Design method for fluid viscous dampers

A basic design method of doubly acting fluid viscous dampers with double guide bars is presented. The flow of the viscoelastic fluid between two parallel plates, one of which is started suddenly and the other of which is still, is analyzed. According to this solution, the velocity and the shear stress of the fluid at the fringe of the piston are solved approximately. A mathematical model of viscous dampers is derived, and the shock test is carried out. From experimental results, the parameters of the mathematical model are determined. Consequently, a semi-empirical design equation is obtained. Applying this equation to a certain practical damper, the damping material is chosen and the physical dimensions of the damper are determined. Shock tests using this damper are performed. Theoretical results are in good agreement with experimental results, which validates the reliability of the calculated physical dimensions of the specimen damper and the validity of the basic design equation. An erratum to this article can be found at     

关于物理潜蚀作用及其概念模型的讨论

在对国内外物理潜蚀作用相关文献进行调研的基础上回顾了潜蚀作用的研究历史,对目前物理潜蚀作用研究中存在的问题进行了总结。指出潜蚀工程地质问题在各类工程建设活动中已经变得越来越突出,但由于潜蚀作用发生环境的多样性、作用方式的复杂性、发生过程的随机性等原因,造成实际应用中将各种潜蚀作用尤其是物理潜蚀作用过程的概念经常混淆。对"管涌"、"渗透压密"、"接触管涌"、"接触冲刷"、"流土"、"突涌"、"接触流土"、"流砂"、"流滑"等物理潜蚀作用的发生机理进行了深入细致的分析,在此基础上对目前一些界定不严格的物理潜蚀相关概念进行了辨析和澄清,初步建立了清晰的物理潜蚀作用概念模型,为潜蚀工程地质进一步研究奠定了基础。     

Design and mechanical characteristics analysis of a new viscous damper for piping system

In this paper, the design of a new viscous damper is presented and its mechanical characteristics are investigated experimentally. The motion equation of a system consisting of a drop machine and the damper is set up. By numerically simulating this equation, the curve of the damper cavity generatrix is obtained on the assumption that the resisting force is constant. Then the new damper with big capacity and high-energy dissipation rate is designed. Drop tests using this damper and a Pro225-damper bought in the market are performed, respectively. On one hand, the experimental resisting forces of the new damper approximate constants, which illustrates that the simulation is viable. On the other hand, some advantages of the new damper over the Pro225-damper are found.     

Slow crack growth resistance of modern PA-U12 grades measured by cyclic cracked round bar tests and strain hardening tests

A critical failure mechanism in long-term applications of plastic structures, such as piping systems, is considered to be crack initiation and subsequent Slow Crack Growth (SCG). Thus, safe installation and operation during service lifetime of such structures are not conceivable without the knowledge of the resistance against SCG for any new material, like Unplasticized PolyAmide 12 (PA-U12). Unfortunately, long-term static tests at elevated temperatures lead to unreasonably long test times and measurements may also be affected by thermal aging and hydrolysis. Against this backdrop, the current study examines two accelerated test methods, namely the cyclic Cracked Round Bar (CRB) test as well as the Strain Hardening (SH) test, in order to characterize the SCG behavior. Both were originally developed for PolyEthylene (PE) and successfully implemented in recent years. While the cyclic CRB test measures SCG directly, accelerated through cyclic loading, the SH test quantifies the molecular disentanglement resistance, which determines craze formation and breakdown. The focus of this work was initially put on the extension of the CRB test towards PA-U12 grades, checking the occurrence of actual crack initiation and propagation. Afterwards a correlation to SH test results was done in terms of SCG resistance. Thereby, adequate test conditions were developed and the influence of the Molecular Weight (MW), expressed by the Viscosity Number (VN) of the PA-U12 grades, was considered. Results confirm the suitability of each method to rank SCG resistance and show a good correlation of the abovementioned SMall scale Accelerated Reliable Test (SMART) methods, highlighting their sensitivity to long-term relevant molecular parameters.