Issue 27

A. Kostina et alii, Frattura ed Integrità Strutturale, 27 (2014) 28-37 ; DOI: 10.3221/IGF-ESIS.27.04 29 theoretical consideration of the phenomena we tried to simulate the energy storage process in Armco iron under homogeneous plastic deformation. The simulation was based on the original statistical model of defect evolution and includes the separation of plastic deformation into dissipative and thermodynamic (structural) parts. The nonlinear constitutive equation for structural sensitive parameters allows us to obtain the qualitative agreement between experimental and theoretical results. M ATERIAL AND EXPERIMENTAL CONDITIONS xperimental study was carried out on the Armco iron specimens. Chemical composition of the examined material is presented in Tab. 1. Fig 1. shows geometry of the specimens. С Mn Si S P Ni Сr Mo 0.004 0.04 0.05 0.005 0.005 0.06 0.038 0.01 Table 1 : Armco iron chemical composition (wt%). Figure 1 : Geometry of specimens. All sizes are in millimeters. After tooling, specimens were annealed in non-oxygen atmosphere with 1073 K temperature during 8 hours. Non-oxygen atmosphere was created by co-annealing of metal and copper samples with developed surface for a better oxidation. Mechanical test was carried out on servo hydraulic machine INSTRON 8500. Before starting of experiments the surface of the specimens was mechanically polished (at the last stage of the polishing the diamond suspension with a characteristic grit size of 3 microns was used). After polishing the surface was covered of matt black paint. It was done to obtain emissivity of the specimen’s surface close to 1 for better conditions of infrared monitoring. Specimens were loaded in uniaxial stretching mode with strain rate 2·10 -3 sec -1 . Infrared camera CEDIP Jade III was used to record the temperature evolution on the surface during mechanical test. The maximum frame size is 320×256 pixels; the spatial resolution is 10 -4 meters. The temperature sensitivity is from 25 mK to 300 K. E NERGY CALCULATION BASED ON THE PROCESSED EXPERIMENTAL DATA nfrared monitoring of the surface of examined specimen during quasistatic tension takes possibility to observe changes in temperature field in loading process. The Fig. 2 presents the stress strain relation and temperature evolution of the gage part of the specimen for investigated materials. We can divide the deformation process into three parts. At the beginning if the process the plastic deformation has a heterogeneous nature. We can observe the propagation of Luders bands (plastic deformation waves) on the specimen surface. This process is accompanied by the temperature wave propagation. The detail study of this part of plastic deformation in Armco iron can be found in [3]. E I