Reinforced Polymer Composite Materials Research Articles

Flexural strengthening of RC beams using natural sisal and artificial carbon and glass fabric reinforced composite system

Sisal fabric reinforced polymer composite system was developed and its tensile and flexural behaviour was characterized and compared with that of carbon and glass fabric reinforced polymer composite. In the present work the efficacy of sisal fabric reinforced polymer composite (SFRP) was compared to carbon fabric reinforced polymer composite (CFRP) and glass fabric reinforced polymer composite (GFRP), by utilizing all the fabric composites for the flexural strengthening of reinforced concrete (RC) beams. The work carried out includes the study of failure modes, flexural strengthening effect on ultimate load carrying capacity and load deflection behaviour of RC beams bonded externally with SFRP, CFRP and GFRP, wrapped as U wraps in single layer, along entire length of the beam in two different wrapping techniques, i.e. full wrapping and strip wrapping technique. SFRC strengthening of RC beams showed good increase in its flexural strength and improvement in load deflection behaviour similar to CFRP and GFRP strengthening. The RC beam strengthened by SFRC showed highest amount of ductility, and also delayed the formation of cracks, without rupture failure of FRP as in the case of CFRP strengthened beams and also without debonding failure of FRP as in the case of GFRP strengthened beams. Therefore sisal fabric reinforced polymer composite system, with its various environmental benefits, being a natural fibre, could be used as alternate fabric reinforcement in FRP, for flexural strengthening of RC beams effectively.

Effect of TiO2 and ZnS Fillers on the Bending Characteristics of GFRP Composites under Varied Flaw Configurations

In the present work an attempt has been made in order to investigate the bending strength and flextural strength of the TiO2 and ZnS filled Glass Fabric Reinforced Polymer (GFRP) composites. The volume fractions in the matrix were chosen as 1, 2 and 3%. The effect of notch orientation on interlaminar and translaminar bending characteristics has been evaluated and Bending strength has been evaluated for specimens with edge cracks with varied crack lengths. The results have showed that, the addition of filler up to 2 vol% has increased the strength of the composite and ZnS as filler is preferred over TiO2.

Multi-scale mechanics of smart material systems and structures

During the last few decades, active composites have been in the focus of intense technological and fundamental researches from industry and academia, respectively. Besides, the wide use of passive composites in transport vehicles and infrastructures led to their functionalisation for their monitoring and control. Good candidates for related sensing, actuation or transduction functions are the so-called smart materials, such as piezoelectric materials, shape memory alloys or polymers, electroor magneto-strictive materials, electroor magnetorheological fluids and electro-active polymers. With the help of integrated control algorithms and processing devices, passive material systems and structures become smart; therefore, due to their multi-physical and multi-disciplinary nature, their multi-scale modelling and simulation are still not yet fully mastered. Hence, in order to reach robust designs of these advanced smart material systems and structures, special fundamental and applied research efforts are still required in order to reach: (i) materials multi-physical effective properties complete and reliable data sets; (ii) efficient multi-scale models and local/global solutions; (iii) mastering integrity and reliability critical issues for wider and safer applications. This focused issue of Acta Mechanica presents six revised, from ten peer-reviewed, manuscripts that were extended after their selection from the twelve contributions presented in two sessions at the Mini-Symposium MS27 on Multi-scale Mechanics of Smart Material Systems and Structures, co-organised by the present guest editors during the 8th European Solid Mechanics Conference held at Graz (Austria) on 9–13 July 2012. These six papers focused on one or more of the above mentioned research issues of Multi-scale Mechanics of Smart Material Systems and Structures; in particular, Micro-mechanics-based numerical homogenisations of magneto-electro-rheological particle and piezoelectric fibre reinforced polymer composite material systems, local (section)-global (structural) analytical models and solutions for the piezoelectric d15 shear-induced torsion actuation and sensing problems, multi-scale fatigue life analyses of polymer encapsulated piezoceramic transducers, and behaviour and response nonlinearities analyses for healthy and cracked piezoelectric transducers at room or cryogenic temperatures. It is hoped that this focused issue contributes to the progress of this topic state-of-the-art and serves the research needs of the Acta Mechanica readers. As a closure, we would like to thank the authors, for their high quality contributions; the reviewers, for their constructive expertises; and the Editor-in-Chief, Professor Hans Irschik, for letting us the entire freedom of this issue management and his editorial administration team for the great help in managing anonymously the managing guest editor’s co-authored contributions.

Damage and fracture in fabric-reinforced composites under quasi-static and dynamic bending

Fabric-reinforced polymer composites used in sports products can be exposed to different in-service conditions such as large deformations caused by quasi-static and dynamic loading. Composite materials subjected to such bending loads can demonstrate various damage modes – matrix cracking, delamination and, ultimately, fabric fracture. Damage evolution in composites affects both their in-service properties and performance that can deteriorate with time. Such behaviour needs adequate means of analysis and investigation, the main approaches being experimental characterisation and non-destructive examination of internal damage in composite laminates. This research deals with a deformation behaviour and damage in carbon fabric-reinforced polymer (CFRP) laminates caused by quasi-static and dynamic bending. Experimental tests were carried out to characterise the behaviour of a CFRP material under large-deflection bending, first in quasi-static and then in dynamic conditions. Izod-type impact bending tests were performed on un-notched specimens of CFRP using a Resil impactor to assess the transient response and energy absorbing capability of the material. X-ray micro computed tomography (micro-CT) was used to analyse various damage modes in the tested specimens. X-ray tomographs revealed that through-thickness matrix cracking, inter-ply and intra-ply delamination such as tow debonding, and fabric fracture were the prominent damage modes both in quasi-static and dynamic test specimens. However, the inter-ply damage was localised at impact location in dynamically tested specimens, whereas in the quasi-static specimens, it spread almost over the entire interface.

Metal Triflates as Catalytic Curing Agents in Self‐Healing Fibre Reinforced Polymer Composite Materials

A self‐healing, high performance, fibre reinforced polymer (FRP) composite material is demonstrated by employing a Lewis acid‐catalysed epoxy self‐healing agent (SHA) within a laminate manufactured using existing industrial methods. Thermal cure analysis and mechanical testing is employed to characterise the self‐healed polymer. A bio‐inspired series of vascules incorporated into an FRP composite material facilitates the delivery of SHAs to exposed fractured crack planes. Healing is effected by ring‐opening polymerisation (ROP) of an epoxy resin using novel metal triflate catalysts injected after Mode I crack opening displacement. Strong adhesive compatibility with the host matrix confers full recovery of mechanical properties (>99% healing).

Scattering Matrix Approach to Informing Damage Monitoring and Prognosis in Composite Bolted Connections

Structural health monitoring refers to the process of making an assessment, based on nondestructive, in-situ, autonomous measurements, about the ability of a structure to perform its intended function. This paper presents work done on a bolted connection in carbon-fiber reinforced polymer composite materials. A composite specimen is bolted in a double lap joint configuration to a test apparatus that applies an increasing tensile load. Ultimately, the load results in bearing failure of the material around the bolt hole. To monitor the progression of damage, macro fiber composite sensors are bonded in a circular array around the bolt hole. These sensors are then used to generate ultrasonic guided waves, a popular technique in nondestructive evaluation because of the favorable combination of propagation distance and sensitivity to damage. As the specimen is subjected to increasing load levels, measurements are taken repeatedly and compared with one another. Because damage will change the local mechanical properties of the material, the ultrasonic waves passing through the damaged region will be scattered differently in each direction, resulting in a different waveform arriving at the other surrounding sensors. By applying appropriate signal processing techniques, these changes may be interpreted as indicating the extent of damage that has occurred in the specimen. Preliminary analysis is presented demonstrating the correlation between changes in received strain signals and increasing damage levels.

A multiaxial fatigue damage model for fibre reinforced polymer composites

A multiaxial fatigue damage model for fibre reinforced polymer composite materials is presented. The model combines (i) fatigue-induced fibre strength and modulus degradation, (ii) irrecoverable cyclic strain effects and (iii) inter-fibre fatigue. The inter-fibre fatigue aspect is based on a fatigue-modified version of the Puck multiaxial failure criterion for static failure. The model is implemented in a user material finite element subroutine and calibrated against fatigue test data for unidirectional glass fibre epoxy. A programme of uniaxial fatigue tests on quasi-isotropic glass fibre epoxy laminates is presented for validation of the novel fatigue damage methodology. The latter is successfully validated across a range of stress levels.

Sustainable waste recycling solution for the glass fibre reinforced polymer composite materials industry

In this paper the adequacy and the benefit of incorporating glass fibre reinforced polymer (GFRP) waste materials into polyester based mortars, as sand aggregates and filler replacements, are assessed. Different weight contents of mechanically recycled GFRP wastes with two particle size grades are included in the formulation of new materials. In all formulations, a polyester resin matrix was modified with a silane coupling agent in order to improve binder-aggregates interfaces. The added value of the recycling solution was assessed by means of both flexural and compressive strengths of GFRP admixed mortars with regard to those of the unmodified polymer mortars. Planning of experiments and data treatment were performed by means of full factorial design and through appropriate statistical tools based on analyses of variance (ANOVA).Results show that the partial replacement of sand aggregates by either type of GFRP recyclates improves the mechanical performance of resultant polymer mortars. In the case of trial formulations modified with the coarser waste mix, the best results are achieved with 8% waste weight content, while for fine waste based polymer mortars, 4% in weight of waste content leads to the higher increases on mechanical strengths.This study clearly identifies a promising waste management solution for GFRP waste materials by developing a cost-effective end-use application for the recyclates, thus contributing to a more sustainable fibre-reinforced polymer composites industry.

Characterisation of the friction and wear behaviour of textile reinforced polymer composites in contact with diamond-like carbon layers

The tribological behaviour of composites, particularly in contact with steel, is to be estimated as relatively weak. As a promising improvement, the application of modern coatings is considered. In this context, the results of frictional and wear investigations of carbon fibre reinforced epoxy and polyethersulfone as well as glass fibre reinforced polypropylene composites in contact with coated and uncoated steel 100Cr6 are presented. The coating consists of diamond-like carbon (ta-C) layer. A remarkable outcome of the study is the substantial decrease of the specific wear rate of the investigated material pairings by the application of carbon coated metal. The tribological system, which is responsible for the excellent tribological characteristics, is determined by predominantly sliding wear and suppressed abrasive wear.

Investigation on the Turning Parameters for Surface Roughness using Taguchi Analysis

One of the important interests in the machining is attaining better surface roughness as well as dimensional accuracy. Polymer materials are continuously displacing the conventional materials. Their machining behavior is different in many aspects from machining of conventional metallic materials. Polymer based composite materials have superior properties for mechanical strength and stiffness, such as high strength-to-weight ratio and high stiffness-to-weight ratio. Fiber reinforced polymer composite materials are the one which are produced closer to the required shape, further machining is often necessary to achieve expected surface characteristics. This experimental study targets the machining of carbon fiber reinforced polymer material made into the form of tube. It examines various process parameters such as cutting speed, feed and depth of cut and their importance in deciding the surface roughness. Surface roughness was measured after machining is carried out under specified machining conditions. This experimental study focuses on the prediction of machining parameters that yield better surface characteristics in order to avoid machining of hard materials such as fiber reinforced composite materials so that enormous money spent in machining could be saved to some extent. For prediction this experimental study makes use of response surface methodology. The Taguchi method is used to solve many engineering problems. This work uses the Taguchi's orthogonal array method to find out the number of experiments to be carried out for turning operations. Also the analysis of variance is used to investigate the cutting parameters. In addition to the optimal cutting parameters for turning operations, the main cutting parameter that affect the cutting performance in turning operations could be found out.

Cutting Characteristics of Titanium Graphite Composite by Wire Electrical Discharge Machining

To improve strength to weight ratios, the fiber reinforced polymer composite materials are often used in conjunction with another material, like metals, to form hybrid structure. This paper reports the feasibility of using wire electrical discharge machining (WEDM) for cutting Titanium/Graphite Hybrid Composites (TiGr). Slit and slot cuts with WEDM process has been performed. Cutting times and process parameters were recorded, and cut surface characteristics were evaluated both with an optical and scanning electron microscopy (SEM). The results in terms of cutting time, workpiece material removal rate, and damage were presented and discussed. It was found that use of WEDM is possible for machining advanced hybrid metal composite laminates with appropriate machine settings.

Evaluation of Delamination in Drilling Rice Husk Reinforced Polyester Composites

Delamination is recognized as one of the most critical defects that can result from the machining composites. Delamination has been a major form of failure in drilled composite materials due to the composites lack of strength in the drilling direction, which results in poor surface finish, reduction in bearing strength, reduction in structural integrity and ultimately poor performance of the composite. Currently, most of the major research reported delamination address specific of machining fiber glass, graphite fiber or carbon fiber reinforced polymer composites. It is not yet clear how different drilling parameters affect the machinability of natural fiber reinforced polymer composite materials and quality of drilled holes. This paper report the investigation in drilling holes on natural fibre reinforced polyester composites and evaluate its hole quality by measuring delamination. Three different type of drill: twist 118o drill, brad drill and end mill were used. Drilling process is carried out for three spindle speed (1500 rpm, 2000 rpm and 2500 rpm) and three feed rate (0.1 mm/rev, 0.15 mm/rev and 0.2 mm/rev). Brad drill experienced higher delamination values compared to twist and end mill. Increasing of feed rate and spindle speed also caused a relevant increase in the delamination values. It is found that Rice husk reinforced polyester composites delamination value is lower when compared to the glass fiber reinforced polymer.

High-speed terahertz reflection three-dimensional imaging for nondestructive evaluation

We demonstrate high-speed terahertz (THz) reflection three-dimensional (3D) imaging based on electronically controlled optical sampling (ECOPS). ECOPS enables scanning of an axial range of 9 mm in free space at 1 kHz. It takes 80 s to scan a transverse range of 100 mm × 100 mm along a zigzag trajectory that consists of 200 lines using translation stages. To show applicability of the imaging system to nondestructive evaluation, a THz reflection 3D image of an artificially made sample is obtained, which is made of glass fiber reinforced polymer composite material and has defects such as delamination and inclusion, and is compared with an ultrasonic reflection 3D image of the sample.

Damage in woven CFRP laminates subjected to low velocity impacts

Carbon fabric-reinforced polymer (CFRP) composites used in sports products can be exposed to different in-service conditions such as large dynamic bending deformations caused by impact loading. Composite materials subjected to such loads demonstrate various damage modes such as matrix cracking, delamination and, ultimately, fabric fracture. Damage evolution in these materials affects both their in-service properties and performance that can deteriorate with time. These processes need adequate means of analysis and investigation, the major approaches being experimental characterisation and non-destructive examination of internal damage in composite laminates. This research deals with a deformation behaviour and damage in woven composite laminates due to low-velocity dynamic out-of-plane bending. Experimental tests are carried out to characterise the behaviour of such laminates under large-deflection dynamic bending in un-notched specimens in Izod tests using a Resil Impactor. A series of low-velocity impact tests is carried out at various levels of impact energy to assess the energy absorbed and force-time response of CFRP laminates. X-ray micro computed tomography (micro-CT) is used to investigate material damage modes in the impacted specimens. X-ray tomographs revealed that through-thickness matrix cracking, inter-ply delamination and intra-ply delamination, such as tow debonding and fabric fracture, were the prominent damage modes.

Analysis of Vibration Measurements in a Composite Material Using an Embedded PM-PCF Polarimetric Sensor and an FBG Sensor

Low frequency vibration measurements in composite materials using embedded optical fiber sensors are presented in this paper. The two types of fiber sensors embedded are a polarization maintaining photonic crystal fiber (PM-PCF) polarimetric fiber sensor and a fiber Bragg grating (FBG) sensor. A glass fibre reinforced polymer composite material sample is fabricated with both fiber optic sensors embedded in it. A comparison between the performance of both the PM-PCF polarimetric fiber sensor and the FBG sensor embedded in the composite material is also presented.

Human Health Impact as a Boundary Selection Criterion in the Life Cycle Assessment of Pultruded Fiber Reinforced Polymer Composite Materials

SummaryThe human health impact of fiber reinforced polymer (FRP) composite materials manufactured by the pultrusion industry is not fully understood. In particular, it is unclear whether the human health impact of toxic chemicals present in low concentrations in fire retardant pultruded FRP materials is disproportionately high. This impact may be an important criterion when making boundary selection decisions in the life cycle assessment (LCA) of these materials. The North American pultrusion industry was surveyed to determine resin mix concentration levels and workplace inhalation toxicity exposure levels. LCAs were then conducted on three building panel resin mixes to determine whether the human health impact of toxic chemicals used in the mixes was low enough to exclude the chemicals from the life cycle inventory (LCI) boundary. The first resin mix represented a typical pultruded product, the second mix removed toxic chemicals present in small concentrations, and the third mix replaced toxic chemicals present in small concentrations with a nontoxic chemical. Results showed that toxicity levels fell below exposure limits and no significant difference in human health impact existed among the LCAs. The research concludes that human health impact is a useful criterion when defining an LCI boundary. Toxic chemicals present in small concentrations in pultruded FRP materials may be excluded from the LCI boundary, as their human health impacts are low. Because these levels are marginal in North American pultrusion factories, no changes in resin mixes are recommended for the pultrusion industry.

Microscopic and Macroscopic Electromagnetic and Thermal Modeling of Carbon Fiber Reinforced Polymer Composites

An electromagnetic and thermal model of carbon fiber reinforced polymer composite material is introduced. This model takes into account the influence of different fiber orientations on the electromagnetic parameters. These parameters are defined in microscopic scale and introduced in finite-element-method model in macroscopic scale.

Evaluation of static and fatigue strength of long fiber GRP composite material considering moisture effects

The paper presents results of a partial experimental programme of evaluation of static mechanical and fatigue properties of long glass-fiber reinforced polymer composite material with a multiaxial orientation of glass fibers to be used for a manufacture of the flywheel hub disc, the main component of the storage unit accumulating kinetic energy of a vehicle during braking for further use during acceleration. Though humidity is not supposed to be an issue in operation of the unit, an experimental programme evaluating the material static strength and durability under combination of static load with vibration component was carried out to complete the overall general material characterisation. Study of an effect of absorbed moisture was a part of the experimental work. Water absorption was a long-term process, without saturation even after several months. Degradation of strength and fatigue properties due to the absorbed distilled water was confirmed for this material. The material sensitivity on vibration component of the load, even with quite low amplitude of 10% of the static load was ascertained. Damage accumulation and continuous stiffness reduction during fatigue tests , which rate was connected with final durability, was an important phenomenon.

Effects of carbon fiber surface treatment on the friction and wear behavior of 2D woven carbon fabric/phenolic composites

To improve the friction and wear behavior of carbon fabric reinforced polymer composites (CFRP), nano-SiO 2 was deposited on the fabric surface. The friction and wear behavior of the resulting composites were investigated on a model ring-on-block test rig. Experimental results revealed that fiber surface treatment contributed to largely improve the tribological properties of the CFRP composites. Scanning electron microscope (SEM) investigation showed that the worn surface of the surface modified CFRP composite was smoother under given load and sliding rate. Field emission scanning electron microscopy (FESEM), FTIR and X-ray photoelectron spectroscopy (XPS) studies of the carbon fiber surface showed that nanostructured Sio 2 thin film can be obtained by SiO 2 sols deposition, which improved the adhesion between the fiber and phenolic matrix and hence to improve the friction-reduction and anti-wear properties of the CFRP composite.

Modeling the variable amplitude fatigue of composite materials: A review and evaluation of the state of the art for spectrum loading

In this article, we review the experimental research and modeling of fiber reinforced polymer composite materials subjected to variable amplitude fatigue. In general, these models are empirical or phenomenological and contain parameters that must be determined using constant, and in some cases variable, amplitude fatigue data for the material system in question. In many cases, the authors who proposed these models simply fit them to their experimental variable amplitude results and thus their predictive ability has remained uncertain. The predictive accuracy of the fatigue models examined in this article was compared by applying them to four material systems for which extensive fatigue data was available. Several approaches are rejected because the data required to fit them are not available or their formulation prevents straightforward application to a spectrum loading with blocks of one cycle in length. Four damage accumulation rules and eight residual strength approaches are fit to the static, constant amplitude fatigue, residual strength, and two block repeated fatigue loading for each data set. Then the models are used to predict the fatigue life under variations of WISPER, WISPERX, and Rayleigh distributed spectrum fatigue loads that were applied experimentally. Results show that the Palmgren–Miner rule is non-conservative in every case and gains in accuracy are possible by using a simple residual strength law such as the one proposed by Broutman and Sahu. More complex residual strength approaches gave more accurate results in some cases, but overall did not provide a significant improvement relative to Broutman and Sahu’s model.