Fig. 1 Normalized transients of A、B flux density B and shear stress τfor a step coil voltage test for
two ratios of λ/Λ. a Start-up. b Shutdown
实验
Laeuge等人(2004)描述了在配备了physica MRD180/1T 磁细胞的physica MCR501上的测量,由Anton Paar Gmbh制造。它的几何尺寸是双板的半径为10毫米,汞柱的差距为0.3毫米。如图4所示,磁通密度的矢量B是竖直向平板剪切,在这种情况下,能够从允许的最大线圈电流中获得高于1T的磁通密度。
磁流变学的挑战之一是磁通与样本间差距的知识,它依赖于磁流变液的磁化强度。通过霍尔探针能够获得实际磁通密度的在线测量。探头是设在一个非磁性
Fig. 4 a Schematic of the magneto-cell modified for an on line measurement of the magnetic flux density. b Photograph of the magneto-cell with Hallp robe (front half of top yoke and rotor removed)
的磁盘的矩形横向通道。磁盘直接位于磁细胞底部之上,充当缝隙固定板的作用。这个附加钢板的厚度是1.5毫秒。霍尔探头的长条与十字架区段是1*4秒,可以放置在各径向场所以确定径向磁通密度的资料。磁通敏感部分的探头直径大约为3毫秒。在固定的位置,霍尔探头在各种线圈电流或依赖时间的磁通瞬态下监测磁通密度(见下文)。
结果
正弦线圈电流可能通过施加线圈电压(图7A)或施加线圈电流(图7B)获得。后者方法有个好处,如果频率改变该电流的幅值不变,而电压幅值在截止频率以上减少。图9为示波器屏幕图,在频率为8HZ和幅值为1A的状态下比较瞬态线圈电流和磁通密度。B的负面迹象由探头的定位来选择。两种信号检测的时间分辨率都优于0.1毫秒。值得注意的是,在零点B延迟2毫秒与J相比,显示了可衡量的涡流的影响。然而,只要磁通密度信号仍然保持为正弦,在这阶段的6度的转移,不应该对图2所介绍的测量剪切应力的比例有影响。
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