Papers by Keyword: Crack

Abstract: The false joint of bearing layer is one of the engineering measures to guide the crack development, in unit double-block ballastless track, it’s usually designed in staggered arrangement with expansion joint of track concrete layer. According to the actual situation, this seam layout is unreasonable. So the thorough study on the design scheme of false joint is presented. The distribution of stress in bearing layer, under temperature load, is first computed, the result shows the bearing layer under expansion joint is more prone to cracking than that at other positions. Then compares the theoretical response got from two different kinds of seam layout under train load. Finally, the false joint design is optimized on the basis of project experience. A conclusion is drawn as follows: the false joint and the expansion joint ought to be aligned in general case, and the false joint setting in the middle of the unit should be canceled. But, when the railway is built on a unstable the lower foundation or in a area with plenty of rainfall, the false joint design ought to adopt the optimized arrangement of break joint.

Abstract: Heat-resistant steel (12%wt. Cr) used in the ultra supercritical set blade was quenched and tempered by vacuum heat treatment furnace, the mechanical properties and metallographic structures at room temperature can meet the specific requirements. However, there are some problems existed on high-temperature short-time lasting performance. To improve the high temperature endurance performance of materials, the experimental testing and analysis were carried out fro different types of specimen. The research showed that short-time rupture is a kind of creep fracture, and short lasting strength was closely related to test temperatures between laths and grain boundary and carbide coarsening. Energy spectrum analysis revealed that cast in the hole had high B element content (19.98%wt.), which meant grain boundaries of the B at high temperature began to migrate and form in the crystal B in that second phase particles are contained, and grain boundary strength was obviously decreased. The enduring high temperature experiment indicated that the strength were declined rapidly and fractured suddenly at high temperature.

Abstract: The aim of the present work was to determine the influence of air plasma spraying (APS) parameters on the microstructure of thermal barrier coatings (TBC) consisting on NiCoCrAlY bond coat and yttria - stabilized zirconia (YSZ) top coat. The scope of the investigation involved macroscopic observation and microstructural analysis by means of light microscopy (LM) and scanning electron microscopy (SEM). For the varied parameters of deposition process quantitative analysis of coatings thickness, porosity, oxide inclusions, metallic inclusions, globular inclusions and cracks were performed. The results of quantitative analysis allowed to establish which APS conditions influence the particular microstructural parameters of TBC coatings.

Abstract: In this paper, we use numerical methods, reveal that the temperature distribution regularity of the concrete box girder, find the direct cause of the temperature gradient, and explain the reason about internal cracks of box girder.

Abstract: Intelligent inspection is wildly used in the integrity management of transmitting pipeline in service. Recently, the intelligent inspection data of one natural gas transmitting pipeline showed that lots of the blistering was found in the pipe inner surface. In this paper, the methods of OM, SEM and EDS et al were carried out to study the reasons of the blistering failure and proposed the safety countermeasures. The results show that the blistering failure of pipeline was mainly related to the hydrogen blistering and the manufacturing technology of the pipe. The sulfide stress corrosion (SSCC) and the manufacturing damage accelerated the blistering failure of the pipe.

Abstract: Compression properties, microstructure evolution and deformation behaviors of cast and extruded AZ31 alloys are investigated. The results show that compressive yield stress, ultimate strength and ultimate compression ratio between extruded and cast AZ31 alloy are quite different. The yielding pattern of as-cast AZ31 alloy is continuous, and the yield pattern of extruded AZ31 alloy demonstrate an obvious yielding plateau mode. The angle between the fractures and specimens axis of as-cast and extruded AZ31 alloy is about 45°. A mass of reliefs and damage can be found on the specimen surface of as-cast AZ31 alloy and the twinning is main deformation sign in as-cast AZ31 alloy as seen a rough surface. The slip activity might be a predominant deformation mechanism in extruded AZ31 alloy judged by smooth surface after fracture.

Abstract: This study was conducted to experimentally investigate the shear behavior of non-ductile squat shear walls with different cement matrixes such as normal concrete, fiber-reinforced concrete(FRC), and strain-hardening cement composite(SHCC). The cement matrix type’s effect in the lightly reinforced squat shear wall was evaluated through the testing of three one-third scale walls with a height-to-length ratio (hw/lw) of 0.55 under top displacement reversals. Experimental results show that the cement matrix type in the non-seismically detailed squat shear walls has a significant effect on the shear behavior and failure mode. Compared to reinforced FRC and SHCC shear walls, reinforced concrete wall exhibited brittle behavior. Reinforcing fibers in the FRC and SHCC mitigated the crack damage of wall and increase the shear strength.

Abstract: This experimental study investigates the flexural behavior and toughness of sprayable strain-hardening cement composite (SHCC) developed to retrofit seismically reinforced concrete structures with non-ductile reinforcement details. Three SHCC mixtures with specified compressive strength of 50 MPa are mixed and tested. All SHCC mixes with different dosage and combination of admixtures such as superplasticizer and powder admixture were reinforced with 2.2 % polyvinyl alcohol (PVA) fibers at the volume fraction. This paper focuses on the flexural toughness based on the flexural test results for 100 x 100 x 400 mm prisms. The flexural toughness is evaluated in accordance with ASTM C 1018. The results indicated that less than 2.5 % dosage of hybrid superplasticizer and powder admixtures respectively provides excellent sprayability and flexural behavior of SHCC mixed in this study. A strong influence of hybrid superplasticizer and powder admixture on the flexural toughness of SHCC mixes was observed.

Abstract: Regarding the internal structure of cement-based materials, some major concerns the mode of distribution of pores, pore size, and the type in which they are connected. A thorough understanding of the distributive rules of pores and the approaches to break their links will be a considerable contribution to enhancing the durability of cement-based materials. There are several methods to discover the pores of cement-based materials, but cannot show the exact location of pores and the structural links. Magnetic resonance imaging (MRI) has been widely applied to physical examinations. This technique has matured and is now able to obtain information and 3-D images about the organs of recipients without causing damage. The signals from MRI indicate where the hydrogen nucleus is located. However, MRI is seldom used for cement-based materials. In this study, we use H2O as the source of MR image signals in the mortar. Through this experiment, we verify that MRI can be used to analyze the distribution of internal cracks in cement-based material.

Abstract: In order to further study the cracks initiation and distribution mechanism of SiC coating, then optimize the coating structure and composition on surface of C/C composites, CVD method is used to deposit SiC coating on C/C composites and pyrolytic carbon. Through the analysis on the reasons of cracks initiation via SEM, the influence of different kinds of substrates and the toughening of SiC whisker on the cracks initiation and distribution are researched. The results show that the cracks easily form in the area near the defects and sample edge, and the cracks also mainly distribute in the direction which are perpendicular to the first fiber layer. Compared with pyrolytic carbon matrix, cracks on C/C composites matrix are width and numerous, and SiC whisker toughening coating can significantly reduce the number of cracks.