In Situ Punch-Shear Testing of Polymers

Area of Science:

• Materials Science
• Polymer Science
• Mechanical Engineering

Background:

• Traditional material aging and testing methods may yield inaccurate results for polymers where fluid absorption is reversible, particularly at higher temperatures.
• In situ testing offers a more accurate assessment of polymer properties under service conditions.
• Previous work established correlations for Polyethylene of Raised Temperature (PERT) using an in situ punch-shear device.

Purpose of the Study:

• To evaluate the influence of sample preparation on mechanical property measurements in thermoplastic polymers.
• To compare tensile and shear property correlations across different polymer grades before fluid exposure.
• To determine the reversibility of mechanical properties after aging in deionized water at elevated temperatures.

Main Methods:

• Utilized an in situ punch-shear device to measure shear properties of various thermoplastic polymers under simulated service conditions.
• Compared tensile (ASTM D638) and shear (ASTM D732) properties before and after aging in deionized water at 95 °C.
• Investigated the effect of different sample preparation techniques on measured properties.

Main Results:

• Sample preparation methods significantly influence the correlation between tensile and shear properties, necessitating standardization for reliable comparisons.
• Distinct correlations between tensile and shear properties were observed for different polymer families.
• Standard tensile testing after a saturation-dehydration cycle resulted in overestimated mechanical properties.

Conclusions:

• Accurate in situ mechanical property assessment of polymers requires standardized sample preparation methods.
• Polymer type influences the relationship between tensile and shear properties, especially under fluid exposure.
• Conventional post-aging tensile tests can provide misleadingly optimistic mechanical property data due to reversible fluid ingress.