剪切对泡沫夹层结构梁弯曲性能的影响

本文以受剪后横截面仍为一平面但与轴线不再垂直为基本假设,采用能量法建立了一种对泡沫夹层结构梁的弯曲性能进行分析的方法。通过对比试验数据以及有限元的计算结果,得到用该方法可较为准确地预测泡沫夹层结构梁的挠度。通过分析,得到了剪切对泡沫夹层结构梁挠度的影响程度随着梁的跨高比的增大而减小,同时讨论了梁横截面正应变及正应力的分布情况。     

FRP梁结构的工程设计

本文提出了梁受到弯曲、剪切载荷时其挠度、应力应变以及局部和整体屈曲载荷、失效载荷的简单的设计公式.并用试验对其精确度和正确性进行了验证.     

夹层复合材料的弯曲理论分析与计算方法研究

对夹层梁弯曲理论进行了深入研究,并用解析的方法计算了夹层梁的弯曲应力和挠度。在高阶夹层梁理论假设的基础上,假设夹芯只存在剪切变形,根据经典的梁弯曲理论,通过对夹层梁微元的受力分析,确定各层、层间的内力分布和各层间的变形协调关系,从而求出夹层梁各层的正应力、层间剪应力和弯曲挠度的解析表达式。最后,用三维有限元计算结果验证了解析算法结果的准确性。研究结果表明,此方法计算公式简单且精度较高。     

拉伸和弯曲耦合层合梁应力分析

本文建立了拉伸和弯曲耦合层合梁的位移微分方程,导出了拉弯耦合层合梁正应力和层间剪应力的计算公式。分析了规则非对称正交层合梁的应力具有非对称特性。当规则非对称正交层合梁的铺层组数大于8时,其应力趋于对称分布。     

混杂纤维增强复合材料梁挠度计算理论研究

本文针对目前土木工程中最新出现的混杂纤维树脂基复合材料梁,以3组不同碳纤维含量的混杂纤维拉挤型材薄壁梁构件作为研究对象,通过模型试验、有限元数值分析和理论分析进行对比。研究表明,与相同截面玻璃钢相比,上下翼缘采用碳纤维增强的混杂纤维拉挤型材抗弯刚度有明显提高,但是抗剪切变形能力提高有限。在进行混杂纤维树脂基复合材料梁的挠度计算时须采用考虑横向剪切变形对挠度影响的铁木辛柯梁理论。     

隔板方向对泡沫芯复材夹芯梁抗剪性能影响的试验研究

采用真空导入工艺制作了3组不同方向(横向、纵向及双向)的隔板增强泡沫芯复材夹芯梁,对其进行了剪跨比为3的三点弯试验研究,获得了其失效过程及破坏模式,分析了隔板布置方向对该复材夹芯梁受剪力学行为的影响。结果表明:1隔板横向、纵向及双向布置时,夹芯梁的破坏模式分别为上面层弯曲折断、侧面层局部屈曲及上面层剪切破坏;2横向隔板可有效阻止泡沫芯材的斜裂缝扩展,从而提高构件在横向荷载作用下的延性,但不能显著提高夹芯梁的刚度和强度;3隔板纵向布置时,构件的承载力和刚度相比于未增强的普通泡沫芯复材夹芯梁分别提高了1.02倍及5.65倍,但延性仅提高了0.23倍;4双向隔板增强泡沫夹芯梁的力学性能与纵向隔板增强泡沫夹芯梁较为相似,其承载力和刚度均明显高于横向隔板。     

无腹筋BFRP筋玄武岩纤维混凝土深梁抗剪性能试验研究

为研究玄武岩纤维对无腹筋BFRP筋混凝土深梁裂缝开展、破坏形态、跨中挠度、剪切开裂承载力及抗剪极限承载力的影响,以玄武岩纤维体积掺率和纤维长度为参数,设计并制作了5根试验梁,通过四分点集中力加载研究深梁的抗剪性能。结果表明:随着纤维特征参数的增大,构件破坏形态出现由斜压破坏向剪压破坏转变的趋势;与普通混凝土深梁相比,相同荷载作用下,玄武岩纤维混凝土深梁跨中挠度和裂缝宽度均随着纤维特征参数的增大而减小;构件剪切开裂承载力和抗剪极限承载力随着纤维特征参数的增大均有所提高。在考虑玄武岩纤维增强作用的基础上,参照GB 50010—2015规范对玄武岩纤维混凝土深梁抗剪极限承载力进行计算,实测值与计算值基本吻合。     

基于模态应变能法功能梯度Euler-Bernoulli梁和Timoshenko梁模型对损伤识别的影响分析

随着功能梯度梁的跨高比从小(厚梁)变到大(薄梁),梁的变形受到剪切变形的影响就会从大变到小。为了准确分析功能梯度梁的变形,跨高比小的厚梁采用Timoshenko梁模型,而跨高比大的薄梁采用Euler-Bernoulli梁模型。采用这两种梁模型进行功能梯度梁自由振动的有限元计算,分析单元刚度矩阵、质量矩阵和模态阵型等存在的差异。通过数值算例,研究了这两种梁模型的差异对模态应变能法的损伤识别指标的影响。对于厚梁,Timoshenko梁模型的损伤指标优于Euler-Bernoulli梁模型;对于很薄的梁(例如,l/h=25时的薄梁),Euler-Bernoulli梁模型的损伤指标优于Timoshenko梁模型。     

单面和双面复合材料粘接修理胶层中的应力分析

胶层在复合材料粘接修理结构中起着载荷传递作用,采用有限元分析方法,研究了单面和双面粘接修理胶层中的应力分布特点,比较了2种不同修理形式胶层的VonMises应力、剥离应力和剪切应力的分布。结果表明,相同载荷下,单面修理的胶层VonMises、端部的剥离应力都较大,受剪切也比较严重。还研究了补片尺寸对胶层应力的影响。     

考虑剪滞和高阶剪切效应的复合材料薄壁箱梁弯曲分析

本文以复合材料层合板理论为基础,用最小势能原理建立了一种能对工程中常见的复合材料薄壁箱梁的剪滞与高阶剪切效应进行分析的方法,结合算例,得到了剪滞与高阶剪切效应对截面应变和梁挠度影响的变化规律,通过与Timoshenko梁理论及剪滞与一阶剪切效应方法结果的比较,表明其变化规律和相应的结果基本正确可靠.     

Experimental characterization of interlaminar shear failure in sandwich structures under three-point bending

We applied an improved six-step phase-shifting method in digital photoelasticity to an adhesively bonded aluminum/epoxy/aluminum sandwich structure in order to study interlaminar shear failure behavior. Before and after three-point bending, a self-balanced thermal residual shear stress appeared on the interface because of the difference in thermal expansion coefficients between aluminum faces and epoxy core interlayer. At the beginning of loading, the shear stress in the core layer distributes continuously and forms shear bands tilting at a 45° direction. It then joins with the upper and bottom aluminum faces in order to realize the shear load transfer. As the bending load increases, the maximum interface shear stress occurs near the supports and a partially debonded region appears at the interface. The interfacial shear stress in the partially debonded region decreases rapidly until a shear failure occurs. A load–flexibility curve of the vibration-damping–type sandwich structure agrees well with the theoretical prediction of a laminated beam.     

Mechanical properties of glass fabric/polyester composites: Effect of silicone coatings on the fabrics

An experimental investigation was carried out to study the effect of a silicone coating on the mechanical properties of polyester/woven glass fabric composites, fabricated by resin transfer molding. E‐glass woven fabrics were coated with a silicone elastomer by solution dip coating. The effect of variation of silicone amounts on the impact resistance, toughness, and mechanical properties of the composite was determined. Short beam shear tests were performed to assess the effect of coating on the adhesion of the fiber to the matrix. The coated specimens exhibited worse interlaminar shear strength over that of uncoated fabrics. Three‐point bending tests were also performed to investigate the effect of the coating on flexural properties. Whereas flexural strength and Young's modulus decreased with increasing amount of coating, the toughness, represented by the area under the stress–strain curve, presented a maximum. Finally, notched Izod impact tests were carried out and the curve for the energy absorbed during impact versus the amount of coating also appeared to have a maximum, indicating an interesting slot for optimum impact performance. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1300–1308, 2004     

芳纶纤维加固钢筋混凝土梁界面粘结应力分析

本文根据弹性梁理论和部分组合截面假定,并且考虑了钢筋混凝土梁和芳纶纤维剪切变形的影响,对两点集中加裁情况下的芳纶纤维加固钢筋混凝土梁的界面粘结剪应力和正应力进行了推导分析,由纤维端部边界条件得出了两种应力的解析解,根据试验梁的基本参数绘出了界面应力的分布曲线,找到了界面应力的分布规律,由此提出了降低纤维布端部应力集中的方法,可供施工参考使用.     

Crack-arrest study in mode II Delamination in composites

Procedures for measuring the crack initiation and arrest toughnesses in Mode II interlaminar fracture in composite materials were analyzed. Different techniques using flexural specimens were studied. The strain energy release rate, G, which is the energy available for crack propagation was calculated using simple beam theory. The calculation takes into account the transverse shear effect. Stable and unstable fractures are analyzed, and conditions required to measure the arrest toughness of interlaminar fracture are discussed. The methodology was applied to the measurement of fracture energy at the onset and arrest of delamination in glass/epoxy laminate.     

层合梁拉伸和弯曲耦合效应分析

建立了规则非对称正交层合梁在拉伸和弯曲耦合时的位移微分方程 ,其耦合效应依赖于铺层的组数和材料主向弹性模量的比值。当铺层组数大于 8时 ,规则非对称正交层合梁可视为正交对称层合梁     

Compression behavior of woven glass/epoxy specimens using a new end‐loaded hybrid specimen

A new compression specimen was applied to woven glass/epoxy laminates. The specimen consists of epoxy layers cast on the sides of the laminate to prevent buckling. Thin‐sheet aluminum ends enable alignment and avoid crushing under end loading, which does not require any special fixture. The compression stress–strain behavior of the laminate was obtained from the specimens by discounting the previously measured stress–strain curve of the epoxy backings. Despite the higher scatter in compression tests, the average modulus was practically identical to the tensile modulus. Moreover, failure occurred away from the ends in nearly all of the specimens tested. The average compressive strength was 84% of the tensile strength and consistent with the flexural strength measured in four‐point bending tests. The present compression specimen could, therefore, become an interesting alternative to the more elaborate standard test methods available. Nevertheless, this new compression testing approach needs further evaluation involving application to other materials. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Physical and mechanical properties of pultruded composites containing fillers and low profile additives

This article deals with the effect of fillers and additives content on the physical and mechanical properties of unidirectional pultruded glass/polyester composites. The physical characterization consisted of determining the void volume fraction (Vv), density, shrinkage ratio, coefficient of thermal expansion (CTE), and dynamic mechanical properties. The mechanical tests consisted of three‐point‐bending tests under static, impact, and fatigue loading. The low profile additive (LPA) has been found to compensate the cure shrinkage by microvoid formation. Dynamic mechanical analysis measurements show that the LPA slightly lowers the glass transition temperature Tg and increases the internal damping Tan δ. The transverse coefficient of thermal expansion was found to be sensitive to the LPA content. Three‐point bending tests show that the interlaminar shear strength (ILSS) is slightly sensitive to the fillers and LPA content, but the flexural strength is not affected. Impact test results on short beam shear and flexural specimens show the same behavior as in the static tests except that the LPA content has a detrimental effect on the flexural impact properties. The fatigue tests performed show that the effect of fillers is not significant, while the LPA effect is mixed. It seems that there is an LPA content for which the fatigue resistance is maximized. Finally, the wide range of behaviors and span‐to‐depth ratios investigated suggest that the ILSS as measured according to the ASTM 2344 recommendations can be largely misleading because of the unavoidable compressive yielding under the loading nose. For the materials investigated, higher span‐to‐depth ratio are more representative of the ILSS. POLYM. COMPOS., 27:71–81, 2006. © 2005 Society of Plastics Engineers     

Rheological modeling and finite element simulation of epoxy adhesive creep in FRP-strengthened RC beams

We have shown that a significant creep occurs at the concrete–fiber reinforced polymer (FRP) interface based on double shear long-term test. The primary test parameters were the shear stress to ultimate shear strength ratio, the epoxy curing time before loading as well as the epoxy thickness. The test results showed that when the epoxy curing time before loading was earlier than seven days the shear stress level significantly affected the long-term behavior of epoxy at the interfaces, and in particular the combined effect of high shear stress and thick epoxy adhesive can result in interfacial failure if subjected to high-sustained stresses. In this paper, based on the previous experimental observations, an improved rheological model was developed to simulate the long-term behavior of epoxy adhesive at the concrete–FRP interfaces. Furthermore, the newly developed rheological creep model was incorporated in finite element (FE) modeling of a reinforced concrete (RC) beam strengthened with FRP sheets. The use of rheological model in FE setting provides the opportunity to conduct a parametric investigation on the behavior of RC beams strengthened with FRP. It is demonstrated that creep of epoxy at the concrete–FRP interfaces increases the beam deflection. It is also shown that consideration of creep of epoxy is essential if part or the entire load supported by FRP is to be sustained.     

纤维混凝土梁研究综述

对纤维增强混凝土梁的国内外研究进展进行了归纳总结,从试验分析方面阐述了纤维对梁力学性能的影响;在理论研究方面对纤维混凝土梁的抗弯和抗剪理论及抗剪承载力计算公式进行了总结并对公式的实用性做了进一步的阐述;在数值模拟方面介绍了纤维混凝土梁数值计算使用的的软件及成果.最后,基于现有的研究成果,提出了目前存在的不足,探讨了未来纤维混凝土梁的发展方向.