Stochastic ultrasonic scattering from the tips of rough cracks

对核能工业中安全关键部件的检查依赖于能够检测到给定严重程度阈值的缺陷的程序；这一验收过程被称为检验确认。检验资格在英国是一项高度发达的正式活动，是世界上最佳实践的代表。然而，如果在预期的测量响应中存在不确定性，则它可能非常保守。一个重要的例子是超声波从粗糙裂纹的尖端散射，如热疲劳裂纹或应力腐蚀裂纹。裂纹尖端的超声散射被广泛用于测量裂纹大小，但是，虽然光滑裂纹的散射性质很好地理解，但粗糙裂纹尖端的散射可能有很大不同，并且不易预测。因此，对粗糙裂纹的超声检查的资格必须服从于严格保守的假设，即使如此，仍然存在误解结果的风险。该项目旨在了解散射的本质，并开发预测建模工具，从而可以安全地侵蚀这些保守的假设并提高检查的可靠性。这将使工业界能够降低制造和维修成本，减少停机时间，并提高对安全关键工厂安全运行的信心。该项目将建立在强大的英国超声散射知识的基础上，包括最近由提议者关于粗糙表面波反射的随机性质的工作。关键目标是提供一种新的分析方法，该方法将预测给定粗糙度特征的裂纹尖端的统计预期散射。这项工作还将包括对真实裂缝的实验研究和数值模拟研究。这些新思想将应用于飞行时间衍射、脉冲回波和阵列成像等主要超声检测技术。这项工作将由帝国理工学院机械工程和数学研究人员合作进行。该提案正在英国NDE研究中心（RCNDE）内提交给其目标研究计划。该提案已由RCNDE内部审查，由RCNDE董事会批准，并得到五个RCNDE工业成员的财政支持。

The inspection of safety-critical components in the nuclear power industry depends on procedures that can detect defects to a given threshold of severity; the acceptance process for this is known as inspection qualification. Inspection qualification in the UK is a highly developed formal activity, and is representative of the best practice in the world. However it can be very conservative if there is uncertainty in the expected measured response. A vital example is the scattering of ultrasound from the tips of rough cracks, such as thermal fatigue cracks or stress corrosion cracks. Ultrasound scattering from crack tips is widely exploited to measure crack sizes, but while the nature of the scattering is well understood for smooth cracks, scattering from the tips of rough cracks can differ significantly, and is not readily predictable. Consequently the qualification of ultrasound inspections for rough cracks has to be subject to severely conservative assumptions, and even so there remains a risk of misinterpreting findings. This project aims to bring understanding to the nature of the scattering, and to develop predictive modelling tools, such that these conservative assumptions can be safely eroded and the reliability of inspections improved. This will enable industry to reduce the costs of manufacturing and repairing, and down-time from outages, as well as improving confidence in the safe operation of safety-critical plant. The project will build on a strong UK heritage of the knowledge of ultrasound scattering, including recent work by the proposers on the stochastic nature of wave reflections from rough surfaces. The key aim is to deliver a new analytical approach that will predict the statistically expected scattering from the tips of cracks of given characteristics of roughness. The work will also include experimental investigation of real cracks and numerical modelling studies. The new ideas will be applied to the primary ultrasound inspection techniques of Time-of-Flight-Diffraction, Pulse-Echo, and array imaging. The work will be undertaken as a collaboration between researchers in Mechanical Engineering and in Mathematics at Imperial College. The proposal is being submitted within the UK Research Centre in NDE (RCNDE) to its targeted research programme. The proposal has been reviewed internally by the RCNDE, approved by the RCNDE board, and supported financially by five RCNDE industrial members.