Development of testing methods for the fatigue crack propagation in steel shot reinforced resins

Abstract

The increasing traffic load on highway bridges provides a need for replacement or improvement of the bridge decks. The design of a new bridge deck using fibre-reinforced polymer (FRP) bridge decks raises questions on the connection of a FRP bridge deck to a steel superstructure. At the Tu Delft a bolted connector injected with steel reinforced resin (iSRR) is developed for the connections between steel superstructure and FRP bridge deck. Steel reinforce resin (SRR) is a combination of steel shot (SS) and resin. The steel shot is added to achieve higher stiffness and reduce the total production cost. The iSRR connection can be produced using multiple methods. For all production methods, the SRR in the connector is produced by pouring SS around the bolt followed by the injection of the resin. The iSRR connector should accompany the fatigue resistance of the FRP bridge deck. A better understanding of crack propagation can help to increase the life expectancy of iSRR connections. However, no standardized method for the testing of crack propagation in SRR exists. This research attempts to find a crack propagation testing method for SRR by investigating the use of compact tension (CT) and semi-circle bending (SCB) testing for the SRR material. For the production 5 different casting methods were compared. From these methods, the closed mould injection casting and ring mould injection casting showed the most promising production method for the production of complicated forms in SRR. From this testing the need to use modified forms of CT and SCB was found, resulting in the use of a doubly tapered compact tension specimen (2TCT) and the design of the short tapered notched beam specimen (STNB). The modified specimen forms are tested under varying loading types. The 2TCT specimen is tested under load controlled, and displacement controlled loading. From this, the incremental increasing loading type was suggested. This loading type was used in the testing of STNB specimens. Lastly with the use of FEA the stress intensity factors for the modified test forms were validated. The validation was done on the analytical formulas provided by literature for the unmodified forms. From this research, it can be concluded that the closed mould injection casting and ring mould injection both achieve good results for the production of complicated shapes with SRR. The incremental increasing displacement loading method leads to more stable crack growth. The 3 point bending testing type leads to the most promising results for crack propagation. With a linear correlation in the small range of K = 20-60 resulting in a Paris Law with 𝐶 = 4.3𝑒 − 7 and 𝑚 = 2.41. It is recommended for further crack propagation testing to produce specimens with the least amount of voids. The voids are expected to have a high contribution to the big spread of data found during the testing. For better insight, the voids in the tested specimens could also be investigated.