## Data Description

A dataset of cracks in photovoltaic backsheets with inner layers of
either ethylene-vinyl acetate or polyethylene exposed to 4,000 hours of
continuous UVA irradiance with an intensity of 1.55 \(w/m^2\) at 340 \(nm\) and a chamber temperature of 70\(^\circ\)C. See the associated journal
article in Polymer Degradation and Stability for details on obtaining
quantitative crack measurements [@klinke_2018_non-destructive].

97 observations of 5 variables are included:

**Response - dAvgNorm:** average crack depth normalized
by the backsheet’s inner layer thickness, dimensionless.
**Stress - uva360dose:** cumulative, integrated
irradiance dose received by the sample for all wavelengths \(<\) 360 \(nm\), in \(MJ/m^2\).
**Mechanism - crys730:** percent crystallinity of
polyethylene regions determined from the ratio of Fourier transform
infrared (FTIR) spectroscopy peak intensities at 731 and 720 \(cm^{-1}\) [@huang_attenuated_1992], dimensionless.
**Mechanism - carb1715:** ketone carbonyl index
determined from the ratio of FTIR peak intensities at 1715 and 2851
\(cm^{-1}\), dimensionless.
**Mechanism - carbPC1:** 1st principal component score
for the carbonyl region between 1500 and 1800 \(cm^{-1}\).

## Load data and run code to build netSEM

```
## Load the crack data set and preview column metadata
data(crack)
?crack
## Run netSEMp1 model
ans1 <- netSEMp1(crack)
## Plot the network model for principle 1
plot(ans1, cutoff = c(0.4, 0.5, 0.6))
## Run netSEMp2 model
ans2 <- netSEMp2(crack)
## Plot the network model for principle 2
plot(ans2, cutoff = c(0.4, 0.5, 0.6))
```

## Network diagram for data

dAvgNorm is the endogenous and all other variables are considered as
exogenous. Based on the plot, the strongest pathway appears to be
uva360dose \(\rightarrow\) carb1715
\(\rightarrow\) dAvgNorm. This can be
confirmed using the `pathwayRMSE()`

function.

## Reference

Huang, J. B., J. W. Hong, and M. W. Urban. “Attenuated Total
Reflectance Fourier Transform Infra-Red Studies of Crystalline-Amorphous
Content on Polyethylene Surfaces.” Polymer (1992) 33: 5173–78. https://doi.org/10.1016/0032-3861(92)90797-Z.

Klinke, Addison G, Abdulkerim Gok, Silas I Ifeanyi, and Laura S
Bruckman. “A Non-Destructive Method for Crack Quantification in
Photovoltaic Backsheets Under Accelerated and Real-World Exposures.”
Polymer Degradation and Stability (2018) 153: 224–54. https://doi.org/10.1016/j.polymdegradstab.2018.05.008.