Papers by Keyword: Proportional Loading

Abstract: This chapter proposes an efficient approach to thermomechanical constitutive modeling for shape memory alloys using a novel separation of a martensite internal variable. This approach assumes that the martensitic internal variable has two components corresponding to two contrary martensite ensembles, which are separated by their opposite signs of contributions to a quantity of transformation strain. The constitutive models, based on a new separating concept, are presented in this chapter for uniaxial and three-dimensional proportional loading. The kinetic relations of these models are constructed using the Brinson model ideas concerning the interphase transformation processes in shape memory alloys. A number of illustrative numerical examples are presented here for one-dimensional modeling. The new separation of the internal variable has prospects for the description of material behavior in cases when mechanical loading may change sign and the phenomena are caused by martensitic reorientation. The conceptual and methodological solutions stated in the present work may be useful for subsequent modeling.

Abstract: This work presents a set of experiments devoted to studying the crack initiation stage under different combined tension-compression and torsion loads. Two different load levels were applied, producing very different fatigue lives. Lower strains generated lives approximately 10 times longer than higher strains. Results allowed retardation and acceleration effects due to microstructure to be clearly visualised.

Abstract: Multiaxial fatigue life of 50CrVA spring steel standard specimens and eccentric specimens under proportional loading was studied with MTS 809 tension-torsion electro-hydraulic servo tester. Both kinds of specimens were calculated by the finite element software ABAQUS and the fatigue life of specimens were predicted based on the finite element results. The results show that the additional bending moment will obviously reduce the life of specimens; only the Manson-Halford model and modified Manson-Halford model can obtain satisfactory results in many prediction models selected.

Abstract: Fatigue life estimation of notched components is mostly dependent on notch stress and strain calculation with non-linear finite element analysis (FEA). For multiaxial cyclic loading, the stress-strain analysis of notch root is rather complex and the non-linear FEA is also very time-consuming. In this paper, a new fatigue life prediction method for notched components under multiaxial loading is proposed. First, a linear elastic solution needs to be solved for notched components under multiaxial cyclic loading. Then, an elastic equivalent parameter is computed using the linear elastic solution. On the basis of the elastic equivalent parameter combined with the Neuber’s rule, an elastic-plastic equivalent parameter is obtained. Finally, the elastic-plastic equivalent parameter is used to estimate fatigue crack initiation life of notched components. The proposed method needs only elastically calculated notch strain history as the basic input and is convenient for engineering application. The method is verified with experimental data of SAE 1045 notched shaft specimens under proportional and non-proportional loading. The results showed that the method can provide good life estimates.

Abstract: Studies about the effect of stress characteristics on multi-axial high-cycle fatigue of metals are still insufficient. Up to now, little work about the effect of different ratio of stress amplitude has been done on multi-axial fatigue under the same equivalent stress. In this paper, the effect of ratio of stress amplitude, under the same Von-Mises equivalent stress is studied from theory and experiment. The results show that the main factor of multi-axial high-cycle fatigue failure is the maximum principal stress. For proportional loading, fatigue life raises when ratio of stress amplitude increase. The variety of fatigue life is not obvious when is larger than a certain value and its value closes to that of pure torsion. For non-proportional loading, when ratio of stress amplitude increases, fatigue life raise at first, then has an inflection point. The value of at the inflection point changes with phase difference and its value is 0.5 while phase angle is 90º. Fatigue life of uniaxial tension was lower than that of pure torsion.