A numerical study of solidification in powder injection molding process

Thermal analysis of mold filling and post-filing solidification has been carried out for the powder injection molding process. The filling material comprised alumina powder and polymeric binder was used to fill a rectangular cavity. The interphase momentum transfer was accounted for using a momentum exchange model due to Wang et al. [Y. Wang, S. Ahuja, C.Beckerman, H.C. de GROH III, Multiparticle interfacial drag in equiaxed solidification, Metall. Mater. Trans. B 26B (1995) 111–119]. Though both the alumina powder and polymeric binder are treated as fluids, as the alumina powder does not undergo a phase change, only the solidification of the binder has to be considered. The liquid fraction of the binder was assumed to follow a linear rule between the liquidus and solidus temperature. An iterative latent heat recovery formulation has been developed to obtain the liquid fraction during solidification. It was found that the predictions for pressure rise at the inlet compares favorably with the results from the single-phase mixture model. However, the multi-phase model could predict the powder segregation unlike the mixture model. The multi-phase model predicts higher temperature compared to mixture model due to powder particle migration.     

海上风电单筒多舱筒型基础筒体屈曲特性研究

对单筒多舱筒型基础入土下沉过程进行稳定性分析,研究其失稳模式与临界屈曲荷载以及分舱板与纵向加劲肋对筒内外压差临界值的影响。结果表明,单筒多舱筒型基础筒体失稳属于极值点失稳,应采用非线性方法确定结构失稳的临界荷载;分舱板和适当间距的加劲肋均可提高筒体的临界屈曲荷载,但随筒顶接近泥面,其提升效果逐渐减小,筒内外压差控制条件转变为防止筒内土体发生渗透破坏。     

Microstructure Evolution and Dynamic Mechanical Properties of Laser Additive Manufacturing Ti-6Al-4V Under High Strain Rate

The dynamic mechanical properties of the Ti-6Al-4V (TC4) alloy prepared by laser additive manufacturing (LAM-TC4) under the high strain rate (HSR) are proposed. The dynamic compression experiments of LAM-TC4 are conducted with the split Hopkinson pressure bar (SHPB) equipment. The results show that as the strain rate increases, the widths of the adiabatic shear band (ASB), the micro-hardness, the degree of grain refinement near the ASB, and the dislocation density of grains grow gradually. Moreover, the increase of dislocation density of grains is the root factor in enhancing the yield strength of LAM-TC4. Meanwhile, the heat produced from the distortion and dislocations of grains promotes the heat softening effect favorable for the recrystallization of grains, resulting in the grain refinement of ASB. Furthermore, the contrastive analysis between LAM-TC4 and TC4 prepared by forging (F-TC4) indicates that under the HSR, the yield strength of LAM-TC4 is higher than that of F-TC4.     

Backside failure analysis case study: Implementation of innovative Local Backside Deprocessing technique

This paper describes a failure analysis case study where innovative Local Backside Physical characterization technique was performed on an automotive custom Mix-Mode device.The full analysis flow is presented, starting with backside sample preparation in order to perform a backside electrical localization of the defect. Then the multiple challenges of that approach were discussed. The continuous need of decreasing the analysis cycle time was addressed without affecting the success ratio of such analysis flow. The part mechanical degradation was avoided with a local removal of the Silicon. That highly localized technique granted a direct access to the fault site.The tools and process used for this case are fully described underlining the main advantages of this technique in comparison to the global backside deprocessing or to other characterization techniques.That successful development was achieved while determining the failure mechanism, in correlation with the failure mode of the qualification reject.     

非饱和重塑黄土应变控制等应力比试验三维离散元分析

黄土地区工程建设中有大量填方工程,填方工程中土体可能承受等应力比压缩荷载,为了研究非饱和重塑黄土在较高应力比下的宏微观力学性质,运用应变控制加载方式开展了不同应力比的非饱和黄土等应力比试验离散元数值分析.数值模拟中,考虑颗粒间转动和扭转抗力及范德华力并采用分层欠压法制备均匀松散黄土数值试样,引入粒间引力反映毛细力作用....     

Heat and mass transfer intensification at steam absorption by surfactant additives

The mechanisms of surfactant admixture effect on heat and mass transfer were studied experimentally at steam absorption by a salt solution at operation of the heat pump absorber. Steam absorption by initially immobile water solution of lithium bromide with additives of n-octanol with concentrations of 25–400 ppm (both lower and higher than the solubility limit) was studied. Thermograms of a layer surface, moving during absorption, were obtained by thermal imaging equipment. Data on surface tension of lithium bromide solution with small additives of n-octanol was analyzed.     

土石混合介质中石料间隙土压实度剪切波速评价研究

采用室内重型击实试验的方法,分别对砂土、粉质黏土、低液限黏性土3种土样的纯土试件和土石混合试件进行了不同含水率、不同含石量情况下试件剪切波速对比试验。引入体积膨胀率
,通过分析
与细粒土剪切波速及
与混合料剪切波速的相关关系,建立土石混合介质不同压实程度时,石料间隙土剪切波速与混合料宏观剪切波速相关性模型。结果表明：石料间隙土剪切波速可由混合料宏观剪切波速推定。研究结果将为采用石料间隙土剪切波速评价混合料压实程度测试技术提供依据。