Thermal Deformation of Carbon Fiber Reinforced Composite by Cure Shrinkage

탄소섬유강화 복합재료 성형시 화학수축에 의한 변형연구

Abstract

As the autoclave process progresses in a given cure cycle, residual stress in the composite product is induced by cure shrinkage of the resin. As a result, It generates the thermal deformation such as spring-in and warpage, and the inaccuracy of the final product increases. It is important to predict thermal deformation in aerospace parts which require precise fabrication. The research has been done on predicting and grasping curing process of composite material. In this study, the cure mechanism of composite materials according to the process is predicted through finite element analysis, and the effect of cure shrinkage on thermal deformation generated by the process is analyzed.

복합재료는 주어진 경화 사이클(cure cycle)로 오토클레이브 공정이 진행됨에 따라 수지의 화학수축, 열팽창계수 등에 의한 제품 내 잔류응력(residual stress)이 발생한다. 이로 인해 spring-in, warpage와 같은 열 변형이 발생하고 최종 제품의 수치 정확성이 감소한다. 구조물의 정밀한 제작이 요구되는 항공우주분야에서는 열변형으로 인한 문제를 해결하는 것이 중요하다. 따라서 복합재료의 경화과정을 예측하고 이해하기 위한 연구가 활발히 이루어지고 있다. 본 연구에서는 공정과정에 따른 복합재료의 경화메커니즘을 유한요소해석을 통해 예측하였고, 공정에 의해 발생하는 열변형에 대한 화학수축의 영향을 열팽창계수와 비교하여 분석하였다.

Fig. 1. Schematic of (a) spring-in, (b) warpage

Fig. 2. Schematic of cure cycle and degree of cure

Fig. 3. Geometry information of plate model

Fig. 4. Displacement(magnitude) of single lay-up models. Unit:[m]

Fig. 5. Displacement(magnitude) distribution of single lay-up models (a) Line-A (b) Line-B

Fig. 6. Photograph [6] and Y-axis displacement contour of (a) lay-up [45/-45] and (b) [0/45/-45] models

Fig. 7. Y-axis displacement distribution along the Line-1 in Fig. 6

Fig. 8. The stress distribution at point-1 of lay-up [0/45/-45]models

Fig. 9. Schematic of geometry information

Fig. 10. Schematic of (a) degree of cure (b) The CS and CTE of longitudinal direction (c) The CS and CTE of transverse direction. CTE unit:[mm/(mm∙K)]

Fig. 11. Schematic of (a) degree of cure (b) The thermal strain of longitudinal direction (c) The thermal strain of transverse direction. CTE unit:[mm/(mm∙K)]

Fig. 12. The comparison of compro and Ref. [4] for the thermal strain of transverse direction [4]

Fig. 13. The stress distribution at point-1

Fig. 14. (a) spring-in position (b) spring-in along the position (line)

Table 1. Constants of cure kinetics

Table 2. Modulus development constants of the M18 resin

Table 3. Elastic properties of the M55J fiber [11]

Table 4. Constants of thermal expansion coefficient and cure shrinkage

Table 5. Final displacement of Y-axis direction in point-1

Table 6. Final thermal strain