Non-Hookean Elastic Behavior and Crystallite Orientation in Carbon Fibers

Djordjević, I.M.; Sekulić, Danioela R.; Mitrić, Miodrag; Stevanović, M.M.

doi:10.1177/0021998309357087

Cited by 22 publications

(12 citation statements)

References 15 publications

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“…The determined increase of the material stiffness in different directions with increasing FVC corresponds to already known material behavior [ 29 , 30 , 31 ]. In addition to the fact that draping effects have an impact on the resulting material stiffness, to define the limitation of use, the strength values and the resulting failure envelopes are evaluated.…”

Section: Discussion and Evaluation Of Draping Effectssupporting

confidence: 65%

“…However, in the case of carbon fibers further parameters are needed. If a load is applied in fiber direction, the misorientation of the crystallites within the fibers leads to an increase or decrease of the modulus

due to reorientation of these crystallites under tensile and compressive strain, respectively [ 29 , 30 , 31 , 32 ]. Since the stress in fiber direction

is directly dependent on the modulus

, the acting strain in fiber direction

is used as the free parameter to define the current modulus.…”

Section: Materials and Experimental Methodsmentioning

confidence: 99%

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The Impact of Draping Effects on the Stiffness and Failure Behavior of Unidirectional Non-Crimp Fabric Fiber Reinforced Composites

et al. 2020

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Unidirectional non-crimp fabrics (UD-NCF) are often used to exploit the lightweight potential of continuous fiber reinforced plastics (CoFRP). During the draping process, the UD-NCF fabric can undergo large deformations that alter the local fiber orientation, the local fiber volume content (FVC) and create local fiber waviness. Especially the FVC is affected and has a large impact on the mechanical properties. This impact, resulting from different deformation modes during draping, is in general not considered in composite design processes. To analyze the impact of different draping effects on the mechanical properties and the failure behavior of UD-NCF composites, experimental results of reference laminates are compared to the results of laminates with specifically induced draping effects, such as non-constant FVC and fiber waviness. Furthermore, an analytical model to predict the failure strengths of UD laminates with in-plane waviness is introduced. The resulting stiffness and strength values for different FVC or amplitude to wavelength configurations are presented and discussed. In addition, failure envelopes based on the PUCK failure criterion for each draping effect are derived, which show a clear specific impact on the mechanical properties. The findings suggest that each draping effect leads to a “new fabric” type. Additionally, analytical models are introduced and the experimental results are compared to the predictions. Results indicate that the models provide reliable predictions for each draping effect. Recommendations regarding necessary tests to consider each draping effect are presented. As a further prospect the resulting stiffness and strength values for each draping effect can be used for a more accurate prediction of the structural performance of CoFRP parts.

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Section: Discussion and Evaluation Of Draping Effectssupporting

confidence: 65%

due to reorientation of these crystallites under tensile and compressive strain, respectively [ 29 , 30 , 31 , 32 ]. Since the stress in fiber direction

is directly dependent on the modulus

, the acting strain in fiber direction

is used as the free parameter to define the current modulus.…”

Section: Materials and Experimental Methodsmentioning

confidence: 99%

The Impact of Draping Effects on the Stiffness and Failure Behavior of Unidirectional Non-Crimp Fabric Fiber Reinforced Composites

et al. 2020

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“…Furthermore, while some of these phenomena are associated with a decrease in modulus, such as plasticity and damage, a competing stiffening effect on the stress-strain curve is induced by others. In the case of loading in the x direction, the primary load carrying carbon fibres in the axial yarns exhibit stiffening due to their non-Hookean constitutive behaviour [26][27][28]. At the same time, minor undulations in axial bundles caused 255 by nesting effects of multiple braid plies diminish as the fibres align progressively with the load.…”

Section: Loading In the Axial (X) Directionmentioning

confidence: 99%

Damage and failure of triaxial braided composites under multi-axial stress states

Wehrkamp-Richter

Hinterhölzl

Pinho

2017

Composites Science and Technology

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Damage and failure of triaxial braided composites under multi-axial stress states was investigated. In order to introduce different multi-axial stress states in the material, uni-axial tensile tests were performed at different off-axis orientations. Three braid architectures, comprising braiding angles of 30 • , 45 • and 60 • were each loaded parallel to their axial, transverse and braid yarn direction. Digital image correlation measurement techniques were used to quantify the effects of the textile architecture and its heterogeneity on the strain field, to identify and locate constituent failure mechanisms and to investigate damage initiation and development. In order to identify the driving physical mechanisms behind the material non-linearity, the evolution of the damage variable and the accumulated inelastic strain was quantified using incremental loading/unloading experiments. A high-speed camera was employed in order to study the dynamic nature of catastrophic failure. The triaxial braids within this study exhibited severe non-linearities in the mechanical response before final failure as a result of extensive matrix cracking. While we found the underlying textile architecture to slightly reduce the elastic properties compared to equivalent tape laminates, it functions as a natural crack arresting grid. As a result of this mechanism, braids under certain load conditions were capable of withstanding a higher strain to failure, even if a large portion of the specimen surface was saturated with matrix cracks. The accompanying mechanical behaviour can be desirable in the design of crash absorbing or pseudo-ductile materials. An additional failure mode intrinsic to the textile architecture was encountered for loading in the heavily undulated braid yarn direction. Due to yarn straightening and out-of-plane movements, braided composites were found to fail as a result of large scale delaminations accompanied by progressive fibre bundle pull-out.

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“…Besides, 2 there is not an obvious yield point or slope change in tensile stress-strain curves of composite materials as seen in metallic materials. In fact, the tensile stress-strain curves of Carbon Fibre Reinforced Polymer (CFRP) laminates show stiffening behaviour because of the non-Hooken behaviour of carbon fibres due to crystallite misorientations [1][2][3][4]. This is more prominent in unidirectional (UD) [0]n type CFRP laminates which have an upwardly concave stress-strain curve.…”

Section: Introductionmentioning

confidence: 99%

Damage mode identification in transverse crack tension specimens using acoustic emission and correlation with finite element progressive damage model

Öz

AhmadvashAghbash

Ersoy

2019

Composites Part B: Engineering

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In this study damage progression in unidirectional composite specimens is investigated. Transverse Crack Tension specimens are used to stimulate damage in a predetermined progressive sequence. Acoustic Emission (AE) registration technique and its location detection capability is used to identify and locate the damage modes during the tension tests. The k-means++ algorithm is applied to cluster similar AE events and obtain reliable correlations between the damage modes and AE characteristics. Damage modes at the end of interrupted tests are identified under an optical microscope and correlated with locations of AE clusters. It is seen that matrix cracks have high amplitude and duration, whereas delaminations have low amplitude and mid-duration, and fibre breaks have high average frequency characteristics. A finite element analysis was performed to predict the progressive failure behaviour including intralaminar failure and delaminations. The correlations between the AE clusters and damage modes are validated with the finite element model. Analysis (FEA)the fibre direction [6,12,13,16,19,25,27].De Groot et. al [6] tested uncured prepreg and cured [0]8 laminates and observed the registration of high peak frequency AE events during UD tension tests which were believed to be due to fibre breaks. Ramirez-Jimenez and Loutas et. al [12,13] proposed a correlation between the high frequency AE events and the

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Non-Hookean Elastic Behavior and Crystallite Orientation in Carbon Fibers

Cited by 22 publications

References 15 publications

The Impact of Draping Effects on the Stiffness and Failure Behavior of Unidirectional Non-Crimp Fabric Fiber Reinforced Composites

The Impact of Draping Effects on the Stiffness and Failure Behavior of Unidirectional Non-Crimp Fabric Fiber Reinforced Composites

Damage and failure of triaxial braided composites under multi-axial stress states

Damage mode identification in transverse crack tension specimens using acoustic emission and correlation with finite element progressive damage model

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