PhD - Characterisation of machining induced damage in composite materials

碳纤维增强聚合物（CFRP）由于具有良好的强度重量比、高耐腐蚀性和优异的抗疲劳性等优异的机械性能，在航空航天和汽车工业中得到了广泛的应用。CFRP的加工是重要的，因为制造的零件需要满足特定工程应用所需的几何约束，具有优异的表面质量。典型的加工诱发问题，如分层、纤维拔出、基体开裂和纤维断裂，是由于与材料性能相关的加工参数配置不正确造成的。为了避免加工引起的损伤，需要更好地理解刀具-材料相互作用，文献中通过正交切削试验对其进行了实验研究。本文提出了一种新的视角，利用在线原位分析方法：高速数字图像相关（HS-DIC）和专门设计的实验切割测试平台来分析UD CFRP层合板的正交切割过程。对已知会影响新加工表面完整性的应变的产生进行监测，并生成应变图，并与切削力和切屑形成机制相关联。材料的抗压强度、剪切模量和剪切强度等性能与应变速率有关，它们决定了切削过程中的塑性变形。深入评估了应变值与切削力、切屑形成和切削参数之间的关系，以优化切削工艺，防止加工零件在使用载荷条件下过早失效。

Carbon fibre reinforced polymers (CFRP) are widely used in the aerospace and automotive industry due to their superior mechanical proprieties such as a good strength to weight ratio, high resistance to corrosion and excellent fatigue resistance. Machining of CFRP is important as the manufactured part needs to meet geometrical constraints having an excellent surface quality required for specific engineering applications. Typical machining induced problems such as delamination, fibre pull-outs, matrix cracking and fibre breakage arise due to the incorrect configuration of machining parameters in correlation with material properties. To avoid the machining induced damage, a better understanding of the tool-material interaction is needed, which in literature is investigated experimentally through orthogonal cutting tests. The present work proposes a new perspective in analysing the orthogonal cutting process of UD CFRP laminates using an on-line, in situ analysis method: High Speed Digital Image Correlation (HS-DIC) and a specially designed rig for experimental cutting tests. The creation of strains, which is known to affect the integrity of the newly finished surface is monitored and strain maps are generated and correlated with the cutting force and chip formation mechanism. The material properties such as compression strength, shear modulus and shear strength are strain rate dependent properties which governs the plastic deformation during cutting. An in-depth assessment of the relation between strain values and cutting forces, chip formation and cutting parameters is done to optimize the cutting process and safeguard against the premature failure of machined parts under in-service loading conditions.