Relationship between structure and mechanical properties for aramid fibres

Young, Robert J.; Liu, Dong; Day, Richard; Knoff, Warren F.; Davis, Heather A.

doi:10.1007/bf00541602

Cited by 169 publications

(96 citation statements)

References 21 publications

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“…The Young's moduli of those materials are different by orders of magnitude (10-100 MPa for latex, 110-450 MPa for PE, and 70-110 GPa for Kevlar) [1,33] and make it possible to design CAMs exhibiting discrete levels of tensile strength over a wide range of strain and stress. The moduli of latex (2.7 MPa), PE (55 MPa) and Kevlar (24 GPa) that we measured showed lower values than those reported in literature (which can be attributed to the different grades of materials), but still showed differences of orders of magnitude (Supporting information, Figure S1).…”

Section: Resultsmentioning

confidence: 99%

Stepped Moduli in Layered Composites

Tayi

Güder

et al. 2014

Adv Funct Materials

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This paper describes adaptive composites that respond to mechanical stimuli by changing their Young's modulus. These composites are fabricated by combining a shorter layer of elastic material (e.g. latex) and a longer layer of stiffer material (e.g., polyethylene and Kevlar), and fixing them together at their ends. Tension along the layered composite increases its length, and as the strain increases, the composite changes the load-bearing layer from the elastic to the stiff material. The result is a step in the Young's modulus of the composite. The characteristics of the step (or steps) can be engineered by changing the number of layers (thereby changing the number of steps in the modulus), the difference in lengths of the layers (thereby changing the range of steps), or the type of materials (thereby changing the tensile modulus at each step). For composites with more than two steps in modulus, the materials within the composites can be layered in a hierarchical structure to fit within a smaller volume, without sacrificing performance.These composites can also be used to make structures with tunable, stepped compressive moduli.For example, when a compressive force is applied axially to an elastomeric cylinder that is wrapped with the composite around its circumference, it expands laterally and applies a tensile force on the composite. An adaptation of these principles can generate an electronic sensor that can monitor the applied compressive strain. Increasing or decreasing the strain closes or opens a circuit and reversibly activates a light-emitting diode.3

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Section: Resultsmentioning

confidence: 99%

Stepped Moduli in Layered Composites

Tayi

Güder

et al. 2014

Adv Funct Materials

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Section: Introductionmentioning

confidence: 99%

“…Abnormal grain growth is very common in the lack of such usual diffusion regulators [9] and the know-how of SiC fibers manufacturers consists in postponing the onset of SiC crystallization and grain growth, since a high correlation is anticipated with mechanical degradation. A close relationship has been evidenced, for instance, between the micro-hardness and short-range ordering in sol-gel prepared nanocrystalline oxides [10] and some authors have already pointed out fibers overall mechanical ability is governed by their microstructure [5,7,11] .The purpose of this paper is to try correlating, to the best extent possible, the tensile strength (σ r ), the Young's modulus (E) and the micro-hardness (μH) of different SiC fibers, either to Raman spectra or to "Raman Extensometry" S coefficient (measuring the straininduced shifts of Raman bands). Unlike most experimental methods intended to measure directly σ r and E, Raman analysis does not require extracting fibers from the matrix, either by mechanical grinding/crushing [12] or by chemical attack [13] .…”

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confidence: 99%

Non-destructive mechanical characterization of SiC fibers by Raman spectroscopy

Gouadec

Colomban

2001

Journal of the European Ceramic Society

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The paper provides a comprehensive study on Raman spectroscopy versatility as a fast and non destructive tool for the prediction of the mechanical properties of SiC fibers derived from a polymeric precursor (NLM™, Hi™, Hi-S™, SA™ and Sylramic™ grades) or produced by CVD (SCS-6™ fiber), including in situ analysis in CMCs or MMCs. We show how the results of very simple spectra fitting are correlated with Young's modulus, tensile strength and microhardness. The reason why such a correlation exists, the common dependency of Raman signal and mechanical behavior to the micro/nanostructure of ceramics, is discussed. Keywords :SiC-fibers / Raman spectroscopy / Mechanical properties / Microstructure / Carbon ∂ Author to whom correspondence should be addressed Fax : 33 (0) 1 49 78 13 18 e-mail : colomban@glvt-cnrs.fr IntroductionThe reinforcement of ceramic materials by long ceramic fibers leads to low density and refractory materials, of high damage tolerance, that should be appropriate for metal alloys substitution in advanced engines (turbines) and waste treatment energy plants [1] . Ceramic fibers can also be incorporated directly in metal matrices to increase their high temperature mechanical properties [1] .SiC fibers, which are among the most stable fibers, have always been produced by the 3D reticulation of a polymeric precursor. This synthesis route leads to a high matter homogeneity and very smooth surfaces, the lack of defects explaining tensile strengths σ r as high as 3 GPa. SiC fibers have been widely studied, especially their aging [2][3][4][5][6][7] which evidenced that densification is linked to compositional changes (for instance the loss of some residual hydrogen [8] ). A peculiarity of ceramics issued from polymeric precursors is no impurities are concentrated at the grains boundaries. Abnormal grain growth is very common in the lack of such usual diffusion regulators [9] and the know-how of SiC fibers manufacturers consists in postponing the onset of SiC crystallization and grain growth, since a high correlation is anticipated with mechanical degradation. A close relationship has been evidenced, for instance, between the micro-hardness and short-range ordering in sol-gel prepared nanocrystalline oxides [10] and some authors have already pointed out fibers overall mechanical ability is governed by their microstructure [5,7,11] .The purpose of this paper is to try correlating, to the best extent possible, the tensile strength (σ r ), the Young's modulus (E) and the micro-hardness (μH) of different SiC fibers, either to Raman spectra or to "Raman Extensometry" S coefficient (measuring the straininduced shifts of Raman bands). Unlike most experimental methods intended to measure directly σ r and E, Raman analysis does not require extracting fibers from the matrix, either by mechanical grinding/crushing [12] or by chemical attack [13] . Only the most resistant fibers are extracted in the former case while fibers surface might be altered in the latter. Besides, it will always be difficult to extract...

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“…In this study, we focus on Kevlar 49, a highermodulus grade of Kevlar designed for load-bearing applications in cables, cloth, and aerospace components [1]. While many studies of the quasi-static behavior of the various types of Kevlar fiber are available [2], there have been far fewer investigations on their dynamic mechanical properties [3]. Those that do exist characterize the storage and loss modulus as a function of temperature without considering the effects of continuously increasing strains, mainly due to the limitations of current dynamic mechanical analysis (DMA) [3].…”

Section: Introductionmentioning

confidence: 99%

Strain-dependent dynamic mechanical properties of Kevlar to failure: Structural correlations and comparisons to other polymers

Raja

Basu

Limaye

et al. 2015

Materials Today Communications

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The processing of Kevlar to certain strengths by hot-drawing can benefit by quantitative understanding of the correlation between structural and mechanical properties during the pre-drawing process. Here, we use a novel continuous dynamic analysis (CDA) to monitor the evolution in storage modulus and loss factor of Kevlar 49 fibers as a function of strain via a quasi-static tensile test. Unlike traditional dynamic mechanical analysis, CDA allows the tracking of straindependent mechanical properties until failure. The obtained dynamic viscoelastic properties of Kevlar 49 are correlated with structural data obtained from synchrotron radiation analysis and with Raman scattering frequencies. Ratedependent stress-strain results from Kevlar are compared to Nomex, spider silk, polyester and rubber, and provide insight into how the mechanical properties of Kevlar originate from its characteristic structural features. We find that as the storage modulus of Kevlar is essentially equal to the Young's modulus, the measured quantitative relationships between storage modulus and strain can provide insights into the tuning of the mechanical properties of aramid materials for specific applications. On the other hand, the technique of continuous dynamic analysis (CDA) combines the advantages of dynamic mechanical analysis with those of the quasi-static tensile test to quantify the evolution of viscoelastic properties as a continuous function of strain [4]. This is achieved through application of a small harmonic (20 Hz) strain during the tensile deformation. Because the harmonic strain is much smaller in magnitude than the applied quasi-static strain, it remains within the limits of linear viscoelasticity and does not affect the behavior of a quasi-static tensile test. Here, using a specialized electromechanical load cell capable of applying small but continually increasing periodic forces, we employ CDA to monitor the dynamic properties of Kevlar 49 fibers as a function of their strain to failure. We then quantitatively correlate our results to the structural tensile data of Kevlar from previous studies utilizing wide-angle X-ray diffraction (WAXD) [5] and Raman spectroscopy [6], to provide insight into the molecular mechanisms by which Kevlar tolerates stress. The dynamic mechanical behavior of Kevlar is further compared to those of other key structural polymers to quantitatively discern its dynamic responses against known benchmarks. As such, this study presents quantitative information on how the drawing of Kevlar changes its mechanical properties, thereby providing guidelines for the systematic optimization of this important engineering fiber.

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Relationship between structure and mechanical properties for aramid fibres

Cited by 169 publications

References 21 publications

Stepped Moduli in Layered Composites

Stepped Moduli in Layered Composites

Non-destructive mechanical characterization of SiC fibers by Raman spectroscopy

Strain-dependent dynamic mechanical properties of Kevlar to failure: Structural correlations and comparisons to other polymers

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