Conventional analytical and numerical methods for the mechanical properties of helical threads are relied on many assumptions and approximations and thus hardly yield satisfied results. A parameterized 3D finite eleme...Conventional analytical and numerical methods for the mechanical properties of helical threads are relied on many assumptions and approximations and thus hardly yield satisfied results. A parameterized 3D finite element model of bolted joints with real helical thread geometry is established and meshed with refined hexahedral elements. The Von Mises plasticity criterion, kinematic hardening rule of materials and interfacial contacts are employed to make it possible for the suggested model be able to approach real assembly conditions. Then, the mechanical properties of bolted joints with different thread pitches, thread numbers and modular ratios are investigated, including the contact pressure distribution at joint interfaces, the axial load distribution and stress concentration in screw threads during the loading and unloading process. Simulation results indicate that the load distribution in screw threads produced by the suggested model agrees well the results from CHEN’s photoelastic tests. In addition, an interesting phenomenon is found that tightening the bolt with a large preload first and then adjusting the clamping force by unloading can make the load distribution more uniform and reduce the maximum residual equivalent stress in thread roots by up to 40%. This research provides a simple and practical approach to constructing the 3D finite element model and predicting the mechanical properties of helical thread connection.展开更多
Based on determination for surface tension of organosilicone solution and its expansion on the solid surface, the biological activity of 5% emameetin ben- zoate WDG with organosilicone against beet armyworm was determ...Based on determination for surface tension of organosilicone solution and its expansion on the solid surface, the biological activity of 5% emameetin ben- zoate WDG with organosilicone against beet armyworm was determined by spraying method to study their synergistic activity. The results showed that organosilicone significandy reduced surface tension of aqueous solution, and the surface tension was reduced to 26raN/m as the concentration of organosilicone was 0.01%. The organosilicone significantly raised expansion of liquid drops on solid surface, and the expansion diameter of 10 μL 0.01% organosilicone was 34 ram. The indoor toxicity results indicated that when addition dosage of organosilieone was 1% -5%, synergistic activity of 5% emamectin benzoate WDG with organosilicone against beet armyworm was significant, and increase extent of synergistic activity slowed down as organosilieone dosage was higher than 5%. Field experiment showed that the control efficacies of 5% emamectin benzoate WDG ＋5% organosilicone 33 mg/ L against beet armyworm were 81.57% and 82.66% after spraying for 3 and 7 d respectively, which were significandy better than treatments of 5% emamectin benzoate WDG 33 rag/L, 24% metaflumizone SC 96 mg/L, 5% chlorantranilip- role SC 33 mg/L, 20% tlubendiamide WDG 40 mg/L and 15% indoxacarb EC 43 mg/L.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 50935006)Major Project of High-end CNC Machine Tool and Basic Manufacturing Equipment of China (Grant No.2011ZX04016-031)National Hi-tech Research and Development Program of China (863 Program, Grant No. 2012AA040701)
文摘Conventional analytical and numerical methods for the mechanical properties of helical threads are relied on many assumptions and approximations and thus hardly yield satisfied results. A parameterized 3D finite element model of bolted joints with real helical thread geometry is established and meshed with refined hexahedral elements. The Von Mises plasticity criterion, kinematic hardening rule of materials and interfacial contacts are employed to make it possible for the suggested model be able to approach real assembly conditions. Then, the mechanical properties of bolted joints with different thread pitches, thread numbers and modular ratios are investigated, including the contact pressure distribution at joint interfaces, the axial load distribution and stress concentration in screw threads during the loading and unloading process. Simulation results indicate that the load distribution in screw threads produced by the suggested model agrees well the results from CHEN’s photoelastic tests. In addition, an interesting phenomenon is found that tightening the bolt with a large preload first and then adjusting the clamping force by unloading can make the load distribution more uniform and reduce the maximum residual equivalent stress in thread roots by up to 40%. This research provides a simple and practical approach to constructing the 3D finite element model and predicting the mechanical properties of helical thread connection.
文摘Based on determination for surface tension of organosilicone solution and its expansion on the solid surface, the biological activity of 5% emameetin ben- zoate WDG with organosilicone against beet armyworm was determined by spraying method to study their synergistic activity. The results showed that organosilicone significandy reduced surface tension of aqueous solution, and the surface tension was reduced to 26raN/m as the concentration of organosilicone was 0.01%. The organosilicone significantly raised expansion of liquid drops on solid surface, and the expansion diameter of 10 μL 0.01% organosilicone was 34 ram. The indoor toxicity results indicated that when addition dosage of organosilieone was 1% -5%, synergistic activity of 5% emamectin benzoate WDG with organosilicone against beet armyworm was significant, and increase extent of synergistic activity slowed down as organosilieone dosage was higher than 5%. Field experiment showed that the control efficacies of 5% emamectin benzoate WDG ＋5% organosilicone 33 mg/ L against beet armyworm were 81.57% and 82.66% after spraying for 3 and 7 d respectively, which were significandy better than treatments of 5% emamectin benzoate WDG 33 rag/L, 24% metaflumizone SC 96 mg/L, 5% chlorantranilip- role SC 33 mg/L, 20% tlubendiamide WDG 40 mg/L and 15% indoxacarb EC 43 mg/L.
