The influence of environmental conditions on the dimensional stability of components injected with PA6 and PA66

The design of assembly components requires special attention to aspects related to their dimensions to ensure their functionality. The goal of this paper is to analyse the influence of case-based environmental conditions, including extreme hydrothermal conditions, on the dimensional stability of a component made from different polyamides throughout the component's working life. The results support the conclusion that components made from PA6 have a higher capacity to absorb humidity than those made from PA66 and, on the other hand, a higher capacity to lose this humidity, which implies a more significant effect on the average error in the dimensions considered (12% for PA6 in comparison to 3% for PA66). With regard to assembly dimensions, components remain within dimensional tolerances under average and extreme humidity conditions and average temperature conditions. Components injected with P66 are more stable for all of the situations analysed.     

Dimensional and Optoelectronic Tuning of Lead-free Perovskite Cs3Bi2I9−nBrn Single Crystals for Enhanced Hard X-ray Detection

Inorganic Bi-based perovskites have shown great potential in X-ray detection for their large absorption to X-rays, diverse low-dimensional structures, and eco-friendliness without toxic metals. However, they suffer from poor carrier transport properties compared to Pb-based perovskites. Here, we propose a mixed-halogen strategy to tune the structural dimensions and optoelectronic properties of Cs₃Bi₂I_9−nBr_n (0≤n≤9). Ten centimeter-sized single crystals are successfully grown by the Bridgman technique. Upon doping bromine to zero-dimensional Cs₃Bi₂I₉, the crystal transforms into a two-dimensional structure as the bromine content reaches Cs₃Bi₂I₈Br. Correspondingly, the optoelectronic properties are adjusted. Among these crystals, Cs₃Bi₂I₈Br exhibits negligible ion migration, moderate resistivity, and the best carrier transport capability. The sensitivities in 100 keV hard X-ray detection are 1.33×10⁴ and 1.74×10⁴ μC Gy_air⁻¹ cm⁻² at room temperature and 75 °C, respectively, which are the highest among all reported bismuth perovskites. Moreover, the lowest detection limit of 28.6 nGy_air s⁻¹ and ultralow dark current drift of 9.12×10⁻⁹ nA cm⁻¹ s⁻¹ V⁻¹ are obtained owing to the high ionic activation energy. Our work demonstrates that Br incorporation is an effective strategy to enhance the X-ray detection performance by tuning the dimensional and optoelectronic properties.     

侧链磺化型聚砜质子交换膜的设计与制备及其性能研究

在制备氯甲基化聚砜(CMPSF)的基础上,以对羟基苯磺酸钠(HBSS)和羟基苯二磺酸钠(HBDSS)为亲核试剂,通过亲核取代反应,在聚砜(PSF)主链上分别键联了以苯磺酸根(BSS)和苯二磺酸根(BDSS)基团为末端基的侧链,制得了亲水磺酸根基团与疏水主链"微相分离"结构的2种侧链型磺化聚砜PSF-BSS和PSF-BDSS,并优化了制备条件.在对磺化聚砜产物进行充分表征(FTIR和1H-NMR谱)的基础上,采用流延成膜法制备了质子交换膜,测定了质子交换膜的基本性能,重点考察了质子交换膜"芳香性"主链和亲疏水微区"相分离"这2种结构因素对交换膜性能的影响.实验结果表明,在极性较强的溶剂中,CMPSF与羟基苯磺酸钠可顺利地发生亲核取代反应,于100℃经40 h反应可制得磺酸根键合量分别为2.07 mmol/g和2.11 mmol/g的磺化聚砜PSF-BSS和PSF-BDSS.所制备的质子交换薄膜具有较高的质子传导率(PSF-BDSS交换膜室温为4.7×10-2S/cm,80℃为8.1×10-2S/cm),优良的尺寸稳定性(室温溶胀率为8.6%,80℃溶胀率为30%),且具有良好的热稳定性与抗氧化稳定性.     

Size-dependent sharp indentation—I: a closed-form expression of the indentation loading curve

In this paper, a closed-form expression of the size-dependent sharp indentation loading curve has been proposed based on dimensional analysis and the finite deformation Taylor-based nonlocal theory (TNT) of plasticity (Int. J. Plasticity 20 (2004) 831). The key issue is to link the results of FEM based on TNT plasticity with those obtained using conventional FEM by taking as the effective strain gradient, η, that presented in the work of Nix and Gao (J. Mech. Phys. Solids 46 (1998) 411), thus avoiding large-scale finite element computations using strain gradient plasticity theories. Two experiments carried out on 316 stainless-steel and pure titanium have been used to verify the effectiveness of the present analytical model; the results demonstrate that the present analytical expression of the size-dependent indentation loading curve corresponds very well to the experimental indentation loading curve. The empirical constant, α, in the Taylor model estimated from the experimental data has the correct order of magnitude. Also, the results presented in this part can be further applied to establish an analytical framework to extract the plastic properties of metallic materials with sharp indentation on a small scale where the size effect caused by geometrically necessary dislocations is significant. This will be discussed in detail in the second part of the paper.     

单镜头三维粒子成像测速

本文提出了一种用单镜头进行三维流场测量的方法，建立了包括摄录系统、数字图象处理及识别系统及流动装置的３Ｄ－ＳＣＰＩＶ系统。完成了现有条件下的原理性定量测量实验。     

Homogenization of Periodically Heterogeneous Thin Beams

Consider an elastic thin three-dimensional body made of a periodic distribution of elastic inclusions. When both the thickness of the beam and the size of the heterogeneities tend simultaneously to zero the authors obtain three different one-dimensional models of beam depending upon the limit of the ratio of these two small parameters.     

A statistical model for global optimization by means of select and clone

A statistical model tor giobai optimization is constructed generalizing some properties ofthe Wiener process to the multidimensional case. A new approach, which is similar to the Branch and Bound approach, is proposed to the construction of algorithms based on statistical models. A two dimensional version of the algorithm is implemented, and test results are presented     

Dimensional considerations on the mechanical properties of 3D printed polymer parts

Additive manufacturing offers a useful and accessible tool for prototyping and manufacturing small volume functional parts. Polylactic acid (PLA) and thermoplastic polyurethane (TPU) are amongst the most commonly used materials. Characterising 3D printed PLA and TPU is potentially important for both designing and finite element modelling of functional parts. This work explores the mechanical properties of additively manufactured PLA/TPU specimens with consideration to design parameters including size, and infill percentage. PLA/TPU specimens are 3D-printed in selected ISO standard geometries with 20%, 60%, 100% infill percentage. Tensile and compression test results suggest that traditional ISO testing standards might be insufficient in characterising 3D printed materials for finite element modelling or application purposes. Infill percentage in combination to design size, may significantly affect the mechanical performance of 3D printed parts. Dimensional variation may cause inhomogeneity in mechanical properties between large and small cross section areas of the same part. The effect was reduced in small cross section parts where reducing the nominal infill had less effect on the resulting specimens. The results suggest that for 3D printed functional parts with significant dimensional differences between sections, the material properties are not necessarily homogeneous. This consideration may be significant for designers using 3D printing for applications, which include mechanical loading.     

Effect of Gaussian size distribution width on minimum fluidization velocity in tapered gas–solid fluidized beds

This paper investigated the effect of Gaussian distribution width, average particle diameter, particle loading, and the tapered angle on minimum fluidization velocity (U_mf) by conducting extensive experiments in tapered fluidized beds. Three powders with Gaussian size distribution and different distribution widths were used in the experiments. An increase in U_mf with increasing the average particle diameter, particle loading, and the tapered angle was observed. There was also a nonmonotonic behavior of U_mf as the Gaussian distribution width increased. An empirical correlation including dimensionless groups for predicting U_mf in tapered beds was developed in which the effect of distribution width was considered. The proposed correlation predictions were in good agreement with the experimental data, with a maximum deviation of 16.5% and average and standard deviations of, respectively, 6.4% and 7.4%. The proposed correlation was also compared with three earlier models, and their accuracy was discussed.