Novel polymer-ceramic composites for protection against ballistic fragments

For the first time, internally reinforced aggregate polymer ceramic composites were evaluated against fragment simulating projectiles (FSPs) of various calibers to investigate their ballistic impact response. Samples were prepared by mechanically mixing B4C and cBN over a range of ratios and combinations with either thermosetting phenolic or epoxy resin and aramid pulp. Dry mixtures were then molded in a closed die using a heated platen press. The resulting tiles were then mounted as ‘‘strike faces’’ to an aramid backing material using an epoxy resin. Backed targets were tested in a fully instrumented firing range against 5.56 mm FSPs to test ballistic limit. A further series of tests using 7.62, 12.5, and 20 mm FSPs was conducted to examine round deformation across a range of fragments calibers. Round deformations were measured after impact and plotted against shot velocity. It was found that the polymer ceramic composite materials were effective round deformers and, like sintered ceramic strike faces, demonstrated improved ballistic performance at an equivalent areal density and impressive multihit capability.

Polymer-ceramic ion-conducting composites

Composites of a Li⁺ ion-conducting ceramic powder in a polyether-based elastomeric electrolyte matrix are described. At 66 wt.% of ceramic the composite can be prepared as a paste and cured into a coherent material having useful elastic and tensile properties. The total conductivity of the composite was found to be (1.9 ± 0.2) × 10⁻⁴ S cm⁻¹ at 40 °C which was approximately 1 order of magnitude higher than the polymer electrolyte component alone. The result was also approximately 1 order of magnitude higher than the total conductivity of the ceramic powders tested in this work.

Prestressed natural fibre spun yarn reinforced polymer-matrix composites

Abstract We report that a prestressing technique similar to that traditionally used in prestressed concrete can improve the mechanical performance of flax fibre spun yarn reinforced polymer-matrix composites. Prestressing a low twist yarn not only introduces tension to the constituent fibres and compressive stress to the matrix similar as in prestressed concretes, but also causes changes to the yarn structure that lead to the rearrangement of fibres within the yarn. Prestressing increases the fibre packing density in yarn, causes fibre straightening, and reduces fibre obliquity in yarn (improved fibre alignment along yarn axis). All these changes contribute positively to the mechanical properties of the natural fibre yarn reinforced composites. Crown

Flax yarn polymer matrix composites: effects of yarn structure and prestressing

 This research focuses on the improvement of mechanical properties of plant fibre based bio-composites using different yarns structures and prestressing technique. Different types of yarns were used to study the effect of structural parameters and prestressing on different properties of the resulting bio-composites.

A simple and effective method to ameliorate the interfacial properties of cellulosic fibre based bio-composites using poly (ethylene glycol) based amphiphiles

In order to overcome interfacial incompatibility issues in natural fibre reinforced polymer bio-composites, surface modifications of the natural fibres using complex and environmentally unfriendly chemical methods is necessary. In this paper, we demonstrate that the interfacial properties of cellulose-based bio-composites can be tailored through surface adsorption of polyethylene glycol (PEG) based amphiphilic block copolymers using a greener alternative methodology. Mixtures of water or water/acetone were used to form amphiphilic emulsions or micro-crystal suspensions of PEG based amphiphilic block copolymers, and their deposition from solution onto the cellulosic substrate was carried out by simple dip-coating. The findings of this study evidence that, by tuning the amphiphilicity and the type of building blocks attached to the PEG unit, the flexural and dynamic thermo-mechanical properties of cellulose-based bio-composites comprised of either polylactide (PLA) or high density polyethylene (HDPE) as a matrix, can be remarkably enhanced. The trends, largely driven by interfacial effects, can be ascribed to the combined action of the hydrophilic and hydrophobic components of these amphiphiles. The nature of the interactions formed across the fibre-matrix interface is discussed. The collective outcome from this study provides a technological template to significantly improve the performance of cellulose-based bio-composite materials.

Effects of micro-structural parameters on mechanical properties of carbon nanotube polymer nanocomposites

A comparison between the elastic modulus of carbon nanotube (CNT) polymer nano composites predicted by classical micromechanics theories, based on continuum mechanics and experimental data, was made and the results revealed a great difference. To improve the accuracy of these models, a new two-step semi-analytical method was developed, which allowed consideration of the effect of the interphase, in addition to CNT and matrix, in the modeling of nanocomposites. Based on this developed method, the inuence of microstructural parameters, such as CNT volume fraction, CNT aspect ratio, partial and complete agglomerations of CNTs, and overlap and exfoliation of CNTs, on the overall elastic modulus of nanocomposites was investigated. ©2014 Sharif University of Technology. All rights reserved.

Student opportunities in materials design and manufacture: Introducing a new manufacturing with composites course

The shift towards strong and lightweight fibre reinforced polymer-matrix composites for many high performance applications has resulted in an increasing need to expose students to composite design and manufacture courses in the undergraduate curriculum. In contrast, student exposure to composite materials is often still limited to a topic within a materials or manufacturing related course (unit). This paper presents the initial offering of a composite materials elective at Griffith University in Australia. The course also addresses environmental concerns through the inclusion of natural fibre composites. An evaluation of student perceptions is considered from Griffith’s Student Experience of Course (SEC) and separate Student Experience of Teaching (SET) surveys. These evaluations demonstrate the high level of student engagement with the course, but also highlighted areas for improvement, including the need to incorporate even more hands-on practical work. Interestingly, the inclusion of natural fibre composites and the related discussion surrounding environmental and societal issues are not focused on in student feedback.

Miscibility, UV resistance, thermal degradation, and mechanical properties of PMMA/SAN blends and their composites with MWCNTs

Poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) (PMMA/SAN) blends, with varying concentrations, were prepared by melt-mixing technique. The miscibility is ensured by fixing the acrylonitrile (AN) content of styrene acrylonitrile (SAN) as 25% by weight. The blends were transparent as well. The Fourier transform infrared spectroscopic (FTIR) studies did not reveal any specific interactions, supporting the well accepted 'copolymer repulsion effect' as the driving mechanism for miscibility. Addition of SAN increased the stability of PMMA towards ultraviolet (UV) radiations and thermal degradation. Incorporation of even 0.05% by weight of multi-walled carbon nanotubes (MWCNTs) significantly improved the UV absorbance and thermal stability. Moreover, the composites exhibited good strength and modulus. However, at higher concentrations of MWCNTs (0.5 and 1% by weight) the thermo-mechanical properties experienced deterioration, mainly due to the agglomeration of MWCNTs. It was observed that composites with 0.05% by weight of finely dispersed and well distributed MWCNTs provided excellent protection in most extreme climatic conditions. Thus, PMMA/SAN/MWCNTs composites can act as excellent light screens and may be useful, as cost-effective UV absorbers, in the outdoor applications.

Crack damage in polymers and composites: a review

Polymer-based materials are extensively used in various applications such as aircrafts, civilian structures, oil and gas platforms and electronics. They are, however, inherently damage prone and over time, the formation of cracks and microscopic damages influences the thermo-mechanical and electrical properties, which eventually results in the total failure of the materials. This paper provides an overview of the principal causes of cracking in polymer and composites and summarizes the recent progress in the development of non-destructive techniques in crack detection. Furthermore, recent progress in the development of bio-inspired self-healing methods in autonomic repair is discussed.

One-step amino-functionalization of milled carbon fibre for enhancement of thermo-physical properties of epoxy composites

Development of new chemical approaches for preparation of engineered carbon-based fillers is critical for high-performance applications. Herein, an efficient method for covalent functionalization of polyacrylonitrile-based carbon fibre through azo radical addition under mild condition is demonstrated. In this way, isobutyronitrile radicals in situ produced from thermal decomposition of 2,2′-azobisisobutyronitrile (AIBN), were covalently grafted on milled carbon fibre (MCF) surface, assisted by microwave irradiation, as evidenced by FTIR, Raman, and TGA analysis. The grafted isobutyronitriles on MCF surface (n-MCF) were applied for further MCF amino-functionalization (a-MCF) via nucleophilic reaction of an amine-rich compound. Then, both pure MCF and a-MCF were incorporated into epoxy matrix; and its curing process and thermo-physical properties were investigated using DSC, rheometry, DMA, TGA, and flexural analysis. The Tg and flexural strength of epoxy/a-MCF composites, compared to epoxy/MCF, increased by ∼3.5% and ∼10.2%, resulting from good adhesion between a-MCF and epoxy matrix which confirmed by SEM observations.

Rapidly cured epoxy/anhydride composites: effect of residual stress on laminate shear strength

The drive towards rapid cure thermosetting composites requires a better understanding of the residual stresses that develop during curing. This study investigates the impact of residual stresses on the interlaminar shear strength of resin-infused epoxy/anhydride carbon-fibre laminates. The magnitude of the residual stress was varied by changing the initial injection cure temperature between 75 °C and 145 °C. The corresponding cycle times and the final glass transition temperature of the resin were also measured. The experimentally measured chemical shrinkage and thermal expansion properties of the resin after vitrification were used as inputs to a finite element analysis to calculate the peak residual stresses in the composite. An increase in the initial cure temperature from 85 to 135 °C resulted in an increase of 25% in the residual stress, which led to an experimentally measured reduction in the composite's short beam shear strength of approximately 16% (8 MPa), in good agreement with model prediction.

固化条件对热塑增韧环氧树脂的固化动力学和相分离的影响

Thermoplastic toughened epoxy resins are widely used as matrices in modern prepreg systems.Different curing conditions play a great role in affecting the cure kinetics and phase behaviour of thermoplastic modified epoxies which further result in different mechanical properties of polymer matrix composites.Since the morphology of the cured thermoplastic/epoxy blends is directly related to the mechanical properties,it is essential to control processing conditions for obtaining desirable morphology.A polyethersulphone (PES) modified multifunctional epoxies,triglycidylaminophenol (TGAP) and tetraglycidyldiaminodiphenylmethane (TGDDM),was used for investigation.The cure kinetics and cured morphology of polymer blends heated at different heating rates and cured at different temperature were studied.It is shown that higher cure temperature and higher heating rate display similar effects in the epoxy conversion and the domain size of phase separated structure.

A comparative assessment of austempered ductile iron as a substitute in weight reduction applications

Manufacturing engineering has had to undergo drastic changes in the approach to material selection in order to meet new design challenges. In the automotive industry, researchers in their effort to reduce emissions and satisfy environmental regulations, have shifted their focus to new emerging materials such as high-strength aluminium alloys, metal matrix composites, plastics, polymers and of late, Austempered Ductile Iron (ADI). ADI is a good choice for design where the criterion is high performance at reduced weight and cost. The unique, ausferrite microstructure gives the material desirable material properties and an edge over other materials. A comparative study of ADI in terms of materials properties and machining characteristics with other materials is desirable to highlight the potential of the material. This paper focuses on a comparative assessment of material and machining characteristics of ADI for different applications. The properties under consideration are machinability, weight and cost savings and versatility. ADI has a higher strength-to-weight ratio than aluminium making it a ready alternative for material selection. In terms of machinability, there are some problems associated with machining of ADI due to its work hardening nature. This paper attempts to identify the possible potential applications of ADI, by critically reviewing specific applications such as machinability, overall economics and service.