STRAIN GAGE TESTING / STRAIN GAUGE TESTING

Strain gauges are devices that measure the deformation or strain of a material under stress. They are widely used in mechanical engineering for stress analysis, structural testing, and quality control. But how do they work, and what are their advantages and disadvantages? In this article, you will learn about the basic principles, types, applications, and limitations of strain gauges.

How strain gauges work

A strain gauge consists of a thin metallic foil or wire that is attached to the surface of a material that undergoes stress. When the material is deformed, the strain gauge changes its electrical resistance proportionally to the strain. By measuring the change in resistance, the strain can be calculated using a formula that depends on the gauge factor, a property of the strain gauge material. The change in resistance is usually very small, so a Wheatstone bridge circuit is used to amplify and convert it into a voltage signal.

Types of strain gauges

Different types of strain gauges exist based on their shape, configuration, material, and bonding method. Uniaxial strain gauges measure strain in one direction, typically arranged in a linear or rosette pattern. Biaxial strain gauges measure strain in two perpendicular directions, often arranged in a T or rectangular pattern. Shear strain gauges measure angular deformation of the material, typically in a delta or V pattern. Semiconductor strain gauges use silicon or germanium as the strain-sensitive material and have a higher gauge factor and sensitivity than metallic strain gauges, but are more sensitive to temperature and humidity variations. Piezoresistive strain gauges use materials that change their resistance when subjected to pressure and are often used for dynamic measurements such as shock and vibration testing.

Applications of strain gauges

Strain gauges are used in mechanical engineering for a variety of purposes, such as stress analysis, structural testing, and quality control. In stress analysis, strain gauges can help determine the internal forces and moments acting on a structure or component and identify critical regions, failure modes, and safety factors. For structural testing, strain gauges measure the actual strains, deformations, and displacements of the test specimen and compare them with expected values. As for quality control, strain gauges can detect defects, flaws, or variations in the material or manufacturing process that could affect product quality or functionality.

Advantages of strain gauges

Using strain gauges for stress measurement has several advantages. They are accurate, reliable, and versatile, able to measure strains from micro to macro levels in static or dynamic situations in various directions and locations on the material. Additionally, they are easy to install and use, as they can be attached to the material with adhesive bonding, spot welding, or soldering and connected to various instruments for data acquisition and analysis. Moreover, strain gauges are cost-effective and durable; they are relatively inexpensive and widely available in different sizes, shapes, and materials, and can withstand harsh environments and repeated loading cycles without significant degradation or drift.