Origin of Residual Stresses

The micro-residual stresses arise from the differential CTE of the fiber and matrix, and the temperature difference. Table 7.4 gives the linear CTE values for various types of reinforcing fibers and matrix materials used widely for composite fabrication. The CTEs of most fibers and ceramic matrices are relatively lower 

Linear coefficients of thermal expansion (CTE) of fibers and matrix materials. 

Three-dimensional distributions of the micro-residual stresses are very complicated, and are affected by the elastic properties, local geometry and distribution of the composite constituents within a ply. Many analytical (Daniel and Durelli, 1962 Schapery, 1968 Harris, 1978 Chapman et ah, 1990 Bowles and Griffin, 1991a, b Sideridis, 1994) and experimental (Marloff and Daniel, 1969 Koufopoulos and Theocaris, 1969 Barnes et ah, 1991 Barnes and Byerly, 1994) studies have been performed on residual thermal stresses, A two-dimensional photoelastic study identified that the sign and level of the residual stresses are not uniform within the composite, but are largely dependent on the location (Koufopoulos and Theocaris, 

A candidate interlayer consisting of dual coatings of Cu and Nb has been identified successfully for the SiC-Ti3Al-I-Nb composite system. The predicted residual thermal stresses resulting from a stress free temperature to room temperature (with AT = —774°C) for the composites with and without the interlayers are illustrated in Fig. 7.23. The thermo-mechanical properties of the composite constituents used for the calculation are given in Table 7.5. A number of observations can be made about the benefits gained due to the presence of the interlayer. Reductions in both the radial, Tr and circumferential, o-p, stress components within the fiber and matrix are significant, whereas a moderate increase in the axial stress component, Tz, is noted. The chemical compatibility of Cu with the fiber and matrix materials has been closely examined by Misra (1991). 

Composite constituents Young s modulus E (GPa) Poisson ratio v Yield Stress Uy (MPa) CTE (10 K ) 

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Since residual coating stresses influence the quality and the service life of coatings, in particular their adhesion and wear performance, it is the goal of any coating development to minimise such stresses. The origin of residual stresses is twofold. First, rapid quenching of the molten particles at the substrate interface results in frozen-in particle contraction according to... 

All of these processes indicate the need to examine the conditions of particle bridging as they relate to the origination of residual stresses in the products of hydration hardening. This approach is... 

Croll, S. G. (1979). The origin of residual internal stress in solvent-cast thermoplastic coatings. I. Annl. Pnivm. Sci.. 23, 847-858. 

With solvent evaporation, the coating becomes to be concentrated with polymers, and the coating becomes to have solid like nature (viscoelasticity). Thus the stresses depend not only on the strain rate, but also strain. Strain is deformation Irom the stress-lfee state. After the solidification point, the solvent evaporation continues, so the stresses persist. Croll analyzed the origin of residual internal stress during drying and correlated the internal stress with the coating properties.The residual internal stress, c, for a coating is... 

Lamedica G, Balucani M, Ferrari A, Bondarenko V, Yakovtseva V, Dolgyi L (2002) Gettering technology based on porous silicon. Solid State Phenom 82-84 405 10 Lei Z, Kang Y, Hu M, Qiu Y, Cen H (2004) Origin mechanism of residual stresses in porous silicon film. Proc SPIE 5641 116-123... 

In summary, one can say that x-ray diffraction stndies have proven the presence of residual stresses in the strnctnres formed in the conrse of hydration hardening and have made it possible to quantitatively estimate their magnitude under varions physical-chemical conditions. The stresses that originate in the conrse of crystal bridging can reach hundreds of kg/cm and manifest themselves in many different ways depending on the hydration hardening conditions. In particular, the stresses can nndergo partial or complete relaxation in the course of the plastic deformation of the... 

The distortions originated from the indentation are of particular interest. Observations under an interference microscope clearly showed the result of the residual deformations caused by the indentation. Images taken in polarized light revealed the presence of a rosette of residual stresses (Figure 7.47). 

Relaxation of the residual stresses induced by autofrettage at 720 MPa (104,400 psi) in reactor tubes k = 2.4), of AISI 4333 M6 at a uniform temperature of 300°C has been studied and it was concluded, on the basis of creep tests for 10,000 h, that after 5.7 years 60% of the original stress would remain (161). 

Stress-corrosion cracks tend to branch along the metal surfaces. Typically, evidence of corrosion, such as accumulations of corrosion products, is not observed, although stains in the cracked region may be apparent. Stress-corrosion cracks tend to originate at physical discontinuities, such as pits, notches, and corners. Areas that may possess high-residual stresses, such as welds or arc strikes, are also susceptible. 

A component may contain residual stresses, weld lines or directional properties due to the conditions of its production. For this reason pieces cut from a component, unless they all originate from the same location, may not be identical. Where tests on a complete component are possible the results are clearly specific to that component. 

Nagy, P. B. and Adler, L. (1989). On the origin of increased backward radiation from a liquid-solid interface at the Rayleigh angle. J. Acoust. Soc. Am. 85,1355-7. [116] Narita, T., Miura, K., Ishikawa, I., and Ishikawa, T. (1990). Measurement of residual thermal stress and its distribution on silicon nitride ceramics joined to metals with scanning acoustic microscopy. /. Japan. Inst. Metals 54,1142-6. [148]... 

A thermally induced residual stress. The origin of the residual stresses is a mismatch of thermal expansion behaviors among the components. Rigid connection of each component with different thermal expansion coefficients causes residual stresses. For example, the electrolyte and electrodes are fabricated and connected at a high temperature. If the thermal expansion behaviors are not identical among the components, residual stresses will occur in the cell at room temperature. For stacks, similar residual stresses will occur by a mismatch of thermal expansion behavior among cells and other stack components. 

Numerical calculations for the residual stresses in the anode-supported cells are carried out using ABAQUS. After modeling the geometry of the cell of the electro-lyte/anode bi-layer, the residual thermal stresses at room temperature are calculated. The cell model is divided into 10 by 10 meshes in the in-plane direction and 20 submeshes in the out-plane direction. In the calculation, it is assumed that both the electrolyte and anode are constrained each other below 1400°C and that the origin of the residual stresses in the cell is only due to the mismatch of TEC between the electrolyte and anode. The model geometry is 50 mm x 50 mm x 2 mm. The mechanical properties and cell size used for the stress calculation are listed in Table 10.5. 

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