Issue34

E. Marcisz et alii, Frattura ed Integrità Strutturale, 34 (2015) 379-386; DOI: 10.3221/IGF-ESIS.34.42 379 Focussed on Crack Paths Influence of control parameters on the crack paths in the aluminum alloy 2024 under bending E. Marcisz, D. Rozumek, Z. Marciniak Opole University of Technology, Poland marciszewa@wp.pl , d.rozumek@po.opole.pl , z.marciniak@po.opole.pl A BSTRACT . The paper presents development of crack paths in aluminium alloy 2024. Fatigue tests were carried out for specimens with rectangular cross-section. The specimens were put to bending at controlled energy parameter amplitude and bending moment amplitude. The proposed method of conducting research with the controlled energy parameter has been presented in [1]. The energy parameter model proposed by Macha has been used in the tests. Tests with controlled energy parameter amplitude allow observing crack growth depending on maximum shearing stress surface. Tests with controlled bending moment amplitude allowed observing two types of crack paths. K EYWORDS . Energy parameter; Bending moment; Crack growth. I NTRODUCTION n majority, engineering structures, machines and technical devices struggle against material fatigue problem. Literature sources broadly specify the methods for fatigue life assessment and diagnosing the reasons of damage. Material fatigue life is described using fatigue characteristics: stress (  a –N f ), strain (  a –N f ) and energy (W a –N f ). Most frequently, fatigue test results are illustrated by Wöhler fatigue characteristic. Manson–Cofin–Basquin formulas describe material fatigue life using strain characteristics. Specification of stress and strain characteristics is defined in the ASTM standard [2, 3]. Whereas, fatigue characteristics obtained during tests with energy parameter control were proposed in the studies [1, 4]. Observations and analyses of crack path development are carried out in order to obtain additional information concerning changes occurring in a material. Different fatigue crack paths are observed during tests, depending on material used and loading type. Growth rate of these paths has direct effect on material life. The aim of the paper is comparison of crack paths in aluminum alloy 2024 for bending tests performed with controlled energy parameter amplitude and bending moment amplitude. T HE MATERIAL AND TEST PROCEDURE he material tested is aluminium alloy 2024, characterised by low resistance to oxidation, non-weldability and average workability. This material is used to make shafts, screws, pistons, couplings, hydraulic valves and aircraft parts. Tab. 1 shows chemical composition of the material and Tab. 2 specifies static properties of aluminium alloy 2024. I T