Wang Mengjun

Bio: Wang Mengjun is an academic researcher from Central South University. The author has contributed to research in topics: Strain rate & Flow stress. The author has an hindex of 3, co-authored 7 publications receiving 47 citations.

Prediction of the flow stress of Al6061 at hot deformation conditions

Abstract: Isothermal compression tests were carried out on Al6061 using a Gleeble-1500 thermal simulator at temperatures ranging from 573 to 723 K and strain rates from 0.5 to 30 s−1. The flow stress of Al6061 was characterized based on an analysis of the true stress–true strain curves. A mathematical mode coupling flow stress with strain, strain rate and temperature for Al6061 has been proposed by using a hyperbolic sinusoidal type equation. The material constant α is 0.01 MPa−1 in the model, whereas other material constants n, lnA and Q are found to be functions of strain. The predicted results from this proposed model are found to be in good agreement with the experimental flow stress curves which can be used to predict the required deformation forces in hot deformation processes.

Deformation behavior of 6063 aluminum alloy during high-speed compression

Abstract: The deformation behavior characteristics of 6063 aluminum alloy were studied experimentally by isothermal compression tests on a Gleeble-1500 thermal-mechanical simulator. Cylindrical specimens of 14mm in height and 10 mm in diameter were compressed dynamically at temperatures ranging from 473 to 723 K and at higher strain rates from 5 to 30s−1. It is found that the flow curves not only depend on the strain rate and temperature but also on the dynamic recovery and recrystallization behavior. The results show that the flow stress decreased with the increase of temperature, while increased with the increase of strain rate. The discontinuous dynamic recrystallization (DDRX) may take place at a high strain rate of 20s−1 under the tested conditions. At 30s−1, the flow curve can exhibit flow softening due to the effect of temperature rise that raised the temperature by about 32 K in less than 0.05s.

A Study on Constructing Index Systems of Construction Market Performance Appraisal

Abstract: Construction market is the essential part of socialist market. Analysis and evaluation of running state is an important task for the market administrators in the management of construction market. Based on the research results about market performance in the Microeconomics, Transaction Cost theory and theory of Industrial Organization, and according to the Relationship between the market structure, conduct and performance, the comprehensive analysis of influential factors of performance in the construction market is presented, and index systems to evaluate construction market performance is established, which can be a basis for the next phase of the performance appraisal and market supervision.

Research on Technological Innovation Dynamic Mechanism of Railway Engineering Project

Abstract: Railway engineering projects,as the forefront and application carrier of technological innovation,are an integral part of the technological innovation system of Chinese railways.In order to improve the efficiency and quality of technological innovations of railway engineering projects,we simulated the technological innovation dynamic system by using the system dynamics,and then we modeled the technological innovation dynamic mechanism of railway engineering projects on the foundation of analyzing the impact factors of technological innovation power.We put forward the technological innovation dynamic mechanism which was guarded by effective system designing and process controlling.This system was based on the incentive restraint mechanism,collaborative cooperation mechanism and interest allocation mechanism.At the same time we elaborated the specific methods and initiatives to realize the aim of the dynamic mechanism.The study provides useful reference to management practice and theoretical research on railway engineering projects technological innovation.

Decision model of project financing based on triangular fuzzy AHP

Abstract: A new infrastructure project financing decision model is constructed by systematically analyzing of project financing modes.It uses the hierarchical decomposition method to decompose the complex project financing mode decision problem and its corresponding evaluation indexes.It uses the Delphi method to evaluate these indexes.Because expert advice is characteristic of fuzzy and uncertainty,expert advice is converted into triangular fuzzy numbers by using the triangular fuzzy language variables.And the fuzzy decision judgment matrixes are constructed.Synthesis weights of all alternative models are obtained and the decisions are made by transforming the judge matrixes and calculating their vectors together with Analytical Hierarchy Process(AHP).The practical case shows that the proposed model provides a good method for the urban infrastructure project finance decision making.

Constitutive models for high-temperature flow behaviors of a Ni-based superalloy

Abstract: The high-temperature deformation behaviors of a typical Ni-based superalloy are investigated by hot compression tests under the strain rate of 0.001–1 s−1and temperature of 920–1040 °C. The experimental results show that the deformation behaviors of the studied superalloy are significantly affected by the deformation temperature, strain rate and strain. The flow stress increases with the increase of strain rate or the decrease of deformation temperature. The flow stress firstly increases with the strain to a peak value, showing the obvious work hardening behaviors. Then, the stress decreases with the further straining, indicating the dynamic flow softening behaviors. Considering the coupled effects of deformation temperature, strain rate and strain on the hot deformation behaviors of the studied Ni-based superalloy, the phenomenological constitutive models are established to describe the work hardening-dynamic recovery and dynamic softening behaviors. In the established models, the material constants are expressed as functions of the Zener–Hollomon parameter. The established constitutive models can give good correlations with the experimental results, which confirm an accurate and precise estimation of the flow stress for the studied Ni-based superalloy.

Constitutive equations for elevated temperature flow behavior of commercial purity aluminum

Abstract: In order to study the high-temperature flow stress of commercial purity aluminum (AA1070), isothermal hot compression tests were conducted at the deformation temperatures varying from 350 to 500 °C and strain rates ranging from 0.005 to 0.5 s−1. The results showed that the flow stress of AA1070 was evidently affected by both the deformation temperature and strain rate. The influence of strain was also incorporated in the constitutive equation by considering the effects of strain on material constants which are consist of β, α, n, A and activation energy Q. The predicted flow stress curves using the proposed constitutive equations well agree with the experimental results of the flow stress for AA1070.

Evolution of activation energy during hot deformation of AA7150 aluminum alloy

Abstract: The hot deformation behavior of a homogenized AA7150 aluminum alloy was studied in compression tests conducted at various temperatures (573–723 K) and strain rates (0.001–10 s −1 ). The flow stress behavior and microstructural evolution were observed during the hot deformation process. A revised Sellars’ constitutive equation was proposed, which considered the effects of the deformation temperature and strain rate on the material variables and which provided an accurate estimate of the hot deformation behavior of the AA7150 aluminum alloy. The results revealed that the activation energy for the hot deformation of the AA7150 aluminum alloy is not a constant value but rather varies as a function of the deformation conditions. The activation energy for hot deformation decreased with increasing deformation temperature and strain rate. The peak flow stresses under various deformation conditions were predicted by a revised constitutive equation and correlated with the experimental data with excellent accuracy.

Hot compressive deformation behavior of 7075 Al alloy under elevated temperature

Abstract: The hot compression tests were conducted with wide strain rates and forming temperature ranges to study the high-temperature deformation behavior of 7075 Al alloy. The material flow behavior and microstructural evolution during hot-forming process are discussed. Based on the measured stress–strain data, a new constitutive model is proposed, considering the coupled effects of strain, strain rate, and forming temperature on the material flow behavior of 7075 Al alloy. In the proposed model, the material constants are presented as functions of forming temperature. The proposed constitutive model gives good correlations with the experimental results, which confirms that the proposed model can give an accurate and precise estimate of flow stress for 7075 Al alloy.

Recent development of design and construction of short span high-speed railway bridges in China

Abstract: High-speed rail (HSR) has become a vital component of the national transportation network in China. A large number of standard short-span bridges were constructed as part of the infrastructure associated with the HSR development. The main focus of this short review is to showcase how the fast HSR construction in China during the past decade was achieved by using typical simply supported bridges and continuous beam bridges. This paper provides a brief historical review of the HSR development in China along with emerging design issues. Design concepts and structural dimensions of two typical spans are discussed, including the superstructure, substructure as well as the auxiliary facilities on the bridge deck. Different construction methods were also discussed.