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In this work, we establish that maintenance and inspection are a risk factor in helicopter accidents. Between 2005 and 2015, flawed maintenance and inspection were causal factors in 14% to 21% of helicopter accidents in the U.S. civil fleet. For these maintenance-related accidents, we examined the incubation time from when the maintenance error was committed to the time when it resulted in an accident. We found a significant clustering of maintenance accidents within a short number of flight-hours after maintenance was performed. Of these accidents, 31% of these accidents occurred within the first 10 flight-hours. This is reminiscent of infant mortality in reliability engineering, and we characterized it as maintenance error infant mortality. The last quartile of maintenance-related accidents occurred after 60 flight-hours following maintenance and inspection. We then examined the “physics of failures” underlying maintenance-related accidents and analyzed the prevalence of different types of maintenance errors in helicopter accidents. We found, for instance, that the improper or incomplete (re)assembly or installation of a part category accounted for the majority of maintenance errors with 57% of such cases, and within this category, the incorrect torquing of the B-nut and incomplete assembly of critical linkages were the most prevalent maintenance errors. We also found that within the failure to perform a required preventive maintenance and inspection task category, the majority of the maintenance programs were not executed in compliance with federal regulations, nor with the manufacturer maintenance plan. Maintenance-related accidents are particularly hurtful for the rotorcraft community, and they can be eliminated. This is a reachable objective when technical competence meets organizational proficiency and the collective will of all the stakeholders in this community. We conclude with a set of recommendations based on our findings, which borrow from the ideas underlying the defense-in-depth safety principle to address this disquieting problem. [ABSTRACT FROM AUTHOR]

The five-axis machine tool has been extensively employed in complex curved surface machining area. The linkage performance of the machine tool is one of the key origins of the machining accuracy. An accuracy measurement based on RTCP (rotation tool center point) is an effective means for multi-axes motion synchronously linkage performance detection. In order to demonstrate the linkage performance more completely, an RTCP trajectory description method is presented, and some trajectories which take account of curvature and speed changes are proposed in this paper. The trajectory sensitivity analysis is applied to examine the sensitivity of RTCP measuring trajectories in mismatch parameters of the five-axis machine tool. Through comparative analysis, some RTCP measuring trajectories are more sensitive to certain error parameters than others. Therefore, the corresponding RTCP measuring trajectories are necessary for various linkage performances detection of the five-axis machine tool. For this purpose, RTCP measuring trajectory is optimized based on sensitivity analysis result. Finally, linkage performance detection experiments based on RTCP are conducted, and the tool tip errors vary for the different linkage performance and different RTCP trajectories, which is consistent with trajectory sensitivity analysis results. These results indicate that the corresponding RTCP measuring trajectories are necessary for various linkage performance detections. Therefore, the RTCP trajectory that is more favourable to detection could be put forward according to the requirements of the five-axis machine tool. Furthermore, series of RTCP trajectories can be combined to exhibit the linkage performance of five-axis machine tools more comprehensively. [ABSTRACT FROM AUTHOR]

No mechanical product will perform reliably unless it is designed specifically for reliability. There are many studies about reliability in mechanical design but most of them focus on the one part of entire reliability problem. The ability to see the bigger picture is essential in the field of mechanical reliability. Reader can gain a holistic viewpoint for the consideration of mechanical reliability by this approach. In this study failure modes, reliability variables, models, measures and methods from mechanical engineering point of view were investigated. From the open literature, published research work was compiled. Search results were classified and evaluated in terms of suitability for mechanical engineering. As an example, the procedure to find the reliability of shaft was investigated in support of our approach. Analysis and documentation of failed mechanical components are essential for preventing designers from repeating the same errors. Therefore, this research is expected to provide an easy way to investigate reliability problems of mechanical components such as shafts. [ABSTRACT FROM AUTHOR]

At present, the error control process of the complex thin-walled workpiece mainly adopts the error suppression and error elimination; the effectiveness of error control depends on the cognition of the process designer about machine accuracy and the error-generating mechanism. This paper proposes a new compensation method to control errors in machining thin-walled workpieces based on the inverse reconstruction model. In this method, the thin-walled workpiece is represented by discrete point cloud (DPC) for error analysis; according to the unified error prediction model, the DPC positions can be obtained companying with the machining errors. Then the new DPC is reconstructed into the workpiece model used inverse reconstruction model. At the same time, a fairing algorithmis developed to deal with the smoothing problem of DPC. So, the new workpiece model is used instead of the original for processing. By this method, the machining precision and surface quality of thin-walled workpieces are ensured. In addition, a case study is presented to demonstrate the effectiveness of the method. [ABSTRACT FROM AUTHOR]

This work analyses two different aspects of the mechanical process of tubes expansion used for the production of heat exchangers. In particular, the influences on the expansion process due to mandrel geometry and geometrical errors in tubes, caused by production tolerances, were studied and analyzed using finite element (FE) models. A 2D axisymmetric model was used to study the influence of mandrel geometry, whereas a 3D solid model was adopted to investigate the influence of geometrical errors in tubes. Experimental tests were carried out on actual materials in order to set up and validate the FE models. Force required for expansion, and variation in tube dimensions due to expansion were investigated and a good agreement was found between experimental and FE results. Additionally, the obtained results showed that the fillet radius is the most important geometrical factor of the mandrel in order to reduce the expansion force. A great influence of the tube geometrical errors was observed on the tube expansion process, which can compromise the performance of the heat exchanger. Finally, it is worth mentioning that the present study provides useful information that might be used to improve tubes expansion processes in general and heat exchangers production in particular. [ABSTRACT FROM AUTHOR]

This paper is an experimental investigation into the dimensional error of the rapid prototyping additive process of powder-binder three-dimensional printing. Ten replicates of a purpose-designed part were produced using a three-dimensional printer, and measurements of the internal and external features of all surfaces were made using a general purpose coordinate measuring machine. The results reveal that the bases of all replicates (nominally flat) have a concave curvature, producing a flatness error of the primary datum. This is in contrast to findings regarding other three-dimensional printing processes, widely reported in the literature, where a convex curvature was observed. All external surfaces investigated in this study showed positive deviation from nominal values, especially in the z-axis. The z-axis error consisted of a consistent positive cumulative error and a different constant error in different replicates. By compensating for datum surface error, the average total height error of the test parts can be reduced by 25.52 %. All the dimensional errors are hypothesised to be explained by expansion and the subsequent distortion caused by layer interaction during and after the printing process. [ABSTRACT FROM AUTHOR]