Seismic Damage Prediction Method for Lining Structures Based on the SEDR Principle

The safety and stability of lining structures are core concerns of tunnel and underground engineering. It is crucial to determine whether a lining structure would crack and which direction the crack would expand with seismic excitation. In previous literature, the principle based on stress and strain has been widely used to predict the seismic damage of lining structures, whereas it cannot specify the cracking modes. Taking account of that deficiency, this paper introduces the strain energy density ratio (SEDR) principle and proposes a seismic damage prediction method for lining structures, which can precisely predict the crack positions and expansion directions. Moreover, numerical simulations of the typical seismic damage sections of two tunnels in the Great Wenchuan Earthquake and a calculating example of the theoretical equations are conducted to verify the proposed method. In summary, the numerical simulation results show that the arch springing cracks first, and the invert cracks next; then the cracks expand to the spandrel, and finally, they form oblique cracks, annular cracks, and longitudinal cracks, whose positions and patterns are in accordance with the field investigation results. In terms of the calculating example results, the obtained two-fold SEDR and cracking angle θ are 1.87 and −6.28°, respectively, which are consistent with the numerical simulation results. Therefore, one can see that the proposed seismic damage prediction method based on the SEDR principle is quite accurate. This method can be used to predict the seismic damage of lining structures and provide a reference for the research of the damage mechanism of tunnels.

Efecto del H2S en la Susceptibilidad al Agrietamiento de Dos Aceros Microaleados para Tubería

Cracking in sour media modes were observed, and these were related mainly to the microstructure produced during the thermomechanical process of two microalloyed steels grade API X 52. Through the use of linear elastic fracture mechanics modified specimens. Steels loaded at similar initial stress intensity factors showed different cracking modes that were related directly to their different microstructures. Steels microstructures indicate different fabrication routes. Testing temperature played an important role on switching the cracking characteristics being remarkable by the ferrite-pearlite steel microstructure. A banded microstructure is susceptible to the effects of hydrogen at room T. While, an acicular ferrite microstructure with carbides patches at grain boundaries is susceptible to anodic dissolution in front of the crack tip, no matter the temperature being tested. Key words: microalloyed steels, sour service, cracking modes, microstructure.

Determination of Fracture Origin in Ceramic Radial Rotor by Taking Photographs at Failure From Two or Three Directions

A technique involving taking moment photographs from two or three directions at failure of ceramic radial rotor was developed to determine the position of fracture origin of the radial rotor revolving at a high speed. The position of the fracture origin of the silicon nitride radial rotor, 60mm in outer diameter and fabricated by injection molding, was demonstrated to be the fillet at the base of the shaft subjected to high stress. Furthermore, the dependence of cracking modes of rotors on the position of fracture origin was demonstrated using ceramic rotors with artificial flaws.

Fundamental and Practical Aspects of Crack Growth under Corrosion Fatigue Conditions

The crack growth mechanism is dependent on environment, frequency and temperature as shown by some examples. Two cracking modes are observed in aluminium alloys: the tensile mode and the shear mode. Examples show that inert environments promote the shear mode whereas aggressive environments promote the tensile mode. Information from constant-amplitude tests need not be applicable to service loading conditions as illustrated by an example. Significant environmental effects on crack growths are observed in aircraft flight-simulation tests. Growth delays induced by severe flights occur in all environments. As a consequence the truncation of the load spectrum at the high level end is a difficult question. The problem of producing relevant information in the laboratory is discussed.