Durability evaluation for existing railway engineering: a review

Purpose – This study aims to analyze the factors, evaluation techniques of the durability of existing railwayengineering.Design/methodology/approach – China has built a railway network of over 150,000 km. Ensuring thesafety of the existing railway engineering is of great significance for maintaining normal railway operationorder. However, railway engineering is a strip structure that crosses multiple complex environments. Andrailway engineering will withstand high-frequency impact loads from trains. The above factors have led todifferences in the deterioration characteristics and maintenance strategies of railway engineering compared toconventional concrete structures. Therefore, it is very important to analyze the key factors that affect thedurability of railway structures and propose technologies for durability evaluation.Findings – The factors that affect the durability and reliability of railway engineering are mainly divided intothree categories: material factors, environmental factors and load factors. Among them, material factors alsoinclude influencing factors, such as raw materials, mix proportions and so on. Environmental factors varydepending on the service environment of railway engineering, and the durability and deterioration of concretehave different failure mechanisms. Load factors include static load and train dynamic load. The on-site rapiddetection methods for five common diseases in railway engineering are also proposed in this paper. Thesemethods can quickly evaluate the durability of existing railway engineering concrete.Originality/value – The research can provide some new evaluation techniques and methods for thedurability of existing railway engineering.

Development of Evaluation Technique of GMAW Welding Quality Based on Statistical Analysis

Nondestructive techniques for appraising gas metal arc welding（GMAW） faults plays a very important role in on-line quality controllability and prediction of the GMAW process. On-line welding quality controllability and prediction have several disadvantages such as high cost, low efficiency, complication and greatly being affected by the environment. An enhanced, efficient evaluation technique for evaluating welding faults based on Mahalanobis distance（MD） and normal distribution is presented. In addition, a new piece of equipment, designated the weld quality tester（WQT）, is developed based on the proposed evaluation technique. MD is superior to other multidimensional distances such as Euclidean distance because the covariance matrix used for calculating MD takes into account correlations in the data and scaling. The values of MD obtained from welding current and arc voltage are assumed to follow a normal distribution. The normal distribution has two parameters： the meanm and standard deviations of the data. In the proposed evaluation technique used by the WQT, values of MD located in the range from zero tom＋3s are regarded as “good”. Two experiments which involve changing the flow of shielding gas and smearing paint on the surface of the substrate are conducted in order to verify the sensitivity of the proposed evaluation technique and the feasibility of using WQT. The experimental results demonstrate the usefulness of the WQT for evaluating welding quality. The proposed technique can be applied to implement the on-line welding quality controllability and prediction, which is of great importance to design some novel equipment for weld quality detection.

A supercritical CO_2 fluid technique for the preparation and evaluation of rhBMP-2-loaded PLLA microspheres

Introduction The use of supercritical fluids such as supercritical CO2（scCO2） has provided a ’clean’ and effective alternative to traditional methods of protein delivery systems.Here。

Value of helical CT volume rendering technique in post-operative evaluation of screw in screw fixation of axis fractures

To explore the value of helical CT volume rendering technique (VRT) in post-operative evaluation of screw fixation of axis fractures.Methods There were 21 cases of screw fixation of axis fractures between February 2002 and May 2004 in the study including six cases with fractures on axis body,five on odontoid process and 10 on axis body and odontoid process.All cases received X-ray plain film,helical CT scanning,multi-planar reformatting(MPR) and VRT.Results Screw fixation through axis body and massa lateralis atlantis was performed in 10 cases and that through axis body and odontoid process in 11.VRT could clearly display full aperture of screw orbit,location of screw and angle of fixation and hence was superior to X-ray plain film and MPR.Multi-angle VRT displayed asymmetrical space of odontoid process and massa lateralis atlantis in four cases and medial deviation of 2～5 mm of half screw in screw fixation through axis body and massa lateralis atlantis in six.Conclusion VRT can eliminate false shadow of fixation screw,clearly display full aperture of screw orbit and hence supply improtant imaging evidence for post-operative evaluation of screw fixation of axis fractures.7 refs,1 fig,1 tab.

PS-G-GERT Effectiveness Evaluation Model of Link-Based GEO Satellite Communication Constellation under Poor Information Background

The effectiveness evaluation of GEO satellite communication constellation not only characterizes the communication capability of the constellation but also provides a basis for optimizing the constellation structure.Whether due to information poverty or the complexity of the system,the impact of uncertain information on the effectiveness evaluation needs to be considered to ensure the accuracy of the evaluation results.To address this issue,this paper develops a model for evaluating the GEO satellite communication constellation’s effectiveness in the context of poor information.Firstly,it analyses the GEO satellite communication constellation plus system based on communication links with an in-depth analysis of the constellation structure.Secondly,an equivalent transfer function algorithm based on the characteristic function and transfer probability is proposed with the help of graphical evaluation and review technique.Then,by analyzing the communication link importance connotation,the algorithm formula of communication link effectiveness and its importance is derived,and the constellation effectiveness and variance are found.Finally,the model constructed in this paper is used to evaluate the effectiveness of a GEO satellite communication constellation,further verifying the accuracy and validity of the model.Through comparative analysis,it is shown that the model can not only solving the effectiveness of the constellation but also analyzing the variation of its effectiveness.It lays a theoretical foundation for the analysis and optimization of the GEO satellite communication constellation effectiveness.

Multi-parameters uncertainty analysis of logistic support process based on GERT

The uncertainty analysis is an effective sensitivity analysis method for system model analysis and optimization. However,the existing single-factor uncertainty analysis methods are not well used in the logistic support systems with multiple decision-making factors. The multiple transfer parameters graphical evaluation and review technique（MTP-GERT） is used to model the logistic support process in consideration of two important factors, support activity time and support activity resources, which are two primary causes for the logistic support process uncertainty. On this basis,a global sensitivity analysis（GSA） method based on covariance is designed to analyze the logistic support process uncertainty. The aircraft support process is selected as a case application which illustrates the validity of the proposed method to analyze the support process uncertainty, and some feasible recommendations are proposed for aircraft support decision making on carrier.

ADC-GERT network parameter estimation model for mission effectiveness of joint operation system

Effectiveness evaluation of the joint operation system is an important basis for the demonstration and development of weapon equipment.With the consideration that existing models of system effectiveness evaluation seldom describe the structural relationship among equipment clearly as well as reflect the dynamic,the analog-to-digital converter-graphical evaluation and review technique(ADC-GERT)network parameter estimation model is proposed based on the ADC model and the joint operation system structure.Firstly,analysis of the joint operation system structure and operation process is conducted to build the GERT network,where equipment subsystems are nodes and activities are directed arches.Then the mission effectiveness of equipment subsystems is calculated by the ADC model.The probability transfer parameters are modified by the mission effectiveness of equipment subsystems based on the Bayesian theorem,with the ADC-GERT network parameter estimation model constructed.Finally,a case study is used to validate the efficiency and dynamic of the ADC-GERT network parameter estimation model.

PERT and CPM in Project Management with Practical Examples

This paper reviewed the concepts of Project Evaluation Review Technique and Critical Path Method in project management with practical examples. The methods and success of quantitative decision-making approaches in project management through the use of project evaluation review technique and the critical path method as regards project duration and critical activities of a project, were discussed. The review found that while both methods are effective in achieving success in project management, the relationship and connectivity of activities involved in a project life cycle are key aspects. The paper concludes that the project evaluation review technique is more effective when the duration of the project is uncertain, while the critical path method is effective when the project’s end time is certain. The paper, therefore, recommends that to achieve maximum operative efficiency in utilizing resources in project management, prior to commencing the execution of a project, all required resources to cover every activity must be assembled and prioritized to eliminate interruptions that could bring delay and unnecessary cost implications. Again, policies focused on improving project execution should be implemented in developing nations to minimize the many cases of failed and delayed projects. Subsequently, stakeholders in projects must be given the right, under the law, to prosecute the government, its agencies and/or the executors of projects for failure to execute a project on schedule.

An adaptive data-driven method for accurate prediction of remaining useful life of rolling bearings

A novel data-driven method based on Gaussian mixture model （GMM） and distance evaluation technique （DET） is proposed to predict the remaining useful life （RUL） of rolling bearings. The data sets are clustered by GMM to divide all data sets into several health states adaptively and reasonably. The number of clusters is determined by the minimum description length principle. Thus, either the health state of the data sets or the number of the states is obtained automatically. Meanwhile, the abnormal data sets can be recognized during the clustering process and removed from the training data sets. After obtaining the health states, appropriate features are selected by DET for increasing the classification and prediction accuracy. In the prediction process, each vibration signal is decomposed into several components by empirical mode decomposition. Some common statis- tical parameters of the components are calculated first and then the features are clustered using GMM to divide the data sets into several health states and remove the abnormal data sets. Thereafter, appropriate statistical parameters of the generated components are selected using DET. Finally, least squares support vector machine is utilized to predict the RUL of rolling bearings.Experimental results indicate that the proposed method reliably predicts the RUL of rolling bearings.

Non-destructive microstructural analysis by electrical conductivity:Comparison with hardness measurements in different materials

The use of non-destructive evaluation(NDE) techniques for assessing microstructural changes in processed materials is of particular importance as it can be used to assess, qualitatively, the integrity of any material/structure. Among the several NDE techniques available, electrical conductivity measurements using eddy currents attract great attention owing to its simplicity and reliability. In this work, the electrical conductivity profiles of friction stir processed Ti6Al4 V, Cu, Pb, S355 steel and gas tungsten arc welded AISI 304 stainless steel were determined through eddy currents and four-point probe. In parallel, hardness measurements were also performed. The profiles matched well with the optical macrographs of the materials: while entering in the processed region a variation in both profiles was always observed. One particular advantage of electrical conductivity profiles over hardness was evident: it provides a better resolution of the microstructural alterations in the processed materials. Moreover, when thermomechanical processing induces microstructural changes that modify the magnetic properties of a material,eddy currents testing can be used to qualitatively determine the phase fraction in a given region of the material. A qualitative relation between electrical conductivity measurements and hardness is observed.