Engineering & Analysis Methods > Material Strength Composites: Laminate Approach

Carpet plots to polynomial

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**RobDexter**:

Hi, Does anyone have any advice on how to fit the polynomial expression for laminate properties to data from carpet plots please?

I've seen recommendations to enter laminate allowables as polynomials. I have carpet plots for several laminate properties, but can't get a reasonable match using the polynomial form. I've been running Excel solver with various constraints, but didn't get anything close.

Alternatively, if I can't get a good match, is there a way to define individual curves for a number of different %0 laminates, rather in the one equation?

**August**:

Here is one suggestion (assuming the raw data used to generate the plot is unavailable):

First, extract data from the carpet plots. I like to use WebPlotDigitizer (https://automeris.io/WebPlotDigitizer/). Extract at least 10 or so data points along each %45 curve. Each data point will have three associated values: allowable, %0, %45.

Next, use the extracted data in Excel to perform multivariate regression to get the terms A-H for the polynomial equation. The allowable will be the dependent variable and the terms of our polynomial will be the independent variables (%0, %0^2, %45, %45^2, etc).

Here's a helpful link for multivariate regression in Excel:

http://cameron.econ.ucdavis.edu/excel/ex61multipleregression.html

-August

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