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Showing 2 results for Gradient Structure
Volume 2, Issue 3 (2-2019)
Abstract
In graded structure aerogels, change of pores diameter through the thickness affects the effective thermal conductivity. As the pores diameter is reversely correlated to the density, the effective thermal conductivity of aerogel is often normalized to the density and it is expressed as the B parameter. Lower values of B would be the optimum conditions for the resulting aerogel. The objective of this work is to simulate the heat transfer of the homogenous structures and to compare it with structures that pore diameter vary through the thickness. For this purpose, the structure characteristics and properties of silica aerogel along with the effect of coupling thermal conductivity have to be taken into consideration. Using the COMSOLMultiphysics®software, the heat transfer was modeled for a number of cases, including homogenous structures with minimum density (L), maximum density (H) and for an optimum structure (OPT) having a minimum value of the B parameter. The results were compared to thestructurally graded aerogels in which the density was varied in two fashions, from higher values to lower (HtL) and from lower to higher values (LtH). The change of temperature with time was tracked for all the cases. Results indicated that the minimum value of heat transfer was obtained for the structurally graded aerogel of the type of LtH (a 2-percent increase of efficiency for LtH when compared to the optimum structure (OPT)). Therefore, this structure introduce as the best candidate for producing a thermal insulator.
Sahel Mohammadi Ghalehney, Mohammad Hossein Sadeghi,
Volume 23, Issue 7 (7-2023)
Abstract
In the first part of this study, the mechanical properties of the uniform auxetic unit cell (negative Poisson’s ratio) have been investigated for application in the hip implant. We used auxetic cells to increase the contact surface between implant and bone under tensile loads. The elastic modulus of the uniform auxetic structure have been obtained by numerical, analytical and experimental methods in y direction. Comparing the elastic modulus in y direction of the analytical and numerical simulation with experimental tests showed there are a good agreement between the results.
In the second part, the gradient structure has been used in order to reduce the stress shielding on the contact surface of the bone and implant, increase the efficiency of implant replacement and reduce infection. In the gradient structure, the elastic modulus in the contact surfaces is considered close to the elastic modulus of the bone, and gradually increases in the next layers. The elastic modulus of the gradient structure was calculated by two numerical and analytical methods. In the numerical method, the elastic modulus was obtained from Abaqus software and coding on MATLAB. The difference of the elastic modulus in these two methods was 4.8%, which shows that there is an acceptable agreement between the results.
