碳纤维增强树脂基复合材料切削机理研究

The Research of Machining Mechanism of Carbon Fiber Reinforced Plastic

碳纤维增强树脂基复合材料(Carbon fiber reinforced plastic,CFRP)在细观尺度上由纤维、树脂及界面不同相组成,在宏观尺度上呈层叠特征,具有非均质性和各向异性。CFRP切削过程的实质是在切削力、热共同作用下同时去除高强度纤维和低强度树脂的复杂过程,极易出现加工损伤。抑制加工损伤的前提是准确揭示CFRP切削机理,而揭示其切削机理的关键是分析材料去除过程。由于纤维是复合材料内部承受主要载荷的组成相,材料的去除过程主要由纤维的断裂过程决定。因此,通过分析切削过程中纤维的受力状态,以双参数弹性地基梁理论为基础,建立了虑及纤维所受法向及切向约束,且兼虑树脂及界面温变特性的单纤维切削模型,可准确表征纤维实际受力状态,实现纤维断裂过程的准确求解。研究发现:切削深度和纤维角度影响纤维变形深度,即切深越大,纤维变形深度越大,更易产生加工损伤;随着纤维角度增加,纤维变形深度减小。同时,为解决单纤维切削模型难以直接验证的难题,利用其求解得到宏观切削力理论值,通过与试验值对比,间接验证了单纤维切削模型的正确性。同时与未考虑被切削纤维所受切向约束和树脂及界面温变特性时相比,同时考虑这两个因素可使CFRP宏观切削力计算精度平均提升20%。所建立的单纤维切削模型不仅能够从细观尺度准确揭示CFRP去除机理,而且可为后续有关损伤抑制的研究提供理论依据。

Carbon fiber reinforced plastic (CFRP) consists of fiber, matrix, and interface at micro level. Meanwhile, it has laminated feature and shows heterogeneous anisotropy at macro level. The essence of the CFRP removal in machining is the complex process including simultaneous failure of the high-strength fiber and low-strength matrix under cutting force and heat, which results in machining damage easily. Analyzing the material removal process deeply is the key to reveal the machining mechanism of the CFRP, which can help to control the machining damage. The material removal process is mainly determined by the facture process of the fiber due to the fact that the fiber bears main load during the CFRP machining. Therefore, a micro-mechanical model of cutting a single fiber is proposed by analyzing the stress state of the fiber based on the two-parameter elastic foundations to describe the fiber fracture process exactly. In order to represent the stress state of the single fiber accurately, the model is considered the normal and shear effect on the fiber deformation, and the property change of the epoxy as well as interface with respect to temperature. The machining mechanism of the CFRP is revealed as follows: the depth of fiber deformation is influenced by the cutting depth and the fiber orientation. The depth of fiber deformation is increased with the increase of the cutting depth, which will result in machining damage more easily. And the depth of fiber deformation decreases with the increase of the fiber orientation. In order to verify the proposed model, the micro-mechanical model of cutting a single fiber is acquired to calculate the macroscopic cutting force. Then the model is validated indirectly through the comparing of the calculated value of macroscopic cutting force with the experimental value. And the calculation accuracy of the cutting force increases 20% on average because of considering the shear effect and the property change of the epoxy as well as interface with respect to temperature. In addition, the model can reveal the machining mechanism of the CFRP at micro level more accurately and provide theoretical basis for subsequent studies of the damage suppression.