Issue 37

J. Albinmousa, Frattura ed Integrità Strutturale, 37 (2016) 94-100; DOI: 10.3221/IGF-ESIS.37.13 95 This paper aims to investigate fatigue damage resulting from multiaxial, proportional and nonproportional, loading by analysing stresses and strains over a full domain of a representative stress-strain element. A new technique for evaluating strain based fatigue damage without consideration of a particular critical plane has been proposed. M ATERIALS AND EXPERIMENTS he material used for this investigation is micro alloyed fine grained structural steel S460N (FeE460) tested by Hoffmeyer et al. [14]. Axial-torsional loading was applied on smooth thin-walled tubes specimens under strain controlled condition and room temperature. Two multiaxial loading paths are considered for parametric analysis: proportional and 90° out-of-phase loading. The monotonic and cyclic properties of S460N steel are listed in Table 1. Details of the proportional and nonproportional cyclic tests can be found in Table 2. This material was selected because of its symmetric cyclic behaviour as shown in Fig. 1. Property Property ܧ (MPa) 208,500 ܿ -0.493 ߥ 0.3 ܭ ௦ ᇱ (MPa) 599 ߪ ଴.ଶ% (MPa) 500 ݊ ௦ ᇱ 0.169 ܭ ᇱ (MPa) 1115 ߬ ௙ ᇱ (MPa) 463.2 ݊ ᇱ 0.161 ߛ ௙ ᇱ 0.224 ߪ ௙ ᇱ (MPa) 969.6 ܾ ௦ -0.071 ߝ ௙ ᇱ 0.281 ܿ ௦ -0.422 ܾ -0.086 Table 1 : Monotonic and cyclic properties of S460N steel [14]. No. Loading ߝ ௔ (%) ߛ ௔ (%) ߪ ௔ (MPa) ߬ ௔ (MPa) N f (Cycles) Nr20 0° Phase 0.173 0.300 244.2 147.3 31,100 Nr26 90° Phase 0.231 0.400 391.5 230.9 6,570 Table 2 : Summary of cyclic tests [14]. Figure 1 : Axial-torsional hysteresis for proportional (Nr20) and nonproportional (Nr26) tests. T