Ply structure

Ply structure is the key to the structural design of carbon fiber composites. How to transfer the excellent performance of single-layer structure to composite structural components, ply structure plays a connecting role. The following points shall be noted with respect to composite paving:

1. Resin is the short board of mechanical properties of carbon fiber composites, so try to avoid adding load directly between layers or resins. In other words, there must be fibers of 0 °, ± 45 ° and 90 °, otherwise the load will tear the parts from the direction without fiber arrangement.

2. In order to prevent the edge cracking of the laminate, repeat the paving in a single direction as far as possible, and the design shall not exceed 5 layers at most.

3. In order to prevent the peeling of the outermost layer, ± 45 ° fibers shall be laid in the main load direction of the component, instead of 0 ° and 90 ° fibers. In addition, avoid discontinuity or incompleteness of the outermost layer.

4. If asymmetric paving is used, each layer will warp due to different thermal expansion coefficients in the same direction. Therefore, symmetrical paving is generally used.

5. When the reinforcing layer is added, the step of each layer shall be at least 3.8-6.4mm, and the symmetrical layer shall also be used for the additional layer as far as possible.

connect

In the development process of carbon fiber composite parts, it is unlikely to adopt integral molding technology. If the connection between parts is required, the connection form needs to be designed.

Generally speaking, there are three forms of connection of carbon fiber composite parts: mechanical connection, cemented connection and hybrid connection. Mechanical connection is applicable to the case of large thickness of connector, high reliability requirements and large concentrated load transmission. Cementation is mainly the use of adhesive to connect parts into an inseparable whole.

Hybrid connection is a combination of cementation and mechanical connection. It can improve the properties of peel resistance, impact resistance, fatigue resistance and creep resistance.

Fatigue and impact damage

Compared with metal materials, temperature, humidity, impact damage and other factors must be considered. In most cases, impact damage covers fatigue in structural design.

fatigue

In general, the tensile fatigue of composites is better than that of metals. In orthogonal laminates, the cracking under fatigue or alternating load is relatively stable, which is slower than that of metal. For composites, attention must be paid to the fatigue failure caused by compression, shear and interlaminar shear after impact under alternating load. The causes of early failure caused by fatigue are as follows:

1. Notch, sharp corner

2. Section mutation

3. Protrusion

4. Extreme eccentric load

5. Bolted joints

6. Quick swing