• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1250-1258
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• 2021

In this paper, the mechanical performance of cracked surface-coated Zircaloy cladding, which has different coating materials, coating thicknesses and initial crack lengths, has been investigated. By analyzing the stress field near the crack tip, the safety zone range of initial crack length has been decided. In order to determine whether the crack can propagate along the radial (r) or axial (z) directions, the energy release rate has been calculated. By comparing the energy release rate with fracture toughness of materials, we can divide the initial crack lengths into three zones: safety zone, discussion zone and danger zone. The results show that Cr is suitable coating material for the cladding with a thin coating while Fe-Cr-Al have a better fracture mechanical performance in the cladding with thick coating. The Si-coated and SiC-coated claddings are suitable for reactors with low power fuel elements. Conclusions in this paper can provide reference and guidance for the cladding design of nuclear fuel elements.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.4
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• pp.99-106
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• 2006

High velocity oxygen-fuel thermal spray coating of the WC-Co cermet material is a well-established process for modifying the surface properties of the structural components exposed to the corrosive and wear attacks, and also these coating are well-known method to improve the fatigue strength of material. In this study, HVOF coated SM490B are prepared to evaluation of the effect of coating on tension and fatigue crack growth behavior. The pre-crack of the fatigue crack growth test specimens machined at deposited material area, heat affected zone and boundary, respectively. Through these test, the following results are obtained: 1) Tensile strength was about 498 MPa, and fracture occurred on base metal area. 2) The fatigue crack of coated specimens propagated more rapidly than non-coated specimen in all specimens. 3) In the same coating thickness specimens, the specimens with pre-crack at boundary more rapidly propagated than the specimens with pre-crack at HAZ and deposited material area. These results can be used as basic data in a structural integrity evaluation of rolled SM490B weldments considering HVOF coating.

• Journal of Power System Engineering
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• v.7 no.4
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• pp.55-60
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• 2003

This paper is to investigate the fatigue crack growth of plasma-sprayed coating steels according to heat treatments. The experimental materials are carbon steels(substrate: S45C) with plasma-sprayed coating layers of Ni-4.5%Al and $TiO_2$. The fatigue test is conducted on compact tension specimen by a servo-hydraulic fatigue testing machine. The specimens are heat-treated at $400^{\circ}C\;and\;800^{\circ}C$, respectively. Loading condition is a constant amplitude sinusoidal wave with a frequency of 10Hz and a load ratio of 0.1. The fatigue crack growth length is automatically measured by a compliance method. In the case of non-heat treated specimens, the fatigue crack growth rates of both substrate and coating specimen are almost same. The crack growth rates of substrates and coating steels by heat treatment are larger than those of the non-heat treated one, because the ductile property increase by heat treatment. In ${\Delta}K<18MPa{\cdot}m^{1/2}$, the crack growth rates of the heat-treated specimens are slightly taster than non-heat treated one. But the both heated and non-heated one are almost same in ${\Delta}K>18MPa{\cdot}m^{1/2}$.

• Corrosion Science and Technology
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• v.5 no.2
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• pp.69-76
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• 2006

Premature cracking of the epoxy coatings applied on ship's ballast tanks(BT) can lead to damage of ship's hulls. To avoid this, it's important to have clear understanding of the underlying mechanism and primary factors of the coating crack. In this study, the efforts were made to clarify the integrated effects of main factors, i.e., initial coating shrinkage, thermally induced strain, steel-structural strain and the intrinsic coating flexibility at the initial and after aging, to the early cracking phenomena of epoxy coating in the ship's ballast tank. The coating crack is caused by combination of thermal stress, structural stress, and internal stresses which is closely related to chemical structures of the coatings. On the other hand, thermal stresses and dimensional stabilities would rarely play a major role in coating crack for ballast tank coatings with rather large flexibility. Crack resistance of the coatings at early stages can be estimated roughly by measuring internal stress, FT-IR and $T_g$ value of the coatings. A new screening test method was also proposed in this study, which can be possibly related to the long-term resistance of epoxy-based paints to cracking.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.04a
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• pp.164-169
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• 2000

The remote measurement system(RMS) as a new experimental method is limited in its application to crack measurements at elevated temperatures because of the oxide layer on the specimen surface. Since TiAlN and Cr coating layers have a high resistance to oxidation and wear, this paper proposed a TiAlN and Cr coating technique for specimens to facilitate the measurement of crack growth behavior using RMS. To investigate the effects of the coating layer, tension and fatigue tests were carried out at room temperature and at 538$^{\circ}C$, using specimens of 1Cr-1Mo-0.25V steel. From the experimental results, it was found that the mechanical properties of the TiAlN and Cr coated specimens were similar to those of the substrate. Accordingly, the TiAlN and Cr coated layer had hardly any influence on the fatigue crack propagation.

• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.1928-1937
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• 2003

Effect of elastic modulus mismatch on the contact crack initiation is investigated to find major parameters in designing desirable surface-coated system. Silicon nitride coated soft materials with various elastic modulus mismatch, E$\_$c//E$\_$s/＝1.06∼356 are prepared for the analysis. Hertzian contact test is conducted for producing contact cracks and the acoustic emission detecting technique for measuring the critical load of crack initiation. The implication is that coating thickness and material strength are controllable parameters to prevent the initiation of contact cracks resulted from the elastic modulus mismatch in the hard ceramic coating layer on the soft materials.

• Journal of Ocean Engineering and Technology
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• v.16 no.2
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• pp.60-66
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• 2002

The remote measurement system(RMS) as a new experimental method is limited in its application to crack measurement at elevated temperatures because of the oxide layer on the specimen surface. Since TiAIN and Cr coating layers have a high resistance to oxidation and wear, this paper proposed a TiAIN and Cr coating technique for specimens to facilitate the measurement of crack growth behavior using RMS. To investigate the effects of the coating layer, tension and fatigue tests were carried out at room temperature and at $538^{\circ}C$. The test material was 1Cr-1Mo-0.25V steel which is widely used as a turbine rotor material. From the experimental results, it was found that the mechanical properties of the TiAIN and Cr coated specimens were similar to those of the substrate. Accordingly, the TiAIN and Cr coated layer had hardly any influence on the fatigue crack propagation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.11
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• pp.957-962
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• 2008

Crack-healing behavior of $Si_3N_4$ composite ceramics has been studied as functions of heat-treatment temperature and amount of additive $SiO_2$ colloidal. Results showed that optimum amount of additive $SiO_2$ colloidal and coating of $SiO_2$ colloidal on crack could significantly increase the bending strength. The heat-treatment temperature has a profound influence on the extent of crack healing and the degree of strength recovery. The optimum heat-treatment temperature depends on the amount of additive $SiO_2$ colloidal. Crack healing strength was far the better cracked specimen with $SiO_2$ colloidal coating on crack surface. After heat treatment at the temperature 1,273 K in air, the crack morphology almost entirely disappeared by scanning prob microscope. At optimum healing temperature 1,273 K, the bending strength with additive $SiO_2$ colloidal 0.0 wt.% without $SiO_2$ colloidal coating recovered to the value of the smooth specimens at room temperature for the investigated crack sizes $100\;{\mu}m$. But that with $SiO_2$ colloidal coating increase up to 140 %. The amount of optimum additive $SiO_2$ colloidal was 1.3 wt.% and crack healed bending strength with $SiO_2$ colloidal coating increase up to 160 % to smooth specimen of additive $SiO_2$ colloidal 0.0 wt.%. Crack closure and rebonding of the crack due to oxidation of cracked surfaces were suggested as a dominant healing mechanism operating in $Si_3N_4$ composite ceramics.

• Journal of Ocean Engineering and Technology
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• v.12 no.3 s.29
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• pp.49-59
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• 1998

The damage mechanism of $Cr_2O_3$ plasma coated soda-lime glass and uncoated glass by steel ball particle impact was analyzed in this study. And the shape variation of the cracks was investigated by stereo-microscope according to the impact velocity and steel ball diameter. In order to improve the damage reduction effect by $Cr_2O_3$ coating layer, crack size was measured and surface erosion state was observed for both of two kinds of specimen after impact experiment. And the results were compared with each other. The 4-point bending test was performed according to ASTM D790 testing method to evaluate the effect of coating layer for bending strength variation. As a result, it was found that the crack size of $Cr_2O_3$ coated specimen was smaller than that of uncoated one, because of the impact absorption by interior pores in the coating layer and the load dispersion by the structural characteristic of the coating layer. For the specimens subjected to the steel ball impact, the bending strength of coated specimen was higher than that of uncoated specimen.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.10
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• pp.1674-1682
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• 1997

Fatigue tests were performed to investigate the effect of ceramic coatings as in TiN and TiCN on fatigue crack growth properties of ceramic coated 1Cr-1Mo-0.25V steel with different coating thickness in laboratory air conditions. The experimental results are described with respect to a Paris equation, da/dN=C(.DELTA.K)$^{m}$ , where the crack growth rate of coated specimens provided as similar growth rate as that of the uncoated specimen regardless of coating thickness. Furthermore, it was observed that the type of coating layer had virtually no effect on crack growth rate in the full region of stress intensity factor range. And it was also appeared that the final crack length of TiCN coated specimens was short compared to that of TiN coated, and the substrate specimens, in which it was inferred due to lowering the toughness of coated material from high hardness of TiCN coating layer itself.