scholarly journals On longitudinal compressive failure of carbon-fibre-reinforced polymer: from unidirectional to woven, and from virgin to recycled

2012 ◽  
Vol 370 (1965) ◽  
pp. 1871-1895 ◽  
Author(s):  
S. T. Pinho ◽  
R. Gutkin ◽  
S. Pimenta ◽  
N. V. De Carvalho ◽  
P. Robinson
Keyword(s):  
Carbon Fibre ◽  
Shear Fracture ◽  
Numerical Models ◽  
Failure Process ◽  
Kink Band ◽  
Compressive Failure ◽  
Electron Microscopic ◽  
Band Formation ◽  
Kink Bands ◽  
Recycled Composites

Modelling the longitudinal compressive failure of carbon-fibre-reinforced composites has been attempted for decades. Despite many developments, no single model has surfaced to provide simultaneously a definitive explanation for the micromechanics of failure as well as validated predictions for a generic stress state. This paper explores the reasons for this, by presenting experimental data (including scanning electron microscopic observations of loaded kink bands during propagation, and brittle shear fracture at 45 ° to the fibres) and reviewing previously proposed micromechanical analytical and numerical models. The paper focuses mainly on virgin unidirectional (UD) composites, but studies for woven and recycled composites are also presented, highlighting similarities and differences between these cases. It is found that, while kink-band formation (also referred to in the literature as microbuckling) is predominant in UD composites under longitudinal compression, another failure mode related to the failure of the fibres can be observed experimentally. It is also shown that the micromechanics of the failure process observed in UD composites is similar to that in other fibre architectures, hence encouraging the adaptation and application of models developed for the former to the latter.

Investigation of the axial compressive behavior of Kevlar fibers using the dynamic loop test

2019 ◽  
Vol 89 (18) ◽  
pp. 3825-3838
Author(s):  
Ahmad Abuobaid ◽  
Raja Ganesh ◽  
John W Gillespie
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Failure Strain ◽  
Kink Band ◽  
Test Method ◽  
Strain Rates ◽  
Compressive Failure ◽  
Band Formation ◽  
Rate Dependent ◽  
Strain And Strain Rate

A dynamic loop test method for measuring strain rate-dependent fiber properties was developed. During dynamic loop testing, the fiber ends are accelerated at constant levels of 20.8, 50 and 343 m/s2. The test method is used to study Kevlar® KM2-600, which fails in axial compression due to kink band formation. The compressive failure strain and strain rate at the onset of kink band formation is calculated from the critical loop diameter ( D C), which is monitored throughout the test using a high-speed camera. The results showed that compressive failure strain increases with strain rates from quasi-static to a maximum strain rate of 116 s−1 by a factor of ∼3. Kink angles (φ) and kink band spacing ( D S) were 60 ° ± 2 ° and 16 ± 3 μm, respectively, over the strain rates tested. Rate-dependent mechanisms of compressive failure by kink band formation were discussed.

scholarly journals Axial-Compressive Behavior, Including Kink-Band Formation and Propagation, of Singlep-Phenylene Terephthalamide (PPTA) Fibers

2013 ◽  
Vol 2013 ◽  
pp. 1-15 ◽  
Author(s):  
M. Grujicic ◽  
S. Ramaswami ◽  
J. S. Snipes ◽  
R. Yavari ◽  
C.-F. Yen ◽  
...  
Keyword(s):  
Detrimental Effect ◽  
Mechanical Response ◽  
Topological Defects ◽  
Kink Band ◽  
Coarse Grained ◽  
Computational Investigation ◽  
Band Formation ◽  
Longitudinal Tensile Strength ◽  
Kink Bands

The mechanical response ofp-phenylene terephthalamide (PPTA) single fibers when subjected to uniaxial compression is investigated computationally using coarse-grained molecular statics/dynamics methods. In order to construct the coarse-grained PPTA model (specifically, in order to define the nature of the coarse-grained particles/beads and to parameterize various components of the bead/bead force-field functions), the results of an all-atom molecular-level computational investigation are used. In addition, the microstructure/topology of the fiber core, consisting of a number of coaxial crystalline fibrils, is taken into account. Also, following our prior work, various PPTA crystallographic/topological defects are introduced into the model (at concentrations consistent with the prototypical PPTA synthesis/processing conditions). The analysis carried out clearly revealed (a) formation of the kink bands during axial compression; (b) the role of defects in promoting the formation of kink bands; (c) the stimulating effects of some defects on the fiber-fibrillation process; and (d) the detrimental effect of the prior compression, associated with fiber fibrillation, on the residual longitudinal-tensile strength of the PPTA fibers.

In-situ compression of high performance polymeric and related fibers within the Scanning Electron Microscope

1990 ◽  
Vol 48 (4) ◽  
pp. 544-545
Author(s):  
Var L. St. Jeor ◽  
C. C. Chau ◽  
Mark Thomsen
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Brittle Failure ◽  
High Performance ◽  
Kink Band ◽  
Compressive Failure ◽  
Polymeric Fibers ◽  
Band Formation ◽  
Stage Of Development ◽  
Scanning Electron

A large portion of the interest currently given high performance polymer fibers stems from their potential use in composite construction. Although many of these fibers display good tensile properties, compressive strength is a major concern. There are many studies which have observed the compressive failure morphology of polymeric fibers. These studies usually involve the postmortem observation of samples which have failed, either partly or completely, following compressive strain. Observations have included such events as kink band formation, brittle failure and other modes as well. But to our knowledge these failure modes have not been recorded, in process, using the scanning electron microscope (SEM). In this article we introduce a technique which allows observation of compressive failure within the SEM, or using light microscopy (LM), in process. We also present some results unique to this procedure. This technique allows us to follow this "process" of compressive failure including both it's initiation and the more advanced stages of failure. Since the compressive failure of polymeric fibers is a process rather than an instantaneous event we have been able to record this process of failure, in it's various stages, in relatively high resolution SEM micrographs. Our methodology involves the use of relatively low accelerating voltages to minimize charging artifacts associated with damaged areas of the fiber. This induced damage can disrupt the 3 - 5nm sputter coating used to prevent such artifact resulting in uncoated fiber being exposed to the electron beam. This technique also lends itself readily to video recording. We have observed compressive failure processes for Kevlar 49®, Spectra 1000®, Hercules AS-4® carbon and various experimental fibers such as Polybenzobisoxazole (PBO). Our observations have included such modes of failure as kink band formation, delamination, buckling and brittle failure. It is noted that some of these processes occur simultaneously in any given fiber, and with the exception of brittle failure, these processes can be recorded at every stage of development visible to the SEM.

scholarly journals Experimental Characterisation of Parameters Controlling the Compressive Failure of Pultruded Unidirectional Carbon Fibre Composites

2010 ◽  
Vol 24-25 ◽  
pp. 15-22 ◽  
Author(s):  
Ole Thybo Thomsen ◽  
K.K. Kratmann
Keyword(s):  
Compressive Strength ◽  
Carbon Fibre ◽  
Test Procedure ◽  
Kink Band ◽  
Image Correlation ◽  
Band Formation ◽  
Shear Properties ◽  
Axial Splitting ◽  
Strength Models ◽  
Carbon Fibre Composites

The classical kink-band formation models predict that the compressive strength of UD carbon fibre reinforced composite materials (UD CFRP) is governed by fibre misalignment as well as of the mechanical shear properties. A new image analysis procedure for experimental determination of the fibre misalignment, the Fourier transform misalignment analysis (FTMA), has been developed. Moreover, a modified asymmetric Iosipescu test specimen geometry has been developed and validated for accurate measurement of the composite material shear properties without parasitic effects due to axial splitting. In the test procedure the shear strain distribution is measured using Digital Image Correlation (DIC) and the results calibrated based on FEA modelling results. Using the measured properties as input, the predictions of the classic compressive strength models have been compared with measured compressive strengths. Finally, an alternative approach to the classical kink band equilibrium has been proposed and demonstrated to provide more accurate predictions than the classical models.

The Kink Band Mechanism for the Compressive Failure of Fiber Composite Materials

1997 ◽  
Vol 64 (1) ◽  
pp. 1-6 ◽  
Author(s):  
R. M. Christensen ◽  
S. J. DeTeresa
Keyword(s):  
Composite Materials ◽  
Failure Criterion ◽  
Fiber Composite ◽  
Kink Band ◽  
Compressive Failure ◽  
Kink Bands ◽  
Physical Variables ◽  
Fiber Misalignment ◽  
Fiber Composite Materials ◽  
The Ideal

A simple strain-based yield/failure criterion for fiber composite materials is incorporated into a kink band analysis of compressive failure. Under realistic conditions of fiber misalignment the analysis predicts compressive failure at load levels about one–fifth of the ideal value, and with kink band inclinations of about 20 deg. Some parametric variations of the relevant physical variables are given in simple graphical forms, and comparisons are made with newly obtained micrographs of kink bands.

Micromechanics of kink band formation in open-hole fibre composites under compressive loading

2018 ◽  
Vol 149 ◽  
pp. 66-73 ◽  
Author(s):  
Vedad Tojaga ◽  
Simon P.H. Skovsgaard ◽  
Henrik Myhre Jensen
Keyword(s):  
Compressive Loading ◽  
Kink Band ◽  
Band Formation ◽  
Fibre Composites ◽  
Open Hole

Dynamic Behavior of Fiber Reinforced Composites Under Multiaxial Compression

1999 ◽  
Author(s):  
Kenji Oguni ◽  
G. Ravichandran
Keyword(s):  
Failure Mode ◽  
Kink Band ◽  
Fiber Reinforced Composites ◽  
Fiber Direction ◽  
Strain Rates ◽  
Reinforced Composites ◽  
Fiber Reinforced ◽  
Band Formation ◽  
Multiaxial Compression ◽  
Axial Splitting

Abstract Results from an experimental investigation on the mechanical behavior of a unidirectional reinforced polymer composite with 50% volume fraction E-glass/vinylester under uniaxial and proportional multiaxial compression are presented. Specimens are loaded in the fiber direction using a servo-hydraulic material testing system for low strain rates and a Kolsky (split Hopkinson) pressure bar for high strain rates, up to 3000 s−1. The results indicate that the compressive strength of the composite increases with increasing levels of confinement and increasing strain rates. Post-test optical and scanning electron microscopy is used to identify the failure modes. The failure mode that is observed in unconfined specimen is axial splitting followed by fiber kink band formation. At high levels of confinement, the failure mode transitions from axial splitting to kink band formation and fiber failure. Also, a new energy based analytic model for studying axial splitting phenomenon in unidirectional fiber-reinforced composites is presented.

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