Issue 42

T.V. Tetyakova et alii, Frattura ed Integrità Strutturale, 42 (2017) 303-314; DOI: 10.3221/IGF-ESIS.42.32 304 inhomogeneous strain fields with different types of deformation bands (A, B, or C) [4]. Despite the considerable investigations that have been conducted on the effects of the inelastic deformation and the irregular plastic flow, the yield delay effect and the PLC effect is still debated. Some research deals with the influence of specimen geometry [5, 6] and chemical composition [4], other research estimates the influence of loading conditions and external test parameters on the PLC effect [7-10] and the Lüders behavior [11, 12]. Advanced materials testing equipment and high-accuracy measuring systems make it possible to represent complicated loading conditions, which are close to operation conditions. When studying the plastic strain inhomogeneity, it is expedient to use optical methods, such as photoelastic technique, speckle pattern interferometry, digital image correlation technique (DIC), and infrared (IR) thermography as well [2, 6, 12]. The purpose of the present study is to detect and analyze the spatiotemporal characteristics of the Lüders behavior and the PLC effect with considering the loading system’s stiffness and the stress concentrators. The DIC-technique and IR-analysis were applied to observe the evolution of the inhomogeneous strain and temperature fields, and to study the morphology and kinetics of the deformation bands in metals during uniaxial tension tests. The irregularity of the plastic flow was correlated with the associated serrations observed on the stress-strain diagrams. The initiation and propagation of the Lüders and the PLC bands were carried out on specimens with complicated geometry. E XPERIMENTAL PROCEDURE Material he materials studied in this research is the carbon steel C1010 and the aluminum-magnesium alloy AA5052. The chemical compositions are given below in Table 1 and Table 2. The flat specimens were made by water jet cutting from thick rolled sheets with a thickness of 3 mm. Specimens were tested in the state as received without the heat treatment process. For the carbon steel the average grain size was 27 µm (Fig. 1). The phase analysis revealed that the proportion of the ferrite in the steel as a structural component was 70 %, and the perlite – 30 %. Fe C Si Mn Cr Ni Cu 99.0 0.18 0.20 0.35 0.04 0.03 0.04 Table 1 : The chemical composition (weight percent) of the carbon steel. Figure 1 : The microstructure of the carbon steel C1010. T