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17 pages, 12060 KiB

Open AccessArticle

Modeling of Preforming Process for Unidirectional Prepreg Composites Using Simplified Linear Friction Model and Fiber-Tracking Method

by Zhefu Li, Qinghua Song, Jun Liu, Weiping Liu, Ping Chen and Guangquan Yue

Polymers 2025, 17(10), 1321; https://doi.org/10.3390/polym17101321 - 13 May 2025

Viewed by 437

Abstract

Hot press preforming of unidirectional prepreg composites plays a key role in the manufacturing of aerospace components. However, defect prevention remains challenging due to complex fiber reorientation and inter-ply friction phenomena that occur during the forming process. To address these challenges, this study proposes an integrated modeling approach comprising three key components: (1) a simplified linear friction model for characterization of inter-ply slip behavior, (2) a fiber-tracking algorithm that accounts for anisotropic deformation characteristics, and (3) a coupled linear shell–membrane formulation for simultaneous modeling of in-plane and out-of-plane deformation behaviors. The proposed approach is validated through comprehensive material characterization, finite element simulation, and experimental comparisons based on a 2 m Ω-stringer geometry. Simulation results align well with experiments, showing the model’s ability to predict defects. Parametric analysis also identifies temperature as a key factor in controlling interfacial friction and improving formability, with optimal results at 75 °C. This integrated modeling approach provides an effective approach for defect prediction and process optimization, contributing to reduced material waste and improved efficiency in aerospace composite manufacturing. Full article

(This article belongs to the Section Polymer Physics and Theory)

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15 pages, 3936 KiB

Open AccessArticle

Magnetism and Thermal Transport of Exchange-Spring-Coupled La_2/3Sr_1/3MnO₃/La₂MnCoO₆ Superlattices with Perpendicular Magnetic Anisotropy

by Vitaly Bruchmann-Bamberg, Isabell Weimer, Vladimir Roddatis, Ulrich Ross, Leonard Schüler, Karen P. Stroh and Vasily Moshnyaga

Nanomaterials 2023, 13(21), 2897; https://doi.org/10.3390/nano13212897 - 3 Nov 2023

Cited by 2 | Viewed by 1473

Abstract

Superlattices (SLs) comprising layers of a soft ferromagnetic metal La_2/3Sr_1/3MnO₃ (LSMO) with in-plane (IP) magnetic easy axis and a hard ferromagnetic insulator La₂MnCoO₆ (LMCO, out-of-plane anisotropy) were grown on SrTiO₃ (100)(STO) substrates by a metalorganic aerosol deposition technique. Exchange spring magnetic (ESM) behavior between LSMO and LMCO, manifested by a spin reorientation transition of the LSMO layers towards perpendicular magnetic anisotropy below T_SR = 260 K, was observed. Further, 3ω measurements of the [(LMCO)₉/(LSMO)₉]₁₁/STO(100) superlattices revealed extremely low values of the cross-plane thermal conductivity κ(300 K) = 0.32 Wm⁻¹K⁻¹. Additionally, the thermal conductivity shows a peculiar dependence on the applied IP magnetic field, either decreasing or increasing in accordance with the magnetic disorder induced by ESM. Furthermore, both positive and negative magnetoresistance were observed in the SL in the respective temperature regions due to the formation of 90°-Néel domain walls within the ESM, when applying IP magnetic fields. The results are discussed in the framework of electronic contribution to thermal conductivity originating from the LSMO layers. Full article

(This article belongs to the Topic Advances in Functional Thin Films)

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12 pages, 5505 KiB

Open AccessEditor’s ChoiceArticle

Photoaligned Liquid Crystal Devices with Switchable Hexagonal Diffraction Patterns

by Inge Nys, Brecht Berteloot and Kristiaan Neyts

Materials 2022, 15(7), 2453; https://doi.org/10.3390/ma15072453 - 26 Mar 2022

Cited by 6 | Viewed by 2491

Abstract

Highly efficient optical diffraction can be realized with the help of micrometer-thin liquid crystal (LC) layers with a periodic modulation of the director orientation. Electrical tunability is easily accessible due to the strong stimuli-responsiveness in the LC phase. By using well-designed photoalignment patterns at the surfaces, we experimentally stabilize two dimensional periodic LC configurations with switchable hexagonal diffraction patterns. The alignment direction follows a one-dimensional periodic rotation at both substrates, but with a 60° or 120° rotation between both grating vectors. The resulting LC configuration is studied with the help of polarizing optical microscopy images and the diffraction properties are measured as a function of the voltage. The intricate bulk director configuration is revealed with the help of finite element Q-tensor simulations. Twist conflicts induced by the surface anchoring are resolved by introducing regions with an out-of-plane tilt in the bulk. This avoids the need for singular disclinations in the structures and gives rise to voltage induced tuning without hysteretic behavior. Full article

(This article belongs to the Special Issue Soft Photonic Crystals and Metamaterials)

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20 pages, 5686 KiB

Open AccessArticle

Effects of Reorientation of Graphene Platelets (GPLs) on Young’s Modulus of Polymer Composites under Bi-Axial Stretching

by Chuang Feng, Yu Wang and Jie Yang

Nanomaterials 2018, 8(1), 27; https://doi.org/10.3390/nano8010027 - 7 Jan 2018

Cited by 36 | Viewed by 5121

Abstract

Effects of bi-axial stretching induced reorientation of graphene platelets (GPLs) on the Young’s modulus of GPL/polymer composites is studied by Mori-Tanaka micromechanics model. The dispersion state of the GPLs in polymer matrix is captured by an orientation distribution function (ODF), in which two Euler angles are used to identify the orientation of the GPLs. Compared to uni-axial stretching, the increase of the stretching strain in the second direction enhances the re-alignment of GPL fillers in this direction while it deteriorates the re-alignment of the fillers in the other two directions. Comprehensive parametric study on the effects of the out-of-plane Young’s modulus, stretching strain, strain ratio, Poisson’s ratio and weight fraction and GPL dimension on the effective Young’s moduli of the composites in the three directions are conducted. It is found that the out-of-plane Young’s modulus has limited effects on the overall Young’s modulus of the composites. The second stretching enhances the Young’s modulus in this direction while it decreases the Young’s modulus in the other two directions. The results demonstrate the increase of Poisson’s ratio is favorable in increasing the Young’s modulus of the composites. GPLs with larger diameter-to-thickness ratio have better reinforcing effect on the Young’s modulus of GPL/polymer nanocomposites. Full article

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14 pages, 3944 KiB

Open AccessArticle

Effects of Reorientation of Graphene Platelets (GPLs) on Young’s Modulus of Polymer Nanocomposites under Uni-Axial Stretching

by Chuang Feng, Yu Wang, Sritawat Kitipornchai and Jie Yang

Polymers 2017, 9(10), 532; https://doi.org/10.3390/polym9100532 - 20 Oct 2017

Cited by 39 | Viewed by 5996

Abstract

The orientation of reinforcement fillers in composites plays a vital role in their mechanical properties. This paper employs the Mori–Tanaka micromechanics model, incorporating the effect of stretching-induced reorientation of graphene platelets (GPL), to predict Young’s modulus of GPL/polymer nanocomposites. Subjected to uni-axial stretching, dispersion of GPLs is described by an orientation distribution function (ODF) in terms of a stretching strain and two Euler angles. The ODF shows that GPLs tend to realign along the stretching direction. Such realignment is enhanced at a higher Poisson’s ratio and under a larger stretching strain. It is found that the out-of-plane Young’s modulus of GPL nanofillers has a limited effect on the overall Young’s modulus of the composites. With an increase in stretching strain and GPL concentration, Young’s modulus increases in the stretching direction while it decreases in the transverse direction. A larger aspect-ratio of GPLs with fewer layers is preferred for enhancing Young’s modulus in the stretching direction, but it is unfavorable in the transverse direction. Moreover, Young’s moduli in both longitudinal and transverse directions are more sensitive to the reorientation of smaller-sized GPLs with a greater concentration in the composites. Full article

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11 pages, 503 KiB

Open AccessCommunication

Magnetic Phase Transition in Ion-Irradiated Ultrathin CoN Films via Magneto-Optic Faraday Effect

by Chiung-Wu Su, Yen-Chu Chang and Sheng-Chi Chang

Materials 2013, 6(11), 5247-5257; https://doi.org/10.3390/ma6115247 - 15 Nov 2013

Cited by 4 | Viewed by 5852

Abstract

The magnetic properties of 1 nm thick in-plane anisotropic Co ultrathin film on ZnO(0001) were investigated through successive 500 eV nitrogen-ion sputtering. Magneto-optical Faraday effects were used to observe the evolution of the ion-irradiated sample in longitudinal and perpendicular magnetic fields. The ferromagnetic phase of the initial in-plane anisotropic fcc β-Co phase transformation to β-Co(N) phase was terminated at paramagnetic CoN_x phase. In-plane anisotropy with weak out-of-plane anisotropy of the Co/ZnO sample was initially observed in the as-grown condition. In the sputtering process, the N⁺ ions induced simultaneous sputtering and doping. An abrupt spin reorientation behavior from in-plane to out-of-plane was found under prolonged sputtering condition. The existence of perpendicular anisotropy measured from the out-of-plane Faraday effect may be attributed to the co-existence of residual β-Co and Co₄N exchange bonding force by the gradual depletion of Co-N thickness. Full article

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