Key Engineering Materials Vols. 385-387

Abstract: Dimple fracture under mixed mode loading condition is studied experimentally and numerically. By the mixed mode loading, it is found that fracture surface becomes much rougher than that of mode I fracture. It is also found that ductile fracture growth direction deviates from the original plane. It becomes clear that there are two factors affecting ductile fracture processes, one is mixed mode ratio and another is thickness effect. Three-dimensional finite element analyses are conducted to study effects of these factors. For the simulation of ductile fracture, Gurson’s constitutive equation is used with large deformation theory. These numerical results agree with experimental observation very well qualitatively.

Abstract: Fatigue crack growth under mixed mode loading conditions is simulated using S-version FEM (Superposition FEM, S-FEM). By using S-FEM technique, only local mesh should be re-meshed and it becomes easy to simulate crack growth. By combining with re-meshing technique, local mesh is re-meshed automatically, and curved crack path is modeled easily.

Abstract: The surface treatment system is one of the best options to extend the service life of marine concrete in terms of cost effectiveness versus durability performance. In order to establish rational maintenance strategies for surface treated concrete structures, however, it is necessary to define how to quantify and how to optimize the performance of the surface treatment system. The solution could be obtained from the prediction of chloride in surface treated concrete. In this study, theoretical solution to predict the behavior of chloride diffusion in surface treated concrete is constructed.

Abstract: To carry out maintenance and assessment of reinforced concrete (RC) structures, a good understanding of the effect of the change in bond behaviour of reinforcement during service life is essential. Steel reinforcement is subjected to corrosion due to carbonation and chloride attack. The former ordinarily induces uniform corrosion, the latter induces generally localised corrosion at cracks level. The existence of cracks and the crack width affect the starting points of corrosion, as indicated by the results of the exposure test carried out by Shiessl et al.[1]. Corresponding techniques, such as non-destructive in-situ testing for concrete cover thickness, permeability and the positions of the reinforcing bars, are helpful to model the real behaviour. Cracked portion around the tensile reinforcement in a flexural member can be considered to be equivalent to a concrete member having a single reinforcement subjected to pull-out force at both ends. In this paper a damage process model is proposed based on slip crack propagation in order to evaluate the effective load capacity.

Abstract: This paper describes the Weibull stress approach in predicting the cumulative probability of cleavage fracture for an axially embedded crack in the wall of a reactor pressure vessel (RPV) subjected to a thermal-mechanical transient typical for an accidental, pressurized thermal shock (PTS) event. This study demonstrates the need for detailed elastic-plastic analyses in the integrity assessment of RPVs under PTS loadings, and proposes both a simplified approach and a refined approach to assess the probability of fracture for RPVs subjected to such events.

Abstract: Microarc oxidation technique (MAO) is an electrochemical process which can be used to make ceramic coatings on the surfaces of titanium and its alloys. In this investigation samples of a commercially pure titanium (TA3) were anodized in 30g/L NaAlO2 solution under 280V voltage for 75 minutes to form a 3-10µm coating. XRD analysis showed that the main phase of the coating is TiAl2O5. Samples of the titanium and the MAO treated titanium were immersed in HCl and H2SO4 acid solutions at 250°C in an autoclave. Results show that in 0.1 mol/L concentration both the titanium and the MAO treated titanium have good corrosion resistance in the acid solutions. However, in 1 mol/L concentration the titanium samples completely dissolved in 24 hour immersion. The MAO-treated titanium samples did not dissolved away although some degree of weight losses took place. SEM shows that there are corrosion products on the surfaces of MAO treated titanium samples. XRD analysis showed that the corrosion products are titanium oxides (rutile and anatase). A corrosion resistance mechanism, which is based on the synergic protection of aluminum titanium oxides and titanium oxides for the titanium substrate, is proposed for explaining the enhancement of the corrosion resistance.

Abstract: This paper estimated the influence of volume of steel fiber on the tensile softening behavior in Ultra High Performance Concrete. Tensile softening curves were obtained from Three-Point Bending Test(TPBT) with notched beam. Inverse analysis method by Uchida et al. was introduced to obtain the tensile softening behaviors from the results of TPBT. We could find out that the increase of volume fraction of steel fiber makes the tensile strength higher but all of the curves converged on an asymptote with crack width. We proposed the equation of softening curve expressed by combination of plastic area and exponential descending area considering the volume fraction of steel fiber and ω0, which is corresponding to the maximum crack width of plastic area. We also carried out the crack propagation analysis using finite element method with smeared crack model and confirmed that the proposed equation had a good agreement with the experimental results.

Abstract: Interactions between solid materials and liquid aluminum lead to a dissolution of solid elements into aluminum, which in turn results in a subsequent growth of intermetallic and intermediate phases. It was established that the growth of the intermetallic phases could be governed by chemical reactions at the interfaces and by interdiffusion of the reacting elements through the different phases. Dissolution on the other hand mainly depends on thermodynamic conditions, experimental parameters such as temperature, stirring time, and reacting holding time and on the degree of the saturation of aluminum as well as on the chemical composition of the solid materials in the reaction zone. The above-mentioned factors play also an important role in the formation of the different phases during dissolution. Nevertheless, a non-uniform distribution of the solute elements may causes a local concentration of these elements into the liquid aluminum, which practically delays the process or alters the equilibrium of the growth of the phases. Thus it is crucial to control the dissolution conditions so that the instabilities induced at the solid materials/aluminum interface are limited. The main objective of this study was to investigate both the formation of intermetallic and intermediate phases in the reaction zone and to examine the development of the diffusion structures of pure aluminum reinforced with TiB particles and to investigate the mechanical properties of the as-produced composite materials.

Abstract: The fibers alignment in steel fiber reinforced high strength concrete (SFR-HSC) has naturally significant influence on the mechanical properties of concrete. Fiber-reinforced concrete being manufactured by means various kinds of specimen shape and diversified filling methods and directions, these variables are likely to produce effect on the fibers alignment leading to large differences in its mechanical properties. This study intended to evaluate the effect of placing and flow direction not only on the fibers alignment but also on the tensile behavior of SFR-HSC. Section analysis using photographic shooting was adopted to investigate the fiber alignment and revealed considerable difference in the fiber alignment according to the placing and flow direction. The best alignment appears to be achieved when placing is done in the direction of the flexural tensile stress and the alignment was change with the flow distance although the same flow direction. Such placing and flow direction produce little difference in the first cracking strength but significant discrepancy up to 50% in the ultimate tensile strength.

Abstract: Crack problems are reducible to singular integral equations with strongly singular kernels by means of the body force method. In the ordinary method, the integral equations are reduced to a system of linear algebraic equations. In this paper, an iterative method for the numerical solution of the hypersingular integral equations of the body force method is proposed. This method is based on the Gauss- Chebyshev numerical integration rule and is very simple to program. The solution is achieved without solving the system of linear algebraic equations. The proposed method is applied to some plane elasticity crack problems and is seen to give convergent results.