Linear Cracks and Angle Frequencies
Angles were measured for linear cracks only. These include BWM, DSM, and BM. As a reminder, all angles were measured with respect to the neutral axis (NA) in each section; and four levels were chosen, 00, 300, 600, and 900. By limiting the alternative of angles to only four possible outcomes, the response variable angle becomes a nominal response variable.
Contingency table analyses for angle and type of damage reveal a significantly low Chi-square P value (P-<0.000 1). The significance predominately relies on the bundles of microcracks damage type. Out of 475 BM quantified, 469 were oriented in the range on 60'-90' from the neutral axis. The remaining linear cracks (BWM and DSM) are more evenly distributed, with higher amounts found 00 from the NA axis (38%o and 35%o, respectively).
Table 3 -11: Angles summary.
Observed Frequencies for Angle, Type of Damage
0 30 60 90 Total
Bundles of Microcracks 2 4 178 291 475
Black Wispy Mesocracks 51 17 36 28 132
Diffuse Stain Mesocracks 53 26 40 31 150