Structurally Embedded Fiber Optic Thermomechanical Strain State Sensor

*9714049 Sirkis将开发一种长度为1厘米的结构嵌入式光纤传感器，能够同时测量结构复合材料内部的(1)温度，(2)平行于光纤轴线的法向应变，(3)垂直于光纤轴线平面内的次主应变，以及(4)次主平面的取向。拟议中的光纤传感器技术的成功开发将为实验者提供一种今天根本无法获得的能力--测量结构材料内部应变状态的关键组件的能力。该传感器基于级联(1)直插式光纤标准具(ILFE)传感器、(2)写入标准低双折射(LoBiI)光纤的饱和Bragg光栅和(3)写入椭圆形包层应力诱导高双折射(1-LiBI)光纤的正常(非饱和)Bragg光栅。11，FE传感器具有很小的本征温度灵敏度，并且只对宿主结构中的轴向应变分量敏感。因此，所提出的传感器的ILFE分量导致了五个必要的独立光学测量之一，所需的五个独立光学测量需要求解所寻求的五个热力学场变量(三个法向应变、温度和第二主方向)。在LoBi型光纤中写入的饱和布拉格光栅产生两个反射的布拉格波长，从而产生另外两个独立的光学测量。最后，写入椭圆包层Hibi光纤中的Bragg光栅利用残余双折射与光纤的各向异性机械响应相耦合来产生最终所需的两个独立的光学测量。多轴热机械应变传感器的解调将采用扫描、抖动法布里-珀罗滤光片布拉格光栅DEM解调和路径匹配的伪外差差分干涉解调相结合的混合相干法/波分复用法。热机械应变将通过使用基于同心圆柱体建模技术的复合材料细观力学模型和嵌套的多重夹杂模型从最终的光学测量中推导出来，传感器系统将通过逐步增加的复杂性测试来评估，测试从未嵌入传感器的单轴拉伸开始，最后对具有嵌入传感器的AS4/3501-6石墨/环氧层压板施加温度和横向压缩的组合。提出的传感器组件的潜在用途包括：(1)材料测量以帮助本构模型的开发；(2)现场测量以验证微观力学模型；(3)实时现场健康监测；(4)过程监测；以及(5)残余应力测量。这种传感器可以为工程师和科学家提供今天根本无法获得的信息，从而实现更具成本效益、安全和高性能的系统。*

*** 9714049 Sirkis A structurally embedded fiber optic transducer of 1 cm gage length will be developed, capable of simultaneously measuring the (1) temperature, (2)normal strain parallel to the optical fiber axis, (3) secondary principal strains in the plane perpendicular to the optical fiber axis, and (4) orientation of the secondary principal plane, inside a structural composite material. Successful development of the proposed fiber optic sensor technology will provide experimentalists with a capability that is simply unavailable today - the ability to measure key components of the strain state inside structural materials. This proposed transducer is based on cascading (1) an in-line fiber etalon (ILFE) sensor, (2) a saturated Bragg grating written into a standard low birefringent (LoBi) optical fiber, and (3) a normal (unsaturated) Bragg grating written into an elliptical clad, stress-induced high birefringent (1-liBi) optical fiber. The 11,FE sensor has very small intrinsic temperature sensitivity, and is sensitive to only the axial strain component in the host structure. As a result, the ILFE component of the proposed sensor leads to one of the five requisite independent optical measurements required to solve for the five sought after Thermo-mechanical field variables (three normal strains, temperature, and secondary principal direction). The saturated Bragg grating written in the LoBi-Fiber produces two reflected Bragg wavelengths, thereby yielding two more independent optical measurements. Finally, the Bragg grating written into the elliptical clad HiBi optical fiber takes advantage of residual birefringence coupled with this fiber's anisotropic mechanical response to yield the final requisite two independent optical measurements. The multiaxial thermo-mechanical strain sensor will be demodulated using a hybrid coherence division/wavelength division multiplexing technique coupled with scanning, dithered Fabry-Perot filter Bragg grating dem odulation and path-matched differential interferometry with pseudo heterodyne ILFE demodulation. The thermo-mechanical strains will be deduced from the resulting optical measurements through the use of composites micromechanics models based on concentric cylinders modeling techniques and nested multiple inclusions models, The sensor system will be evaluated through tests of progressively increasing complexity, starting with uniaxial tension of an unembedded sensor and ending with the combination of temperature and transverse compression applied to AS4/3501-6 graphite/epoxy laminates with embedded sensors. The potential uses of the proposed sensor assembly include: (1) material measurements to aid constitutive model development; (2) field measurements to verify micromechanics models; (3) real-time in-situ health monitoring; (4) process monitoring; and (5) residual stress measurements. This sensor can provide information to engineers and scientists that is Simply unavailable today, thus enabling the realization of more cost-effective, safe and highperformance systems.***