×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Microhardness testing on polymers

Microhardness testing on polymers

Microhardness testing on polymers

(OP)
Hi,

I am trying to perform microhardness tests either in terms of Vickers or Knoop on Nylon 6,6 samples which have been weathered for quite a long time from 1 to 5 years.

The samples are cylindrical in shape with a diameter of 30mm and a length of 17mm but the most important thing to note is that surface cracks (max crack width measured was about 80 microns) were present mostly on the circular surface of the samples due to weathering.

Consequently, the problem I am having right now is that I cannot perform indentation directly on the circular surface because it is difficult to distinguish and hence to measure the indentations due to the presence of cracks.

Will I need to perform the tests rather on the cross-section of the samples or are there any other better alternatives? I am asking this because if I perform the tests on the cross-sections, I will need to machine the cross-sectional surfaces such that they are both flat and parallel to the bottom surface and I am not sure if machining the surface will affect the hardness measured.

Regards.




Regards

RE: Microhardness testing on polymers

The polymer goes hard as it is degraded by UV light. Your problem is that anything that removes the cracked surface will also remove the hardened polymer. I am presuming you are trying to measure the change in hardness due to the weathering, so removing the surface ruins that. Measuring other surfaces also ruins that.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules

RE: Microhardness testing on polymers

(OP)
Yes you are right, I am trying to measure the change in hardness of my samples. It seems that I will need to study alternative test methods but thank you for replying!

RE: Microhardness testing on polymers

Why is the surface hardness relevant? What does the customer care about? It's probably one of two things.

1. Appearance. In that case measure gloss versus weathering time. The gloss decreases because the microcracks scatter light. This measurement is cheap, quick and meaningful.

2. Mechanicals. Specifically impact (and elongation) decrease as the cracks act as stress concentration sites. When stresses the cracks grow and the part fails.

Unless you were ordered to measure surface hardness I'd change my focus to another method.

Chris DeArmitt - PhD FRSC CChem
Plastic & Additives Webinars
Instant Downloads & Inexpensive
www.plastictraining.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources