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Liu Y.,Tsinghua University | Wang H.-K.,China Special Equipment Inspection And Research Institute | Zhang X.,Tsinghua University
International Journal of Mechanics and Materials in Design | Year: 2013

The equation of state (EOS) plays an important role in high-velocity impact process since phase transformation, melting, and even vaporization may happen under such extreme loading conditions. It is desired to adopt an accurate EOS covering a large range of points in the phase space. This paper proposes a combined molecular dynamics and material point method approach to simulate the high-velocity impact process. The EOS data are first obtained from a series of molecular dynamics computations, and the parameters are fitted. Then the EOS parameters are adopted in the material point method simulation to model the impact process. Simulation results show that the fitted EOS can be very accurate compared to experimental results. The shape of the debris cloud obtained by our multiscale method agrees well with that of the experiments. An empirical equation is also proposed to predict the fraction of melting material in the high-velocity impact process. © 2013 Springer Science+Business Media Dordrecht. Source


Chen G.,China Special Equipment Safety Supervision Administration | Deng Y.,China Special Equipment Inspection And Research Institute
Chinese Journal of Mechanical Engineering (English Edition) | Year: 2011

By increasing the yield strengths of austenitic stainless steels for pressure vessels with strain hardening techniques, the elastic load bearing capacity of austenitic stainless steel pressure vessels can be significantly improved. Two kinds of strain hardening methods are often used for austenitic stainless steel pressure vessels: Avesta model for ambient temperature applications and Ardeform model for cryogenic temperature applications. Both methods are obtained from conventional design rules based on the linear elastic theory, and only consider the hardening effect from materials. Consequently this limits the applications of strain hardening techniques for austenitic stainless steel pressure vessels because of safety concerns. This paper investigates the effect of strain hardening on the load bearing capacity of austenitic stainless steel pressure vessels under large deformation, based on the elastic-plastic theory. Firstly, to understand the effect of strain hardening on material behavior, the plastic instability loads of a round tensile bar specimen are derived under two different loading paths and validated by experiments. Secondly, to investigate the effect of strain hardening on pressure vessels strength, the plastic instability pressure under strain hardening is derived and further validated by finite element simulations. Further, the safety margin of pressure vessels after strain hardening is analyzed by comparing the safety factor values calculated from bursting tests, finite element analyses, and standards. The researching results show that the load bearing capacity of pressure vessels at ambient temperature is independent of the loading history when the effects of both material strain hardening and structural deformation are considered. Finite element simulations and bursting tests results show that the minimum safety factor of austenitic stainless steel pressure vessels with 5% strain hardening is close to the recommended value for common pressure vessels specified in the European pressure vessel standard. The proposed study also shows that in the strain hardening design of austenitic stainless steel pressure vessels, the calculation for plastic instability pressure could use theoretical formula or finite element analyses based on geometrical dimensions and material property parameters before strain hardening, but a 5% strain should be employed as a design limit. The proposed research can be used for the strain hardening design of austenitic stainless steel pressure vessels safely. © 2011 Chinese Journal of Mechanical Engineering. Source


Wang Z.D.,Beijing Jiaotong University | Yao K.,Beijing Jiaotong University | Deng B.,Beijing Jiaotong University | Ding K.Q.,China Special Equipment Inspection And Research Institute
NDT and E International | Year: 2010

Compared to traditional nondestructive testing methods, the technique of metal magnetic memory (MMM) is a more effective way in evaluating early damages of ferromagnets due to the existence of material stresses. In practical engineering, this technique has been extensively applied in different fields. However, very limited quantitative research has been carried out on quantitatively studying the relations between the stress state and self-magnetic flux leakage (SMFL) signal. In this paper, the distribution of SMFL is investigated based on the theory of magnetic charges. A linear description of the magnetic charge and the stress state is given. The theory can capture some basic characteristics of the SMFL distribution in the stress concentration of ferromagnets, e.g. the tangential SMFL component HP(x) reaching a maximum value and the normal component HP(y) changing positive-negative sign in the maximum stress concentration zone (SCZ). Moreover, the effects of the stress-concentration range and lift-off value on SMFL signals are discussed as well. © 2010 Elsevier Ltd. All rights reserved. Source


Wang Z.D.,Beijing Jiaotong University | Yao K.,Beijing Jiaotong University | Deng B.,Beijing Jiaotong University | Ding K.Q.,China Special Equipment Inspection And Research Institute
NDT and E International | Year: 2010

The technique of metal magnetic memory (MMM) has attracted great attentions in the field of non-destructive tests due to its unique advantages of easy-operation, low cost, and high efficiency. However, a thorough understanding of the physical mechanism of MMM phenomenon has not been clearly addressed. Generally, MMM tests can only find the possible locations of defects without quantitative descriptions about the defect characteristics. To promote study in this area, a linear magnetic-charge model is employed to analyze the self-magnetic flux leakage (SMFL) distribution in the local stress-concentration zone. Theoretical results based on this model can capture some basic characteristics of SMFL signals of ferromagnets observed in experiments. Specially, the model provides some quantitative results about the effects of defect depth and location (surface- or inner-defects) on SMFL signals. © 2010 Elsevier Ltd. All rights reserved. Source


Duan Z.-X.,China Special Equipment Inspection And Research Institute
Gongcheng Lixue/Engineering Mechanics | Year: 2012

By the strain analysis and energy method, the expressions of the axial stress and circumferential stress of an elbow under the action of an in-plane bending moment are gained, and the high order stress solution for an elbow subjected to an in-plane bending moment is suggested. The high order stress solution for an elbow subjected to an in-plane bending moment is compared with the solution using the other methods. It is obtained from the comparison that the high order solution is more accurate and is suitable for elbows without the limit of λ. The high order stress solution is suitable for an elbow under an in-plane close-bending moment or an in-plane open-bending moment. Source

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