Investigation of the damage and modal behavior of fast rotating geometrically complex structures using in-situ measurement systems

复合材料由于其高比刚度和强度以及可调节的连续损伤行为而提供用于现代高性能转子的优异性能。材料的非均匀性和各向异性需要新的数值模型来设计和描述受损转子的结构行为，特别是损伤引起的固有频率的变化。这种模型的验证需要现场测量技术来确定作为复杂载荷条件的函数的损伤状态和模态行为。在第一个资助期间，系统地研究了衍射光栅法（DGM），并用于验证数值模型。损伤的传播和振动可以作为一个功能的旋转速度和空间分辨速度>260米/秒。光学相干断层扫描（OCT）的静态和动态加载的复合材料的调查的可能性进行了论证，整个三维结构的转子可以可视化。偏振敏感（PS）OCT用于同时检测试件的应力变化、纤维间断裂和变形场。测量和模拟结果显示，未受损结构的测量结果与模拟结果高度一致，但受损和加热结构的测量结果与模拟结果不一致。此外，通过测定固有频率的变化，发现微小的损伤是很难检测的。因此，在第二个资助期内，将对阻尼性能作为微小损伤的指标进行调查。此外，数值模型将扩展到包括温度场的影响，并从多层盘转子推广到更复杂的3D结构。因此，通过光栅的直接激光干涉图案化、测量范围扩展和使用自适应光学的原位校准，DGM的系统偏差将减小到<100 με。OCT将首次用于快速旋转的复杂试样，通过旋转光学元件跟踪测量光束，对损伤演化进行3D检测。在静态试件上，首次利用PS-OCT定量测量空间分辨应变和应力，检验和改进损伤演化模型，建立一个数值模型，预测几何复杂复合材料结构的动态行为与旋转速度、温度场和损伤状态的关系。此外，新的和强大的方法以及传感器将可用于现场验证的数值模型。

Composite materials offer excellent properties for use in modern high performance rotors due to their high specific stiffness and strength and their adjustable successive damage behavior. The heterogeneity and anisotropy of the material requires novel numerical models for the design and description of the structural behavior of damaged rotors and, in particular, the damage-induced shift in their natural frequencies. Validation of such models requires in-situ measurement techniques to determine the damage state and modal behavior as a function of the complex load conditions.During the first funding period, the Diffraction Grating Method (DGM), with which the optical far field of diffraction gratings - applied to elementary rotor structures – was measured, was systematically investigated and used to validate the numerical model. Damage propagations and vibrations could be measured as a function of the rotational speed and spatially resolved at velocities >260 m/s.The possibilities of optical coherence tomography (OCT) for the investigation of statically and dynamically loaded composite materials were demonstrated and the entire 3D structure of a rotor could be visualized. Polarization-sensitive (PS) OCT was used to simultaneously detect stress changes, inter-fiber fractures, and the deformation field of the specimen.Measurement and simulation results show high agreement for undamaged, but not for damaged and heated structures. Furthermore, it became apparent that minor damages are difficult to detect by determining the shift of the natural frequency.Consequently, in the second funding period, the damping behavior will be investigated as an indicator for small damages. In addition, the numerical models will be extended to include the influence of temperature fields and generalized from multilayer disk rotors to more complex 3D structures. Therefore, systematic deviations of the DGM will be reduced to <100 με by Direct Laser Interference Patterning of the gratings, measurement range extension, and in-situ calibration using adaptive optics. OCT will be used for the first time on rapidly rotating, complex specimens for 3D detection of damage evolution by tracking the measurement beam via rotating optical elements. On static specimens, PS-OCT will be used for the first time to quantitatively measure spatially resolved strain and stress to test and improve models of damage evolution.The result will be a numerical model that can predict the relationship of the structural dynamic behavior of geometrically complex composite structures as a function of rotational velocity, temperature field, and damage state. In addition, novel and robust methods as well as sensors will be available for an in-situ validation of the numerical model.