Study of Critical Material Parameters for Curing Deformation of Aerospace Wing Composites before Numerical Simulation

Introduction

Due to the deformation of the wing of a certain type of UAV in the curing and molding species, the bulk deformation exceeds the assembly tolerance, and there are serious hidden dangers endangering flight safety if it is assembled on the aircraft by strong stress. Before there is no deformation prediction method, it can only rely on expensive experimental verification, resulting in a long development cycle to meet the delivery time of the equipment. In the U.S., NASA also attaches great importance to numerical analysis and prediction of composite manufacturing processes, for which the U.S. government in 2017 on NASA's Advanced Composites Research Program (AC), specifically enumerated the numerical analysis and prediction of composite manufacturing processes project for research [1,2]. The American Association of Veterinary Parasitologists (AAVP) is also proposing research programs for UAVs and applying composite manufacturing prediction techniques to the X-35. The prediction of curing deformation is the difficulty of curing deformation-molding technology, and is the main research direction of thermosetting resin-based composite materials.

The monolithic molding process for large composite components reduces the weight of the structure and the number of parts, thus reducing costs and assembly expenses. The characteristics of monolithically formed composites can cause interactions between the parts and the mold. The shrinkage of the material and the anisotropy of the material itself can lead to recoil deformation and deformation after release from the mold. This phenomenon is particularly evident in composite parts used in civil aviation and unmanned aerial vehicles, both of which produce certain dimensional deviations during the manufacturing process, making large composite components unsuitable for the stress-free installation conditions of modern aircraft.

Currently, the deformation of composite components is often studied. Parameters are optimized to reduce deformation. However, it is difficult to accurately determine the actual deformation of composite components without conducting experiments. Current scientific studies have confirmed that the variations in curing molding can include mechanical deformation, chemical shrinkage deformation and deformation due to mold action. The prediction of curing deformation is a difficult aspect of curing deformation-molding technology and is the main research direction for thermoset resin-based composite materials.

Curing Deformation is Influenced by the Following Factors Unstable or poor molding processes directly affect the resin content of the material components, which in turn affects the mechanical properties, expansion coefficient and curing shrinkage. Different curing process profiles directly affect the deformation of the cured molding through process parameters such as temperature and molding pressure. Since the molding stage contains a warming and holding and cooling process, the thermal expansion coefficients of the resin are different at different stages under the effect of temperature, and also after curing, the thermal expansion coefficients of the fibers, resin and mold are different, which are responsible for the curing deformation.

During the curing and molding process, there are folds and defects in the fiber lay-up, and in the composite structural parts containing corner types, which also have an effect on the rebound deformation of the composite structural parts. The prepare break and lap type can have an effect on the curing deformation of composite members. In addition, temperature gradients are generated due to different thermal conductivity. Among these are thickness gradients from the composite material, and unbalanced curing distribution, and these imbalances can lead to the generation of residual stresses and thus curing deformation.

In addition, considering the thermal force of the mold on the molded part, the surface roughness of the mold design can have an impact on the generation of frictional forces provided by the curing deformation, and the fact that the mold material and the structural material and the thermal expansion coefficient of the component do not match can have the following effects: in the case of molding with a negative mold, the deformation rebound angle of the part after demoulding is equal to the rebound angle of molding with a positive mold, and the rebound direction is just reversed; in the case of composite molds, the deformation is related to the mold structure and the design compensation method if the thermal expansion is consistent.

After the resin of the composite undergoes a transition between the viscous flow state rubber state and the glass state, the overall mechanical properties change dramatically due to a series of physical and chemical changes. The kinetic study of the numerical curing process must be carried out first. This is because the residual stresses and strains in their composites are formed during the curing process. The kinetic model of the curing reaction describes mathematically the relationship between the resin conversion rate at a given time or temperature and the resin conversion rate. Currently, domestic and foreign scientists mainly through the development of curing kinetic models describe the curing process.

Materials and Methods

The general framework technical line of research in this paper is shown in Figure 1. In addition, the superimposed coupling of cured deformation shown in Figure 2. After the resin of the composite undergoes a transition between the viscous flow state rubber state and the glass state, the overall mechanical properties change dramatically due to a series of physical and chemical changes. The kinetic study of the numerical curing process must be carried out first. This is because the residual stresses and strains in their composites are formed during the curing process. The kinetic model of the curing reaction describes mathematically the relationship between the resin conversion rate at a given time or temperature and the resin conversion rate. Currently, domestic and foreign scientists mainly through the development of curing kinetic models describe the curing process.

A non-isothermal DSC test based on the equipment model: NETZSCH DSC 200F3 was used. In this paper, a carbon fiber prepreg from Weihai Guangwei Company, grade 6508, was used, and the epoxy resin contained 40% of adhesive. The resin material used in the DSC test was physically stripped from the prepreg, and the DSC test was used to establish the curing kinetics model. Weighing samples were weighed 5~10mg using the subtractive method, and the specimens were put into the crucible as required by the experimental apparatus, as shown in Figure 3. A differential scanning calorimeter was used for the samples, and a non-isothermal test was taken, with a heating rate: 5K/min~25K/min and nitrogen gas input, flow rate: 10~20ml/min, and the apparatus was turned on to perform the experiment and record the results, as shown in Figure 4.

Materials and Methods

The general framework technical line of research in this paper is shown in Figure 1. In addition, the superimposed coupling of cured deformation shown in Figure 2. After the resin of the composite undergoes a transition between the viscous flow state rubber state and the glass state, the overall mechanical properties change dramatically due to a series of physical and chemical changes. The kinetic study of the numerical curing process must be carried out first. This is because the residual stresses and strains in their composites are formed during the curing process. The kinetic model of the curing reaction describes mathematically the relationship between the resin conversion rate at a given time or temperature and the resin conversion rate. Currently, domestic and foreign scientists mainly through the development of curing kinetic models describe the curing process.

A non-isothermal DSC test based on the equipment model: NETZSCH DSC 200F3 was used. In this paper, a carbon fiber prepreg from Weihai Guangwei Company, grade 6508, was used, and the epoxy resin contained 40% of adhesive. The resin material used in the DSC test was physically stripped from the prepreg, and the DSC test was used to establish the curing kinetics model. Weighing samples were weighed 5~10mg using the subtractive method, and the specimens were put into the crucible as required by the experimental apparatus, as shown in Figure 3. A differential scanning calorimeter was used for the samples, and a non-isothermal test was taken, with a heating rate: 5K/min~25K/min and nitrogen gas input, flow rate: 10~20ml/min, and the apparatus was turned on to perform the experiment and record the results, as shown in Figure 4.