PSI - Issue 23

Barbara Nasiłowska et al. / Procedia Structural Integrity 23 (2019) 583 –588 Nasiłowska B. / Structural Integrity Procedia 00 (2019) 000 – 000

584

2

(Jeleńkowski et al. (2015), Nakonieczny (2002), Napadłek et al. (2011), Piekarski (2001)). In result of action of dynamic load on metal, positions of atoms in crystal lattice go beyond the minimum kinetic energy level which disrupts creation of the primary lattice and produces stresses. Only part of atoms keeps their primary position while the rest takes new positions which is the main cause of creation of spontaneous stresses inside the material (Piekarski (2001)). The state of spontaneous stress depends also on mechanical properties of the worked material. The influence of a shot stream energy on surface roughness, state of partial stress, fatigue life, and selected mechanical properties of the 7075 aluminium alloy are presented in the paper (Jeleńkowski et al. (2015)) . An interesting work is the manuscript (Takahashi et al. (2018)) in which measurement results on the influence of shot peening (SP) and cavitation peening (CP) on fatigue strength to bending of the 7075 aluminium alloy with a surface defect similar to fracture is presented. Presented results showed increase in fatigue life and improvement of functional properties after upper layer shot peening. The authors of (Takahashi et al. (2018)) demonstrated an improvement in fatigue properties after upper layer strengthening in result of shot peening of an aluminium alloy with a surface defect similar to fracture. The analysis of deformation strengthening of 6101 and 6082 aluminium alloys was described using strengthening curves (plastic stress versus real deformation) in the paper (Sobota et al. (2017)). Strengthening of upper layer, except of pneumatic shot peening, can be also made using pulse laser radiation. This process was described in (Napadłek et al. (2018)) . In this work attempts of modification of upper layer of the PA31 aluminium alloy using Nd:YAG laser beam with 0.5 J energy and 10 ns pulse length were also presented. Tests and analyses of the modified surface were carried out using scanning microscopy (SEM) and profilometry of surface topography. Now, in the available literature, there is a lack of analysis of influence of shot peening on a change of elemental composition in upper layer with reference to mechanical properties. 1. Testing methodology 1.1. Formation of welded joints The TIG joints were made using production technology in Plants for the Construction of Chemical Apparatus - Azoty Group in Tarnów. After prior beveling of an edge (V) a welding was carried out with fivefold passage from the face (front) side and next the ridge was undercut and surfaced by welding (built up). 1.2. Shot peening process Double sided shot peening of joints welded with the TIG method of the 5754 aluminium alloy upper layer was performed in the Institute of Precision Mechanics in Warsaw using stainless shot of 0.5 mm diameter under 0.3 MPa pressure. 1.3. Tensile tests Tensile tests were made in the single-axial Instron 8862 with strength measuring head in the range of ± 100 kN (Fig.1). Deformation measurement results were registered using an extensometer. Mechanical properties of flat samples of the size shown in Fig.1 were carried according to the PN-EN ISO 6892-1:2016 standard. 1.4. Structural tests For structural and remaining fractures tests the Quanta FEG 250 electron scanning and the Smartzoom 5 Zeiss light microscopes were used. Surface roughness was measured using the LSM 800 Zeiss scanning confocal microscope.