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Strain Measurement

Strain Gauge Comparison

In this example a Vic-3D measurement with 5MP CMOS Camera was performed. The acryl specimen is fixed in a tensile testing machine. A strain gauge is attached at the back in combination with a SCAD 500 strain gauge amplifier. The output of the SCAD 500 was connected to the DAQ of the DIC system. The strain results are recorded parallel with the Vic-3D measurement and plotted in a diagram. The camera type is equipped with Sony 5Mpx Pregius sensor, 75 fps.

Strain Gauge Comparison-1  Strain Gauge Comparison-1a

Image 1: Vic-3D measurement of the acryl specimen

Strain Gauge Comparison-2

Image 2: Comparison of strain gauge data (red curve) and DIC Strain data (black curve)

The Vic-3D data match nearly perfect with the strain gauge data. Even at low strains the difference is less than 25 micro strain.

Strain Measurement on a Gearwheel

Challenges

Assembled components typically have complex interactions with one another. Contact points can vary during operational cycles due to part movement. This means that the locations of peak strains can be hard to predict, and they are often not stationary. The movement of parts can also make it impractical to maintain electrical connections with gauges. Even when they are stationary and easy to locate, the highest strains can be concentrated in very small areas or have high gradients. Peak values may be lost to the averaging effect produced by gauges.

Solution

Vic-3D provided a means for making strain measurements across the entire profile of the gear tooth. Because it provides full-field measurements, it was not necessary to choose a particular point at which measurements would be made. This allowed the peak strains to be clearly visualized and accurately measured at various stages of the operational cycle. Vic-3D also measured displacement in three dimensions. This feature allowed our customer to recognize and quantify twisting of the gear tooth under load.

Microscopic Strain Measurement

Combination of a special stereomicroscope with Vic-3D digital image correlation on electronic components.

 

Uni Wien Mikroskop

Measurement set up: Stereo microscope mounted

on x-y-z-microtable (backside) and tensile machine (right).

 

Uni Wien Mikroskop2

Uni Wien Mikroskop3

Servered ceramic capacitor chip under bending load (image width approx. 4mm):
Strain in x-direction (upper image) and y- direction (lower image).

 

Uni Wien Mikroskop4

Uni Wien Mikroskop5

Standard derivation (upper) under load : An increased value occurs on the middle against the reference
state by the locally small bulge at the contact between chip and board (see 3D conture below). This might be caused
by material , which is pressed together between the two parts (including the colour layer). In the upper area the
increased values of the standard derivation is caused by the reduced speckle density.

 

Vic-3D High-Speed Vibration Analysis System

Vibration1               Vibration2

 

The Vic-3D™ Vibration Analysis System by Correlated Solutions, Inc. is a new addition to the Vic-3D product line of measurement solutions. Vic-3D Vibration enables full-field 3D viewing, measurement, and analysis of transient events. Full-field operational deflection shapes in the frequency domain can easily be seen and compared with levels of accuracy in the nanometer range.

The image above on the left is a mounted model jet plane which has undergone a transient vibration event.  To the right, the 3D vibration data obtained from the event is shown as a 2D contour overlay on this image.  The data overlay enables the user to see exactly how much deformation is occurring and where it is occurring.  This information is available at each frequency where deflection shapes occur.

The data below displays one operational deflection shape obtained with the VIC-3D™ Vibration Analysis System. Three-dimensional displacements, strains, velocities, and accelerations can all be computed in the analysis software.  The result is not only visual, but also enables the user to export quantitative data (ASCII, MatLab, CSV, etc.) from the sample’s behavior for FEA analysis and validation.  A 3D animation of the model jet’s operational deflection shape at 441 Hz is shown below, with only 12 microns of displacement amplitude.

 

Film Vibration3D_W_431Hz

 

What is transient vibration analysis? 

Transient vibration analysis is the process of monitoring, measuring, and analyzing the condition of samples during a transient event. Material properties can also be observed through the analysis of operational deflection shapes and mode shapes created by the event. These full-field 3D shapes can provide useful information which can be used to improve and correct a sample’s balance, displacement, flexure, rigidity, and overall product performance.  Measuring operational deflection shapes can help answer the question: “How much is this structure actually moving at a particular frequency?”

 

Why is it important to you?

Operational deflection shapes created from transient tests show how a sample can have a nonuniform thicknesses, surface irregularities, weak points, cracks and/or other imperfections & flaws.  This information can be useful at any point in the process of achieving your overall goal, from writing a project proposal to testing a functional or failing part in the field: The Vic-3D™ Vibration Analysis System

  • Has a justifiable price point when writing proposals
  • Can be used:
    • To create and validate FE models when designing parts & equipment
    • During the research and design process
    • In the product testing phase
    • To provide manufacturing quality assurance
    • To certify and assure equipment is operating as expected and required
    • To measure and analyze parts post-installation
    • To ensure product quality and performance over time and in the field
    • When reassessing product functionality over time

 

Examples of transient events which can be measured are the following:

▪ Door Slams ▪ Modal Hammer Strikes
▪ Engine Start-ups ▪ Drop Tests
▪ Explosive Testing ▪ Ballistic Testing

 

System Features 

  • View, compare, animate, graph, extract, and export data for easy FEA comparison
  • Measure 3D full-field, high frequency mode shapes with nanometer resolution
  • Measure extremely low amplitudes with extremely high accelerations
  • Full-field strain, deformation, and shape variables are still available
  • Easy procedures, accurate results
  • User friendly interface
  • Only a fraction of the price of a laser vibrometer system

 

Advantages over other measurement techniques

While traditional vibration measurement techniques can be useful, they also have many drawbacks.  For example, accelerometers can become unglued during testing, can mass-load a sample, and can only provide point to point measurements, often only in a single plane. Pre-testing and testing can also take days or even weeks to perform on large structures.  With the Vic-3D™ Vibration Analysis system, there are no adhesives, wires, signal analyzers, power amplifiers, or load cells necessary for detailed vibration results.  Obtaining thousands of data points for a tiny, complex structure or a large one is as easy as changing a pair of lenses. Similar to digital image correlation, laser vibrometers can provide a non-contact measurement solution, but similar to accelerometers, they are also only able provide point to point measurements.  A 3D measurement can be achieved with multiple scanning vibrometers, but these are usually mounted on large robot arms which can take up valuable laboratory space and cannot be moved easily once installed.  Additionally, these systems are unreasonably expensive for many applications.  The Vic-3D™ Vibration Analysis system can be taken into the field with any compatible laptop and together with the Vic-3D™ Workstation, the system can become mobile and secure inside your facility.  Vic-3D Vibration Analysis is only a fraction of the price of a 3D scanning laser vibrometer system, and since the module can be added onto any existing 3D system, it’s even more affordable.