Characterization of fretting wear experiments on spline couplings by principal component analysis

Fretting wear is a quasi-static process in which repeated relative surface movement of components results in wear and fatigue. Fretting wear is quite significant in the case of spline couplings which are frequently used in the aircraft industry to transfer torque and power. Fretting wear depends on materials, pressure distribution, torque, rotational speeds, lubrication, surface finish, misalignment between spline shafts, etc. The presence of so many factors makes it difficult to conduct experiments for better models of fretting wear and it is the case whenever a mathematical model is sought from experimental data which is prone to noisy measurements, outliers and redundant variables. This work develops a principal component analysis based method, using a criterion which is insensitive to outliers, to realize a better design and interpret experiments on fretting wear. The proposed method can be extended to other cases too.

A Hybrid Molecular Dynamics/Atomic-Scale Finite Element Method for Quasi-Static Atomistic Simulations at Finite Temperature

In this paper, a hybrid quasi-static atomistic simulation method at finite temperature is developed, which combines the advantages of MD for thermal equilibrium and atomic-scale finite element method (AFEM) for efficient equilibration. Some temperature effects are embedded in static AFEM simulation by applying the virtual and equivalent thermal disturbance forces extracted from MD. Alternatively performing MD and AFEM can quickly obtain a series of thermodynamic equilibrium configurations such that a quasi-static process is modeled. Moreover, a stirring-accelerated MD/AFEM fast relaxation approach is proposed in which the atomic forces and velocities are randomly exchanged to artificially accelerate the “slow processes” such as mechanical wave propagation and thermal diffusion. The efficiency of the proposed methods is demonstrated by numerical examples on single wall carbon nanotubes.

A Comparison of Constitutive Equations for the Energy-Based Lifing Method

Alternatives to quasi-static and dynamic constitutive relationships have been investigated with respect to a previously developed energy-based fatigue lifing method for various load profiles, which states: the total strain energy dissipated during both a quasi-static process and a dynamic process are equivalent and a fundamental material property. Specifically, constitutive relationships developed by Ramberg–Osgood and Halford were modified for application to the existing energy-based framework and were compared to the lifing method originally developed by Stowell. Extensive experimentation performed on Titanium 6Al-4V (Ti-64) combined with experimental data generated for Aluminum (Al) 6061-T6 at various temperatures were utilized in support of this investigation. This effort resulted in considerable improvements to the accuracy of the lifing prediction for materials with an endurance limit through application of a modified-Halford approach. Additionally, the relative equality in predictive accuracy between the modified-Stowell approach the modified-Ramberg–Osgood approach was demonstrated.

An Energy-Based Axial Isothermal-Mechanical Fatigue Lifing Method

An energy-based fatigue lifing method for the determination of the full-life and critical-life of in-service structures subjected to axial isothermal-mechanical fatigue (IMF) has been developed. The foundation of this procedure is the energy-based axial room-temperature lifing model, which states: the total strain energy dissipated during both a quasi-static process and a dynamic (fatigue) process is the same material property. The axial IMF lifing framework is composed of the following entities: (1) the development of an axial IMF testing capability; (2) the creation of a testing procedure capable of assessing the strain energy dissipated during both a quasi-static process and a dynamic process at elevated temperatures; and (3) the incorporation of the effect of thermal loading into the axial fatigue lifing model. Both an axial IMF capability and a detailed testing procedure were created. The axial IMF capability was employed to produce full-life and critical-life predictions as functions of temperature, which were shown to have an excellent correlation with experimental fatigue data. For the highest operating temperature, the axial IMF full-life prediction was compared to lifing predictions made by both the universal slopes and the uniform material law prediction and was found to be more accurate at an elevated temperature.

An Energy-Based Axial Isothermal-Mechanical Fatigue Lifing Method

An energy-based fatigue lifing method for the determination of the full-life and critical-life of in-service structures subjected to axial isothermal-mechanical fatigue (IMF) has been developed. The foundation of this procedure is the energy-based axial room-temperature lifing model, which states: the total strain energy dissipated during both a quasi-static process and a dynamic (fatigue) process is the same material property. The axial IMF lifing framework is composed of the following entities: (1) the development of an axial IMF testing capability; (2) the creation of a testing procedure capable of assessing the strain energy dissipated during both a quasi-static process and a dynamic process at elevated temperatures; and (3), the incorporation of the effect of thermal loading into the axial fatigue lifing model. Both an axial IMF capability and a detailed testing procedure were created. The axial IMF capability was employed to produce full-life and critical-life predictions as functions of temperature, which were shown to have excellent correlation with experimental fatigue data. For the highest operating temperature, the axial IMF full-life prediction was compared to lifing predictions made by both the Universal Slopes and the Uniform Material Law prediction and was found to be more accurate at elevated temperature.

PHENOMENOLOGICAL MODELING FOR PORE OPENING, CLOSURE AND RUPTURE OF THE GUV MEMBRANE

In this paper, the pore opening and closure on the giant unilamellar vesicle GUV membrane are studied under different theoretical schemes. The opening process is considered as a dynamics process; while the closure process is considered as a quasi-static process. The opening criterion is set based on an energy release rate theory, similar to the Griffith theory for crack initiation. On the other hand, the closure process is described by a non-equilibrium thermodynamic theory. When the size of initial pore is smaller than a critical value, the pore is stable, and followed by the closure process. Otherwise, the pore is unstable, which leads to the rupture of the vesicle.

Flow-Induced Corrosion Simulation on a Plate by Finite Element Methods

Flow-induced localized corrosion is regarded as one of the main degradation mechanisms of materials. As an initial step of the simulation of a pipe, a plate is chosen to simplify the problem. In this paper, finite element method is used to simulate the corrosion process in the plate by employing nonlinear geometry and physics equations of the material to describe the quasi-static process. An elastic modulus iterative procedure was performed to obtain the material parameters in consideration of the nonlinear physical properties of corrosion. The effect of corrosion is then considered by introducing a criterion between depth and time, calculating corrosion depth at progressive given time. Dead and live finite elements are employed to consider the invalidation of the material. Thus the movable boundary conditions can be taken into account and the dynamic status of corrosion can be simulated. Stress corrosion process under flowing fluid condition is analyzed and then the results of representative examples are compared with published results.