Autofrettage is a metal cold forming technique in which a pressure vessel is subjected to enormous pressure , causing internal portions of the part to yield plastically, resulting in internal compressive residual stresses once the pressure is released. The goal of autofrettage is to increase the durability of the final product. Inducing residual compressive stresses into materials can also increase their resistance to stress corrosion cracking ; that is, non-mechanically-assisted cracking that occurs when a material is placed in a corrosive environment in the presence of tensile stress. The technique is commonly used in manufacture of high-pressure pump cylinders, warship and tank gun barrels, and fuel injection systems for diesel engines. While autofrettage will induce some work hardening , that is not the primary mechanism of strengthening.

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Analysis of autofrettaged metal tubes. Thick-walled cylinders are widely used as compressor cylinders, pump cylinders, high pressure tubing, process reactors and vessels, nuclear reactors, isostatic vessels and gun barrels. In practice, cylinders are generally subjected to sudden and frequently drastic pressure fluctuations, such as the pressure generated in a gun barrel upon the firing of the weapon, pressure reversals in pump cylinders or in process reactors employing high-pressure piping, necessitating enhanced strength of such cylinders.

A process for enhancing the strength of thick-walled cylinders has been in service, and is referred to as ' autofrettage '. It extends the service life of the cylinder. The autofrettage is achieved by increasing elastic strength of a cylinder with various methods such as hydraulic pressurization, mechanical swaging , or by utilizing the pressure of a powder gas. This research work deals with the hydraulic and mechanical autofrettage of metal tubes with the objective to attain enhanced strength.

Five metal tubes are taken randomly for analysis purpose. The experimental data for five metal tubes is obtained to analyze the behavior of different parameters used during, before, and after autofrettage process.

For this research, two-stage autofrettage is taken into consideration. The results are validated using available experimental and numerical data. Analysis of the ATR fuel element swaging process. This report documents a detailed evaluation of the swaging process used to connect fuel plates to side plates in Advanced Test Reactor ATR fuel elements.

The swaging is a mechanical process that begins with fitting a fuel plate into grooves in the side plates. Once a fuel plate is positioned, a lip on each of two side plate grooves is pressed into the fuel plate using swaging wheels to form the joints.

Each connection must have a specified strength measured in terms, of a pullout force capacity to assure that these joints do not fail during reactor operation.

The purpose of this study is to analyze the swaging process and associated procedural controls, and to provide recommendations to assure that the manufacturing process produces swaged connections that meet the minimum strength requirement. The current fuel element manufacturer, Babcock and Wilcox B ampersand W of Lynchburg, Virginia, follows established procedures that include quality inspections and process controls in swaging these connections.

The procedures have been approved by Lockheed Martin Idaho Technologies and are designed to assure repeatability of the process and structural integrity of each joint. The results presented in this report demonstrate that the pullout strength of the swaged connections is assured by the current manufacturing process with several recommended enhancements without the need for- testing each element in the HTF.

Microstructures and mechanical properties of pure Mg processed by rotary swaging. Gan, W. Bulk and gradient textures in the RS processed Mg were characterised by neutron and synchrotron diffractions, respectively. Grains of the pure Mg were gradually refined with increase in the RS passes, which largely contributed to an increase in the tensile yield strength.

A dominated basal fibre texture was observed in the RS processed pure Mg. Accommodated twinning deformation was also observed. Both the optical observations and texture analyses through the diameter of the swaged rod showed a gradient evolution in microstructure.

Cold- swaging is one of a cold deformation processes , and ceramic-reinforcement nano-composite coatings can effectively improve the performance of metal matrix surface. Therefore, the two processes are innovatively combined to further improve the surface properties of the metal matrix in this paper.

Furthermore, the coatings were compared with those without cold- swaging coatings at the same time. The result shows that the cold- swaging process can further enhance the tensile strength, micro-hardness and the wear resistance of the composite coating. This study can be used as a reference for further strengthening of laser cladding nano-composite coatings in future research. The alloy can provide a cost benefit over Ti-6Al-4V due to improved machinability and formability.

In the present work, evolution of mechanical properties in terms of tensile and hardness values is investigated as a function of deformation degrees imposed via rotary swaging RS. Optical microscopy and scanning electron microscopy using electron back scatter diffraction were utilized to document the evolution of the microstructure.

Tensile tests were conducted to characterize mechanical properties. RS, to a true strain of 3. An alternative design method for the double-layer combined die using autofrettage theory.

Directory of Open Access Journals Sweden. Full Text Available The double-layer combined die is used for its longer life in forging. Autofrettage is a well-known elastic—plastic technology that increases the durability of thick-walled cylinders.

This study explores an alternative design method of the double-layer combined die using autofrettage theory. The relationship between the autofrettage pressure and the yield radius of the die insert is obtained, and expressions of residual stresses and displacements, which are directly related to geometric parameters, material properties and internal pressure, are derived.

The finite-element simulation of a specific case is performed, and good agreement between theoretical calculations and simulation results is found. Furthermore, the effects of important parameters, including the ratio of the plastic area and yield strength of the die insert and the outer diameters of the die insert and stress ring, on the autofrettage effect are investigated.

Compared with the conventional combined die, the autofrettaged die can bear larger working pressure, as expected. The use of the autofrettaged die can reduce the amount of expensive material required for the die insert and the working space of the die set, which would benefit the practical forging process.

Conditioning of material properties by micro rotary swaging. Cold forming initiates a change of the material properties like flow stress and hardness. Due to work hardening and the accompanied loss of formability some intermediate heat treatment may become necessary in multi-stage forming processes. One possibility to avoid this heat treatment is to adjust the forming characteristics in terms of flow stress and formability by rotary swaging. This process is particularly suitable not only for producing of the target geometry but also for modifying of the material properties during the process and thus, rotary swaging can prepare the parts for further forming, such as extrusion.

In this contribution, the process chain "rotary swaging - extrusion" for austenite stainless steel AISI was investigated. The forming characteristics of the semi-finished products for the extrusion were influenced by the previous swaging process. The conditioning by changing of the microstructure, the work hardening and the geometry of the processed wires was achieved by the process design. In particular, the novel geometry of the swaging dies with extraordinary sloped faces generated a non-symmetric material flow with severe shear deformation and thus an extreme change of the microstructure.

The required forming force of the following extrusion process reflected the range of achievable conditioning. The micro rotary swaging process positively improved the formability of AISI by work softening. Investigation of residual stresses in thick-walled vessels with combination of autofrettage and wire-winding. Wire-winding and autofrettage processes can be used to introduce beneficial residual stress in the cylinder of thick-walled pressure vessels. In both techniques, internal residual compressive stress will increase internal pressure capacity, improve fatigue life and reduce fatigue crack initiation.

The purpose of this paper is to analyze the effects of wire-winding on an autofrettaged thick-walled vessel. Direct method which is a modified Variable Material Properties VMP method has been used in order to calculate residual stresses in an autofrettaged vessel.

For this reason, a new wire-winding method based on Direct Method is introduced. The obtained results for wire-wound autofrettaged vessels are validated by finite element method. The results show that by using this approach, the residual hoop stresses in a wire-wound autofrettaged vessel have a more desirable distribution in the cylinder. Bursting pressure of autofrettaged cylinders with inclined external cracks.

Autofrettaging a pressure vessel improves its pressure capacity. In this paper, the effects of external surface cracks on bursting pressure of autofrettaged cylinders are studied. This reduction increases for high levels of the applied autofrettage. External axial cracks have more effects than inclined cracks. Comparing experimental and numerical results show that the numerical methods can acceptably predict the bursting pressure of the autofrettaged cracked cylinders. These predictions are valid when the fracture parameter J-Integral is calculated from the modified equation that takes into account the effects of residual stresses.

Seifi, Rahman, E-mail: rseifi basu. This is reliable if there isn't any crack or other type of flaws. Black-Right-Pointing-Pointer External axial cracks reduce considerably the pressure capacity of cylinders. Black-Right-Pointing-Pointer External circumferential cracks have not considerable effects on bursting pressure.

Black-Right-Pointing-Pointer Autofrettage has contrary effects on external crack in compared with internal crack. Dry rotary swaging with structured and coated tools. Rotary swaging is a cold bulk forming process for manufacturing of complex bar and tube profiles like axles and gear shafts in the automotive industry. Conventional rotary swaging is carried out under intense use of lubricant usually based on mineral oil. Besides lubrication the lubricant fulfills necessary functions like lubrication, flushing and cooling, but generates costs for recycling, replacement and cleaning of the workpieces.

Hence, the development of a dry process design is highly desirable, both under economic and ecological points of view. Therefore, it is necessary to substitute the functions of the lubricant. This was realized by the combination of newly developed a-C:H:W coating systems on the tools to minimize the friction and to avoid adhesion effects. With the application of a deterministic structure in the forging zone of the tools the friction conditions are modified to control the axial process forces.

In this study infeed rotary swaging with functionalized tools was experimentally investigated. Therefore, steel and aluminum tubes were formed with and without lubricant. Different structures which were coated and uncoated were implemented in the reduction zone of the tools.

The antagonistic effects of coating and structuring were characterized by measuring the axial process force and the produced workpiece quality in terms of roundness and surface roughness. Thus, the presented results allow for further developments towards a dry rotary swaging process. Manufacturing operations, such as swage autofrettage , shot peening, and overload processes , have been used to impart advantageous residual stresses to improve fatigue life in components used in high Influence of the relative rotational speed on component features in micro rotary swaging.

Full Text Available Micro rotary swaging is a cold forming process for production of micro components with determined geometry and surface. It is also possible to change the microstructure of wires and hence the material properties. Swaging dies revolve around the work piece with an overlaid radial oscillation. Newly developed tools Flat Surface Dies, FSD feature plain surfaces and do not represent the geometry of the formed part as in conventional swaging. Using these tools allows for producing wires with triangle geometry cross section as well as a circular shape.

To test the influence of FSD on material properties by micro swaging a new method is investigated: the variation of the relative speed between the specimen and dies in infeed rotary swaging.



Autofrettage is a technique used on tubular metal components in which enormous amounts of internal pressure causes portions of the part to yield plastically, resulting in internal compressive residual stresses once the pressure is released. The goal of autofrettage is to increase the durability of the final product by inducing residual compressive stresses into the material. With our specialized equipment and high pressure experience, Maximator Test can assist you with your autofrettage project large or small; whether you have 5 parts or 5, we can help determine how best to seal your components and develop the process to help increase their fatigue life. The autofrettage process is widely used in various industries for increasing operating pressures for advanced industrial, automotive, aerospace and defense systems; the application of autofrettage process is required to improve component fatigue life. The technique is commonly used in the manufacture of high-pressure pump cylinders, fuel injection systems for diesel engines and warship and tank gun barrels. Similarly, the process is also used in the expansion of tubular components in oil and gas wells. Essentially, autofrettage works as if the pressure carrying element has a band clamp on its outer circumference, minimizing or eliminating the pressure vessel ID from experiencing the negative effects of pressure pulsations.





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