1. Dr. Steven Danyluk/Stephen Zagarola
POLARITEK TECHNOLOGY FOR QUANTITATIVE STRESS EVALUATION OF PET CONTAINERS
Dr. Steven Danyluk/Stephen Zagarola
Atlanta - June 25-26, 2018
PETnology AMERICAS 2018

2. 1978 THE BIRTH OF A NEMESIS

3. INTRODUCTION TO POLARITEK POLARITEK STRESS MEASUREMENT
OUTLINE
INTRODUCTION TO POLARITEK
POLARITEK STRESS MEASUREMENT
THREE CASE STUDIES
CONCLUSIONS

4. POLARITEK SYSTEMS, INC. Founded in 2012 by Dr. Steven Danyluk
Patented technology for quantitative full field stress measurement for the polymer, photovoltaics, and aerospace industries
Based on > 20 years of development at the Georgia Institute of Technology
POLARITEK SYSTEMS, INC.

5. POLARITEK STRESS MEASUREMENT

6. STRESS FUNDAMENTALS
Stresses in solids - externally imposed or internal (fabrication & processing)
Internal (residual) stresses - not subject to mechanical equilibrium ( 𝐹≠0 , 𝑀≠0 )
Forces causing residual stresses - balanced on a microscale: grain boundaries, dislocations and molecular stretching
Fracture – results when residual stresses superimposed on external stresses exceed strength of material.
Patented Polaritek technology - photoelastic stress measurement method

7. STRESS FUNDAMENTALS
Measurements w/light of various wavelengths using digital photoelastic methods.
Measurements can be of stress, strain, displacement or other material properties.
Applications in this presentation are residual stresses in PET.

8. LIGHT TRANSMISSION IN BIREFRINGENT MATERIALS
Local (privileged) direction due to stress
Polarizer
Light source, P and QWP
A, QWP and camera
Transmitted intensity depends
on the wavelength and
retardation
Light source
(white)
Many wavelengths polarized due to polarizer
*Local Intensity will depend on retardation and wavelength, polarizer/analyzer orientation, and the orientation of the stress relative to the polarizer
*Image appears colored since --
particular wavelengths slow up on traversing the thickness and
the local stress magnitude and orientation

9. PHYSICS OF LIGHT TRANSMISSION IN BIREFRINGENT MATERIALS
Stress (Plane Stress condition in PET Stretching)
Transmitted intensity due to in-plane stretching
Optic axis
PET becomes biaxial when stress is applied or formed during stretching.
In normal incidence light travels along the optic axis, and the orientation and magnitude of the stress are determined from the local color and fringe density.

10. POLARITEK STRESS MEASUREMENT
Light source, P and QWP
A, QWP and camera
Bottle Measurement Geometry

11. POLARITEK STRESS MEASUREMENT
Stress algorithm produces Fringe and Stress Maps
Stress Map 1 2
Data Acquisition
(automated)
Ten images by rotating optic elements 10
Fringe Map

12. POLARITEK STRESS MEASUREMENT
Whole-field maximum shear stress distribution of bottle/preform base, preform body
Determining the mode of stretching
Radial Stretching (Uniaxial)
Biaxial Stretching
Micro Cracks
Location of Biaxial Points relative to the gate center
Symmetry of Stretching
StressMap
Stress Map

13. POLARITEK STRESS MEASUREMENT
StressMap
Whole-field maximum shear stress distribution of bottle/preform base, preform body
Determining the mode of stretching
Radial Stretching (Uniaxial)
Biaxial Stretching
Micro Cracks
Location of Biaxial Points relative to the gate center
Symmetry of Stretching
Fringe map

14. POLARITEK STRESS MEASUREMENT
StressMap
Primary Biaxial Point
Biaxial Point near GATE
Secondary Biaxial Point
Whole-field maximum shear stress distribution of bottle/preform base, preform body
Determining the mode of stretching
Radial Stretching (Uniaxial)
Biaxial Stretching
Micro Cracks
Location of Biaxial Points relative to the gate center
Symmetry of Stretching

15. STRESS MEASUREMENT IN PET CONTAINER BASES
THREE CASE STUDIES

16. PET STRESS MEASUREMENT
KEY MEASUREMENT AREAS

17. PET STRESS MEASUREMENT3 4 5 1 2
KEY MEASUREMENT AREAS

18. PET STRESS MEASUREMENT3 4 5 1 2
KEY MEASUREMENT AREAS

19. PET STRESS MEASUREMENT
Biaxial Stress Pt.
Max Stress
STRESS MAGNITUDE
ISOCHROMATIC FRINGES
Isochromatic fringes in Measured Area

20. PET STRESS MEASUREMENT
Distance
Biaxial Stress
STRETCHING
Gate
ISOCHROMATIC FRINGES
Isochromatic fringes in Measured Area

21. PET STRESS MEASUREMENT
Irregular Stress
Field
Spherulite
Defect
VISUAL QUALITY
ISOCHROMATIC FRINGES

22. PET STRESS MEASUREMENT
SYMMETRY
Greater differences in Fringe Counts = More Asymmetric
DIFFERENCE IN FRINGE COUNT ALONG RADIAL AXIS

23. CORRELATION OF STRESS CRACK RESISTANCE WITH STRESS MEASUREMENTS
CASE STUDY 1
CASE STUDY 1
CORRELATION OF STRESS CRACK RESISTANCE WITH STRESS MEASUREMENTS

24. Biaxial Pt. Distance = 7.6 mm
CASE STUDY 1
MAX SCR = *91 min
Stress = 16.0 MPa,
Biaxial Pt. Distance =
6.5 to 7.6 mm
MIN SCR = *7 min
Stress = 23.5 MPa,
Biaxial Pt. Distance = 7.6 mm
*56 PSI – 22 deg C – 0.2% caustic

25. CASE STUDY 1 MAX SCR = 91 min MIN SCR = 14 min Stress = 16.0 MPa,
Asymmetry = 6
MIN SCR = 14 min
Stress = 23 MPa,
Asymmetry = 18
*56 PSI – 22 deg C – 0.2% caustic

26. STATISTICALLY SIGNIFICANT > 99.9% CONFIDENCE LEVEL
CASE STUDY 1
STATISTICALLY SIGNIFICANT > 99.9% CONFIDENCE LEVEL
R2 = 70% VARIATION IN SCR ACCOUNTED FOR
(minutes to failure) 79 43 20
Measured
Predicted 7 1
P-Value < 0.001
R2 = 0.70
Predicted
(7)
(7) 1 7 20 43 79

27. CASE STUDY 2
CASE STUDY 2
PROCESS CHANGE VS.
STRESS VS. SCR

28. CASE STUDY 2 Δ injection packing weight = 0.3 gm
7% Δ dist. to biaxial pt.
49.3 gm.
11 min Δ SCR
49.0 gm.

29. CASE STUDY 2
Δ lamp zone 6 = 10%
24% Δ stress
9 min Δ SCR

30. CASE STUDY 2
Δ pre-blow cam = 8 deg.
14% Δ stress
5 min Δ SCR

31. Ability to Detect Process Change with Control Charts
CASE STUDY 3 DETECTING PROCESS CHANGE WITH BASE THICKNESS VS. STRESS MEASUREMENT

32. Thickness – Injection Point, Transition Point
PROCESS CONTROL VIA BASE THICKNESS
Thickness – Injection Point, Transition Point
GATE THICKNESS
Subgroup Number
FOOT THICKNESS
Subgroup Number
Process Change Detected

33. DISTANCE TO BIAXIAL POINTS
PROCESS CONTROL VIA STRESS MEASUREMENT
AVERAGE STRESS
Subgroup Number
DISTANCE TO BIAXIAL POINTS
Subgroup Number
Process Change Detected

34. Stress & Dist. To Biaxial Pts.
PROCESS CONTROL VIA STRESS MEASUREMENT
Stress & Dist. To Biaxial Pts.
AVERAGE STRESS
NO Post Mold Spray
Earlier PB
Hotter Base
Reduced stretch-rod gap
Original Process
DISTANCE TO BIAXIAL POINTS

35. CONCLUSIONS
CONCLUSIONS

36. CONCLUSIONS
Stress Crack Failure Risk Still with Us After 40 Years
Historical Gaps in Capability to Control Processes for SCR
New Quantitative Stress Measurement Technology:
Closes Gaps in Assessing PET Container SCR
Provides Valuable Input for Process Optimization
Excellent Detection of Consequential Process Change

37. CONCLUSIONS
THANK YOU!