Numerical study of Brazilian tests of UHPFRC by using elements with embedded cohesive crack and cohesive joint elements

Ultra-high performance fibre-reinforced concrete (UHPFRC) is an emergent material with outstanding mechanical properties which still needs research regarding the characterisation and modelling of its fracture behaviour.The present work focusses on the determination of the tensile strength, conceived as the stress corresponding to crack initiation.The Brazilian test is a convenient experimental option in the case of plain concrete which provides a sufficient accurate value of the tensile strength obtained from the maximum load of the test, provided that it is performed with the adequate conditions of geometry and load rate, because the peak load occurs very soon after crack initiation.However, in the case of fibre-reinforced materials, the peak load can occur much after crack initiation and so the apparent splitting strength be much higher than the true tensile strength.Nevertheless, in previous experimental and numerical works it has been assessed that a local maximum occurs in many cases at a splitting stress close to the tensile strength of the material.It means that the stress corresponding to initiation of cracking can be determined in Brazilian tests provided that the test is properly designed and instrumented taking into account the size-effect to ensure detection of the local maximum.As shown in a previous numerical study, numerical simulations are an essential tool for this purpose; however, a systematic parametric study is still necessary.The current work analyses the main alternatives for dimensionless simulations within the finite element framework COFE (Continuum Oriented Finite Element).In this study, the results of simulations of the Brazilian tests by considering a domain in which all the elements can crack are compared with those obtained by using joint elements with a cohesive behaviour along of the foreseeable cracking plane, and the main aspects of the dimensionless simulations are analysed in detail.