Effect of Loading History on Elastic Modulus of HDPE

2015 ◽  
Author(s):  
P.-Y. Ben Jar
Keyword(s):  
Elastic Modulus ◽  
Stress Triaxiality ◽  
Damage Parameter ◽  
Cross Sectional Area ◽  
Test Method ◽  
Sectional Area ◽  
Loading History ◽  
Cross Sectional ◽  
Test Speed ◽  
Area Strain

This paper presents results from an experimental investigation about the influence of loading history on the elastic modulus of high-density polyethylene (HDPE). The study uses a new approach, named two-test method, to introduce the loading history using the first test and at least one month later, to measure the elastic modulus using the second test. The period of minimum one month between the two tests is to ensure that recovery of the viscous deformation from the first tests does not affect the measured elastic modulus from the second tests. Parameters considered to vary the loading history include maximum deformation (with the area strain up to 0.5 in most cases), loading mode (monotonic, cyclic and creep tension), test speed (from 0.005 to 30 mm/min), and stress triaxiality (through the change in the specimen gauge length), in which the area strain is defined as the logarithmic ratio of the original cross sectional area (i.e., the cross sectional area of virgin specimen) to the deformed cross sectional area. All of the second tests were conducted under monotonic tension at the crosshead speed of 0.001 mm/min. The results show the general trend of decrease of the elastic modulus, measured from the second tests, with the increase of the strain applied in the first tests. The results further indicate that test speed for deformation introduced in the first tests may have a significant influence on the elastic modulus measured from the second tests. The elastic modulus is used to determine damage parameter D based on the damage concept, based on influence of the loading history on the mechanical properties of HDPE is characterized.

In spontaneously hypertensive rats alterations in aortic wall properties precede development of hypertension

2000 ◽  
Vol 278 (4) ◽  
pp. H1241-H1247 ◽  
Author(s):  
Ad W. van Gorp ◽  
Dorette S. Van Ingen Schenau ◽  
Arnold P. G. Hoeks ◽  
Harry A. J. Struijker Boudier ◽  
Jo G. R. de Mey ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Elastic Modulus ◽  
Spontaneously Hypertensive Rats ◽  
Aortic Wall ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Hypertensive Rats ◽  
Cross Sectional ◽  
Spontaneously Hypertensive ◽  
Wall Properties

In hypertension arterial wall properties do not necessarily depend on increased blood pressure alone. The present study investigates the relationship between the development of hypertension and thoracic aortic wall properties in 1.5-, 3-, and 6-mo-old spontaneously hypertensive rats (SHR); Wistar-Kyoto rats (WKY) served as controls. During ketamine-xylazine anesthesia, compliance and distensibility were assessed by means of a noninvasive ultrasound technique combined with invasive blood pressure measurements. Morphometric measurements provided in vivo media cross-sectional area and thickness, allowing the calculation of the incremental elastic modulus. Extracellular matrix protein contents were determined as well. Blood pressure was not significantly different in 1.5-mo-old SHR and WKY, but compliance and distensibility were significantly lower in SHR. Incremental elastic modulus was not significantly different between SHR and WKY at this age. Media thickness and media cross-sectional area were significantly larger in SHR than in WKY, but there was no consistent difference in collagen density and content between the strains. Blood pressure was significantly higher in 3- and 6-mo-old SHR than in WKY, and compliance was significantly lower in SHR. The findings in this study show that in SHR, in which hypertension develops over weeks, alterations in functional aortic wall properties precede the development of hypertension. The decrease in compliance and distensibility at a young age most likely results from media hypertrophy rather than a change in intrinsic elastic properties.

A new method for analyzing data from continuous depth-sensing microindentation tests

1990 ◽  
Vol 5 (1) ◽  
pp. 123-126 ◽  
Author(s):  
D. L. Joslin ◽  
W. C. Oliver
Keyword(s):  
Surface Roughness ◽  
Elastic Modulus ◽  
Cross Sectional Area ◽  
New Method ◽  
Sectional Area ◽  
Depth Sensing ◽  
Cross Sectional ◽  
The Cross ◽  
Effect Of Surface

A new parameter, hardness/modulus2 (H/E2), has been derived from the equations used to calculate the hardness and elastic modulus from data taken during continuous depth-sensing microindentation tests. This paper discusses the use of this parameter to treat the data obtained from a sample whose surface roughness was of the same scale as the size of the indents. The resulting data were widely scattered. This scatter was reduced when the data were plotted in terms of H/E2 versus stiffness. The effect of surface roughness on the hardness and elastic modulus results is removed via stiffness measurements, provided single contacts are made between the indenter and the specimen. The function relating the cross-sectional area of the indenter versus the distance from its point is not required for calculation of H/E2, but the hardness and modulus cannot be determined separately. The parameter H/E2 indicates resistance to plastic penetration in this case.

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