Developing Condition-Based Triggers for Bridge Deck Maintenance and Rehabilitation Treatments

The bridges in the U.S. highway system suffer from deficiencies in both their structural condition and functionality. In an effort to improve the condition of bridges, highway agencies continually seek effective and efficient approaches to maintenance and rehabilitation (M&R) treatments for their bridges. However, one drawback to new approaches is that highway agencies have long relied on the subjective judgment of their engineers to determine the time or condition at which to implement the treatments as well as the types of treatments to be applied. The literature shows that previous researchers mainly focused on time-based M&R strategies, but there have been some efforts toward developing condition-based strategies, such as the Indiana Bridge Management System (IBMS). While IBMS and similar systems were laudable efforts, they also were developed on the basis of the judgment and experience of bridge management personnel and were not data-driven

Simulation of Titanium and Titanium Alloy Powder Compact Forging

Simulation can be divided into two types: physical simulation and interactive numerical simulation. Physical simulation depends on testing smaller or cheaper samples rather than real objects to simplify models; Interactive simulation, which is also been called numerical simulation is depending on mathematical models and computer program to get the detailed results of the model. In this thesis, 48 compression test samples of sintered powder compacts of pure titanium (HDH) and Ti-6Al-4V were tested by using Gleeble 1500 thermal simulation testing machine. The height reduction of all samples was set as 70% and the other experiment conditions were set as three different temperatures and two strain rates. The stress-strain curves of all samples have been collected in the computer which could be considered as basic for the 3D-FEM simulation. Metal plastic forming is a coupled thermo-stress process in which the workpiece is loaded and restricted in some boundary conditions which include force, temperature, velocity, geometry, friction and so on. Thus, the scientific objective of plastic forming simulation is to be able to predict and control these phenomenon and transformation.The upsetting of powder compacts of pure titanium (HDH) and Ti-6Al-4V (GA) was studied in this thesis based on theoretical and physical models and numerical simulation. Based on the constituent model in ABAQUS and the results of thermo-simulation, the upsetting of 3D-FEM model was built which involved heat transfer, deformation and densification. The temperature field, Mises stress field, strain rate field, strain field and relative density field of pure titanium (HDH) and Ti-6Al-4V (GA) powder compacts were attained. Comparing the density distribution of the metallographic phases in optical microscope with the results of simulation, basically, the experimental results are in general agreement with the results of simulation

Ordering graphs with small index and its application

AbstractWe consider the problem of ordering connected graphs by index (the largest eigenvalue). The asymptotic ordering for the connected graphs with index less than 2+5 is determined. Its application to the study of acyclic Kekulean molecules with big HOMO–LUMO separation is also given