Viscoelastic and Processing Effects on the Fiber-Matrix Interphase Strength. Part I. The Effects of Loading Rate, Test Temperature, Fiber Sizing and Global Strain Level

The effects of loading rate, fiber sizing, test temperature and global strain level on the adhesion strength between carbon fibers and a thermosetting epoxy (Epon 815) are studied using the single fiber fragmentation test procedure. Analytical methodology describing the viscoelastic behavior observed is also presented. The possibility of rate-temperature-interphase thickness superposition for the interfacial strength function is illustrated based on the analytical models discussed. Experimental data are discussed using Weibull statistics and also presented in the form of percent relative frequency histograms for the fiber fragments in a collective fashion. The use of histograms allows for interpretation of the skewness in the data population.     

Viscoelastic and Processing Effects on the Fiber-Matrix Interphase Strength. Part II. The Effects of Cure Temperature Time and Curing Agent Content

The effects of curing agent content, cure temperature and time on the adhesion strength between carbon fibers (treated with epoxy sizing) and a thermosetting epoxy (Epon 815) are studied using the single fiber fragmentation test procedure. Theoretical equations describing a majority of the phenomena affecting the adhesion process are also reviewed. The possibility of superposition between percent curing agent content, cure temperature and time is illustrated based on the analytical models presented. Experimental data are presented in the form of percent relative frequency histograms for the fiber fragments in a collective fashion. Such presentation of the data allows for interpretation of the skewness in the data population. Optimum curing agent, cure temperature and time values resulting in highest interfacial strength are also determined.     

Viscoelastic and Processing Effects on the Fiber-Matrix Interphase Strength. Part II. The Effects of Cure Temperature Time and Curing Agent Content

The effects of curing agent content, cure temperature and time on the adhesion strength between carbon fibers (treated with epoxy sizing) and a thermosetting epoxy (Epon 815) are studied using the single fiber fragmentation test procedure. Theoretical equations describing a majority of the phenomena affecting the adhesion process are also reviewed. The possibility of superposition between percent curing agent content, cure temperature and time is illustrated based on the analytical models presented. Experimental data are presented in the form of percent relative frequency histograms for the fiber fragments in a collective fashion. Such presentation of the data allows for interpretation of the skewness in the data population. Optimum curing agent, cure temperature and time values resulting in highest interfacial strength are also determined.     

Compressive Fiber Fragmentation in Carbon/Polypropylene Composites: Effects of Residual Thermal Stresses and Transcrystallinity

The effects of fiber volume fraction and transcrystallinity in single fiber composites, on the phenomenon of compressive fiber fragmentation due to residual thermal stresses, are studied. A concentric cylinder model is used, jointly with experimental data, to predict the Weibull shape parameter of the compressive strength distribution of pitch-based high and medium modulus (HM and MM) carbon fibers, with isotactic polypropylene as the semi-crystalline embedding matrix. A severe effect of the fiber content on the thermal residual stress in the fiber and, thus, on the fiber break density, is predicted and experimentally confirmed. The effect of the presence of isothermally grown polypropylene transcrystalline interlayers (using pitch-based HM carbon fibers as a substrate) on the compressive stresses induced upon subsequent quenching is investigated, both experimentally and theoretically. Cooling rate results are also presented. The thermoelastic constants of the interlayer are predicted to have a severe effect on the residual stresses generated in the fiber, the interphase, and the matrix. There is therefore, a definite need for direct experimental measurements of these constants.     

纤维长度对玻璃纤维单丝强度测定的影响

研究了纤维长度对玻璃纤维单丝强度测定的影响。试验数据显示,纤维越长,纤维单丝的平均强度越低。这是由于纤维上存在很多大大小小的缺陷,而纤维单丝强度取决于纤维上的最大缺陷,单丝的有效长度越长,出现大的缺陷概率越高,因此测得的强度越低。通过Weibull分布理论也可验证这一结果。     

Effects of organo‐montmorillonite on the mechanical and morphological properties of epoxy/glass fiber composites

Epoxy composites filled with glass fiber and organo‐montmorillonite (OMMT) were prepared by the hand lay‐up method. The flexural properties of the epoxy/glass fiber/OMMT composites were characterized by a three‐point bending test. The flexural modulus and strength of epoxy/glass fiber were increased significantly in the presence of OMMT. The optimum loading of OMMT in the epoxy/glass fiber composites was attained at 3 wt%, where the improvement in flexural modulus and strength was approximately 66 and 95%, respectively. The fractured surface morphology of the epoxy/glass fiber/OMMT composites was investigated using field emission scanning electron microscopy. It was found that OMMT adheres on the epoxy/glass fiber interface, and this is also supported by evidence from energy dispersive X‐ray analysis. Copyright © 2007 Society of Chemical Industry     

Interfacial Characteristics of Sisal Fiber and Polymeric Matrices

Sisal-fiber-reinforced composites, as a class of eco-composites, have attracted much attention from materials scientists and engineers in recent years. In this article, the effects of fiber surface treatment on fiber tensile strength and fiber-matrix interface characteristics were determined by using tensile and single fiber pullout tests, respectively. The short beam shear test was also employed to evaluate the interlaminar shear strength of the composite laminates. Vinyl ester, epoxy, and high-density polyethylene (HDPE) were chosen as matrix materials. To enhance the interfacial strength, two kinds of fiber surface-treatment methods, namely, chemical bonding and oxidisation, were used. The results obtained showed that different fiber surface-treatment methods produced different effects on the tensile strength of the sisal fiber and fiber-matrix interfacial bonding characteristics. Hence, valuable information on the interface design of sisal fiber–polymer matrix composites can be obtained from this study.     

Residual Stresses in Microcomposites and Macrocomposites

Existing models for built-in residual stresses in composite materials are reviewed and discussed. In particular, the thermal longitudinal stress present in the fiber prior to a single-fiber fragmentation experiment is studied using various model composite data. It is found that this stress is typically compressive in nature and that, quantitatively, it depends on the fiber content, the degree of undercooling, and the thermoelastic constants of the fiber and the matrix. In the case of single-fiber composites (or microcomposites), the thermal longitudinal stress present in the fiber is high enough to either induce fiber sinewave buckling (such as in E-glass/epoxy), or extensive fiber fragmentation (such as in graphite HM/polypropylene) that may then be used to measure the dependence of compressive fiber strength upon length. This has to be accounted for in quantitative models that calculate interfacial adhesion parameters using single-fiber tests, such as the fragmentation test or the microbond test. Implications for high fiber content composites (or macrocomposites) are discussed.     

Interfacial Characteristics of Sisal Fiber and Polymeric Matrices

Sisal-fiber-reinforced composites, as a class of eco-composites, have attracted much attention from materials scientists and engineers in recent years. In this article, the effects of fiber surface treatment on fiber tensile strength and fiber-matrix interface characteristics were determined by using tensile and single fiber pullout tests, respectively. The short beam shear test was also employed to evaluate the interlaminar shear strength of the composite laminates. Vinyl ester, epoxy, and high-density polyethylene (HDPE) were chosen as matrix materials. To enhance the interfacial strength, two kinds of fiber surface-treatment methods, namely, chemical bonding and oxidisation, were used. The results obtained showed that different fiber surface-treatment methods produced different effects on the tensile strength of the sisal fiber and fiber-matrix interfacial bonding characteristics. Hence, valuable information on the interface design of sisal fiber-polymer matrix composites can be obtained from this study.     

Viscoelastic and Processing Effects on the Fiber-Matrix Interphase Strength. Part III. The Effects of Postcure

A novel method for tailoring the interphase of carbon fiber-polymer composites by resistive electric heating is presented. The single-fiber fragmentation test is used to investigate the adhesion and fracture properties of the interphase. Electric resistive heating is shown to increase adhesion and toughness at the interphase region. In analyzing the results, the strength and fracture energy of the interphase are related to the thermal postcure conditions created by resistive electric heating. For this purpose, a difference analysis method is used to obtain a numerical solution for the heat conduction problem in the single-fiber test specimen and the temperature distributions are determined. Improvements obtained by using resistive electric heating of the carbon fiber are compared with those obtained by postcuring of the whole sample via convective thermal postcuring. The results obtained using these two different postcure methods seem to be similar.     

Statistics on the fracture strength of bamboo fibers

Tensile strength is a key mechanical property of fibers used as sustainable reinforcements for advanced fiber‐reinforced composites. This study aims to conduct experimental investigation on the fracture strength of bamboo fibers of different dimensions subjected to longitudinal tensile loading. The statistical distributions of the fracture strength in bamboo fibers are correlated with the effects of fiber length and diameter variation. These are described according to Weibull statistics, which exhibit the random nature of fiber strength. The Weibull function parameters used for strength prediction are obtained from the test specimens. A comparison of predicted results and experimental data is presented to assess the accuracy of using weak‐link scaling. Furthermore, the findings of this study also indicate that fiber strength statistics dominate size dependence of tensile strength. POLYM. COMPOS., 221–228, 2016. © 2014 Society of Plastics Engineers     

Viscoelastic and Processing Effects on the Fiber-Matrix Interphase Strength. Part III. The Effects of Postcure

A novel method for tailoring the interphase of carbon fiber-polymer composites by resistive electric heating is presented. The single-fiber fragmentation test is used to investigate the adhesion and fracture properties of the interphase. Electric resistive heating is shown to increase adhesion and toughness at the interphase region. In analyzing the results, the strength and fracture energy of the interphase are related to the thermal postcure conditions created by resistive electric heating. For this purpose, a difference analysis method is used to obtain a numerical solution for the heat conduction problem in the single-fiber test specimen and the temperature distributions are determined. Improvements obtained by using resistive electric heating of the carbon fiber are compared with those obtained by postcuring of the whole sample via convective thermal postcuring. The results obtained using these two different postcure methods seem to be similar.     

Inspection of geometry influence and fiber orientation to characteristic value for short fiber reinforced ceramic matrix composite under bending load

For use of short fiber reinforced ceramics the knowledge of the influence of coupon geometry on the failure mode and the determined resistance in bending tests is necessary. In contrast to the continuous fiber reinforced ceramic matrix composites (CMC), for short fiber reinforced CMC there are only few studies and no standard on consideration of size effects. In the present work, the influence of coupon geometry and test conditions on the average value and distribution of flexural strength has been investigated. Two short fiber CMCs with different fiber length were examined under four point bending load. Moreover, the relationship between fiber orientation in the loaded area, failure location and measured flexural strength was investigated through high resolution X-ray computer tomography (μCT) and SEM. The presented outputs will be proposed to a future standard for bending test of short fiber reinforced CMC materials with different fiber length.     

Continuous monitoring of the fragmentation phenomenon in single fiber composite materials

A continuously monitored single-filament composite (CM-SFC) test was conducted to measure the stress at which successive fiber breaks occur in the single fiber fragmentation process. This exercise was performed with a limited number of samples of various types. The purpose was to explore the possibility of using this test as a simple alternative means of (i) measuring the size effect in single fibers, (ii) calculating the Weibull shape and scale parameters for fiber strength, (iii) calculating the fiber/matrix interfacial shear strength from the extrapolated value of fiber strength using the loading history of a single fragmentation test, rather than from the value of fiber strength extrapolated from extensive testing of single fibers at various gage lengths, as is usually done. These are aspects of the SFC test that have largely been ignored so far. The results presented here confirm the possibility of using the CM-SFC test for such purposes, with a certain degree of approximation, as discussed. Additional information supplied by this test as well as a possible effect of fiber pre-tensioning on fragmentation results (including the value of the interfacial shear strength) are also briefly discussed.     

玄武岩纤维掺量对页岩轻骨料混凝土强度性能影响的研究

<中作者单位六>=研究了不同玄武岩纤维体积掺量对页岩轻骨料混凝土各项强度的影响.试验结果表明,玄武岩纤维的掺入会在一定程度上提高轻骨料混凝土的抗压、抗折强度和弹性模量;纤维掺量0.2%时,抗压与抗折强度达到最大值,分别提高11.49%、20%;轻骨料混凝土的劈裂抗拉强度随着纤维掺量的增加而增加,在纤维掺量0.3%时,劈裂抗拉强度达到最大值,强度提高54.59%;玄武岩纤维掺入页岩轻骨料混凝土中不仅对各相强度有一定提高,且一定程度上改善了轻骨料混凝土的脆性缺陷,起到增强增韧作用.     

纤维与水泥砂浆界面黏结性能研究

本文采取“8字”型试件进行单根粗纤维拉拔试验,通过混合正交试验研究了纤维类型、纤维直径、纤维埋置长度及砂浆基体水胶比对纤维-砂浆界面黏结强度显著性优先次序,以及纤维与砂浆间最佳组合的影响。同时得到了纤维最大拔出荷载及荷载-滑移曲线,系统分析了纤维与水泥砂浆的界面黏结性能。试验结果表明,直径为0.6 mm、埋置长度为20 mm的聚丙烯粗纤维,水胶比为0.51的砂浆基体的界面黏结强度最大,其中平均黏结强度为7.71 MPa,等效黏结强度达到13.25 MPa。直径为0.6 mm、埋置长度为10 mm的聚乙烯醇(PVA)纤维,水胶比为0.41的砂浆基体的界面黏结强度次之。四种因素对界面黏结强度的影响优先次序为纤维种类、纤维直径、砂浆水胶比、纤维埋置长度,其中纤维种类对界面平均黏结强度的影响较为显著,纤维直径对界面等效黏结强度的影响较为显著。     

结合均匀化理论对钢纤维混凝土梁的疲劳性能分析

钢纤维混凝土(SFRC)在工程中应用日益广泛,为了探究其疲劳破坏现象内在机理,本文结合Mori-Tanaka均匀化理论预测了不同体积掺量下钢纤维混凝土的弹性模量,并以此为基础建立钢纤维混凝土梁四点弯曲有限元模型,采用Miner疲劳损伤准则,分别进行了静力抗弯试验和疲劳试验的数值模拟。模拟结果与相关试验结果拟合较好,验证了模型的可靠性。利用疲劳分析软件,预测了钢纤维混凝土梁的疲劳寿命和疲劳强度,分析了纤维掺量、尺寸效应和纤维长度对疲劳寿命的影响。结果表明:钢纤维可以大幅提高混凝土梁的疲劳寿命,应力水平越低、纤维掺量越大,增幅越大;尺寸效应对疲劳强度和疲劳寿命有一定影响,但随着构件尺寸增加对疲劳性能影响减小;纤维长度越长,梁的抗疲劳性能越好。     

Comparative Studies on the Mechanical,Degradation and Interfacial Properties between Jute and E-Glass Fiber-Reinforced PET Composites

Jute fiber mat (hessian cloth) reinforced PET-based composites (50% fiber by weight) and E-glass fiber matreinforced PET based composites (50% fiber by weight) were fabricated by compression molding and the mechanical properties tensile strength (TS), tensile modulus (TM), elongation at break (%), bending strength (BS), bending modulus (BM), impact strength (IS) and hardness (Shore-A) of the composites were evaluated and compared. The interfacial properties of the both composites were also compared. Water uptake test and soil degradation test were also investigated.     

Test methods for bond strength of glass fiber posts to dentin: A review

ABSTRACT

In this paper, a review of the test methods for bond strength of glass fiber posts to dentin is presented. The main variables that influence the bond strength tests are related to substrate, to specimen properties, specimen preparation, and test methodology. The impact of these variables on the test outcome is analyzed. The search was performed on studies published between 2007 and 2015. Most of the tests carried out, in the literature, were the push-out (75%), pull-out (13%), and microtensile (11.9%) tests, showing an inversion compared to the results found in studies published between 2005 and 2010, when push-out test was used in a proportion of 2% and microtensile test in a proportion of 67%. The push-out test emerged as a practical tool for evaluating the interfacial shear strength between fiber post and root canal walls.     

Polymer modified grass fiber,part 1: Characterization of grass fiber and assessment of properties of polymer modified fiber

Natural fibers are used for reinforcement of ecofriendly green composites. These grass fibers have wide range of applications for the preparation of various domestic goods and handicraft items. But the chemical composition of the grass fiber has not been reported; therefore composition analysis of grass fiber was carried out. Morphology of the dry grass was studied by using scanning electron microscopy. Since the grass fiber contains around 22% water‐soluble matters, we have studied its influence on the tensile strength and aging characteristics. The tensile strength of the grass fiber was measured before and after water leaching. This study has shown a definite scope for the suitability of grass fiber in composite applications. To improve the strength of grass fiber, modification with various polymers such as P‐F resin, polyurethane and acrylamide was carried out. Moisture absorption property of unleached, water‐leached and different polymer modified fiber was also evaluated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1095–1103, 2007