Papers by Keyword: Autofrettage

Abstract: The mechanical properties of single layer thick-walled cylinder under the working condition and common failure forms were analyzed, and the results showed that there’s limitation to improve the load supporting capacity only by increasing the wall thickness and the strength of materials. The effective way to improve the stress distribution of single layer thick-walled cylinder is to make the cylinder forced by prestressing. The prestress on the cylinder can counterbalance a portion of the working tensile stress. Firstly, this paper describes the structural of prestressed cylinder of multilayer shrink-on and points out its disadvantage. Secondly, based on the shrink-on cylinder, three kinds of improved cylinder structure of split block shrink-on type, autofrettaged shrink-on type and wire intertwined type are elaborated. The principle, the key technology and the process methods of prestressed processing are parsed. Finally, research directions on the innovative cylinder structure with high load supporting capacity are put forward.

Abstract: The fatigue life of autofrettaged thick-walled cylinders with a radial cross-bore is investigated by applying inelastic finite element analysis with cyclic pressure loading. A non-linear kinematic hardening model considering bauschinger effect is used for determining cyclic plastic strain ranges in fatigue evaluations. A macro is written in ANSYS to calculate the equivalent alternating stress intensity, based on the ASME Boiler and Pressure Vessel Code. For a specific cyclic load level, a distinct optimum autofrettage pressure is identified by plotting autofrettage pressure against the equivalent alternating stress intensity and the number of cycles from design fatigue data. The optimum autofrettage pressure was found in the range of 80.5%-92.5% of limit pressure. The hydrotest had little influence on the fatigue life when the thick-walled cylinder was autofrettaged with an optimum autofrettage pressure.

Abstract: Selectively induced compressive residual stress depth profiles are gaining increasing importance as design tool for internally pressurized components. Hydraulic Autofrettage (AF) is a well-known manufacturing process to induce pronounced compressive residual stresses. However, AF does not stand alone in the technical process chain. In this paper, results from neutron diffraction experiments performed on thick-walled cylinders are presented and compared to finite-element simulations with Abaqus/CAE. The impact on the final residual stress depth profile after pre-machining, Autofrettage and post-machining is discussed.

Abstract: – Pressure vessels often have a combination of high pressure together with high temperature such as gun barrels and high pressure hydraulic rams. For high pressure application, the cylindrical vessels are made to withstand the working pressure. These types of pressure vessels are made by two techniques, one is shrink-fit cylinders and other one is autofrettage cylinders. Autofrettage technique is used to ensure the pressure vessel highly strengthened due to prestressed effect causing the internal portion of the part to yield and resulting in internal compressive residual stresses. The present work is concerned about the elastoplastic stress analysis of thick cylinders. The numerical analysis is carried out on four different materials which are widely used in pressure vessels by using finite element software ANSYS. The elastic breakdown pressure, overstrain pressure, and bursting pressure of the cylinder are found out and the results are compared with experimental results.

Abstract: Internally pressurized components in hydraulic systems are subjected to high mechanical stresses. In case of dynamic pressure profiles this may lead to fatigue and hence a limited lifetime. This is particularly the case for fuel injection systems in combustion engines. Components of diesel injection systems in automobiles are popular examples for these demands. They have to withstand pressures of 2,200 bar and higher for at least 250,000 km. The increasing usage of high-strength materials and higher wall thicknesses will lead to a dead end as the weight and the complex manufacturing will tie up costs and resources. Autofrettage is a manufacturing process with high potential for the lightweight design of highly stressed hydraulic components. By considering the same wall thickness and applying optimal parameters, the fatigue strength may be increased by a factor of 3.5. If transferred to lightweight concepts wall thickness reductions as well as cost and resource savings by more than 45 % may be realized. However, from the manufacturing perspective the Autofrettage process poses some challenges. This paper presents results from Finite Element simulations and experiments and discusses the interaction between manufacturing processes with respect to residual stresses and deformations. The scientific findings may be used to tear down barriers in the application of Autofrettage and to optimize process chain layouts. It also serves to make a significant contribution to weight reduction in car manufacturing and other high performance hydraulic applications. Abbreviations: AF : Autofrettage; AFM : Abrasive Flow Machining; ECM : Electro-Chemical Machining; FEA : Finite Element Analysis; K-ratio : outer to inner radius ratio; L = length of the cylinder (mm); pAF : Autofrettage pressure (bar); pWP : working pressure (bar); piY : pressure to initiate yielding at the bore (bar); Ra : roughness average (μm); Rz : average maximum height of the roughness profile (μm); RPM : Revolutions Per Minute (1/min.); ri : inner radius (mm); ro : outer radius (mm); ρ : density (kg/dm3); σVM : von Mises equivalent stress (MPa); σy : yield stress (MPa); σt : tensile stress (MPa); σY : yield strength (MPa); SF : Safety Factor;

Abstract: Autofrettage process is now widely used to improve fatigue strength of high pressure components. This paper focuses on the fatigue life improvement of the high-pressure cylinder treated by autofrettage process. In this process, a high pressure cylinder treated by autofrettage process has been simulated by using FEA software, and surface variation of the cylinder has been analyzed. To further understand this process, theoretical fatigue analysis has also been carried out.

Abstract: The incremental hole-drilling method is a well-known mechanical measurement procedure for the analysis of residual stresses. The newly developed PRISM® technology by Stresstech Group measures stress relaxation optically using electronic speckle pattern interferometry (ESPI). In case of autofrettaged components, the large amount of compressive residual stresses and the radius of the pressurized bores can be challenging for the measurement system. This research discusses the applicability of the measurement principle for autofrettaged cylinders made of steel AISI 4140. The residual stresses are measured after AF and after subsequent boring and reaming. The experimental residual stress depth profiles are compared to numerically acquired results from a finite element analysis (FEA) with the software code ABAQUS. Sample preparation will be considered as the parts have to be sectioned in half in order to access the measurement position. Following this, the influence of the boring and reaming operation on the final residual stress distribution as well as the accuracy of the presented measurement setup will be discussed. Finally, the usability of the FEA method in early design stages is discussed in order to predict the final residual stress distribution after AF and a following post-machining operation.

Abstract: The research of advanced gun barrels focuses on materials or the combination between advanced materials and new innovative processes that enable the increase of the life cycle and performances of all calibers cannons. In addition to the investigation of new materials, considerable efforts were made for developing new techniques. The paper describes a theoretical framework validated with the experimental tests for increasing mechanical properties of thick-walled tubes subjected to high interior pressure loads. The theoretical model established a mathematical model of calculus for non-linear environments in the case of self-hooping or autofrettaging of the thick-walled tubes. The mathematical model was validated with experimental tests performed in the Mechanical Engineering Laboratory of the Military Technical Academy in Bucharest on a standard tension test specimens collected from the abutment barrel made out of alloyed steel. Finally, the present paper introduces some theoretical guidelines of hydrostatic procedure in the field of artillery barrels manufacturing, as well as experimental data obtained after using the autofrettage procedure.

Abstract: The design of extrusion die has been investigated by autofrettage technique considering the characteristics of the extrusion die. Ideal elastoplastic autofrettage model was established and the stress formulae of three loading procedures were derived and the theoretical calculation method of the maximum autofrettage pressure and working load was put forward. The simulations of stress distribution and the inwall displacement of the autofrettaged extrusion die were performed using MARC finite element software, and the results coincided well with the theoretical derivations. It was observed that the autofrettaged extrusion die can raise the elastic loading capacity under the inner displacement limit , without the appearance of reverse yielding and reyielding under the working load. The results show that the autofrettage technique is appropriate for the design of extrusion die.

Abstract: Swage autofrettage is one of the methods used for increasing life time of tubes and thick wall cylinders under the dynamic loading condition. In this paper swage autofrettage process of thick walled tubes are simulated using ABAQUS commercial code and effect of tool design on the residual stress distribution are investigated. For validating numerical results some experiments were performed and results of experimental and numerical methods showed good agreement with each others.