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Frequently Asked Questions
What are the advantages of making automated strain measurements over manual strain measurements?
Consistent Accuracy Obtain Reliable Data
Color Contour Strain Distribution Quickly Identify Critical Areas
Forming Limit Diagram (FLD) Display Helps Diagnose Forming Problems
Strain Vector Diagram Identifies Material Flow
Who uses ASAME Technology products?

Collection and analysis of strain data is an important activity in the automotive, aerospace, and metals manufacturing industries. Many research organizations and university programs need to acquire experimental strain data. A selection of the many ASAME and GPA users includes Ford Motor Company, AK Steel, Tenneco Automotive, Johnson Controls, ARCELOR Group, ALCOA, Michigan Technological University, Alcan, Aalborg University, General Motors, Boeing, Wuhan Iron and Steel Group, Baosteel Group, University of Nottingham, Aceralia Corp., FIAT, SSAB, Hyundai HYSCO, Dongbu Steel, and many other corporations and organizations throughout the world.

ASAME
How does ASAME measure surface geometry and strain?
  • A grid is applied to the undeformed object. Typically this is a regular grid of squares or circles, though other options are available.
  • The part is deformed via stamping, hydroforming, or other method.
  • Two or more photographs are taken of the area to be measured, where the specially designed target cube is also in the photographs.
  • The position of the target cube and the map of the grid pattern are located in each photograph.
  • The 3D coordinates of the grid are determined based on the grid location in the photographs and the camera position when the photograph was taken.
  • Strain data are calculated based on the difference between the known initial grid (undeformed grid) and the current (deformed) grid.

Also see the ASAME Target Model Quick Reference Card.

What grid patterns can ASAME measure?

The ASAME program is most commonly used with a square grid pattern, although circle girds are also used.

Grid shape - the preferred grid patterns are square grids, butted-circle grids, and single-circle grids. If the grids are high quality, all of these work well. If the grid is low quality, square grids are easier to work with.

Grid size - the ASAME system has been used to measure grids from 0.5 mm  to 100 mm in size.  Smaller and larger grids can be measured, but require special lenses and/or custom targets.

Grid application - the grid pattern can be applied to the surface of the part using:

Electrochemical etching (typically the easiest to set up)
Silk screening (typically the sharpest looking)
Laser etching
Manually drawn -- this requires a measurement before deformation as well as the measurement after deformation, but a measurement can be made on almost any surface using this process.

How long does it take to make a measurement with ASAME?

On average, it takes somewhere between 10 and 30 minutes per measurement area, depending on user experience, part size, part complexity, and grid quality.

If the grid has been damaged in some areas, can it still be measured?

Yes. ASAME is equipped with many editing features for accurately repairing damaged grid lines in the photograph. These features including drawing capability with the mouse, photographic overlay of the grid, and direct adjustment of the located grid.

What is the geometric accuracy of ASAME measurements?

The ASAME systems obtain an approximate geometric accuracy of 1 part in 1000. The dimensional accuracy is dependent on the area that is visible. For example, if the photograph shows an area that is 20 mm across, the grid intersections will be located to ±0.02 mm. Similarly, if the photograph shows 50 mm, the accuracy is ±0.05 mm.

Using more photographs can improve this accuracy in a similar proportion to how the strain accuracy is increased.

GPA
How does the GPA measure surface strain?
  • A hand-held camera is used to examine one square or circle at a time.
  • When the computer screen shows a square or circle that the user wants to measure, the user pushes a button on the camera to take a photograph and measure the grid.
  • The GPA computer program locates the deformed circle or square and computes the strain.
  • Measured strain data are automatically displayed on a Forming Limit Diagram or section plot.

Also see the GPA-100 Model Quick Reference Card.

What grid patterns can the GPA measure?

Grid shape - the GPA program can measure square grids, butted-circle grids, single-circle grids, or the squares or circles in some mixed grids. If the grids are high quality, all of these work well. If the grid is low quality, single-circle grids work best. Some complicated circle and/or square grid patterns can be measured manually using the GPA camera unit and software.

Grid size - the GPA system can measure grids from 1.6 mm (0.06 inches) to 7 mm (0.25 inches) in size.

How long does it take to make a measurement with the GPA?

On average, it takes about 2 seconds for the GPA to make an automatic measurement. If an automatic measurement cannot be made, the manual feature can be used to make a measurement by identifying several points on the circle or square grid with the mouse. The manual feature usually takes less than 5 seconds per measurement.

If the grid has been damaged in some areas, can it still be measured?

Yes. The GPA has a manual measurement feature which can be used if the program fails to automatically find a circle or square. To make a manual measurement, the user clicks on a few points along a circle or on the corners of a square; the strains are computed from the user-located grid pattern.

How does the GPA compare to the ASAME systems?

The ASAME systems measure both surface strain (e1, e2) and surface geometry (x, y, z). The GPA measures surface strain only (e1, e2).

The GPA makes a single measurement much faster than the ASAME system. The ASAME systems measure a large area much faster and with more types of data than the GPA.