Localized Finishing of Freeform Geometries using Dynamic Magnetic Field-Manipulated Magneto-Viscoelastic Fluids

对生物医学假体植入物的需求（例如，全髋关节）每年以5%的速度增长，预计到2019年该市场将超过350亿美元。 对各种接头表面的目标区域进行局部精加工对于保证其使用寿命至关重要。该行业在很大程度上依赖于费力和昂贵的手工或化学蚀刻方法进行局部抛光。该奖项支持基础研究，可以导致新的机床，使用磁能和磨料混合的磁性“斑点”（半固体小球在一个可再生流体）的局部表面精加工。这些机床对于定制的、功能性的自由形状零件（例如，耐用的单件假体部件）。本研究的重点是磁流体的组成以及外部磁场的时空变化对选择性和材料去除率的影响超过1-10平方米。在由抗磁性或弱顺磁性材料制成的自由形状部件上， 第一个研究目标是建立定量关系的磁流体滴的流变特性与他们的胶体组成和外部磁场的时空变化：这方面的知识是必不可少的选择磁场模式，可以创建梯度有利于最佳的流动和选择性的磁流体，并使一个滴施加适当的向下压力。为了实现这一目标，将进行一项实验研究，采用专门的流变仪仪表阵列的磁铁，高斯米，以及力和振动传感器。流变仪提供了一种受控的手段来估计磨料颗粒流体的磁粘弹性（基于橡胶弹性理论）以及不同流体成分和工件表面的材料去除率，并测量感应磁场、力和下压力。第二个目标是建立在磁团上感应的局部磁场梯度与所施加的时空磁场之间的关系：所得到的知识将提供指导，以实现在指定位置处的尖锐磁场梯度，并设计能够创建这些图案的磁性外壳。为了实现这一目标，将采用一种新的隐式粘弹性建模方法。该方法使用从第一目标收集的属性关系来提供计算上有效的手段来捕获团块行为，包括从磁弹性固体状响应到磁粘弹性流体的响应的平滑过渡。

Demand for biomedical prosthetic implants (e.g., total hip joints) is growing by 5 percent annually and this market is expected to exceed $35B by 2019. Local finishing of targeted regions of the surfaces of various joints is essential for their life assurance. The industry largely depends on laborious and expensive manual or chemical etching methods for localized finishing. This award supports fundamental research that can lead to new machine tools that use magnetic energy and abrasive-mixed magnetic "blob" (semisolid globule in a nonmagnetic fluid) for localized finishing of surfaces. These machine tools can be vital for affordable manufacturing of custom, functional free-form parts (e.g., durable, single piece prosthetic components). The focus of this research is on the effects of the composition of the magnetic fluid as well as the spatio-temporal variation of the external magnetic fields on the selectivity and material removal rates over 1-10 sq. cm area on freeform parts made of diamagnetic or weak paramagnetic materials. The first research objective is to establish quantitative relationships connecting the rheological properties of magnetic fluid blobs with their colloidal compositions and the spatio-temporal variation of external magnetic fields: This knowledge is essential to select magnetic field patterns that can create gradients conducive for optimal flow and selectivity of magnetic fluids, and make a blob exert appropriate down pressures. To achieve this objective, an experimental study will be conducted employing a specialized rheometer instrumented with array of magnets, Gauss meters, as well as force and vibration sensors. The rheometer provides a controlled means to estimate both the magneto-viscoelastic properties of the abrasive granular fluid (based on rubber elasticity theory) as well as the material removal rates for different fluid compositions and workpiece surfaces, and measure the induced magnetic field, forces, and the down pressure. The second objective is to establish a relationship between the localized magnetic field gradients induced over a magnetic blob and the applied spatio-temporal magnetic field: The resulting knowledge will provide guidance to realize sharp magnetic gradients at specified locations, and design magnetic enclosures capable of creating these patterns. To achieve this objective, a novel implicit viscoelastic modeling approach will be employed. This approach uses the property relationships gathered from the first objective to provide a computationally efficient means to capture the blob behaviors, including smooth transition from a magneto-elastic solid like response to that of a magneto-viscoelastic fluid.