Equations have been derived to predict degradation effects of microresidual stresses on impact resistance of unidirectional fiber composites. Equations also predict lamination residual stresses in multilayered angle ply composites

Chamis, C. C.

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April 1973	 B73-10063 
NASA TECH BRIEF 
Lewis Research Center 
NASA Tech Briefs announce now 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 XI, Washington, D.C. 20546. 
RESIDUAL STRESS EFFECTS ON THE IMPACT
RESISTANCE AND STRENGTH OF FIBER COMPOSITES 
The Problem: 
Fiber composites are made by embedding fibers in a 
matrix when the matrix is near, or at, its molten state, i.e., 
at elevated temperatures. Subsequently, the composites 
are reduced to room or use temperatures which are 
usually considerably less than the temperatures at which 
the composites are made. Cooling down of the composites 
from their process temperatures to their use temperatures 
introduces residual stresses in both fiber and matrix. The 
presence of residual stresses can be detrimental to both 
impact resistance and strength of the fiber composites. 
Therefore, prediction of the magnitude of residual stresses 
and their influence on composite impact resistance and/or 
strength is of utmost importance. 
The Solution: 
Equations have been derived to predict the degradation 
effects of microresidual stresses on the impact resistance 
of unidirectional fiber composites. Equations have also 
been derived to predict the lamination residual stresses in 
multilayered angle ply composites. These equations are in 
terms of fiber and matrix mechanical and thermal 
properties, fiber and void volume ratios, processing 
temperature, and ply orientation angle.
How It's Done: 
Fiber composite micro- and macromechanics and lami-
nate theory are used to derive the governing equations. 
The governing equations are coded into computer pro-
grams. The computer programs are used to investigate the 
influence of the variables on the magnitude of composite 
impact resistance and lamination residual stress. Typical 
results are plotted in Figures 1 and 2. 
Notes: 
1. The detrimental effects of microresidual stress are of 
interest to engineers. It is also of interest to analysts 
and researchers in the fiber composite community. 
2. Prediction of lamination residual stress magnitudes is 
of great interest to designers, researchers, fabricators 
and users of fiber composites. 
3. Ply residual transverse tensile and intraply shear 
stresses can reach magnitudes comparable to corre-
sponding ply strengths. As a result, they can produce 
transply cracks. 
4. The ply residual stresses are very sensitive to ply 
orientation angle, number of plies in each direction, 
and fiber volume ratio. They are relatively insensitive 
to the void content. 
20x1a2
 
14o1O'
MATRIX CONTROLLED 
-- FIBER CONTROLLED 
12-
16 -
WITH RESIDUAL STRESS-
;F
	
10- 
8- -K---- 
Fn
ii
6> rAL 
c)	 4 "WITH RESIDUAL STRESS > 
- 12-
I	 I	 I	 I	 I	 I	 I 0-
0	 .1	 .2	 .3	 .4	 .5	 .6	 .7	 0	 30	 60	 90 
FIBER VOLUME RATIO, k 1	 Ply orientation angle, degrees 
.	 Fig. 1. - Theoretical longitudinal impact resistance of boron-silicon carbide! 	 Fig. 2. - Ply residual stress in the +8 ply at composite 8[2(0),.2(:W), 2ML 2101]. 
	
titanium unidirectional composite. Processing temperature, 1008 0 K (15000 F)	 Thornet-50!epaxy composites. Processing temperature, 4220 K (3000 F). 
and assuming 	 interfacial bonding. 
- -	
-	 (continued overleaf) 
	
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Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
	
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5. Transply cracking due to residual stress can generally 
be prevented by increasing the transverse tensile and 
shear strengths of the ply, decreasing the processing 
temperatures, decreasing the difference between fiber 
and matrix thermal coefficients of expahsion, or by 
some combination of these adjustments. 
6. In specific designs, the magnitude of ply residual 
stresses can be reduced by selecting suitable ply 
orientation and stacking sequence and/or increasing the 
fiber volume ratio. 
7. The following documentation may be obtained from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: NASA TN-D-6464 (N71-32243), Design 
for Impact Resistance with Unidirectional Fiber 
Composites 
Reference: NASA TN-D-6146 (N71-16847), Lami-
nation Residual Stresses in Multilayered Fiber 
Composites 
Reference: NASA TM-X-52881 (N70-4 1457), 
Lamination Residual Stresses in Cross-Plied Fiber 
Composites 
Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B73-10063
Source: Christos C. Chamis 
Lewis Research Center 
(LEW-1 1984) 
B73-10063	 Category 04


Residual stress effects on the impact resistance and strength of fiber composites

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