(Fe70Ni30)80B14Nb4Si2 MANC-Epoxy Composite Tensile Test Data
Description
This data provides the failure stresses for tensile tests of single-, five-, and ten-layer (Fe70Ni30)80B14Nb4Si2 MANC-epoxy composite test specimens. When plotted as a Weibull distribution, it can be shown that the Weibull Modulus improves as more layers are laminated together. This result is significant because it shows that laminated MANC composite specimens can survive the fracture of individual layers without inducing specimen failure. Thus, stress-sensitive components such as electric motors made as a laminated stack of MANC ribbons can safely operate at higher speeds than would be inferred from single ribbon data.
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AMR alloys of composition (Fe70Ni30)80B14Nb4Si2 were fabricated using a METGLAS batch mode planar flow casting process. The ribbon tested exhibited a calculated average thickness of 19.8µm. Ribbons were cut across their width with shears to a length of 150 mm and annealed in an air atmosphere at 440 ºC, between T_x1 and T_x2, for 15 min., as determined to be optimal for the soft magnetic properties of this alloy in prior work. The ribbon ends were attached to sheet metal tabs using cyanoacrylate adhesive. The assembly prevents tensile machine grip serrations from fracturing the ribbon when tightening prior to the test. Resulting tensile specimens were 100 mm long between grip tabs and 25 mm wide. Similar processes of annealing and grip tab adhesion were followed in preparing tensile specimens from laminated ribbon stacks of five or ten layers. To prepare laminated stacks, multiple annealed MANC ribbons were placed between Teflon blocks and the stack bound with wire. The assembly was then subjected to a standard vacuum pressure impregnation process. The impregnation resin used was VonRoll 74030, which was subsequently cured in air at 160 ºC for 4 hours. After curing, the impregnated stack of many layers was separated by peeling into smaller stacks, as facilitated by the interspersed as-cast ribbons. A random sample of laminated ribbon stacks was measured with a micrometer to determine overall stack thickness in ten locations across the stack. The total ribbon thickness in the stack was subtracted from this measurement to find the total epoxy thickness. From these measurements, the average epoxy layer thickness ranged from 3.7 to 6.5 𝜇m, similar to that achieved in an 80% fill factor tape-wound core. Since the epoxy cross-sectional area is ~20% that of the ribbon and the epoxy has a Young’s Modulus ~0.8% of the ribbon, the epoxy stiffness contribution to the stack is negligible. Thus, so long as the epoxy adequately wets and bonds the ribbon layers, a change in epoxy thickness should not change the tensile behavior significantly. Accordingly, the area considered for stress calculation from tensile tests is only the cross-sectional area of the ribbon layers. Since the annealed ribbons shatter by a brittle failure mechanism and because specimens had no reduced test section to ensure fracture away from tensile grips, a high-speed camera was required to determine if the initial ribbon fracture location was sufficiently far from the stress concentrator associated with the grips. Tensile tests were conducted using an Instron model 4469 with a deformation rate of 3.0 mm/min while monitored with a Phantom Vision v1211 high-speed camera at 66,000 frames/s (15.2 µs between frames, 7 µs exposure time). If a specimen failed away from the grips (where stress concentrators are located), that specimen was used in the tensile strength population to determine Weibull statistics.