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During the operation of plate type radiator used in a certain project, the stainless steel corrugated heat exchanger plate experienced a leakage fault. In this paper, the leakage causes of corrugated heat exchanger plate were comprehensively analyzed by means of macro morphology analysis, chemical composition analysis, metallographic microstructure examination, observation of microscopic morphology by scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS). Results indicated that the roughness of the high temperature oxidation film formed on corrugated heat exchanger surface, especially the center of Newton's ring, was large. This point was also the bulge of the cold stamping groove with high density of dislocations. And this point was the protrusion of the cold stamping groove, with a higher dislocation density. During the process of long-term operation, Cl- continuously accumulated at this location, forming pitting nuclei and ultimately inducing pitting. In addition, under the effect of the cold stamping residual stresses remained in the heat exchanger substrate, the stress corrosion in local areas would also be triggered. With the increasing degree of pitting corrosion and stress corrosion, the thickness of the corrugated heat exchanger plate was gradually decreased and ultimately led to leakage. It was suggested that the source of Cl element and the formation causes of high-temperature oxide films should be investigated, then the targeted improvement measures could be developed.

It is well known that fire-induced spalling usually occurs to high-strength and ultra-high performance concretes. However, experiments have shown that thermal spalling can also occur to normal strength concrete (NSC) and the high moisture content is conducive to the occurrence of spalling of specimens and structures of NSC. In view of the fact that the spalling analysis of NSC is still lacking and the spalling mechanism of NSC is still not well understood, in this paper, the thermo-chemo-hydro-mechanical behavior of a NSC cube specimen with 90% moisture content exposed to fire is numerically studied at a mesoscale based on the experiment reported in the literature. By analyzing the nonlinear mechanical effects of the vapor pressure and the thermal stress, the spalling mechanism is investigated. It is concluded that, instead of explosive spalling, surface spalling induced by the vapor pressure occurs to the specimen. This conclusion is also confirmed by a strain energy analysis. Furthermore, with the energy analysis, the feature of non-explosive spalling of NSC under fire heating is also explained. [ABSTRACT FROM AUTHOR]

This paper develops a mesoscopic numerical method for evaluating the fracture energy of concrete. In this method, concrete is modeled as a three‐phase composite material, composed of mortar, coarse aggregate, and the interface between them. The actual mixed‐mode I–II crack growth path in mode I fracture tests is traced by applying crack propagation criteria. After verifying the numerical method by a series of three‐point bending tests, the effects of aggregate location, aggregate size, and crack propagation path on the fracture energy of concrete are evaluated. It is found that for the fracture mode of crack bypassing aggregates, the actual fracture energy of concrete is significantly affected by the aggregate location but independent of the aggregate size and the crack propagation path. Highlights: A mesoscopic numerical method is proposed for the fracture energy of concrete.The actual mixed‐mode I–II crack growth path is traced by applying crack growth criteria.The actual fracture energy of concrete is significantly affected by aggregate location.The actual fracture energy of concrete is independent of crack growth path. [ABSTRACT FROM AUTHOR]

Reinforcement corrosion induced by chloride penetration is a major threat to reinforced concrete structures in marine environments. The use of surface treatments to improve the durability of reinforced concrete structures has drawn increasing attention in recent decades due to their cost-effectiveness and convenience in construction. However, current knowledge of a practical, durable design to protect surface-treated concrete structures from chloride-induced steel corrosion remains insufficient. On this account, a rapid numerical approach was developed in this study to analyse the chloride diffusion in bilayer materials. In this approach, the time-dependency was considered for the chloride diffusion coefficients of both the surface-treated layer and the underlying concrete substrate and for the surface chloride content. The validity of this approach was verified with the finite element method and the computation time was only one hundred-thousandth that of the latter. This proposed approach makes it feasible in practice to estimate the probability of corrosion initiation in surface-treated concrete structures via Monte Carlo simulation. [ABSTRACT FROM AUTHOR]