Finite element method for viscoelastic medium with damage and the application to structural analysis of solid rocket motor grain

This paper studies the damage-viscoelastic behavior of composite solid propellants of solid rocket motors(SRM).Based on viscoelastic theories and strain equivalent hypothesis in damage mechanics,a three-dimensional(3-D)nonlinear viscoelastic constitutive model incorporating with damage is developed.The resulting viscoelastic constitutive equations are numerically discretized by integration algorithm,and a stress-updating method is presented by solving nonlinear equations according to the Newton-Raphson method.A material subroutine of stress-updating is made up and embedded into commercial code of Abaqus.The material subroutine is validated through typical examples.Our results indicate that the finite element results are in good agreement with the analytical ones and have high accuracy,and the suggested method and designed subroutine are efficient and can be further applied to damage-coupling structural analysis of practical SRM grain.     

A dislocation dynamics study of the strength of stacking fault tetrahedra. Part I: interactions with screw dislocations

We present a comprehensive dislocation dynamics (DD) study of the strength of stacking fault tetrahedra (SFT) to screw dislocation glide in fcc Cu. Our methodology explicitly accounts for partial dislocation reactions in fcc crystals, which allows us to provide more detailed insights into the dislocation–SFT processes than previous DD studies. The resistance due to stacking fault surfaces to dislocation cutting has been computed using atomistic simulations and added in the form of a point stress to our DD methodology. We obtain a value of 1658.9 MPa, which translates into an extra force resolved on the glide plane that dislocations must overcome before they can penetrate SFTs. In fact, we see they do not, leading to two well differentiated regimes: (i) partial dislocation reactions, resulting in partial SFT damage, and (ii) impenetrable SFT resulting in the creation of Orowan loops. We obtain SFT strength maps as a function of dislocation glide plane-SFT intersection height, interaction orientation, and dislocation line length. In general SFTs are weaker obstacles the smaller the encountered triangular area is, which has allowed us to derive simple scaling laws with the slipped area as the only variable. These laws suffice to explain all strength curves and are used to derive a simple model of dislocation–SFT strength. The stresses required to break through obstacles in the 2.5–4.8-nm size range have been computed to be 100–300 MPa, in good agreement with some experimental estimations and molecular dynamics calculations.     

Effect of fused silica subsurface defect site density on light intensification

The effect of defect density on the modulation of incident laser waves is investigated. First, based on the actual defect distribution in the subsurface of fused silica, a three-dimensional (3D) grid model of defect sites is constructed. The 3D finite-difference time-domain method is developed to solve the Maxwell equations. Then the electrical field intensity in the vicinity of the defect sites in the subsurface of fused silica is numerically calculated. The relationships between the maximal electrical field intensity in fused silica and the geometry of the defect sites are given. The simulated results reveal that the modulation becomes more remarkable with an increase of the defect density. In addition, the effect of the distribution mode of defects on modulation is discussed. Meanwhile, the underlying physical mechanism is analyzed in detail.     

硅酸铋(BSO)晶体闪烁性能研究

报道对BSO晶体闪烁性能研究的若干结果. 包括晶体的激发光谱和荧光光谱、光产额、发光衰减时间和抗辐照能力等特性.     

关于复合式微动的研究

在新型径向微动试验装置上 ,改变试样的倾斜角度 ,实现了径向微动和切向微动的复合 .考察了 GCr15钢球 /2 0 91铝锂合金在倾斜 30°和 45°以及不同外加载荷条件下的复合微动损伤行为 ,并分析了其磨痕特征     

含纳米粒子溶液对单晶硅表面的冲蚀磨损损伤实验研究

利用高分辨透射电子显微镜和原子力显微镜观察了含纳米颗粒溶液冲蚀硅片表面损伤行为,考察了纳米颗粒碰撞单晶硅片所导致的微观物理损伤.结果表明:冲蚀30 s后,在高分辨透射电子显微镜下可见硅片表面呈现方向性损伤,并可观察到大量非均匀的晶格缺陷;当冲蚀10 min时,硅片表面出现微观划痕和凹坑,在划痕一端可见原子堆积,亚表面可观察到镶嵌晶粒的非晶损伤层;继续延长冲蚀时间将加剧其表面损伤.     

Radiation damage to protein specimens from electron beam imaging and diffraction: a mini‐review of anti‐damage approaches,with special reference to synchrotron X‐ray crystallography

Recent research progress using X‐ray cryo‐crystallography with the photon beams from third‐generation synchrotron sources has resulted in recognition that this intense radiation commonly damages protein samples even when they are held at 100 K. Other structural biologists examining thin protein crystals or single particle specimens encounter similar radiation damage problems during electron diffraction and imaging, but have developed some effective countermeasures. The aim of this concise review is to examine whether analogous approaches can be utilized to alleviate the X‐ray radiation damage problem in synchrotron macromolecular crystallography. The critical discussion of this question is preceded by presentation of background material on modern technical procedures with electron beam instruments using 300–400 kV accelerating voltage, low‐dose exposures for data recording, and protection of protein specimens by cryogenic cooling; these practical approaches to dealing with electron radiation damage currently permit best resolution levels of 6 Å (0.6 nm) for single particle specimens, and of 1.9 Å for two‐dimensional membrane protein crystals. Final determination of the potential effectiveness and practical value of using such new or unconventional ideas will necessitate showing, by experimental testing, that these produce significantly improved protection of three‐dimensional protein crystals during synchrotron X‐ray diffraction.     

Optimal conditions for submonolayer nanoisland growth in ion beam assisted deposition

We study the optimal conditions for nanoisland growth in ion beam assisted deposition (IBAD). This situation occurs when adatom islands remain small enough to prevent the onset of three-dimensional growth, while at the same time preventing ion-induced surface erosion. To this end, we develop a rate equation model of IBAD, which embodies continuous deposition of adatoms and creation of vacancies, recombination of vacancies at adatom island edges, as well as recombination of adatoms at vacancy island edges. These rate equations are solved by numerical simulations based on the particle coalescence method. To determine the optimal growth condition, we find the largest mean size of the vacancy islands leading to their survival. We show that at this onset between the rough and smooth layer-by-layer growth regimes there is a simple exponential relation between the largest size of the vacancy islands and the external control parameters of the growth.     

Nuclear magnetic resonance-based metabolomics for prediction of gastric damage induced by indomethacin in rats

Non-steroidal anti-inflammatory drugs (NSAIDs) have side effects including gastric erosions, ulceration and bleeding. In this study, pattern recognition analysis of the ¹H-nuclear magnetic resonance (NMR) spectra of urine was performed to develop surrogate biomarkers related to the gastrointestinal (GI) damage induced by indomethacin in rats. Urine was collected for 5 h after oral administration of indomethacin (25 mg kg⁻¹) or co-administration with cimetidine (100 mg kg⁻¹), which protects against GI damage. The ¹H-NMR urine spectra were divided into spectral bins (0.04 ppm) for global profiling, and 36 endogenous metabolites were assigned for targeted profiling. The level of gastric damage in each animal was also determined. Indomethacin caused severe gastric damage; however, indomethacin administered with cimetidine did not. Simultaneously, the patterns of changes in their endogenous metabolites were different. Multivariate data analyses were carried out to recognize the spectral pattern of endogenous metabolites related to indomethacin using partial least square-discrimination analysis. In targeted profiling, a few endogenous metabolites, 2-oxoglutarate, acetate, taurine and hippurate, were selected as putative biomarkers for the gastric damage induced by indomethacin. These metabolites changed depending on the degree of GI damage, although the same dose of indomethacin (10 mg kg⁻¹) was administered to rats. The results of global and targeted profiling suggest that the gastric damage induced by NSAIDs can be screened in the preclinical stage of drug development using a NMR based metabolomics approach.