Abstract
Currently, research on structural health monitoring systems is focused on direct integration of the system into a component or structure. The latter results in a so-called smart structure. One example of a smart structure is a component with integrated strain sensing for continuous load monitoring. Additive manufacturing, or 3D printing, now also enables such integration of functions inside components. As a proof-of-concept, the Fused Deposition Modeling (FDM) technique was used to integrate a strain sensing element inside polymer (ABS) tensile test samples. The strain sensing element consisted of a closed capillary filled with a fluid and connected to an externally mounted pressure sensor. The volumetric deformation of the integrated capillary resulted in pressure changes in the fluid. The obtained pressure measurements during tensile testing are reported in this paper and compared to state-of-the-art extensometer measurements. The sensitivity of the 3D printed pressure-based strain sensor is primarily a function of the compressibility of the capillary fluid. Air- and watertightness are of critical importance for the proper functioning of the 3D printed pressure-based strain sensor. Therefore, the best after-treatment procedure was selected on basis of a comparative analysis. The obtained pressure measurements are linear with respect to the extensometer readings, and the uncertainty on the strain measurement of a capillary filled with water (incompressible fluid) is ±3.1 µstrain, which is approximately three times less sensitive than conventional strain gauges (±1 µstrain), but 32 times more sensitive than the same sensor based on air (compressible fluid) (±101 µstrain).
Highlights
Strain measurements are used in multiple steps of engineering projects
A test sample can be designed to be compatible with most of the available strain measurement techniques. When it comes to design validation, design freedom cannot be addressed via a validation technique, and strain measurements have to be carried out at a given location on the component, with the corresponding shape and size
The tensile test samples were designed in order to compare the state-of-the-art extensometer results with the strain measurements of the proposed monitoring system
Summary
Strain measurements are used in multiple steps of engineering projects. Material characterization, design validation and load monitoring of structures are just some examples. Most strain sensors (e.g., strain gauges, extensometers, and Fibre Bragg Gratings (FBG)) are externally installed, which often limits their range of use. A test sample can be designed to be compatible with most of the available strain measurement techniques. When it comes to design validation, design freedom cannot be addressed via a validation technique, and strain measurements have to be carried out at a given location on the component, with the corresponding shape and size. The use of strain sensors becomes even more complicated when continuous load monitoring is involved—a new and evolving monitoring technique that forms the basis of condition-based
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