Macroscopic and Microscopic Residual Stresses in Ceramics Due to Contact Loading
The paper deals with microplastic deformation and macroscopic residual stresses in silicon nitride ceramics due to contact loading and their effect on the near-surface strength. Depth-resolving X-ray residual stress measurements on shot peened samples detect high microplastic deformation and macroscopic compressive residual stresses up to 1.3 GPa at the surface decreasing to zero within 10 pm. These high compressive stresses enhance the load bearing capacity in the ball-on plate test up to 50 % compared to polished samples.
Geometry of X‐ray based measurement of residual strain at desired penetration depth
X‐ray based measurement of residual lattice strains at chosen penetration depth is one of the methods for investigating strain inhomogeneities in near‐surface layers of polycrystalline materials. The measurement relies on determining shifts of Bragg peaks for various directions of the scattering vector with respect to the specimen. At each of these directions, to reach a given the penetration depth, a proper specimen orientation is required. The task of determining such orientations, albeit elementary, is quite intricate. The existing literature describes only partial solutions with unspecified domains of application, which fail if applied to beyond the domains. Therefore, geometric aspects of the measurement are analyzed in details. Explicit bounds on measurement parameters are given. The equation fundamental for the procedure is solved with respect to specimen orientations. For a given direction of the scattering vector, there are generally four different specimen orientations leading to the same penetration depth. This simple fact (overlooked in previous analyses) can be used for improving reliability of measurement results. Analytical formulas for goniometer angles representing these orientations are provided.
Evaluation of buckling load and dynamic performance of steel shear wall retrofitted with strips made of shape memory alloy
One of the most imperfections of the steel shear wall is out of plane displacements that cause severe damage in both structural and non-structural elements. In this paper, the effects of shape-memory alloys on steel shear walls are investigated. First, a numerical analysis using the finite element method in ABAQUS software has been carried out according to an experimental test. The results of the numerical analysis have been verified with experimental results. Next, shape-memory alloy fibers have been added vertically and horizontally to various parts of the steel shear wall. The results show that retrofitting with the shape-memory alloy reduces the out-of-plane displacement of the steel shear wall under both cyclic and seismic loadings. Besides, the buckling load in the steel shear wall increases when it is retrofitted with the shape-memory alloy. Also, the total out-of-plane movement (accumulated absolute displacements) of the steel shear wall and non-structural damage are controlled by the characteristic of a shape-memory alloy material called “super-elastic”.