# Material Properties: Kevlar 49 (Composite)

### Data Available:

• Thermal Conductivity
 Thermal Conductivity UNITS W/(m-K) a -2.65 b 1.986637 c 1.24851 d 0.57 e -8 f 0.777857 data range 6-302 equation range 0-350 curve fit standard error relative to data 7.4

 Has equation of the form: Therefore k Solves as:

Where: Coefficients a – f   are summarized in the table, T is the temperature in K (x-axis), and y is Thermal Conductivity (k) to solve for. "erf(x)" is the Gauss error function and "exp()" is the exponential.

NOTE: The error function (sigmoid shape) is used to blend fits over separate temperature ranges.

 The error function ‘erf(x)’ (also known as the Gauss error function) is defined as: (When x is negative, the integral is interpreted as the negative of the integral from x to zero.) In Excel the error function may be calculated by employing the following format ‘ERF( lower_limit, upper_limit)‘ or simply ‘ERF(value of x)‘. For example ERF(0, 1.5) = ERF(1.5) which results in the integral of error function between 0 and 1.5. Excel 2010 and later evaluate correctly for both possitive and negative values of x. Whereas earlier versions can only evaluate for positive values of x (ie x > 0). Thus one must employ –ERF(x) = ERF(-x) to evaluate negative values of x properly in earlier versions of Excel (prior to 2010).

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