International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 04 Issue: 07 | July -2017
p-ISSN: 2395-0072
www.irjet.net
Material Modelling of PVC for change in tensile properties with variation in Strain Rate Nilesh Chavan1, M.V.Walame2, Mihir Ponkshe3 1P.G
Student, Vishwakarma Institute of Technology, Mechanical Department, Maharashtra, Pune Vishwakarma Institute of Technology, Mechanical Department, Maharashtra, Pune 3 Home Cleaning Department, Gtec-Whirlpool of india Ltd., Pune ---------------------------------------------------------------------***--------------------------------------------------------------------2. POLYMER (PVC) BEHAVIOUR Abstract - Design of plastic part is totally different in 2Professor,
comparison to metal parts. PVC belongs to polymer whose modulus does not change with change in strain rate. Material modelling of such material can be done in LS-DYNA with MAT24 model. During impact or crash simulation of polymer material modelling was first step to perform as material properties of polymer varies with change in strain rate of loading. Tensile testing with change in strain rate is carried out on PVC specimen and validation performed using LS-DYNA software. The linear fit of yield strength against log of strain rate was developed for PVC and refined material model was developed using modelling parameters. Key Words: MAT24, LS-Dyna, Eyring equation, Hypermesh
1.INTRODUCTION Polymer shows complex behaviour in comparison of metal parts under loading conditions. To account this behaviour in CAE package with available material model, material modelling of polymer is important [3]. Parts made of polymers were common in many systems of the home appliances and automobiles due to advantages polymer such as light in weight, easy to form complex shape, cost effective etc. The material selected for study is used for display lens in home appliances which have electronic components enclosed in it. To account non-linear behaviour of the material simple material models were defined in LS-DYNA [8]. During impact simulation selection of exact material model as per material behaviour is important [4]. Parts supporting electronic, electrical components and part of aesthetics assembly were subjected to impact load testing in home appliances [10]. Hence material modelling of selected material with change strain rate is required. Objectives of study as follows:
The polymer behavior cannot be categorized as totally nonlinear and hyper-elastic. The mechanical properties of plastic show variation with change in strain rate, change in temperature and other parameters. Most of plastic shows nonlinear elastic behaviour prior to yielding region. Trend of polymer response depends upon the type of polymer [5].The behaviour of the PVC may be considered as analogues to steel in yielding region [2]. PVC shows reaching maximum stress beyond which it may undergo necking formation which cause strain hardening of material and sudden increase in stress value after showing yielding behaviour. The yield value of the PVC depends on strain rate and temperature. Due to increase in strain rate and decrease in temperature its value got more influenced. In this paper, PVC is used for material modelling. The behaviour of the selected PVC is slightly different than normal PVC behaviour. It does not have abrupt stress increase in post yield region. Hence material modellling of it is quite difficult than other PVC. In general during simulation negatives slopes in stress-strain curve were mostly avoided [3].
3. MATERIAL PREPARATION
MODELLING
AND
SPECIMEN
The material modelling starts with specimen preparation for tensile testing. For impact simulations it was essential to have material data with change in strain rate of testing. For fidelity of results obtained from experimentation ASTM standards needs to follow as per material. Figure.1 shows general flow chart to follow in material modelling procedure.
Verify effect of element form, element size and meshing type on simulation results. To have equation for predicting change in yield strength as per change in strain rate of the material. Material modelling of the given material in LS-DYNA to account change in yield strength value with variation in strain rate of loading.
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