Polymers

740 KiB

Open AccessArticle

Maintaining Structural Stability of Poly(lactic acid): Effects of Multifunctional Epoxy based Reactive Oligomers

by Sahas R. Rathi, Edward Bryan Coughlin, Shaw Ling Hsu, Charles S. Golub, Gerald H. Ling and Michael J. Tzivanis

Polymers 2014, 6(4), 1232-1250; https://doi.org/10.3390/polym6041232 - 22 Apr 2014

Cited by 36 | Viewed by 9479

Abstract

In order to reduce the effects of hydrolytic degradation and to maintain sufficient viscosity during processing of biomass based poly(l-lactic acid) (PLLA), various epoxy functional reactive oligomers have been characterized and incorporated into the degraded fragments as chain extenders. The molecular weight of [...] Read more.

In order to reduce the effects of hydrolytic degradation and to maintain sufficient viscosity during processing of biomass based poly(l-lactic acid) (PLLA), various epoxy functional reactive oligomers have been characterized and incorporated into the degraded fragments as chain extenders. The molecular weight of PLLA increased with the increase in functionality of the reactive oligomers. No further increase in molecular weight was observed for oligomers with functionality of greater than five. Under our experimental conditions, no gelation was found even when the highest functionality reactive oligomers were used. This is attributed to the preferential reaction of the carboxylic acid versus the negligible reactivity of the hydroxyl groups, present at the two ends of the degraded PLLA chains, with the epoxy groups. The study provides a clear understanding of the degradation and chain extension reaction of poly(lactic acid) (PLA) with epoxy functional reactive oligomers. It is also shown that a higher functionality and concentration of the reactive oligomers is needed, to bring about a sufficient increase in the molecular weight and hence the hydrolytic stability in circumstances when PLA chains suffer significant degradation during processing. Full article

(This article belongs to the Special Issue Polymers from Biomass)

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660 KiB

Open AccessReview

Does Electrical Conductivity of Linear Polyelectrolytes in Aqueous Solutions Follow the Dynamic Scaling Laws? A Critical Review and a Summary of the Key Relations

by Cesare Cametti

Polymers 2014, 6(4), 1207-1231; https://doi.org/10.3390/polym6041207 - 22 Apr 2014

Cited by 10 | Viewed by 7516

Abstract

In this review, we focus on the electrical conductivity of aqueous polyelectrolyte solutions in the light of the dynamic scaling laws, recently proposed by Dobrynin and Rubinstein, to take into account the polymer conformations in different concentration regimes, both in good and poor [...] Read more.

In this review, we focus on the electrical conductivity of aqueous polyelectrolyte solutions in the light of the dynamic scaling laws, recently proposed by Dobrynin and Rubinstein, to take into account the polymer conformations in different concentration regimes, both in good and poor solvent conditions. This approach allows us to separate contributions due to polymer conformation from those due to the ionic character of the chain, and offers the possibility to extend the validity of the Manning conductivity model to dilute and semidilute regimes. The electrical conductivity in the light of the scaling approach compares reasonably well with the observed values for different polyelectrolytes in aqueous solutions, over an extended concentration range, from the dilute to the semidilute regime. Full article

(This article belongs to the Special Issue Polyelectrolytes 2014)

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655 KiB

Open AccessArticle

Simplified Modeling of Rectangular Concrete Cross-Sections Confined by External FRP Wrapping

by Gian Piero Lignola, Andrea Prota and Gaetano Manfredi

Polymers 2014, 6(4), 1187-1206; https://doi.org/10.3390/polym6041187 - 17 Apr 2014

Cited by 24 | Viewed by 7073

Abstract

The goal of this research project is to model the effect of confinement by means of fiber reinforced polymer (FRP) externally bonded wrapping, hence to provide a simplified closed form solution to determine directly the ultimate confined concrete strength. Common cross-section shapes for [...] Read more.

The goal of this research project is to model the effect of confinement by means of fiber reinforced polymer (FRP) externally bonded wrapping, hence to provide a simplified closed form solution to determine directly the ultimate confined concrete strength. Common cross-section shapes for reinforced concrete (RC) columns are considered herein, namely square and rectangular. The simplified model is derived from a more refined iterative confinement model proposed by the same authors to evaluate the entire stress-strain relationship of confined concrete. Based on a detailed analysis of the stress state through Mohr’s circle, a simplified closed form solution is proposed to account for the non-uniformly confined concrete performance exhibited in non-axisymmetric sections. The non-uniform confining stress field exhibited in such cross-sections is explicitly considered by means of the mean value integral of the pointwise variable stress state over the cross-section. The key aspect of the proposed methodology is the evaluation of the effective equivalent pressure to be inserted in any triaxial confinement model, to account for the peculiarities of square and rectangular cross-sections. Experimental data, available in the literature and representative of a wide stock of applications, were compared to the results of the theoretical simplified model to validate the proposed approach, and satisfactory results were found. Full article

(This article belongs to the Special Issue Selected Papers from "SMAR 2013")

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567 KiB

Open AccessArticle

Chitosan Membranes Exhibiting Shape Memory Capability by the Action of Controlled Hydration

by Cristina O. Correia, Sofia G. Caridade and João F. Mano

Polymers 2014, 6(4), 1178-1186; https://doi.org/10.3390/polym6041178 - 17 Apr 2014

Cited by 20 | Viewed by 7181

Abstract

Chitosan membranes can undergo a glass transition at room temperature triggered by hydration. The mechanical properties of the membranes were followed by a tension test and dynamic mechanical analysis (DMA), with the sample in wet conditions after being immersed in varying compositions of [...] Read more.

Chitosan membranes can undergo a glass transition at room temperature triggered by hydration. The mechanical properties of the membranes were followed by a tension test and dynamic mechanical analysis (DMA), with the sample in wet conditions after being immersed in varying compositions of water/ethanol mixtures. Results show that with the increasing of water content, the Young’s and storage modulus decrease systematically. For water contents of ca. 35 vol%, chitosan (CHT) exhibits a glass transition, showing an elastomeric plateau in the elastic modulus above this hydration level and the occurrence of a peak in the loss factor. Due to the semi-crystalline nature of CHT, membranes of this biomaterial present a shape memory capability induced by water uptake. By fixation of the permanent shape by further covalent cross-linking, the membranes can have different permanent shapes appropriate for different applications, including in the biomedical area. Full article

(This article belongs to the Collection Polysaccharides)

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3546 KiB

Open AccessArticle

On the Interaction of Adherent Cells with Thermoresponsive Polymer Coatings

by Katja Uhlig, Hans G. Boerner, Erik Wischerhoff, Jean-François Lutz, Magnus S. Jaeger, André Laschewsky and Claus Duschl

Polymers 2014, 6(4), 1164-1177; https://doi.org/10.3390/polym6041164 - 15 Apr 2014

Cited by 23 | Viewed by 8861

Abstract

Thermoresponsive polymer coatings allow the control of adhesion of cells on synthetic substrates. In particular, decreasing the temperature below the lower critical solution temperature (LCST) of the polymer triggers the non-invasive detachment of cells from their cultivation substrate. Widening the range of applications [...] Read more.

Thermoresponsive polymer coatings allow the control of adhesion of cells on synthetic substrates. In particular, decreasing the temperature below the lower critical solution temperature (LCST) of the polymer triggers the non-invasive detachment of cells from their cultivation substrate. Widening the range of applications of these coatings in cellular biotechnology requires a better understanding of their interaction with cells. By monitoring the morphological changes of cells during their detachment at various temperatures, we provide evidence that cell detachment is an active process. Analyses of cell residues that are left behind by the cells on the substrate during their detachment, further support this notion. In the second part of this work, we show that the kinetics of adhesion and the efficiency of detachment of cells can be controlled through the coadsorption of molecules bearing the peptide motif RGD (arginine-glycine-aspartic acid) with the polymers. Full article

(This article belongs to the Special Issue Polymer Colloids)

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951 KiB

Open AccessArticle

Some New Concepts of Shape Memory Effect of Polymers

by Abbas Tcharkhtchi, Sofiane Abdallah-Elhirtsi, Kambiz Ebrahimi, Joseph Fitoussi, Mohammadali Shirinbayan and Sedigheh Farzaneh

Polymers 2014, 6(4), 1144-1163; https://doi.org/10.3390/polym6041144 - 11 Apr 2014

Cited by 40 | Viewed by 10462

Abstract

In this study some new concepts regarding certain aspects related to shape memory polymers are presented. A blend of polylactic acid (PLA) (80%) and polybutylene succinate (PBS) (20%) was prepared first by extrusion, then by injection molding to obtain the samples. Tensile, stress-relaxation [...] Read more.

In this study some new concepts regarding certain aspects related to shape memory polymers are presented. A blend of polylactic acid (PLA) (80%) and polybutylene succinate (PBS) (20%) was prepared first by extrusion, then by injection molding to obtain the samples. Tensile, stress-relaxation and recovery tests were performed on these samples at 70 °C. The results indicated that the blend can only regain 24% of its initial shape. It was shown that, this partial shape memory effect could be improved by successive cycles of shape memory tests. After a fourth cycle, the blend is able to regain 82% of its shape. These original results indicated that a polymer without (or with partial) shape memory effect may be transformed into a shape memory polymer without any chemical modification. In this work, we have also shown the relationship between shape memory and property memory effect. Mono and multi-frequency DMA (dynamic mechanical analyzer) tests on virgin and 100% recovered samples of polyurethane (PU) revealed that the polymer at the end of the shape memory tests regains 100% of its initial form without regaining some of its physical properties like glass transition temperature, tensile modulus, heat expansion coefficient and free volume fraction. Shape memory (with and without stress-relaxation) tests were performed on the samples in order to show the role of residual stresses during recovery tests. On the basis of the results we have tried to show the origin of the driving force responsible for shape memory effect. Full article

(This article belongs to the Special Issue Shape-Memory Polymers)

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1071 KiB

Open AccessArticle

Mechanical Analysis of Stress Distribution in a Carbon Fiber-Reinforced Polymer Rod Bonding Anchor

by Peng Feng, Pan Zhang, Xinmiao Meng and Lieping Ye

Polymers 2014, 6(4), 1129-1143; https://doi.org/10.3390/polym6041129 - 11 Apr 2014

Cited by 40 | Viewed by 10793

Abstract

This paper presents an elastic shear stress distribution theoretical model at the carbon fiber-reinforced polymer (CFRP)-adhesive interface of a single-rod and a multi-rod straight-pipe bonding anchor. A comparison between theoretical and finite element analysis results reveals that the accuracy of the theory can [...] Read more.

This paper presents an elastic shear stress distribution theoretical model at the carbon fiber-reinforced polymer (CFRP)-adhesive interface of a single-rod and a multi-rod straight-pipe bonding anchor. A comparison between theoretical and finite element analysis results reveals that the accuracy of the theory can be used to guide the preliminary design of CFRP rod bonding anchors. The mechanical performance of the inner cone bonding anchor for multi-rods are evaluated within different coefficients of friction and inner inclined angles. Numerical results indicate that the straight-parabolic inner cone bonding anchor has a significant effect on reducing the shear force at the loading end. Full article

(This article belongs to the Special Issue Fiber-Reinforced Polymer Composites in Structural Engineering)

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961 KiB

Open AccessArticle

Connexin 43 Gene Therapy Delivered by Polymer-Modified Salmonella in Murine Tumor Models

by Wei-Kuang Wang, Yu-Diao Kuan, Chun-Yu Kuo and Che-Hsin Lee

Polymers 2014, 6(4), 1119-1128; https://doi.org/10.3390/polym6041119 - 11 Apr 2014

Cited by 11 | Viewed by 5900

Abstract

The use of preferentially tumor-targeting bacteria as vectors is one of the most innovative approaches for the treatment of cancer. This method is based on the observation that some obligate or facultative anaerobic bacteria are capable of selectively multiplying in tumors and inhibiting [...] Read more.

The use of preferentially tumor-targeting bacteria as vectors is one of the most innovative approaches for the treatment of cancer. This method is based on the observation that some obligate or facultative anaerobic bacteria are capable of selectively multiplying in tumors and inhibiting their growth. Previously, we found that the tumor-targeting efficiency of Salmonella could be modulated by modifying the immune response to these bacteria by coating them with poly(allylamine hydrochloride) (PAH), and these organisms are designated PAH-S.C. (S. choleraesuis). PAH can provide a useful platform for the chemical modification of Salmonella, perhaps by allowing a therapeutic gene to bind to tumor-targeting Salmonella. This study aimed to investigate the benefits of the use of PAH-S.C. for gene delivery. To evaluate this modulation, the invasion activity and gene transfer of DNA-PAH-S.C. were measured in vitro and in vivo. Treatment with PAH-S.C. carrying a tumor suppressor gene (connexin 43) resulted in inhibition of tumor growth, which suggested that tumor-targeted gene therapy using PAH-S.C. carrying a therapeutic gene could exert antitumor activities. This technique represents a promising strategy for the treatment of tumors. Full article

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1679 KiB

Open AccessArticle

Finite Element Analysis for Fatigue Damage Reduction in Metallic Riveted Bridges Using Pre-Stressed CFRP Plates

by Elyas Ghafoori, Gary S. Prinz, Emmanuel Mayor, Alain Nussbaumer, Masoud Motavalli, Andrin Herwig and Mario Fontana

Polymers 2014, 6(4), 1096-1118; https://doi.org/10.3390/polym6041096 - 11 Apr 2014

Cited by 42 | Viewed by 10273

Abstract

Many old riveted steel bridges remain operational and require retrofit to accommodate ever increasing demands. Complicating retrofit efforts, riveted steel bridges are often considered historical structures where structural modifications that affect the original construction are to be avoided. The presence of rivets along [...] Read more.

Many old riveted steel bridges remain operational and require retrofit to accommodate ever increasing demands. Complicating retrofit efforts, riveted steel bridges are often considered historical structures where structural modifications that affect the original construction are to be avoided. The presence of rivets along with preservation requirements often prevent the use of traditional retrofit methods, such as bonding of fiber reinforced composites, or the addition of supplementary steel elements. In this paper, an un-bonded post-tensioning retrofit method is numerically investigated using existing railway riveted bridge geometry in Switzerland. The finite element (FE) model consists of a global dynamic model for the whole bridge and a more refined sub-model for a riveted joint. The FE model results include dynamic effects from axle loads and are compared with field measurements. Pre-stressed un-bonded carbon fiber reinforced plastic (CFRP) plates will be considered for the strengthening elements. Fatigue critical regions of the bridge are identified, and the effects of the un-bonded post-tensioning method with different pre-stress levels on fatigue susceptibility are explored. With an applied 40% CFRP pre-stress, fatigue damage reductions of more than 87% and 85% are achieved at the longitudinal-to-cross beam connections and cross-beam bottom flanges, respectively. Full article

(This article belongs to the Special Issue Selected Papers from "SMAR 2013")

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973 KiB

Open AccessArticle

Fed-Batch Control and Visualization of Monomer Sequences of Individual ICAR ATRP Gradient Copolymer Chains

by Dagmar R. D'hooge, Paul H. M. Van Steenberge, Marie-Françoise Reyniers and Guy B. Marin

Polymers 2014, 6(4), 1074-1095; https://doi.org/10.3390/polym6041074 - 10 Apr 2014

Cited by 61 | Viewed by 7644

Abstract

Based on kinetic Monte Carlo simulations of the monomer sequences of a representative number of copolymer chains (≈ 150,000), optimal synthesis procedures for linear gradient copolymers are proposed, using bulk Initiators for Continuous Activator Regeneration Atom Transfer Radical Polymerization (ICAR ATRP). Methyl methacrylate [...] Read more.

Based on kinetic Monte Carlo simulations of the monomer sequences of a representative number of copolymer chains (≈ 150,000), optimal synthesis procedures for linear gradient copolymers are proposed, using bulk Initiators for Continuous Activator Regeneration Atom Transfer Radical Polymerization (ICAR ATRP). Methyl methacrylate and n-butyl acrylate are considered as comonomers with CuBr₂/PMDETA (N,N,N′,N′′,N′′-pentamethyldiethylenetriamine) as deactivator at 80 °C. The linear gradient quality is determined in silico using the recently introduced gradient deviation (<GD>) polymer property. Careful selection or fed-batch addition of the conventional radical initiator I₂allows a reduction of the polymerization time with ca. a factor 2 compared to the corresponding batch case, while preserving control over polymer properties (<GD> ≈ 0.30; dispersity ≈ 1.1). Fed-batch addition of not only I₂, but also comonomer and deactivator (50 ppm) under starved conditions yields a <GD> below 0.25 and, hence, an excellent linear gradient quality for the dormant polymer molecules, albeit at the expense of an increase of the overall polymerization time. The excellent control is confirmed by the visualization of the monomer sequences of ca. 1000 copolymer chains. Full article

(This article belongs to the Special Issue Controlled/Living Radical Polymerization)

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1664 KiB

Open AccessReview

Organic Semiconductor/Insulator Polymer Blends for High-Performance Organic Transistors

by Wi Hyoung Lee and Yeong Don Park

Polymers 2014, 6(4), 1057-1073; https://doi.org/10.3390/polym6041057 - 8 Apr 2014

Cited by 80 | Viewed by 21050

Abstract

We reviewed recent advances in high-performance organic field-effect transistors (OFETs) based on organic semiconductor/insulator polymer blends. Fundamental aspects of phase separation in binary blends are discussed with special attention to phase-separated microstructures. Strategies for constructing semiconductor, semiconductor/dielectric, or semiconductor/passivation layers in OFETs by [...] Read more.

We reviewed recent advances in high-performance organic field-effect transistors (OFETs) based on organic semiconductor/insulator polymer blends. Fundamental aspects of phase separation in binary blends are discussed with special attention to phase-separated microstructures. Strategies for constructing semiconductor, semiconductor/dielectric, or semiconductor/passivation layers in OFETs by blending organic semiconductors with an insulating polymer are discussed. Representative studies that utilized such blended films in the following categories are covered: vertical phase-separation, processing additives, embedded semiconductor nanowires. Full article

(This article belongs to the Special Issue Semiconducting Polymers for Organic Electronic Devices)

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440 KiB

Open AccessReview

FRP Composites Strengthening of Concrete Columns under Various Loading Conditions

by Azadeh Parvin and David Brighton

Polymers 2014, 6(4), 1040-1056; https://doi.org/10.3390/polym6041040 - 3 Apr 2014

Cited by 95 | Viewed by 14101

Abstract

This paper provides a review of some of the progress in the area of fiber reinforced polymers (FRP)-strengthening of columns for several loading scenarios including impact load. The addition of FRP materials to upgrade deficiencies or to strengthen structural components can save lives [...] Read more.

This paper provides a review of some of the progress in the area of fiber reinforced polymers (FRP)-strengthening of columns for several loading scenarios including impact load. The addition of FRP materials to upgrade deficiencies or to strengthen structural components can save lives by preventing collapse, reduce the damage to infrastructure, and the need for their costly replacement. The retrofit with FRP materials with desirable properties provides an excellent replacement for traditional materials, such as steel jacket, to strengthen the reinforced concrete structural members. Existing studies have shown that the use of FRP materials restore or improve the column original design strength for possible axial, shear, or flexure and in some cases allow the structure to carry more load than it was designed for. The paper further concludes that there is a need for additional research for the columns under impact loading senarios. The compiled information prepares the ground work for further evaluation of FRP-strengthening of columns that are deficient in design or are in serious need for repair due to additional load or deterioration. Full article

(This article belongs to the Special Issue Selected Papers from "SMAR 2013")

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905 KiB

Open AccessArticle

Strain Rate Effects in CFRP Used For Blast Mitigation

by Sarah. L. Orton, Vincent P. Chiarito, Christopher Rabalais, Matthew Wombacher and Stephen P. Rowell

Polymers 2014, 6(4), 1026-1039; https://doi.org/10.3390/polym6041026 - 3 Apr 2014

Cited by 15 | Viewed by 6937

Abstract

The purpose of this research is to gain a better understanding of strain rate effects in carbon fiber reinforced polymer (CFRP) laminates exposed to blast loading. The use of CFRP offers an attractive option for mitigating structures exposed to blasts. However, the effect [...] Read more.

The purpose of this research is to gain a better understanding of strain rate effects in carbon fiber reinforced polymer (CFRP) laminates exposed to blast loading. The use of CFRP offers an attractive option for mitigating structures exposed to blasts. However, the effect of high strain rates in CFRP composites commonly used in the civil industry is unknown. This research conducted tensile tests of 21 CFRP coupons using a hydraulically powered dynamic loader. The strain rates ranged from 0.0015 s⁻¹ to 7.86 s⁻¹ and are representative of strain rates that CFRP may see in a blast when used to strengthen reinforced concrete structures. The results of the testing showed no increase in the tensile strength or stiffness of the CFRP at the higher strain rates. In addition, the results showed significant scatter in the tensile strengths possibly due to the rate of loading or manufacture of the coupon. Full article

(This article belongs to the Special Issue Fiber-Reinforced Polymer Composites in Structural Engineering)

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641 KiB

Open AccessArticle

Effects of Polybenzoxazine on Shape Memory Properties of Polyurethanes with Amorphous and Crystalline Soft Segments

by Senlong Gu and Sadhan Jana

Polymers 2014, 6(4), 1008-1025; https://doi.org/10.3390/polym6041008 - 1 Apr 2014

Cited by 33 | Viewed by 8728

Abstract

This paper evaluates the role of minor component polybenzoxazine (PB) on shape-memory properties of polyurethanes (PU) with glassy and crystalline soft segments. The polymer compounds were prepared in two steps. In the first step, benzoxazine, polyurethane pre-polymer, and chain extender butanediol (BD) were [...] Read more.

This paper evaluates the role of minor component polybenzoxazine (PB) on shape-memory properties of polyurethanes (PU) with glassy and crystalline soft segments. The polymer compounds were prepared in two steps. In the first step, benzoxazine, polyurethane pre-polymer, and chain extender butanediol (BD) were mixed into a solution followed by chain-extension of the pre-polymer with BD. In the second step, benzoxazine was polymerized at 180 °C for 3 h to obtain shape memory polymer compounds. The atomic force microscopy images revealed that the PB-phase formed uniform dispersions in PU. The presence of PB-phase induced shape-memory behavior in non-shape memory PU with amorphous soft segment and significantly improved the values of shape fixity, recovery ratio, and recovery stress in shape memory polyurethane with crystalline soft segment. Full article

(This article belongs to the Special Issue Shape-Memory Polymers)

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820 KiB

Open AccessArticle

New Guanidine-Pyridine Copper Complexes and Their Application in ATRP

by Alexander Hoffmann, Olga Bienemann, Ines Dos Santos Vieira and Sonja Herres-Pawlis

Polymers 2014, 6(4), 995-1007; https://doi.org/10.3390/polym6040995 - 1 Apr 2014

Cited by 31 | Viewed by 10276

Abstract

The guanidine hybrid ligands, (tetramethylguanidine)methylenepyridine (TMGpy) and (dimethylethyleneguanidine)methylenepyridine (DMEGpy), were proven to be able to stabilize copper complexes active in the solvent-free polymerization of styrene at 110 °C using 1-phenylethylbromide as the initiator. The polymerization proceeded after first-order kinetics, and polystyrenes with polydispersities [...] Read more.

The guanidine hybrid ligands, (tetramethylguanidine)methylenepyridine (TMGpy) and (dimethylethyleneguanidine)methylenepyridine (DMEGpy), were proven to be able to stabilize copper complexes active in the solvent-free polymerization of styrene at 110 °C using 1-phenylethylbromide as the initiator. The polymerization proceeded after first-order kinetics, and polystyrenes with polydispersities around 1.2 could be obtained. Using the ligand, DMEGpy, three new copper guanidine-pyridine complexes could be synthesized and structurally characterized. Their structural characteristics are discussed. Full article

(This article belongs to the Special Issue Controlled/Living Radical Polymerization)

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2053 KiB

Open AccessArticle

Analysis of the Influence of the Fiber Type in Polymer Matrix/Fiber Bond Using Natural Organic Polymer Stabilizer

by Carlos Rivera-Gómez, Carmen Galán-Marín and Fiona Bradley

Polymers 2014, 6(4), 977-994; https://doi.org/10.3390/polym6040977 - 31 Mar 2014

Cited by 42 | Viewed by 11043

Abstract

This research study compares the effect of polypropylene and wool fibers on the mechanical properties of natural polymer based stabilized soils. Biocomposites are becoming increasingly prevalent and this growth is expected to continue within a number of sectors including building materials. The aim [...] Read more.

This research study compares the effect of polypropylene and wool fibers on the mechanical properties of natural polymer based stabilized soils. Biocomposites are becoming increasingly prevalent and this growth is expected to continue within a number of sectors including building materials. The aim of this study was to investigate the influence of different fiber reinforced natural polymer stabilized soils with regards to mechanical properties and fiber adhesion characteristics. The polymer includes alginate, which is used in a wide range of applications but has not been commonly used within engineering and construction applications. In recent years, natural fibers have started to be used as an ecological friendly alternative for soil reinforcement within a variety of construction applications. Test results in this study have compared the effects of adding natural and synthetic fibers to clay soils and discussed the importance of an optimum soil specification. A correlation between the micro structural analysis using scanning electron microscope (SEM), fiber typology, fiber–matrix bonds and the mechanical properties of the stabilized soils is also discussed. Full article

(This article belongs to the Special Issue Natural Polymers 2014)

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2999 KiB

Open AccessArticle

Nonlinear Progressive Damage Analysis of Notched or Bolted Fibre-Reinforced Polymer (FRP) Laminates Based on a Three-Dimensional Strain Failure Criterion

by Yue Liu, Bernd Zwingmann and Mike Schlaich

Polymers 2014, 6(4), 949-976; https://doi.org/10.3390/polym6040949 - 31 Mar 2014

Cited by 11 | Viewed by 8768

Abstract

Notching and bolting are commonly utilised in connecting fibre-reinforced polymer (FRP) laminates. These mechanical methods are usually superior to other connections, particularly when joining thick composite laminates. Stress distributions, damage modes and ultimate strengths in notched or bolted FRP laminate designs are of [...] Read more.

Notching and bolting are commonly utilised in connecting fibre-reinforced polymer (FRP) laminates. These mechanical methods are usually superior to other connections, particularly when joining thick composite laminates. Stress distributions, damage modes and ultimate strengths in notched or bolted FRP laminate designs are of particular interest to the industrial community. To predict the ultimate strengths and the failure processes of notched or bolted composite laminates, nonlinear progressive damage analyses (PDA) based on the finite element method (FEM) at the meso-scale level are performed in this paper. A three-dimensional strength criterion in terms of strains, which can distinguish different damage modes, was developed and adopted in the analysis model to detect damage initiation in the laminates. Different material degradation methods and the influence of cohesive layers were discussed and compared with results of verification experiments. The results showed that the analysis model that used the succinct strength criterion proposed in this paper could properly predict the damage initiation and the ultimate strengths of notched or bolted FRP laminates. The errors between the numerical results and experimental data were small. The material degradation method with continuum damage mechanics (CDM)-based exponential damage factors using the damage index as the independent variable achieved greater accuracy and convergence than the method with CDM-based exponential damage factors using the square index as the independent variable or than the method with constant damage factors. Adding cohesive layers in the model had negligible influence on the final results, largely because the succinct analysis model proposed in this paper is sufficiently accurate in cases of small delamination. Full article

(This article belongs to the Special Issue Selected Papers from "SMAR 2013")

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Polymers, Volume 6, Issue 4 (April 2014) – 17 articles , Pages 949-1250

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