Strain in ceramic glued to a brick

[Sjab]

Hi Experts,

I posted this elsewhere and got no answer. May be somebody here can help.

I have a piece of ceramic(E=270000 N/mm2) glued with a two component epoxy to another much softer material like brick ( E=14000 N/mm2). The brick is much bigger than ceramic as in the attached diagram.

compressive force is applied on the brick which will deform following to Hook's law.

How much of this strain will be on the ceramic piece? or what is the strain in the ceramic.

What role has the epoxy modulus of elasticity?

thank you for any help

Jabir

 

[mrgoldthorpe]

Of course, the strain in the ceramic will be relatively small in accord with its 20x modulus. However, the crucial area will be the edge of the joint, where there will be a large increase in strain as the edge is approached. It's a bit like a bolted joint: the majority of load is taken by the first few threads.

As you indicate, the elastic modulus of the epoxy is crucial - and its failure strain if there is such a thing.

Taking the extreme of a very low modulus epoxy, lower than the brick, the mis-match between brick and ceramic will be accommodated by the epoxy; provided the latter can accommodate the large strains experienced near the joint edge.

If the epoxy has a modulus nearer that of the brick then there isn't the means of accommodating the strain mis-match between brick and ceramic.

I've had a little exposure to such problems in the past in the context of lap joints in composite materials. Try doing a relevant search.

 

[blakmax]

See my comment in the Adhesives and sealants stream.

blakmax

 

[jedward]

Does the brick actually deform or does it fracture like most ceramic-like materials?
If it does not deform then the epoxy characteristice are not important since no strain will ever occur at the ceramic.

 

[Sjab]

The intention is to measure the brick deformation by the sensor. The brick does not fracture and the sensor reads a smaller strain than expected (P/A)/Eb.

 

[rstupplebeen]

Why not just model it up or toss a strain gauge on it?

Rob Stupplebeen

 

[Sjab]

Sure ! but we know already the strain. The problem is the ceramic sensor behavior and modeling.

 

[IRstuff]

Sounds like a ceramic sensor isn't the way to go, since it's apparently substantially modifying your results. Have you looked into a regular strain gage, i.e., resistive flex tape mounted?

TTFN

FAQ731-376