Hi Pete,
Here are some answers;
1. The cross head speed of a tensile machine is set in "unit of length"/"unit of time" (mm/sec, for instance). The IPC spec you referred to says "per minute of the length of the reduced section", which basically means the gage length. In other words, the spec talks about the deformation, not elongation rate. It's a common approach in materials testing.
In general, the cross head speed could affect the deformation (again, not elongation) value but it shouldn't be the case for your test.
2. In general it's not true. But again, one should talk about deformation not elongation. Elongation will always increases with increasing in the gage/sample length. However, the tensile strength, for the same material won't change simply because it depends on the material properties, but not the sample size.
3. The presence of humidity in a sample (board) could change it's mechanical properties.
Hopefully, it will help.
Regards,
Vladimir
Vladimir Igoshev, Ph. D.
Senior Materials Researcher
Research in Motion
451 Phillip St.
Waterloo, ON, N2L 3X2
Voice: (+1) 519-888-7465, ext. 5283
Fax: (+1) 519-886-0863
E-mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Pete menuez
Sent: Thursday, January 27, 2005 8:37 AM
To: [log in to unmask]
Subject: [TN] Tensile Strength and Elongation Questions
Group:
I have a some questions regarding T/E I'm hoping someone can help.
1. IPC-TM-650 2.4.18.1A paragraph 5.3.4.2 requires a Cross head speed of
between .05 - .5mm/mm (.00197-.0197 in/in) but does not specify the speed to
use in the test. It seems to me that the cross head speed could affect the
elongation values. The slower the speed the higher the elongation. Is
there any validity to my thought or does speed not make a difference?
2. Tensile strength and elongation have an inverse relationship. Higher
elongation = lower tensile. Is this true?
3. Paragraph 5.2 requires a Pre Test bake. Why? Does this bake affect T/E?
What if the board shop also baked the sample for 4 - 6 hours - Would a
double bake have twice the affect.
Thanks in advance for any help.
pete
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