Effects of Different Test Setups on the Experimental Tensile Behaviour of Basalt Fibre Bidirectional Grids for FRCM Composites

Fibre-reinforced cementitious matrix (FRCM) composites have been effectively used during the last ten years for the strengthening of existing concrete and masonry structures. These composite materials are made of medium- and high-strength fibre meshes embedded in inorganic matrices. Synthetic fibres are the ones that are currently the most used; however, natural fibres, such as basalt fibres, have recently been receiving growing attention. This work presents an extensive experimental study on the mechanical characterisation of a primed basalt fibre bidirectional grid. Fifty monotonic tensile tests on basalt grid strips were performed by varying different parameters, such as the dimension of the specimens, the clamping system, the measurement system and the test rate. Some of the tests were carried out using a video-extensometer to measure each specimen’s strain. The aim of the study was to find the most suitable setup for the tensile characterisation of basalt textiles, in particular, to prevent slippage of the samples at the gripping area and fully exploit the tensile capacity of the grid.

Characterization of tensile property of high-performance fiber bundles combined with epoxy resin using advanced video extensometer

The increased desire to use high-performance fibers in the fields of industry and aerospace requires better understanding of their mechanical behaviors, especially in polymer matrix composite structure. By means of an advanced video extensometer using digital image correlation, the tensile properties of six kinds of high-performance organic and inorganic fiber bundles combined with epoxy resin were successfully determined in this paper, which have testing difficulties using contacting extensometer because of curved surface and small diameter of sample. The advanced video extensometer system was initially used for three kinds of carbon fibers impregnated and cured with epoxy resin to determine the optimum experimental conditions. The comparative tests demonstrate that the accuracy of the results is affected by light source and sampling frequency, but independent on crosshead speed. The tensile properties of other five kinds of epoxy impregnated fibers were subsequently measured using optimal conditions. The results show excellent agreement with the measurement of contacting dynamic extensometer for all studied fibers, and both relative error of Young’s modulus and elongation at break are in acceptable ranges. The capability of the advanced video extensometer system to record real-time, high-accuracy, and complete strain enables it to directly measure elongation. Then, Young’s modulus at different strain ranges was further studied. Different changing trends of Young’s modulus of various impregnated fibers with increasing strain were seen, which are related to the changes of fiber structure during testing.

Research of Edge Detection Algorithm Based on Canny Algorithm and Hough Transform

In order to solve the difficulty of low contrast feature extracting between labeled features and background, a new method combined the Hough transform and Canny algorithm is put forward for tensile test using the video extensometer, and a new algorithm edge detection is also obtained based on Canny an feature region tracking as well. The algorithm has proved to be a high positioning accuracy and computational efficiency in the test.