Glue is glue…..right? So, why can’t I use regular glue products available at the local retail store to bond strain gages? Well, actually, you can. The more pertinent question is, how important is your time and your data?
Box store glue does a good job of holding things together. And if all you cared about is that the strain gage remains stuck to the specimen, then one of these glues could do the job for you. But strain gages are intended to measure strain. And they achieve this goal via shear loading through the bonding adhesive. Therefore, the adhesive used to bond strain gages must have a high stiffness to carry the strains from the specimen into the gage. Most retail store glues contain added plasticizers to help with flexibility and peel strength; because, if all you want is for the two pieces to stick together, then these are two important performance characteristics.
Additionally, to achieve faithful transmission of surface strain through the adhesive, the glue line must be thin. Most off the shelf glues contain thickening agents to help fill gaps encountered during normal household gluing jobs. Often, poor performance from commercial glues will not exhibit itself until after loading. At this point, you may encounter excessive creep and high sensitivity to temperature changes caused by the added plasticizers and thickening agents.
Micro-Measurements goes to great lengths to manufacture, qualify and test and control the storage conditions and shelf life of all its adhesives to ensure performance to exacting standards. Even the best adhesives available from retail establishments have not been qualified for strain measurement and the shelf life is not monitored. If the strain gage installer chooses one of these unqualified adhesives, he/she assumes all responsibility for qualifying the adhesive. Even if a “garden variety” adhesive works once, there is no guarantee that it will work again since shelf life is not controlled.
An age old quip is that if you only want your gage to stick, then try well-used bubble gum! But to achieve good strain data on purpose requires using quality strain measuring components. Rely on Micro-Measurements strain gages and accessories to make your test program successful.