Muddasar Khan

Hydraulic Autofrettage Technology: A Review

Thick-walled cylinders play a unique role in military, automobiles, aircraft and oil fields. The autofrettage method is used to increase the fatigue life of thick-walled components like gun barrel, titanium alloy tubes, nuclear reactor vessels, high pressure oil field pipes and LDPE. There are three types of autofrettage processes and hydraulic is the one applied mostly. The autofrettage process uses a pressure that is high enough to plastically deform the bore of the part but not so high that it bursts the component, is applied to the inside of tube. The result is that after the pressure is removed, the elastic recovery of the outer wall put the inner wall into compression, providing a residual compressive stress. In this research paper a study has been carried out to investigate the progress made in different fields by the hydraulic technique and proposals are sought for future work.Copyright

Modeling and Simulation of Multi-Stage Autofrettage in Pressure Vessels

Thick-walled cylinders play a unique role in cutting edge technologies. These are used in armament industry, aircraft field, automobiles and nuclear reactors. Autofrettage is an effective technique of increasing the fatigue life and bearing capacity of thick-walled cylinders. The most commonly used methods of autofrettage are mechanical, hydraulic and powder gas. In this research paper a study has been carried out of the multi-staging autofrettage process of pressure vessels. The analysis of the autofrettage process is carried out using finite element based software ANSYS, COSMOS. The stress visualization is obtained in the most powerful graphical tool MATLAB. The results obtained are compared with available experimental data.© 2009 ASME

A Comparative Parametric Study of Single Step and Double Step Swage Autofrettage in Swaged Metal Tubes

Computerized software based on finite element programming plays a unique role in the design and development of different engineering fields e.g. mechanical, electrical and civil technologies. Specifically these finite element based software analysis plays a vital role in increasing the fatigue life of structural components. To prevent crack failure and to increase the pressure-carrying capacity of thick-walled components, a common practice is auto-frettage treatment of the cylinder prior to use. The applications are typically heavy walled tubes, diesel engine, hydraulically expanded tubular systems, water jet and oil field components. In this research paper, a simple analysis of single step and double step swage auto-frettaged metal tubes is done using available computerized software based on finite element programming and results are validated using available experimental data, and recommendations are sought for the improvement in the design of multi-stage swage process.Copyright

Analysis of Swage Autofrettage in Metal Tube

Autofrettage (self-hooping) is used to induce advantageous residual stresses into pressure vessels to enhance their fatigue lifetime. The process 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 swage or mechanical autofrettage of metal tubes. The objective is to attain a bore size of 125mm. Normally such a bore size is achieved with hydraulic autofrettage. However, we have used two-stage mechanical autofrettage to achieve the desired bore size. At first stage the swage diameter achieved is 118mm, and in the second stage, the diameter achieved after machining is 125mm. The temperature variation for swage is 38°C to 50°C. The applied pressure varies from 85 to 180 bars inside the tube. The process was applied to a number of tubes selected randomly. The swage autofrettage process was also analyzed using numerical simulation based on finite element method. The results of numerical simulation are compared with design parameters.Copyright

Modeling and Simulation of Residual Stresses in Mechanical Autofrettage

The autofrettage process is used to induce advantageous residual hoop stresses into pressure vessels to enhance their fatigue lifetime. Such pre-stressed pressure vessels are routinely used in power, nuclear, process, armament, and food industries. The autofrettage process can be accomplished by applying hydraulic or mechanical pressure or by the pressure of powder gas to the bore of a thick cylinder to induce residual stresses. The two processes are referred to as hydraulic and mechanical autofrettage respectively. The objective of this research is to analyze mechanical or swage autofrettage, which is achieved by ramming an oversized conical mandrel into the bore, thus driving it into the plastic regime. When the mandrel is removed, the outer elastic portion compresses onto the inner plastic regime, thus causing compressive residual stresses. The percentage of material that undergoes plastic deformation determines the level of autofrettage. A computer code based on finite element method is developed to analyze residual stresses including Bauschinger effect duly incorporating failure criteria such as von Mises and Tresca conditions. The computer code developed is benchmarked using analytical solutions based on Lame’s equations. Using this code, parametric studies are carried out to optimize the depth of penetration of the plastic regime into the material thickness of the bore. The results based on modeling and simulations are validated by using other available computer codes and experimental data.Copyright