Coupled functional and structural fatigue of shape memory alloy actuators

该项目旨在更好地了解NiTi基形状记忆合金(SMA)致动器中的功能和结构耦合疲劳(CFSF)。SMA在被热激活时，在强烈的(显然是塑性的)变形后，表现出重建其初始几何形状的迷人能力。今天，热形状记忆效应在不同类型的高科技工程应用中被利用，其中SMA被用于耦合、移动质量或控制流道等。对于应用，通常要求SMA执行器能够提供大量的功能循环而不会遭受严重的退化。因此，CFSF很重要，因为它限制了使用寿命，特别是在需要大量功能循环的情况下。CFSF的特点是功能退化，同时也有疲劳裂纹的形成和扩展。到目前为止，尽管CFSF在新的执行器应用中控制着使用寿命，但它没有得到足够的科学关注。在本项目中，来自材料科学和产品设计/生产技术领域的科学家合作，以建立对CFSF的更好了解，并提高疲劳寿命和部件可靠性。在材料科学和工程教席上，将研究CFSF的材料科学方面。重点放在识别基本的CFSF机制，以及微观结构和合金成分的作用。在生产系统教席上，将研究SMA中CFSF的疲劳寿命以及执行器操作条件和执行器设计方面的影响。必须强调的是，将研究不同的合金和材料状态，这些合金和材料将在波鸿生产和测试。这也包括执行器原型，这些不同的SMA将被集成在一起。通过更好地了解CFSF，可以开发和选择优化的SMA，并针对新的应用调整执行器设计解决方案和执行器操作条件。在拟议的项目中，双方合作伙伴联手提供对形状记忆技术进步至关重要的答案。

The project aims for a better understanding of coupled functional and structural fatigue (CFSF) in NiTi-based shape memory alloys (SMAs) actuators. SMAs exhibit the fascinating ability to re-establish their initial geometry after a strong (apparently plastic) deformation when being thermally activated. Today, the thermal shape memory effect is exploited in different types of high-tech engineering applications, where SMAs are used for coupling, to move masses or to control walves (etc.). For application, it is often required that SMA actuators are able to provide a large number of functional cycles without suffering critical degradation. Therefore, CFSF is important, as it limits service life, especially when large numbers of functional cycles are required. CFSF is characterized by a functional degradation and simultaneously by the formation and growth of fatigue cracks. So far, CFSF has received insufficient scientific attentions although it governs service life in new actuator applications. In the present project, scientists from the fields of materials science and product design / production technology collaborate in order to establish a better understanding of CFSF and to improve fatigue life and component reliability. At the Chair for Materials Science and Engineering, materials science aspects of CFSF will be studied. The focus is placed on the identification of elementary CFSF mechanisms, and on the roles of microstructures and alloy compositions. At the Chair for Production Systems, CFSF fatigue life in SMAs and the effects of actuator operating conditions and actuator design aspects will be studied. It is important to highlight that different alloys and material states will be investigated which will be produced and tested in Bochum. This also includes actuator prototypes where these different SMAs will be integrated. A better understanding of CFSF allows to develop and to select optimized SMAs, and to adapt actuator design solutions and actuator operating condition for novel applications. In the proposed project, both partners join forces to provide answers which are important for the progress in shape memory technology.