纵梁前段全工序回弹预测与控制

目的结合高强度钢板纵梁前段工艺难点及特征,提出对该零件回弹进行预测和控制的方法。方法采用经验设计和CAE分析技术相结合的方法,对零件全工序成形及回弹过程进行了仿真模拟分析,同时对零件产生回弹的原因进行了深入分析,提出了回弹问题的解决方案。结果通过采取有效措施对回弹进行控制,成功解决了零件质量问题,回弹控制在了1 mm之内,平均合格率达到了91.8%,满足了装车要求。结论全工序CAE分析可有效预测高强度钢板梁类零件的成形质量缺陷和回弹状态,并指导工艺设计和模具型面补偿,合理的梁类扭曲回弹解决方案为类似零件模具的开发提供了参考。     

析出相对Monel K-500合金冲击韧性的影响

通过一系列实验研究了Monel K-500合金的冲击韧性。结果表明,合金经550~650℃时效后其冲击断口呈沿晶形貌;在750~850℃时效时,其冲击韧性与强度呈正相关关系。根据对合金在不同热处理状态的析出相形态及分布的研究,揭示了形成这些现象的原因。合金在550~650℃时效时,在晶内析出的γ’相呈球状均匀分布,而在部分晶界附近的γ’相呈条棒状或排成帘状垂直于晶界分布,由此导致时效态合金在断裂时,裂纹沿晶界扩展。在750~850℃时效会导致合金形成大量沿晶界网状分布的二次MC相,从而降低合金的冲击韧性。     

粉末冶金零件生产用润滑剂的性能改进与选择

在粉末冶金零件生产中,压制成形与脱模过程中都需要进行润滑,最常用的方法是将润滑剂添加于金属粉末的预混合粉中。润滑剂的类型不仅影响粉末的压制性能,而且影响混合粉的其他性能和零件的生坯与烧结性能。评述了最常用的润滑剂的使用性能,并介绍最近20多年来粘结剂/润滑剂系统的性能改进与进展。     

塑料包装袋热合强度的失效模式分析

热合强度是考核复合塑料包装袋热合面封口牢固度的一个重要指标,检测标准中并没有说明测量热合强度时的失效模式。根据QB/T 2358—1998《塑料薄膜包装袋热合强度试验方法》,对PET/Al/PA/RCPP结构、OPP/VMPET/PE结构、PET/RCPP结构、PET/Al/PA/RCPP结构薄膜和阴阳镀铝复合薄膜几种不同材质塑料包装袋进行了热合强度试验,总结得出了5种失效模式,即热封层剥离、热封边缘断裂、薄膜断裂、薄膜分层、先分离后撕裂,结合测量曲线图与失效模式图,分析了各失效模式的形成原因,以便有效指导与改进塑料包装袋的生产工艺。     

海水条件下矿山充填应用粉煤灰的可行性研究

三山岛金矿充填用水中Cl-、SO2-4和Mg2+等离子浓度较高,影响充填体的强度。根据海水和粉煤灰的化学成分检测结果,分析研究海水中氯盐、硫酸盐、镁盐对充填体的破坏机理以及在尾砂胶结充填中粉煤灰在活性效应、粉末效应和形态效应3个方面的作用机理。分析认为,海水成分中的硫酸盐、氯盐和海水的弱碱性成分对化学激发粉煤灰活性发挥重要作用。因此,为了提高海水条件下充填体的强度,添加粉煤灰不仅可以减少海水中相关离子对充填体强度的影响,而且海水中的部分化学成分对粉煤灰活性的激发作用可以进一步提高粉煤灰的胶凝作用。     

Formulation and pharmacokinetics of gelucire solid dispersions of flurbiprofen

Context: Development of solid dispersions is to improve the therapeutic efficacy by increasing the drug solubility, dissolution rate, bioavailability as well as to attain rapid onset of action.

Objective: The present research deals with the development of solid dispersions of flurbiprofen which is poorly water soluble to improve the solubility and dissolution rate using gelucires.

Materials and methods: In this study, solid dispersions were prepared following solvent evaporation method using gelucire 44/14 and gelucire 50/13 as carriers in different ratios. Then the formulations were evaluated for different physical parameters, solubility studies, DSC, FTIR studies and in vitro dissolution studies to select the best formulation that shows rapid dissolution rate and finally subjected to pharmacokinetic studies.

Results and discussion: From the in vitro dissolution study, formulation F3 showed the better improvement in solubility and dissolution rate. From the pharmacokinetic evaluation, the control tablets produced peak plasma concentration (C_max) of 9140.84?±?614.36?ng/ml at 3?h T_max and solid dispersion tablets showed C_max?=?11?445.46?±?149.23?ng/ml at 2?h T_max. The area under the curve for the control and solid dispersion tablets was 31?495.16?±?619.92 and 43?126.52?±?688.89?ng h/ml and the mean resident time was 3.99 and 3.68?h, respectively.

Conclusion: From the above results, it is concluded that the formulation of gelucire 44/14 solid dispersions is able to improve the solubility, dissolution rate as well as the absorption rate of flurbiprofen than pure form of drug.     

The Improvement in Mechanical and Barrier Properties of Poly(Vinyl Alcohol)/Graphene Oxide Packaging Films

In this study, poly(vinyl alcohol) (PVA)‐graphite oxide and PVA‐graphene oxide (XGO) films were prepared by simple and environmentally friendly method. Fourier transform infrared spectroscopy, X‐ray diffraction and scanning electron microscope revealed the strong hydrogen‐bonding interactions between XGO and PVA matrix and the layered structure of tensile fracture surfaces of exfoliated PVA‐XGO films. These resulted in a remarkable improvement on mechanical and barrier properties of XGO/PVA nanocomposite films. The addition of 0.3 and 2.0 wt.% XGO showed an increase in tensile strength (49%) and failure stain (13–22%), in comparison with the neat PVA films. The dramatic improvement of 144% in elastic modulus was observed in PVA/2.0 wt.% XGO. Both O₂ and water vapour permeability coefficients of PVA film decreased by about 76% and 21% at an XGO loading of 2.0 wt.%, respectively. Preliminary test was performed to determine the use of nanocomposite films to extend the shelf life of bananas. It was found that bananas packaged in nanocomposite films were ripened slower than those unpackaged or packaged in PVA films. These results demonstrate that such films could dramatically promote the application of PVA‐based films in the packaging industry. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of drawing condition on mechanical properties and molecular orientation of self-reinforced poly(lactic acid) screws

Effects of extrusion ratio (ER) during extruding on mechanical properties of poly(lactic acid) (PLA) screws were investigated in terms of shear and twist strength. Shear strength increased by drawing, while twist strength decreased. This might be due to orientation of molecular chains during drawing. In order to evaluate orientation of molecular chains, orientation function in extruded billets was measured as a function of ER. Since orientation function increased with ER, drawing is effective method to improve shear strength of screw, where fibrous structure which was formed during extruding resisted shear stress in cross-section perpendicular to screw axis. Although orientation functions for billet extruded at ER 1.3–4 were equivalent, both strengths changed for the screw extruded at the range of this ER. Infrared spectra suggested transforming from α to β crystal for the billet extruded at the range of this ER. This result suggested that mechanical properties of screw also depended on the crystal forms.     

Studies on the potential risk of liquid metal assisted cracking (LMAC) in normal‐temperature and high‐temperature hot‐dip galvanizing of high strength bolts of dimensions greater M24

Liquid metal assisted cracking (LMAC) mainly occurs due to an unfavorable interaction of three factors: a susceptible material condition, presence of a liquid metal and sufficient tensile stress. Hot‐dip galvanizing of high‐strength bolts induces high thermal loads in bolts made of tempered steel in the presence of a zinc melt and thus, provides the boundary conditions for the above mentioned critical factors to interact. The focus of this study is on investigating thermally‐induced stresses in large diameter bolts and their impact on the formation of liquid metal assisted cracking (LMAC). In order to calculate the thermal loads in hot‐dip galvanizing, simulations were carried out regarding the thermo‐mechanical behavior of bolts during the hot‐dip galvanizing process. The simulations illustrate that cracks are most likely to occur in the first thread turn. This prediction is confirmed by experimental observations.