A high-cycle fatigue apparatus at 20 kHz for low-cycle fatigue/high-cycle fatigue interaction testing

High-cycle fatigue (HCF) failures in aircraft engines are attributed to material damage states, created during processing or by in-service loading and environmental conditions, and then propagated to failure by HCF loading. The loading configuration experienced by aircraft engine turbine blades consists of an axial load caused by the centrifugal acceleration during rotation combined with the tensile and compressive loads caused by the natural vibrations of the blades themselves. To simulate these loading conditions a new testing apparatus was developed that is capable of providing interactive low-cycle fatigue/high-cycle fatigue (LCF/HCF) loading, in ratios (of magnitude and frequency) that give a realistic simulation of the actual flight loads experienced by engine components. This testing apparatus is based on a HCF cell operating at 20  kHz. The cell can also be integrated to a servo-hydraulic load frame, which provides a second fatigue cycle. The objective of this study was to demonstrate the capabilities of the new HCF apparatus via thermographic measurements and by performing LCF/HCF interaction tests.     

Machines for testing the fatigue strength of metals in various media

Machines for fatigue tests in rotating bending on specimens of the cantilever type are described. The machines can be used for tests at 20–1000° C in a molten metal stream, in inert atmospheres and in vacuum.     

A monitoring system for contact fatigue crack testing

A new monitoring system is developed to detect crack initiation and propagation in the surface layer during contact fatigue running. The magnetic head of a commercial tape recorder is used as a probe. A combination of leakage and eddy current methods is ussed for the contact roller specimen on the JPM-1 machine. Experimental results show that this system is very sensitive to artificial defects and can distinguish defects on the surface from those beneath the surface. The defect signals agree well with their positions. Testing of an ion-nitrided specimen shows that a tiny subsurface crack (∼ 1 μm), which can only be examined under a microscope with 200 × magnification, is observable with this system.     

A technique for dynamic tensile testing of metals

A technique is described for obtaining full dynamic stress/strain curves in tension up to strain rates of 100^s-1. In conjunction with a high speed servo-hydraulic machine, a low inertia extensometer has been developed to facilitate measurement of specimen tensile strain up to fracture.
The benefits of the technique are highlighted in relation to currently available methods for dynamic stress/strain measurement.     

A damaged evolution model for strain fatigue of ductile metals

This paper, based on Lemaitre's potential of dissipation, derives a damaged evolution model for strain fatigue of ductile metals. Then the equation of fatigue-life prediction and the criterion of cumulative fatigue damage are deduced. Experiments for steel were conducted and the experiment data agreed with the model excellently. Thus the model can predict the damaged evolution during the strain fatigue process.     

A procedure for fatigue testing of shaft-sleeve glued connections

We describe a procedure for testing-shaft-sleeve glued connections using anaerobic materials for high-cycle fatigue, present a scheme of numerical analysis of stresses in glued connections, and propose a criterion of the limiting state of these connections attained in the course of fatigue tests under conditions of excitation of vibrations in the resonance mode.     

An apparatus for quantitative fretting testing

The design and construction of an apparatus for performing quantitative fretting fatigue experiments is described. The device allows accurate measurement and control of normal contact force, tangential contact force, relative displacement between contacting surfaces and bulk fretting loads, as well as measurement of average friction coefficients. Its design is simple, and includes interchangeable fretting contact pads, allowing the use of various pad geometries without major adjustment. The device incorporates many points of adjustment for alignment and compliance, making it a robust frame for a wide variety of fretting fatigue conditions involving different materials. The capabilities of this device are also verified by results of fretting fatigue experiments conducted on a 7075-T6 aluminium alloy.     

A frame-level measurement apparatus for performance testing of ATM equipment

Performance testing of asynchronous transfer mode (ATM) equipment is dealt with here. The attention is principally paid to frame-level metrics, recently proposed by the ATM Forum because of their suitability to reflect user-perceived performance better than traditional cell-level metrics. Following the suggestions of the ATM Forum, more and more network engineers and production managers are interested today in these metrics, thus increasing the need of instruments and measurement solutions appropriate to their estimation. Trying to satisfy this exigency, a new VME extension for instrumentation (VXI) based measurement apparatus is proposed in the paper. The apparatus features a suitable software, developed by the authors, which allows the evaluation of the aforementioned metrics by simply making use of common ATM analyzers; only two VXI line interfaces, capable of managing the physical and ATM layers, are, in fact, adopted. Some details concerning ATM technology and its hierarchical structure, as well as the main differences between frames, specific to the ATM adaptation layer, and cells, characterizing the underlying ATM layer, are first given. Both the hardware and software solutions of the measurement apparatus are then described in detail, paying particular attention to the measurement procedures implemented. In the end, the performance of a new ATM device is assessed through the proposed apparatus.     

A novel high-throughput fatigue testing method for metallic thin films

Abstract

Thin films are used in a wide variety of computing and communication applications although their fatigue behavior and its dependence on alloying elements are not very well known. In this paper, we present an experimental implementation of a novel high-throughput fatigue testing method for metallic thin films. The methodology uses the fact that the surface strain amplitude of a vibrating cantilever decreases linearly from the fixed end to the free end. Therefore, a thin film attached to a vibrating cantilever will experience a gradient of strain and corresponding stress amplitudes along the cantilever. Each cantilever can be used to extract a lifetime diagram by measuring the fatigue-induced damage front that progresses along the cantilever during up to 10⁸ load cycles.     

A model of fatigue crack propagation in metals

A model of the formation and evolution of a local plastic deformation zone at the crack tip is proposed based on the analysis of the main physical processes taking place in a metallic material under the action of cyclic loads. An equation of fatigue crack growth rate curves, which explicitly accounts for the loading frequency, was derived. The equation applies to the whole range of crack lengths from short cracks to macroscopic ones. __________ Translated from Problemy Prochnosti, No. 1, pp. 35–43, January–February, 2009.     

Grip for fatigue testing pure aluminium

A simple method of clamping pure aluminium for fatigue tests at cryogenic temperatures is described. Easily machined cylindrical specimens are aligned and held firmly by collet grips that counteract sample shrinkage during cooldown. Specimens are quickly mounted and removed after testing without distortion or thermal treatment 99.999% aluminium, aluminium alloys and copper were gripped successfully through tens of thousands of fully reversed tension-compression cycles at 295, 77 and 4.2 K.