layers and carbon-fiber layers in each inventive example form groups. All of the groups are successfully allocated to pairs. In accordance with the invention, all of the compression-loaded groups have lower group stiffness, and the inventive example 1 therefore provides a preferred variant of a torsion spring of the invention.

TABLE-US-00001 TABLE 1 Ply wall Layer wall Layer Ply Layer Group Pair Orientation Material thickness thickness diameter Li Sj Gk Pn Classification Loading [degrees] Mj LWi [mm] Wj [mm] Dj [mm] 1 1 1 1 loadbearing compression 45 2 1.10 1.10 8.55 2 2 2 loadbearing tension 45 1 0.40 0.40 9.30 3 3 3 2 loadbearing compression 45 2 1.10 1.10 10.05 4 4 4 loadbearing tension 45 1 0.40 0.40 10.80 5 5 5 3 loadbearing compression 45 2 1.10 1.10 11.55 6 6 6 loadbearing tension 45 1 0.40 0.40 12.30 7 7 7 4 loadbearing compression 45 2 1.10 1.10 13.05 8 8 8 loadbearing tension 45 1 0.40 0.40 13.80 9 9 non-loadbearing 3 0.50 0.50 14.25 Cross-sectional Layer Group Group exten- Group Ply Layer Group Pair area Mass FR stiffness stiffness sional stiffness ratio Li Sj Gk Pn [mm2] [kg/m] [%] [GPa] [GPa] [kN] GVn 1 1 1 1 14.77 0.03 0.50 44.70 44.70 660.37 1.03 2 2 2 5.84 0.01 0.50 116.00 116.00 677.83 3 3 3 2 17.37 0.03 0.50 44.70 44.70 776.22 1.01 4 4 4 6.79 0.01 0.50 116.00 116.00 787.16 5 5 5 3 19.96 0.04 0.50 44.70 44.70 892.08 1.00 6 6 6 7.73 0.01 0.50 116.00 116.00 896.48 7 7 7 4 22.55 0.04 0.50 44.70 44.70 1007.93 1.00 8 8 8 8.67 0.01 0.50 116.00 116.00 1005.81 9 9 11.19 0.01 only plastic non-loadbearing non-loadbearing non-loadbearing non-loadbearing

TABLE-US-00002 TABLE 2 Mate- Stiff- Den- Example configuration - 50% FEC rial ness sity E1 E2 G12 no. Type class [kg/m.sup.3] [GPa] [GPa] nu12 nu21 [GPa] 1 CF HT 1500 116 5.4 0.28 0.01 2.3 2 GF S2 1870 44.7 6.4 0.29 0.04 2.4 3 Plas- PA6 1140 2.8 2.8 0.3 0.3 1.1 tic

[0114] The inventive example 2 shows a spring wire arrangement of the invention composed of wound textile plies and of a hollow core (FIG. 6). Tables 3 and 4 show the properties of the arrangement of the spring wire and the properties of the materials used. By virtue of the technical possibility of applying identical fiber material and identical fiber angle in relation to the longitudinal axis, the plies 1 and 2 form only one layer (S.sub.1). Application of fiber with identical fiber angles and fiber material in a plurality of plies can prove to be advantageous when by way of example in the case of a coiling process the individual rovings are intended to form a uniform applied structure, and the intention is to prevent displacement of the individual rovings toward one another and/or partial overlapping of the individual rovings. The layer S.sub.1 provides the group G.sub.1. Carbon fibers were used for this compression-loaded group, located well toward the inside of the spring wire, because tensile strength values arising here are relatively low, and the loadbearing capacity of the material is therefore not exceeded. The ply 4 in the inventive example 2 is composed of a carbon-fiber ply with a fiber angle of 0. This is a layer with a fiber angle outside of the range from 20 to 70 or of the range from 20 to 70, said layer therefore being classified as non-loadbearing. This type of layer has an advantageous effect on robustness in relation to transverse loading of the spring wire wound helically around the spring axis, and is therefore useful up to a certain proportion by mass. In this case the proportion by mass of non-loadbearing layers is about 16%, and therefore less than 25% based on the total mass of the spring wire. The compression-loaded plies (L.sub.5, L.sub.6, L.sub.8) situated further outward are composed of basalt-fiber plies. In accordance with the invention, the basalt-fiber plies have lower group stiffness than the tension-loaded ply with the highest group stiffness (e.g. L.sub.9). The group stiffness of L.sub.5 here is lower by 58%, and that of the plies L.sub.6 and L.sub.8 is lower by 62%. The proportion by mass of the compression-loaded fiber plies that have lower group stiffness is 82%, because only the masses of the plies L.sub.1 and L.sub.2 fail to comply with this criterion. At the same time, the group stiffness of the tension-loaded ply L.sub.9 is 139 GPa, this therefore being significantly above the required 60 GPa. All of the tension-loaded plies here are composed of carbon fibers. The inventive example 2 is a preferred variant of the torsion spring of the invention. All of the groups are successfully allocated to pairs.

TABLE-US-00003 TABLE 3 Ply wall Layer wall Layer Ply Layer Group Pair Orientation Material thickness thickness diameter Li Sj Gk Pn Classification Loading [degrees] Mj LWi [mm] Wj [mm] Dj [mm] 1 1 1 1 loadbearing compression 45 1 0.5 0.5 7.25 2 loadbearing compression 45 1 0.7 0.7 7.85 3 2 2 loadbearing tension 45 1 1.05 1.05 8.725 4 3 non-loadbearing 0 1 1.35 1.35 9.925 5 4 3 2 loadbearing compression 45 2 0.4 0.4 10.8 6 5 loadbearing compression 40 2 1 1 11.5 7 6 4 loadbearing tension 45 1 0.5 0.5 12.25 8 7 5 3 loadbearing compression 40 2 1.1 1.1 13.05 9 8 6 loadbearing tension 45 1 0.4 0.4 13.8 Cross-sectional Layer Group Group exten- Group Ply Layer Group Pair area Mass FVG stiffness stiffness sional stiffness ratio Li Sj Gk Pn [mm2] [kg/m] [%] [GPa] [GPa] [kN] GVn 1 1 1 1 5.69 0.009 60% 139.00 139.00 1991.27 1.00 2 8.63 0.013 60% 139.00 3 2 2 14.39 0.022 60% 139.00 139.00 2000.27 4 3 21.05 0.033 60% non-loadbearing non-loadbearing non-loadbearing non-loadbearing 5 4 3 2 6.79 0.014 60% 58.00 53.96 1340.96 1.00 6 5 18.06 0.038 60% 52.45 7 6 4 9.62 0.015 60% 139.00 139.00 1337.34 8 7 5 3 22.55 0.047 60% 52.45 52.45 1182.58 1.02 9 8 6 8.67 0.013 60% 139.00 139.00 1205.24

TABLE-US-00004 TABLE 4 Mate- Stiff- Example configuration - 60% FVG rial ness Den- E1 E2 G12 no. Type class sity [GPa] [GPa] nu12 nu21 [GPa] 1 CF HT 1550 139 6.3 0.26 0.01 3.8 2 BF 2100 58 8 0.28 0.04 3.5

Key

[0115] L.sub.i Ply i (numeric index i within the finite range of the natural numbers [1,I]) [0116] LW.sub.i Wall thickness of the ply i [0117] S.sub.j Layer j (numeric index j within the finite range of the natural numbers [1,J]) [0118] .sub.j Angular orientation in relation to the longitudinal axis of the layer S.sub.i [0119] 1 Spring wire core (optionally present) [0120] M.sub.j Material of the layer S.sub.j [0121] D.sub.j Diameter of the layer S.sub.j [0122] W.sub.j Wall thickness of the layer S.sub.j [0123] E.sub.S.sub.j Stiffness of the layer S.sub.j [0124] E.sub.1 Stiffness longitudinally in relation to the fiber of the material M.sub.j [0125] E.sub.2 Stiffness perpendicularly to the fiber direction of the material M.sub.j [0126] G.sub.12 Shear modulus of the material M.sub.j [0127] .sub.12 Major Poisson's ratio of the material M.sub.j [0128] .sub.21 Minor Poisson's ratio of the material M.sub.j [0129] G.sub.k Group k (numeric index k within the finite range of the natural numbers [1,K]) [0130] A.sub.S.sub.j Cross-sectional area of the layer S.sub.j [0131] E.sub.G.sub.k Group stiffness of the group G.sub.k [0132] F.sub.G.sub.k Group extensional stiffness of the group G.sub.k [0133] P.sub.n Pair n (numeric index n within the finite range of the natural numbers [1,N]) [0134] GV.sub.n Group ratio n, calculated from a tension- and compression-loaded group [0135] D.sub.a External diameter of spring wire [0136] CF Carbon fiber [0137] GF Glass fiber [0138] BF Basalt fiber [0139] S2 Higher-stiffness glass fiber [0140] E Normal-stiffness glass fiber [0141] HT Normal-stiffness (high-tenacity) carbon fiber

NON-PATENT LITERATURE CITED

[0142] Helmut Schrmann: Konstruieren mit Faser-Kunststoff-Verbunden [Design with fiber-plastics composites], 1st edition, Springer Verlag 2005