| Summary: | 博士 === 國防大學理工學院 === 國防科學研究所 === 98 === For the pipe structure to withstand the internal pressure, the stresses between inner circle and outer circle of pipe wall is uneven due to the thickness of the wall. The thicker the wall, the greater the difference of stresses between inside and outside the wall. Therefore, this non-uniform stress distribution of pipe structure can not fully withstand the stress as it is expected. In the past, the applications of jacketed pipe or plastic deformation imposed pre-stress ways were used to improve the stress distribution of pipe structure. This study proposed another autofrettaged pipe as an alternative, by adopting the advanced material design concept which combines the composite with the shape memory alloy (SMA). This composite structure possesses not only the specific strength and adjustable design characteristics, but also has the shape memory effect and a higher recovery stress from SMA to replace the traditional pre-stressing autofrettage method. This proposed design method of autofrettage has been proved by this study to improve the concentration of stress and the stress deficiency of the cylindrical pressure vessel. This research investigates the improvement obtained by adopting the advanced material structure concept in the analysis and design of the tube structure with thick wall and applying the SMA laminated in various order and the activated temperature to the structure.
This study first constructs a one-dimensional constitutive relation of shape memory alloy. The layer-wise linear 3D elastic analysis model is adopted to explore the displacement and stress conditions of the composite tube combined with the SMC. In the analysis process, the material behaviors, such as change in stiffness after the activation of the SMA and the activated recovery stress, are integrated into the structure mechanical model of the laminated tube. By further re-computing the overall stress-strain relationship, the reaction of the tube caused by activating the alloy with heat can be analyzed.
This study result shows that SMA laminated structure placed in the outer tube is better placed in the inner tube as arising from the autofrettaged effect. This design has been proved that design of appropriate SMA laminats after activating can effectively reduce the hoop stress and the shear stress for the tube structure. The improvement of the axial stresses can be reduced relatively. However, there is no effect for improving the radial stress. With regard to the overall efficiency, the advanced concept of material structure can reduce the maximum stress, changes the whole stress distribution well, strengthens the capability against the blasts, improves the delamination of the laminates, achieves the objective of auto-frettage and stress-adopted, and enhances the load-bearing effectiveness of the tube structure.
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