A Suitable Mathematical Model Of Pet For Fea Drop-Test Analysis

IJCSNS International Journal of Computer Science and Network Security, VOL.10 No.5, May 2010

215

A Suitable Mathematical Model of PET for FEA Drop-Test
Analysis
Mohammad kh.Abunawas2,
2

General Required Department, Northern Border University, Saudi Arabia

Summary
Attempting the use of finite element analysis ( FEA ) in aiding
plastic – product design has yielded unacceptableresults due to
the limited knowledge of the material properties . this enigma
even found greater pitfall when facing the drop – test
requirement – which is a dynamic problem , where the
mechanical property of the material is time dependent . this
paper introduces a suitable mathematical model of material
property for drop – test analysis . polyethylene terephthalate
( PET ) , as the popularlyplastic used for beverage bottles was
selected for this research . the proposed mathematical model of
PET was tasted physically and digitally and compared with the
FEA results . the MSC . Dytran , as a FEA solver , with our
material model gave 1.303 % error of the peak impact force on
ground.

Key words:
PET, FEA, Drop test,bottle.

1. Introduction
Every day consumers use millions ofplastic bottles. the
plastic bottles, not only help us to preserve the quality and
freshness of fruits juice, soft drink, water and cooking, oil,
they must be safe and durable enough during the
transportation, storage and accidentally dropping.
polyethylene terephthalate (PET or PETE) has become the
material of choice for bottled beverages because it is
lightweight and shatter resistant. PETis one of the most
common consumer plastics used. The PET bottles are
manufacturing by injection stretch blow molding process.
An important durability test of the bottle is the drop test
{1}. the test is conducted by filling the bottle with water at
full capacity, and dropping it from a certain height onto a
hard steel or concrete floor. The bottle is then observed for
the breakage {2}. Thisconventional drop test method is
costly and time consumed. With the introduction of
commercially available finite element analysis (FEA)
software, the drop test for the PET bottle can be digitally
simulated for strength without molding and testing {3, 4}.
FEA enables prediction the performance of the bottle
under any realistic loading situations. However the FEA
solution for analysis thedrop test has a disadvantage in the
material data .
This paper describes the formulation for the mathematical
model of the PET thermoplastic material for FEA drop –
Manuscript received May 5, 2010
Manuscript revised May 20, 2010

test simulation. The stress strain relation of PET under
several strain rates is proven to be a suitable model .our
introduction of the mathematical function ofthe material
property in the nonlinear – plastic region by n-power
function and Cowper – symond equation. The time
function of impact force from experimental data and FEA
result is compared to show the accuracy .

2. Modeling the Material Property
2.1 Modeling Plastic Strain Hardening
Polyethylene terephthalate or PET exhibits the exhibits –
plastic behavior. For an isotropic material ,the stress
strain relation of the elastic – plastic material is linear
elastic at low strains or up to the yield stress ; follows by
nonlinear plastic deformation for large strains. The linear
elastic is characterized by the young's modulus (E) poisons
ration (v) and proportional limit or yield stress. The
nonlinear plastic deformation associates with the effects of
stain hardening. Thehardening behaviors is required,
specially when the FEA is employed for studying the drop
test where large deformation is commonly found.
Since PET is aviscoelastic material, then the hardening
curve also depends on the strain rate associated with the
applied tensile load {5}.
Hence the hardening behaviors is a plot of true tensile
against the true tensile plastic strain. The true strain ЄT is...