摘要 :
The demand of various industries ofmicro-miniature modern technology to find new solutionmethods in a highly efficient mass production for a variety of micro-part is increasing.Hydroforming has a great potential to be used in mass...
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The demand of various industries ofmicro-miniature modern technology to find new solutionmethods in a highly efficient mass production for a variety of micro-part is increasing.Hydroforming has a great potential to be used in mass production.Problems that occur in the field ofthe process production of micro sheet is when the sizes of materials is reduced at sub millimeter range,grain size have a major effect on material properties,plastic deformation,and the overall process the establishment,The size effect causes formability of micro sheet to be poor.To improve the formability ofmicro sheet,new methods are needed.In this project a new method is presented,namely the use of Teflon to help improve the fonnability of micro sheet.This paper discusses the basics of the sheet hydroforming system,detects the Teflon material properties,and explains the process of micro sheet hydroforming with Teflon material in improving the micro sheet formability.For the experiment,micro sheet hydroforming with single pressure is used.Teflon material is used in the formation process.
Free bulge test is done to investigate the size effect and influence of Teflon sheet on the formability of SS304micro-sheet metal.Research results reveal that:l)the flow stress increases with the thickness of the SS304micro sheets;2)the elongation of material sheet decreases with thickness weakening;3)the use of Teflon material can increase the crack pressure of the micro sheet.In other words,it shows that Teflon material has positive effect on micro sheet formability.Teflon can generate higher bulge levels and also reduce the thinning rate of the thickness compared to the conventional micro sheet hydroforming.
Subsequently,Finite Element Method was used to simulate the Teflon assisted bulging processes of the micro sheet.To validate the prediction obtained from the simulation.a number of micro sheet hydroforming experiments were conducted.
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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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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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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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The effort has been made in recent years to increase the generation of sustainable power energy,such as wind energy.The wind turbine industry expands quickly and wind turbines keep on growing in both size and numbers.Morover, new ...
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The effort has been made in recent years to increase the generation of sustainable power energy,such as wind energy.The wind turbine industry expands quickly and wind turbines keep on growing in both size and numbers.Morover, new construction sites are incorporated as large areas are required in order to construct the wind turbine farms.This means that onshore area will not fulfill the requirement and offshore wind farms are being built increasingly farther from the coast and in deeper waters.The offshore wind turbines are often placed at water depths of 15m-30m.The most effectively and efficient offshore foundation for wind turbines are monopiles.These monopiles foundation often have an embedded length of 20-35 m and a diameter of 4m-8m.After a brief outline of the current state-of-the-art of the wind energy industry and an explanation about the significance of monopiles on offshore wind industry, the specificities of their geotechnical design, specifically the lateral-load design of these piles, is addressed.The interaction between the soil and pile is usually characterized by a load-displacement curve, to which several theories were established over the years and is the basis of current lateral-load design of offshore monopiles.The aim of this thesis is to evaluate and compared experimental results of laterally loaded large scale monopiles located in East China Sea with same parameter of finite element model (FEM) of Plaxis3D, which is characterized by its flexible behavior, used as foundations for offshore wind turbines in different layers of soil.In this thesis, a 3D analysis of nonlinear with an elastic plastic soil model, an elastic pile material and interface elements are used to model the pile and soil displacement.The study involves an investigation of the laterally loaded hollow steel monopile piles with 2.8 m outer diameter, with its displacements, followed by an interpretation and validation of the results with the existing theoretical principles of soil mechanics on this area of expertise.Furthermore, a three-dimensional investigation of fin monopile with different parameter,laterally loaded (at 45°and 90°fms) is presented.The behavior of fin piles is difficult to explain by using simple pile-soil theories or two dimensional numerical analyses because of the complicated geometry of the piles.The recent study and experimental data confirmed that the predicted behavior of a monopile was acceptable leading to a more detailed study of the impact of fins and its length upon the lateral resistance.The load-displacement relation of the fin piles are presented in this paper.By placing of fins in monopile, resultant the increase in lateral resistance of pile which is illustrated by plotting the lateral load against displacement of the pile head for various geometries of the pile.It shows, the efficiency of the fins in monopile which also compared with the monopile without fins.The efficiency of the piles increases as the changing in length and direction of the fins.
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Permanent Raised Beds (PRB) are systems where the crop and traffic zones (furrows)are clearly separated.In these system beds are constructed by piling up loose soil, usually from a tilled, flat surface, in such a manner that they ...
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Permanent Raised Beds (PRB) are systems where the crop and traffic zones (furrows)are clearly separated.In these system beds are constructed by piling up loose soil, usually from a tilled, flat surface, in such a manner that they regularly alternate with furrows.Recently PRB cropping systems, as a soil management systems, have been implemented in a wide range of irrigated and rainfed conditions.In the irrigated areas, one of the big drivers for using PRBs has been the concern over increasing levels of water scarcity, and hence the need to convert less efficient, traditional flood-irrigated systems to furrow irrigation based on PRBs; efficiency can be poor in the former systems especially when there is no access to laser leveling.Preliminary research on raised beds on P.R.China suggested that a 25-30％ saving in water is possible without yield loss for spring wheat.The conventional shape of the furrow in the PRB systems is the V-shaped furrow.Experience with PRB systems showed that the depth of the V-shaped furrow reduces with successive irrigations due to the earth slumping from the steep slope sides of that furrow.
The contribution of this research was to develop a furrow opener that could create a trapezoidal shaped furrow with moderately slope sides to alleviate the problem of earth slumping.The proposed furrow opener looks more or less similar to the conventional ones; with the big difference being the use of flat cutting share in a form of trapezoidal flat blade (TFB) instead of the conventional symmetrical wedge (SW) shaped cutting share.Therefore, the first step in the development of the furrow opener was to optimize the design of the TFB.The design of the TFB was optimized by the use of the finite element method (FEM); a recently available numerical technique that being used in the area of tillage tools design.A static three-dimensional nonlinear FEM model was developed, using ANSYS software, to investigate the effects of TFB geometry (bottom width and inclination angle) on the blade draft force, soil displacement field, and blade stresses.The mechanical behavior of the soil was simulated, based on the elastic-perfectly plastic theorem, by the use of Drucker-Prager (DP)model.Three sets of TFBs were tested all were having the same top width that equal to 150 mm,but varied in their bottom widths (W) which were set to be equal to 50, 75, and 100 mm.These blades were inclined to the horizontal by angles (R) of 20°, 25°, and 30°.The length of each set of the TFB depends on its inclination angle.
The combination of (W×R) gave a theoretical FEM experiment with nine treatments.Results of the FEM simulation showed that there is a direct relationship between blade draft force and the inclination angle, but the draft force of the blade increased with width in a less proportional relation.The least draft force was predicted for TFB that having 50 mm bottom width and 20° inclination angle (605.58 N).The maximum predicted draft force was for TFB that having 100 mm bottom width and inclined to the horizontal by 30° (748.58 N).Two sets of the TFBs that inclined to the horizontal by angles of 20°, and 30° were selected to be used as furrow opener flat cutting shares to validate the results of the FEM simulation.A prototype furrow opener was designed and developed.The proposed prototype was aimed to give a furrow with a fiat bottomed width and moderately slope sides.The performance of the furrow opener prototype was evaluated by Soil bin tests.In the soil bin experiments SW share was used with the furrow opener prototype just as a reference to compare the furrow opener forces; since in these experiments the only variable is the TFB geometry.During the soil bin experiments the working depth and speed were set constant at 200 mm and 0.1 m/s, respectively for all the tests.Results of the soil bin tests confirmed the predicted ones.
The least furrow opener force (9.52 KN) was measured for the furrow opener that used TFB with 50 mm bottom width and inclined to the horizontal by 20° angle.The maximum furrow opener force (10.73 KN) was measured for the furrow opener which used TFB with 100 mm bottom width and inclined to the horizontal by 30° angle.The measured furrow opener force when used SW as a cutting share was found to be 9.49 KN.The power requirements for the various geometry types of the furrow opener followed the same trend of the furrow opener forces; since the working speed was set to be constant.Although the least measured force of the furrow opener that used TFBs as cutting shares exceeded that of the furrow opener when used SW as cutting tillage point by 0.32％; but the ultimate aim is to have a furrow opener that could create a trapezoidal shaped furrow with slightly slope sides.The prototype furrow opener created a trapezoidal shaped furrow with bottomed width equal to 150 mm, top width of 600 mm, and depth of 200 mm.
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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...
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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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