D.J. Morrison

Prototyping a Composite SMC/Steel Axial-flux PM Wind Generator

This paper outlines the design and prototyping of an SMC-based axial-flux PM wind generator with a composite SMC/steel stator core. The machine topology has SMC teeth fitted into a laminated silicon steel stator yoke. A simple pressed fit and wedge/retaining ring arrangement is proposed for fixing the SMC teeth into the yoke. The machine is sized based on wind speed requirements and SMC core samples available for the research. Preformed coils are used to form a concentrated, non-overlapping stator winding, which are inserted from the stator yoke side. Consequently, the slot openings are small, thereby reducing harmonics associated with the slot openings. Detailed finite element analysis results are presented for the machine topology under investigation. The SMC cores are machined by means of a cost effective and easily accessible process using an end-mill. A discussion is provided of the detrimental effect of this machining process on the SMC core. However, a chemical processing technique is investigated for treating the smear of the iron particles on the machined surfaces of the SMC core. Microscopic images are shown to illustrate the successful elimination of the smear on the machined surfaces. Assembly of the prototype is discussed in detail and experimental results are provided

Performance Assessment of a PM Wind Generator with Machined SMC Cores

This paper presents the performance of an axial- flux PM wind generator with a composite SMC/steel stator core. The machine topology has SMC teeth fitted into a laminated silicon steel stator yoke. The SMC teeth were produced by machining cylindrical SMC cores with a cost effective and easily accessible process using an end-mill. A discussion is provided of the detrimental effect of this machining process on the SMC core. However, a chemical processing technique is investigated for treating the smear of the iron particles on the machined surfaces of the SMC core. Detailed experimental results are provided of the performance of two wind generators with untreated and acid treated stator cores.

Characterization of Fatigue Fractures in Closed-Cell Aluminum Foam Using x-ray Micro-Computed Tomography

A post-mortem study of Alporas closed-cell aluminum foam specimens previously failed under strain-controlled fully reversed tension-compression fatigue was conducted using x-ray micro-computed tomography (μCT). Volumetric renders of the 3D structure of the material were produced. Fractures were identified and marked throughout voxel-based images of the specimens. This produced a 3D plot of fracture locations. At high strain amplitudes (0.175-0.5%), fractures formed an interconnected planar zone oriented approximately perpendicular to the loading axis; typically, the angle of the plane differed from that of a tension failure. Conversely, at low strain amplitudes (0.05-0.1%), short fractures have been formed diffusely within the specimen. In both cases, observed fractures were tortuous. Our previous work with surface strain mapping via digital image correlation (DIC) suggested that for all strain amplitudes, a crack, evidenced by a zone of high extensile strain, was formed and propagated through the material. This result was confirmed at high strain amplitudes, but not at low strain amplitudes. The discrepancy is attributed to three potential causes. Using DIC, short cracks cannot be accurately resolved with relatively coarse light intensity patterns. DIC images indicate fractures under load, while μCT imaging was conducted under zero load. Finally, the localized extension seen in DIC images could be attributed to strain with no resultant fractures.

Microstructures and mechanical properties of welded Fe-12Cr-20Mn austenitic stainless steel

The effects of welding on the tensile and fatigue properties of fully annealed and cold-worked Fe-12Cr-20Mn austenitic stainless steel were evaluated. Room temperature and 500 °C tensile tests and room temperature cantilever beam fatigue tests were accomplished on specimens that contained autogenous bead-on-plate welds. The tensile and fatigue properties of the fully annealed material were not significantly influenced by welding. The tensile properties of the welded cold-worked material were also not significantly affected by the presence of a weldment. However, welding caused a large reduction of the fatigue life of the cold-worked material. Fatigue cracks preferentially initiated at large Mn-Si inclusions that formed in the fusion zones of the weldments.

Hydrogen Diffusion in Alloy 686 (UNS N06686) and Alloy 59 (UNS N06059)

We report the hydrogen diffusion coefficients in Alloy 686 (UNS N06686) and Alloy 59 (UNS N06059), using the electrochemical hydrogen permeation method. Optical microscopy and SEM indicate the presence of a second phase inclusion concentrated along the grain boundaries in Alloy 686 specimens, but distributed randomly in Alloy 59 specimens. TEM and X-ray mapping showed the presence of bcc Mo-rich inclusions. Effective diffusion coefficient (Deff) values for hydrogen during successive rise transients reveals the nature of trap sites to be predominantly reversible in Alloy 686, while both reversible and irreversible in Alloy 59. Multiple permeation transients show an increase in diffusion coefficient values for the decay transients (3.88 × 10−11 cm2/s) compared to the rise transients (1.49 × 10−11 cm2/s) in Alloy 686 specimens. The Deff values alternate for each pair of rise and decay transients, which suggests that hydrogen transport is controlled by a high density of reversible trap sites in Alloy 686 spec...