高宽比效应对厚壁复合材料固化过程的影响:Ⅰ.数值模拟(英文)

Determination of the Height-to-Width Aspect Ratio Effects on Thick-Walled Composites Curing:Ⅰ. Numerical Simulation

纤维增强聚合物基复合材料(FRP)面临制造厚度为10mm以上的零件的技术挑战。这是因为零件体积与表面积比的增大以及纤维与树脂的较低的热导率,使得树脂固化过程中产生的大量的热量无法及时散去。随着零件的厚度增加,树脂温度会因为反应热的增加而超过其降解温度。因而,本文着眼于厚壁复合材料零件的高宽比效应对单组分树脂系统RTM6在制造商推荐的固化周期(MRCC)下的最大成型厚度及其固化模式的影响。RTM6是特别为航空业树脂传递塑模(RTM)工艺开发的树脂系统。首先通过差示扫描量热仪(DSC)和参数拟合确定RTM6的固化动力学参数,然后采用有限元法进行模拟分析零件最大成型厚度和固化前沿的扩展过程并与文献结果相比较。结果表明,高宽比对厚壁复合材料零件的最大成型厚度和固化前沿扩展模式均有显著影响。零件最大成型厚度与文献结果的吻合度误差范围为1～7%。相同零件厚度下,随着高宽比的增加,会产生胶凝顺序"由外至内"和"由内至外"两种截然相反的固化前沿扩展模式。通过用户自定义固化周期(UDCC),可以实现将固化前沿扩展模式"由外至内"优化为"由内至外"。综上所述,纤维增强厚壁复合材料零件设计制造过程中,零件的高宽比是一个必须考虑的重要因素。

Fiber reinforced polymer(FRP)composites are often confronted with the challenge of manufacturing parts with a thickness above ten millimeters.This can be attributed to the large amount of heat generated by the exothermic reaction during the curing process,which can hardly diffuse away due to an increased ratio of volume-to-surface ratio and low thermal conductivity of both fibres and resin.As a consequence,the resin might degrade at increased thickness because the reaction temperature may exceed the degradation temperature.The objective of this paper is to determine the effects of the height-to-width aspect ratio on the maximum achievable part thickness of thick-walled composites and their curing pattern under the Manufacturer's Recommended Cure Cycle(MRCC)of RTM 6 which is a mono-component resin system,specifically developed for the aerospace industry in advanced Resin Transfer Molding(RTM)process.The cure kinetics of RTM 6 resin were first characterized by differential scanning calorimetry,followed by a thermo-chemical analysis with the finite element method.The maximum achievable part thickness and the progression of the curing front were investigated with the characterized kinetic parameters and compared with the results obtained by using kinetic parameters of RTM 6 from literature.The results indicate that the height-to-width aspect ratio has a big effect on both,the maximum achievable part thickness of thick-walled composites and the curing pattern.With kinetic parameters characterized by different groups,the maximum thickness results are in accordance with an error range of 1 to 7 percent.Two different cure patterns,gel point start from outside-to-inside and inside-to-outside were observed when increasing the height-to-width aspect ratio with a constant thickness.The former one can be optimized with a so-called User Defined Cure Cycle(UDCC)to get the preferred inside-to-outside progression of the curing front instead of an outside-to-inside one.In conclusion,height-to-width ratio is an important factor,which should be taken into consideration when designing thick-walled FRP composites.