| Aligned steel fibre cement-based composite material(ASFRC),of which the steel fibre in the matrix has the same or similar orientation with the tensile stress,could be a new type of fibre composite material.Comparing to traditional steel fibre cement-based composite materials(SFRC),a perfect fibre alignment in stress direction on ASFRCs will offer the highest fibre efficiency.In addition to increasing the mechanical properties of steel fibre reinforced composite materials significantly,steel fibre orientation distribution can also reduce the dosage of steel fibres,thus decreasing the cost of raw materials greatly.In consideration of the advantages on ASFRC,the size-dependent effects on mechanical properties and fibres distribution has been investigated in this paper.At first,the preparation principle and methods of ASFRCs were introduced.The specimens of different fibre fraction under random and aligned fibre distribution has been casted to investigate the fibre dispersion in this paper.The number of steel fibres on the cross-section and calculating the orientation coefficient have been calculated and the fibres dispersion degree was analyzed by distribution coefficient and fibres distance.The results show that:the direction of steel fibres not only has impact on the number of fibres in cross-section,and also has significant effects on t he distribution coefficient and fibre distance.By regression analysis,the linear relationship was found between distribution coefficient and fibres distance in aligned steel fibre cement-based composite materials.Then,a three-point bending test has been made to investigate the influence of steel fibres distributions on mechanical properties and the size effect of parameters such as flexural strength,normalized deflection,normalized toughness and fracture energy.The test results shown that: the initial cracking load,initial cracking deflection,peak load and deflection corresponding to peak load were improved obviously.On the other hand,it can be seen that the distribution of aligned steel fibre increases crack resistance of the materials evidently from crack failure mode.O n the aspect of parameters study,aligned steel fibre distribution improve the ability of flexural and fracture behavior effectively.The size effect on flexural strength of ASFRCs in this specimen size range can be neglected.The normalized deflection and normalized toughness are not decreasing with the increase of specimen size.For SFRCs,the fracture energy is increasing gradually with the increase of specimen size,and this trend is reflected in ASFRCs more obvious.O n the study of size effect,This paper established a simple power law of the effective K-R model base on Wallin model and fracture mechanics theory for fibre reinforced cement based composites by Mai.The results show that the law obtained by the K-R resistance curves can describe the fracture process of steel fibre cement based composites for different fibre distributions effectively,and the peak load of theoretical results evaluated by law can accord with those of experimental results.The model can provide a new method to study the fracture parameters of steel fibre reinforced cement based composites of size effect.Finally,the influence of steel fibre distribution uniformity on the fracture energy of cement-based composite materials has been investigated.The distribution uniformity of steel fibre in the matrix can be changed through adding an external uniform magnetic field in the process of vibrating.Here,a three-point non-notch beam test was applied to study the fracture energy of steel fibre cement-based composite materials under different steel fibre distribution uniformities.The formulation to describe the relationship between steel fibre distribution uniformity and fracture energy was established when the dosage of steel fibre is 0.9%. |
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