摘要 :
Micro forming is a well-suited technology to manufacture tiny mechanical parts,particularly for mass production.Compared to other manufacturing technologies,micro forming features specific economic and ecological advantages.In the...
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Micro forming is a well-suited technology to manufacture tiny mechanical parts,particularly for mass production.Compared to other manufacturing technologies,micro forming features specific economic and ecological advantages.In the micro sheet hydroforming process,size effects play an important role in plastic deformation.Size effects are mainly concerned with the number of grains,size,and frictional behavior.At the micro-level,Parts composed of a limited number of grains,so material properties are highly dependent on orientation and tendencies of each grain,which not only effects the flow stress but also results in poor formability.
PTFE(Teflon)is used in this study to improve the formability in the sheet hydroforming process,which helps to reduce friction,wear,and energy consumption of machinery.The research on micro-sheet hydroforming of SS304and copper sheets was performed.The mechanic''s information on micro-forming was reviewed;later on,a micro-sheet hydroforming test rig was designed.Additionally,the experiments on the micro-SS304sheet and copper sheet with and without the addition of PTFE at different thickness distribution,bulge heights,and cracking pressure were carried out.Finally,finite element analysis(FEA)was performed by analyzing crucial parameters such as sheet thickness,profile shape,and dome height of the micro-sheet.The application of PTFE material in the interface of micro-sheet and die can significantly increase the cracking pressure,the bulge height,while reducing wall thickness.The results showed that the application of the PTFE materials in the bulging test could significantly increase the pressure of the explosion.The addition of PTFE material Indicates that materials had a positive effect on the formability of micro-sheets.Furthermore,PTFE helps to enhance the deformation effect when the thickness of the micro sheet decreases,also the PTFE(Teflon)material helps to generate a high level of bulges hence producing an increase in the thinning range of wall thickness as compared to the conventional micro sheet hydroforming besides,resulting in thinner walls.Further study of the methods to improve the micro-formability(FEA)method with different coefficient of friction was studied.The results indicated that the utilization of Teflon could reduce the friction coefficient from0.15-0.01.The experimental and numerical study was successful in developing new methods to improve the formability of micro-sheet hydroforming and the advantages of Teflon in improving the formability of micro-sheet.The FEA analysis result has good agreement with experimental findings.
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摘要 :
Spacer fabric,a three-dimensional(3D)textile,consists of two outer layers and a spacer layer.The spacer monofilamentsjoinedand kept apart the two outer layers to form a unique3D structure.Due to their unique structure,spacer fabri...
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Spacer fabric,a three-dimensional(3D)textile,consists of two outer layers and a spacer layer.The spacer monofilamentsjoinedand kept apart the two outer layers to form a unique3D structure.Due to their unique structure,spacer fabrics possess goodcompressive characteristics,good moisture permeability with thermoregulation,and good energy absorption,with multiple rangesof applications,including automotive textiles,personal protective clothing,sport textiles,and medical textiles.The geometric structure and compression behaviour of a typical3D mesh warp-knitted spacer fabric were investigated experimentally and numerically in this study.First,a comprehensive structural analysis on a mesh spacer fabric(thickness10.3mm)of which meshed outer layers were knitted with600D/192F polyester multifilament and the spacer layer was knitted with0.22mm diameter polyester monofilament was conducted in order to place a solid foundation to enhance the understanding of structural features and mechanical behaviour.The exact geometric structure of the spacer fabric was reconstructed by scanning the fabric via Micro X-ray computed tomography(μCT).The geometric variations of the spacer monofilaments and monofilament loops in the outer layers were analysed quantitatively.It was found that the spacer monofilaments are different in length,curvature,and torsion.The monofilament loops in the outer layers also vary in height,width,and enclosed area.After investigating the structural variations,finite element(FE)method was applied to reveal the compression mechanism of this type of spacer fabric.Therefore,a series of FE models with different constraints at spacer monofilament endpoints and boundary conditions were created.Based on the FE model FE-0.5-b,which agrees well with the experimental load–displacement curve,the compression mechanism in the linear elastic,plateau,and densification stage were analysed.Finally,a parametric study was conducted by adjusting the verified FE model FE-0.5-b to investigate the structure–property relationships of3D mesh spacer fabrics under static compression.It was found that spacer fabrics with lower fabric thickness,coarser spacer monofilaments,higher Young’s modulus,and closed outer layers have a higher compression resistance.This study provides an in-depth understanding of the geometric structure and compression behaviour of a typical3D mesh warp-knitted spacer fabric.
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摘要 :
This paper focuses on design of smooth bore gun tube according to the interiorballistics data. The main contents are included as follows: The first, theory andprinciple about the barrel component and the design of gun tube are dis...
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This paper focuses on design of smooth bore gun tube according to the interiorballistics data. The main contents are included as follows: The first, theory andprinciple about the barrel component and the design of gun tube are discussed. Interiorballistics curves, chamber requirements, bore, rifling, temperature distribution, designpressure, strength requirements, equivalent stress, pressure stresses, shrinkage stresses,thermal stresses, special applications for artillery tube analyses, gun tube material andmanufacturing procedures are briefly discussed in this section. The second, calculationand construction of gun tube design according to the interior ballistics data aresubmitted. The third, solid model of gun tube is constructed according to the calculateddata and finite element model analysis is done by I-DEAS engineering simulationsoftware. After modeling and analyzing, these results are analyzed in detail, especiallyfor the strength requirement of gun tube.
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摘要 :
In order to satisfy the requirement of Maritime Organization and ship owner,IACS established the common Structural Rules for Oil Tanker (CSR), which came into effect at 1st April 2006.The CSR is based on the concept of target ship...
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In order to satisfy the requirement of Maritime Organization and ship owner,IACS established the common Structural Rules for Oil Tanker (CSR), which came into effect at 1st April 2006.The CSR is based on the concept of target ship; it has contained the experience and latest research results of members of IACS. The yielding and buckling, which are usually defined two main failure modes for ship structure, are especially defined in CSR. This paper mainly researches the assessment of yielding strength by FEM and advanced buckling analysis according to the CSR. The main contents are appended below:1) Introduce the technology of FEM in CSR, including modeling, loading,definition of Load cases and the adjustment of shear force and bending moment. Research the theoretical background of FEM according to the CSR by use of basic mechanics principles and equal design wave approach (EDW).2) The midship cargo tank FE model is established by means of ANSYS software.3) Research on the advanced buckling analysis in CSR; discuss the main impactions and theoretical background of the advanced buckling analysis.Give a brief review of the theoretical background, design principles and purpose of PULS, which is procedure recommended by IACS to assess the buckling strength.4) Research on the buckling assessment method in software of PULS,including a simplified method for elastic large angle deflection analysis of plates and stiffened panels due to local buckling.5) The yielding strength, buckling strength assessment was done according to the JTP Rules. According to the conclusion of results, the different impactions of Load cases are suggested.
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