BatteryTrayFEAReport.. - global composite

reelingripebeltUrban and Civil

Nov 15, 2013 (3 years and 9 months ago)

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Global Composite Solutions

Global Composite Solutions


USPS BATTERY TRAY

ASSEMBLY FEA

Project Report

2

Global Composite Solutions


Background

3


Based on the review of Phase

3 report with A123, we were


asked to incorporate a different methodology.


The new methodology consisted of applying

initial velocities


along with the full pulse at the mounting points.

Global Composite Solutions


4

Methodology/Assumptions


The mounts
were assumed to be rigid i.e. they
hold their form during
impact.


The velocities were applied to the entire structure.


The sandwich is modeled as 3 layers with Balsa core encapsulated between


two layers of RTM.


Material was assumed isotropic. The average properties used for analysis
were taken from the data provided by A123.


The other assumptions related to bonding are same as they were in the
previous work.


The NCAP, Side 50
th

and Side 5
th

pulse were evaluated as these were the
most severe pulses based on the velocities.



For the remaining pulses there was no information on whether the barrier
moves or the car moves and they were at significantly lower velocities
(Thus
these were not evaluated).

Global Composite Solutions


5

Baseline

Global Composite Solutions


NCAP Baseline

6

The

RTM

Cover

is

showing

a

peak

tensile

stress

of

235

MPa

at

the

corners
.



The

RTM

Base

is

showing

a

peak

stress

of

(
206
MPa,

-
173
MPa)
.

The

regions

with

stress

above

140

MPa

are

shown

in

red
.

Signed VonMises Stress plot

Global Composite Solutions


7

The

steel

strap

is

showing

a

peak

stress

of

(
276
MPa,

-
236
MPa)
.

The

regions

with

stress

above

274

MPa

are

shown

in

red
.

NCAP Baseline

Signed VonMises Stress plot

Global Composite Solutions


8

NCAP Baseline

Signed VonMises Stress plot

Bolt forces

are within the threshold of 8100 N.

Global Composite Solutions


Side 5th
-

Baseline

9

The

RTM

cover

is

showing

a

peak

tensile

stress

of

32

MPa
.



The

RTM

Base

is

showing

a

global

stress

of

80

MPa
.

The

areas

exceeding

140

MPa

would

be

shown

in

red
.

Signed VonMises Stress plot

Global Composite Solutions


10

The

steel

strap

is

showing

a

peak

stress

of

(
270
MPa,

-
248
MPa)
.

The

areas

above

274

MPa

would

only

be

in

red
.

Side 5th
-

Baseline

Signed VonMises Stress plot

Global Composite Solutions


11

Side 5th
-

Baseline

Bolt forces

for two bolts exceed the threshold of 8100 N.

Global Composite Solutions


Side 50
th

-

Baseline

12

The

RTM

cover

is

showing

a

peak

tensile

stress

of

32

MPa
.



The

RTM

Base

is

showing

a

global

stress

of

80

MPa
.

The

areas

exceeding

140

MPa

would

be

shown

in

red
.

Global Composite Solutions


13

The

steel

strap

is

showing

a

global

stress

of

300

MPa
.

The

areas

above

274

MPa

would

only

be

in

red
.

Side 50
th

-

Baseline

Signed VonMises Stress plot

Global Composite Solutions


14

Bolt forces

are within the threshold of 8100 N.

Side 50
th

-

Baseline

Global Composite Solutions


Observations

15


The bolt forces exceed the threshold of 8100 in the Side

5
th

pulse.


Stresses for the RTM base are higher than threshold of 140
MPa

for Frontal
NCAP. These stresses are localized at couple of regions only.


Stresses on the cover are higher than threshold of 140
MPa

for Frontal
NCAP in two corners only.


Stresses in other places are within the allowable limits.

Global Composite Solutions


Design Modifications

16


In

order to improve the load bearing capacity of the floor i.e.
to withstand
the large forces seen in two bolts, the thickness of the base RTM was
increased to 4 mm from baseline thickness of 2 mm.


The thickened results are corresponding to this increased base thickness to
4 mm.


Henceforth, all the thickened designs would refer to the RTM
layer with
the
thickness of 4 mm.


Other pulses would also be run with this thickened floor to evaluate the
implication of this change on the composite structure.

RTM: 2 mm

Balsa: 6 mm

RTM: 2 mm

RTM: 4 mm

Balsa: 6 mm

RTM: 4 mm

Baseline

Design

Modified

Design: Thickened Base

Global Composite Solutions


17

Modified Design &


Recommendation

Global Composite Solutions


NCAP
-
Thickened

18

Signed VonMises Stress plot

The

RTM

cover

is

showing

a

peak

tensile

stress

of

234

MPa
.

The

regions

with

stress

above

150

MPa

are

shown

in

red
.


The

RTM

Base

is

showing

a

peak

stress

of

(
111
MPa,

-
82
MPa)


Global Composite Solutions


19

The

cooling

pads

is

showing

a

peak

stress

of

134

MPa

at

the

corners
.



The

steel

strap

is

showing

a

peak

stress

of

(
276
MPa,

-
236
MPa)
.

The

regions

with

stress

above

274

MPa

are

shown

in

red
.

NCAP
-
Thickened

Signed VonMises Stress plot

Global Composite Solutions


20

NCAP
-

Thickened

Bolt forces

are within the threshold of 8100 N.

Global Composite Solutions


Side 5th


Thickened

21

The

stresses

in

all

the

components

are

within

permissible

limits

for

the

Side

5
th

pulse

with

thickened

base
.

Signed VonMises Stress plot

Global Composite Solutions


22

Side 5th


Thickened

Bolt forces

for all bolts are within the threshold of 8100 N.

Global Composite Solutions


Side 50th


Thickened

23

The

RTM

base

is

showing

a

peak

tensile

stress

of

100

MPa
.

The

areas

above

140

MPa

would

be

in

red
.


The

steel

strap

is

showing

a

peak

stress

of

(
250
MPa,

-
159
MPa)


Signed VonMises Stress plot

Global Composite Solutions


24

Side 50th


Thickened

Bolt forces

for all bolts are within the threshold of 8100 N.

Global Composite Solutions


Bolt Force Comparison

25

Beam ID

NCAP

NCAP
-
thk

side
-
50th

side
-
50th
-
thk

side5th

side5th
-
thk

136498

1454

1424

487

410

1217

1312

136516

2680

2633

1091

828

807

986

136545

1143

1613

496

586

1170

1585

136561

6548

6118

2831

2800

1570

1715

136568

1415

1823

1031

1546

3110

4169

136586

2205

2418

2099

2160

4548

5122

136604

1081

1027

484

776

5551

4865

136621

2335

2280

1341

1562

4490

3644

136645

2116

2201

758

799

5424

5655

136663

2143

2167

1124

1233

6914

5285

136695

2035

2631

669

765

6810

5169

136712

567

979

1664

2223

7156

5329

136721

3051

2837

3019

2759

6138

4794

136753

1768

2239

887

1228

6761

5143

136763

4973

5095

675

1489

9064

6762

136779

3652

3653

1988

2016

8894

6524

136798

4821

4718

1442

1406

7159

5750

136815

4031

3870

508

552

8077

6715

136833

2053

2449

1159

1729

5502

5014

136851

2561

2534

1291

1868

6057

6411

Global Composite Solutions


Bolt Force Plot

26

0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
136498
136516
136545
136561
136568
136586
136604
136621
136645
136663
136695
136712
136721
136753
136763
136779
136798
136815
136833
136851
NCAP
NCAP-thk
side-50th
side-50th-thk
side5th
side5th-thk
Baseline Thickness

Base Thickened

Bolt forces

are within the threshold of 8100 N for thickened base.

thk



Base Thickened


Global Composite Solutions


Observations
:


1
)

The

bolt

forces

for

2

bolts

exceed

the

threshold

force

with

the

baseline

thickness

for

the

Side

5
th

pulse
.



2
)

The

stresses

are

within

permissible

levels

for

the

base

of

the

assembly
.


3
)

The

cover

shows

couple

of

spots

with

high

stresses

and

solution

to

lower

those

stresses

is

part

of

the

recommendations
.



27

4)
The

stresses

in

the

steel

straps

are

within

the

permissible

levels
.

Yielding

is

observed

in

the

steel

straps
.


Phase
IV
Observations

Update of 12/15/2009

Global Composite Solutions


Recommendations

28

1.
The battery tray using sandwich
construction carrying a massive
weight of battery stacks needs
higher stiffness. This can be
achieved by:


A.
Use of more glass content in the
composite skin by improving the
process or using vacuum or using
infusion.


B.
Use
of higher density/compressive
strength core.

C.
Use
alternate material/processes
for the skin.

D.

Improving adhesion between the
core and the skin.
Change to
PLIOGRIP 7400 series adhesives
which are resistant to exposure to
elevated temperatures, moisture,
fuel, most solvents and chemicals.
An established application pattern
should be developed. Additional
test data would be needed.










2.
To

remove

the

high

stress

local

spots,

we

recommend

that

isolation

pads

be

added

to

where

the

steel

straps

are

mounted

to

the

vehicle
.


3.
The

battery

tray

holes

design

for

bolts

need

improved

design
.

This

can

be

achieved

by
:


A.
Modeling

the

holes

as

clearance

holes
.

B.
Do

not

have

raw

balsa

exposed

in

the

thru
-
plane

direction

at

the

holes
.

C.
Use

a

compressive

sleeve

top

arrest

loading

of

composite

skin
.

D.
Compressive

sleeve

should

use

an

isolator

grommet

to

avoid

transferring

the

vibration
.

This

should

address

the

skin

stresses

seen

in

the

high

stress

areas
.

Global Composite Solutions


Recommendations

29

3. The corner high stresses of 234
MPa

on the cover could be
addressed using local patches of
bidirectional fabric of E
-
Glass or
Carbon Fiber along with
continuous fiber mat as shown
below. These solutions would
improve the threshold stress value
to 300
MPa
.










Local patches of 5
-
in circles at the

locations highlighted above