Multi-walled Carbon Nanotubes Cement Base Composite Material Fatigue Performance Study

Cement based composite materials are brittle ones with low tensile strength.In order to improve the mechanical properties of cement based composite materials,many researchers have added macro fibers into it.The destruction of cement based composites is mostly caused by the expansion of micro cracks under load.Multi-walled carbon nanotubes contians nano-fiber with excellent mechanical properties,it is a kind of toughening material that improves the structure of the matrix microscopically.Multi-walled carbon nanotubes can figure out problems such as the emergence and development of microporous cracks that can not be obstructed.In this paper,different amouts of multi-walled carbon nanotubes were incorporated into cement based composites,and after a certain test procedures,specimens of 40 mm×40 mm×160 mm trabecules were made.The effect of different amounts of multi-walled carbon nanotubes on the mechanical properties of the specimens was studied,and the optimum value of the dosing amount was obtained.By analysing the distribution of multi-walled carbon nanotubes in the matrix through SEM,the improvement of the microstructure of the cement matrix by carbon nanotubes was studied.The fatigue test was performed on six groups of specimens with different amounts of multi-walled carbon nanotubes,and the effects of the amount of multi-walled carbon nanotubes added on the fatigue life of the specimens were studied.Then the envelope diagrams of strain changes with the number of cyclic loading were analyzed.The two parameter Weibull distribution statistical theory was used to analyze the distribution of fatigue life.The parameters of the fatigue equation were obtained with different failure probability p′(survival rate p),and analyzed the curve p′-S-N.The main conclusions of this study are:(1)The mixing of a small amount of multi-walled carbon nanotubes can effectively improve the mechanical properties of cement based composites materials.Carbon nanotubes can reduce and impede the generation and development of microcracks,it can also fill the microvoids in the matrix.The cement is connected with the carbon tube,the carbon tube is connected with the carbon tube,and a network system is constructed by the force of chemical bond in the cement base.The multi-walled carbon nanotubes act as a bridge and has the function of pulling out.(2)Under different stress levels,the strain fatigue life curves of carbon nanotubes with different amounts are divided into three stages,namely,strain rapid generation stage,strain stable development stage,and strain rapid development stage.(3)The correlation coefficient of fatigue life regression analysis of multi-walled carbon nanotubes cement matrix composites materials is close to 1,as linear correlation,comply with Weibull distribution regularity.(4)Considering the fatigue life under different failure probabilities,regression analysis of the relationship schema of double logarithmic fatigue equations and establishment of a double logarithmic fatigue equation in the condition of 5.0’p(28).The correlation coefficient is analyzed and it is found that the double logarithmic fatigue equation was suitable for plain cement composite specimens and specimens with less multi-walled carbon nanotubes.