Analysis of Residual Stress Gradients Below the Surface of a Material Using a Multi-Energy Method
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ANALYSIS OF RESIDUAL STRESS GRADIENTS BELOW THE SURFACE OF A MATERIAL USING A MULTI-ENERGY METHOD Yanan Xiao1,2, Tim Graber2, Myungae Lee1, Dale E. Wittmer1, and Susan M. Mini3 1 Southern Illinois Univ, Dept of Mechanical Engineering and Energy Processes, Carbondale, IL 2 The Center for Advanced Radiation Sources, The University of Chicago, Argonne, IL 3 Northern Illinois Univ, Dept of Physics, De Kalb, IL and Materials Science Division, Argonne National Laboratory, Argonne, IL
ABSTRACT The residual-stress-gradient distribution just below the surface of a material is an important factor to consider during the engineering and design of a component. With the availability of an intense energy-tunable synchrotron x-ray source, it becomes easier to analyze the stress gradient below the surface, using a multi-energy x-ray diffraction method. A program was developed to efficiently determine possible experimental parameters using a sample with a known stress gradient distribution. In addition, this program can also calculate the stress gradient distribution below the surface taking into account experimental results. It also includes a subroutine for calculating the x-ray absorption coefficients of all of the elements, generalizing it for use with any material. As an example, in the present study, the relationship between x-ray energy and the residual stress gradient is discussed according to the calculated result for a silicon nitride composition.
INTRODUCTION It is well known that no material exists completely free of residual stresses (RS). Especially in structural parts, a great variety of RS-states can exits as a result of physical treatments and manufacturing processes. Since RS can have both detrimental and favorable effects on the behavior of a material under certain conditions, RS must be taken into account during the design of a component. Therefore, the stress state is a very important characteristic of the overall material. Consequently, many RS analysis (RSA) methods have been developed to meet various design requirements. Progress in material science and technology, such as advanced multiphase materials, thin-film-substrate composites, ceramics, etc., have brought to prominence the challenges of studying RS, requiring advances in measurement techniques as well as evaluation methods. Recently, problems have arisen due to depth gradients of RS within the microstructure of a material. Although theoretical and experimental studies have dealt with this complex situation, further progress must be achieved. [1] Knowledge of the distribution of RS, especially after thermal and mechanical treatments, has been a goal of RS determination methods from their inception. Today’s research programs are studying the RS-state of near-surface regions, using several testing methods. Typically, three types of non-destructive x-ray techniques are used to investigate the depth dependence of RS. The first is based on the variation of the observed stresses as a function of the penetration depth of the x-ray beam at various energies [1
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