ALBERT

Description: High speed photography by Caustics method using Cranz–Schardin camera was used to study crack propagation and divergence in thermally tempered glass. Tempered 10 mm thick glass plates were used as a specimen. New crack generation by two crack collision was observed. Regarding the presence/absence of new cracks, the dependence of the two cracks on the collision angle was confirmed. Considering that it is based on the synthesis of stress ?CR generated at the crack tip, tensile stress necessary for the generation of new cracks could be created.

Description: BACKGROUND: A rolling bearing bush alloy of a feed water pump that is part of a waste heat boiler of an oil refinery has failed. OBJECTIVE: We try to analyze the reasons that caused the working surface of the bearing bush of the water pump to fall off and then give some suggestions to this failure. METHODS: The composition, microstructure, pit, and crack morphology of the bearing bush alloy were analyzed by the X-ray fluorescent analysis, the energy spectrum analysis, the optical microscope and the scanning electron microscope, respectively. RESULTS: The content of Pb in the bearing bush alloy was high, and the Cu content was low. The primary crystal Cu6Sn5 was low, and the crystal of SnSb with low density moved upward and segregated. The above phenomenon reduced the fatigue resistance of the babbitt alloy. The bearing bush was subjected to alternating loads in service, and several small cracks were generated on the bearing bush alloy working surface. The cracks continued to expand and connected with each other. Fatigue pitting occurred on the bearing bush working surface, a large number of pits were formed, and several large alloy blocks fell off. CONCLUSIONS: The Pb content in the failed bearing bush alloy was too high and did not meet the requirements of the Sn-based babbitt alloys in the national standard. At the same time, the primary crystal Cu6Sn5 formed by Cu and Sn was low due to the low Cu content, and the crystal SnSb with a small density moved upward and segregated. The composition of the babbitt alloy, especially the Cu content, should be strictly controlled to ensure the safe and reliable operation of the bearing.

Description: BACKGROUND: The analysis of seismic stability of structure is important in the field of engineering. OBJECTIVE: This study aims to verify the reliability of numerical simulation in seismic stability of reinforced concrete (RC) frame structure. METHODS: Based on the numerical simulation, the material constitutive model of RC frame structure was introduced and then a finite element model was established through ABAQUS to analyze its seismic stability. RESULTS: The simulation results of ABAQUS were similar to the test values, the tangent slope of the skeleton curve of the structure decreased gradually, the interstorey displacement of storey 1 was the largest, the maximum error of the interstorey displacement angle was 0.005, and the ductility coefficient was 4. CONCLUSIONS: The experimental results verify the reliability of the numerical simulation method and provide some theoretical support for its better application in the study of seismic stability.

Description: The objective of the work is to derive analytical solutions based on the Riemann–Hilbert (R–H) approach for semipermeable strip saturated two unequal collinear cracks in arbitrary polarized piezoelectric media. We particularly consider the influence of far field electromechanical loadings, poling direction and different crack-face boundary conditions. The problem is mathematically formulated into a set of non-homogeneous R–H problems in terms of complex potential functions (related to field components) using complex variable and extended Stroh formalism approach. After solving these equations, explicit solutions are obtained for the involved unknown complex potential functions and hence, the stress and electric displacement components at any point within the domain. Furthermore, after employing standard limiting conditions, explicit expressions for some conventional fracture parameters such as saturated zone lengths (in terms of nonlinear equations), local stress intensity factors and crack opening displacement are obtained. Numerical studies are presented for the PZT-4H material to analyze the effects of prescribed electromechanical loadings, inter-cracks distance, crack-face conditions and poling direction on the defined fracture parameters.

Description: High speed photography by Caustics method using Cranz-Schardin camera was studied for crack propagation and divergence in thermally tempered glass. Tempered 10 mm thick glass plates were used as a specimen. Two types of bifurcation and branching as the crack divergence could be observed and clarified even in 10 mm thick tempered glass. The difference of the shadow spot sizes between bifurcation type and branching type could be confirmed.

Description: In the component operated at elevated temperatures, the life evaluation should be made in consideration of both creep and fatigue (creep-fatigue) such as the linear damage summation rule. However, the concept of creep-fatigue life evaluation has not spread well in the industry. In order to consider the reason, a series of past creep-fatigue research was surveyed, namely experimental methods, life evaluation procedures and strength design guidelines. As a result, it was revealed that the mechanism of creep-fatigue interaction has not been fully clarified yet, which results in obscuring the necessity of creep-fatigue life evaluation. The necessity of creep-fatigue life evaluation was reviewed and consequently it proved to be necessary in two cases. One is the case where the creep-fatigue interaction is significant for some kinds of material, loading modes and temperatures. The other is one where the amount of creep damage is almost the same as that of fatigue damage even though the creep-fatigue interaction is insignificant.

Description: High speed photography using the Cranz-Schardin camera was performed to study the crack divergence and divergence angle in thermally tempered glass. A tempered 3.5 mm thick glass plate was used as a specimen. It was shown that two types of bifurcation and branching existed as the crack divergence. The divergence angle was smaller than the value calculated from the principle of optimal design and showed an acute angle.

Description: BACKGROUND: Under plane strain conditions, a crack model was developed on a plane interface between two different materials, which assumes the existence near its tip of the faces contact area and a narrow lateral pre-fracture zone in a less crack-resistant material of the composite compound. The pre-fracture zone is modeled by the line of normal displacement rupture, on which the normal stress is equal to the tensile strength of the material. Assuming that the dimensions of the pre-fracture zone and the contact zone have the same order of magnitude and are significantly smaller than the crack length, the problem is reduced to the vector Wiener–Hopf equation. METHODS: An approximate method for solving the vector Wiener–Hopf equation was developed, which was used to obtain the equations for determining the sizes of the pre-fracture zone and the contact faces area. The pre-fracture zone orientation was determined from the condition of the potential energy maximum accumulated in the zone. Numerical calculations of the indicated parameters and analysis of their dependences on the configuration and module of external load are executed. RESULTS: A significant mutual influence of the pre-fracture zone and crack faces contact on their sizes and orientation of the zone was revealed.

Description: Tensile stiffness of interfacial layered rock is the basis of studying the law of interlaminar propagation of hydraulic cracks. We used similar materials to make simulated specimens of sand-mud layered rock with prefabricated cracks, and used the digital image correlation (DIC) technique together with the three-point bending (TPB) test to obtain the strain field near the prefabricated crack tip in tensile state. Combined with the tensile stress in the corresponding area calculated by the load of the tester, the tensile stress-displacement curve at the interface of layered rock is obtained, and the tensile stiffness and interfacial fracture law at the interface of layered rock is calculated by the curve. The results show that in the process of tensile failure, before reaching its peak value, the interfacial tension stress of layered rock has a linear elastic deformation stage followed by a short hardening stage. Upon reaching the peak value, it is accompanied by interfacial failure and macro-cracks, and then the load decreases and enters the softening stage, which results in the complete destruction of the interface. The tensile stiffness values of layered rock with different sizes vary greatly, which indicates that the interfacial tensile stiffness values are sensitive to the specimen size and have a size effect. The results are of great significance to the study of the law of hydraulic fracture propagation in the interface of layered rock.

Description: Scaling effects governing the creep behaviour of unnotched and uncracked metallic specimens are investigated by applying similarity considerations and fractal modelling to experimental results provided in the literature. The focus is on stress rupture tests conducted at elevated temperatures on Cr-Mo-V steel cylindrical bars of different sizes. The observed specimen-size effects on the ? versus tR creep resistance diagrams are interpreted in terms of incomplete self-similarity and fractal weakening (lacunarity) of the specimen reacting cross-section. That leads to a scale-invariant (fractal) formulation of the creep rupture law in terms of renormalized stress.