某发动机装药结构完整性分析

基于三维粘弹性有限元模型,应用MSC/NASTRAN软件对某发动机分别在固化降温、燃气内压载荷条件下的装药结构完整性进行分析,并对该发动机在固化降温、燃气内压两种载荷联合作用下的装药结构完整性进行评估。结果表明,该发动机的装药结构完整性满足要求。     

PVA基粘弹性磁性磨具的实验研究及加工参数优化

目的检验新研制的PVA基粘弹性磁性磨具的表面光整加工性能,掌握配比参数、加工条件等因素对加工效果的影响规律,并对加工参数进行优化以达到最佳加工效果。方法以6061铝合金管外圆表面为光整加工实验对象,通过先导实验首先确定出影响加工效果的主要因素及其参数范围,而后基于响应曲面法实验,对主轴转速、两相质量比、磨粒尺寸及加工时长等因素与工件表面粗糙度下降率(%?Ra)之间的关系进行了探究分析。结果最后通过对实验结果进行方差分析,建立了PVA基粘弹性磁性磨具加工铝合金管外表面的%?Ra预测模型,并对影响参数进行了优化设计,得到在最佳实验条件下(加工时间46 min、两相质量比1.45、主轴转速635r/min、磨粒尺寸65目),工件表面粗糙度下降率为92.5%,最低表面粗糙度为59 nm,显著改善了加工效果。结论作为一种新型光整加工介质PVA基粘弹性磁性磨具,其具有良好的自适应性及流动性,能达到较好的光整加工效果。影响%?Ra的单因素显著性从强到弱依次为:加工时长、主轴转速、磨粒尺寸、两相质量比。交互作用显著的因子为两相质量比+主轴转速、加工时长+主轴转速、两相质量比+磨粒尺寸。在主轴转速、加工时长取高水平,两相质量比取中等水平,磨粒尺寸取低或高水平时,能得到较好的表面加工效果。     

黏弹性阻尼减震层的吸能特性试验研究

柔性减震技术在隧道等地下工程结构震害控制中的应用已被广泛认可,为了能够进一步推动柔性减震技术的全面发展和应用,基于黏弹性阻尼理论在桥梁建筑抗震领域中应用的认识,提出一种拟应用于地下隧道工程抗震领域的黏弹性阻尼减震层结构。通过改进分离式Hopkinson(SHPB)试验系统对不同的岩石–阻尼层–混凝土组合试件进行冲击试验,以此来分析黏弹性阻尼减震层的吸能特性。对比探讨了橡胶、硅胶不同阻尼层材料及蜂窝状、波纹状、圆柱状阻尼层结构在冲击试验中的吸能规律及其吸能效果;同时在相同阻尼层材料及其结构形状条件下,对比分析了不同厚度阻尼层的吸能规律,探讨了黏弹性阻尼减震层中阻尼层的最佳厚度;研究结果表明：与对照组（岩石–混凝土组合试件）相比,不同阻尼层的阻尼减震层结构吸收的入射能均提高了10%以上,表明该结构优越的吸能特性,同时高阻尼的橡胶比硅胶作为阻尼层材料具有更好地吸能效果;在3种不同形状的阻尼层中,蜂窝状阻尼层结构具有更好的吸能效果;对比分析不同厚度阻尼层结构的吸能效果时发现效果最佳的阻尼层厚度为20mm;研究成果将为隧道地下工程抗震结构设计提供理论和数据支撑。     

Influence of morphology on high-temperature rheological properties of bitumen modified with styrene-butadiene-styrene (SBS) copolymer

Different microstructures of the same polymer-modified bitumen (PMB) were obtained by subjecting the bitumen modified with styrene-butadiene-styrene (SBS) copolymer to isothermal annealing at various temperatures. The effects of the morphology on the rheological properties of SBS-modified bitumen were investigated within the high-temperature range. The PMB microstructures were quantitatively evaluated using image analysis. A dynamic shear rheometer was used to measure the rheological parameters of the PMB samples and perform the multiple stress creep and recovery (MSCR) test. A quantitative basis could be established on which to discuss the relationship between the PMB morphology and rheology. The image analysis indicated that conditioning by isothermal annealing evidently led to a difference in the microstructure of the samples. Variation of the thermal history is demonstrated to be a practical way to vary the morphology of the PMB with the same raw materials and formulation. Compared with the two-phase morphology, the single-phase microstructure tended to have a narrower linear viscoelastic (LVE) region of the PMB. Within the LVE region, especially at low frequencies, the homogenous PMB can store more energy when experiencing loadings and is more elastic. Outside the LVE region, based on the MSCR test results, the homogenous morphology could assist in reaching a higher percentage of strain recovery after the creep period.     

FBGA封装翘曲的黏弹性仿真与验证

窄节距焊球阵列(FBGA)封装在现代电子产品中应用广泛,翘曲是这种条带形式封装结构的一个重要性能指标.封装翘曲主要是在模塑工艺中产生的,一方面是降温过程中材料间热膨胀系数不匹配,另一方面是环氧模塑料(EMC)在模塑过程中的化学收缩造成的.另外,模塑材料后固化(PMC)过程中的应力松弛效应也是影响翘曲的重要因素.运用有限元分析(FEA)方法,研究了热失配、EMC化学收缩及其黏弹性特性三个因素对FBGA翘曲的影响.仿真结果表明,EMC化学收缩可以有效补偿热失配引起的翘曲;同时,EMC应力松弛效应也能明显改善翘曲.FBGA产品在模塑和后固化工艺后的翘曲测量值与有限元预测结果具有较好的一致性.     

Highly soluble and thermally stable copolyimides modified with trifluoromethyl and siloxane

A series of highly soluble aromatic polyimides with excellent thermal properties were fabricated by traditional two‐step polycondensation reaction of dianhydride monomer 4,4′‐(4,4′‐isopropylidenediphenoxy)bis(phthalic anhydride) or 4,4‐(hexafluoroisopropylidene)diphthalic anhydride with diamine monomer 1,3‐bis(4‐aminophenoxy)benzene or 1,3‐bis(3‐aminopropyl) tetramethyldisiloxane in N,N‐dimethylacetylamide solvent. Results revealed that copolyimide of PI‐4 containing trifluoromethyl and tetramethyldisiloxane possessed excellent solubility and remarkable thermal properties. PI‐4 could dissolve well in common low boiling point solvents such as THF of up to 80 mg/mL and acetone of 40 mg/mL. Moreover, the 10% weight loss temperature of the PI‐4 was 539°C and the T_g value of the PI‐4 was 311°C. PI‐4 might be easily cast into flexible and tough films applied in optoelectronic devices. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41713.     

Flame retardation of dibromoneopentyl glycol on intumescent flame‐retardant/low‐density polyethylene composites

On the basis of ammonium polyphosphate (APP) microencapsulated with pentaerythritol/dibromoneopentyl glycol (DBNPG) mixed phosphate melamine salt as an intumescent flame retardant (IFR), the influence of DBNPG on the flame retardancy of IFR/low‐density polyethylene was investigated. The results prove that DBNPG could influence the combustion heat and the thermal barrier properties of the char layer in combustion. The intumescent degree (ID), compactness, and closure were the determinants of the thermal barrier properties of the char layer. A greater ID below 500°C and then a more compact and closed char layer above 500°C contributed to the better thermal barrier properties. An appropriate DBNPG reduced the combustion heat and promoted the formation of a compact and closed char layer by increasing of the melting viscosity of the composites. However, excessive DBNPG destroyed the closure of the char layer and increased the combustion heat because of a decrease in the melting viscosity of the composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41244.     

Nitrile rubber/hindered phenol exterminated hyperbranched polyester materials with improved damping and mechanical performance

Hindered phenol exterminated hyperbranched polyester (mHBP) is fabricated by esterification reaction. The mHBP is introduced into nitrile rubber (NBR) to prepare NBR/mHBP blends. Structure, damping and mechanical properties of NBR/mHBP blends are investigated by Fourier transform infrared spectroscopy (FTIR), ¹H‐NMR, dynamic mechanical thermal analyzer (DMTA), and tensile tester. FTIR spectra of the blends illustrate the intermolecular hydrogen bonding between the NBR and mHBP, contributing to the improvement of damping and mechanical properties. The results indicate that, with the increasing mHBP content, the T_g of the blends shifted to a higher temperature with a broadening temperature range and improved mechanical properties, showing an application in adjusting the T_g and temperature range without decreasing of loss factor. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42605.     

Fabrication of high‐viscosity biodegradable poly(butylene succinate) (PBS)/solid epoxy (SE)/carboxyl‐ended polyester (CP) blends

Expanding the applications of poly(butylene succinate) (PBS) in processing fields requiring high melt strength, PBS/solid epoxy (SE)/carboxyl‐ended polyester (CP) blends with high melt viscosity were fabricated by the in‐situ crosslinking reaction using SE and CP. The influence of SE/CP had been studied in terms of the rheological property, crystallization behavior, and mechanical property of PBS. The results showed that the melt viscosity of PBS could be enhanced significantly by three orders of magnitude, when the loading ratio of SE to CP was over 15/15. Furthermore, it had also been found that SE/CP component had positive impact on the mechanical properties of PBS, inclusive of reduction of brittleness. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42193.