Damage detection of long-span bridges using stress influence lines incorporated control charts

Numerous long-span bridges have been built throughout the world in recent years.These bridges are progressively damaged by continuous usage throughout their long service life.The failure of local structural components is detrimental to the performance of the entire bridge,furthermore,detecting the local abnormality at an early stage is difficult.This paper explores a novel damage detection method for long-span bridges by incorporating stress influence lines(SILs)in control charts,and validates the efficacy of the method through a case study of the Tsing Ma Suspension Bridge.Damage indices based on SILs are subsequently proposed and applied to hypothetical damage scenarios in which one or two critical bridge components are subjected to severe damage.The comparison study suggests that the first-order difference of SIL change is an accurate indicator for location of the damage.To some extent,different levels of damage can be quantified by using SILs incorporating with X-bar control chart.Results of this study indicate that the proposed SIL-based method offers a promising technique for damage detection in long-span bridges.

Theoretical Investigation of Influence of Mechanical Stress on Magnetic Properties of Ferromagnetic/Antiferromagnetic Bilayers Deposited on Flexible Substrates

Effect of mechanical stress on magnetic properties of an exchange-biased ferromagnetic/antiferromagnetic bilayer deposited on a flexible substrate is investigated. The hysteresis loops with different magnitudes and orientations of the stress can be classified into three types. The corresponding physical conditions for each type of the loop are deduced based on the principle of minimal energy. The equation of the critical stress is derived, which can judge whether the loops show hysteresis or not. Numerical calculations suggest that except for the magnitude of the mechanical stress, the relative orientation of the stress is also an important factor to tune the exchange bias effect.

An Application of the Modified Shear Lag Model to Study the Influence of Thermal Residual Stresses on the Stiffness and Yield Strength of Short Fiber Reinforced Metal Matrix Composites

The modified shear lag model proposed recently was applied to calculate thermal residual stresses and subsequent stress distributions under tensile and compressive loadings. The expressions for the elastic moduli and the yield strengths under tensile and compressive loadings were derived which take account of thermal residual stresses. The asymmetries in the elastic modulus and the yield strength were interpreted using the derived expressions and the obtained results of the stress calculations. The model predictions have exhibited good agreements with the experimental results and also with the other theoretical predictions

THE INFLUENCE OF DEFORMATIONCONDITIONS ON THE FLOW STRESS ANDMICROSTRUCTURE OF ALLOY GH169

In this paper the dependence of flow stress in alloy GH169 on the deformation temperature, strain and strain rate based on the data of hot working simulation test is defined for the first time. Experimental results indicate that for the alloy GH169 the values of flow stress at high temperatures are much higher than those of alloy steel and the work hardening is remarkable. The deformation conditions have significant influence on the flow stress and microstructure of alloy GH169. It is found that under certain conditions fine grain structure can be obtained even though the deformation processes are carried out at high temperatures. This finding is beneficial to the raise of productivity of forming processes. Increasing the cooling rate after deformation is also favourable to the development of fine grain structure. To sum up, the microstructure of alloy GH169 can be controlled effectively through thermomechanical treatment.

Numerical analysis of elastic coated solids in line contact

A line contact model of elastic coated solids is presented based on the influence coefficients(ICs) of surface displacement and stresses of coating-substrate system and the traditional contact model. The ICs of displacement and stresses are obtained from their corresponding frequency response functions(FRF) by using a conversion method based on fast Fourier transformation(FFT). The contact pressure and the stress field in the subsurface are obtained by employing conjugate gradient method(CGM) and discrete convolution fast Fourier transformation(DC-FFT). Comparison of the contact pressure and subsurface stresses obtained by the numerical method with the exact analytical solutions for Hertz contact is conducted, and the results show that the numerical solution has a very high accuracy and verify the validity of the contact model. The effect of the stiffness and thickness of coatings is further numerically studied. The result shows that the effects on contact pressure and contact width are opposite for hard and soft coatings and are intensified with the increase of coating thickness; the locations of crack initiation and propagation are different for soft and hard coatings; the risk of cracks and delaminations of coatings can be brought down by improving the lubrication condition or optimizing the non-dimensional parameter h/bh. This research offers a tool to numerically analyze the problem of elastic coated solids in line contact and make the blindness and randomness of trial-type coating design less.

The influence of Chinese sentence stress on pitch and duration

The key to improve the naturalness of the synthetic speech is to build a perfect prosodic model. Thus the preliminary study of the influence of sentence stress on prosodic features in Standard Chinese is presented, in which the relationship between duration and pitch under different sentence stress levels is revealed. The results show that: (a) The pitch is the most important factor which carries the sentence stress, with the increase of the sentence stress level, the distribution of pitch moves towards high frequency area. (b) In the case of 'Stress' and 'Light', two peaks are found in the distribution of duration, which means that the duration of some words are affected by sentence stress, but of others are not. (c) The relationship between pitch and duration in 'Normal', 'Stress' and 'Light' are un-correlated, positive correlation and negative correlation respectively. The research lays a foundation for building a perfect prosodic model for standard Chinese speech synthesis system. The results of research are also used to classify sentence stress using a neural network, and 63% identification ratio has been obtained in an open set test. An automatic method for the sentence stress labeling is also suggested.