The Influence of Load Misalignment During Uniaxial Low‐cycle Fatigue Testing—i: Modelling

Abstract

A quantitative model has been proposed which predicts the extent of lifetime scatter in low-cycle fatigue due to the influence of bending caused by load misalignment. The main components of the model are the mechanism of bending, the type of extensometer used to control strain and the fatigue characteristics of the material being assessed. Three mechanisms of bending have been studied and it is F. A. KANDIL and B. F. DYWN tb = maximum bending strain tbx = bending strain at point x cbe = maximum bending strain at axial compressive peak strain tb, = maximum bending strain at axial tensile peak strain cC = control-strain amplitude t, = strain amplitude at point x L,, = strain amplitude at the centre of testpiece t , = maximum strain amplitude t2 = minimum strain amplitude A6 = strain range Atb = bending strain range ( = t b t f k ) = control-strain range Act = elastic strain range AcP = plastic strain range Au = stress range ub =bending stress 8 = angle in the circular cross-section between the intersections of the maximum bending plane and the extensometer plane

Uncertainty in fatigue loading: Consequences on statistical evaluation of reliability in service

“…Kandil and Dyson [8,9], by analyzing inter-laboratory low cycle fatigue datasets [10], also showed that, even if a test is performed under the stringent conditions imposed by the ASTM standard E 606-80 [11] concerning the maximum allowable bending stress in axial fatigue tests (smaller than 5%), the ratio of the reproducibility limits of the fatigue life reaches the value of six suggesting a reappraisal of the British Standard BS 7270:1990 [12] and ASTM standards E 606-80 [11] and E 1012-89 [13]. The above cited results were confirmed in a further research supported by the Versailles Project on Advanced Materials and Standards [14,15].…”

Influence of bending on low cycle fatigue life of cylindrical test pieces at elevated temperature

“…With fatigue cyclic-through-zero-testing, Kandil and Dyson [1,2] differentiate between misalignment due to ''non-reversed'' bending and ''reversed'' bending ( Figure 2). Non-reversed bending misalignment is caused by angular or lateral offset of the test piece axis with respect to the grips.…”

“…Here, bending strains change sign in a tension-compression cycle and therefore contribute to cyclic strain loading. Load -strain offset is believed to be more damaging to fatigue testing than angular or lateral offset [1,2].…”

“…Consequently, this is the motivation for the systematic study of bending influences on fatigue properties presented here. This study was part of a research project [6] dealing with the validation of the Code of Practice for the measurement of bending in uniaxial low cycle fatigue (LCF) testing [3] as well as with the validation of the prediction methodologies [1,2].…”

A New Loading-Constraining Device for Mechanical Testing With Misalignment Auto-Compensation

“… 1 and 2 , it is remarked that low‐cycle fatigue test results are often characterized by a great repeatability, if the experimentation is performed on the same machine in the same laboratory, but in Refs. 1–3 the scatter among results coming from different laboratories is emphasized. So, in this case uncertainties in measurement have a strong impact over the consistency of results coming from different working groups.…”