The measurement of Digital Image Correlation (DIC) technology relies on the preparation of random high contrast speckle on the surface of the specimen to obtain the most accurate measurement results. In practice, if the speckle is too sparse, too dense, or too large, it will damage the spatial resolution of the measurement. On the contrary, if the scattered spots are too small and mixed, it may lead to noisy data. In order to reduce measurement noise and uncertainty, it is necessary to prepare an ideal speckle pattern that conforms to the field of view (FOV) scale and camera resolution. The purpose of the VIC speckle preparation kit is to assist users in easily preparing ideal speckle on the surface of the specimen without the need for precise knowledge of the specimen area. This kit is easy to use and flexible, suitable for various application scenarios of VIC-2D or VIC-3D systems. This kit actually eliminates potential measurement deviations caused by improper specimen preparation.

Digital Image Correlation (DIC)relies on a high-contrast random pattern applied to the specimen’s surface to produce the most accurate results. In practice, if the pattern is too sparse, too dense, or the speckles are too large, spatial resolution of the measurement will suffer. Conversely, if the speckles are too small, aliasing may result causing noisy data. To reduce noise and lower uncertainty, the ideal speckle pattern for the desired field of view (FOV) and camera resolution must be applied. TheVIC Speckle Pattern Application Kitenables the user to easily apply the ideal pattern to the surface of the specimen without anypreciseknowledge of sample area. The kit is easy-to-use, flexible, and available for a wide range of applications suitable with your VIC-2D or VIC-3D system. The kit virtually eliminates the potential bias that would result from poor sample preparation.

The speckle preparation kit provided by CSI company includes a series of tools for new and old DIC users to quickly create ideal speckle patterns. For different combinations of fields of view and image collector resolutions, a recommendation table for speckle size is also provided. The items included in the kit are listed below.

The speckle application kit from Correlated Solutions provides an array of tools which can be used by new and experienced DIC users alike to quickly create the ideal speckle pattern. Speckle size suggestion tables for multiple fields-of-view and sensor resolution combinations are also provided. The items included in the kit are shown and listed below.

Six embossing rollers with automatic ink dispensers Six interchangeable adhesive transfer plates and one acrylic handle An ink pad box and an additional bottle of refilled ink Hardware can be customized to create larger speckle patterns according to user needs Six stamp rollers with self-inking inserts Six interchangeable stamps with one acrylic rocker One ink pad with an extra bottle of ink Hardware to create larger dots available upon request

Although there are many speckle pattern preparation techniques available on the market, many of them provide inconsistent or non-standard speckle sizes, which can lead to inconsistent results. This can be particularly disappointing when performing repeated testing. The speckle size generated using CSI's VIC speckle preparation kit is reproducible and consistent, enabling the rapid creation of speckle patterns with predictable and controllable accuracy, thus achieving the highest level of consistent and accurate results

There is a wide range of speckle pattern application techniques, but many provide inconsistent dot sizes from sample to sample, which also yield inconsistent results. This can be especially frustrating when recurring tests are performed. Producing repeatable dot sizes with theVIC Speckle Pattern Application Kitfrom Correlated Solutions provides the ability to quickly create predictable and controlled speckle patterns, which allows for the highest level of accurate and consistent results.

Why is the quality of speckle patterns important for our measurementsWhy Is Your Speckle Pattern Important?

The ideal speckle pattern is high contrast, the speckle distribution is random, the speckle size is consistent, and the black and white distribution density on the surface of the specimen is equal. If all these conditions are met, our measurement focus area can benoisecontrolAt a very low level and capable of tracking measurements with a very high degree of error certainty.

The ideal speckle pattern is high contrast, contains random speckles, consistent dot sizes, and equal amounts of black and white on the sample’s surface. If all of these conditions are met, the area of interest will produce low levels of noise and may be tracked with very high levels of certainty.

The following are examples of how various speckle patterns affect measurement noise. The pattern in the middle area was created using the rollers in the VIC speckle preparation kit, while the patterns on the other two outer areas were created using spray paint. As you can see, the roller from the speckle preparation kit produces high contrast patterns with black and white coverage of approximately 50%, while the pattern created by spray painting only has lower contrast and inconsistent sizes of speckle.

Below is an example of how various speckle patterns can effect measurement noise. The middle pattern was created using a roller from theVIC Speckle Pattern Application Kit, while the patterns on either side were created using spray paint. As you can see, the roller from the speckle pattern kit produces a high contrast pattern with approximately 50% black and white coverage, while the painted pattern produces a lower contrast pattern with inconsistent dot sizes.

Figure 1: Z-value confidence analysis of a flat panel with three different speckle patterns

Figure 1:A relatively flat plate with three different speckle patterns analyzed to show the variable Sigma_Z

Figure 1 shows the two-dimensional data overlay of the variable Sigma_Z, which represents the confidence level of measurements taken in the Z direction (out of plane shape measurement). The closer the Sigma value is to zero, the more likely the displayed value is to be the correct one. The contrast of the pattern in the left area is low and overly delicate, resulting in a high Sigma_Z value, indicating low confidence. The middle area shows a lower Sigma_Z value, indicating high confidence in the measurement. The results in the figure are obvious.

Figure 1 shows a 2D data overlay of the variable Sigma_Z, which is the confidence margin of the measurements taken in the Z direction (out-of-plane shape measurement). The closer Sigma is to zero, the more statistically likely the value shown is indeed the correct value. The outside patterns are low in contrast and overly fine which result in larger Sigma_Z values, which indicates less confidence. The middle pattern shows lower Sigma_Z values, which indicates high confidence in the measurement. The results speak for themselves.

Figure 2: The 3D plot of Sigma_Z shows poor speckle resulting in low confidence intervals and noisy shape measurement results

Figure 2:The 3D plot of Sigma_Z displays how poor patterns create low confidence margins and noisy shape measurements.

Why is Sigma Important?

High Sigma values in VIC-2D and VIC-3D indicate higher measurement uncertainty, which may lead to increased measurement noise in shape, displacement, and strain data. As shown in Figure 2, the Z-value range displayed on both sides of the sample is larger than that of the flat sample, while the deviation displayed in the central area is smaller.

High Sigma values in VIC-2D and VIC-3D indicate higher measurement uncertainty, which can result in an increase in measurement noise in the shape, displacement, and strain data. As Figure 2 shows, the outside patterns show a larger range of Z values of a relatively flat sample, while the center pattern shows much smaller bias.

In Figure 3 below, the data of the variable exx (transverse strain in the X direction) after rigid body rotation is shown, and the result should be 0 strain. The range of strain values displayed in the strain cloud map is much higher in the outer regions on both sides than in the central region, indicating that the measurement of local regions on both sides produces strain noise results that should not exist, which can lead to inaccurate data. This can well illustrate how poor speckle patterns can lead to noise affecting measurements, while good speckle patterns (using speckle kits) can produce better results.

In Figure 3 below data for the variable exx (transverse strain in the X direction) is shown for the same plate after a rigid body translation, where there should be zero strain. The range of strain values shown in the contour plot are much higher on the outside patterns than the center pattern. The result shows that the local strain measurements on the outside patterns are more noisy and will produce data that is less accurate. This is a good illustration of how poor speckle patterns can result in noisy measurements, while favorable patterns (applied with the speckle kit) will produce much better results.

By using the VIC speckle preparation kit, users can obtain the best speckle pattern, resulting in less noise and more accurate data in their results.

By applying the optimal speckle pattern using theVIC Speckle Pattern Application Kityour results will be less noisy and more accurate.

Figure 3: Lateral strain information displayed after rigid body deflection. Due to poor speckle quality on the outer side, the outer side of the board exhibits much higher noise than the middle of the board.

Figure 3: Transverse strain is shown after a rigid body translation. The outsides of the plate display a much higher level of noise than the middle of the plate due to the poor speckle patterns.

VICThe speckle preparation kit will improve your measurement resultsTheVIC Speckle Pattern Application KitWill Improve Your Results:

The VIC speckle preparation kit from Related Solutions, Inc. can help maintain very low noise and high confidence in DIC measurement results. The speckle preparation kit provides new and experienced DIC users with the same ability to create ideal, repeatable speckle patterns for almost any combination of lenses and image collectors with different sizes of fields of view. Having this feature can simplify the specimen preparation process, ensure consistency in repeated test results, and work with VIC-2D or VIC-3D systems to achieve consistent low strain noise for all measurementsresult.

TheVIC Speckle Pattern Application Kitfrom Correlated Solutions, Inc. can help produce very low noise and very high confidence results for DIC measurements. The speckle kit allows both newandexperienced DIC users to create ideal and repeatable patterns for many fields of view for nearly any lens and sensor size combination. Having this capability can streamline the sample preparation process, ensure consistent patterns for recurring tests, and provide a means to obtain a consistently low strain noise floor for all measurements acquired with your VIC-2D or VIC-3D system.

VIC Speckle Tool Kit ParametersThe VIC Speckle Pattern Specifications: