Dose and Temperature Dependence of Void Swelling in Electron Irradiated Stainless Steel

In a high voltage electron microscope, solution treated Type 316 stainless steel was electron-irradiated at temperatures in the range of 370–630°C to a dose of about 30 dpa. The swelling (ΔV/V) induced by the irradiation beyond about 5 dpa is well described by an empirical equation, ΔV/V=A(dpa) ⁿ , under constant void and dislocation densities. With increasing irradiation temperature, the fluence exponent n increases and the pre-exponent term A decreases. At 550°C irradiation, the fluence exponent takes the value of 1.5 due to the diffusion-limited void growth. The value of n larger than 1.5 at higher temperature (>550°C) is attributable to the surface reaction-limited void growth. The smaller value of n for the low temperature (?500°C) irradiation appears to arise from the dislocation assisted vacancy diffusion. The peak swelling temperature of the specimen irradiated to 30 dpa is about 570°C, which shifts to a higher temperature with increase in electron dose.     

级配变化对混合料性质及路用性能的影响

通过对不同离析程度混合料的级配及沥青含量的理论分析与试验研究表明,离析在一定范围内对混合料的性质没有太大影响,当离析超过一定限度时,混合料质量恶化。离析对路面空隙率有直接影响,当空隙率超过一定限度时,对路用性能影响很大。     

Surface Effect on Void Swelling Behavior of Stainless Steel

The nucleation and growth of voids have been observed successively in different thickness specimens of Type 316 stainless steel electron-irradiated at 550°C in a high voltage electron microscope. In a bulk representative 1.5 μm thick specimen, the void number density increases rapidly and saturates during the initial stage of irradiation and then decreases with following dose by void coalescence. The swelling increases proportionally with (dpa)^1-5 up to about 30 dpa. In a thin specimen, of 0.4 μm thickness, on the other hand, the void number density increases continuously with dose up to about 25 dpa. The swelling of the thin specimen showed a tendency to saturation due to the disappearance of voids at the specimen surfaces. The difference in swelling behavior between the 1.5 and 0.4;μm thick specimens can be ascribed to the different effects of the specimen surfaces, which serve as a dominant sink for both radiation-produced point defects and dislocations.     

A three dimensional view of high temperature creep damage

Abstract

A three dimensional view of creep voids in a hydrogen reformer tube is presented. By separating and reconstructing various microstructural features present, the proper representation of creep voids in 3D can be fully studied. Useful measurements of parameters such as void volume, void-to-void distance, and grain boundary angles were obtained. The data presented here represent the initial collection of creep void information for use in various creep void nucleation and growth models. Additional data are currently being collected for material subjected to different service conditions.     

Spatial Behavior in Linear Theory of Thermoviscoelasticity with Voids

In the present article we study the spatial behavior of the solutions to the initial boundary value problem associated with the linear theory of thermoviscoelastic materials with voids. We prove a set of properties for an appropriate time-weighted surface power function, which allows us to obtain an idea of the domain of influence in linear thermoviscoelasticity with voids. Some spatial estimates of the Saint–Venant type, for bounded bodies, and Phragmén–Lindelöf type, for unbounded bodies, are obtained. Such estimates are characterized by time-dependent as well as time-independent decay and growth rates.     

沥青混合料试件成型方法试验对比

利用Superpave旋转压实成型机和马歇尔自动击实仪,对具有相同级配的沥青混合料进行成型,通过对比两种试件的体积特性来初步分析两种成型方法的差异。研究发现,125次旋转压实成型的试件与75次马歇尔击实成型试件的体积特性差异受细料品质影响很大,马歇尔击实和旋转压实成型有着本质的区别。针对马歇尔击实次数建立等效的旋转压实次数是不现实的。     

3D damage characterisation and the role of voids in the fatigue of wind turbine blade materials

The fatigue mechanisms of Glass Fibre Reinforced Polymer (GFRP) used in wind turbine blades were examined using computed tomography (CT). Prior to mechanical testing, as-manufactured [+45/−45/0]_3,s glass/epoxy specimens were CT scanned to provide 3-dimensional images of their internal microstructure, including voids. Voids were segmented and extracted, and individual characteristics and volumetric distributions were quantified. The coupons were then fatigue tested in uniaxial loading at R = −1% to 40% of the nominal tensile failure stress. Some tests were conducted to failure for correlation with the initial void analysis and to establish failure modes. Other tests were stopped at various life fractions and examined using CT to identify key damage mechanisms. These scans revealed transverse matrix cracking in the surface layer, occurring predominantly at free edges. These free-edge cracks then appeared to facilitate edge delamination at the 45/−45° interface. Propagation from sub-critical, surface ply damage to critical, inner ply damage was identified with either a −45/0° delamination, or a 0° fibre tow failure allowing a crack to propagate into the specimen bulk. Final failure occurred in compression and was characterised by total delamination between all the 45/−45° plies. A quantitative void analysis, taken from the pre-test CT scans, was also performed and compared against the specimens’ fatigue lives. This analysis, to the authors’ knowledge the first of its kind, measured and plotted approximately 10,000 voids within the gauge length of each specimen. The global void measurement parameters and distributions showed no correlation with fatigue life. A local ply-level investigation revealed a significant correlation between the largest void and fatigue life in the region of the laminate associated with the crack propagation from sub-critical to critical damage.     

多孔沥青路面级配组合与油石比确定

对多孔沥青路面的原材料性能进行了试验,确定了目标孔隙率及最大粒径,向沥青中加入4种不同改性剂对沥青进行改性,通过析漏试验确定最佳油石比,制成多组不同级配试件进行了马歇尔试验和驻波管试验,试验结果表明SBS改性沥青粘度、软化点等均符合要求,满足路用性能指标,优于其他三种改性剂.     

Formation of interfacial voids in composites with a weakly bonded viscoplastic matrix

The formation and evolution of interfacial voids are investigated in the case of metal matrix composites (MMCs) reinforced by ceramic fibres and subjected to high compressive loads. The resulting compression flows of a viscoplastic aluminum matrix around rigid fibres are described by a nonlinear free-boundary problem. A new finite element model with boundary-fitted mesh motion is introduced to simulate the formation of interfacial voids. The fibre–matrix interface is weak and allows yielding and sliding with separation at a dynamic contact line connecting three phases. The fibre–matrix interaction is simulated via a modified O'Donovan–Tanner constitutive model and a phenomenologically defined interface potential. The shape of the interfacial surface undergoing large deformation is not known a priori and found as a part of the solution. The influence of hydrostatic stress and constitutive characteristics of the matrix on the evolution of interfacial voids and their growth rates are examined. As the transverse strain increases, the evolution of interfacial voids occurs through a sequence of convex profiles. Numerical simulations are carried out for a special case involving small values of the yield stress and the viscosity of yielded matrix in order to compare them with similar results for linear viscous solids. The numerical results are also compared with the experiments involving similar compression flows of viscoplastic model materials.     

The Effect of Initial Defects on Overall Mechanical Properties of Concrete Material

Considering the fact that the initial defects, like the imperfect interfacial transition zones (ITZ) and the micro voids in mortar matrix, weaken the mechanical properties of concrete, this study develops corresponding constitutive models for ITZ and matrix, and simulates the concrete failure with finite element methods. Specifically, an elastic-damage traction-separation model for ITZ is constructed, and an anisotropic plastic-damage model distinguishing the strength-difference under tension and compression for mortar matrix is proposed as well. In this anisotropic plastic-damage model, the weakening effect of micro voids is reflected by introducing initial isotropic damage, the distinct characteristic of tension and compression which described by decomposing damage tensor into tensile and compressive components, and the plastic yield surface which established on the effective stress space. Furthermore, by tracking the damage evolution of concrete specimens suffering uniaxial tension and compression, the effects of imperfect status of ITZ and volume fraction of initial voids on the concrete mechanical properties are investigated.