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A limited number of material models or flow curves are available in commercial finite element softwares at varying temperature and strain rate ranges for plasticity analysis. To obtain more realistic finite element results, flow curves at wide temperature and strain rate ranges are required. For this purpose, a material model for a medium carbon alloy steel material which is used for fastener production was prepared. Firstly, flow curves of the material were obtained at 4 temperatures (20, 100, 200, 400 °C) and 3 strain rates (1, 10, 50 s-1). Then, experimental data was used to construct an artificial neural networks model (ANN) for the material. 75% of the experimental data was used to train the model and the rest was employed for validation and verification. ANN model used in flow curve prediction was developed using the scikit-learn library on Python. Temperature, strain rate and strain were employed as input parameters and flow stress as output parameter in ANN model. In order to increase the accuracy of the ANN model, the number of hidden layers and the number of neurons were also optimized by mean squared error approach. As a result of studies, an ANN-based material model that can be used for wide range of temperature and strain rate values were developed based on the experimental data.

In this study, fatigue behavior of Zn-Cr+3 and zinc flake coated bolts was investigated experimentally by considering corrosion effects. Fatigue tests were conducted on M8x50x1.25 8.8 DIN 933 bolts at normal and corroded conditions at force amplitudes between 2.35 and 5.36 kN at test frequency of 75 Hz. A part of bolts was subjected to salt atmosphere for corrosion. According to the Wöhler curves obtained from fatigue tests before corrosion, zinc flake coated bolts showed 1.55 times higher fatigue life compared to Zn-Cr+3. After corrosion, fatigue tests showed that the fatigue life difference increased to 2.10 times for the zinc flake coating. Moreover, corrosion was found to be ineffective on crack initiation region. For both coatings and corrosion conditions, fatigue cracks were seen to initiate from the thread roots.

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