Abstract
The present paper is concerned with the formulation of an elasto-plastic strain based approach suitable for assessing fatigue strength of notched components subjected to in-service variable amplitude cyclic loading. The hypothesis is formed that the crack initiation plane is closely aligned with the plane of maximum shear strain amplitude, its orientation and the associated stress/strain quantities being determined using the Maximum Variance Method. Fatigue damage is estimated by applying the Modified Manson-Coffin Curve Method (MMCCM) along with the Point Method (PM). In the proposed approach, the required critical distance is treated as a material property whose value is not affected either by the sharpness of the notch being assessed or by the profile of the load spectrum being applied. The detrimental effect of non-zero mean stresses and degree of multiaxiality of the local stress/strain histories is also considered. The accuracy and reliability of the proposed design methodology was checked against several experimental data taken from the literature and generated under different uniaxial variable amplitude load histories. In order to determine the required local stress/strain states, refined elasto-plastic finite element models were solved using commercial software ANSYS®. This preliminary validation exercise allowed us to prove that the proposed approach is capable of estimates laying within an error factor of about 2. These preliminary results are certainly promising, strongly supporting the idea that the proposed design strategy can successfully be used to assess the fatigue lifetime of notched metallic components subjected to in-service multiaxial variable amplitude loading sequences.
Highlights
I n situations of practical interest, real engineering components are characterised by complex geometries resulting in local stress/strain concentration phenomena
In the recent past, a tremendous effort has been made by the international scientific community to device specific design techniques suitable for accurately assessing the durability of notched components subjected to in-service variable amplitude load histories [1]
This paper summarises the results from a preliminary investigation aiming at developing an elasto-plastic strain based approach capable of predicting fatigue lifetime of notched components subjected to variable amplitude load histories
Summary
I n situations of practical interest, real engineering components are characterised by complex geometries resulting in local stress/strain concentration phenomena. The Modified Manson-Coffin Curve Method (MMCCM) is a strain-based fatigue criterion that allows uniaxial/multiaxial fatigue damage in real mechanical components subjected to in-service time-variable load histories to be estimated accurately [9, 10]. The engineering aim of this section is to summarise a fundamental Theory of Critical distance and using the theory to estimate the effective local stress/strain states at the vicinity of notch apex different than notch tip, to predict fatigue lifetime of notched components. From a practical point of view, to indicate the critical distance for a specific material, the best way is running an appropriate experimental investigation by testing specimens containing with known notched geometry under fully reversed constant amplitude axial force. To sum up, according to the theory of critical distance, for a given material, the hypothesis is formed that such a distance is always the same in the same material regardless of notch geometry and notch sharpness
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