Shrinkage Fracture Research Articles

Phase field modeling of irradiation-induced shrinkage fracture in TRISO fuel particle

With the features in retaining fission products and maintaining structural stability, TRISO fuel particle has been widely implemented and studied in the development of advanced nuclear fuel element. During service, however, the key silicon carbide (SiC) layer of TRISO may fail due to irradiation-induced shrinkage fracture of inner pyrolytic carbon (IPyC) layer. Hence, it has great significance to analyze the fracture characteristics of TRISO for its application in engineering. This work presents a phase field model of brittle fracture for the shrinkage cracking, which is capable of simulating the propagation of IPyC crack and interfacial crack between IPyC and SiC naturally. At first, the physical model of TRISO and phase field model have been verified respectively. Subsequently, the crack evolution has been investigated under different parameters, including the Bacon Anisotropy Factor (BAF) of IPyC, fuel temperature and density of IPyC. Simulation results reveal that increasing the BAF or decreasing the density and temperature, the fracture of IPyC will be accelerated and the crack deflection may also occur subsequently. In contrast, the fracture of IPyC can be put off and relieve the stress concentration in SiC. The combination effect of shrinkage and stress relaxation from creep ultimately determines the crack evolution, which in turn influences the stress distribution within SiC.

Optimizing the thermophysical qualities of innovative clay–rGO composite bricks for sustainable applications

This work concerned the development of a unique reduced graphene oxide (rGO) nano-filler to provide innovative opportunities in enhancing the thermophysical performance of clay composite bricks. Whereas, a series of clay–rGO composite bricks were produced, doped with various levels of rGO nanosheets (i.e., 0, 1, 2, 4, and 6 wt% clay). Each clay–rGO composite’s microstructure, shrinkage, morphology, density, porosity, and thermophysical characteristics were carefully investigated, and the thermal conductivity performance was optimized. Incorporation of different levels of rGO NPs to the clay matrix allowed all the peaks intensity to rise relative to the untreated one in the XRD pattern. Meanwhile, the inclusion of these doping resulted in a grew in the crystallite sizes and apparent porosity within the compositions. In this vein, shrinkage fracture of fabricated brick composites varied depending on dopants type and levels during the drying and firing processes. Moreover, there are some changes in chemical compositions, as well as wave shifts, suggesting that functional groups of rGO may have contributed to partially introduce carbonyl groups in clay–rGO composites. Besides, the porous topography and bulk density improved rapidly with respect to the plane of the rGO nanosheets within the composites. The differ-dense microstructure displayed in the SEM micrographs supports these outcomes. Remarkably, clay–(4%)rGO compound not only has an optimum thermal conductivity value (0.43 W/mK), but it also has a high heat capacity (1.94 MJ/m3K). These results revealed the exceptional features of rGO sheets such as large surface area with high porosity within the modified clay composites.

Determination of Fe2+/Fe3+ Ratios of Magnetite using Different Methods: A Case Study from the Qimantag Metallogenic Belt

AbstractDetermination of Fe2+/Fe3+ ratios from metallogenic belts to explore controlling physical and chemical conditions of rock formation is of great significance. In order to explore magnetite Fe2+/Fe3+ ratios of the Qimantag metallogenic belt, part of the Eastern Kunlun orogenic belt in the northeastern margin of the Qinghai–Tibetan plateau, western Central Orogenic Belt of China, and overcome the limitation of the traditional electronic probe, five different measurement methods are proposed and their respective advantages and disadvantages evaluated, with the composition data of the magnetite obtained using electron probe microanalysis (EPMA). The direct oxygen measurement method has a significant impact on the determination results of FeO and Fe2O3, but the accuracy and uniformity of the results are low. The valence method (Flank method) based on the spectral intensity ratio of Lα to Lβ for iron is also unreliable for FeO and Fe2O3 measurements because it is difficult to establish a relationship between Lβ/Lα, the spectral intensity ratio, and the Fe2+/Fe3+ content ratio. In comparison, the charge difference method, the surplus‐oxygen method and the Mössbauer spectrum method are still the most favorable. Mössbauer spectroscopy, with its isomer movement particularly sensitive to the oxidation state of iron, yields results closer to 0.5, which is relatively reliable. Earlier magnetite deposits are located in intrusions or contact zones and formed by magmatic fluids with high Fe2+/Fe3+ ratios, whereas later magnetite deposits are farther away from intrusions and have low Fe2+/Fe3+ ratios. The transformation mechanism of hematite and magnetite in the Qimantage metallogenic belt is also studied. No large volume changes, such as pore filling and shrinkage fracture, were detected in the metallogenic belt, and the transformation mechanism is more similar to a reoxidation and reduction mechanism.

Experimental Study on the Effect of Mineral Composition on Shrinkage Fractures: Implications for the Origin of the Diagenetic Shrinkage Fractures in Marine–Continental Transitional Shales

Natural fractures in shale have been commonly recognized as a vital factor in shale gas production. Diagenetic shrinkage fracture is an important type of natural fracture; however, its formation mechanism and prediction remain largely unexplored. Given the similarity between diagenetic shrinkage fractures and desiccation cracks, the influence of smectite, kaolin, quartz, and feldspar on shrinkage fractures were investigated using the physical simulation experiment of desiccation in this study. Here, water evaporation, surface cracks initiation and propagation processes were monitored during the whole desiccation. The morphological characteristics of cracks patterns were quantitatively described. Diagenetic shrinkage fractures of transitional shale with different minerals were observed using SEM. The results show that the development and morphology of cracks are affected by the mineral composition, and the sediments with higher clay content tend to form more complex fracture networks. We further propose a morphological prediction model for cracks and compare this model with diagenetic shrinkage fractures under SEM. We found that the effects of mineral composition on both were similar, with more well-developed diagenetic shrinkage fractures in those clay-rich samples. Taken together, this study implies the feasibility of using physical simulation experiment of desiccation cracks to invert diagenetic shrinkage fractures and provides new insights into the mechanism and development regularity of diagenetic shrinkage fractures.

Simulation of crack patterns in quasi-brittle materials under thermal shock using phase field and cohesive zone models

Complex crack patterns are usually formed on the surface of brittle and quasi-brittle solids under thermal shock. In this paper, the phase field coupled cohesive zone model is established to simulate the brittle and quasi-brittle fracture processes in three-dimensional solids, especially to reproduce the complex crack patterns under thermal shock. Several examples are given to illustrate the effectiveness of the model to complex fracture problems under thermal shock: from uniaxial tensile and thermal shrinkage fracture of a one-dimensional rod to nucleation, propagation, and crack pattern formation of thermal shock crack of a three-dimensional ceramic bottle. In addition, the formation mechanism of crack patterns in ceramic bottle is discussed, especially the dominant role of the difference in thermal expansion coefficients between the ceramic matrix layer and the glaze layer in the formation of crack patterns and the final crack density.

Effect of compression loading speeds on the room temperature mechanical properties of as-extruded AZ31 magnesium alloy

The room temperature compression experiments of as-extruded AZ31 magnesium alloy under different loading speeds were carried out on a universal tensile testing machine. The fracture failure characteristics and mechanism of the alloy under different compression loading speeds were analyzed by scanning electron microscope (SEM) and optical microscope (OM). The results show that during the compression test, the crushed AZ31 magnesium alloy sample has a certain pier coarseness, the macro fracture of the sample is located at one third of the sample, and the macro fracture mode is 45° shear fracture with the sample axis; With the increase of loading speed, the coincidence degree of macro fracture becomes worse, and its compressive strength changes in an undulating manner. When the loading speed is 2mm/min, the compressive strength reaches the peak value of 413MPa, and the fracture morphology of the sample shows a typical flat and flat rock like ductile brittle mixed fracture. With the increase of loading speed, the proportion of brittle fracture components increases, the shape of shrinkage fracture is rock like fracture, and the fracture fluctuation is relatively slow, the dimples distributed on the fracture surface are elongated and torn, and the compression speed has no obvious effect on the fracture morphology.

Influence of the Activator Concentration and Solid/Liquid Ratio on the Strength and Shrinkage Characteristics of Alkali‐Activated Slag Geopolymer Pastes

Geopolymers have distinct advantages such as having energy‐saving properties, being an environmentally protective material, and having high mechanical strength and durability. However, the shrinkage of the geopolymer materials is one of the major problems to affect its practical application. In this study, blast furnace slag‐based geopolymer pastes were prepared using sodium silicate and sodium hydroxide as activators to investigate the effect of the activator concentration and solid/liquid ratio on strength and shrinkage properties. For a better understanding of the reaction mechanism and microstructure of the geopolymer pastes, a multitechnique approach including scanning electron microscopy, X‐ray diffraction, and Fourier transform infrared spectra was carried out. The results showed that the geopolymers compressive strength increased significantly as the activator concentration increased. The increase in activator concentration first increased the flexural strength and then decreased and reached the maximum when the activator concentration was 40%. A higher activator concentration, as well as a lower solid/liquid ratio, generally led to serious geopolymers drying shrinkage. These findings are expected to be ascribed from the changes in the content of the alkali‐activated product (i.e., hydrate calcium aluminosilicate), which depends on the activator concentration. The increase in C‐A‐S‐H gel (hydrate calcium aluminosilicate) compacts paste densifiers but causes shrinkage fracture concerns. These results provide an appropriate proportion for alkali‐activated slag geopolymer pastes with better mechanical strength and antidry‐shrinkage cracking properties, which are beneficial for the further applications of geopolymer materials.

The influence of fracture development on quality and distribution of volcanic reservoirs: a case study from the carboniferous volcanic reservoirs in the Xiquan area, eastern Junggar Basin

The distribution pattern of fractures in the Carboniferous volcanic rocks controls the oil and gas distribution in the Xiquan area located in the eastern Junggar Basin. This paper describes the types, characteristics, distribution of fractures in the volcanic rocks, and the evolutionary history of fractures, as well as the influence of fractures on the reservoir distribution in this area, based on analyzing cores, casting thin sections, imaging logging data, the measurement of the physical properties and integrated with the production testing. The lithology of these Carboniferous volcanic rocks is primarily andesite and volcanic breccia. Basalt, dacite, tuff, breccia lava, tuffaceous sandstone, and tuffite were also present. The fracture types are mainly shrinkage fractures, weathered fractures, dissolution fractures, and structural fractures, the majority of which are structural fractures and weathered fractures. The distribution of fractures has obvious zonation characteristics in the vertical direction. Fractures are mainly distributed at four intervals under the top surface of the Carboniferous unconformity: 0–50 m, 65–115 m, 125–155 m, and 170–210 m. There are mostly weathered fractures and dissolution fractures in the 0–50-m interval. The physical properties and oil production of andesite are the highest, and weathering fractures and dissolution fractures play a major role in controlling the secondary pores of volcanic lava and the formation of favorable reservoirs in this interval. The structural fractures were developed in the intervals of 65–115 m, 125–155 m, and 170–210 m. The physical properties and oil production of volcanic breccia are the highest, and therefore, structural fractures mainly control the formation of favorable reservoir in volcanic breccia in these three intervals. The evolution of fractures in the Carboniferous volcanic rocks experienced four phases: the condensation and shrinkage fracture stage, which developed the primary pores in the middle-late Carboniferous period; the weathered fracture and dissolution fracture stage, which greatly increased the porosity in the late Carboniferous period to the early-middle Permian period; the structural fracture and weathered fracture stage, which greatly increased the porosity and permeability of the reservoir from the end of the Triassic to the early Cretaceous period; and the filled fracture and dissolution fracture stage, which can also greatly increase the porosity of the volcanic reservoir and occurred wholly within the late Cretaceous period until the present.

Influence of Polymer Additives on Mechanical Fracture Properties and on Shrinkage of Alkali Activated Slag Mortars

Alkali-activated slags represent an alternative to ordinary Portland cement due to reducing the environmental impact of the building industry. In spite of the numerous advantages of alkali activated slag mortars, alkali-activated aluminosilicates have big disadvantage – high value of shrinkage followed by formation of microcracks. This effect is caused by both autogenous and drying shrinkage and it finally results in volume contraction, microcracking and deterioration of the mechanical fracture properties. Therefore, using various types of polymer admixtures can overcome these problems. The aim of this paper is to present the effect of shrinkage-reducing admixture Peramin® SRA 40, polymer polyethylene glycol 1000 and polypropylene glycol on shrinkage and mechanical fracture characteristics of alkali-activated slag mortars. These admixtures were used in amount 0–2.0% weight of slag. The results showed that with increasing content of admixtures compressive and flexural strength decreased. Fracture tests with acoustic emission activity during this testing were carried out. Addition of 2% Peramin® SRA decreased shrinkage by 55%, but with 1% of Peramin® SRA the shrinkage was reduced only by 10%. Specimen with 1% of Peramin® is the most durable material, but more brittle compared to specimens with 1 and 2% of polypropylene glycol.

Research of Mo Powder’s Densification during Sintering

Mo powder was pressed into rods by cold isostatic pressing and sintered by multi-function furnace. Physical and chemical properties of sintering samples at different temperature were tested such as chemical elements, density, area shrinkage ratio and fracture surface morphology. Through the investigation we can draw the conclusions as following: Mo powder softens at 1353K. The temperature of beginning metallization is 1833K. In the range of 1713K~1953K, impurity contents such as C and O drop down fast and density increases sharply. When sintering temperature rises from 1833K to 1953K, the grains of sintering rods are fine. When the sintering temperature surpasses 2073K, the grains grow up very fast. The sintering shrinkage ratio enlarges quickly.

Application of Vibration Test Methods in Cement-Treated Aggregate

The disease causes by the application of cement-stabilized macadam in our country first-class highway mainly performance as serious shrinkage fracture and other destructions like decreased capacity etc.This mainly related to test, design and other methods of the cement stabilized macadam. In the cement stabilization granular base construction,according to the standard job practice, uses the inorganic binding stable material compaction test to perform the standard compaction test. Doing compactness test at the scene, always present that the dry weight density is bigger than the maximum value result made by compaction test, result made by compactness test can more than 100%.The compaction principle of vibration compaction test is through pressure exciting force over the compacted materials,forced the downing of solid materials have a "resonance", In this state, the small particles aggregate can filling the gap between the large particles aggregate, to achieve the dense state. And during this process do not need too much water as lubricant. Therefore the vibration compaction test definite intensity result tallies with the scene reality. To imitation effects of roller compacted to improve the performance of cement stabilized gravel, the use of vibration method designed cement stabilized gravel is very necessary and timely.

Nano structure and transformation mechanism of white layer for AISI1045 steel during impact wear

Impact wear was carried out for annealed AISI1045 steel in this study. With the impact frequency of 600 times per min, an 8.29 kN impact load was applied on the constant contact area of 540.08 mm 2 at the individual attack angles 60° and 90°. The microstructure of white layer for annealed AISI1045 steel was examined by SEM, TEM and HRTEM. It was found that nano structures with ferrite and cementite have been formed in white layer after impact of AISI1045 steel. Nano crystallization mechanism for ferrite is from moving, interacting and rearranging of dislocations, resulting in production of dislocation walls. With increasing strain, the density of pinned dislocations, whose Burgers vectors are usually vertical to the wall, correspondingly increases along the dislocation wall, i.e., θ/ b increases. That, finally, forms subgrain boundaries with small angle θ. In addition, the density of slippery or shear-susceptible dislocations, whose Burgers vectors are often parallel to dislocation walls, also increases at the same time. The slipping of dislocations in many places along the boundary of subgrains will result in the rotation of crystals to form boundaries with large angles. Nano crystallized mechanism for cementite is mainly due to shearing fracture, neck-like shrinkage fracture and carbides dissolving under the impact. The cementite thinning and the formation of slipping stages will increase the surface energy per volume, which causes the dissolution of cementite. The chemical potential energy difference between carbon atoms and cementite is a driver for dissolving cementite. The moving, reacting and proliferating of dislocations promote carbon atoms diffusing and migrating to distant ferrite from the boundary of cementite, which accelerates the dissolution of cementite.

Laboratory device for restrained shrinkage fracture of soil-cement mixtures : Penev, D; Kawamura, M Mater StructV25, N146, March 1992, P115–120

Laboratory device for restrained shrinkage fracture of soil-cement mixtures : Penev, D; Kawamura, M Mater StructV25, N146, March 1992, P115–120

A laboratory device for restrained shrinkage fracture of soil-cement mixtures

A procedure of shrinkage fracture testing for soil-cement mixtures made using a new laboratory test device is described. The strain energy release rates for some soil-cements are obtained from the experimental data. The creep behaviour of soil-cement mixtures under the restrained shrinkage test conditions are compared with that under a constant compressive load. Characteristics of shrinkage cracking of soil-cement mixtures can be explained from the viewpoint of the strain energy release rates obtained by use, of the device.