Evaluation of styrene-butadiene latex as a vibration damping admixture for concrete: a micromechanical analysis

Abstract

The styrene-butadiene latex as an admixture for Portland cement concrete is evaluated in this study using a numerical simulation approach aided by a series of laboratory experiments conducted for material parameter determination and numerical model validation. Using the discrete element method (DEM), a three-dimensional (3D) beam of concrete was built with due consideration of the concrete microstructural features. The beam was employed to simulate the cyclic three-point flexural test at three loading frequencies: 0.2, 1 and 5 Hz and a representative in-service temperature: 25 °C. The effects of admixture usage and loading frequency on the overall damping properties of concrete were evaluated to explore the vibration-reduction mechanisms of the latex-admixtured concrete. Results show that a 20 percent usage of styrene-butadiene latex (by weight of cement) was found to significantly enhance the storage and loss moduli and the loss tangent of concrete. The developed 3D DEM model realistically accounts for the micro-structural features of concrete matrix and can potentially be used for evaluating and designing high performance concretes against detrimental dynamic loads.     

Enhancing damping features of advanced polymer composites by micromechanical hybridization

A hybrid configuration at the micromechanical level is presented and described as a suitable approach to enhance the damping features of advanced polymer composites. A micro-level hybridization was achieved on dry preform reinforcements by embedding visco-elastic fibres within standard carbon tows. Unidirectional composites with two viscoelastic volume fractions (2.5% and 5% vol/vol) were manufactured by a vacuum infusion process and later tested by dynamic mechanical analysis along the principal directions. Final results reveal a significant enhancement (+80% and +56%) of the damping properties, respectively, for the longitudinal and the transverse directions in the case of the highest viscoelastic fibre content.In turn, the elastic properties of the final composite were greatly reduced (−37% and −35%) with respect to the standard composite. Final results support further work in the direction of micromechanical hybridization looking at the potential exploitation of standard textile configurations with different viscoelastic fibre content to enhance damping properties.     

减振型扣件理论研制和室内试验研究

扣件系统是影响轨道结构振动特性的关键因素,其刚度过大钢轨与轨枕或轨道板耦合作用减弱,钢轨的振动衰减率变小,过大耦合作用增强,会导致轨枕或轨道板振动增强。基于此,应用轮轨系统耦合动力学思想,得出一定轨道和车辆结构参数下的扣件的最佳匹配刚度。并基于铁路轨道设计规范设计制作了减振型扣件样品,通过疲劳测试和动力特性室内测试表明：疲劳前后静刚度损失为1.2kN/mm,扣压力损失为1.67kN,纵向阻力损失为1.6kN,表明扣件系统设计合理,组装疲劳性能合格;垂向激励和横向激励下,在0～5000HZ频段内,减振扣件对轨头、轨腰和轨脚的减振作用均很显著。     

Micro-stress analysis and identification of lightweight aggregate’s failure strength by micromechanical modeling

This work is based on a dual approach of experiments and micromechanical modeling in order to characterize the failure behaviors of lightweight aggregate concretes (LWAC). Many classes of LWAC were tested, based on five families of lightweight aggregates (LWA) and three types of mortar matrices: normal, high performance (HP) and very high performance (VHP). Micromechanical modeling is based on an iterative homogenization approach and associated localization: local stress distributions during the uniaxial compression tests can be predicted in LWAC’s components and at their interface. Experimental compressive strengths were measured on manufactured 16 × 32 cm cylindrical specimens. The confrontations between micromechanical modeling and experiments were used to identify LWA’s failure strengths which are difficult to measure, and to quantify the inaccuracies related to conventional methods. These corrected values of LWA’s failure strength were introduced into a failure criterion modeling: associated predictions of LWAC’s compressive strength are in good agreement with the experimental measurements.     

Characterization of the vibration damping loss factor of glass and graphite fiber composites

Material damping of laminated composites is experimentally determined by the half-power bandwidth method for cantilever beam specimens excited with an impulse excitation. Data acquisition and manipulation are carried out using both an IBM PC-AT and a GenRad 2500 Series FFT Analyzer. Unidirectional continuous fiber 0° and 90° laminates were fabricated from glass/epoxy (Hercules S2-Glass/3501-6), graphite/epoxy (Hercules AS4/3501-6) and graphite/poly (ether ether ketone) (ICI AS4/PEEK[APC-2]) to investigate the effect of fiber and matrix properties as a function of frequency, up to 1000 Hz, on the damping of composites. The S2-glass/3501-6 composite had a higher loss factor than the AS4/3501-6 in the 0° orientation with the loss factor for the AS4/3501-6 exhibiting a linear increase with increasing frequency and the loss factor for the S2-glass varying nonlinearly with frequency. The 90° material exhibited a higher damping loss factor than the 0°, varying nonlinearly with increasing frequency. In the 90° orientation, the glass fiber composite had loss factors that were approximately fourfold greater than the 0° orientation at frequencies greater than 200 Hz. The 0° AS4/PEEK had a loss factor that was approximately equal to that of the 0° AS4/3501-6. The 90° AS4/PEEK had a loss factor that was approximately 50% less than the AS4/3501-6 and 25% greater than the S2-glass/3501-6 composite.     

市内复杂环境下大药量爆破降振及振动监测分析的研究

在周边高楼林立,人员密集,车流量大的环境下进行地基与地下车库大爆破开挖,对周边建筑进行爆破振动实时监控,并对所监测的振动数据进行分析。发现：爆区周边各测点峰值较小（小于1cm/s）,不会对周边结构造成危害;同等水平高度下,东西方向（纵向）测点各相关量（爆破振动峰值、持时、主频和信号能量）均高于南北方向（横向）测点各相关量;纵向测点频谱能量分布比横向测点频谱能量分布更为集中,各测点竖直向振动信号能量主要集中在3.90625-62.5Hz范围内。爆破振动在高楼楼层之间传播时,随着楼层高度的增加,竖直向爆破振动峰值和信号响应能量增大,信号频谱能量分布更加集中,顶层振动峰值约为底层振动峰值的2倍,顶层信号响应能量约为底层信号响应能量的3倍     

Nonlinear damping and forced vibration analysis of laminated composite beams

The purpose of the present work it to study the damping and forced vibrations of three-layered, symmetric laminated composite beams. In the analytical formulation, both normal and shear deformations are considered in the core by using the higher-order zig-zag theories. The harmonic balance method is coupled with a one mode Galerkin procedure for a simply supported beam. The geometrically nonlinear coupling leads to a nonlinear frequency amplitude equation governed by several complex coefficients. In the first part of the paper, linear and nonlinear damping parameters of laminated composite beams are obtained. In the second part, nonlinear forced vibration analysis is carried out for small and large vibration amplitudes. The frequency response curves are presented and discussed for various geometric and material properties.     

The interfacial shear strength of Kevlar fiber/epoxy composite measured by the microdroplet test

Epoxy chloropropane (ECP) grafting modification method was used for the surface treatment of Kevlar fiber to improve the interfacial adhesion of the Kevlar fiber reinforced epoxy composite. The surface characteristics of untreated and treated Kevlar fiber were characterized by Fourier transform infrared (FT‐IR) spectroscope. The interfacial shear strength between epoxy and Kevlar fiber was analyzed by measuring from microdroplet specimens adhered onto a single carbon fiber. Microdroplet specimens exhibited different results of the interfacial strength due to the Kevlar fiber surface treatment. The results showed that a larger shear stress concentration arose along the interface for the surface treated model than for the untreated one.     

An RVE-based micromechanical analysis of fiber-reinforced composites considering fiber size dependency

An RVE-based micromechanical elastic damage model considering fiber size dependency is presented to predict the effective elastic moduli and interfacial damage evolution in fiber-reinforced composites. To assess the validity of the present model, the predictions based on the proposed micromechanical elastic model are compared with Hashin’s theoretical bounds [Hashin Z. Analysis of properties of fiber composites with anisotropic constituents. J Appl Mech: Trans ASME 1979;46:543–50]. The proposed micromechanical elastic damage model is then exercised under uniaxial loading conditions to show the overall elastic damage behavior of the proposed micromechanical framework and to illustrate fiber size effect on the behavior of the composites. Moreover, comparisons between the present prediction and experimental data are made to further illustrate the capability of the proposed micromechanical framework for predicting the elastic damage behavior of fiber-reinforced composites.     

Significance of memory-dependent derivative approach for the analysis of thermoelastic damping in micromechanical resonators

Mechanics of Time-Dependent Materials - Thermoelastic damping is becoming a leading factor for determining the quality of the micromechanical resonators in terms of their sensitivity. The present...     

Molecular dynamics study of the interfacial strength between carbon fiber and phenolic resin

The interfacial strength between carbon fiber and phenolic resin is studied using molecular dynamics simulations to demonstrate that carbon fiber-reinforced carbon matrix composites (C/C composites) have improved tensile strength. Simulations are performed using two carbon fiber models, one of which has only carbon atoms and the other has carbon atoms and some fluorinated carbon groups. The carbon fiber models are regarded as two-layer graphite, and the phenolic resin model is treated as cross-linked structures. All force field parameters are based on the Dreiding force field. The tensile stress and interfacial fracture energy are calculated for the estimation of the interfacial strength. The results show that the model including the fluorinated carbon groups has lower interfacial strength than the model having only carbon atoms, up to a certain coating ratio of fluorinated carbon groups. Similarly, within the limits of the coating ratio, the interfacial fracture energy of the fluorinated carbon fiber model is lower than that of carbon fiber model having only carbon atoms.     

纤维角度对变角度层合板减振性能的影响

自动铺丝技术可以实现复杂曲率曲线铺放,可极大提高角度设计的自由度。本文以改善复合材料层合板动态特性为目的,对变角度层合板的减振性能进行了研究分析。首先对不同角度变化变角度层合板进行自由衰减试验,研究了纤维角度变化与变角度层合板阻尼比的关系。然后对含相应角度变角度夹层板进行随机试验,研究了层合板随机激励条件下的振动响应,并采用共振峰处传递函数(Transition function,TF)和拾振点加速度总均方根(Root mean square,RMS)两种指标评价减振效果。结果表明:层合板阻尼比在纤维变化角度为±<45|60>时最大,纤维变化角度为±<73|88>时最小。基于RMS减振评价指标,±<45|60>夹层板较传统直线板减振性能提高27.13%;基于共振峰TF减振评价指标,纤维角度变化对不同共振峰减振效果规律差异明显。研究表明,变角度层合板减振性能明显优于传统直线层合板,相关实验结果将对变角度层合板减振设计及优化提供一定的参考意义。      

Evaluation of interfacial strength between fiber and matrix based on cohesive zone modeling

This paper presents a measurement technique of interfacial strength considering non-rigid bonding on a fiber/matrix interface modeled as a cohesive surface. By focusing on the stress concentration near a fiber crack obtained from a single-fiber fragmentation test, the stress contours in matrix observed by photoelasticity can be related to the interfacial strength by defining a characteristic length. An equation expressing the relationship between the characteristic length on the stress contour and the interfacial strength was derived, and validated using finite element analysis. The primary advantage of proposed measurement technique is that only a single fiber crack, which usually occurs within elastic deformation of matrix, is required for the evaluation of interfacial strength, whereas saturated fiber fragmentation is necessary in the conventional method. Herein, a sample application was demonstrated using a single carbon fiber and epoxy specimen, and an average interfacial strength of 23.8 MPa was successfully obtained.     

Synergy of fiber length and content on free vibration and damping behavior of natural fiber reinforced polyester composite beams

This work addresses the results of experimental investigation carried out on free vibration characteristics of short sisal fiber (SFPC) and short banana fiber (BFPC) polyester composites. Influence of fiber length and weight percentage on mechanical properties and free vibration characteristics are analyzed. Composite beam specimen is fabricated with random fiber orientations at17 MPa compression using compression molding machine. Natural frequencies and associated modal damping values of the composite laminates were obtained by carrying out the experimental modal analysis. It is found that an increase in fiber content increases the mechanical and damping properties. For SFPC, 3 mm fiber length and 50 wt% fiber content yielded better properties, whereas for BFPC, 4 mm fiber length and 50 wt% fiber content was the best combination. Scanning electron microscopy was performed to study the interfacial mechanism.     

Controlling of the interfacial shear strength between thermoplastic resin and carbon fiber by adsorbing polymer particles on carbon fiber using electrophoresis

In order to control the interfacial adhesion between carbon fibers and thermoplastic resins, poly(methyl methacrylate) (PMMA) particles have been adsorbed on the carbon fiber surfaces using an electrophoresis process. The amount of PMMA particles adsorbed on the modified carbon fibers was varied using the electrophoresis technique performed in polymer colloids for a short time. Additionally, the interfacial shear strength between the modified carbon fiber and the resin was controlled by a modification of the present process. An improved interaction and a strengthened surface adhesion between the carbon fiber coated with particles and the PMMA resin were observed.     

Continuous micro-indenter push-through technique for measuring interfacial shear strength of fiber composites

This paper describes a continuous push-through, micro-indentation technique for measuring the fiber-matrix interfacial shear strength. E-glass fibers embedded perpendicular to the plane of thin polished specimens of epoxy matrix, with and without coupling agents, were indented with a micro-indenter until failure of the interface occurred and the fibers were pushed through the epoxy. The results show over 60% higher interfacial shear strength for fibers with coupling agent than for fibers without coupling agent. Average shear strength values obtained via the indentation technique are in good agreement with those obtained from the single-fiber-composite test. Absence of acoustic emission signals for debonding of the fibers coupled with no sudden drops in load vs indentation depth suggest that in this geometry the debonding is a slow, continuous process for both fiber surface treatments.     

Analysis of interfacial failure in a composite microbundle pull-out experiment

Modeling of the failure of polymer-matrix composites requires substantial information about the mechanisms of failure at the interface, and load redistribution around fiber breaks in the composite. Current interface experiments involving the use of ‘microcomposites’ of single embedded fibers in a matrix generally do not include all the key geometric features of the real composite; in particular, they do not include the effects of fiber volume fraction and the higher matrix shear resulting from closely neighboring fibers. A new experiment was recently devised to assess some of these effects: it is referred to as the single-fiber pull-out from microbundle (SFPOM) experiment. It consists of a hexagonal arrat of seven fibers in a matrix where the outer six fibers are restrained and the center fiber is pulled out. Recent experimental data from tests with this geometry are analyzed here using three mechanical models of the failure process, and parametric studies of the data are performed to assess the appropriateness of each model. Two of the models, based on fracture energy considerations as applied earlier to single embedded fibers in a matrix and adapted to our geometry, were found to model data from the SFPOM experiments poorly. The third model assumes the existence of three zones near a fiber break, including elastic, plastic and frictional debond zones, and was found to provide reasonable fit to the data under realistic assumptions.     

Single fibre pull-out test versus short beam shear test: comparing different methods to assess the interfacial shear strength

Mechanical characteristics of fibre-reinforced composites are decisively influenced by the fibre/matrix interactions. This work is focused on the comparison of the single fibre pull-out test and the short beam shear test to assess the main advantages of both methods in terms of resource requirements and reliability. Lyocell fibres are used raw and enzymatic modified in thermoplastic (PLA and PP, both methods) as well as thermoset (PTP and Biresin, only short beam shear test) matrices. The IFSS values of the pull-out test are all in the range from 10.93 ± 3.63 to 14.87 ± 5.22 N/mm². The results of the short beam shear test provide significant differences in apparent ILSS for the analysed fibre/matrix combinations. The results of the single fibre pull-out test show no significant differences in IFSS and have a higher variance, but enable a better estimation of the potential of the examined fibre–matrix combination.     

大气下空气滑膜阻尼对微机械惯性传感器的影响

 设计并制作了一种可在大气下工作的栅结构电容式微机械加速度传感器,并对其空气滑膜阻尼特性进行了研究．测试结果表明该种结构机械品质因子Q值在大气压下能达到504．这种具有高Q值的栅形电容检测结构可以应用到微机械陀螺的检测模式,它无需真空封装,可以在大气环境下工作,且灵敏度提高．对陀螺原型的测试结构表明,其在大气下检测模态的Q值可以达到715。