| Plastic pipe reinforced by cross helically wound steel wires (PSP), which has excellent performance, is a new type of plastic-matrix steel composite pipe. PSP is composed of steel wire twined skeleton as the enhanced body and high density PE as the base. The enhanced body and the base are cohered together with a kind of high quality resin. Because of the unique structure, PSP not only integrates the advantages of high load-applying of steel pipes and good corrosion resistance of plastic pipes, but also overcomes drawbacks of plastic-matrix metal composite pipes, for example, delaminating easily under long-time alternating stress. With the high productivity and excellent performance, PSP could be used widely in various fields.Up to now, researching on PSP is only about its manufacture, assembly and application. At the same time, its mechanical properties have not been reported in literatures. So, mechanical properties of PSP, such as the stress-strain, failures and strength etc., are studied systematically in this dissertation for the first time. Based on the structural model, the failure modalities, strength and optimization of PSP are discussed. The main research results are as follows:(1) Based on the micro mechanics, the elastic parameters of PSP are obtained. The structural model of PSP consists of three continuous layers, i.e., inner PE layer, composite layer and outer PE layer. The composite layer is comprised by two monolayer plates. Elastic parameters of the monolayer were obtained with rectangle, series and parallel models and semi-rational formula of Halpin-Tsai. Then elastic constants of the composite layer and the whole pipe are calculated on the method of P.C.Chou about macro elastic modulus of Multi-Layer Boards. The results show that the hoop rigidity of PSP is enhanced obviously by steel skeleton and the axis rigidity of PSP doesn't change much.(2) Stress analysis under different loads and performance analysis of external pressure are studied. Using secant method, elastic and elastic-plastic deformationsunder internal pressure were studied. Stress analysis of PSP under bending moment and internal pressure was also discussed. An equation was deduced to evaluate the external pressure resistivity of PSP. Good agreement between theoretical results and experimental data shows that the presented model can well predict stresses and strains of PSP, and the equation can be used to calculate the critical buckling pressure of PSP.(3) Short-time burst strength at room temperature of PSP was studied. Strength characters of monolayer in principal direction were obtained by micro mechanics. Maximum strain theory and maximum stress theory are considered as the failure criteria of the monolayer. Equations for burst strength of PSP were gained according to the failure of steel wires. The experimental results show that, calculated results are close to experimental data, their relative error is within -4.7%~6.9%, and the formula can be used for predicting the short-time burst strength well.(4) The method of parametric unitary optimization of PSP is presented in this dissertation. Influences of different design variables on strength and cost of PSP are analyzed. Based on the method of strength analysis, physical dimensions of PSP, i.e., winding angle, number of steel wires, diameter of steel wire, position of composite layer and wall thickness of PSP, are optimized. The cost can be decreased by 1.2% and 5.2% or burst pressure can be increased by 30.9% and 40.9% in virtue of optimization. |
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