This technique is at the moment the most simple and reproducible method (Laurent et al 2016), but suffers from several limitations. Quantitative, non-invasive assessment of arterial mechanical properties could therefore be highly beneficial in the clinics for both early diagnosis of arteriosclerosis and follow up of treatment.Ĭurrent commercially-available methods aim at measuring global arterial stiffness by detecting the pulse wave velocity (PWV) between two arterial sites. Notably, increase in arterial stiffness has proven to be an independent predictor for many cardiovascular diseases (Laurent 2006, Hamilton et al 2007, Palatini et al 2011, Scuteri et al 2014), which are the leading cause of death in the world (WHO 2011). As arteries become stiffer, the arterial compliance throughout the cardiac cycle decreases, increasing the work on the heart to pump blood throughout the vascular tree (O'Rourke 2007, Maksuti et al 2016a). Therefore, wall thickness should correctly be measured in arterial SWE applications for accurate mechanical properties estimation.Ĭhanges in arterial mechanical properties strongly affect cardiovascular function and blood pressure levels (Hamilton et al 2007, Chirinos et al 2012, Palatini et al 2011). An underestimation of 0.1–0.2 mm in wall thickness introduces an error 4–9 kPa in hollow cylinders with shear modulus of 21–26 kPa. Wall thickness had a larger effect than diameter on the dispersion curves, which did not have major effects above 400 Hz. The phase velocity curves obtained from experiments and simulations were compared in the frequency range 200–1000 Hz and showed good agreement ( R 2 = 0.80 ± 0.07 for plates and R 2 = 0.82 ± 0.04 for hollow cylinders). In addition, simulations in hollow cylinders with wall thickness difficult to achieve in phantoms were performed ( h = 0.5–1.3 mm, D = 5–8 mm). In this study the influence of geometry on the estimated mechanical properties of plates ( h = 0.5–3 mm) and hollow cylinders ( h = 1, 2 and 3 mm, D = 6 mm) was assessed by experiments in phantoms and by finite element method simulations. Nevertheless, the effect of arterial geometry in SWE has not yet been systematically investigated. Arterial wall thickness ( h) and inner diameter ( D) vary with age and pathology and may influence the shear wave propagation. Arterial shear wave elastography (SWE) and wave velocity dispersion analysis have previously been applied to measure arterial stiffness. Thickness offset above 0.5 mm is not acceptable.Quantitative, non-invasive and local measurements of arterial mechanical properties could be highly beneficial for early diagnosis of cardiovascular disease and follow up of treatment. At 0.25 mm and 0.5 mm thickness offset tubes can safely expand up to 9.5% and 7.8%WR, respectively.
Thickness offset of 0.125 mm tubes does not severely affect joint strength when expanded to 12%WR. There are evident severe plastic strain and grain rotation at the thinner sections. Thickness offset tubes' reduction in pull-out force was observed compared to uniform thickness tubes at higher %WR. The result shows that the hardness value has a linear relationship with pull-out force up to 12%WR for uniform thickness tubes. This paper focuses on tube thickness offsets of 0.125, 0.25, and 0.5 mm, microstructure and hardness values of expanded tubes and pull-out force at various %WR. Hydraulic expansion pressure of 190 MPa, and roller expansion pressure corresponding to 6, 8, 10, and 12%WR were used. Hybrid expansion of hydraulic and roller expansion was considered for this study.
Apparent wall reduction (%WR) is used to evaluate the expansion joint strength. Thickness offset at the swaged ends of tubes reduces the joint strength and leak-proof characteristics of joints. Uniform wall thickness all around the circumference is significant to get the right tube-to-tube sheet expansion joint pull-out strength.
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