# The Basis for Reliability-Based Mechanical Properties of Structural Aluminium Alloys
## 1 Introduction
[PERSON] [14] investigated the variability of mechanical properties (ultimate strength, 0.2% proof strength, and modulus of elasticity) using a series of tensile tests performed on aluminium bars made from EN AW-6060 and EN AW-5754 alloys. The author stated that the coefficient of variation for both ultimate strength and 0.2% proof strength was less than 1%, concluding that aluminium has a much lower scatter of mechanical properties than steel. [PERSON] [14] also hypothesised that the stochastic variance of mechanical properties of aluminium alloys is so small that there is negligible effect on coefficient \(\gamma_{\text{M}}=1.1\) given in Eurocode 9 [15]. [PERSON], [PERSON], and [PERSON] [5] explored the variability of mechanical properties of aluminium alloys with emphasis on 0.2% proof strength and ultimate tensile strength. The authors collected results from published literature and expanded them with experimental work. In total, 404 tensile test results for both welded and unwelded samples were obtained and processed. Distributions were fitted to mechanical properties of aluminium, and characteristic values were determined. Based on nominal to characteristic value ratios, it was concluded that nominal values of mechanical properties of aluminium can be unsafe or have a margin of safety in excess. Accordingly, the authors proposed new nominal values. [PERSON] et al. [16] presented a series of stress-strain curves obtained for aluminium alloy 6061-T651. Coupons were taken from nine lots of several aluminium producers and tested under six different temperatures. A total of 100 uniaxial tensile tests were performed as well as 54 plane strain tensile tests. [PERSON] et al. [17] analysed 36 stress-strain curves from alloys 6082-T6 and 6060-T66 and compared their suitability with eight constitutive laws. Although the mentioned authors investigated the variability of the main mechanical properties of aluminium alloys, their databases were insufficient for global conclusions. Another important issue related to the variability of mechanical properties is the market area, i.e., the regional context of alloy use. Based on the proximity of production, regional areas are supplied by different producers, which due to numerous variables may produce products in conformity with related specifications but with greater or lower variability. This is due to differences in minimum values of strength for the same alloy and temper [5]. Consequently, as a first step for the development of probabilistic design procedures for the reliable design of aluminium structures, quantification of the variability of a large quantity of data of relevant mechanical properties of aluminium must be conducted. With this goal in mind, 12,524 material test certificates and tensile test results of various aluminium construction products that can be found on the European market were collected. At this stage of the research, only 0.2% proof strength, ultimate tensile strength, Young's modulus, and Poisson's ratio were analysed since they are the four main properties for the design of aluminium structures. Furthermore, the safety levels of the current nominal (guaranteed) values were evaluated. To provide the required input data for the calibration of resistance factors and other reliability studies, this paper presents the statistical characterisation of the variability and distribution functions of the main random parameters affecting the strength of aluminium structures. The purpose of this paper is to statistically evaluate the variability of mechanical properties in a European context considering test results from a large and robust databank. An additional goal is to provide a reliability analysis basis for further research and considerations of current reliability levels in the valid normative documents, considering that calibration exercises for target probability are mostly derived directly from specific failure modes [5], contrary to the design methodology given in EN 1990 [18].