Engineering, 2013, 5, 518-521 Published Online October 2013 (
Copyright © 2013 SciRes. ENG
Comparative Finite Element Analysis of Jaipur Foot
and Polyurethane Foot
Priya Sharma, Shubhda Sharma, S. Vidhya, M. K. Mathur
Centre for Biomedical Research, VIT University Vellore, Tamilnadu Jaipur, India
Received 2013
FEA is amongst best methods that help us e rs to solve complex problems. There are fixed number of nodes in each ele-
ment of the model that define the element boundaries to which boundary condition and loads can be applied. The geo-
metry of the structure, the lo ad applications, stress and displacement gradients can be approximated in a accurate man-
ner, if the mesh is finer. The problem with the foot was unusual cracks in JP Foot and early breakage of PU Foot due to
crack propagation [1]. To solve this problem we modelled the foot using SolidWorks and performed FEA Analysis for
single leg below knee amputee patients. After analysis, it has been concluded that JP Foot as compared to PU Foot has
more stress bearing capacity but has less displacement threshold due to its material properties [2]. This work will lead to
optimization of both the feet thus enhancing the durability of foot.
Keywords: Load Applications; Crack Propagation; Durability; Solid Works; Stress; Displacement
1. Introduction
A Finite element analysis usually consists of three prin-
cipal steps:
1) Pre-processing: The user constructs a model on which
analysis needs to be done and its geometry gets divided
into multiple number of discrete elements, or sub regions,
which forms nodes while connecting at discrete poin ts [3].
2) Analysis: The user s elects restraints and proper
loads needed to be applied on the model and optimizes
the limits for stress, tolerance and factor of safety ac-
3) Post processing: Reports with stress and displace-
ment tables as well as plots are generated for a particular
loading condition applied on the model. FEA provides a
solution by predicting failure of designed model due to
unperceived stress by repr esenting problem areas in used
material and allowing analyst to analyse all the specula-
tive stresses within. This designing and testing of Foot
can be successfully done using SolidWorks 2008 software.
COSMOSXp r ess is a simulation technique of solid-
works which performs FEA of solid models. It en-
sures the performance and quality of the design be-
fore it reaches to production stage. Comprehensive
analysis tools perform digital model testing for in-
sight at early stage in the process of designing [3]. It
is suitable for stress analysis of simple parts, provid-
ing the ability to simulate effect of force or pressure
loads on those parts. Thus it helps in determining
various methods to reduce material costs and weight,
to improve manufacturability and durability, to opti-
mize boundaries, and finally to compare design alter-
natives best suited to customer requirements. A 3d
model of Foot size 6 was designed using Solid Works
and FEA analysis has been performed.
2. Materials and Methodology
Materials Required for Jaipur Foot are Microcellular
rubber compound, Cosmetic rubber, Cushion rubber, and
Tread rubber. Materials Required for Polyurethane Foot
are Polyurethane foam made up of (polyol + isocynate)
and Polyurethane elastomer [2]. Physical (Density), me-
chanical (Elastic Modulus, Shear Modulus, Poisson Ratio,
Tensile Strength and Yield Strength) and thermal proper-
ties (Thermal Expansion and Thermal Conductivity) [2]
values were taken for both the foot and according to that
the material was finalized. Properties were given as an
input to software as material property before analysis.
2.1. Software Required
Software used for modelling is SOLID WORKS 2008.
Software used fo r FEA is COSMOSXp r es s Analysis
Wiz ard (A simulation Technology of Solid Works 2 008)
2.2. Data Collection
Data collection regarding the weights of the patients suf-
Copyright © 2013 SciRes. ENG
fering from single leg (below knee) amputee of varying
age group (Figure 2) in differe nt gait cycle conditions [4]
(mid stance, heel strike, heel off) [5] was done.
3. Steps of Analysis
These are the various steps being followed (Figures 1-5)
during COS-MOSX press simulation for FEA analysis.
4. Results and Discussion
4.1. Factor of Safety (FOS)
FOS is the ratio of material strength to design load.
Standard FOS for JP & PU foot is considered to be 1
(as material strength should always be more then design
load in any condition). The data collected for various
weights and conditions from below knee single amputee
Figure 1. Step 1 and 2 of FEA.
Figure 2. Step 3 and 4 of FEA.
Figure 3. Step 5 and 6 of FEA.
Figure 4. Step 7 and 8 of FEA.
Figure 5. Step 9 and 10 of FEA.
patients of JP & PU Foot were incorporated in COS-
MOSXpress Simulation Wizard for the FEA analysis of
both the Feet. FOS values obtained for JP Foot are al-
ways higher than the FOS values obtained for PU Foot at
the given loads in different conditions of gait cycle [6],
so it can be concluded that material strength of JP Foot is
better than material strength of PU Foot. Thus JP Foot
bears a lower ris k of failure due to crack propagation.
4.2. Results of Stress Analysis
When various loads were applied to the model in differ-
ent gait cycle conditions [7], maximum & minimum stress
values were obtained for PU & JP Foot which is shown
through graphical representation (Graphs 4.2.1-4.2.5).
According to stress values (max. & min.) obtained
during analysis, it is concluded:
During midstance & heel strike maximum stress con-
dition, JP foot is much safer than PU foot as polyure-
thane being soft material cannot withstand larg e
amount of load. So max. Stress values of PU foot are
During midstance & heel strike minimum stress con-
dition, PU foot is much safer than JP foot compara-
tively as polyurethan e is a flexible material and it can
absorb a certain amount of shock that occurs at min-
imum stress condition [8].
Copyright © 2013 SciRes. ENG
Graph 4.2.1. Comparative stress values for midstance.
Graph 4.2.2. Comparative stress values for heel strike max.
Graph 4.2.3. Comparative stress values for heel strike min.
During heel off (max. & min.) stress condition, JP
foot is always safer than PU foot as the phalanges &
metatarsals region bear the full load, the threshold
stress absorbance level of polyurethane material get
exceeded and thus PU foot is vulnerable to early
cracks due to stress applied.
4.3. Results of Displacement Analysis
When various loads were applied to the model in differ-
ent gait cycle conditions displacement values were
Graph 4.2.4. Comparative stress values for heel off max.
Graph 4.2.5. Comparative stress values for heel off min.
obtained and comparative analysis of displacement has
been performed for JP & PU Foot which is shown
through graphical representation (Graphs 4.3.1-4.3.3).
5. Conclusion and Optimization
Over the last decade there has been an adequate incre-
ment of computer applications in the field of rehabilita-
tion and prosthetic designing. FEA is also one amongst
these revolutionary ways to analyze an existing or future
model for prediction of its breakage point, durability,
stress bearing capacity and displacement. We performed
FEA analysis of JP and PU Foot to test the stress bearing
capacity, to compare the durability, displacement and
crack propagation in both the foot. After analyzing stress
and displacement according to their values obtained as
well as their location points it is concluded that JP Foot
has a better material strength and stress be aring capacity
than PU Foot although PU Foot displacement threshold
is higher than JP Foot due to its property “resilience”
which is very high for polyurethane foam and due to that
PU Foot is able to regain its shape back up to a certain
extent and displacement appears to be lower than JP Foo t.
We have done a proper FEA analysis of both the foot
without compromising the quality of model and results.
Copyright © 2013 SciRes. ENG
Graph 4.3.1. Comparative displacement values for mid-
Graph 4.3.2. Comparati ve displac ement values for heel strike
max. and min.
Graph 4.3.3. Comparative displacement values for heel off
max. and min.
For better resu l ts in future this comparative FEA analy-
sis could be done using Force Plate which can predict the
stress and displacement during dynamic gait cycle.
Through the results obtained, design can be optimized
in following ways:
Material strengthening of JP Foot at maximum stress
areas by increasing the proportion of cosmetic and
cushion rubber to avoid future crack propagation in
those areas.
JP Foot can have less displacement than the present
model if it has a layer of PU Foam inside it which
will provide an optimal resilience level to the foot
along with the usual ratio of other types of rubber
compounds which will provide the same strength as
the foot have up till now.
PU Foot can have similar stress bearing capacity as
JP Foot if the outer polyurethane elastomeric layer of
the foot is prepared separately with the thickness 25%
more than that of present model.
PU Foot being lighter in weight (approx 30%) less
than JP Foot has a brighter probability of being used
in future if the above mentioned modifications are
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Stress around Distally Osseointegrated Implant for Artifi-
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