Today, there is a growing interest in wood as a sustainable building material. In the face of this trend, the Department of civil engineering at the University of Queensland and related structural laboratories have developed a new innovative structure. Thin layer fiber reinforced polymer (FRP) is combined with veneer or plank to create high performance, light weight and easy construction structural parts. This new composite is called hybrid FRP wood (HFT) thin-walled structure. In addition, in order to study the structural behavior of this kind of beam, four point bending tests were carried out on a series of beam samples. In order to measure the strain and displacement accurately, both contact and non-contact systems are used.  

Four point bending test was carried out on HFT beam. The main purpose of the test is to find out the bending capacity, structural behavior and failure mode of these beams when they are bent. The 3D digital image correlation system is used to focus on the area with the largest stress, and it has been proved that the full field data and 3D measurement are of great value. The traditional 1D strain gauges and linear potentiometers can obtain the required measurement results in the key beam area which does not need a complete 3D data set.

The universal testing machine of the university is used in the displacement control to cause appropriate load on the HFT beam test sample. In order to collect the measurement data of all critical points on the beam completely and accurately, the above-mentioned equipment has been used. In the figure above, the upper and lower flanges of the beam are connected with strain gauges. The linear potentiometer is also connected to the lower flange to collect the displacement of the beam in the loading direction. Finally, the stereo camera of 3D DIC system is installed horizontally to measure the whole field displacement and strain distribution of the front panel of the beam. The front spoke is the most important analysis area in this test.

This system configuration adopts two different but equally beneficial ways, which is very efficient. From the perspective of data requirements, strain gauges and potentiometers are used in the sample area with sufficient data at the target point, while full field (continuous) DIC data are used in the area where anisotropy and / or out of plane displacement may occur. In this example, the contact device is also useful in all areas outside the camera's field of view. From the perspective of total test time, the test setup time is significantly saved by using DIC instead of strain gauge in the spoke area. Using the full field function of DIC, the setting speed in the same field of view is always faster than connecting multiple strain gauges.

One advantage of multiple measurement systems has not been fully utilized, which is the area of adjacent and redundant data. In this scheme, the strain continuity of the outer layer of fiber reinforced polymer (FRP) is studied by comparing the upper and lower strain gauge data with the DIC data of the upper and lower panel area. The out of plane displacement data of DIC is compared with the redundant displacement data of potentiometer. To what extent can adjacent data and redundant data be used to verify test results, and confidence in the final analysis can be established.

1 for more detailed information on this new type of building structure called "hybrid fiber reinforced polymer timber thin walled structure members", you can read the journal article "hybrid fiber reinforced polymer timber thin walled structure members" first published by Fernando et al. On December 15, 2017. Doctoral student Weiqi Cui and chief scientific officer Chris Russ made additional contributions to the case study.