An Analysis of Relationship between the Microfracture Features and Mineral Morphology of Granite

Using the techniques of X-ray diffraction, polarizing microscopy, uniaxial compression, and scanning electron microscopy (SEM), the relationships between the microfracture features and mineral morphology of granite were studied. The results showed that feldspar, quartz, and biotite are the main components of the granite samples in this study. Biotite has a self-shaped flake structure with perfect cleavage. K-feldspar has a lattice double crystal structure with two groups of cleavage. Plagioclase has a semi-self-shaped plate structure with two groups of cleavage. Quartz is prismatic or granular and exhibits noncleavage. The microfracture features of biotite are flaky with exfoliation, and flake cleavage fracture is mainly determined by its peculiar flaky cleavage. Feldspar (K-feldspar and plagioclase) is plate, layered, or two groups of cleavage and is also mainly determined by its peculiar two groups of cleavage. The microfracture features of quartz are highly irregular, with many randomly distributed intergranular and transgranular cracks, small particles or granule bulges, similar to quartz crystal, and this is due to the noncleavage feature of quartz itself. It is demonstrated that microfractures are preferentially ruptured along cleavage planes for these granite minerals under the action of external forces.

Dynamic deformation and fracturing properties of concrete under biaxial confinements

The study of deformation and fracturing properties of concrete is essential to understand failure mechanisms of concrete material, especially under extreme and complex loading conditions, e.g. high strain rates and multiple confinements. In this study, dynamic deformation and fracturing behaviour of ordinary concrete under biaxial confinements are investigated by using a triaxial Hopkinson bar system, three-dimensional digital image correlation, and synchrotron X-ray computed tomography techniques. Results show that compressive strain localisation areas appear around aggregates due to the elastic difference between aggregate and matrix, where accompanied with initiation of interfacial cracks and propagation of main cracks. Transgranular cracks can also be observed in the central of specimen in CT slices due to the effect of strain concentration. In addition, CT slices with distinct properties in various directions indicate the anisotropic fracturing behaviour of concrete due to the effect of biaxial confinements.

Microcrack Growth Properties of Granite under Ultrasonic High-Frequency Excitation

The failure of most rock materials is essentially a process of crack initiation and propagation. It is of great significance to study the microcrack growth characteristics of granite under ultrasonic high-frequency excitation for understanding the failure mechanism of rock under ultrasonic vibration. In this paper, the experimental and numerical simulation methods are used to study the propagation characteristics of rock cracks under ultrasonic vibration. Scanning electron microscopy (SEM) was used to observe the growth of microcracks in granite samples after ultrasonic vibration for 0 min, 2 min, and 4 min. A discrete element software PFC2D was used to simulate and solve the cracking mechanism of rock cracks under ultrasonic vibration. Also, it is found that the action of ultrasonic vibration can effectively promote the development of microcracks in the granite samples. The main three cracks causing the failure of quartz under the ultrasonic high frequency are intragranular cracks, transgranular cracks, and grain boundary cracks. The breakage of transgranular cracks usually contributes a shell-like fracture, that is, a regular curved surface with a concentric circular pattern appears on the fracture surface, which is a typical quartz brittle fracture mode. In addition, the feldspar grain failure is mainly caused by intragranular crack and transgranular crack. Microcracks are wavy expansion in feldspar grain. Mica failure is mainly caused by grain boundary crack, and the effect of lamellar cleavage on the failure of mica is significant. Moreover, it is also found that the mechanism of microcrack propagation is tensile failure. The failure of feldspar grains is mainly contributed to the failure of granite.

Microstructural Evolution in SAC305 and SAC-Bi Solders Subjected to Mechanical Cycling

Fatigue failure of solder joints is one of the most common methods by which electronic packages fail. Electronic assemblies usually must cope with a temperature varying environment. Due to the mismatches in coefficients of thermal expansion (CTEs) of the various assembly materials, the solder joints are subjected to cyclic thermal-mechanical loading during temperature cycling. The main focus of this work is to investigate the changes in microstructure that occur in SAC305 and SAC+Bi lead free solders subjected to mechanical cycling. In this paper, we report on results for the SAC+Bi solder commonly known as SAC_Q or CYCLOMAX. Uniaxial solder specimens were prepared in glass tubes, and the outside surfaces were polished. A nanoindenter was then used to mark fixed regions on the samples for subsequent microscopy evaluation. The samples were subjected to mechanical cycling, and the microstructures of the selected fixed regions were recorded after various durations of cycling using Scanning Electron Microscopy (SEM). Using the recorded images, it was observed that the cycling induced damage consisted primarily of small intergranular cracks forming along the subgrain boundaries within dendrites. These cracks continued to grow as the cycling continued, resulting in a weakening of the dendrite structure, and eventually to the formation of large transgranular cracks. The distribution and size of the intermetallic particles in the inter-dendritic regions were observed to remain essentially unchanged.

Effects of V2O5 and ZrO2 on Chipping Ratio of MnZn Ferrite Core

Cracking and chipping of MnZn Ferrites usually occur during the grinding process although proper additives such as V2O5can restrain development of cracks. To study the mechanisms, the effects of adding V2O5or ZrO2to MnZn ferrite were investigated by the rattler test. It was confirmed that adding V2O5could improve the toughness of MnZn ferrite while addition of ZrO2showed opposite result. Based on micro-structure analysis, it was found that adding V2O5increased ratio of intergranular fracture mode to the transgranular but adding ZrO2caused more transgranular cracks. Besides, V2O5addition changed its grain size distribution and resulted in some larger grains. Possible mechanisms of the toughness improvement were proposed according the above findings.

Stress Corrosion Cracking of Stainless Steel Expansion Joint for Heat-Supply Network

Tree-like transgranular cracks were found at the bottom of a expansion joint bellow that had been used for heat-supply network at 90°C and 0.8MPa. A failure analysis was conducted, including visual, microstructural, compositional, and mechanical characterization, to determine the cause and source of the degradation. Branched, brittle cracks were observed in the failure region and exhibited transgranular propagation. The results showed that the concentration of the chloride in the deposit was 248 ppm in the intermittent wet/dry cycles situation. It was determined that the likely cause of failure was neutral pH, Concentrated chloride-induced stress corrosion cracking.

Statistical behaviour of the deformation for first loading of polycrystalline ice

A statistical analysis of the lengths of grain-boundary and transgranular cracks induced during the initial straining of columnar-grain ice by a compressive load applied perpendicular to the long direction of the columns is presented. The analysis shows that the crack lengths are randomly distributed and form distinct but correlated populations.The lognormal distribution function is shown to be a good descriptor of the populations for 5–90% of their range. Statistical models are presented for the lognormal behaviour of the crack-length distribution and for the strain dependence of the crack density. The models assume that a change in the value of the random variable of the respective population depends on the population value of the variable at the time of the change. It is shown that the model for the strain dependence of the crack density is suitable for the strain dependence of the acoustic emission, measured in both columnar-grain and granular ice subject to constant compressive loads. Evidence is also presented for a lognormal dependence of the dislocation density on strain. The analysis demonstrates that the cracks that form during the initial straining of polycrystalline ice are independent, random events and that the resulting crack populations are precursors to failure by fracture.

Deformation and Comminution of Shock Loaded α-Al2O3 in the Mescall Zone of Ceramic Armor

Incursion of high density penetrators into ceramic armor is preceded by the formation of a finely comminuted rubble bed at the penetrator tip, the Mescall zone. The deformation and failure processes that result in the Mescall zone are critical to understanding penetration resistance and to modeling penetration behavior. Transmission electron microscopy (TEM) was used to examine shock loaded material in the vicinity of an explosive detonation in α-Al2O3 and to infer the phenomenology of plasticity and fracture occurring at the tip of an advancing penetrator in ceramic armor. Comminution proceeds by intergranular fracture until the fragment size approaches the grain size. Further fragmentation proceeds by transgranular cracks, which nucleate at preexisting microvoids and at intersections of basal twins and primary and secondary slip bands.