Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/81930
Title: Finite element model for predicting the pressure comfort and shaping effect of wired bras
Authors: Sun, Yue
Advisors: Yick, Kit-lun (ITC)
Yu, Winnie (ITC)
Lau, Newman (SD)
Keywords: Brassieres
Clothing and dress measurements
Issue Date: 2019
Publisher: The Hong Kong Polytechnic University
Abstract: Women often wear ill-fitting bras which cause pain, discomfort and sagging due to the over-simplified bra-sizing system used in the manufacture of commercial bras. In addition, a long development process is required for conventional bra design from creating the prototype to manufacturing the final product, which include the key steps of material selection, pattern making and grading. Thus, in order to reduce the time of the product development cycle and assist bra designers in determining individual bra fit that provides an optimal supportive shape and comfortable pressure, numerical simulation is a potential new tool. The objective of this study is to comprehensively provide information to bra designers so that they gain a better understanding of the interaction process between the breasts and bras with different design features by using numerical simulation. In order to achieve this objective, a study that involves three main stages is conducted: determining the realistic material coefficients of breast tissues to be used for building an accurate biomechanical FE model; developing a subject-specific FE model to simulate the wear process of a bra; and providing a parametric design for different bra features to evaluate the shaping effects of the breasts and pressure distribution on the body.
To determine the non-linear material coefficients of the soft tissues of the breasts, an optimal approach based on static and dynamic FE models with the corresponding deformations during different movements is used. The Mooney-Rivlin material parameters of the breasts in-vivo are iteratively modified through an optimization process until the predicted deformation of breasts matches the experimental results. The resultant, optimally generated, Mooney-Rivlin coefficients for the hyper-elastic material of the breasts are C10=0.041 kPa, C01=0.043 kPa, C11=0.31 kPa, C20=0.65 kPa, and C02=0.52 kPa. These are 1/7.25 of the original ex-vivo coefficients of the breasts obtained from a previous investigation. Based on the proposed method for determining the optimal material coefficients of the breast tissues, a biomechanical model is constructed with high accuracy for simulating the interaction between bra and breast tissues. The simulation of bra wear is done by using an FE contact model in a user-defined coordinate system. Three primary steps are involved: 1) obtaining a stress-free sub-model of both the breasts and bra; 2) applying the gravity load and closing the bra strap and underband at the center of the back of the body; and 3) adjusting the bra position by using "virtual hands". The contact force of the bra and the gravity of the breasts can achieve equilibrium after carrying out these three steps. The contour maps generated by using FE software are used to visually evaluate the amount of breast deformation and contact pressure and quantitatively analyze the results. The simulated results in terms of the breast shape and pressure distribution are validated with a fit trial based on an underwire bra. It is shown that the FE model can predict the deformation of the breast shape with reasonable accuracy. The parametric design study examines different bra features including the material properties of the bra cup fabric, bra style (underwired vs. wireless bra) and different gore sizes. It is found from the simulation results that, amongst the three types of cup materials studied, a rigid material has a better performance in shaping the breasts but induces a higher contact pressure at the bottom of the breasts. Although soft flexible material could reduce the contact pressure at the bottom of the breasts, its poor support creates a pressure hotspot at an intersecting point between the shoulder and the neck. The wireless bra induces less pressure on the breasts, however, the underwired bra has better shaping effects in terms of lifting, gathering and supporting of the breasts. The effectiveness of the wireless bra on breast deformation is only three-fifths of that of the underwired bra and this relationship could be used to predict the deformation of breasts with different materials of underwires in the early stages of bra design. The simulation results of different bra gore size show that this design feature can change the breast shape to a certain extent and also cause fitting problems if the gore size is not appropriate. It is observed that a reduction in the length of the upper part of the gore contributes to the gathering effect of the breasts, thus resulting in a deep cleavage. The length of the bottom part of the gore can readily change the lifting effects and the position of the bra underwire, thus leading to poor fit of the bra against the breast roots and wear discomfort. It is believed that the wear system based on a biomechanical model can predict bra fit on the real human body, and produce the ultimate shape and amount of pressure, which provide the fundamentals of fit evaluation for bra designers. The FE contact model proposed in this study can help to provide a better understanding of the interaction process between breasts and a bra by predicting the amount of deformation and contact pressure with reasonable accuracy. Bra manufacturers will benefit from this numerical simulation method so that they can determine more suitable fabrics and pattern for bras in the early stages of the bra design process.
Description: xxi, 214 pages : color illustrations
PolyU Library Call No.: [THS] LG51 .H577P ITC 2019 Sun
URI: http://hdl.handle.net/10397/81930
Rights: All rights reserved.
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