Numerical study of the mechanics of indentation bending tests of thin membranes and inverse materials parameters prediction

Indentation bending tests are an important testing method for thin rubber-like materials. The choice of material laws in finite element (FE) simulations of the test directly influences the accuracy of the numerical model and material properties predicted through inverse FE modelling. In this work, the effect of using a linear elastic or hyperelastic model on the material parameters predicted from indentation bending tests of a thin rubber sheet over a low strain range were studied. An inverse program has been developed based on the Kalman filter method to predict the material properties from experimental tests and to assess the uniqueness of the converged results for different material models. The predicted results were compared to standard tests carried out on the same material. Results showed that the Young's modulus of the material with the linear elastic model can be accurately predicted while the converged parameters (C 10 and C 01) for the Mooney-Rivlin model were not unique; data analysis showed that parameters C 10 and C 01 of the converged data were associated with the shear modulus of the material. © 2011 Elsevier B.V. All rights reserved

An Experimental and Numerical Program to Study the Properties of Thin Biological Membranes and Water Filling Process

Many organs such as the bladder consists of a water filled structure. An accurate measurement of the properties of the wall tissues and the liquid filling process is very important for the study of their mechanics and interaction with other organs. In this work, a new method has been developed to test thin membranes and inversely predict their mechanical properties based on indentation bending tests. A testing frame has been developed to test thin sheet of different length scales with finite element (FE) model mimicking each testing condition developed. The material properties of the membrane were predicted based on a parametric study approach. Tests have been performed using thin rubber sheet as a model material and the elastic property has been successfully predicted by matching the numerical and experimental data. The predicted material properties were then used in modelling water filling process of a balloon mimicking the bladder filling process

Numerical Study of Effects of Bladder Filling on Prostate Positioning In Radiotherapy

The success of radical prostate radiotherapy depends on delivery of high dose radiotherapy to a defined tissue volume with a high degree of positional accuracy. Modern techniques such as conformal and intensity-modulated radiotherapy (IMRT) can deliver increased radiation dose to the tumour without increased toxicity, but at the expense of requiring smaller delineated treatment margins, which is often difficult to control due to complex organ interactions. In prostate cancer radiotherapy, the position of the prostate is influenced by many factors in particular bladder and rectum filling. It is essential to study the mechanics of these processes and its interaction with adjacent structures to improve the understanding of their influences on the position of the intended irradiated area. In this work, a detailed 3D finite element model has been developed using patient specific MRI images to study the interaction between the bladder, prostate and rectum. Bladder filling was simulated by modelling the physical process to predict deformation fields with volume changes. The movement of the prostate associated with Bladder volume change in the anterior-posterior (AP), superior-inferior (SI) and right-left (RL) directions as well its rotational movement has been predicted. The numerical results were compared to repeated images and showed good agreement with some published clinical data. © 2009 Springer Berlin Heidelberg

MRI image-based FE modelling of the pelvis system and bladder filling

In this study, high-resolution magnetic resonance imaging was performed in the transaxial, coronal and sagittal planes to provide comprehensive structural details of the bladder and surrounding systems. Detailed finite-element (FE) models that were specific to each participant were developed by rendering the images, and the process of bladder filling was simulated. The overall model of bladder deformation was compared with repeated images of the filled bladder that were obtained using computed tomography to validate the FE models. The relationship between the changes in the key dimensions of the bladder and the increase in bladder volume during the filling process was also investigated. The numerical results showed that the bladder dimensions increased linearly with its volume during the filling process and the predicted coefficients are comparable to some of the published clinical results