Innovative photomechanical approaches in identification of the dynamic mechanical behaviour of materials

在许多工程领域，材料的变形率很高。当结构受到冲击、碰撞、爆炸等时，也可以在冲压或机械加工等材料成型时使用。因此，对于设计工程师来说，有可靠的力学模型来预测材料在这种应用中的行为是至关重要的。数值模拟的惊人进展加强了这一点，现在可以对非常复杂的情况进行详细的计算。然而，完善的高应变率变形模型的鲁棒实验识别是滞后的，并且阻碍了为社会带来更安全的基础设施（建筑物，桥梁，水坝），更安全的交通工具（车辆的耐撞性）等数字模拟的全部潜力。事实上，为了进行高应变率材料模型的实验鉴定，工程师们只有一个非常有限的工具箱，基于几十年前开发的测试程序。最好的例子是所谓的分离式霍普金森压力杆（SHPB），它已被证明非常有用，但由于处理测试数据所需的严格假设，它具有重要的内在局限性。这些假设是由于开发此类测试的仪器非常有限的结果，通常是标准SHPB设置的几个应变片读数。最近使用成像技术进行全场变形测量的出现，使得新方法得以开发，令人兴奋的新测试程序首次被想象出来。本项目的目标是基于数字成像技术的可用性，为材料动态测试的新时代奠定基础，以提供非常高速的全场变形测量。然后，可以将这些信息与有效的数值反识别工具（如虚拟场方法）相结合，设计新的测试程序，以高速率识别材料参数。其基础新颖性是利用在高应变率载荷下产生的惯性效应。迄今为止，这些在常规测试中被认为是不可取的。然而，在识别过程中，它们可以扮演体积分布称重传感器的角色，其读数嵌入在全场变形测量中。这个想法是突破性的，因为它有可能解除当前高应变率测试的主要限制，即小试样和恒定速度。本提案旨在为申请人提供一个平台，以便在材料，加载配置和应变率范围方面为许多不同类型的情况开发这种方法。该项目有可能彻底改变材料的高应变率测试，从而提高我们对材料性能的了解。从长远来看，这将反过来使工程和社会的许多部门受益。

In many areas of engineering, materials suffer deformation at high rates. This is the case when structures undergo impact, crash, blast, etc. but also in material forming like stamping or machining for instance. Therefore, it is essential for design engineers to have reliable mechanical models to predict the behaviour of the materials in such applications. This is enhanced by the spectacular progress in numerical simulation which now enables to perform detailed computations of very complex situations. However, robust experimental identification of refined high strain rate deformation models is lagging behind and hinders the delivery of the full potential of numerical simulations for the benefit of society: safer infrastructures (buildings, bridges, dams), safer means of transportation (crashworthiness of vehicles) etc. Indeed, in order to perform experimental identification of high strain rate material models, engineers only have a very limited toolbox based on test procedures developed decades ago. The best example is the so-called Split Hopkinson Pressure Bar (SHPB) which has proved extremely useful but has important intrinsic limitations due to the stringent assumptions required to process the test data. These assumptions are the consequence of the very limited instrumentation for which such tests were developed, usually a few strain gauge readings for the standard SHPB set-up. The recent advent of full-field deformation measurements using imaging techniques has allowed novel approaches to be developed and exciting new testing procedures to be imagined for the first time. The objective of the present project is to lay the foundations of a new era in dynamic testing of materials based on the availability of digital imaging technology to provide full-field deformation measurements at very high speeds. One can then use this information in conjunction with efficient numerical inverse identification tools such as the Virtual Fields Method to design novel test procedures to identify material parameters at high rates. The underpinning novelty is to exploit the inertial effects developed in high strain rate load. These have hitherto been regarded as undesirable in conventional testing. However, in the identification process they can play the role of a volume distributed load cell for which readings are embedded in the full-field deformation measurements. The idea is ground breaking as it has the potential to lift the current major limitations of high strain rate test, i.e. small specimen and constant velocity. The present proposal aims at providing a platform for the applicant to develop this methodology for many different types of situations in terms of materials, loading configuration and strain rate range. The project has the potential to revolutionize high strain rate testing of materials and hence enhance our knowledge of material behaviour. This will in turn benefit many sectors of engineering and society in the long term.