Su'e LIU
,
Zhong ZHU and Wei KE(State Key Lab. of Corrosion and Protection
,
Institute of Corrosion and Protection of Metals
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China) D.Hardie(Dept. of Mechanical
,
Materials and Manufacturing Engineering
,
Universi
材料科学技术（英文）
Hydrogen embrittlement of Type 4340 steel has been investigated by straining round-notchedspecimens in 105 Pa hydrogen atmosphere at a constent cross-head spead of 1.4x 10-4 mm/s.The circumferentially notched specimens exhibited a significant embrittlement when their me-chanical behaviour in hydrogen was compared with that in air. Although the effect of notch depthon fracture strength in air is negligible, an increase in the depth of notch increase susceptibility toembrittlement when testing in gaseous hydrogen. However, analysis of the effects is complicatedby the facts that (i) the specimens show some degree of notch severity even when strained inair and (ii) the behaviour is complicated by the localised plastic deformation that may occur forrelatively shatlow notches. Such effects are eliminated at high stress concentration factors, sothere is a systematic loss in fracture stress in hydrogen as the notch sensitivity increases fromK=2.6 to 5.7 (where a 87% reduction of fracture stress occurs) but a relatively stable value isthen reached even for very severe notching bj fatigue pre-cracking. Whether or not the effectis due to increasing concentration of hydrogen in the triaxial stress region ahead of the notch,there is no doubt that increasing the stress concentration makes hydrogen more effective as anembrittlement agent.
关键词:
B.Y. Yu*
,
C.L. Bao
,
H.W. Song
,
Z. Liu
金属学报(英文版)
The effect of extrusion ratio on microstructures and mechanical properties of magnesium alloy AZ91D extruded tube at 430℃ has been studied. After the evolution of microstructure and mechanical properties of AZ91D during extrusion were studied, the following parameters were obtained: tensile strength reached the climax value of 306.9MPa and elongation peak value of 10.1% at an extrusion ratio of 7.125, and with the increase of the extrusion ratio to 7.45, yield strength reached a top value of 285.795MPa with decreased tensile strength and elongation. It was concluded that mechanical properties of magnesium alloys AZ91D could be enhanced by adjusting the extrusion ratio near recrystallization.
关键词:
magnesium
,
挤压
,
管材
,
组织
,
力学性能
Journal of Alloys and Compounds
The influence of magnetic fields on the mechanical loss (Q(-1)) of Terfenol-D/PbZr(0.52)Ti(0.48)O(3)/Terfenol-D three-layer laminated composites is investigated systemically using the technique for measuring the resonance magnetoelectric (ME) effect. The results indicate that Q(-1) varies non-monotonically with dc magnetic fields and shows a maximum near 500 Oe for all the samples with different layer thickness ratios (n) of Terfenol-D (Tb(0.3)Dy(0.7)Fe(1.92)). Considering various kinds of mechanical energy dissipation, it is found that Q(-1) is mainly dominated by the mechanical damping due to the domain wall motion in Terfenol-D under the actions of dc and ac magnetic fields as well as the stress at the interface. In addition, the effect of eddy current losses on the energy dissipation of the system is also discussed. (C) 2011 Elsevier B.V. All rights reserved.
关键词:
Magnetoelectric composite;Mechanical energy dissipation;Domain wall;motion;magnetomechanical damping capacity;terfenol-d;magnetostriction;alloys;tb0.27dy0.73fe2;tb0.3dy0.7fe1.95
Y. YU
,
X.X. Pan
,
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
,
null
,
null
,
null
杨金瑞
,
余尚先
,
顾江楠
高分子材料科学与工程
通过对resol(羟甲基酚化合物和低分子量羟甲基酚树脂)DEPT135图谱的分析讨论,得到一系列计算resol微细结构参数的经验公式.根据DEPT135图谱可判断是否发生缩聚反应,根据经验公式可计算酚单体各个活性点参与反应百分率或酚羟基导入率、不同类型缩聚所占百分率及低分子量羟甲基酚树脂的平均核体数.
关键词:
羟甲基酚化合物
,
羟甲基酚树脂
,
DEPT135
,
结构参数
Carbon
In order to improve the mechanical and ablation properties of 2D-carbon/carbon composites, a SiC filler was added to a 2D-preform before isothermal chemical vapor infiltration densification by using a powder infiltration technique. Backscattered electron images showed that the SiC filler was mainly concentrated between the fiber bundles and between the layers. The tensile and flexural strengths of the composites were improved by the addition of the SiC filler because of the increase of interfacial surface areas between the bundles and between the layers, the less residual open porosity, and also the strong bonding between the SiC particles and the pyrocarbon matrix. The composites with filler experienced a 15.2% lower thickness erosion rate and a 51.7% lower mass erosion rate, compared to those C/C without filler. This was attributed to the low oxygen permeability of the SiO2 shielding the exterior inter-bundle pores as well as to a thermal barrier effect. (c) 2006 Elsevier Ltd. All rights reserved.
关键词:
carbon/carbon composites;chemical vapor infiltration;scanning electron;microscopy;mechanical properties;ablation;carbon-carbon composites;thermal-expansion;silicon-carbide;oxidation;behavior
Khodamorad Abbaszadeh
材料科学技术（英文）
The effect of bainite morphology on mechanical properties of the mixed bainite-martensite microstructure in D6AC low alloy ultra-high strength steel has been studied in the present work. For this purpose, samples austenitized at 910 °C for 40 min were quenched in three different ways. Some of the samples were directly oil-quenched, some others were quenched in salt bath at 330 °C and the remaining samples were quenched in salt bath at 425 °C for various holding times. All samples were tempered at 200 °C for 2 h. Microstructures were examined by optical microscopy (OM) and scanning electron microscopy (SEM). Fracture surfaces also were studied by SEM. Results showed that the mixed microstructure containing martensite and 28 vol.% of
the lower bainite exhibited higher yield and tensile strengths than the fully martensitic microstructure. This could be mainly attributed to the partitioning of the prior austenite grains by the lower bainite and enhancing the strength of lower bainite in the mixed microstructure by plastic constraint. Charpy V-notch (CVN) impact energy and ductility were improved by increasing the volume fraction of the lower bainite. This is not the case about the mixed microstructure containing the upper bainite and martensite. As a result, the tensile and CVN impact properties of mixed upper bainite-martensite microstructure are lower than those of the fully martensitic microstructure. Finally, fractography studies showed cleavage fracture at the surface of CVN impact specimens with martensitic and upper bainitic microstructures confirming the tendency to brittle behavior.
关键词:
Upper bainite
