epoxy tensile strength vs tensile shear strength

[Tmoose]

A famous US epoxy supplier applications engineer just sent me an e-mail saying tensile shear strength is listed as tensile strength in their literature for a ceramic filled epoxy product.

Does this sound right?

thanks,

Dan T

 

[CoryPad]

For adhesives, you can get a variety of names. Here are some examples:

ASTM D 1002 Test Method for Apparent Shear Strength of Single-Lap-Joint Adhesively Bonded Metal Specimens by Tension Loading (Metal-to-Metal)

ASTM D 2919 Standard Test Method for Determining Durability of Adhesive Joints Stressed in Shear by Tension Loading

ASTM D 3165 Standard Test Method for Strength Properties of Adhesives in Shear by Tension Loading of Single-Lap-Joint Laminated Assemblies

ISO 4587 Adhesives -- Determination of tensile lap-shear strength of rigid-to-rigid bonded assemblies

ISO 9664 Adhesives -- Test methods for fatigue properties of structural adhesives in tensile shear

ISO 11003 Adhesives -- Determination of shear behaviour of structural adhesives -- Part 2: Tensile test method using thick adherends

This is why defined terminology (and adherence to it) is so important.

 

[MintJulep]

But no, it doesn't sound right. In fact, the phrase "tensile shear strength" doesn't sound right.

 

[Tmoose]

re: tensile shear strength - real or imaginary

Physical property "adhesive tensile shear" about 9 down here -

http://www.devcon.com/UserFiles/File/Metals-Putties(1).pdf

Polymer scientists sometimes publish article with names like
"Effects of symmetrical bonding defects on tensile shear strength of lap joints having ductile adhesives"

http://www3.interscience.wiley.com/journal/104022446/abstract?CRETRY=1&SRETRY=0

my dilemma is tables exist where "tensile shear strength" and "shear strength" co-exist, and the value of tensile strength is likely to be 2 or 3 X higher.

 

[MintJulep]

You'll have to look at ASTM D1002 to find how the term is defined.

My guess is that the standard defines a test coupon of given bond area with a lap joint configuration. Then test the thing in "tension" - which would really load the adhesive interface in a combination of shear and pealing, dependent upon the thickness of the test coupon pieces and offset between the loading planes.

 

[CoryPad]

Tmoose,

For the Devcon example, they list:

Adhesive tensile shear (ASTM D1002). This method measures the shear strength of a lap joint. The "tensile" nature of the test arises from the use of rectangular specimens that are loaded in the axial direction, which places them under (mostly) tension.

Tensile strength (ASTM D638). This is a test method for determining tensile mechanical properties of plastics using a standard dumbbell-shaped specimen. This provides a true tensile strength of the material.

In summary, I can only restate that there are multiple loading modes and methods, and terminology is very important. You have to be vigilant because suppliers may not be.

 

[MintJulep]

So would a D638 tensile strength for an epoxy be a dumbbell of pure epoxy?

That would tell you nothing about bond strength would it?

 

[Tmoose]

peel strength appears as a separate physical property, sometimes.

I'm just trying to ball park the stresses from differences in CTE of a formed in place wear resistant tile. Don't want it to pop off and fall down the pipe. Mfrs data is making this kind of hard to decide. Terms like .

I've pretty much decided if the shear stress at the bond line > 2000 psi I don't think it is trustworthy, and needs mechanical support.

 

[CoryPad]

Mint,

We can speculate that the tensile strength value is for a dumbbell-shaped specimen of the adhesive, or perhaps two half dumbbell-shaped specimens that are joined by the adhesive. The first would provide the adhesive's tensile strength, while the latter provides the bond strength when loaded in tension.

 

[SWComposites]

Tmoose - call/email the supplier and ask what test method (ASTM, EN, etc) was used to produce the published value. They should have listed it in their literature.

If the shear stress value from the supplier is from a lap shear test (likely as mentioned above), then the stress value is an average P/A value and is only valid for the specific lap length of the test specimen (likely 0.5 inch).

If you are calculating an average shear stress, 2000 psi may be too high for a design value, depending on the joint configuration, environment, etc. IF you are calculating a peak shear stress value, then 2000 psi may be ok, depending again on a bunch of things.