Fatigue tests on notched specimens of G20Mn5QT cast steel and life prediction by a new strain-based method
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(2020) 20:113
ORIGINAL ARTICLE
Fatigue tests on notched specimens of G20Mn5QT cast steel and life prediction by a new strain‑based method Qinghua Han1,2,3 · Yaru Wang3 · Yue Yin2,3 · Song Zhang3 Received: 7 May 2020 / Revised: 11 August 2020 / Accepted: 31 August 2020 © Wroclaw University of Science and Technology 2020
Abstract Fatigue performance of notched specimens of G20Mn5QT cast steel was investigated experimentally and analytically. Fatigue tests on a total number of 22 semi-circular notched specimens were conducted with the load ratios of − 1 and 0.1. Nominal stress-fatigue life relationship was obtained, and mean stress correction rules were verified for the notched specimens based on the test results. A new strain-based approach, strain field intensity (SNFI) method, was proposed, in which fatigue life of materials is predicted based on the weighted average strain in the fatigue damage region. The fatigue lives of the test specimens were predicted using three strain-based approaches, modified Neuber’s rule, equivalent strain energy density (ESED) method and the proposed SNFI method. The fatigue life prediction by the SNFI method was in very good agreement with the test results, which verified the rationality and applicability of the proposed SNFI method and also the adopted fatigue properties of G20Mn5QT cast steel. Both the modified Neuber’s rule and the ESED method gave conservative prediction of the fatigue life of the notched specimens. The necessity of the 3-dimensional fatigue damage region was also discussed for the proposed SNFI method. Keywords Fatigue life prediction · Strain field intensity method · G20Mn5QT cast steel · Fatigue tests · Notched specimens List of symbols b Fatigue strength exponent c Fatigue plastic exponent E Elastic modulus K ′ Cyclic hardening coefficient Kf Fatigue notch factor Kt Theoretical stress concentration coefficient n′ Cyclic hardening exponent Nfin Number of cycles corresponding to fatigue crack initiation Ni Number of cycles at a certain time Nf Number of cycles corresponding to fatigue fracture * Yue Yin [email protected] 1
Key Laboratory of Earthquake Engineering Simulation and Seismic Resilience of China Earthquake Administration, Tianjin University, Tianjin 300350, China
2
Key Laboratory of Coast Civil Structure Safety of China Ministry of Education, Tianjin University, Tianjin 300350, China
3
School of Civil Engineering, Tianjin University, Tianjin 300350, China
R Load ratio, minimum load divided by maximum load Rε Strain ratio, minimum strain divided by maximum strain reff The effective radius V Volume of the fatigue damage region Ws Nominal strain energy density Wσ Local strain energy density ε Local strain ε1 Maximum principal strain εa Local strain amplitude 𝜀′f Fatigue plastic coefficient εnom Nominal strain on the net cross section 𝜀SNFI Strain field intensity 𝜀SNFI, a Strain field intensity amplitude Δε Local strain range Δεnom Nominal strain range on the net cross section 𝜌 Notch radius σ Local stress 𝜎f
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