Hill Engineering Blog

Overview of a strain gage

We talk about strain gages a lot in our blogs, vlogs, and all over our website. That’s because strain gages are a crucial element of the work we do at Hill Engineering. Our little rectangular friends are very important sensors for residual stress measurements. That something so small can be so important is astounding, but how exactly do strain gages work?

Put simply, a strain gage is a sensor which measures strain in a material. The most common type of strain gage contains a grid of conductive material, which when resting, exhibit a particular known resistance. The gage is bonded to the surface of the measurement coupon. As the coupon deforms, the strain gage elongates or shrinks, which changes the resistance in the grid.

The grid of a strain gage. The elongation or shrinkage of the grid area provides the strain data we use to calculate residual stress.

In order to account for temperature effects on the coupon material, we match the thermal coefficient of expansion of the strain gage to that of the coupon (although, as an added measure, we also perform residual stress measurements isothermally). In this way, we can measure the change in dimension of a coupon relative to a reference dimension (known as “strain”) as stress is released in the material. From there, we can indirectly calculate residual stresses in the coupon from strain readings taken during a measurement.

Strain gages aren’t the only method for measuring strain, but they are a reliable and highly sensitive sensor which we opt to utilize at Hill Engineering. We use them for slitting, hole drilling, and ring core method measurements, as well as in various other circumstances that require the monitoring of strain changes.

If you have more questions about how we utilize strain gages to deliver high-quality residual stress results, or about any of the other residual stress measurement services we offer, please contact us.

Below is a vlog entry about how we apply strain gages in our lab.