Area under matrix of typical stress-strain diagram bounded by one percent strain is good index for priority assessment of matrix contribution to composite strength. Initial tangent modulus to stress-strain curve is useful parameter in translating matrix properties to composite properties

Chamis, C. C.

Hanson, M. P.

Serafini, T. T.

English

NASA Technical Reports Server

Marêh 1974	 B74-10005 
NASA TECH BRIEF 
Lewis Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield. Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Criteria for Selecting Resin
Matrices for Improved Composite Strength 
ri::
The Problem: 
There are a large number of resins currently available 
for use as matrices in fiber reinforced plastic composites. 
These matrices have properties differing in modulus, 
toughness, elongation, strength, and strength retention at 
elevated temperatures. In addition, the mechanical proper-
ties of any one matrix can be substantially altered by 
suitable additives. The researcher and/or designer is 
confronted with the problem of selecting the best matrix 
from the large number of available matrices which will 
provide composites with improved mechanical properties 
for a specific application. The main difficulty in selecting 
a matrix resin is that matrix mechanical properties do not 
transfer to composite mechanical properties in a parallel 
correspondent manner. 
In recent years, considerable effort has been directed 
toward correlating matrix properties with composite 
strength. These efforts have concentrated on correlating 
composite strength with matrix ultimate strength, ulti-
mate elongation, fracture toughness and other final matrix 
properties. Taken individually or jointly, no criterion has 
emerged from the aforementioned efforts which can be 
used to assess the matrix contribution to composite 
strength. 
20403
ERLA 4617!m PDA 
ERL 22561ZZ1 0820 
12 —
__—INITIAL TANGENT 
vI 
'I,
8 -I-
---INITIAL AREA 
2	 3	 4	 5 
PERCENT STRAIN
The Solution: 
Considering a typical stress-strain diagram for various 
matrix resins (see figure), the area under the matrix 
stress-strain diagram bounded by the one percent strain is 
a good index for a priority assessment of the matrix 
contribution to composite strength. The initial tangent 
modulus to the stress-strain curve (see figure) is a useful 
parameter in translating matrix properties to composite 
properties. In general, the greater the value of these 
parameters, the greater the matrix contribution to 
composite strength and composite mechanical properties. 
How It's Done: 
Micromechanics are used in conjunction with experi-
mental data generated at the Lewis Center, and also taken 
from the literature, to identify those matrix properties 
which influence composite unidirectional strength. Uni-
directional specimens were made from graphite fibers and 
low-modulus, intermediate-modulus, and high-modulus 
resins. These specimens were tested for strength in 
longitudinal flexure, transverse tension, and compression, 
and interlaminar shear The corresponding literature 
composite strength data included longitudinal tension and 
compression, transverse tension, and interlaminar shear. 
Comparisons of composite strength data (see table) with 
the various matrix properties led to the identification of 
convenient and practical criteria which can be used to 
assess the matrix contribution to composite strength. 
Notes: 
I. The criterion should be useful to fiber/resin-matrix 
composite designers, fabricators and researchers for the 
aerospace, marine, automotive, building, appliances, 
and sporting goods industries. 
2. The criteria can be used to guide polymer researchers 
to develop new resins. 
3. Further information is available in the following 
report: 
NASA TM-X-68166 (N73-15597), Criteria for 
Selecting Resin Matrices for Improved Composite 
Strength
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19740000005 2020-03-17T13:42:59+00:00Z
Property Units Resin 
ERLA 2772a
	
ERLA 2256b ERLA 
Matrix 6 
Initial modulus 10	 psi 0.4 0.56 0.82 
Proportional limit stress 103 psi 3.3 4.5 7•3 
Proportional limit strain percent 0.75 0.8 1.0 
Ultimate strength 103 psi 7.8 14.0 17.6 
Ultimate elongation percent 6.9 4.3 3.0 
Toughness	
soEult	
de 103 in-lb/in. 2	 0.417 0.368 0.310 
Impact-strength in.-lb 10.5 3.07 2.15 
Proportional limit stress times in.-lb/in. 3 24.8 36.0 73.0 
proportional limit strain 
Initial modulus times impact 106 1b 2 /in. 4.2 1.72 1.76 
strength 
Composites (50 percent fiber volume)
d Composite longitudinal flexure 10	 psi 122. e .150. 205e 
strength (SLllp) 
Composite transverse tensile 10	 psi 6.1 6.3 6.0 
strength (SL22T) 
Composite transverse compressive 103 psi
--- 25.6 25.8 
strength (SL220 
Composite interlaminar shear 10	 psi 7.8 11.5 15.0 
strength (Sg) 
a - Hardener ZZL 0822 (20.0 phr)	 c - Hardener MPDA/BF3MEA (27.0/1.5 phr) 
b - Hardener ZZL 0820 (27.0 phr)	 d - Compression failure 
e - Tensile failure 
Copies may be obtained at cost from: 
Aerospace Research Applications Center 
Indiana University 
400 East Seventh Street 
Bloomington, Indiana 47401 
Telephone: 812-337-7833 
Reference: B74-10005 
4. Specific technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B74-10005 
Patent Status: 
NASA has decided not to apply for a patent. 
Source: C.C. Chamis, M.P. Hanson, 
and T.T. Serafini 
Lewis Research Center  
(LEW-12057)
. 
B74-10005	 Category 04 


Criteria for selecting resin matrices for improved composite strength

Criteria are presented which can be used a priori to select matrices to yield composites with improved unidirectional strength. The criteria evolved from an investigation including both theoretical and experimental efforts. Composite micromechanics were used in conjunction with suitable experiments and reference data to identify those matrix properties which influence composite strength properties. Composites of graphite fibers and low, intermediate and high-modulus resins were investigated. It was found that the area under the matrix stress/strain diagram limited to one percent strain is a good index for an a priori assessment of the matrix contribution to composite strength. The corresponding initial modulus is a useful parameter in translating matrix properties to composite properties. Matrix properties such as ultimate strength, ultimate elongation, toughness, and fracture toughness are misleading in translating matrix properties to composite strength

Criteria for selecting resin matrices for improved composite strength

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