Shear cell testing, want to understand it completely

[Educateme]

Hello,

I am working on a project where I will have to do some shear cell testing, I have some basic under standing (very basic). and I have done some research on the internet. I have a shear cell tester. it is very basic, geared motor with a rod to push on sample , which is under a weight. I believe what I am looking for is cohesive strength of a material. Between the rod and sample I will have a load cell which is hooked up to a data acquisition unit. This will let me record the applied force on the side of the sample. I believe this will give me a "shear force" value. My question is how do I determine the cohesive strength?? I am sorry If this question seem vague. I am left with this project on my hands , and I am trying to do my best to figure it out. I never had the opportunity to learn the whole theory behind shear cell testing from my prior boss (left the company), which was the guy who normally did the tests. Thank you all.

 

[FredGarvin]

Have you looked under any ASTM guidelines for this type of testing? It appears that this type of testing is very well used in the pharmaceutical world.

 

[Educateme]

yes, well I found a spec.( which I have to purchase a copy) I am working on it as wee speak. Thanks

 

[Gokul43201]

To find the cohesive strength you need to shear the sample till it fractures. The shear force at fracture divided by the shearing cross section is the cohesive strength.

Note: I've only heard the term "cohesive strength" used in tensile testing. Are you certain it is a shear test that you want to perform?

 

[chemisttree]

Are you testing adhesive failure of a lap shear joint? As Gokul indicated, strength is defined by the load at break/bond area. The test may be sensitive to strain rate.

ASTM D-1002 (adhesively bonded single lap joint), D-3654 (time to failure, static load), D-903 (180 degree peel), D-1876 (T-peel)

Remember, you will be testing the whole method including surface prep, surface energy, adhesive type, cure chemistry/schedule, temperature, etc...
Be aware that thinner samples can cause a change in geometry during the application of stress and could convert a lap-shear to a cleavage type shear.

 

[Educateme]

Well after a discussion with another engineer , I believe I now understand what will be need to do. The test is similar in nature to a shear cell test, how ever it will not be a S/C test. It will be more of a tension test I believe. I will be using an old shear cell test set, which I had to make repairs to. What I will be doing is measuring the force it takes to shear a sample against a few different pieces of steel. I will be looking to the static and kinetic Cohesive strengths. Thank you all for your help.