The carbon-fiber-reinforced polymer (CFRP) is a mainstream material for lightweight products from the end of the 20th century to the present day. Its compression molding process has obvious advantages in mass production. This paper attempts to establish the constitutive models of compression molding of the CFRP materials and study their mechanism. Based on anisotropic linear elastic mechanics, viscoelastic mechanics, and thermodynamics, as well as the Maxwell viscoelastic constitutive model, we first establish the constitutive model of thermorheologically simple CFRP materials (TSMs). Then, considering the influence of temperature on the initial stiffness and equilibrium stiffness, the concept of temperature stiffness coefficient is introduced, and the Cartier coordinate system is converted into a cylindrical coordinate system, thereby establishing the constitutive model of thermorheologically complex materials (TCMs) using the tensor form. Finally, by comparing to the structure of the Zocher model, the two constitutive models established in this study are verified. The research findings have important theoretical research significance for studying the compression molding mechanism of carbon fiber and further improving the quality of product molding.
With its excellent fatigue performance and high damage tolerance and other irreplaceable advantages, FMLs have gradually increased the demand in aerospace, rail transit, ship and other fields, and have put forward higher requirements for the speed and accuracy of its performance test and index evaluation. In this paper, the methods of performance test, analysis and index evaluation of FMLs are introduced from three aspects with carbon fiber and composite materials, mechanical properties and numerical simulation technology, details the common test methods, the latest technology and progress, and analyzes their advantages and disadvantages, so as to provide direction and reference for the performance test method and index evaluation of FMLs. Finally, the main development directions of the current performance testing methods and index evaluation of FMLs are briefly discussed.
This paper attempts to solve the turbine failures reported by a hydropower station, namely, the violent vibration in the runner region under a special working condition and the blade cracking on the outlet edge near the lower ring. For this purpose, the entire flow channel of the turbine was simulated by computational fluid dynamics (CFD) on ANSYS, and the runner strength and mode of shaft assembly system (SAS) were computed by the liquid-solid coupling algorithm. The calculation results show that severe low (negative) pressure appeared on the outlet edge near the lower ring, excess stress was observed in that area, and the resonance occurred as the fifth and sixth order natural frequencies of the SAS were the same with the rotation frequencies of the blade. On this basis, the original blade was modified repeatedly. Through the modification, the flow field distribution in the runner region and the blade strength were both greatly improved, and the SAS natural frequencies were kept away from the various external excitation frequencies, laying a solid basis for the safe and stable operation of the turbine.
Curing is a critical process in the compression molding of carbon fiber reinforced polymer (CFRP). It directly bears on the quality of the molded products. Based on the curing theory of resin-based polymers, a thermo-mechanical-chemical multi-field coupling model for CFRP curing in the form of thermal-chemical subprocess, matrix flow-compaction sub-process and residual stress-deformation subprocess, and sets up its data exchange and mutual call relationship. Considering the thermal physics and chemical properties of composites change with temperatures, the authors introduced the thermal viscosity stiffness coefficient and took AS4/3501CFRP molded laminate as an example, and carried out a multi-field coupling simulation of the CFRP curing through compression molding, using the finite-element software COMSOL. The proposed model was proved correct through calculation of an example in the literature. Further, the CFRP curing mechanism was revealed through a detailed analysis on the evolution of temperature, curing degree, stress and strain of the CFRP curing through compression molding. The results show that the large internal temperature gradient during the compression molding of laminates is the main reason for the residual stress of materials and the deformation of laminate. Finally, an AS4/3501CFRP molded laminate was prepared, and its temperature field was monitored by fiber Bragg grating (FBG) transducers. The temperature evolution law of the material was consistent with the finite element simulation results, which demonstrate the correctness of the simulation.
As high-end equipment requires a higher and higher sealing effect, sealing forms such as packing seals expose problems such as considerable wear and high heat generated by friction. Based on the theoretical analysis of the instability at the liquid-liquid interface and the pressure resistance of the seal structure, considering the rotating speed of the rotating shaft, this paper reconstructs the formula for calculating the pressure resistance value of the seal structure. On this basis, a magnetic fluid seal structure is designed for a large horizontal shaft diameter in liquid. Based on the magnetic field analysis software Maxwell, the magnetic field of the magnetic fluid seal is analyzed, and the mapping relationship between the different tooth widths of the pole teeth, the size of the permanent magnet, and the difference in the magnetic induction intensity of the seal gap is obtained. Built in the ring seal test system, the pressure test of the horizontal large shaft diameter seal structure under different rotating speeds was carried out to verify the effectiveness of the seal structure. The results have specific theoretical research significance and engineering application value for designing and applying magnetic fluid seal structures.
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