Research on the Characteristics of Water in the Sleeper Void of Double-Block Ballastless Track

According to the investigation and survey of the service condition of the double-block ballastless track in China, the breakage rate in the rich rainfall areas or the poor drainage lots of double-block ballastless track runs much faster than the dry areas. Some typical diseases, such as sleeper loose, contact loss between sleeper and roadbed slab, will lead to water still in the sleeper void. Free water underneath the sleepers would become dynamic water with certain pressure and flow rate under the high speed and high frequency action of train loads. Dynamic water is able to accelerate crack growth rate and scour the bonding interfaces between sleeper and roadbed slab[1,, affecting the safety ,durability and riding quality of track structure. It is meaningful for us to research on sleeper loose of double-block ballastless track under the coupling action of train load and dynamic water and prove the mechanism of sleeper loose in double-block ballastless track under action of dynamic water. Calculating the value of water pressure and velocity of flow and then providing references for study on the hydrodynamic characteristics.

Fatigue and Fracture of Engineering Alloys

This chapter provides information and data on the fatigue and fracture properties of steel, aluminum, and titanium alloys. It explains how microstructure, grain size, inclusions, and other factors affect the fracture toughness and fatigue life of these materials and the extent to which they can be optimized. It also discusses the effect of metalworking and heat treatment, the influence of loading and operating conditions, and factors such as corrosion damage that can accelerate crack growth rates.

Remaining life of a vessel containing an internal corner crack under repeated thermal shock

The remaining life for a hypothetical pressure vessel containing a defect which is subject to thermal shock has been calculated. Twelve cases of thermal shock loads of different severity characterized by the dimensionless parameters, Biot (B) and Fourier (F) numbers, were analysed by finite element modelling (FEM). The estimation of remaining life for each case was carried out based on the PD6493 defect assessment procedure (1). The effect of thermal shock on the crack growth rate was quantified showing that more severe shocks accelerate crack growth while less severe shocks may lead to slow growth or eventual crack arrest.

Fatigue Crack Propagation in Low-Alloy Heat-Treated Steels

The rates of fatigue crack propagation in several heat-treated steels were determined for several alloy steels heat-treated to yield strengths in the range 70,000 to 125,000 psi. For one steel crack growth rates were determined for both a thick notch bend specimen and for thin notched plate specimens. It is observed that the concepts of Griffith-Irwin fracture mechanics successfully correlate crack growth rates in the various geometry and thicknesses employed. However, the specific relationship is dependent on yield strength level. Microscopic examination suggests in some instances that inclusion segregates act effectively to locally accelerate crack growth rates.