Balanced angle connection

The balanced angle composite is a composite of two unidirectional layers of a fiber-plastic composite . The unidirectional layers have the same amount of fiber angle, but different signs . The layer thicknesses of the unidirectional layers are identical.

The balanced angle compound is abbreviated as AWV , followed by the amount of the fiber angle . It is referred to in English as a balanced ply laminate . ${\displaystyle \omega }$

In winding technology and network theory , the balanced angle connection plays a particularly important role. It can also be found in multiaxial layers made from woven fabrics. Balanced angle connections in the form of the AWV45 are used as shear-resistant layers.

The AWV45 is a special case of a cross connection with the same layer thickness.

Use of balanced angle connections

Sketch of a balanced angle connection

Balanced angular bonds are created when rovings are laid down using the fiber winding technique. The modulus of elasticity and the shear modulus of the laminate can be varied over a wide range via the angle of the angular bond without causing anisotropy. Therefore it can be used very flexibly.

The AWV45 has the maximum shear stiffness of a two-layer laminate with regard to the axes of symmetry. Therefore, the AWV45 is often used in push bars or drive shafts. An inexpensive way to create an AWV45 is to use a balanced fabric , the cross tie . If you turn the fabric by 45 ° around the fabric normal, you get an AWV45.

In addition to the cross connections , balanced angular connections are required to construct a quasi-isotropic layer structure ( quasi-isotropic laminate ).

Properties of balanced angle connections

The balanced angle connection is orthotropic as a disk . The individual unidirectional layers rotated from the orthotropic axes are anisotropic. However, due to the fiber angle differing only in sign, the displacement-elongation terms have different signs. When the laws of elasticity of both unidirectional layers are superimposed, the couplings are canceled. The classic laminate theory makes the disappearance of the compression-strain coupling clear.

Outside the axes of symmetry, the balanced angle connection is anisotropic.

As a plate, the two-layer, balanced angle connection is anisotropic. It has a flex-twist and a flex-stretch coupling. This disadvantage can be prevented by a symmetrical layering or a fine-layer structure. Due to the fine-layer structure, the static moments are small and thus the plate-plate coupling (see: classic laminate theory ). The fine-layer structure is especially the case with wound components.

Special fiber angles

AWV45

Rigidity of a balanced angular connection over its angle

The AWV 45 is used in thrust-loaded components such as wound drive shafts. The particular suitability of this composite is based on the pure normal stress load on the fibers. Theoretically, the matrix is ​​not claimed.

In a pure state of shear stress, the main normal stresses are rotated by 45 ° to the direction of shear (see: Mohr's circle of stresses ). The reinforcement fibers in the AWV45 run exactly in this direction.

AWV54.7

The AWV54.7 is mainly used for pipes or containers that are subject to internal or external pressure. The main stress ratio in such components results from the boiler formula to . The fiber angle of is calculated from the network theory . ${\displaystyle {\frac {\sigma _{\rm {I}}}{\sigma _{\rm {II}}}}={\frac {1}{2}}}$ ${\displaystyle \arctan {\sqrt {2}}\approx 54{,}7^{\circ }}$

The pressure load can theoretically be absorbed with an AWV54.7 without stressing the matrix. This is particularly important for pipes and lines that are only provided with a dry fiber winding.