LIU Yongning
,
ZHU Jinhua
,
ZHOU Huijiu Xi'an Jiaotong University
,
Xi'an
,
China A.Kildegaard
,
J.A.Kristensen Department of Mechanical Engineering
,
Aalborg University
,
Denmark Dept.of Materials Science and Engineering Xi'an Jiaotong University
,
Xi'an 710049
,
China
金属学报(英文版)
The dynamic fracture toughness of a mild steel has been studied at different loading rates and temperatures.The material exhibits a transition from tough to brittle fracture with the chang- ing loading rate alone.Analysis of the fracture process by the theory of thermal activation suggests that the fracture activation energy approximates to the bond energy of the{100}of a unit cell.The toughness can be resolved into two parts,J-(fd)=J_a+J_l,where J_a is the athermal part,being independent on temperature and loading rate,while J_l=(K/K_o)~(1/n)exp(Q_f/nkT),which controls the fracture process is temperature and load- ing rate dependent.The transition of fracture mechanism caused by both temperature and loading rate is associated with the thermal movement of atoms.
关键词:
mild steel
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null
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null
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null
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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null
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null
Mehdi Ebrahimian-Hosseinabadi Fakhredin Ashrafizadeh Mohammadreza Etemadifar Subbu S. Venkatraman
材料科学技术（英文）
In this paper, preparation of nano-biphasic calcium phosphate (nBCP), mechanical behavior and load-bearing of poly (lactide-co-glycolide) (PLGA) and PLGA/nBCP are presented. The nBCP with composition of 63/37 (w/w) HA/β-TCP (hydroxyapatite/β-tricalcium phosphate) was produced by heating of bovine bone at 700°C. Composite scaffolds were made by using PLGA matrix and 10-50 wt% nBCP powders as reinforcement material. All scaffolds were prepared by thermally induced solid-liquid phase separation (TIPS) at -60°C under 4 Pa (0.04 mbar) vacuum. The results of elastic modulus testing were adjusted with Ishai-Cohen and Narkis models for rigid polymeric matrix and compared to each other. PLGA/nBCP scaffolds with 30 wt% nBCP showed the highest value of yield strength among the scaffolds. In addition, it was found that by increasing the nBCP in scaffolds to 50 wt%, the modulus of elasticity was highly enhanced. However, the optimum value of yield strength was obtained at 30 wt% nBCP, and the agglomeration of reinforcing particles at higher percentages caused a reduction in yield strength. It is clear that the elastic modulus of matrix has the significant role in elastic modulus of scaffolds, as also the size of the filler particles in the matrix.
关键词:
Scaffold
Materials Science & Engineering C-Biomimetic Materials Sensors and Systems
Bamboo, one of the strongest natural structural composite materials, has many distinguishing features. It has been found that its reinforcement unit, hollow, multilayered and spirally-wound bast fiber, plays an extremely important role in its mechanical behavior. In the present work, on the basis of the study on bamboo bast fiber and wood tracheid, a biomimetic model of the reinforcing element, composed of two layers of helically wound fiber, was suggested. To detect the structural characteristics of such a microstructure, four types of macro fiber specimens made of engineering composites were employed: axially aligned solid and hollow cylinders, and single- and double-helical hollow cylinders. These specimens were subjected to several possible loadings, and the experimental results reveal that only the double-helical structural unit possesses the optimum comprehensive mechanical properties. An interlaminar transition zone model imitating bamboo bast fiber was proposed and was verified by engineering composite materials. In our work, the transition zone can increase the interlaminar shear strength of the composite materials by about 15%. These biomimetic structural models can be applied in the design and manufacture of engineering composite materials.
关键词:
bamboo;bast fiber;biomimetics;engineering composites
Science
Strengthening materials traditionally involves the controlled creation of internal defects and boundaries so as to obstruct dislocation motion. Such strategies invariably compromise ductility, the ability of the material to deform, stretch, or change shape permanently without breaking. Here, we outline an approach to optimize strength and ductility by identifying three essential structural characteristics for boundaries: coherency with surrounding matrix, thermal and mechanical stability, and smallest feature size finer than 100 nanometers. We assess current understanding of strengthening and propose a methodology for engineering coherent, nanoscale internal boundaries, specifically those involving nanoscale twin boundaries. Additionally, we discuss perspectives on strengthening and preserving ductility, along with potential applications for improving failure tolerance, electrical conductivity, and resistance to electromigration.
关键词:
strain-rate sensitivity;stacking-fault energy;nano-scale twins;cu-al;alloys;nanocrystalline metals;mechanical-properties;activation;volume;copper;deformation;behavior
Andrej Atrens
材料科学技术（英文）
Corrosion research by Atrens and co-workers has made significant contributions to the understanding of the service performance of engineering materials. This includes: (1) elucidated corrosion mechanisms of Mg alloys, stainless steels and Cu alloys, (2) developed an improved understanding of passivity in stainless steels and binary alloys such as Fe-Cr, Ni-Cr, Co-Cr, Fe-Ti, and Fe-Si, (3) developed an improved understanding of the melt spinning of Cu alloys, and (4) elucidated mechanisms of environment assisted fracture (EAF) of steels and Zr alloys. This paper summarises contributions in the following: (1) intergranular stress corrosion cracking of pipeline steels, (2) atmospheric corrosion and patination of Cu, (3) corrosion of Mg alloys, and (4) transgranular stress corrosion cracking of rock bolts.
关键词:
Stress corrosion cracking
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null
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null
Biomedical Materials
In this work, porous magnesium (Mg) with a three-dimensional open-cellular structure, potentially employed as bone tissue engineering scaffolds, was fabricated by the mechanical perforation method. The influences of porosity, pore size and pore arrangement on compressive behavior and the anisotropy of new porous Mg were analyzed theoretically using orthogonal arrays and the finite element method (FEM). The results showed that the parameters of porosity, pore size and pore arrangement had different effects on the compressive properties. The compressive strength could be improved by optimizing these parameters. The anisotropy of porous Mg was also verified in this study. The theoretical results showed good agreement with the experimental ones before the strain reaches 0.038.
关键词:
unidirectional solidification;pore-size;hydroxyapatite;replacement;cartilage;porosity;matrix
Y.G. Cao
,
X.Y. Sun
金属学报(英文版)
J-integral and crack opening displacement δ(COD) were important parameters for characterization of fractures in engineering materials. The relationship between J-integral and COD has been investigated for a long time and was enerally represented as J = m σyδ, where σy is the yield strength and m is a function of specimen geometry and material properties. To determine the value of m, extensive studies and experiments have been performed. The method that used the fracture-surface topography analysis (FRASTA) for determining J-integral from fracture surfaces of materials was introduced. On the basis of the relationship between COD and fracture surface average profile, the relationship between J-integral and COD was deduced and compared with the generally used equation. The method was experimentally confirmed to be able to provide a new way to determine the relationship between J-integral and COD.
关键词:
FRASTA
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null
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null
