Matrix damage

To be able to understand the detailed mechanisms whereby matrix damage influences RPV embrittlement, one needs to determine  

Such a requirement makes it apparent that it is not simply the application of microstructural techniques that is important but that such microstructural studies have to be combined with careful determination of the hardening produced in neutron-irradiated samples. Here, single-variable experiments making use of controlled variation in steel composition in well-characterised irradiations in a MTR are key, see for example IVAR.  

No single technique has successfully identified the exact form of the matrix damage clusters. Of the techniques applied, PA has been the most successful to date.The capability of microstructural techniques is summarised in Table 9.4. 

PA studies on RPV steels are important because they have the potential to provide information on matrix defects. However, since interpretation is difficult, many studies have focused on model alloys rather than steels. In this section, we review a selection of PA data from the literature, focusing first on model alloys and then on steels. For both types of material, researchers have found it useful to combine PA measurements with postirradiation annealing so that the thermal stability of the features observed can also be characterised. 

The work of Akamatsu et al ° was particularly illuminating from a mechanistic perspective. They examined a series of electron-irradiated 

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In most composites with desirable tensile properties, linear elastic fracture mechanics (LEFM) criteria are violated.30,31 Instead, various large-scale nonlinearities arise, associated with matrix damage and fiber pull-out. In consequence, alternate mechanics is needed to specify the relevant material and loading parameters and to establish design rules. Some progress toward this qbjective will be described and related to test data. This has been achieved... 

The development of damage in the form of matrix cracks within 1-D CMCs subject to tensile loading has been traced by direct optical observations on specimens with carefully polished surfaces, and by acoustic emission detection,7 9 62,79-81 as well as by ultrasonic velocity measurements.82 Interrupted tests, in conjunction with sectioning and SEM observations, have also been used. Analysis of the matrix damage found in 1-D CMCs provides the... 

Abstract The Lifshitz - Slezov theory is applied to study the metastable states of the matrix damage clusters, MA, and the copper enriched clusters, CEC, in neutron irradiated steels. It was found that under irradiation conditions the CE Cs are at the Ostwald stage for a neutron fluence of about 0.0002 dpa. The time dependence of number density, MDn, is determined by summarizing all differential equations of the master equation for MA with neglecting of dimmers concentration in comparison with concentration of the single vacancies and subtraction of the number CEC that replace the MA, namely vacancy clusters, due to the diffusivity of copper and other impurity atoms to them. For binary Fe-0.3wt%Cu under neutron irradiation with dose 0.026, 0.051, 0.10 and 0.19 dpa the volume content of the precipitates from the SANS experiment is found to be about 0.229, 0.280, 0.237 and 0.300 vol% respectively. The volume fraction of CEC, in these samples is 0.195 vol% and the calculated volume fraction ofMA is 0.034, 0.085, 0.042 and 0.105 vol% for doses 0.026, 0.051, 0.10 and 0.19 dpa respectively. 

To illustrate the matrix damage problem in the reservoir and scale formation in production wells an application using the numerical code is presented. In this example, sulfate scaling occurs by mixing of injected water (seawater rich in sulfate and poor in Ca", Sr" and Ba ) with a connate water rich in Sr and Ba" cations. From this mixing strontium sulfate salt (SrSOj) and barite (BaS04) precipitations are expected. This kind of scaling is typical from the North Sea (Osborne et al., 1994) and also common in Campos Basin, Brazil (Silva et al., 2001). 

Notch effect. There may be fibre and matrix damage through the thickness, causing a local loss of stiffness. This has the same effect as an insertion or hole that raises a stress concentration, but probably less than 3 as in the case of a circular hole. 

The progression of damage at hole 1, hole 2 and hole 3 in the C3 C3 C1 joint is shown in Figures 11.28, 11.29 and 11.30, respectively. As can be seen, in contrast to the C1 C1 C1 joint, considerable compressive matrix damage is present at hole 3 at just 10 kN apphed load, which is due to all the load initially being taken by... 

Optical Light absorption, reflection and transmission coefficients Reinforcement or matrix damage, reinforcement ratio, fatigue damage, geometry... 

The variation in specimen temperature can be used as well as a damage analogue for composite materials. Increasing specimen temperature is a result of increasing (matrix) damage. 

The typical stress-strain curves for 2D CVI SiC/SiC composites shown in figure 2, summarize trends in the mechanical behavior. This composite behaves linearly to a strain of about 0.03%, and then it exhibits a curved domain of non-linear stress-strain relations. The curved domain of deformation results essentially from transverse cracking in the matrix (the cracks are perpendicular to fibers in the loading direction). Saturation of matrix damage is indicated by the end of the curved domain. Then the linear portion of the curve reflects the... 

The basic damage phenomena in unidirectional composites involve multiple microcracks or cracks that form in the matrix, perpendicular to the loading direction, and that are arrested by the fibers and deflected at the interface between the fiber and the matrix. In the composites reinforced with fabrics of fiber bundles, matrix damage is influenced by the microstructure [21]. The microstructure of 2D CVI SiC/SiC is heterogeneous, as a result of the presence of woven infiltrated tows, large pores (referred to as macropores) located between the plies or at yarn intersections within the plies and a uniform layer of matrix over... 

Ultimate failure generally occurs after completion of matrix cracking (saturation). The fibers break under loads close to the maximum. Matrix damage and ultimate failure thus appear to be successive phenomena. 

At high temperatures, additional phenomena contribute to the extension of matrix damage and debond. Oxidation and creep are involved. 

FIGURE 10. Load/deflection curves of WHIPOX CMCs with alumina plus mullite matrix. Damage-tolerant fracture behavior upon firing at 1500°C and 1600°C is indicated. 

Steels for WWER-type RPVs are of low-alloyed type, mostly with bainitic microstructure, and thus their radiation damage nature is, in principle, identical with all other RPV steels, with matrix damage, formation of copper-rich precipitates and solute segregation in grain boundaries. Additionally, in materials with a high nickel content, the existence of a late blooming phase is not excluded. 

Fe or Ni ion irradiation with energies of a few MeV is mostly used for studies of radiation damage of RPV steels. Previous studies have provided information on the effects of Cu, Mn and other elements, carbides, dose rate and tensile stress on hardness, matrix damage evolution and solute cluster formation in model alloys and commercial steels (e.g. Fujii and Fukuya, 2005 Murakami et al., 2009). These data provide clear evidence of the effects of various metallurgical parameters on hardening and microstructural evolution in Fe-based alloys and RPV steels, although these data cannot be directly or quantitatively correlated to data from neutron-irradiated materials. 

In the first part of this chapter, we provide an overview of the radiation damage processes that control the form of the irradiation-induced microstructure under the radiation conditions reactor pressure vessel (RPV) steels experience in service. We demonstrate that the irradiation damage in RPV steels can broadly be classified as matrix damage (for instance voids, interstitial clusters, dislocation loops, complexes trapped at sinks such as... 

In Section 9.13 we focus on the mechanistic framework that incorporates insight into matrix damage and solute clusters... 

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