In order to study the hot melt extrusion process in fused deposition modeling(FDM),this study mainly explores the effects of printing temperature,heated block length,feeding speed on the exit morphology and mechanical...In order to study the hot melt extrusion process in fused deposition modeling(FDM),this study mainly explores the effects of printing temperature,heated block length,feeding speed on the exit morphology and mechanical properties of FDM printed Polylactic acid(PLA)samples.High-speed camera is used to capture the exit morphology of molten PLA just extruded to the nozzle.According to exit morphology,the outlet states of extruded molten material can be divided into four categories,namely,bubbled state,coherent state,expanding state,and unstable state.Tensile test results show that printing temperature,heated block length and printing speed have significant influence on tensile properties and fracture mode of FDM printed samples.When the heated block length is 15 mm and 30 mm,there is a ductile-brittle transition in fracture mode with the increase of printing speed.The printing process window under different heated block lengths and printing temperatures has been figured out and the distribution of printing process window under different printing speeds has been discussed.There is a maximum printing process window under the heated block length of 30 mm.This finding provides a frame work for performance prediction of FDM printed parts and theoretical guidance for expanding the scope of printing process window.展开更多
The corrosion fatigue behavior of epoxy-coated Mg-3Al-1Zn alloy was investigated in air and 3.5 wt%NaCl solution. Epoxy coating as a new method was used to improve the corrosion fatigue property of the material.Result...The corrosion fatigue behavior of epoxy-coated Mg-3Al-1Zn alloy was investigated in air and 3.5 wt%NaCl solution. Epoxy coating as a new method was used to improve the corrosion fatigue property of the material.Results show that the fatigue limit（FL） of the coated specimens is higher than that of the uncoated specimens in3.5 wt% NaCl solution because of the strengthening and blocking functions of the epoxy coating. The FL of the coated specimens in 3.5 wt% NaCl solution is as high as that in air. It implies that the coated specimens are not as sensitive to the environment as the magnesium alloy. The low tensile strength and the short elongation of the pure epoxy coating lead to that the fatigue crack of the coated specimen is always initiated from the epoxy-coating film Pores and pinholes accelerate the fatigue crack initiation process. Pinholes are caused by the corrosion reactions between the epoxy coating and the NaCl solution.展开更多
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.11502269 and 11672304)plan of Beijing Municipal Commission of Science and Technology(Grant No.Z181100003818015).
文摘In order to study the hot melt extrusion process in fused deposition modeling(FDM),this study mainly explores the effects of printing temperature,heated block length,feeding speed on the exit morphology and mechanical properties of FDM printed Polylactic acid(PLA)samples.High-speed camera is used to capture the exit morphology of molten PLA just extruded to the nozzle.According to exit morphology,the outlet states of extruded molten material can be divided into four categories,namely,bubbled state,coherent state,expanding state,and unstable state.Tensile test results show that printing temperature,heated block length and printing speed have significant influence on tensile properties and fracture mode of FDM printed samples.When the heated block length is 15 mm and 30 mm,there is a ductile-brittle transition in fracture mode with the increase of printing speed.The printing process window under different heated block lengths and printing temperatures has been figured out and the distribution of printing process window under different printing speeds has been discussed.There is a maximum printing process window under the heated block length of 30 mm.This finding provides a frame work for performance prediction of FDM printed parts and theoretical guidance for expanding the scope of printing process window.
基金financially supported by the National Natural Science Foundation of China (Nos. 51001079, 21201129, 51208333, and 51374151)Natural Science Foundation of Shanxi Province (No. 201101102002)+1 种基金the China Postdoctoral Science Foundation (No. 20100471586)the Doctoral Fund of Ministry of Education of China (No. 20091402110010)
文摘The corrosion fatigue behavior of epoxy-coated Mg-3Al-1Zn alloy was investigated in air and 3.5 wt%NaCl solution. Epoxy coating as a new method was used to improve the corrosion fatigue property of the material.Results show that the fatigue limit（FL） of the coated specimens is higher than that of the uncoated specimens in3.5 wt% NaCl solution because of the strengthening and blocking functions of the epoxy coating. The FL of the coated specimens in 3.5 wt% NaCl solution is as high as that in air. It implies that the coated specimens are not as sensitive to the environment as the magnesium alloy. The low tensile strength and the short elongation of the pure epoxy coating lead to that the fatigue crack of the coated specimen is always initiated from the epoxy-coating film Pores and pinholes accelerate the fatigue crack initiation process. Pinholes are caused by the corrosion reactions between the epoxy coating and the NaCl solution.
