Ply Deformation Level
Ply deformation level is used to help determine layup rate--see Ply Placing Operation for Hand Layup, Ply Placing Operation for Automated Tape Layup, and Ply Placing Operation for Automated Fiber Placement.
Deformation levels are intended to classify plies according to degree, uniformity, and localization of curvature:
• Level 1: flat
• Level 2: mild curvature
• Level 3: large but uniform curvature
• Level 4: large, non-uniform, but localized curvature
• Level 5: large, non-uniform, non-localized curvature
The following illustration shows various surfaces and their deformation levels:
• 
A ply’s deformation level is determined based on three geometric characteristics of the ply, which are expressed as dimensionless quantities:
• Total average curvature: this is the product of the GCD properties Average Curvature (average curvature per square millimeter) and Surface Area Filled.
• Total max curvature: this is the product of the GCD properties Max Curvature (maximum curvature per square millimeter) and Surface Area Filled.
• Total curvature standard deviation: this is the product of the GCD properties Curvature Deviation (standard deviation of curvature per square millimeter) and Surface Area Filled.
Deformation level is determined from these characteristics as follows, in starting point VPEs:
• Level 1: a ply has level 1 deformation if it is flat: total average curvature is 0.
• Level 2: otherwise, it has level 2 deformation if total average curvature is less than 1. In this case, curvature is considered small.
• Level 3: otherwise, it has level 3 deformation if total max curvature is less than 3 total curvature standard deviations away from total average curvature. In this case, curvature is considered large, but uniform. This is an application of the 3 sigma rule.
• Level: 4: otherwise, it is level 4 if less than 1% of the ply surface has curvature near Max Curvature. In this case, curvature is considered large and non-uniform, but localized.
The percentage of the surface that has curvature near Max Curvature is estimated as the ratio of total curvature variance (the square of total curvature standard deviation) to the square of the maximum total deviation (difference between total max curvature and total average curvature).
• Level 5: otherwise it has level 5 deformation. In this case, curvature is considered large, non-uniform, and non-localized.
VPE administrators can use the following cost model variables to customize these thresholds:
• plyCurvatureMildThreshold (1 in starting point VPEs): curvature is considered mild if total average curvature is less than this value.
• plyCurvatureDeviationThreshold (3 in starting point VPEs): curvature is considered uniform if total max curvature is less than this many standard deviations away from total average curvature.
• plyCuravtureLocalizedThreshold (0.01 in starting point VPEs): curvature is considered localized if the fraction of the ply surface that has curvature near Max Curvature is less than this value.
In terms of these cost model variables, deformation level is determined as follows:
• Level 1 if
Total Average Curvature = 0
• Otherwise, level 2 if
Total Average Curvature < plyCurvatureMildThreshold.
• Otherwise, level 3 if
Total Max Curvature – Total Average Curvature <
Total Curvature Standard Deviation * plyCurvatureDeviationThreshold
• Otherwise, level 4 if
Total Curvature Standard Deviation2 /
(Total Max Curvature – Total Average Curvature)2 <
plyCuravtureLocalizedThreshold.
• Otherwise, level 5