A brief analysis on the lay-up process of carbon fiber tubes

Compared with the winding process, the carbon fiber tube produced by the rolling process has better resin content stability, which can effectively solve the problem of uneven integral strength of the line segment caused by uneven temperature during the curing process. Of course, the rolling process also has shortcomings, its design is not as good as the winding process, and the strength calculation is more complicated. This article will make a simple analysis of the carbon fiber tube rolling process.

1. Layer limit

From the producer's point of view, continuous layering can save time and cost, but too many continuous layers will inevitably bring about negative problems such as Poisson effect and micro-cracks. When the material is elongated or shortened along the loading direction, the part perpendicular to the loading direction will be shortened or elongated, which is the Poisson effect. The Poisson effect directly affects the stiffness and application effect of the product. Products with a large Poisson effect are not suitable for high pressure, high temperature and high load working environments. Therefore, the Poisson effect should be well controlled during the process of carbon fiber coiling. The number of layers in the same direction in the general carbon fiber laminate is 8%-67%, and it is best to design it separately according to the actual application requirements.

In addition to the Poisson effect, too many continuous layers will increase the shear and coupling strength between the continuous layers at the same angle and other layers, causing the fracture surface to appear significantly layered, the product strength will be greatly reduced, and the service life will be serious. Shortening, especially in humid, sandy and high temperature environments, the impact is more severe.

Limiting the maximum number of continuous layers at the same laying angle can effectively reduce the formation of micro-cracks. Jiangsu Boshi recommends that the thickness of continuous layers at the same angle should not be greater than 1mm, the maximum number of continuous layers at the same angle should not exceed 4, and the thickness of a single layer should be greater than or equal to 1 mm. For layers equal to 0.3mm, the number of consecutive layers at the same angle cannot exceed 3 layers.

2. The laying angle

Reasonable design of the laying angle can effectively improve the overall performance of carbon fiber products. Currently, the commonly used laying angles are 0°, ±45°, and 90°. If the design of the layup angle is unreasonable, the weight and cost of the product will increase, and the performance advantages of carbon fiber composite materials will be difficult to reflect.

The lay-up angle design must pay attention to balance, and a balanced lay-up angle can reduce the residual stress of carbon fiber composite parts during the curing process, thereby avoiding warping deformation. When the carbon fiber tube is made by the coiling process, because the cross section is uniform, it is necessary to ensure that the layup is balanced in the load-bearing direction, which is particularly important during the curing process. The different layup angles should be evenly distributed in the layup sequence. In order to minimize the interlayer shear, the deviation of the angle between the two adjacent layers should be minimized; in order to minimize the coupling effect, the layers should be laid as far as possible ±45° during the laying process.

In addition, in the layer transition area, the overall symmetry and balance should be maintained, and the removed layer position should be alternately applied to the area near or far from the middle line of the layer; External plies should cover the entire surface continuously without faults; try to avoid removing plies on the outside, avoid removing two or more adjacent plies at the same point, and alternately removing plies between successive plies as much as possible; In practical applications, there should be at least one continuous layer between every two faults.