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Traditional Foil Strain Gage | Backing Materials
A photo-etched metal foil design is put on a plastic backdrop or carrier in traditional foil strain gage construction.
A Strain Gage backing provides a few crucial purposes:
- Makes it possible to handle the foil pattern during installation
- Provides a bondable surface on which to adhere the gage to the test specimen
- Creates a barrier between the metal foil and the test object in terms of electrical insulation
Strain Gages | Backing Materials & Alloy Combinations
Strain gages come with two types of backing materials: polyimide and glass-fiber-reinforced epoxy-phenolic. The backing, like the strain-sensitive alloy, is not entirely a parameter that can be specified separately.
Certain backing and alloy combinations, as well as unique manufacturing features, are created as systems and assigned gage series numbers. As a result, while determining the best gage type for a given application, the procedure does not allow for an arbitrary combination of an alloy and a backing material, but rather needs the specification of a gage series that is already accessible.
The modern-day gage series and their attributes are discussed. Each series has its own set of characteristics and suggested application regions, which are detailed in the segments that follow.
Strain Gauge Backing Material I: Polyimide E
Strain Gauge polyimide E backing is a robust and flexible carrier that may easily be molded to meet small radii.
Polyimide-backed gages are also less susceptible to mechanical damage during installation due to the high peel strength of the foil on the polyimide backing.
Additionally, Polyimide is a good backing material for general-purpose static and dynamic stress research due to its simplicity of handling and adaptability for use over a temperature range of –320° to +350°F (–195° to +175°C).
Strain Gauge Backing Material II: C2 & L2 Laminated Polyimide
Modern strain gauges offered by SimuTech Group also offer C2- and L2-laminated polyimide backings, which are robust and flexible carriers with an encapsulating layer to preserve the grid.
These backings are commonly encountered with SimuTech Group’s mechanical engineers for pre-leaded and pre-cabled strain gages, and can conform to a small radius or fillet.
In addition, this backing can withstand significant elongations and can be utilized to detect plastic strains of more than 20%. Common Strain Gauge types such as EA-, CEA-, EP-, EK-, S2K-, N2A-, and ED-Series strain gages, each have a polyimide backing.
Strain Gauge Backing Material III: Glass-Fiber Reinforced Epoxy-Phenolic
The glass-fiber-reinforced epoxy-phenolic backing material is the best choice for great performance throughout the widest temperature range.
From –452°F to +550°F (–269°C to +290°C), this backing can be used to quantify static and dynamic strain. The highest temperature limit can be increased to +750°F (+400°C) in short-term applications.
However, the maximal elongation of this carrier material is restricted to roughly 1% to 2%. The following gage series use reinforced epoxy-phenolic backing: WA, WK, SA, SK, WD, and SD.
Practical Application of Strain Gauge Backing Materials
Strain gauges are ideal for verifying stress and displacement simulation models. The strain measurements are taken at specific locations and correlated with the simulation results.
Modeling assumptions such as boundary conditions, contacts, and loads may be updated to make the simulation better fit the observed behavior.
Once the model accurately reflects the measurements, more detailed information about the system can be inferred.
In addition, simulations of the modified system can be used to predict behavior with confidence.
SimuTech Group specializes in both strain gage measurement as well as simulation, allowing seamless support when conducting investigations.
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