Full Exploitation of Lightweight Design Potentials by Generating Pronounced Compressive Residual Stress Fields with Hydraulic Autofrettage

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;

• Periodical: Advanced Materials Research (Volume 907)
• Pages: 17-27
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.907.17
• Online since: April 2014
• Authors: Horst Brünnet*, Dirk Bähre
• Keywords: Autofrettage, Finite Element Analysis (FEA), Lightweight Design, Residual Stress

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