Scaling effect on the tensile properties of [±45/0/±45/0/±45] Polypropylene/Twaron laminates

The effects of scaling on the mechanical response under tension of balanced nonsymmetrical laminates were investigated for a thermoplastic composite: Polypropylene reinforced with Twaron^® fibers. The composite baseline was an 8-ply laminate which consisted of unidirectional plies arranged in the sequence [±45/0/±45/0/±45]. The influence of specimen size on the tensile properties was studied for one (thickness), two (in-plane) and three (volume) dimensional scaling. The stress-strain curves suggested some variation in laminate behavior owing to the dimensional scaling; nevertheless, a further analysis with the classical lamination theory demonstrated that the observed effect was due to small variations in the fiber volume fraction of the laminates. It was concluded that the mechanical properties of these thermoplastic laminates do not exhibit scaling effects. The failure mechanism of the laminates was studied at macroscopic level; a scale effect of the fracture mechanism was observed.     

有序介孔材料: 历史、 现状与发展趋势

有序介孔材料是指孔径在2~50 nm之间的多孔材料, 是一类具有均匀孔径、 高有序度纳米孔道和高比表面积的新材料. 在过去30年里, 有序介孔材料的研究取得了长足的进步, 在可控合成、 结构设计和调控及功能化等方面形成了系统的理论. 同时, 其应用领域也不断被拓展, 包括能源存储与转化、 催化、 生物医药和传感等方面. 本文首先回顾了有序介孔材料的发展历史, 简要介绍发展过程中“里程碑式”的研究工作; 然后根据构效关系总结了其在不同领域应用的最新进展; 最后讨论了有序介孔材料领域进一步发展所面临的挑战与机遇, 并对未来前景进行了展望.     

层间剪切带粒度分形几何特征及工程地质意义

本文对分形几何方法表征土的粒度组成加以了补充, 并用它来描述和表征层间剪切带的粒度组成, 据此将其划分为五个类型。在此基础上较为深入地阐述了其工程地质意义, 并着重讨论了用它来识别层间剪切带所遭受的构造变形破坏程度、演化阶段问题等。     

General admissibility for linear estimators in a general multivariate linear model under balanced loss function

A generalization of Zellner’s balanced loss function is proposed. General admissibility in a general multivariate linear model is investigated under the generalized balanced loss function. And the sufficient and necessary conditions for linear estimators to be generally admissible in classes of homogeneous and nonhomogeneous linear estimators are given, respectively.     

An optimal co-reinsurance strategy

This article considers a co-reinsurance strategy that (1) protects insurance companies against catastrophic risks; (2) enables insurers to gather sufficient information about the different risk attitudes of reinsurers and diversify their reinsured risks; (3) enables insurers to create better risk-sharing profiles by balancing the risk tolerances of reinsurers; (4) has the benefit of allowing reinsurers to accumulate experience with risks with which they are unfamiliar; (5) reduces the overall direct cost of a reinsurance contract; (6) allows a government to back some insurance products, such as the terrorism insurance programs that were established in many countries after the September 11th terrorist attacks; and (7) reflects the practical reinsurance industry of some countries, such as Iran. Such a co-reinsurance strategy can be fully determined by estimating its parameters whenever three optimal criteria are satisfied and prior information about the unknown parameters is available. Two simulation-based studies have been conducted to demonstrate (1) the practical applications of our findings and (2) the possible impact of any type of dependency between the co-reinsurance’s parameters and the evaluated optimal co-reinsurance strategy.     

我国工程地质学发展战略的思考

本文就我国工程地质学在”十一五”期间的发展战略进行了讨论,包括工程地质学面临的机遇和挑战;围绕的科学问题;在我国地球系统科学发展中的作用以及今后的发展趋势等。     

Biobased PLA/NR-PMMA TPV with balanced stiffness-toughness: In-situ interfacial compatibilization,performance and toughening model

Using rubber to toughen polylactide (PLA) is always accompanied by the sharp reduction in stiffness. Herein, PLA/poly (methyl methacrylate) grafted natural rubber (NR-PMMA) thermoplastic vulcanizates (TPVs) with balanced stiffness-toughness were fabricated. With the addition of 40 wt % NR-PMMA, the impact strength and tensile toughness of PLA/NR-PMMA TPV significantly improved to about 102.7 kJ/m² and 66.1 MJ/m³, respectively, compared with those of 2.7 kJ/m² and 2.4 MJ/m³ for the pure PLA. Meanwhile, the yielding stress was maintained at 34.5 MPa. Fourier transform infrared spectroscopy (FTIR) confirmed the formation of in-situ interfacial compatibilization between PLA and rubber phases. Both tensile and impact toughening mechanism were studied and deduced as considerable energy dissipation provided by the continuous rubber phase. Instrumented notched impact tests demonstrated that the energy dissipating in crack propagation process contributed to the main part of impact toughness. In addition, a novel toughening model based on bicontinuous structure was incorporated, which showed good applicability in predicting the impact strength of PLA/NR-PMMA TPVs.     

汶川地震地质灾害后效应分析

汶川地震过去3a了。3a来,大量的国内外学者对地震灾区地震地质灾害的发育分布规律、形成机理及防治对策给予了高度关注,发表了大量的研究成果。人们在关注同震地质灾害的同时,更对地震灾区今后地质灾害的发生规律及演化趋势、持续时间倾注了极大的关心,因为震后连续3a,尤其是2010年,灾区地质灾害的频率和规模均出现较震前显著增大的现象。本文收集整理了震前和震后灾区地质灾害的数据资料,尤其研究了震后3a灾区重大地质灾害的特点和发生规律,在此基础上,分析了震后灾区地质灾害可能的持续时间、演化趋势以及高风险区的范围。分析和研究结果认为,震后汶川地震灾区的地质灾害将持续20~25a; 在这段时间内,地质灾害将以4~5a一个高峰为周期,呈震荡式的衰减下降,并最终恢复到震前的水平。震后地质灾害的高风险区将出现在耿达-映秀、小鱼洞、红白-茶坪、擂鼓-陈家坝和青川东河口-窝前这5个地段上。