Carbon nanotube fibers can be fabricated by the chemical vapor deposition spinning process.They are promising for a wide range of applications such as the building blocks of high-performance composite materials and micro-electrochemical sensors.Mechanical twisting is an effective means of enhancing the mechanical properties of carbon nanotube fibers during fabrication or by post processing.However,the effects of twisting on the mechanical properties remain an unsolved issue.In this paper,we present a two-scale damage mechanics model to quantitatively investigate the effects of twisting on the mechanical properties of carbon nanotube fibers.The numerical results demonstrate that the developed damage mechanics model can effectively describe the elastic and the plastic-like behaviors of carbon nanotube fibers during the tension process.A definite range of twisting which can effectively enhance the mechanical properties of carbon nanotube fiber is given.The results can be used to guide the mechanical twisting of carbon nanotube fibers to improve their properties and help optimize the mechanical performance of carbon nanotube-based materials.