Browse Topic: Durability
Rotorcraft components, which are often made with reinforced fiber composites, are subjected to severe fatigue loadings due to increased performance demands. Therefore, considerable research interest exists in improving fatigue life of conventional fiber reinforced composites. Nanocomposites are a new class of materials which seek to improve mechanical performance of materials by creating nanoscale crack-nanofiller interactions. In this study we demonstrate the fatigue life improvement of conventional composites by addition of SiO2 nanofillers. The epoxy resin was initially modified with nanofillers to test the static fracture toughness. Once the improvement in static facture toughness was confirmed, three phase modified fiber reinforced composites were made using the modified resin. Cyclic tests were performed at various stress level which demonstrate that three phase nanocomposites perform better than conventional fiber reinforced composites. Fractographic analysis suggests that nanofiller de-bonding from the matrix as well as crack deflection around nanofiller clusters contributes to the improved fracture toughness and fatigue life.
This SAE Standard provides a definition of a rainflow file format. This type of simple text file would contain all relevant information about the rainflow cycle content of a time history. Included information are Comments, Signal Range, Signal Mean, Number of Cycles, Signal Maximum, Signal Minimum. Rainflow cycle counting has become the most accepted procedure for identifying material fatigue relevant cycles in complex variable amplitude load time histories. The cycle counting methods account for the effects of material plasticity and material memory of prior deformation, and the resulting compressed history information is used by durability analysts to estimate the effects of a given service or test history. Standardization of the rainflow counting methods output files, which is the format addressed by the present standard, is important for reliable information transfer between test and design groups, or different calculation software packages, and thus forms a critical step in the evaluation of components and vehicles. Further background information can be found in the SAE publication AE-10 cited in 2.1.1.
ABSTRACT A coupled fluid-structure interaction (FSI) simulation was developed to evaluate a new design feature in the LIVE® vibration isolation system of the 505 Jet Ranger X. Efficient modeling of fluid and elastomeric characteristics is enabled by simplifying the internal fluid boundaries and adjusting fluid compressibility. The approach provides an accurate analysis of the internal loading within the LIVE structure. Computed results substantiate the LIVE design in terms of strength, durability, and component deflection. The FSI simulation also supports dynamic tuning of the LIVE to achieve the target operating frequency. Validation is demonstrated by comparison to laboratory test measurements. Correlation to test results, in terms of fluid pressure, is within 3.5% and correlation to natural frequency is within 5%.
Automotive engineering has been a game of delivering more value with minimal resources confronting conflicting design choices at every design step. As more and more electronics enters the game, it becomes imperative to critically evaluate various design choices to deliver a robust hardware backbone which guarantees a robust performance on an ever-reducing budget. Hardware interface with the outside environment in particular needs to be equipped with a significant robustness. Harsh transients, tough environmental conditions, further complicate the rules to the game.
There is an ongoing effort in the industry to develop an accelerated corrosion test for automotive heat exchangers. This has become even more important as automakers are focusing on corrosion durability of 15 years in the field versus current target of 10 years. To this end an acid immersion test was developed and reported in a previous paper for condensers (1). This paper extends those results to evaporators and establishes the efficacy of the test using these results and those reported in the literature. The paper also discusses variability in corrosion test results as observed in tests such as ASTM G85:A3 Acidified Synthetic Sea Water Test (SWAAT), and its relation to field durability.
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