Photoelasticity for opaque objects

折射率差是在材料中沿沿着不同轴出现的折射率差。在某些材料中，由于原子结构，这种效应是固有的。在其他材料中，人工双折射可以由在材料中产生各向异性的机械应力引起。偏振波根据其偏振方向以不同的速度通过应力区域。这种现象在光弹性的成熟技术中得到了利用，其中感兴趣的组件的模型由光学透明的塑料材料制成，并放置在偏振光学器件之间。诱导双折射与在给定点处经历的应力成正比：主应力的恒定差的轮廓和主应力方向的轮廓呈现为条纹图案。该技术在实验力学、设计和制造中发挥了重要作用。本项目涉及测量在可见光波长下不透明的材料中的应力诱导双折射。我们将使用0.3和1.5 THz之间的THz照明，其中一些部分通过一系列非极性材料（包括陶瓷，塑料和复合材料）传输。测量应力引起的双折射将提供关于在可见光波长下不透明的真实的组件中的内部应力分布的信息，从而消除了在透明塑料中对其进行建模的需要。这种新的独特的应力可视化技术可能被认为是“不透明物体的光弹性”，尽管更精确的技术将用于测量照明的偏振分量之间产生的相位差。从真实的部件的测量还能够直接验证数值模型。这些新技术将在制造应用过程中实现过程控制和服务质量保证，对于目前无法提供的一系列材料，使所使用的制造工艺和可以生产的组件能够逐步改变。该项目将提供基础研究，以确定在太赫兹频率下测量应力诱导双折射是否可行。这种现象在文献中尚未报道。基于应力光学系数的基本测量，THz系统将被构建用于测量陶瓷和聚合物材料中的残余应力分布和由直接加载产生的应力。太赫兹频率下的非光谱成像尚未得到很好的发展，使得新的相位测量技术能够用单点检测器和最先进的线检测器来实现。该项目汇集了工业相关计量和工业合作者在光学仪器方面的研究专业知识，这些合作者在高价值制造应用的创新方面有着良好的记录。

Birefringence is a difference in refractive index that occurs along different axes in a material. In some materials this effect is intrinsic due to the atomic structure. In other materials, artificial birefringence can be induced by a mechanical stress that produces anisotropies in the material. Polarized waves travel at different velocities through the stressed regions depending on their polarization direction. This phenomenon is exploited in the well-established technique of photoelasticity, in which a model of the component of interest is made in an optically transparent plastic material and placed between polarizing optics. The induced birefringence is directly proportional to the stress experienced at a given point: contours of constant difference in the principal stresses and contours of the principal stress direction appear as fringe patterns. The technique has played a fundamental role in experimental mechanics, design and manufacturing.This project is concerned with measuring the stress-induced birefringence in materials that are opaque at visible wavelengths. We will use THz illumination between 0.3 and 1.5 THz where some fraction is transmitted through a range of non-polar materials including ceramics, plastics and composites. Measuring the stress-induced birefringence will provide information on the internal stress distribution in real components that are opaque at visible wavelengths, removing the need to model it in transparent plastic. This new unique stress visualisation technique might be considered as 'photoelesticity for opaque objects', although more accurate techniques will be used to measure the phase difference that arises between the polarized components of the illumination. Measurement from the real components also enables direct validation of numerical models. These new techniques will enable in-process control during manufacturing applications and in-service quality assurance, for a range of materials where this is not currently available, enabling step changes in the manufacturing processes used and the components that can be produced.This project will provide the underpinning research to determine if measuring stress-induced birefringence at THz frequencies is feasible. The phenomenon has not been reported in the literature. Based on the fundamental measurements of the stress-optic coefficients, THz systems will be built to measure residual stress distributions and stresses produced by direct loading in ceramic and polymer materials. Non-spectroscopic imaging at THz frequencies is not well developed, enabling novel phase measurement techniques to be implemented with single point detectors and start-of-the-art line detectors. The project brings together research expertise in optical instrumentation for industrially relevant metrology and industrial collaborators with strong track records in innovation for high value manufacturing applications.