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Load Cycles (load + cycle)

Distribution by Scientific Domains
Polymers and Materials Science80%

Selected Abstracts

Fatigue of Lead Zirconate Titanate Ceramics II: Sesquipolar Loading

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2007
Nina Balke
Piezoelectric actuators generally are driven with unipolar electric load cycles. Although the obtainable strain is increased by small excursions into the negative field regime, this type of load cycle is rarely considered, as its long-time reliability has been questioned. Here, we investigate the degradation of lead zirconate titanate during cycling between high positive and low negative electric fields. Measurements of the large and small signal parameters are used to quantify changes of the material. The fatigue behavior shifts from one best described with existing models of unipolar fatigue to bipolar-like fatigue with increasing field amplitude. [source]

A reliability-based data treatment system for actual load history

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2005
J. J. XIONG
ABSTRACT This paper seeks to establish an integrated and practical data treatment system for actual load history reliability analysis. A convergence,divergence counting procedure is presented to extract all load cycles from a load history of divergence,convergence waves. The lowest number of load history sampling is established on the basis of the damage-based prediction criterion. A parameter estimation formula is proposed for hypothesis testing of the load distribution. The examples of its application for the data treatment of actual load history are given. The proposed data treatment system has been shown to have valid and practical characteristics in analysing reliability results. [source]

Ratcheting and fatigue-led wear in rail,wheel contact

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2003
F. J. FRANKLIN
ABSTRACT A computer model, which simulates the ratcheting wear of a ductile material subject to repeated loading, is presented and discussed in detail. Variation of material properties is a feature of the model, failure by ductility exhaustion occurring at isolated points or extending regions of failure. Such regions form crack-like features. Mechanisms for removal of weakened material from the surface as wear debris are described. The wear process causes a degree of surface roughness. The simplicity of the model enables simulation of millions of load cycles in only a few hours' computer time. The computer model is used to study the effect of partial slip on wear rate. When creepage is relatively low, the wear rate increases sharply with creepage. When creepage is relatively high, the wear rate is largely insensitive to the creepage. [source]

Fatigue of Lead Zirconate Titanate Ceramics II: Sesquipolar Loading

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2007
Nina Balke
Piezoelectric actuators generally are driven with unipolar electric load cycles. Although the obtainable strain is increased by small excursions into the negative field regime, this type of load cycle is rarely considered, as its long-time reliability has been questioned. Here, we investigate the degradation of lead zirconate titanate during cycling between high positive and low negative electric fields. Measurements of the large and small signal parameters are used to quantify changes of the material. The fatigue behavior shifts from one best described with existing models of unipolar fatigue to bipolar-like fatigue with increasing field amplitude. [source]

Effects of Cyclic Stretch Waveform on Endothelial Cell Morphology Using Fractal Analysis

ARTIFICIAL ORGANS, Issue 6 2010
Nooshin Haghighipour
Abstract Endothelial cells are remodeled when subjected to cyclic loading. Previous in vitro studies have indicated that frequency, strain amplitude, and duration are determinants of endothelial cell morphology, when cells are subjected to cyclic strain. In addition to those parameters, the current study investigated the effects of strain waveform on morphology of cultured endothelial cells quantified by fractal and topological analyses. Cultured endothelial cells were subjected to cyclic stretch by a designed device, and cellular images before and after tests were obtained. Fractal and topological parameters were calculated by development of an image-processing code. Tests were performed for different load waveforms. Results indicated cellular alignment by application of cyclic stretch. By alteration of load waveform, statistically significant differences between cell morphology of test groups were observed. Such differences are more prominent when load cycles are elevated. The endothelial cell remodeling was optimized when the applied cyclic load waveform was similar to blood pressure waveform. Effects of load waveform on cell morphology are influenced by alterations in load amplitude and frequency. It is concluded that load waveform is a determinant of endothelial morphology in addition to amplitude and frequency, and such effect is elevated by increase of load cycles. Due to high correlation between fractal and topological analyses, it is recommended that fractal analysis can be used as a proper method for evaluation of alteration in cell morphology and tissue structure caused by application of external stimuli such as mechanical loading. [source]