Necessary and Sufficient Fracture Criteria for a Composite with a Brittle Matrix. Part 2. High-Strength Reinforcement

Experimental results on fracture of composite specimens with a brittle matrix are given. A modification is proposed for the shear model that describes deformation of a composite with failed matrix. A three-parameter sufficient criterion of quasibrittle strength of the composite is constructed, based on the equations of an orthotropic medium. Simple analytical expressions that relate the macrocrack length to the loading, structural, stiffness, and strength parameters of the composite medium are obtained. An approach for constructing multi-parameter criteria that take into account special features of deformation of the materials of the composite components is discussed.     

In‐situ thermal reduction and effective reinforcement of graphene nanosheet/poly (ethylene glycol)/poly (lactic acid) nanocomposites

This study aims to achieve a molecule‐level dispersion of graphene nanosheets (GNSs) and a maximum interfacial interaction between GNSs and a polymer matrix. GNS‐reinforced poly (ethylene glycol) (PEG)/poly (lactic acid) (PLA) nanocomposites are obtained by a facile and environment‐friendly preparation method. Graphite oxide and GNSs are characterized by atomic force microscopy, Raman spectroscopy, and X‐ray diffraction. Scanning electron microscopy shows that the state of dispersion of the GNS in the PEG/PLA matrix is distribution. The tensile strength and Young's modulus increases by 45% and 188%, respectively, with the addition of 4.0 wt% GNSs. The thermal stability of the GNS‐based nanocomposites also improves. Differential scanning calorimetry indicates that GNSs have no remarkable effect on the crystallinity of the nanocomposites. The effective reinforcement of the nanocomposites is mainly attributed to the highly strong molecular‐level dispersion of the GNSs in the polymer matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Stability and initial postbuckling behavior of anisotropic cylindrical shells under external pressure

A solution is obtained to describe the stability and initial postbuckling behavior of cylindrical shells made of composites with one plane of symmetry. The solution is based on the Donnell-Mushtari-Vlasov nonlinear theory of anisotropic shells and Koiter’s theory of buckling and postbuckling behavior. Calculated results are presented for boron plastic shells with reinforcement of different types under external pressure. It is shown that the conventional model of a composite as an orthotropic material is erroneous for many types of reinforcement __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 3, pp. 86–103, March 2007.     

碳化硼颗粒增强二硅化钼复合材料的摩擦学性能

采用快速热压烧结法制备了 B4 C颗粒增强 Mo Si2 基复合材料 ,研究了填料含量对材料的微观结构、力学性能以及摩擦学性能的影响 .结果表明 ,随 B4 C含量的增加 ,复合材料的硬度增大 ,摩擦系数及磨损率降低 .其原因在于 B4 C抑制 Mo Si2 的氧化、减少颗粒间玻璃相的生成 ,从而提高了颗粒间的界面结合强度 .此外 ,摩擦过程中生成的摩擦化学产物也有助于提高材料的摩擦学性能     

内压作用下球壳开孔接管的塑性极限分析

本文运用双矩弱作用屈服条件，分析了密集补强型球壳开孔接管的五类九种破坏机构的完全解，并给出了各类机构所适用的参数范围；从而为建立一种开孔补强设计方法提供了理论基础。本文算例和实验结果符合得很好。     

某既有建筑物改造工程地基加固质量的综合检测

随着既有建筑物的增层改造工程的发展和技术的日益成熟 ,为了提高原有建筑物地基土强度和变形能力 ,对其基础加固处理也愈加频繁。如何准确有效地评价其地基加固质量及其空间变化的均匀性是关系此类工程安全可靠的重要保证。本文以某一工程为例 ,讨论既有建筑物增层改造工程的地基加固质量的检测和综合评价方法。该建筑物建于 5 0年代 ,原设计为 5层 ,现增层为 6层 ,采用高压注浆方法进行地基加固处理.     

Plasticity induced fatigue crack growth retardation model for steel elements reinforced by composite patch

Fatigue tests on notched steel plates reinforced by composite patch showed that the application of carbon fiber reinforced polymers (CFRP) strips with pretension of the overlays prior to bonding. This resulted in a significant amount of additional fatigue life. In particular, the pre-tension produces a compressive field in the steel plate which reduces the stress ratio that enhances crack growth retardation. The fatigue crack propagation rate is postulated to be a function of the effective strain energy density factor range. Fatigue crack growth data showed that standard crack growth retardation model cannot be used to evaluate the minimum effective stress. Hence, an ad hoc plasticity model is introduced and validated using experimental results. The proposed technique is an extension of the well know Newman’s model. The bridging effect due to the reinforcing strips is analytically modeled in order to estimate the reduction of crack opening displacement and finally the magnification of the crack growth retardation. Numerical and experimental results match well and show a significant influence of the pre-tension level on the expected fatigue crack growth rate of a reinforced steel plate.     

Recent progress in electrospun nanofibers: Reinforcement effect and mechanical performance

Composite materials are becoming increasingly important as structural materials for aeronautical and space engineering, naval, automotive, and civil engineering, sporting goods, and other consumer products. Fiber‐based reinforcement represents one of the most effective manufacturing strategies for enhancing the mechanical strength and other properties of composite materials. Electrospinning has gained widespread interest in the last two decades because of its ability to fabricate continuous ultrafine nanofibers with unique characteristics. The impact of electrospinning on fiber synthesis and processing, characterization, and applications in drug delivery, nanofiltration, tissue scaffolding, and electronics has been extensively studied in the past. In this article, the authors have focused on a comprehensive review of the mechanical performance and properties of electrospun nanofibers as potential reinforcements as well as their advanced nanocomposites. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1171–1212     

Synergistic effect of cellulose nanowhiskers reinforcement and dicarboxylic acids crosslinking towards polyvinyl alcohol properties

In the presented work, a significant increase in the tensile strength of the PVA composite material is reported. The obtained best value of 122 MPa and 14.6% swelling shows the excellent synergistic effect of both crosslinker and reinforcement material. The composite films were prepared by simple mechanical dispersion of reinforcement material, bacterial cellulose nanowhiskers (BCNW) into PVA solution followed by crosslinking with diacids, succinic acid (SuA), and adipic acid (AdA). The effect of aliphatic carbon chain length of crosslinker on thermal, mechanical, and water uptake properties is evaluated and discussed in detail. Neat PVA had the strength of 37.3 MPa. With 5% reinforcement of BCNW, that is, without crosslinking, it exhibited 97% increase, that is, 74.5 MPa. With crosslinking of 15 mmol of SuA and AdA PVA films for 2 h had excellent thermal properties with swelling percentage of 19 and 26.6% and tensile strength of 103 and 67 MPa, respectively. The best result obtained was for 5% BCNW–PVA films crosslinked with 15 mmol SuA. These results were explained on the basis of synergetic crosslinking and extended hydrogen bonding between PVA and reinforcement material. The composite films can be used as biological implants, a membrane for pervaporation and filtration system, etc. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2515–2525