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Stress Data (stress + data)

Distribution by Scientific Domains
Polymers and Materials Science60%

Selected Abstracts

Dynamic Analysis of Exercise Oxygen Consumption Predicts Outcomes in Advanced Heart Failure

CONGESTIVE HEART FAILURE, Issue 6 2007
Guy A. MacGowan MD
It is unclear whether cardiopulmonary stress testing provides prognostic information in patients with very advanced heart failure receiving contemporary medical therapy. Analysis of cardiopulmonary treadmill stress data in a group of patients with advanced heart failure and severe functional impairment was performed (N=102, peak exercise oxygen consumption [VO2] ,14 mL/kg/min, 47% receiving ,-blockers). Dynamic variables (peak - baseline values) better predicted outcomes than did single value peak measurements, especially ,VO2. Multivariate analysis showed that usage of ,-blockers and ,VO2 (both P<.05) independently and significantly predicted outcomes. Subgroup analysis showed that ,VO2 was particularly useful in predicting outcomes in patients with ischemic cardiomyopathy or who were not receiving ,-blockers. Thus, in patients with very advanced heart failure, cardiopulmonary stress testing-derived ,VO2 provides important prognostic information useful to help predict clinical deterioration or death, particularly for patients with ischemic cardiomyopathy or who are not receiving ,-blockers. [source]

Advanced Experimental and Simulation Approaches to Meet Reliability Challenges of New Electronics Systems

ADVANCED ENGINEERING MATERIALS, Issue 4 2009
Dietmar Vogel
Abstract This paper focuses on some advanced aspects of physics of failure approaches. Tracing of failure modes under realistic loading is a key issue to separate relevant failure sites to be studied in more detail. In the past design of experiment (DoE) tools have been developed to handle this problem. They allow to optimize design and/or material selection with respect to different failure mechanisms and sites. The application of these methods is demonstrated by optimizations performed for fracture problems. Interface fracture has been chosen as one of the most important failure mechanisms. Finally, local stress and strain measurement tools developed over the past years are presented at the end of the paper. They are tools to validate simulation results and therefore the underlying mechanical modeling. Namely, local stress measurement tools under development are needed to make realistic assumptions of loading conditions and to provide residual stress data for FEA. [source]

Mean stress effects in stress-life fatigue and the Walker equation

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2009
N. E. DOWLING
ABSTRACT Mean stress effects in finite-life fatigue are studied for a number of sets of experimental data for steels, aluminium alloys and one titanium alloy. Specifically, the agreement with these data is examined for the Goodman, Morrow, Smith,Watson,Topper and Walker equations. The Goodman relationship is found to be highly inaccurate. Reasonable accuracy is provided by the Morrow and by the Smith,Watson,Topper equations. But the Morrow method should not be used for aluminium alloys unless the true fracture strength is employed, instead of the more usual use of the stress-life intercept constant. The Walker equation with its adjustable fitting parameter , gives superior results. For steels, , is found to correlate with the ultimate tensile strength, and a linear relationship permits , to be estimated for cases where non-zero mean stress data are not available. Relatively high-strength aluminium alloys have ,, 0.5, which corresponds with the SWT method, but higher values of , apply for relatively low-strength aluminium alloys. For both steels and aluminium alloys, there is a trend of decreasing , with increasing strength, indicating an increasing sensitivity to mean stress. [source]

Present-day stress in the surroundings of 2009 L'Aquila seismic sequence (Italy)

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010
Maria Teresa Mariucci
SUMMARY The axial zone of the Apenninic belt in central Italy is a tectonically active region affected by post-orogenic Quaternary extension. The present-day stress field is characterized by a minimum horizontal stress (Shmin) , NE,SW oriented, derived mainly from earthquake focal mechanisms and secondarily from borehole breakouts and fault data. The paper describes the computation of the Shmin orientation along two deep boreholes located in the vicinity of the area hit by the 2009 April 6, Mw 6.3 L'Aquila earthquake. The analysed wells show breakout zones at a depth range between 1.4 and 4.6 km, giving precious information on a depth interval usually not investigated by any other data. The results show an Shmin N81 ± 22° and N74 ± 10° oriented for Varoni 1 and Campotosto 1 wells, respectively. The comparison among the breakouts, the 2009 seismic sequence, the past seismicity and the Quaternary faults indicates a small rotation of Shmin orientation from , NE, in the southern, to , ENE in the northern sector of the study area, where the wells are located. These differences are linked both to the natural variations of data and to the orientation of the main tectonic structures varying from NW,SE in the Abruzzi region to , N,S moving toward the Umbro-Marchean Apennines. The identification of constant Shmin orientations with depth derived from all the examined active stress data, confirms the breakouts as reliable stress indicators also for aseismic areas. [source]

Melt processing effects on the structure and mechanical properties of PA-6/clay nanocomposites

POLYMER ENGINEERING & SCIENCE, Issue 8 2006
Nitin K. Borse
Polyamide-6 nanocomposites were prepared using two organoclays, Cloisite 30B and Cloisite 15A, and Cloisite Na+, which is unmodified sodium montmorillonite (Na-MMT) clay. Nanocomposites were prepared using two twin-screw extrusion systems: System B employing conventional mixing and residence time conditions, while System A was modified to achieve longer residence time and higher mixing efficiency. The work considers the effects of mixing conditions, residence time, and interactions between the polymer and clay surface on the structure and mechanical properties of polyamide-6 (PA-6)/clay nanocomposites. Furthermore, a comparison was made between experimental data and the predictions of composite models usually employed to predict mechanical properties of nanocomposites. The melt processing of Cloisite 30B in System A produced the highest degrees of exfoliation and the largest enhancement of mechanical properties. The aspect ratios of the filler particles in the nanocomposites were estimated from TEM micrographs and from composite models. Yield stress data were employed to calculate the values of parameter B in Pukanszky's equation, which incorporates the effects of the interfacial interaction, interfacial strength, and specific surface area of the filler particles. POLYM. ENG. SCI. 46:1094,1103, 2006. © 2006 Society of Plastics Engineers [source]