Laboratory Testing: SMARTProfile sensitivity test

Case study: DiTeSt System

SMARTProfile applied on metallic structure
Comparison with theoretical predictions
Evaluation of sensitivity and strain transfer

Project Description

Summary: SMARTprofile sensor sensitivity test on metallic beam subject to deflection. Strain profile is measured using the DiTeSt system and compared with theoretical predictions.

Clients: SMARTEC SA

Place: Lugano (Switzerland)

Period: 2006 - N/A

Installation: SMARTEC SA

Structure's short description: The tests were performed using a five meters long aluminum beam with cross-section 25x25 mm. The first and the last meter of the beam were reinforced with small additional beams with cross-section of 6x6 mm. The PE SMARTprofile was glued to the beam in a zig-zag manner. The total length of the applied PE SMARTprofile is 25 m approximately. Free zones were left (see blue color in the Figure) in order to make ?smooth? transition from connectors to the sensor and from one sensor position to another (up ? lateral ? down). The PE SMARTprofile was glued to the beam respecting the standard installation procedure. The beam was installed between two massive tables by mean of G-cramps. The clear distance between the tables was 3 m, and it coincided with the middle 3 m of the beam. The first and the last meter of the beam were fixed to each to one table using two G-cramps at beginning and at the end of its length. Taking into account the way of fixation and the higher bending stiffness of the first and last meter of the beam, one can considered that the static system of the middle three meters of the beam as bi-encastered. The load was applied in the middle of the span using the weights and controlled with dynamometer. The displacement in the middle of the span was measured using mechanical dial gage.

Aim of monitoring: The big issue with distributed strain sensors is the transfer of the strain from the monitored structure to the optical fiber. In case of PE SMARTprofile, the polyethylene material serves as a strain transfer medium. In order to evaluate the performance of the PE SMARTprofile and its different configurations used commonly in practice, several straining tests were performed. Two tests were performed in order to examine the performance of the sensor. The heavy load test confirmed the ability of sensor to qualitatively and quantitatively describe the strain distribution in the structures. The 1 mm detection test confirmed the capability of the system to detect and localize small deformation of the structure. The results of the tests are compared with values obtained by numerical predictions.

Number of sensor: 2

Main Results: The assumed static system of the beam is bi-encastered simple beam with span of 3 m, constant cross-section of 25x25 mm, loaded in the middle of the span with vertical force. The influence of spatial resolution is taken into account during the comparison between the theoretical and measured strain profiles. Small discrepancies in comparison between theoretical and measured values were noticed and explained by imperfections due to not full encastering at extremities of the beam, sudden changes of strain distribution, imperfection of sensor shape etc. However, taking into account the influence of these imperfections the heavy load test is considered as successful and confirmed the ability of sensor to qualitatively and quantitatively describes the strain distribution in the structures. With the similar comments as in case of the heavy load tests it is concluded that the 1 mm detection test confirmed the capability of the system to detect and localize small deformation of the structure. In addition, the installation of the sensor by gluing have show good performance in terms of strain transfer from the structure (beam) to the PE body of sensor, and the PE body of the sensor itself was good medium of strain transfer to the strain sensing optical fibers.

Simplified schematic position of SMARTprofile on the beam, lateral veiw and two characteristic cross-sections

Photographs taken during the test showing beam with sensors, encastering point, and the dial gage and load

Comparison between the non-dimensional functions that characterize the theoretical strain distribution (blue color) and expected reading from sensor due to influence of spatial resolution (red color)

Heavy load test, average strain registered by different strain fibers; S1-up and S2-up are comparable, S1-down and S2-down are comparable, and all are comparable with theoreticaly expected strain distribution

1mm movement detection test; although close to resolution of the system, 1 mm movement in the middle of the beam is clearly detected

Bibliography:

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