Fatigue behaviour of welded joints from magnesium alloy (AZ31) according to the local strain concept

A B S T R A C T The present paper reviews and contains simple modifications to extend the applicability of global and local fatigue concepts to thin-welded specimens with pronounced weld terminations (starts/ends). Experimental fatigue data reported by Kaffenberger and Vormwald have been used for the validation of the proposed procedures. Special attention is paid to the notch strain concept. The material state is explicitly considered by means of corresponding strain-life curves in conjunction with P SWT , P Morrow or the experimental mean stress sensitivity factors proposed by Olivier. The accuracy of Neuber's sharp and mild notch formulas, Seeger-Beste's formulation and Glinka's strain energy density rule within the context of the notch strain approach has been investigated. Simple rules accounting for stress relaxation effects have been additionally proposed and implemented into the calculations. Comparison of experimental with theoretical fatigue lives validates the accuracy and robustness of the proposed procedures to calculate fatigue design S-N curves.Keywords fatigue; effective notch stress; notch strain approach; thin-welded joints; weld terminations. N O M E N C L A T U R EA [%] = elongation at fracture a * [mm] = micro-structural support length A nom [mm 2 ] = nominal sheet area A w [mm 2 ] = nominal weld area b = fatigue exponent c = ductility exponent c f = fatigue notch factor (expressed versus nominal loads) c t = elastic notch factor (expressed versus nominal loads) e* = nominal strain ENSC = effective notch stress concept FAT = fatigue assessment curves FEA = finite element analysis FE = finite element FKM = Forschungskuratorium Maschinenbau HAZ = heat affected zone HCF = high cycle fatigue HRA = Rockwell-A hardness IIW = International Institute of Welding K ' [N/mm 2 ] = cyclic hardening coefficient K f = fatigue notch factor (expressed versus nominal stresses) K p = fully plastic limit factor K t = elastic notch factor (expressed versus nominal stresses) L [N] = nominal load LCF = Low Cycle Fatigue L w [mm] = weld length m = slope Correspondence: Michail Malikoutsakis.

Section: Fatigue Conceptsmentioning

confidence: 99%

Fatigue assessment of thin‐welded joints with pronounced terminations

Malikoutsakis

Savaidis

2014

“…In this case, testing is carried out under stress‐control mode where the specimen is subjected to elastic deformation where the failure takes place through localized plastic deformation leading to cyclic lives in excess of 10 5 cycles. Recent studies on HCF showed use of parametric approach for predicting fatigue life . In this context, Karakas et al has used SWT parameter and local strain concept through Ramberg‐Osgood equation towards prediction of fatigue life in Mg‐welded joints.…”

Section: Introductionmentioning

confidence: 99%

“…Recent studies on HCF showed use of parametric approach for predicting fatigue life . In this context, Karakas et al has used SWT parameter and local strain concept through Ramberg‐Osgood equation towards prediction of fatigue life in Mg‐welded joints. Similar approaches were also used at high temperatures up to 573 K by Karakas et al for fatigue life prediction in Al alloys.…”

Section: Introductionmentioning

confidence: 99%

Fatigue design curve under LCF as well as combined LCF and HCF regime at 923 K in a type 316LN stainless steel

Sarkar

Nagesha

2019

The paper presents a novel approach towards developing fatigue design curve under combined loading involving low cycle fatigue (LCF) and high cycle fatigue (HCF), in a type 316LN austenitic stainless steel. The total strain life curve used for fatigue design is modified taking into account the effect of varying load history. The methodology relies on the test data obtained to previous studies by authors pertaining to LCF‐HCF interaction using a sequential pattern at 923 K. Modified design curves are generated at 923 K where the effect of varying degree of prior LCF exposure at strain range of 0.12% is accounted for, on HCF.

“…Zhu and Huang 2 proposed a new viscosity-based model based on DE model with high precision in the prediction of LCF. Karakas et al [3][4][5] calculated the P SWT -damage parameters for further investigations of the effect of mean stress at various temperature. The energy-based approach has been widely used for predicting LCF failure process, and it is applicable to combine prediction accuracy with a clear physical mechanism.…”

Section: Introductionmentioning

confidence: 99%

A new energy‐based method to evaluate low‐cycle fatigue damage of AISI H11 at elevated temperature

Luo

Wang

et al. 2017

AISI H11 (X38CrMoV5‐1) hot‐work tool steel is widely used for making extrusion tools because of its good mechanical properties at high temperature and moderate cost. To predict its lifetime, an energy conservation‐based model was proposed in this paper by introducing the damage rate, which is expressed as the product of damage force and plastic strain rate. The strain‐controlled low‐cycle fatigue tests were conducted to obtain the parameters of the proposed model, while the stress‐controlled low‐cycle fatigue tests were used to validate the proposed model. The results demonstrate that the proposed model is accurate and reliable. Furthermore, the local misorientation was investigated by electron backscatter diffraction to analyse the correlation between the microstructure evolution and the cyclic behaviour, and crack propagation behaviour was identified.