I want to bond a strain gauge on to a stainless steel bar.I 2.5 to 3mm in diameter.A video said that it was similar to superglue(
http://www.elfy.com/epoxies.htm).This is a company that produces superglue over here.I can mange to get their products.
A flexible bond since i will bend the steel bar not completely but to some extent.
The "This" is to a missing URL. Elfy products on the linked page are all epoxies. The first few appear to be 1:1 mix and are fast setting. The last may or may not be 1:1 ratio, but is at least slow setting.
As a rule of thumb, the stronger epoxies are not 1:1 and are usually 1:2 to 1:4 ratios of hardener to resin. If you see ratios of 1:10 or greater, it's a chance that the adhesive is acrylic or polyester, not epoxy, and the catalyst is a peroxide. The biggest drawback from some epoxies is that they tend to be brittle compared to, say, polyurethanes.
For your application and with the Efly products that you show as available, I would recommend using the slow setting epoxy. If it is too brittle and you are into experimentation, you can make epoxies a little more flexible by adding a small amount of neoprene rubber. This will remove some of the brittleness, but not make them truly flexible like rubber. That is why I asked about Pliobond or similar "contact" adhesives you may also have available. You can mix Pliobond with the resin (not hardener). Then, mix the epoxy as usual and apply. I have used up to abut 10% vol/vol Pliobond. The solvent in Pliobond (or other neoprene-based contact adhesive) will delay final curing, as it must evaporate. If the joint construction is such that evaporation cannot occur (e.g., a large sealed surface), then allow the solvent to evaporate from the resin before mixing with hardener. Last time I did this was about 10 years ago. Since then, I have been able to get modified epoxies that are slightly flexible.
Finally, the aircraft industry is heavy into metal bonding. Many of the processes that have been developed are proprietary or only available by license (e.g., Boeing's method for preparing aluminum). However, you can find similar methods for phosphate priming that are "open source." The most important thing in bonding something like stainless is to be sure the surface is suitably abraded and cleaned. Degrease, media blast, then degrease again is a typical sequence. You may also find specific references on the Internet to chemical etchants or other surface preps that will enhance bonding.
John