A strain-gradient formulation for fiber reinforced polymers: hybrid phase-field model for porous-ductile fracture

AbstractA novel numerical approach to analyze the mechanical behavior within composite materials including the inelastic regime up to final failure is presented. Therefore, a second-gradient theory is combined with phase-field methods to fracture. In particular, we assume that the polymeric matrix material undergoes ductile fracture, whereas continuously embedded fibers undergo brittle fracture as it is typical e.g. for roving glass reinforced thermoplastics. A hybrid phase-field approach is developed and applied along with a modified Gurson–Tvergaard–Needelman GTN-type plasticity model accounting for a temperature-dependent growth of voids on microscale. The mechanical response of the arising microstructure of the woven fabric gives rise to additional higher-order terms, representing homogenized bending contributions of the fibers. Eventually, a series of tests is conducted for this physically comprehensive multifield formulation to investigate different kinds and sequences of failure within long fiber reinforced polymers.

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Assessing the performance of electrospun nanofabrics as potential interlayer reinforcement materials for fiber-reinforced polymers

Composites and Advanced Materials ◽

10.1177/26349833211002519 ◽

2021 ◽

Vol 30 ◽

pp. 263498332110025

Author(s):

Katerina Loizou ◽

Angelos Evangelou ◽

Orestes Marangos ◽

Loukas Koutsokeras ◽

Iouliana Chrysafi ◽

...

Keyword(s):

Polyvinylidene Fluoride ◽

Mechanical Response ◽

Mechanical Performance ◽

Polyamide 6 ◽

Processing Parameters ◽

Fiber Reinforced Polymers ◽

Fiber Reinforced ◽

Scanning Calorimetry ◽

Multiwalled Carbon ◽

Reinforced Polymers

Multiscale-reinforced polymers offer enhanced functionality due to the three different scales that are incorporated; microfiber, nanofiber, and nanoparticle. This work aims to investigate the applicability of different polymer-based nanofabrics, fabricated via electrospinning as reinforcement interlayers for multilayer-fiber-reinforced polymer composites. Three different polymers are examined; polyamide 6, polyacrylonitrile, and polyvinylidene fluoride, both plain and doped with multiwalled carbon nanotubes (MWCNTs). The effect of nanotube concentration on the properties of the resulting nanofabrics is also examined. Nine different nanofabric systems are prepared. The stress–strain behavior of the different nanofabric systems, which are eventually used as reinforcement interlayers, is investigated to assess the enhancement of the mechanical properties and to evaluate their potential as interlayer reinforcements. Scanning electron microscopy is employed to visualize the morphology and microstructure of the electrospun nanofabrics. The thermal behavior of the nanofabrics is investigated via differential scanning calorimetry to elucidate the glass and melting point of the nanofabrics, which can be used to identify optimum processing parameters at composite level. Introduction of MWCNTs appears to augment the mechanical response of the polymer nanofabrics. Examination of the mechanical performance of these interlayer reinforcements after heat treatment above the glass transition temperature reveals that morphological and microstructural changes can promote further enhancement of the mechanical response.

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Evaluation of the mechanical response of calcarenite specimens confined with fiber reinforced polymers after high temperature exposure

Journal of Building Engineering ◽

10.1016/j.jobe.2021.102504 ◽

2021 ◽

Vol 42 ◽

pp. 102504

Author(s):

L. Estevan ◽

F.J. Baeza ◽

F.B. Varona ◽

S. Ivorra

Keyword(s):

High Temperature ◽

Mechanical Response ◽

Fiber Reinforced Polymers ◽

Fiber Reinforced ◽

Reinforced Polymers ◽

High Temperature Exposure ◽

Temperature Exposure

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Characterization of the Physical Origins of Acoustic Emission (AE) From Natural Fiber Reinforced Polymers (Nfrps) Machining Processes

10.21203/rs.3.rs-485377/v1 ◽

2021 ◽

Author(s):

Zimo Wang ◽

Ruiqi Guo ◽

Qiyang Ma ◽

Faissal Chegdani ◽

Bruce Tai ◽

...

Keyword(s):

Acoustic Emission ◽

High Speed ◽

Random Distribution ◽

Natural Fiber ◽

Matrix Material ◽

Machining Process ◽

Fiber Reinforced Polymers ◽

Depth Of Cut ◽

Fiber Reinforced ◽

Reinforced Polymers

Abstract Natural fiber reinforced polymers (NFRPs) are environmentally friendly and are receiving growing attention in the industry. However, the multi-scale structure of natural fibers and the random distribution of the fibers in the matrix material severely impede the machinability of NFRPs, and real-time monitoring is essential for quality assurance. This paper reports a synchronous in-situ imaging and acoustic emission (AE) analysis of the NFRP machining process to connect the temporal features of AE to the underlying dynamics and process instability, all happen within milliseconds during the NFRP cutting. This approach allows directly observing the surface modification and chip formation from a high-speed camera (HSC) during NFRP cutting processes. The analysis of the HSC images suggests that the complex fiber structure and the random distribution introduce an unsteady, almost a freeze-and-release type motion pattern of the cutting tool with varying depths of cut at the machining interface. More pertinently, a prominent burst pattern of AE from time domain was found to emanate due to the sudden penetration of the tool into the surface of the NFRP workpiece (increasing the depth of cut), as well as a release motion of the tool from its momentary freeze position. These findings open the possibility of tracking AE signals to assess the effective specific energy and surface quality that are affected by these unsteady motion patterns.

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Phase-Field Modeling of Damage and Fracture in Laminated Unidirectional Fiber Reinforced Polymers

FES Journal of Engineering Sciences ◽

10.52981/fjes.v9i2.687 ◽

2021 ◽

Vol 9 (2) ◽

pp. 110-116

Author(s):

Aamir Dean ◽

Pavan Kumar ◽

Ammar Babiker ◽

Martin Brod ◽

Salih Elhadi Mohamed Ahmed ◽

...

Keyword(s):

Phase Field ◽

Composite Structures ◽

Failure Mechanisms ◽

Matrix Cracking ◽

Fiber Reinforced Polymers ◽

Failure Behavior ◽

Fiber Reinforced ◽

Reinforced Polymers ◽

Unidirectional Fiber ◽

Damage And Fracture

The damage and fracture behavior of Fiber Reinforced Polymers (FRPs) is quite complex and is different than the failure behavior of the traditionally employed metals. There are various types of failure mechanisms that can develop during the service life of composite structures. Each of these mechanisms can initiate and propagate independently. However, in practice, they act synergistically and appear simultaneously. The difficulties that engineers face to understand and predict how these different failure mechanisms result in a structural failure enforce them to use high design safety factors and also increases the number of certification tests needed. Considering that the experimental investigations of composites can be limited, very expensive, and time-consuming, in this contribution the newly developed multi Phase-Field (PF) fracture model [1] is employed to numerically study the failure in different Unidirectional Fiber Reinforced Polymers (UFRPs) laminates, namely, fracture in single-edge notched laminated specimens, matrix cracking in cross-ply laminates, and delamination migration in multi-layered UFRPs. The formulation of the PF model incorporates two independent PF variables and length scales to differentiate between fiber and inter-fiber (matrix-dominated) failure mechanisms. The physically motivated failure criterion of Puck is integrated into the model to control the activation and evolution of the PF parameters. The corresponding governing equations in terms of variational formulation is implemented into the Finite Element (FE) code ABAQUS utilizing the user-defined subroutines UMAT and UEL.

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