scholarly journals Turning Residual Stresses in Functionally Graded Steel Components

2008 ◽  
Vol 571-572 ◽  
pp. 309-314 ◽  
Author(s):  
Petr Lukáš ◽  
Miroslav Vrána ◽  
Jef Vleugels ◽  
Guy Anné ◽  
Omer Van der Biest

Graded Al2O3/Y-ZrO2 ceramics are developed to receive a construction material combining favourable properties of both constituent components, alumina (low wear rate, high hardness) and zirconia (high strength and toughness). The high performance of this material can be reached by optimising the internal residual stress distribution resulting mainly from phase specific stresses after cooling from the sintering temperature. For this purpose, non-destructive neutron diffraction mapping of residual stresses has been employed. However, the application of the conventional method does not provide straightforward results on macroscopic residual stresses. This experimental technique uses the crystal lattice plane as a built in microscopic strain gauge and the measured quantities are then lattice strains detected in each constituent phase separately. Based on these experimental resources, the paper proposes a procedure of separation of the residual macroscopic stress from phase specific stresses. The application of the presented method is demonstrated on functionally graded materials (FGM) prepared by electrophoretic deposition (EPD).


2008 ◽  
Vol 575-578 ◽  
pp. 1044-1049
Author(s):  
Zhi Ying Ou ◽  
Dong Xia Lei ◽  
Lian Sheng Ma

The residual stresses induced in fiber-reinforced functionally graded composites cooling down from the processing temperature are determined with concentric cylinder model and analytical solutions of inhomogeneous governing equations for displacement components, which include particular solution and general solution of the corresponding homogeneous equations. The analytical solutions presented here are general for power-law variations of the elastic moduli of the functionally graded matrix. With a power exponent, analytical expressions for the residual stresses of fiber-reinforced functionally graded composites can be obtained. By changing the power exponent and the coefficient of the power terms, the solutions obtained here could be applied to fiber-reinforced functionally graded composites with different properties. The results show that the large difference exists between functionally graded composites and common-used composites consisting of two phases of homogenous materials. The variation of matrix modulus and fiber percentage have a great deal of effects on the residual stresses in functionally graded composites.


Author(s):  
Tiago A. N. Silva ◽  
Maria A. R. Loja

Thermal residual stresses often arise due to a manufacturing process, involving localised thermal induction, or to the existence of structural components with different thermal expansion coefficients. The existence of thermal residual stresses within a structural member is usually undesired, as it decreases the mechanical resistance of structures. Hence, it is desirable to obtain both a minimum level of residual stresses and smoother stresses transitions in the materials interfaces. Regarding the mitigation of thermal residual stress concentration, the use of materials which properties can vary along the component directions has great interest. This work addresses the use of dual-phase functionally graded materials, which microstructure varies gradually from a material to another according to a given gradation function. On the order hand, it is also addressed the use of a population based optimization algorithm in order to attain the referred minimum stress level. Summarizing, the current work presents an educational platform directed to structural mechanics students, which aims to give the tools to understand both the influence of design parameters in the thermal residual stress level and distribution along the material and the advantages of using a structural optimization technique in order to minimize the drawback thermal residual stresses effects.


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