testing of composite materials for use in pressure vessels in a

Testing of Composite Materials for Use in Pressure Vessels in a Cryogenic Environment

H y P e r C o m p

E n g in e e r in g , In c .

Dan Swenson

Utah State University

4130 Old Main Hill

Logan, Utah 84322

danswens@cc.usu.edu

Dr. Thomas Fronk

Utah State University

4130 Old Main Hill

Logan, UT 84322

Thomas.fronk@usu.edu

Jared NordaHypercomp Engineering1080 N. Main Suite 2P.O. Box 505Brigham City, Utah 84302jaredn@hypercompeng.com

SummaryFuture NASA missions will rely on the use of composite overwrapped pressure vessels (COPVs) to store fuels,

oxidizers, and other cryogenic fluids for launch and space

missions. The COPV must be able to operate at the cryogenic conditions imposed by typical propellants, liquid

oxygen (90K) and liquid methane (110K), in addition to withstanding the effects of low energy impact from space

debris.

In order to develop reliable composite structures for use as cryogenic fuel storage, human habitation, or other

mission critical applications, a solid understanding of constituent material environmental capabilities is required.

The database of properties is growing to include the effects

of load, strain, and temperature on resins, fibers, interfaces, and the incorporation of impact resistance and metal-to-

composite bonding capabilities are also needed.Utah State University and Hypercomp Engineering have

begun to evaluate aerospace-grade composite materials for

use in composite overwrap pressure vessels (COPVs) in a cryogenic-impact environment. This study incorporated two

high performance fibers (both separately and in combination) and two epoxy resins (one widely used and one

experimental).

USU and Hypercomp Engineering have also evaluated the impact resistance of several different neat (pure resin

without fiber) resin systems at ambient and cryogenic temperatures. These resin systems include “typical” wet and

prepreg resin systems as well as a variety of experimental

systems.

Neat ResinsAmbient and Cryogenic Izod Impact of Resins

Average Breaking Energy Minus 3σ

0

5

10

15

20

25

30

Epon 828 Epon

862/W

UF3325* CTD 7.1 MX 130

10%

MX 130

20%

MX 130

30%

Urethane HEI 535 TD 72204 TD

111103

Resin System

*Minus 3 Deviations of UF3325 is less than zero for Cryo

Bre

akin

g E

nerg

y (

in-l

bs)

(-3σ

)

Ambient

Cryo

Tensile Tests Results

0

100

200

300

400

500

600

700

800

Epon 828 HEI 535 Epon 828 HEI 535 Epon 828 HEI 535

IM7 Zylon IM7/Zylon

Fiber/Resin System

De

liv

ere

d F

ibe

r S

tren

gth

(k

si)

Ambient

Cryo No Damage

Cryo Low Impact

Cryo High Impact

Tube Specimen Coupon SpecimenCoupon specimen made of IM7, Zylon, and an IM7/Zylon mix were

made using Epon 828 and HEI 535

resins. They were then tensile tested to failure at both ambient

and cryogenic temperatures. Before some of the specimen were

tensile tested at cryogenic

temperatures they were subjected to different levels of impact loading.

Several resins were subjected to

Izod impact testing at ambient and

cryogenic temperatures. The energy required to fracture the

specimen provides a quantitative measure of the impact strength.

From the results of the of the impact tests, two resins were

chosen for the composite

cryogenic impact testing. These two were Epon 828 a

common commercial resin and HEI 535 an experimental

resin.

It was discovered that the biggest

challenge when testing the tubes was obtaining a good bond

between the steel inserts and the composite tubes. Aggressive

surface preparation with a tap on

the inner surface of the tubes produced the best results.

The tensile tests were designed to

produce a fiber failure. However, this type of failure was never achieved.

When a satisfactory bond between the insert and tube was achieved the

inner layers of fibers pulled away

from the outer layers of fibers. When different lay-ups were used, shear

failure occurred.

From the results of the of the impact tests, two resins were chosen for the

composite cryogenic impact testing. These two were Epon 828 a common commercial resin and HEI 535 an experimental resin.