Analysis of the skin wrinkling in out-of-plane joints of CFRP hat-shaped structure

Abstract Out-of-plane joints, between hat (omega) stiffeners and skin panels are asymmetric parts of the composite structure. Studies show that physical-mechanical conditions in these joints significantly affect skin forming quality. In the present article, aimed to investigate the mechanism of the skin wrinkle in the joints of carbon fiber reinforced plastics (CFRP) hat-shaped structure, the pressure testing apparatus based on the Pascal principle is used to surveillance the resin pressure dynamically in out-of-plane joints. In this regard, several influencing factors such as first-order holding time, forming pressure and relative volume of unidirectional fillers are studied. Obtained results show that increasing the first stage holding time can prolong the viscous flow state of the resin, and time to achieve pressure equalization at each detection point, thereby improving the dispersion of the pressure and reducing the possibility of wrinkles. It is found that as the forming pressure increases, the degree of skin wrinkles in the out-of-plane joints ameliorates. Moreover, for fillers with a relative volume within the range of 0–50%, the pressure transfer effect and the skin flatness is relatively dissatisfactory. It is concluded that the filler with a relative volume of 80–120% improves the skin wrinkle in out-of-plane joints.

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A 2.5D APPROACH TO SKIN WRINKLES SEGMENTATION

Image Analysis & Stereology ◽

10.5566/ias.1925 ◽

2019 ◽

Vol 38 (1) ◽

pp. 75 ◽

Cited By ~ 1

Author(s):

Etienne Decencière ◽

Amira Belhedi ◽

Serge Koudoro ◽

Frédéric Flament ◽

Ghislain François ◽

...

Keyword(s):

Point Clouds ◽

Skin Surface ◽

Fringe Projection ◽

Physical Parameters ◽

Projection System ◽

Beneficial Effects ◽

3D Point Clouds ◽

Novel Method ◽

Skin Wrinkles ◽

Skin Wrinkling

Wrinkles or creases are common structures on surfaces. Their detection is often challenging, and can be an important step for many different applications. For instance, skin wrinkle segmentation is a crucial step for quantifying changes in skin wrinkling and assessing the beneficial effects of dermatological and cosmetic anti-ageing treatments. A 2.5D approach is proposed in this paper to segment individual wrinkles on facial skin surface described by 3D point clouds. The method, based on mathematical morphology, only needs a few physical parameters as input, namely the maximum wrinkle width, the minimum wrinkle length, and the minimum wrinkle depth. It has been applied to data acquired from eye wrinkles using a fringe projection system. An accurate evaluation was made possible thanks to manual annotations provided by three different experts. Results demonstrate the accuracy of this novel method.

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Graphite Nanoplatelet Modified Epoxy Resin for Carbon Fibre Reinforced Plastics with Enhanced Properties

Journal of Nanomaterials ◽

10.1155/2017/5194872 ◽

2017 ◽

Vol 2017 ◽

pp. 1-10 ◽

Cited By ~ 14

Author(s):

Yan Li ◽

Han Zhang ◽

Zhaohui Huang ◽

Emiliano Bilotti ◽

Ton Peijs

Keyword(s):

Carbon Fibre ◽

Epoxy Resin ◽

Flexural Modulus ◽

Graphite Nanoplatelets ◽

Reinforced Plastics ◽

Out Of Plane ◽

Finely Disperse ◽

Interlaminar Shear ◽

Carbon Fibre Reinforced Plastic

A simple approach to deliver graphene or graphite nanoplatelets (GNPs) into carbon fibre reinforced plastic (CFRPs) to enhance the multifunctional properties of carbon/epoxy laminates was demonstrated. GNPs improved the typically low interlaminar mechanical, thermal, and electrical properties of CFRPs after direct vacuum infusion of GNP doped resin obtained via in situ exfoliation by three-roll milling (TRM). Compared to high shear mixing or probe ultrasonication, TRM produces higher shear rates and stresses to exfoliate and finely disperse GNP particles within an epoxy matrix. This environmentally friendly and industrial scalable process does not require the use of solvents, additives, or chemical treatments. The flexural modulus and interlaminar shear strength (ILSS) of CFRPs was increased by 15% and by 18%, respectively, with the addition of 5 wt.% in situ exfoliated GNP in the doped epoxy resin. Out-of-plane electrical and thermal conductivity, at the same filler content, were, respectively, improved by nearly two orders of magnitude and 50%.

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Fabrication, testing, and analysis of sandwich structure with composite skin and additive manufactured core

Journal of Reinforced Plastics and Composites ◽

10.1177/0731684421995883 ◽

2021 ◽

pp. 073168442199588

Author(s):

Dooyoul Lee ◽

Hyeok-Jun Kwon ◽

Seongun Yang ◽

Min-Saeng Kim

Keyword(s):

Sandwich Structure ◽

Fused Deposition Modeling ◽

Failure Modes ◽

Three Point Bending ◽

Fused Deposition ◽

Out Of Plane ◽

Different Temperatures ◽

Deposition Modeling ◽

Ductile To Brittle Transition ◽

Skin Wrinkling

The mechanical behavior of a sandwich structure made of woven glass/epoxy skins and an additive manufactured (AM) core was studied. The AM core was fabricated using polyetherimide and fused deposition modeling. This combination was chosen to increase the out-of-plane strength of an AM aircraft part. Tensile, flexural, and puncture tests were conducted for both the AM core and sandwich structure. The behavior of the beams was governed by the skins; however, the effect of the AM core for one-sided beams was significant. The tensile strength predicted by the simple mixture rule was in good agreement with the experimental results. For the flexural test specimen, sandwich beams were tested under three-point bending. The addition of composite skins increased the elastic modulus and flexural strength in both directions. The prevalent failure modes were skin wrinkling and core failure, and failure of the compressive skin was more likely. Puncture tests were conducted at three different temperatures. Owing to the increased bending stiffness, the sandwich structure did not exhibit ductile-to-brittle transition behavior.

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Designing Hierarchical Honeycombs to Mimic the Mechanical Behaviour of Composites

Journal of Composites Science ◽

10.3390/jcs5010017 ◽

2021 ◽

Vol 5 (1) ◽

pp. 17

Author(s):

Ziyue Yang ◽

Parvez Alam

Keyword(s):

Mechanical Behaviour ◽

Structural Hierarchy ◽

Reinforced Plastics ◽

Mechanical Metamaterials ◽

Stiffness Properties ◽

Model Rule ◽

Out Of Plane ◽

Plane Direction ◽

Strength And Stiffness ◽

Unidirectional Fibre

Honeycombs are used ubiquitously in engineering applications as they have excellent out-of-plane strength and stiffness properties with respect to weight. This paper considers the properties of honeycombs in the in-plane direction, a direction that is significantly weaker and less stiff than the out-of-plane direction. We assess how judiciously locating structural hierarchy within a honeycomb array can be a geometric design principle with direct consequences on the mechanical behaviour of the honeycomb. Here, we use finite element methods to design reinforced honeycomb mechanical metamaterials that mimic the mechanical behaviour of unidirectional fibre reinforced composites. We specifically incorporate structural hierarchy within hollow honeycomb cells to create mechanical metamaterial pseudo-composites, where the hierarchical parts are pseudo-fibres, and the hollow parts are the pseudo-matrix. We find that pseudo-fibre contribution coefficients are higher than the fibre contribution coefficient of carbon fibre reinforced plastics (CFRP). We also find that the elastic modulus of unidirectional pseudo-composites can be predicted using the (Voigt model) rule of mixtures with a good level of accuracy.

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Free Flow of Sweat due to Loss of Surface Tension at Sweat Droplet Causes Water-Induced Skin Wrinkling

10.7287/peerj.preprints.57v3 ◽

2013 ◽

Author(s):

Soumya Marasakatla ◽

Karunakar Marasakatla

Keyword(s):

Surface Tension ◽

Blood Flow ◽

Water Flow ◽

Water Immersion ◽

Sympathetic Nerves ◽

The Body ◽

Free Flow ◽

Sweat Glands ◽

Skin Wrinkles ◽

Skin Wrinkling

Water immersion skin wrinkling appears to be the result of breaking the balance between secretory pressure of sweat glands and the pressure exerted by the surface tension of sweat droplet at the pore. When a hand is immersed in water, sweat droplet easily merge within the water causing pressure to drop at the pore. The resulted imbalance in pressure enables the sweat to flow freely into the water. Flow of sweat continues as long as there is a blood flow to hand. To prevent the loss of sweat from the body and to maintain homeostasis, sympathetic nerves trigger the reduction of blood flow to hand causing vasoconstriction. The overlying skin wrinkles due to loss of volume under the skin.

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A failure criterion for honeycomb structures considering the onset of instability under out-of-plane loads

Journal of Sandwich Structures & Materials ◽

10.1177/1099636220932821 ◽

2020 ◽

pp. 109963622093282

Author(s):

Weiping Li ◽

Cheng Qiu ◽

Zengshan Li ◽

Hong Nie

Keyword(s):

Failure Criterion ◽

Plate Theory ◽

Damage Model ◽

Experimental Studies ◽

Nonlinear Function ◽

Bloch Wave ◽

Honeycomb Core ◽

Honeycomb Structures ◽

Reinforced Plastics ◽

Out Of Plane

A failure criterion for predicting the damage of honeycomb structures under combined compression and transverse shearing is put forward in this paper. An analytical method using the Bloch wave function and von Kármán plate theory is employed to predict the onset of damage based on the fact that failure of honeycomb structures is closely related to the buckling behavior of its core. After obtaining a bunch of data points of different stress conditions where damage occurs, a failure envelop for honeycomb cores under out-of-plane loads is formed and fitted by a nonlinear function. In order to validate the proposed failure criterion, experimental studies are performed on honeycomb sandwich structures consisting of Nomex honeycomb core and CFRP (carbon-fiber reinforced plastics) facesheets including in-plane compression, three-point bending and combined-compression-shearing. The accuracy of the proposed criterion is evaluated by comparing experiments with results predicted by progressive damage model incorporating the failure envelope of honeycomb core.

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Determination of stresses, strains and failure types in multidirectional laminates under pure bending

Journal of Composite Materials ◽

10.1177/0021998320932301 ◽

2020 ◽

Vol 54 (28) ◽

pp. 4397-4413

Author(s):

E Petersen ◽

E Kappel ◽

J Koord ◽

O Völkerink ◽

C Hühne

Keyword(s):

Failure Analysis ◽

Image Correlation ◽

Pure Bending ◽

Plane Failure ◽

Failure Type ◽

Reinforced Plastics ◽

Curved Structures ◽

Out Of Plane ◽

Failure Types

Curved structures made of fibre-reinforced plastics tend to show an out-of-plane failure type, when loaded under bending. One method to determine the related tensile strength in thickness direction, is the standardised unfolding test related to ASTM D6415 with L-profile specimens. However, the standard shall be used for unidirectional materials only, which is not the case for multidirectional laminates. Therefore, this publication presents methods to determine the layer-wise stress and strain state as well as occurring failure types of multidirectional laminates. An extension of the Lekhnitski formulae is presented and its results are validated by comparison with high resolution strain measurements by Digital Image Correlation. Based on the analytical solution, a failure analysis using Cuntze’s Failure Mode Concept is conducted. It was revealed, that the failure load and position can be predicted accurately, if a failure type related strength –in-plane or out-of-plane failure– is used. In the presence of [Formula: see text]-layers higher deviations occur between test and prediction and therefore limits the validity of the presented analytical failure analysis.

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Grain separation enhanced magnetic coercivity in Pt/Co multilayers.

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100151027 ◽

1993 ◽

Vol 51 ◽

pp. 1038-1039 ◽

Cited By ~ 1

Author(s):

G.A. Bertero ◽

R. Sinclair

Keyword(s):

Remanent Magnetization ◽

Strong Influence ◽

Uniaxial Anisotropy ◽

Magnetic Coupling ◽

Recording Media ◽

Magnetic Media ◽

Signal To Noise ◽

Out Of Plane ◽

Longitudinal Recording ◽

The Relationship

Pt/Co multilayers displaying perpendicular (out-of-plane) magnetic anisotropy and 100% perpendicular remanent magnetization are strong candidates as magnetic media for the next generation of magneto-optic recording devices. The magnetic coercivity, Hc, and uniaxial anisotropy energy, Ku, are two important materials parameters, among others, in the quest to achieving higher recording densities with acceptable signal to noise ratios (SNR). The relationship between Ku and Hc in these films is not a simple one since features such as grain boundaries, for example, can have a strong influence on Hc but affect Ku only in a secondary manner. In this regard grain boundary separation provides a way to minimize the grain-to-grain magnetic coupling which is known to result in larger coercivities and improved SNR as has been discussed extensively in the literature for conventional longitudinal recording media.We present here results from the deposition of two Pt/Co/Tb multilayers (A and B) which show significant differences in their coercive fields.

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