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的连续损伤行为，为现代高性能转子提供了优异的性能。材料的非均质性和各向异性需要新的数值模型来设计和描述损坏转子的结构行为，特别是损坏引起的固有频率的移动。这种模型的验证需要现场测量技术来确定损伤状态和模态行为作为复杂载荷条件的函数。在第一期资助期内，系统研究了应用于基本转子结构的衍射光栅远场测量的衍射光栅法（DGM），并用于验证数值模型。损伤传播和振动可以作为转速的函数进行测量，并在速度为> - 260 m/s时进行空间分解。论证了光学相干层析成像（OCT）用于研究静态和动态载荷复合材料的可能性，并实现了转子的整个三维结构的可视化。利用偏振敏感OCT同时检测试样的应力变化、纤维间断裂和变形场。测量和模拟结果表明，对于未损坏的结构，一致性较高，但对于损坏和加热的结构，一致性不高。此外，很明显，通过确定固有频率的位移很难检测到轻微的损伤。因此，在第二个资助期内，阻尼行为将作为小损伤的指标进行研究。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三维结构。因此，通过光栅的直接激光干涉图、测量范围的扩展和自适应光学的原位校准，可以将DGM的系统偏差降低到<100 με。OCT将首次用于快速旋转的复杂样品，通过旋转光学元件跟踪测量光束，对损伤演变进行3D检测。在静态试样上，PS-OCT将首次用于定量测量空间分解应变和应力，以测试和改进损伤演化模型。结果将是一个数值模型，可以预测几何复杂复合结构的结构动力行为作为旋转速度，温度场和损伤状态的函数关系。此外，新的鲁棒方法和传感器将可用于数值模型的原位验证。

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.