Short Fiber Composite Fatigue Test Data Collected by F.D.+E Comm.

Short Fiber Composites, Room Temp. Collected data:

After examining a number of test data sets obtained from various
sources in the literature, it was decided that it might be possible
to "merge" the data into one single file or graph. The technique
applied in the following is similar to that proposed in the article:

"A Methodology for Fitting Fatigue Life Calculation Curves to SRIM Composite Data"

The same technique has been applied to encompass more results from the literature. Specifically, data from

1. http://www.fatigue.org/data.html
   (click on "Composite") A summary report on the SRIM Fatigue Test Results,
   presented by P.Kurath to the F.D.+E. Comm.
   
   
2. "The Mechanical Properties of an SMC-R50 Composite" D.L.Denton ed.
   Owens-Corning Fiberglass Corp. 1979.
   
   
3. J.F. Mandell, D.D.Huang, and F.J.McGarry, "Fatigue of Glass and Carbon Fiber
   Reinforced Engineering Thermoplastics," Polymer Composites,
   V2 N3 July 1981, pp.137-144
   
   
4. more data sets will be entered when available.
   
   

• Neuber Plot of Collected Data:
  
  (Click image to enlarge)
  Fig. 1: Plot of Neuber Product or Equivalent Stress amplitude vs Cycles
  to Failure for test data of various un-notched, axially loaded
  short fiber composite materials.

  As explained in the article linked at the top of the page, much of the testing
  was done in load control with R ratios (R=Smax/Smin) of -1 or approximately
  0.1

• Stress vs Strain Relationship:
  Most of the test data of the literature does not include measurement
  of the strain amplitudes during testing, and it was therefore necessary
  to arbitrarily adopt the SRIM cyclic stress-strain curve measured in
  reference [1] above. See also: article

  SRIM Cyclic Stress-Strain Curve : A digital fit of the data
  Created by constructing a median cyclic stress-strain curve.

• Fitted High, Median and Low Lines to Neuber Plot:
  
  (Click image to enlarge)
  Fitted lines and points shown in black

  On the above plot the vertical ratio of stress, at a given life, is
  equivalent to a Kt type stress concentration factor in an elastic stress
  analysis. At short life the ratio between Upper and Lower boundary lines
  is approximately 1.72 At long life the ratio is about 1.63 We shall
  assume that a typical ratio for this material between the median and the
  upper or lower boundary lines is 1.33 This factor will be used below
  in the fatigue life calculator.

• Computing the Fitted Stress-Strain-Life Curve:
  In order to combine the information from the adopted cyclic stress-strain
  curve (above) and the Neuber median line it is necessary to compute the
  Neuber Product (NeuberAmpl. = SQRT( StressAmpl. * StrainAmpl. * E ) for
  each of the cyclic stress-strain curve points and then enter the Neuber
  plot above to determine the appropriate life. The result, in terms
  of such a fitted Curve is displayed as the median line in the Neuber plot:
  
  (Click image to enlarge)
  Fitted lines and points shown in black

  The resulting Fitted Curve and the High, Median and Low Calculators are
  available in the links below.

• Fitted Curves and Calculators:

  In the High and Low Calculators below the same Median Fitted Curve is used
  to describe the Stress-Strain-Life behavior of the deformation and fatigue
  data. The only difference is that a Magnification factor of 1.33 is applied
  to all input calculator stresses to simulate the "Low" curve, while a
  attenuation multiplier of (1/1.33) is applied to all calculator stresses
  to simulate the "High" curve. Since the stresses input by a calculator
  user must be elastic, this is simiar to the application of a traditional
  Kt stress concentration factor.

  • High: __ | __ (Same Fitted Curve) __ | __ High Curve life Calculator
    
  • Median: __ | __ Fitted Curve __ | __ Median Curve life Calculator
    
  • Low: __ | __ (Same Fitted Curve) __ | __ Lower Curve life Calculator

Background: