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The axle pin is one of the most critical components of a wind turbine. Because 2 bearings are mounted on the axle pin, it is not subjected to torque and is designed only to carry bending stresses. The axle is usually made by a casting process, which can induce defects. After casting of the axle pin, radial surface cracks were detected outside by ultrasonic and magnetic particle inspection. The first goal of this paper is to establish defect tolerance in the design of the axle pin, ie, at what critical crack size can we expect failure of the axle pin? The second aim is assessing the remaining lifetime of the defected axle pin used in operation of a wind turbine. Both issues are important to prevent unexpected failure and establish a system for on-line structural health monitoring. This paper presents a procedure for the structural integrity assessment of axle pins by considering their material properties and fatigue crack growth parameters and comparing them with their fatigue design curve. [ABSTRACT FROM AUTHOR]

Abstract: The concept of configurational forces is applied to demonstrate the application of the concept of configurational forces in the numerical simulation of crack growth and fracture processes. It is shown, how material property variations at an interface affect the crack driving force and how the criterion of maximum dissipation is used to evaluate the direction of crack propagation. Fatigue crack growth experiments were conducted on diffusion welded bimaterial specimens consisting of a high-strength steel and soft ARMCO iron. Two cases are considered: (1) specimens with an interface perpendicular to the initial crack orientation, and (2) specimens with an inclined interface. The numerical simulation with the concept of configurational forces show that not only variations of the elastic modulus and/or the yield stress have a tremendous influence on the crack driving force, the crack growth rate, and the curvature of the crack path, but also the thermal residual stresses that resulted from a rather small difference of the coefficient of thermal expansion. [ABSTRACT FROM AUTHOR]

Abstract: The concept of configurational forces is applied to demonstrate the application of the concept of configurational forces in the numerical simulation of crack growth and fracture processes. It is shown, how material property variations at an interface affect the crack driving force and how the criterion of maximum dissipation is used to evaluate the direction of crack propagation. Fatigue crack growth experiments were conducted on diffusion welded bimaterial specimens consisting of a high-strength steel and soft ARMCO iron. Two cases are considered: (1) specimens with an interface perpendicular to the initial crack orientation, and (2) specimens with an inclined interface. The numerical simulation with the concept of configurational forces show that not only variations of the elastic modulus and/or the yield stress have a tremendous influence on the crack driving force, the crack growth rate, and the curvature of the crack path, but also the thermal residual stresses that resulted from a rather small difference of the coefficient of thermal expansion. [ABSTRACT FROM AUTHOR]

Retardation of fatigue crack growth rate due to the introduction of thin, compliant and/or soft interlayers is investigated. The mechanism is the reduction of the crack driving force in the interlayer. Fatigue tests are conducted on composites made of high-strength aluminum alloy as matrix and technically pure aluminum or adhesive as interlayer material. The adhesive interlayer causes an increase in fatigue life by a factor 20 or more, whereas the aluminum interlayer yields only a moderate improvement. Numerical simulations based on the configurational force concept are utilized for understanding. The results show new possibilities for the design of fatigue-resistant materials. [ABSTRACT FROM AUTHOR]