Strain Gauge Applications

What is a Strain Gauge?

Strain gauges are sensors that measure the deformation (strain) of an object when subjected to external forces. A strain gauge typically consists of a thin, flexible backing with a metallic foil, which deforms when the test subject deforms and is used to predict how long an object will perform under load before failure. As a type of transducer, strain gauges are used to convert physical stresses, such as pressure, torque, shear, tension and compression into a readable electrical signal.

This conversion is crucial for applications where understanding and monitoring structural integrity are necessary. Strain, a dimensionless measurement, is defined as the ratio of the change in length of a material to the original, unaffected length. Strain can be positive due to elongation or negative due to contraction. Stress is a measurement of the force applied divided by the initial cross-sectional area of an object, or the internal resisting capacity of an object. Stress (σ) and Strain (ε) are related by the Young’s Modulus (E), denoted by σ = Eε.

When an object stretches or contracts, its electrical resistance changes, and this change is measured using a Wheatstone Bridge circuit. By relating the output Voltage (VO), excitation Voltage (VEX) and gauge factor (GF), the strain response is obtained. By monitoring the strain over time with various loading cycles, the fatigue life can be predicted, making strain gauges indispensable in various fields of engineering and material science.

How are Strain Gauges Used and Their Applications?

Strain Gauges are widely used in a wide number of applications in most industries. Here at Techni Measure, we offer a huge range of TML strain gauges, over 600 different types. We are sure to find the right strain gauge for you.

Here are some examples of the major industries where strain gauges are commonly found.

The Automotive Industry

In the automotive industry, strain gauges are essential sensors used to measure the mechanical deformation of vehicle components under stress. By converting this physical strain into an electrical signal, engineers can analyse structural integrity, optimise designs for performance, and ensure compliance with safety standards.

Key applications include:

  • Crash Testing: Strain gauges are installed on bumpers and crumple zones to monitor impact forces during crash simulations. Crash test dummies are also equipped with these sensors to measure the forces experienced during a crash.
  • Occupancy Detection: Sensors embedded in passenger seats utilise strain gauge technology to detect the weight of an occupant. This data determines whether an airbag should deploy and at what speed.
  • Suspension Analysis: Strain gauges are used to measure both dynamic and static loads on suspension systems, axles, and vehicle frames, ensuring they can bear weight according to design specifications.
  • Powertrain and Engine Testing: Engineers use them on drive shafts, crankshafts and gearboxes to measure torque and power output. They also monitor thermal and mechanical strain in radiators, intercoolers and exhaust manifolds.
  • Aerodynamics and Body Panels: Strain gauges can be applied to body panels to observe how they move and vibrate under different road conditions and speeds.

Civil Engineering and Construction

In civil engineering and construction, strain gauges are primarily used for Structural Health Monitoring (SHM). They detect minute micro-deformations in materials to ensure safety and prevent catastrophic structural failures.

Key applications include:

  • Bridge Monitoring: Sensors are strategically placed on steel beams, concrete footings, cables, and trusses to track load distribution and identify any signs of fatigue or cracks. In the realm of “smart bridge” technology, these sensors deliver real-time data related to the bridge’s response to heavy traffic or wind.
  • Concrete Structures: Specialised gauges are often embedded within concrete during the pouring process, attached to rebar, to monitor internal stresses in buildings, dams, and foundations.
  • Dam and Tunnel Safety: These sensors are used to measure the immense pressures on dams and assess the stability of tunnel linings and supporting ribs within underground cavities.
  • Pile and Foundation Testing: Strain gauges are implemented in piles and slurry walls to measure load-bearing capacity and monitor settlement over time.
  • Railway Infrastructure: Sensors are installed on rails and expansion joints to track stress caused by high-speed trains or ground shifts (such as those from mining activities or frost), helping to prevent derailments.
  • Earthquake Engineering: Gauges evaluate how structures react to seismic forces, providing valuable data on building deformation during and after an earthquake.

Aerospace Applications

In the aerospace industry, strain gauges are used to validate design models, monitor structural health, and ensure the safety of aircraft and spacecraft under extreme flight conditions.

Key applications include:

  • Structural and Fatigue Testing: Gauges are strategically positioned on wings, fuselages, and landing gear to assess stress distribution during both static and dynamic structural tests. They monitor cyclic stresses during takeoff, flight, and landing to estimate fatigue life and avert potential failures.
  • Flight Testing and Real-Time Monitoring: In live flight tests, hundreds of gauges gather data on how airframes react to aerodynamic forces and turbulence. This information is crucial for validating Computer-Aided Design (CAD) and Finite Element Analysis (FEA) simulations.
  • Engine and Turbomachinery Analysis: Sensors are installed on rotating components such as fan blades, turbines, and engine mounts to measure vibration, torque, and power output. Custom gauges are often necessary to endure extreme temperatures and corrosive conditions.
  • Flight Controls and Actuators: Contemporary “active stick” flight controls utilise strain-gauge-based force sensors to capture pilot inputs, replacing older spring-and-position systems. They also keep track of actuators responsible for the deployment of flaps and landing gear.
  • Spacecraft and Satellite Testing: Gauges are employed to monitor rocket components during launch, ensuring they can withstand severe vibrations and thermal loads. Additionally, they are used to weigh entire aircraft to accurately determine their centre of gravity

These are just some examples of strain gauge applications. However, they can be used in most industries for specific applications. We offer a wide range of strain gauges, and we are sure we will find the right solution for you!