We concluded that the stem failure was initiated by a fretting fatigue mechanism and was propagated by a pure bending fatigue mechanism. Risk factors for fractures of the modular junction include excessive body weight and inadequate proximal osseous support because of trochanteric osteotomy, reduced preoperative bone stock, osteolysis, loosening, and/or implant undersizing. Surgeons should consider the use of implants with strengthened junctions when using modular stems in such patients.

Condition monitoring of dynamic systems based on oil analysis is well known for closed-loop systems. The motivation for this work stemmed from repeating failures of Wankel engines. Failure analysis identified contact fatigue as the failure mechanism, but could not identify the cause. Thus, the objective of the work was to develop a method for condition monitoring of open-loop oil systems. A variety of analytical techniques was evaluated, including directreading ferrography, analytical ferrography combined with computational image analysis, atomic emission spectroscopy, and scanning electron microscopy combined with energy dispersive X-ray spectroscopy. Procedures for collection and separation of oil samples were developed. Analytical ferrography was found most useful in condition monitoring. Six engines were detected in their early failure stage. Those engines were disassembled, and contact fatigue failures in the bearing needles were observed. The quantitative image analysis allowed for a fairly objective rating of the wear level. The method developed in this work has already been implemented on a daily basis for monitoring the health of Wankel engines, with much success.

Additive manufacturing attracts much interest for manufacturing and repair of structural parts for the aerospace industry. This paper presents comparative characterization of aircraft items made of Al 4047 alloy, Ti-6Al-4V alloy, and 17-4 precipitation hardened (PH) (AISI 630) stainless steel, either manufactured or repaired by laser engineered net shaping (LENS). Chemical analysis, density, and surface roughness measurements, X-ray micro-computed tomography (μ-CT) analysis, metallography, and micro-hardness testing were conducted. In all three materials, microstructures typical of rapid solidification were observed, along with high density, chemical composition, and hardness comparable to those of the counterpart wrought alloys (even in hard condition). High standard deviation in hardness values, anisotropic geometrical distortion, and overbuild at top edges were observed. The detected defects included partially melted and unmelted powder particles, porosity, and interlayer lack of fusion, in particular at the interface between the substrate plate and the build. There was a fairly good match between the density values measured by μ-CT and those measured by the Archimedes method; there was also good correlation between the type of defects detected by both techniques. Surface roughness, density of partially melted powder particles, and the content of bulk defects were significantly higher in Al 4047 than in 17-4 PH stainless steel and Ti-6Al-4V alloy. Optical gaging can be used reliably for surface roughness measurements. The implications of these findings are discussed.

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