You are here
Experiment 3: Mechanical Testing- Tensile Testing
The mechanical properties of a material are directly related to the response of the material when it's subjected to mechanical stresses. Since characteristic phenomena or behavior occur at discrete engineering stress and strain levels, the basic mechanical properties of a material are found by determining the stresses and corresponding strains for various critical occurrences.
A wealth of information about a material's mechanical behavior can be determined by conducting a simple tensile test in which a cylindrical or flat specimen of uniform cross-section is pulled until it ruptures or fractures into separate pieces. The original cross sectional area and gage length are measured prior to conducting the test and the applied load and gage displacement are continuously measured throughout the test using computer-based data acquisition. Based on the initial geometry of the sample, the engineering stress-strain behavior (stress-strain curve) can be easily generated from which numerous mechanical properties, such as yield strength and elastic modulus, can be determined.
Universal testing machines, which can be hydraulic or screw based, are generally utilized to apply the test displacement/load in a continuously increasing (ramp) manner according to ASTM specifications.
Return back to experimental course: Materials of Engineering Laboratory
node/1061
| Attachment | Size |
|---|---|
 handout3.pdf | 218.84 KB |
- Henry Tan's blog
- Log in or register to post comments
- 31392 reads
Comments
how do you choose a tensile testing machine
Hi Henry,
I am trying to decide on which universal testing machine to purchase. My application is viscoelastic testing soft tissues and polymers, which means low force, large strains, saline environment, temperature control, multicyclic loading (i.e. 10 cycles or less at ~1Hz or less) and static loading. I'm considering an screw driving machine, the MTS Insight 1,for its low cost, but I don't know much about screw driven machines. Would you mind sharing your experiences with screw driven machines, their pluses and drawbacks? I would very much appreciate the info.
Vicky Nguyen
tensile machines for low-force applications
Hi Vicky,
I'll take a stab at this question since I test the same sorts of materials as you do. I think a screw-driven machine is fine for what you're talking about testing although it's important to note that for viscoelastic testing you do not get superb fast-rate performance and thus a step-loading approximation won't work. The most important factor with these instruments that I find is that a horizontal test-frame is far easier to work with if your samples are hydrated. MTS used to have one called a "Tytron" and I believe Instron now has a machine that is perhaps the best of both worlds, in that it is on a hinge and is convertible from horizontal to vertical testing modes (http://www.instron.us/wa/products/spec_equip/microtester.aspx?). I'd also check out the instruments from Bose/Enduratec. I have never needed a load cell in the KN range for these types of materials, I have maxed out with a 250 N cell and had a second low-force cell (5 N or thereabouts) for these types of materials.
Testing machine options
-Hi Vicky,
I would suggest a Zwick materials testing machine for the application you describe. Zwick offers a very high end solution and competitive university pricing. Please contact me at dan.lopez@zwickusa.com for technical information specific to your needs. Also please check the Zwick website at www.zwick.com.
Dan Lopez-
Comparing universal testing machines
Thanks all for your replies. Another person did remark that I should consider a horizontal configuration. I did check out the Bose Electroforce 3100 because of its ability to do both static and dynamic testing, but it has a very short stroke. I'll check out the Instron. Do you remember if it's the 3340 series? I'd also like to use the machines to test polymers since I also work on shape memory polymers (who isn't?) thus the larger second load cell...
On a more general note. Why isn't there a comparison website out there on the various mechanical testers? An amazon like page where people can post anonymously or not their comments regarding their experiences with various machines.
forum for experimental mechanics here
Well perhaps not anonymous but there is a underutilized forum here on iMech for experimental mechanics . Why don't you start a thread on testing instruments there and see what else gets mentioned? I'd be happy to post some of my experiences with different tensile and indentation instruments to join the fray.
link
http://imechanica.org/node/2462
What is the role of
What is the role of data sampling, data capture rate and bandwidth in case of electromechanical static tensile test. what are their optimum values for a static tensile test of metals.