members as a set of example files for the construction of web based material fatigue

property databases. They are meant for information and research use only, not for design.

**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

- 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.

- "The Mechanical Properties of an SMC-R50 Composite" D.L.Denton ed.

Owens-Corning Fiberglass Corp. 1979.

- 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

- 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: articleSRIM 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 blackOn 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 blackThe 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

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

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