H.P. Chen and Z.J. Deng (State Key Lab. for Mechanical Behavior of Materials
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Xi'an Jiaotong University
,
Xi'an 710049
,
China)
金属学报(英文版)
The effect of specimen thinkness on JR resistance curve has been investigated using low and middle strength steels. As the J dominance regime is reached, the initial J-integral values, J(i), are definite even if the elastic component Ji(e) and plastic component Ji(p)vary with the thinkness of specimen. The wider the specimen width, the larger the Ji(e)/Ji and the smaller the Ji(p)/Ji. The crack propagation resistance, dJR/da and dJp/da, decreases, while dJe/da increases linearly with increasing specimen thinness.Based on the above experimental results, an empirical formula dJ/da = α+β. B is given, which can be used to evaluate the safety of practical structural components.A modified J-integral is presented, upon which a new view is Put forward that the increase in crack growth resistance is induced mainly by the increase in the plastic J-integral component with the crack propagation,
关键词:
: fracture mechanics
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Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science
A stable face-centered cubic (fcc) stainless steel was H charged by exposing it to 9.8 MPa H gas at 300-degrees-C for 14 days. The concentration of H was determined to be 65 ppm. The mechanical testing at room temperature has shown that after H charging, the yield strength of the steel increases, and the behavior of the transient creep and the short-term stress relaxation becomes more intensive. All the results can be interpreted qualitatively, and part of the results can be quantitatively calculated by the theory of mobile dislocation density proposed by Alden. The analysis indicates that the essential effect of H is to obstruct the movement of dislocations, so that the strength and inelastic viscousness of the steel increase.
关键词:
tensile properties;hydrogen;deformation;iron
Journal of Materials Research
The morphology of the dark and bright regions observed by transmission electron microscopy for the Zr(64.13)Cu(15.75)Ni(10.12)Al(10) bulk metallic glass strongly depends on the ion beam parameters used for ion milling. This indicates that the ion beam could introduce surface fluctuation to metallic glasses during ion milling.
关键词:
room-temperature
Materials and Corrosion-Werkstoffe Und Korrosion
Electrochemical corrosion behavior of electroless Ni-P coating in NaCl and H(2)SO(4) solutions were studied by potentiodynamic polarization curves and electrochemical impedance spectra techniques, as well as the corrosion morphology was characterized. The results indicate that electroless Ni-P coating with about 25 mu m is stable in 30 days immersion in NaCl solution. Although it was corroded with prolonged immersion days, the corrosive medium has not penetrated through the coating. During the H(2)SO(4) concentration ranging from 5 to 10%, the corrosion current density of electroless Ni-P coating increased due to the intensified anodic dissolution process; in 15% H(2)SO(4) solution, electroless Ni-P coating shows obvious anodic passivation effect.
关键词:
F.Q.Tian
金属学报(英文版)
Welded joint is a mechanical heterogeneous body, and mechanical heterogeneity has great effect on dynamic fracture behaviour of welded joints. In the present investigation, dynamic response curve and dynamic J-integral of practical undermatched welded joint and whole base and whole weld three-point-bend (TPB) models containing longitudinal crack are computed. Dynamic J-integral is evaluated using virtual crack extension (VCE) method and the computation is performed using MARC finite element code. Because of the effect of inertia,dynamic load response curve of computed model waves periodically. Dynamic J-integral evaluated by VCE method is path independent. The effect of inertia has little influence on dynamic J-integral curve. The value of dynamic J-integral of undermatched welded joint is lower than that of whole base metal and higher than that of whole weld metal. The results establish the foundation of safety evaluation for dynamic loaded welded structures.
关键词:
virtual crack extension
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Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science
The half-width values of the X-ray diffraction profiles are frequently used to characterize the static strength of a strengthened surface, or the depth distribution of this mechanical parameter, in a strengthened surface layer, especially in a shot-peening affected layer. However, for the unpeened surface and the base material of the shot-peened specimen of an alloy steel treated in hard state, the experimental results shown in this article indicate that uniaxial tensile or compressive plastic deformation increases the yield strengths while it decreases the half-width values. The half-width values of the shot-peened surface and surface layer greatly decrease, whereas the yield strength of this surface remarkably increases. Accordingly, in the authors' opinion, the half-width values could not correctly describe the static strengths of hard metallic materials, and, contrary to the viewpoint put forward by a lot of researchers, the shot-peened surfaces of such materials are work hardened instead of work softened. A model demonstrating that plastic deformation reduces the half-width values by decreasing the second kind internal stresses is developed.
关键词:
Wear
The abradability of porous seal materials has been evaluated using a single-pendulum scratch device. The results shows that the specific energy e (= E/V) and the tangential dynamic hardness H(T)(= F(T)/A(T)) for small incursion depth are obviously higher than those for greater incursion. The specific energy e and tangential dynamic hardness H(T) have been proposed as two equivalent criteria of abradability of seal materials. The abradability of porous seal materials is dependent on both mechanical properties of the materials and extent of densification. A careful balance between them is the key to a satisfactory seal material.
关键词:
abradability;seal materials;scratch device
Y. YU
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X.X. Pan
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Y.H. Rong
金属学报(英文版)
To simulate the mechanical behavior of the FCC crystal with the lower Peierls stress, the stiff property and physical meaning of the differential equation group consisted of dislocation evolution and mechanical state based on the 3-D discrete dislocation dynamics, the results indicate that the differential equation group is serious stiff, namely the external stress changes more quickly than dislocation evolution. Using the established numerical algorithm, we simulate the mechanical behavior of FCC crystal with the dislocations located in the parallel slip planes, and discuss the effect of strain rate on the dislocation configuration and mechanical behavior, and the saturation process of mobile dislocation. The simulation results indicate that our numerical algorithm can efficiently simulate the dislocation dipole and the low strain rate loading.
关键词:
FCC crystal
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