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Residual stress Force remaining in a body when all external loads are removed Gives rise to a residual strain (movement) which can be measured and used.

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Presentation on theme: "Residual stress Force remaining in a body when all external loads are removed Gives rise to a residual strain (movement) which can be measured and used."— Presentation transcript:

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2 Residual stress Force remaining in a body when all external loads are removed Gives rise to a residual strain (movement) which can be measured and used to estimate the degree of residual stress In arteries, residual strain can be quantified by measuring opening angle A O B

3 Helps to balance forces within the arterial wall Controls the remodelling process by altering the local loading on VSMC Required to define the zero stress state A O B Why is residual stress important?

4 Circ. Stress  [kPa] Inner Outer Normalised radius No residual stress:  inner /  mean = 6.5 Residual stress:  inner /  mean = 1.4 Residual stress evens out the stresses in the vessel wall

5 Pressurised tubes Heat Cool

6 Steel rod Wet concrete in a mold Stretch steel while Concrete sets When concrete sets, tension in steel bends beam Beam withstands higher Load without bending 16 tons

7 Cross and cupola 700 tons St. Paul’s Cathedral

8 Residual strain in vegetables

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10 With thanks to Stephen Gottlieb

11 mm 8 Rat aorta

12 Age [weeks] Opening angle [°] Rat aorta No sex differences

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14 Age [yr] Males Females Opening angle [ ° ] Human aorta

15 Where does residual stress reside? Which part of the wall –Selective removal of layers, by lathing frozen specimens Which components of the wall –Selective digestion/destruction experiments, using enzymes to remove elastin/collagen and freezing to destroy muscle

16 Artery lathe

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18 Fraction of vessel remaining Opening Angle [degrees] Material removed from outside Material removed from inside Material removed from both sides Localisation of residual strain Greenwald, S. E., et al. (1997). ASME Journal of Biomechanical Engineering 119:

19 Original After elastase treatment

20 Original After collagenase treatment

21 Original Minutes after freezing Months after freezing

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23 FROZEN CONTROL Position (%) Opening Angle (°)

24 CollagenaseElastaseFreezing Entire aorta Thoracic Abdominal OA ratio [Treatment/Control]

25 Residual stress: conclusions Increases with age Greater in men than women Compressive at inner side of vessel wall Tensile at outer side Resides primarily in the elastic component –and to a lesser extent, in muscular component


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