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Hao S.,ACII INC | Strom B.W.,Northwestern University | Gordon G.,Honeywell | Krishnaswamy S.,Northwestern University | Achenbach J.D.,Northwestern University
Research in Nondestructive Evaluation | Year: 2011

Scattering of time-harmonic Lamb wave modes by a partial spherical corrosion pit in a plate is investigated. By using superposition, the total field consists of the incident and scattered fields, where the latter is generated by tractions on the surface of the cavity. In the approximation advanced in this article these tractions are represented by time-harmonic body forces on a trace of the cavity in the interior of the plate. The acoustic radiation from the resultants of these body forces applied to the surface of the plate approximates the scattered field. The resultant forces are decomposed in symmetric and anti-symmetric systems, which generate symmetric and anti-symmetric radiating modes. The time-harmonic elastodynamic form of the reciprocity theorem is employed to obtain an analytical solution to the scattered field amplitudes. We obtain the ratio of scattered to incident Lamb mode amplitudes, which in a closed generalized form include material properties, geometry of the pit and layer, and angular frequency of the incident wave. Results of this study yield graphical representations for the amplitude ratios with respect to pit geometry and has the potential to lead to a unique solution of the inverse problem under some conditions. © American Society for Nondestructive Testing.

Structures Congress 2011 - Proceedings of the 2011 Structures Congress | Year: 2011

This article discusses the issues in structural design revealed by the highway I35W Bridge's collapse that occurred at August 1st, 2007, based on an analysis of the bridge's original design drawings, a series of detailed finite elements computations, and the material evidences disclosed by National Safety Transportation Safety Board (NTSB) official investigation. These issues include (i) the redundancy consideration for multi-span bridge; (ii) the reason for those undersized designs in that bridge; (iii) the effects of lateral force on gusset plates' load capacity in steel-truss structure; (iv) the criterion of gusset plate's stability and a thin-plate theory-based model for load-rating. This analysis concludes that the lessons learned from the I35W Bridge may have certain significance for the safety assessments of those similarly-structured steel bridges. A bridge's service life is 75 years or longer. According to a NTSB's document [37], there are more than hundreds this kind of aged bridges still in service [4]. © ASCE 2011.

IOP Conference Series: Materials Science and Engineering | Year: 2014

August 1st of 2007, 6:05PM, the interstate highway I35W Bridge in the City Minneapolis, Minnesota, collapsed suddenly. The 8 traffic-lane, 1000-foot-long deck of the 1907-foot-long bridge fell into Mississippi River within seconds, resulted in 13 fatalities and 145 injuries. This paper is based on a report of a preliminary analysis of this disaster [27], which was submitted to the related administrative agencies at the September of 2007. By comparing the results in that report with the materials' evidences of National Safety Transportation Safety Board (NTSB) official investigation[1,2] and recent in-depth analyses [28,29], it seems that the issues addressed in this earlier analysis may still have certain significance for the safety assessment of those similarly-structured steel bridges today. A bridge's service life is 75 years or longer. According to a NTSB's document [37], there are more than hundreds this kind of bridges still on service [4]. © 2010 IOP Publishing Ltd.

A three-dimensional phase field model of anisotropic polycrystalline solids has been developed. In this model the system's free energy is derived in a generalized form based on Ginzburg-Landau's (GL) theory [1], which is a function of lattice's parameters and electron density. A grain boundary in this model is viewed as a discontinuity of periodic atoms array, represented by the Read-Shockley dislocation representation [3]. The Peierls-Nabbaro's dislocation potential [84] has been built into the model to characterize grain boundary's adhesion. Therefore, the model establishes the links between lattice's structure, sub-atomic quantum physics, and the evolutions of grains and grain-boundaries, leading to a meso-scopic constitutive law that governs grains' nucleation, growth, and distortion in a polycrystalline system. This also provides a means to pursue analytical solutions of an alloy's micro-structure's evolution and establishes a framework for corresponding numerical analysis. © 2011 Elsevier B.V. All rights reserved.

Hu B.,China Communications Construction Company Ltd. | Zhang G.J.,China Communications Construction Company Ltd. | Feng L.P.,China Communications Construction Company Ltd. | Hao S.,ACII INC.
Bridge Maintenance, Safety, Management and Life Extension - Proceedings of the 7th International Conference of Bridge Maintenance, Safety and Management, IABMAS 2014 | Year: 2014

This article introduces a procedure on developing for the fatigue residual life evaluation and associated health monitoring design of the orthotropic steel deck part ofJianghai Navigation Bridge(JNB) of Hongkong-Zhuhai-Macao Bridge (HZMB). This bridge is a 6-span cable stayed structure with two main spans of258m-long each and a continuous steel box girder that stretches over about one kilometer, among the 30 kilometer-long HZMB system. Due to the common fatigue issuesthat have presented in many orthotropic steel bridge decks in services, the structural behavior and its effects on fatigue damage evolution have been investigated, although the bridge is stillat its very beginning stage of design. The analytical results will be used for assistingfuture structural health monitoring program once the bridge is erected. © 2014 Taylor & Francis Group.

Hao S.,ACII Inc.
Journal of Bridge Engineering | Year: 2010

The I-35W bridge over the Mississippi River in Minneapolis, Minnesota, collapsed suddenly on August 1, 2007. This note briefly summarizes an analysis based on original design drawings, an investigation of material evidence provided by the National Transportation Safety Board (NTSB), and a full-scale load rating of the bridge superstructure. The results of the investigation and conclusions of the analysis include. (i) The thickness of gusset and the thickness of the side wall of the upper chords were designed proportional to the bending moment solution of a one-dimensional influence line analysis. This fact reveals that the NTSB-disclosed undersized gusset plates are the consequence of a bias toward a "one-dimensional model" in the original design that did not give sufficient consideration to the effects of the forces from diagonal truss members. (ii) Although the bridge's truss-cell structure was appropriately designed, the design of the node that connected the floor members to the main truss-frame was inadequate to effectively distribute live and dead loads. Consequently, the local redundancy provided by the truss-cells was significantly reduced. (iii) A three-dimensional, nonlinear, finite-element, computation-based load rating indicates that some of the gusset plates had almost reached their yield limit when the bridge experienced the design load condition. The bridge was sustained by the additional safety margin provided by the ultimate strength of the ductile steel that comprised the gusset plates. © 2010 ASCE.

Hao S.,ACII INC. | Hao S.,Northwestern University | Lin H.,Dana Canada Corporation | Binomiemi R.R.,Dana Canada Corporation | And 2 more authors.
Computational Materials Science | Year: 2010

It is well-known that atomic-electronic structures determine materials' macro-scale physical properties; however, broad varieties in microstructures and heterogeneities from different scales may significantly amplify or dilute the mechanical behavior of an alloy presented at quantum scale. Hence, breakthrough of computational alloy's design lies in the capabilities to quantitatively and completely integrate key-mechanisms from different scales at each processing step, so as to obtain a unified procedure for establishing quantitative relationships between composition, process, structure, properties, and performance. For this purpose, a multi-scale hierarchical model of intergranular fracture has been developed for polycrystalline systems. As an application example, a carburized steel, which is used for gears and other components in heavy power transmission system, has been analyzed for exploring the ways to improve fracture toughness. As experimental study indicates that the low toughness is often caused by intergranular cracking, this analysis reveals that such a crack initiation can be triggered by the stress concentration at the junctions of grain boundaries when grain boundary adhesion is weak. Therefore, an improved toughness can be achieved by reducing impurities' grain boundary segregation while increasing grains' ductility. © 2010 Elsevier B.V. All rights reserved.

ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) | Year: 2010

The past several decades can be remembered as the most successful period for engineering, which has also brought up great challenges to engineers to digest rapidly-developed ideas, new tools, and novel methodologies while to assure industrial designs and daily operations being safe, economic, and technologically advancing. This article discusses some particular issues in structural design, focused on the lessons learned from the highway I35W Bridge's collapse that occurred at August 1st, 2007, based on a preliminary analysis of this disaster and an associated report submitted to the related administrative agencies [27]. By comparing the results in that report with the materials' evidences of National Safety Transportation Safety Board (NTSB) official investigation[1,2] and the recent in-depth analyses [28,29], it seems that the issues addressed early may still have certain significance for the safety assessments of those similarly-structured steel bridges today. A bridge's service life is 75 years or longer. According to a NTSB's document [37], there are more than hundreds this kind of bridges still on service [4]. Copyright © 2010 by ASME.

Hao S.,ACII Inc.
Bridge Maintenance, Safety, Management, Resilience and Sustainability - Proceedings of the Sixth International Conference on Bridge Maintenance, Safety and Management | Year: 2012

This article briefs the analysis and major conclusions of an independent investigation for the Minneapolis highway I35W Bridge's collapse based on the information released to public and the materials' evidences disclosed by US National Transportation Safety Board (NTSB), discussing the lessons learned in the following three respects: (i) structural design, (ii) issues for maintains and load-rating, (iii) health monitoring. © 2012 Taylor & Francis Group.

Hao S.,ACII INC. | Weertman H.,Northwestern University
ASME 2011 International Mechanical Engineering Congress and Exposition, IMECE 2011 | Year: 2011

A dislocation kinetics-based analysis has been carried out on the toughening mechanisms of alloys. It is concluded that both improved strength and toughening can be achieved through adjusting the short range interatomic interactions between embedded solute atoms, or other point defects, that affect Peierls-Nabarro energy barrier, and the long range interactions between dislocation loops and heterogeneities such coherent precipitates, second phase particles, and crystallography; the latter determines dislocation loops' patterns such as kink-jog formation. In order to quantify the effects of lattice heterogeneities, a variation principle that defines the energy minima of dislocation line configuration has been derived, which includes the effects of three-dimensional stress states and crystallography, instead of the conventional line energy-based Eular formulation that only considers the case under shear stress. This provides an analytical means and associated numerical tool to determine the favorite dislocation loop's patterns in an alloy. The further analysis reveals that double-kinks within single slip-plane have limited effect on toughening while the corresponding bow-out solution may lead to a lower-bound estimate of precipitate strengthening. Therefore, a proposed strategy for toughening is to create dispersed softening centers in strengthened matrix that trap accumulated dislocation loops in the form of mixed double-kinks and jog-induced climbings, for example, helices. These kinds of dislocation patterns are able to spread out localized dislocations from single or close packed parallel slipping planes to many cross-over planes in multiple slip-systems, so as to delay the formation of shear bands while maximize the magnitude of bowing-out induced strengthening. Copyright © 2011 by ASME.

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