Various chemometric methods were used to analyze and model potable water quality data. Twenty water quality parameters were measured at 164 different sites in three representative areas (low land, semi-mountainous, and coastal) of the Thessaly region (Greece), for a 3-month period (September to November 2006). Hierarchical cluster analysis (CA) grouped the 164 sample sites into two clusters (CA-group 1 and CA-group 2) based on the similarities of potable water quality characteristics. Discriminant analysis was assigned about 94.5% of the cases grouped by CA. Factor analysis (FA) was applied to standardized log-transformed data sets to examine the differences between the above clusters and identify their latent factors. For each of the above two clusters (CA-group 1 and CA-group 2), FA yielded six latent factors that explain 68.7% and 73.4% of the total variance, respectively. FA was also identified the latent factors that characterize each cluster. The identification was obtained, using (a) descriptive statistics, (b) t test for equality of cluster means, (c) box plot, (d) error bar, (e) factors score plots, (f) matrix scatter score means plot and (g) scatter plot of the six significant latent factors from the factor set of A. Papaioannou (B) · P. Plageras A. Papaioannou et al. all samples group. The classification scheme obtained through cluster analysis was confirmed by discriminant analysis and explained by factor analysis.
High-strength aluminum alloys of the 7XXX series have a high potential for safety and crash-relevant components due to their advantageous density-to-strength ratio. Currently, the use of these alloys is limited because of the low formability at room temperature. By using thermal supported forming strategies, failure-free deep drawing is possible for these materials. At present, several thermal-assisted forming processes exist, but so far there is no comparison between these forming operations. For this purpose, this study compares the deep drawing behavior of the alloy AA7075 by using different thermally-assisted forming operations. Aim of this work is to enhance the understanding and comparability between different thermally-assisted forming processes for high-strength aluminum alloys. First, a thermal simulator is used to investigate the mechanical material behavior according to different temperature-time curves by using uniaxial tensile tests. Subsequently, the formability and springback behavior is determined numerically and experimentally in a model test. Finally, for one thermally assisted forming method, the experiments are scaled up to a real size process with drawbeads to validate the transferability. This study can help to improve the scientific knowledge for the use of these materials in future.
High-strength aluminum alloys provide great potential for weight reduction in vehicle and aircraft production. Nevertheless, forming of these materials is limited at room temperature. Thermally supported forming operations such as hot forming and quenching (HFQ®) allow forming of components without failure and reduced springback. Currently, the adhesive wear and high friction limit the use of HFQ®-operations for high-strength aluminum alloys. Out of this reason, the present paper describes the tribological performance of new developed dry lubricants at elevated temperatures for the alloy AA7075. For this purpose, strip drawing tests were carried out in a modified open tribological system at temperatures between 20 °C and 400 °C. Additionally, the melting behavior of these lubricants, as well as the variation of the lubricant thickness, were investigated. The results show a reduction of the coefficient of friction at elevated temperatures.
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