Zhang Boming

Effects of Contact Resistance on Heat Transfer Behaviors of Fibrous Insulation

Abstract In this article, a numerical model combining conduction and radiation is developed based on two flux approximation to predict the heat transfer behavior of fibrous insulation used in thermal protection systems. Monte Carlo method is utilized to determine the modified radiative properties with experimentally measured transient external temperature as high as 1 000 K. It is found that the estimated radiative properties become time-independent after about t = 3 000 s. By comparing the predicted to the measured results in transient state, the contact resistance exerts significant influences upon the temperature distribution in the specimen. Results show that the averaged absolute deviation is 3.25% when contact resistance is neglected in heat transfer model, while 1.82% with no contact resistance.

Experimental Investigation of the Longitudinal Compressive Strength of Carbon Fibres with a Direct Measurement System

Characterization of the mechanical properties of carbon fibres is crucial to the design of fibre reinforced composite materials. However, little has been done due to the complexity and inaccuracy of some of the necessary tests. In order to study the compressive properties of single fibres, a direct system for single carbon fibre compressive strength was set up based on previous studies; several kind of PAN-based carbon fibres were examined at specimen gauge lengths from 20 to 150 μm using this system. It was discovered that the experimental compressive strength was constant when the length of carbon was in the range of 20~90 um; when the samples length was beyond 90 μm, the compressive strength decreased sharply. The reason is that its deformation mode was not compressive but buckling. In order to compare with corresponding tensile behaviour, a tensile strength test was also carried out, and it was discovered that the compressive strength was about 50% of the tensile strength for single fibres.

Prediction of Process-induced Geometrical Deformations for Stiffened Thermosetting Composite Panels

Stiffened thermosetting composite panels are primary structure of aircraft and fabricated with co-curing processing. The process-induced residual stresses resulted in geometrical deformation when the stiffened composite panel was fully cured and removed from the tool. An investigation into the three-dimensional cure simulation of T-shape stiffened thermosetting composite panels was presented to predict the process-induced deformation during co-curing. And flexible tools and locating tools were considered in the cure simulation. Simulation examples were presented to demonstrate use of the present finite element procedure for predicting composite parts deformations. The T300/BMI structure was analyzed provide insight into the non-uniform curing process. The temperature was higher in the interface between web and flange during the entire cure cycle. And the distortions of skin and webs for T-shape stiffened thermosetting composite panel were remarkable.

Research with CFX Software on Frame Mould Temperature Field Simulation in Autoclave Process

For autoclave technology in large complex structure manufacturing of composite materials, temperature distribution is the most important factor in process control. Previous researchers have mainly focused on composite exothermic curing reaction and exterior temperature coupling. For the exterior temperature field (especially mould temperature field), a simplified approach of uniformity was also conventionally adopted in those researches. Actually, moulds commonly utilised in autoclave processes have a frame structure and their temperature field variation is a combined heat transfer mechanism involving solid heat conduction, air heat conduction and forced convection. Hence in any phase of an autoclave process, the mould temperature field is non-uniform in the spatial domain. This non-uniform distribution of mould temperature has an important impact on the curing degree distribution and leads to residual stress. In this work, using ANSYS CFX computational fluid dynamics (CFD) software, simulation methodology for frame mould temperature field in autoclave process has been established, and its effectiveness has been verified experimentally. On this basis, a series of frame mould simulation examples has been developed and the impact of mould design parameters on the temperature field was achieved. The results will be of value in frame mould design and manufacturing defect control of composite structures.