Variable Amplitude Loading on a Resonance Test Facility

Pöting, S.; Traupe, Markus; Hug, Joachim; Zenner, Harald

doi:10.1520/jai19038

Cited by 6 publications

(1 citation statement)

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“…This led to a substantial time and cost reduction for variable amplitude tests. A comparison of test results achieved on a resonance test facility controlled by a variable amplitude control and test results from a servohydraulic test rig controlled by a regular service load controller for variable amplitudes showed equal mean values in numbers of cycles to failure 1 . Variation of the applied stress amplitudes with time is shown in Fig.…”

Section: Introductionmentioning

confidence: 93%

Parameter C lifetime calculation for the high cycle regime

Pöting

Zenner

2002

Fatigue Fract Eng Mat Struct

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An analytical fatigue lifetime prediction using the nominal stress concept and the Palmgren‐Miner‐Rule is performed. A comparison of prediction and experiment shows a large uncertainty. Miner‐Rule modifications have been developed to improve the fatigue lifetime prediction. Stress amplitudes below the fatigue limit are assumed to contribute to the damage at different ratings. The modifications have a significant influence on the predicted fatigue lifetime especially in the high cycle regime. When the maximum stress value is just above the fatigue limit, this influence is most significant. Because there are not many test results of variable amplitude loads available for the high cycle regime, a verification is difficult. In the present paper a new modification for the lifetime prediction is applied. The modification was introduced in 1988 by Hück and suggests a variable slope of a reference S–N‐curve for the damage accumulation. A parameter C and the relation between the maximum stress value of the load spectrum distribution and the fatigue limit determine the slope of the reference S–N curve. The aim is to characterize the influence factors of the parameter C using test results for the high cycle regime achieved on a new test facility and from published test data. This would lead to an improvement of the lifetime prediction in the high cycle regime.

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Section: Introductionmentioning

confidence: 93%

Parameter C lifetime calculation for the high cycle regime

Pöting

Zenner

2002

Fatigue Fract Eng Mat Struct

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Damage initiation and structural degradation through resonance vibration: Application to composite laminates in fatigue

Magi

Maio

Sever

2016

Composites Science and Technology

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. AbstractThe definition of failure is fundamental to the characterisation of fatigue strength of components and structures and is often expressed as a percentage of stiffness degradation. This article proposes a new method to capture damage initiation and structural degradation during a fatigue test, by exploiting resonance vibrations. The method entails monitoring dynamic parameters, including the phase angle between excitation and response, which suddenly changes as soon as the overall stiffness changes as a consequence of damage. In this paper, a theoretical approach based on equations of motion is presented in order to describe the possible scenarios in which a component undergoes structural degradation. In the proposed approach, an abrupt change in the time history of the stiffness of the component is assumed and analysed in both the quasi-static case at low excitation frequencies and the dynamic case, when the excitation frequency is close to the resonance frequency.The resulting analytical solution shows that any small stiffness variation is amplified by the dynamic response of the component as a large phase change, even when it is too small to be captured by the quasi-static response. The idea is successfully applied to capture the initiation of delamination in CFRP laminates, and the relative S-N curve to initiation is drawn. The experimental evidence of a critical event in the fatigue life of a component is found both in the dynamic phase response and in the base acceleration. The critical event is captured from a sudden change in the dynamic parameters of the structure as soon as a delamination is initiated. Thermography, C-scan and micrograph confirmed that the onset of delamination occurs at the moment of the critical event,after an initial stage of microcracking.

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