Materials Science Forum Vols. 490-491

Abstract: Residual stresses play an important role on the mechanical behavior of composite laminate. The development of new methods to determine the residual stresses gradient within the laminates is necessary. This article presents the adaptation of the compliance method in the case of composite laminates carbon/epoxy [02/902]s. The incremental drilling of a constant width groove allows for each increment to measure the strains (using strain gages) and displacements (using an optical device) of particularly points of the structure surface. These experimental data are compared with results given by a finite elements simulation. This comparison allows to raise the residual stresses in the composite laminate.

Abstract: In this work it is shown how the microscopic residual stress state in 6061Al-15vol%SiCw composites can be modified by plastic strain and by isothermal annealing (the latter, affecting also the precipitation state). The composites were obtained by a powder metallurgical route, which involves extrusion of Al-SiCw powder blends. Neutron diffraction measurements were carried out to determine the RS state. Several degrees of plastic strain, from 1% up to 15% in compression, have been applied ex-situ to the same specimen on several composite materials. Furthermore, the m-RS was also investigated in one of the composites at several precipitation states as resulting from isothermal annealing at 300°C during different times. Investigations were carried out from a fully hardened state, T6 up to an overannealed condition, OV (obtained after annealing during 100 h). The results show that quenching from solid solution treatment temperature prior to annealing at 146°C to achieve the T6 condition provokes a RS state, which does not relax during this treatment. No decrease of the deviatoric component and partial relaxation of the hydrostatic term of the micro- RS developed in the composite occur when treating from the T6 to the OV condition. Instead, only 1% plastic strain is sufficient to produce total relaxation of the hydrostatic term of the m-RS. Even inversion of the radial component occurs on higher straining. Again, no relaxation of the deviatoric component occurs. This may be explained bearing in mind that the deviatoric component is linked to the geometry of the reinforcing particles (whiskers degree of orientation). The hydrostatic term does not relax totally after heat treatment because is partially re-generated on cooling, while the plastic deformation is ‘locked’ in the microstructure via dislocation activity.

Abstract: The surface modification of titanium by micro-arc oxidation under different voltages was processed to achieve good direct oseointegration. The new technique of two-dimensional X-ray diffraction was used to measure the residual stress of the layer. The results show that a porous titania layer containing Ca and P is obtained by micro-arc oxidation. The pore size and Ca/P of the layer are affected by the voltage. The high voltage can induce forming CaTiO3. The residual stress under different voltage is compressive stress and increases with the improvement of the voltage.

Abstract: The thermal expansion behaviors of aluminum borate whisker and Fe3O4 reinforced pure aluminum matrix composite with different thermal treatments were studied. Using transmission electron microscopy (TEM) the microstructures of the composite were investigated. The results indicated that the thermal expansion coefficient of the new composite was low. It can be found that the thermal expansion coefficient of as-cast composite is much lower than that of quenched and annealed composites. On the basis of phase transformation analysis of Fe3O4 particles in the composite, the mechanism of low CTE of the composite was discussed.

Abstract: In this paper the internal stresses had been measured on Ti-6Al-4V/7TiC, Ti-3Al-2.5V/7TiC and TP650 composite using the XRD method, the results show no other phases separate out besides the alpha(major phase, for over 90 percent), bate and TiC in the course of heating treatment. Compared the internal stress between prior of heat-treatment and latters, the internal stress was induced in Ti matrix and reinforcement (TiC particles). With temperature of heat-treatment enhancing, internal stress increases gradually, respectively. The relation between the internal stress and strength properties shows the static tensile strength of T64,T32 and T650 developed gradually with compressive internal stress increasing on TiC particle. The compressive stress induced in reinforcement relieved the stress intensity on surface of particle and develops the fracture toughening.

Abstract: The initial fixation of the cemented hip prosthesis relies on the resistance of the interface between the metallic stem of the implant, the PMMA, and the adjacent bone. During the operation, the bone cement still in a liquid form is inserted between the implant and the bone. During polymerisation of the cement, residual stresses are generated in the bulk cement. An experiment has been devised to reproduce the in vivo behaviour of a cemented hip prosthesis, and to develop a technique to measure the residual stresses of the bone cement at the stem-cement interface. An idealized prosthesis (19-mm diameter) was placed inside a synthetic bone (outer diameter of 40 mm, inside diameter of 30 mm). The bone cement was poured between the stem and the bone. A sub-miniature load cell was inserted inside the idealized stem to measure directly the radial stresses generated by the cement curing on the hip stem. The tests are conducted at body temperature of 37°C to simulate the in-vivo conditions.

Abstract: In-situ observation of thermal stress in thin films deposited on a silicon substrate was made by synchrotron radiations. The specimens prepared in this experiment were nano-size thin aluminum films with SiO2 passivation. The thickness of the films was 10 nm, 20 nm and 50 nm. Residual stress in the as-deposited state was tensile. Compressive stress was developed in the heating cycle up to 300 oC and tensile stresses developed in the cooling cycle. The thermal stresses in the 50 nm film showed non-linear behavior in the first heating cycle from the room temperature to 300 oC. However, they linearly behaved in the first cooling cycle and the second thermal cycle. On the other hand, the thermal stresses in the 10 nm film behaved almost linearly without any hysteresis in the first and the second thermal cycles. The mechanism of thermal stress behavior of thin films is discussed.