Strain Gage Testing Services

 
 

Response Dynamics provides strain gage testing services, including: installation, measurement, and analysis in conjunction with our Vibration Consulting Services on a wide variety of projects. Our strain testing work ranges from PCB Strain Testing (printed circuit boards), to strain testing of objects ranging from small delicate medical devices to large industrial structures. We have over three decades of experience in the art and science of strain measurement.

As strain gage consultants, our strain gage measurement services include the experimental design, that will often include other sensors. We select the proper strain gages, install them carefully with attention to surface prep. We consider the expected strain field in selecting strain gage locations, given the geometry of the structure and applied loads. We provide the cabling, signal conditioning, recording, monitoring, and time and frequency domain analysis, as part of our strain gage consulting services.

A strain gage is a thin wire pattern printed on an elastomeric backing to measure stretch in a material. From a measurement of strain, and using known cross sectional geometry and material properties, we can make estimates of the tensile and compressive forces, moments, torques, and shears that result from this measurable stretch. The units are often given in micro-strain (με), which is a tiny bit of stretch, a mm of stretch for a kilometer of structure, or a micron of stretch for a meter of length.

Photo links below provide specific information by topic

PCBs, Electronics, Semiconductors
Medical Device
Food Industry
Rotating Equipment
Power Generation
Automotive Industry
1/1

 

Our strain gage services include:

  • PCB Strain Testing, Printed Circuit Board, (PCBA)/Solder Joint & Component testing

  • Experimental design, discussion of problem scope, strain gage selection and installation methods

  • Strain gage installation

  • Strain measurement

  • Strain analysis

  • Stress analysis

  • Multi-variable measurement and analysis of acceleration, velocity, displacement, force, torque, temperature, or any other system parameter

  • Rotating systems

  • Finite Element Analysis (FEA), Review of existing FEA models, and model validation through proper comparison with experimental test results

  • In-situ testing, On-Site testing

  • Testing in our lab

  • Analysis, troubleshooting, engineered solutions

Although strain measurement is often a key part of a root cause diagnosis, our Diagnostic Testing often also involve measurements of other parameters such as acceleration, relative displacement, pressure, temperature, flow, speed, load, dynamic stiffness, etc, to explore multiple parameters that may have a cause/effect relationship with the problem at hand. These measurements form part of a fact based hypothesis for the cause of the problem at hand. We use strain gage testing and/or strain modeling and analysis, in conjunction with our structural dynamics expertise to characterize all the important pieces of the puzzle that come into play with dynamic strain issues.

We often use Finite Element Analysis to create dynamic models of portions of a complex vibration/thermal/strain system that are time and frequency dependent, and may involve resonant amplification. We also use FEA to estimate stress concentrations on a location that is either too small to instrument, or has geometry that is too irregular to instrument with a strain gage. With our broad background in these relevant fields we are able to quickly and very efficiently characterize the problem and make recommendations.

FEA of stress concentrations and strain gradients

FEA of stress concentrations and strain gradients

The Test Plan - Our strain measurement services include the experimental design, which is the key to extracting meaningful data. There are important considerations in selecting and installing strain gages, such as the type of environment (high-temperature, marine, corrosive material, destructive elements). Errors due to thermal expansion, thermal noise, non-linearities, and electrical noise must be considered. The geometry of the expected strain field under the expected loads, stress concentrations, high strain levels, the different strain fields that may result if the loads and boundary conditions are not as expected, are also a fundamental part of the experimental design that is necessary to allow the gathering of meaningful test data. (See our discussion on Vibration Induced Fatigue Cracking).

 

The pitfalls and "gotchas" in strain gage measurement are endless. We have decades of experience identifying what is good data and what is bad data, and extracting meaningful information with meaningful error estimates.

Prototype fan blade strain testing

Prototype Fan Blade Strain Testing, 
Graph of strain gage data showing AC strain spectra at 894 RPM

Multi-Gage Testing - Multiple strain signals must be measured to discern the nature of the strain field. Three strain signals are necessary to determine the magnitude of maximum strain, if the axis of the strain is not known. A "rosette" of three strain gages is often used for this purpose. We often report strain in its principal axes that resolve the strain field estimate at a point into two orthogonal axial strains. The strain field at a point can also be represented by two orthogonal axial strains and a shear strain resolved in any arbitrary axes, using Mohr's Circle.

Multiple strain signals can also be combined mathematically to infer the nature of the load applied; i.e. axial force, bending moment, torque, and shear force. In the past this was done with various bridge arrangements (circuits of multiple strain gages) that will tend to give little output to the strains caused by axial force, and respond with a reinforced signal to bending, shear, or torque.

Today, multi-channel measurement allows for the digital processing of strain measurements to combine them mathematically with relative ease. For instance, our VMS1 Monitoring System will combine signals mathematically to produce a live digital signal of principal strain, bending strain, shear strain, torque, or any combination our clients may need to track, record, trigger off of, and characterize in the Time or Frequency domains. When necessary, a bridge circuit of multiple strain gages is still helpful, however, to improve signal to noise at the sensor location.

strain gage testing through a steam pipe support

Strain gage testing to estimate force though steam pipe support

Call us or email us below, to discuss your strain testing application!