Fundamental analysis of the machining process of a composite material made of concrete and CFRP with diamond grinding tools

• Applicant: Professor Dr.-Ing. Dirk Biermann
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 391502479

Although concrete is able to bear high compressive loads, its possibility to withstand tensile loads is very low. Hence, in construction elements steel bars are embedded as reinforcement. To avoid corrosion, a thick concrete covering of the steel bars is necessary. Due to the substitution of these steel elements with elements made of carbon fibre reinforced plastic (CFRP) it is possible to reduce the amount of the concrete covering. This provides the opportunity for thinner and lighter construction elements made of reinforced concrete. Regarding recent developments in the construction industry and existing research programs it can be assumed that the amount of CFRP reinforced concrete elements will increase in the next few years and therefore efficient cutting toolsfor this kind of composite material are required. Within this research program it is planned to conduct basic analysis work regarding the machining process of the new composite material madeof CFRP and concrete. Scratch tests are a fundamental testing method to understand the fundamental mechanism of material removal. Therefore path- and force-controlled tests with single diamond grains will be carried out to analyse the fundamental interdependencies of the machining process. Diamond grains with defined shape are used to estimate the mechanical loads and the occurring wear. Further knowledge is gained by conducting tests with single diamond impregnated segments. Based on the single grain scratch tests, it is planned to carry out path- and force controlled tests.Within the investigations, the mechanical and thermal load during the cutting of CFRP reinforced concrete will be analysed. It can be assumed that high process temperatures probably lead to a thermal damage of the CFRP-matrix material as well as in clogging of the segments. Furthermore, the feasibility of alternative cooling strategies can be assessed. Additionally, investigations on the lateral wear of the segments due to fraying and uncut fibres of the CFRP are of special interest, especially how these influences may reduce the tool life. Based on the quantitative and qualitative results of single grain scratch tests and diamond impregnated segment tests single- and multi-scale process models will be generated. As an example the dependency of material and grain alignment and its influence on the material removal will be analysed. This knowledge can be used for the optimisation of the machining process of the multiphase material CFRP reinforced concrete. Due to the comprehensive analysis of single and multi-grain tests a global understanding of the specific mechanisms of material removal is reached.Hence, these investigations constitute the fundamental basis for the development of efficient diamond tools for the machining of CFRP reinforced concrete.

• DFG Programme: Research Grants