Dwell Sensitive Fatigue Response of Titanium Alloys for Power Plant Applications

Author(s):  
Martin R. Bache ◽  
W. John Evans

The phenomenon of “dwell sensitivity” in the α+β and near α titanium alloys and the intrinsic relationship with quasi-cleavage facet formation is discussed. In the present paper, particular emphasis is placed upon the role of “cold creep” and ambient temperature strain accumulation under cyclic loading. A process of stress redistribution between microstructurally distinct regions that demonstrate different strengths is proposed as the fundamental cause of facet development and subsequent dwell failures. A model to describe the redistribution process is validated through a matrix of fatigue testing designed to assess the effects of microstructural form, stress axiality and periods of dwell loading at peak stress on cyclic strain accumulation.

2002 ◽  
Vol 125 (1) ◽  
pp. 241-245 ◽  
Author(s):  
M. R. Bache ◽  
W. J. Evans

The phenomenon of “dwell sensitivity” in the α+β and near α titanium alloys and the intrinsic relationship with quasi-cleavage facet formation is discussed. In the present paper, particular emphasis is placed upon the role of “cold creep” and ambient temperature strain accumulation under cyclic loading. A process of stress redistribution between microstructurally distinct regions that demonstrate different strengths is proposed as the fundamental cause of facet development and subsequent dwell failures. A model to describe the redistribution process is validated through a matrix of fatigue testing designed to assess the effects of microstructural form, stress axiality, and periods of dwell loading at peak stress on cyclic strain accumulation.


2019 ◽  
Vol 746 ◽  
pp. 394-405 ◽  
Author(s):  
Tea-Sung Jun ◽  
Xavier Maeder ◽  
Ayan Bhowmik ◽  
Gaylord Guillonneau ◽  
Johann Michler ◽  
...  
Keyword(s):  

1980 ◽  
Vol 17 (4) ◽  
pp. 498-508 ◽  
Author(s):  
R. N. Yong ◽  
D. Taplin ◽  
G. Wiseman

The importance of disturbance and remoulding to the alteration of mechanical properties of sensitive soils has been well documented in the geotechnical literature both in terms of laboratory and field behaviours. Man-made transient dynamic input such as dynamite blasting, heavy vehicles, and train movement have been suspected of being capable of causing a reduction in the in situ strength parameters of sensitive clays. A laboratory test program was undertaken to determine whether dynamic loading at peak stress levels below normal failure strength caused similar changes in the mechanical properties, and specifically to quantify the phenomena.In order to simulate highly overconsolidated conditions most of the tests were carried out under conditions of no confining pressure, although supplemental data were obtained from consolidated undrained tests. Some of the variables examined in this program were confining pressure, mean deviatoric stress, cyclic deviatoric stress, cyclic strain, number of applications, frequency, and reference strength. In order to compare the effect of dynamic input with the long-term creep phenomena, a simultaneous constant load program was undertaken.In general terms, the study indicates that under the prestated laboratory test conditions no major reduction in peak strength was found under dynamic loading, and that failure would occur at comparative stress levels under dead-load conditions, but required a greater time. In addition, examination of the sample after failure revealed that any remoulding of the sample appeared to be restricted to the area adjacent to the shear zone.


2013 ◽  
Vol 113 (suppl_1) ◽  
Author(s):  
Kristin M French ◽  
Marcos J Fierro ◽  
Todd D Johnson ◽  
Karen L Christman ◽  
Michael E Davis

Introduction: Cell therapies have grown in popularity for myocardial regeneration post-infarction, but still suffer from poor retention, maturation and integration of delivered cells. Mechanical strain has been shown to alter cell size, shape, adherence and gene expression in cardiac cells. As a more recently identified cell type, the effect of mechanical strain on cardiac progenitor cells (CPCs) is unknown. This work aims to elucidate the role mechanical strain plays in CPC phenotype and if this response is matrix protein specific. We hypothesize that mechanical strain will improve CPC alignment and potential for connectivity. Methods: To examine the role of mechanical strain on CPCs, CPCs were seeded on FlexCell plates in the presence of a naturally-derived cardiac extracellularmatrix (cECM), collagen I (COL) or no protein (TCP) and strained 0% (static) or 10% at 1 Hz for 24 hours in a BioFlex system. CPC elongation, alignment, and size were evaluated by rhodamine-phalloidin staining. Connexin-43 expression was measured by Western and normalized to GAPDH. Data were analyzed by two-way ANOVA and Bonferroni post-test. Results: CPC area, independent of culture conditions, was 1020 ± 40 um2, corresponding to neonatal cardiomyocyte area. The aspect ratio (major/minor axis) of CPCs showed a trend for increased elongation with strain at (e.x. 2.0±0.2 for unstrained cECM compared to 2.7±0.1 for strained cECM; n=4, p>0.05). Static culture conditions, independent of matrix coating, showed 20±3% alignment of CPCs. Under strain, alignment increased to 30±2% on COL (n=4; p>0.05 for strained COL verus static COL) and 48±8% on cECM (n=4; p< 0.01 for strained cECM versus strained COL and p<0.001 for strained cECM verus static cECM). A fold change >2 for connexin-43 protein in strained versus static conditions, independent of matrix, was observed (n=2, p>0.05) and confirmed by immunocytochemistry. Conclusion: This work suggests that mechanical strain alters CPC phenotype. Increased strain-induced alignment appears to be matrix dependent. In conclusion, these studies provide insight into the role of both mechanical forces and biochemical responses in the function of CPCs; which could lead to improved outcomes following cellular transplantation.


Sign in / Sign up

Export Citation Format

Share Document