Showing papers in "Composites Part B-engineering in 2009"

Natural fibre-reinforced composites for bioengineering and environmental engineering applications

Abstract: Recently, the mankind has realized that unless environment is protected, he himself will be threatened by the over consumption of natural resource as well as substantial reduction of fresh air produced in the world Conservation of forests and optimal utilization of agricultural and other renewable resources like solar and wind energies, and recently, tidal energy have become important topics worldwide In such concern, the use of renewable resources such as plant and animal based fibre-reinforce polymeric composites, has been becoming an important design criterion for designing and manufacturing components for all industrial products Research on biodegradable polymeric composites, can contribute for green and safe environment to some extent In the biomedical and bioengineered field, the use of natural fibre mixed with biodegradable and bioresorbable polymers can produce joints and bone fixtures to alleviate pain for patients In this paper, a comprehensive review on different kinds of natural fibre composites will be given Their potential in future development of different kinds of engineering and domestic products will also be discussed in detail

Characterization of treated date palm tree fiber as composite reinforcement

Abstract: Recently, great interest was paid to new technologies dealing with environmental aspect. Preservation of natural resources such as natural fibers forced the composite industry to search and examine “eco-friendly” components. Studies to find alternative reinforcements and resin systems that are environmentally friendly while providing the same performance as their synthetic counterparts are in continuous progress. The aim of this study is to investigate effect of different treatment process on the data palm fiber (DPF). Raw DPF underwent different surface modification methods such as alkali treatment with concentrations 0.5%, 1%, 1.5%, 2.5% and 5%, and acid treatment with 0.3, 0.9 and 1.6 N. All treatments were performed at 100 °C for 1 h. The surface morphology, thermal gravimetry analysis (TGA), Fourier transform infrared spectroscopy (FTIR), mechanical properties and chemical analysis, of treated DPF were investigated. Specimen treated with 1% NaOH showed optimum mechanical properties. Hydrochloric acid treatment resulted in deterioration in mechanical properties.

Experimental study of bond behaviour between concrete and FRP bars using a pull-out test

Abstract: This paper presents the results of an experimental programme concerning 88 concrete pull-out specimens prepared according to ACI 440.3R-04 and CSA S806-02 standards. Rebars (reinforcing bars) made of carbon-fibre and glass-fibre reinforced polymer (CFRP and GFRP), as well as steel rebars, with a constant embedment length of five times the rebar diameter were used. The influence of the rebar surface, rebar diameter and concrete strength on the bond–slip curves obtained is analysed. In addition, analytical models suggested in the literature are used to describe the ascending branch of the bond–slip curves. To calibrate the analytical models, new equations that account for the dependence on rebar diameter are presented.

Effect of glass fiber hybridization on properties of sisal fiber–polypropylene composites

Abstract: Natural fiber reinforced polymer composites became more attractive due to their light weight, high specific strength, and environmental concern. However, some limitations such as low modulus, poor moisture resistance were reported. This study aimed to investigate the effect of glass fiber hybridization on the physical properties of sisal–polypropylene composites. Polypropylene grafted with maleic anhydride (PP-g-MA) was used as a compatibilizer to enhance the compatibility between the fibers and polypropylene. Incorporating glass fiber into the sisal–polypropylene composites enhanced tensile, flexural, and impact strength without having significant effect on tensile and flexural moduli. In addition, adding glass fiber improved thermal properties and water resistance of the composites.

Mechanical and thermal properties of chicken feather fiber/PLA green composites

Abstract: Chicken feather fiber (CFF)/reinforced poly(lactic acid) (PLA) composites were processed using a twin-screw extruder and an injection molder. The tensile moduli of CFF/PLA composites with different CFF content (2, 5, 8 and 10 wt%) were found to be higher than that of pure PLA, and a maximum value of 4.2 GPa ( 16 % ↑ ) was attained with 5 wt% of CFF without causing any substantial weight increment. The morphology, evaluated by scanning electron microscopy (SEM), indicated that an uniform dispersion of CFF in the PLA matrix existed. The mechanical and thermal properties of pure PLA and CFF/PLA composites were compared using dynamic mechanical analysis (DMA), thermomechanical analysis (TMA) and thermogravimetric analysis (TGA). DMA results revealed that the storage modulus of the composites increased with respect to the pure polymer, whereas the mechanical loss factor (tan δ ) decreased. The results of TGA experiments indicated that the addition of CFF enhanced the thermal stability of the composites as compared to pure PLA. The outcome obtained from this study is believed to assist the development of environmentally-friendly composites from biodegradable polymers, especially for converting agricultural waste – chicken feather into useful products.

Micromechanics of spatially uniform heterogeneous media: A critical review and emerging approaches

Abstract: Outside of the classical microstructural detail-free estimates of effective moduli, micromechanical analyses of macroscopically uniform heterogeneous media may be grouped into two categories based on different geometric representations of material microstructure. Analysis of periodic materials is based on the repeating unit cell (RUC) concept and the associated periodic boundary conditions. This contrasts with analysis of statistically homogeneous materials based on the representative volume element (RVE) concept and the associated homogeneous boundary conditions. In this paper, using the above classification framework we provide a critical review of the various micromechanical approaches that had evolved along different paths, and outline recent emerging trends. We begin with the basic framework for the solution of micromechanics problems independent of microstructural representation, and then clarify the often confused RVE and RUC concepts. Next, we describe classical models, including the available RVE-based models, and critically examine their limitations. This is followed by discussion of models based on the concept of microstructural periodicity. In the final part, two recent unit cell-based models, which continue to evolve, are outlined. First, a homogenization technique called finite-volume direct averaging micromechanics theory is presented as a viable and easily implemented alternative to the mainstream finite-element based asymptotic homogenization of unit cells. The recent incorporation of parametric mapping into this approach has made it competitive with the finite-element method. Then, the latest work based on locally-exact solutions of unit cell problems is described. In this approach, the interior unit cell problem is solved exactly using the elasticity approach. The exterior problem is tackled with a new variational principle that successfully overcomes the non-separable nature of the overall unit cell problem.

Effect of surface treatment on performance of pineapple leaf fiber–polycarbonate composites

Abstract: This research is to study the properties of pineapple leaf fiber reinforced polycarbonate composites (PC/PALF). Surface of pineapple leaf fiber (PALF) was pre-treated with sodium hydroxide (PALF/NaOH) and modified with two different functionalities such as γ -aminopropyl trimethoxy silane (PALF/Z-6011) and γ -methacryloxy propyl trimethoxy silane (PALF/Z-6030). The effects of PALF content and chemical treatment were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy and mechanical testing. The modified pineapple leaf fibers composite also produces enhanced mechanical properties. Young’s modulus is the highest in the case of the PALF/NaOH composites. The PALF/Z-6011 composites showed the highest tensile strength and impact strength. In thermal property, the results from thermogravimetric analysis showed that thermal stability of the composites is lower than that of neat polycarbonate resin and thermal stability decreased with increasing pineapple leaf fiber content.

Effect of volume fraction and wall thickness on the elastic properties of hollow particle filled composites

Abstract: Hollow particle filled composites, called syntactic foams, are widely used in applications requiring high damage tolerance and low density. The understanding of the mechanics of these materials is largely based on experimental studies. Predictive models that are capable of estimating the elastic properties of these materials over wide variation of particle wall thickness, size, and volume fraction are not yet fully developed. The present study is focused on developing a modeling scheme to estimate the elastic constants for such materials. The elastic properties of an infinitely dilute dispersion of microballoons in a matrix material are first computed by solving a dilatation and a shear problem. A differential scheme is then used to extrapolate the elastic properties of composites with high volume fractions of microballoons. The results show that the model is successful in predicting the Young’s modulus for syntactic foams containing microballoons of a wide range of wall thickness and volume fraction.

Modelling the tensile fracture behaviour of CFRP scarf repairs

Abstract: An experimental and numerical study concerning the tensile behaviour of adhesively-bonded carbon–epoxy scarf repairs is presented, using scarf angles ranging from 2° to 45°. A mixed-mode cohesive damage model adequate for ductile adhesives was used to simulate the adhesive layer. The cohesive laws of the adhesive layer, composite interlaminar and composite intralaminar (in the transverse and fibre directions) in pure modes I and II, necessary to simulate numerically the experimental failure paths, were previously characterized using an inverse method. Validation of this methodology was accomplished in terms of repair initial stiffness, maximum load and the corresponding displacement, as well as the failure mode. A good agreement between the numerical predictions and the experiments showed that the proposed methodology can be successfully applied to joints or repairs bonded with ductile adhesives.

Effect of elevated service temperature on bond between FRP EBR systems and concrete

Abstract: The method to increase the ultimate capacity of reinforced concrete elements, by means of Fiber Reinforced Polymers bonded on their substrate with thermosetting resins, represents a technique useable worldwide. The bonding materials used, generally epoxy resins, are sensitive to a temperature increase. In fact, the curing process of epoxies leads to low glass transition temperature (Tg) values, that may cause a relevant decay of the mechanical properties of the adhesive, even under service thermal conditions. The reduction can influence the bond performance, compromising the effectiveness of the reinforcing technique. In this work the interface behaviour FRP–concrete at elevated service temperatures is analyzed. The experimental results show a relevant influence of the temperature on bond performance, in terms of type of failure of the interface, effective bond length and bond strength.

Hygrothermal effects on high VF pultruded unidirectional carbon/epoxy composites: Moisture uptake

Abstract: Moisture uptake and desorption response of a high fiber volume fraction pultruded carbon/epoxy composite is studied through immersion of specimens in deionized water at three temperatures It is seen that uptake response is best characterized by a two-stage model indicating an initial diffusion based response followed by a relaxation and deterioration based response Desorption and short-term resorption responses are Fickian in nature and show the clear effect of prior history The ratios of longitudinal to transverse diffusivity of desorption indicate a decrease with increasing level of initial temperature of immersion in deionized water These values are significantly higher than those listed in the literature for lower fiber volume fraction composites, and are attributed to the high levels of fiber loading, with local areas of fiber-to-fiber contact Viscoelastic characterization through dynamic mechanical thermal analysis clearly differentiates between plasticization and further network/interface deterioration based phenomena

Mechanical properties and flammability of sisal/PP composites: Effect of flame retardant type and content

Abstract: In this research, magnesium hydroxide (Mg(OH) 2 ) and zinc borate, as flame retardants, were incorporated into sisal/PP composites. Maleic anhydride grafted polypropylene was also used as a compatibilizer. Adding flame retardants into sisal/PP composites reduced burning rate and increased thermal stability of the composites. No synergistic effect was observed when both magnesium hydroxide and zinc borate were incorporated in the sisal/PP composites. In addition, the sisal/PP composites exhibited insignificant difference of shear viscosity at high shear rate indicating that types of flame retardants used in this study had no impact on the processability of the composites. Good distribution of flame retardants and sisal fiber in PP matrix was also observed. All PP composites had lower impact strength than the neat PP. However, the sisal/PP composites with the addition of Mg(OH) 2 and zinc borate exhibited comparable tensile and flexural properties to the sisal/PP composites without adding those flame retardants. Therefore, the addition of Mg(OH) 2 and zinc borate enhanced flame retardancy of sisal/PP composites without sacrificing their mechanical properties.

Materials and mechanical properties of pretreated coir-based green composites

Abstract: Chemical composition modification and surface modification of coir fibers are made in view of their use as reinforcement in coir-based green composites. Composites were prepared using coir fiber treated with varying pretreatment condition. The changes in the proportion of chemical composition and morphological properties of coir fibers with different coir pretreatment condition were discussed. It is observed that the mechanical properties of coir-based green composites; modulus of rupture and internal bond, increase as a result of chemical composition modification and surface modification. Scanning electron microscopy (SEM) investigations show that surface modifications improve the fiber/matrix adhesion.

The effect of hybridization on the GFRP behavior under high velocity impact

Abstract: In the present study, experimental and analytical investigations for the behavior of E-glass fiber reinforced composite hybridized with a layer of Kevlar 29 fiber, under high velocity impact, were performed. The experimental work includes the placement of the Kevlar layer at four different locations to verify the effects of the stacking sequence on the impact behavior. Three different projectile geometries, namely, flat-ended, hemispherical and conical were used. The experimental results reveal that hybridization improves the laminates performance under dynamic penetration. The results also indicate that the laminates response was found to be highly sensitive to the projectile geometry. In the case of analytical modeling, two energy models were conducted to calculate the projectile residual velocities. The results obtained from the two models were compared with those obtained experimentally and some conclusions were drawn.

Design optimization of functionally graded dental implant for bone remodeling

Abstract: Despite a great success, one of the key issues facing in dental implantation clinic is a mismatch of mechanical properties between engineered and native biomaterials, which makes osseointegration and bone remodeling problematical. Functionally Graded Material (FGM) has been proposed as a potential upgrade to some conventional implant materials like titanium for selection in prosthetic dentistry. The idea of FGM dental implant is that the property would vary in a certain pattern to match the biomechanical characteristics required at different regions in the hosting bone. However, mating properties do not necessarily guarantee the best osseointegration and bone remodeling. No existing report has been available to develop an optimal design of FGM dental implant for promoting a long-term success. This paper aims to explore this critical issue by using the computational bone remodeling and design optimization. A buccal–lingual sectional model, which consists of a single unit implant and four other adjacent teeth, was constructed from computerized tomography (CT) scan images. Bone remodeling induced by use of various FGM dental implants is calculated over the period of 4 years. Based upon remodeling results, response surface method (RSM) is adopted to develop a multi-objective optimal design for FGM implantation FGM designs.

Fiber path definitions for elastically tailored conical shells

Abstract: Elastic stiffness tailoring of laminated composite panels by allowing the fibers to curve within the plane of the laminae has proven to be beneficial and practical for flat rectangular plate designs. In this paper the field of application of this variable-stiffness concept is extended to three-dimensional conical shells with arbitrary dimensions that can be fabricated using advanced fiber placement machines. This paper presents the detailed derivation of four theoretical fiber path definitions for generalized conical shell surfaces. The different path definitions and resulting laminate geometries are discussed. Implementation of fabrication details and constraints in terms of the steering radius of curvature based on advanced tow-placement technology are demonstrated.

Bio-nano reinforcement of environmentally degradable polymer matrix by cellulose whiskers from grass

Abstract: Cellulose nanofiber reinforced composite exhibits remarkable improvement in properties of many polymer matrixes at low filler concentration. Grass of Korea was treated with acid, and cellulose whiskers (∼ 10 – 60 nm thickness) were extracted after mechanical treatment. The composites were fabricated with poly (lactic acid) in presence of compatibilizer. Comparison of cellulose modification on the structure and properties was carried out by monitoring the functional group variation, thermal behavior, surface morphology, and crystallinity through FT-IR, TGA, SEM, and XRD, respectively. It was found that cellulose whiskers have lower thermal stability than alkali treated long fiber whereas the crystalline nature of composites decreased significantly with concentration of filler.

Multi-step blended stacking sequence design of panel assemblies with buckling constraints

Abstract: In this paper, we propose a multi-step framework for design of composite panel assemblies and subsequent blending of the designs to ensure laminate continuity across multi-panel configurations. Multilevel optimisation is frequently used for solving complex optimisation problems. In composite design this approach leads to stacking sequence mismatch among adjacent structural components which is generally referred to as blending problem. To overcome stacking sequence mismatch, a guide-based genetic algorithm (GA) is used which in essence forces the design to be completely blended at any step in the design process. A serious drawback of guide based approach is that it necessitates repeated analysis of the entire structure within the GA iterations. A multi-step framework is proposed where the structure is first optimised using panel thickness and lamination parameters as continuous design variables. The continuous optimisation is performed using a successive convex approximation scheme. In the second step, discrete blended stacking sequences are obtained using a guide-based genetic algorithm. The fitness function in the guide-based GA is evaluated using convex approximations of the response. In this fashion, the cost of evaluating structural response within the GA optimisation is eliminated. The proposed framework is demonstrated via design of an eighteen panel horseshoe configuration, where each panel is optimised individually subject to a local buckling constraint. Numerical results indicate that the present algorithm is capable of producing near-optimal fully blended designs at a small fraction of the computational cost of traditional blending algorithms.

Mechanical repair of timber beams fractured in flexure using bonded-in reinforcements

Abstract: The flexural properties of strength class C16 spruce beams have been compared to the flexural properties of the same beams repaired with bonded-in reinforcements in the form of steel or composite pultruded rods. Reinforcing materials included rectangular sections of mild steel, pultruded carbon fibre reinforced plastic (CFRP), glass fibre reinforced plastic (GFRP) and a thermoplastic matrix glass fibre reinforced polyurethane (FULCRUM). Grooves were routed into the faces of the fractured beams following straightening and the reinforcements adhesively bonded into the top, bottom or both faces of the beams. The steel and CFRP reinforcements are most effective in restoring the flexural strength which often exceeds its original value. These reinforcements are also effective in enhancing flexural strength but the CFRP reinforcement endows the greatest transformed flexural strength. The fracture mechanisms in the repaired beams depend on the placement of reinforcement and the quality of the adhesive to reinforcement bond. All properties are optimised by bonding reinforcement into both faces of the fractured beams.

An experimental investigation on the bearing failure load of glass fibre/epoxy laminates

Abstract: This paper deals with an experimental investigation on the bearing failure load of glass fibre/epoxy (GFRP) laminates. The effects of fibre-to-load inclination angle and laminate stacking sequence on the bearing load capacity have been determined experimentally on two different type of laminates: unidirectional and bi-directional (cross-ply). Significant reductions in bearing failure load when fibre inclination angle increases are highlighted. Bearing design formulas are also proposed based on the results of the experiments.

Optimization of laminated composites considering different failure criteria

Abstract: The purpose of the present work is to analyse how different the optimal structures are when different first ply failure criterion are considered in the optimization of laminated composites. Two problems are solved: the minimum weight and the minimum material cost of laminated plates subjected to in-plane loads. The failure criterion is taken into account by means of constraints introduced in the optimization problem. Three different failure criteria are tested independently: maximum stress, Tsai–Wu and the Puck failure criterion (PFC). Emphasis is given to the PFC as it appears to agree better with practical observations. The design variables are the ply orientations, the number of layers and the layer material, and the optimization problem is solved by a genetic algorithm (GA). The results show that optimal structures highly differ when different failure criterion are considered and that none of the failure criteria is always the most or the least conservative when different load conditions are applied.

Swelling behavior of polyacrylamide/laponite clay nanocomposite hydrogels: pH-sensitive property

Abstract: In this study, an investigation is carried out on the influence of varying clay contents (25–43%), pH values (2–11 buffer solutions), heat treatment, temperatures (25–60 °C) and ionic strengths (saline solution, 10−7–0.1 M) on the water absorbency of polyacrylamide (PAAm)/laponite nanocomposite (NC) hydrogels in the absence of polyelectrolyte. For the influence of pH value on swelling behaviors, a maximum swelling ratio occurs at pH 11. Heat treatment of the hydrogels significantly improved the swelling capacity and created an obvious pH sensitive area (pH 3–4). The swelling capacity of the hydrogels was enhanced by increasing the temperature of the absorbing media. The results of swelling at different ionic strengths also indicate that the ionic strength can considerably weaken the swelling abilities of the NC hydrogels.

Novel nanocellulosic xylan composite film

Abstract: Nanocellulosic-xylan films were prepared employing oat spelt xylan, cellulose whiskers and a plasticizer. The mechanical properties of the films were evaluated using tensile testing under controlled temperature and humidity conditions. The tensile data showed that the addition of sulfonated cellulose whiskers lead to a substantial improvement in strength properties. Addition of 7 wt% of sulfonated whiskers increased the tensile energy absorption of xylan films by 445% and the tensile strength of the film by 141%. Furthermore, films to which 7% cellulose whiskers were added showed that nanocellulose whiskers produced with sulfuric acid (sulfonated whiskers) were significantly better at increasing film strength than cellulose whiskers produced by hydrochloric acid hydrolysis of cellulosic fibers. (C) 2009 Elsevier Ltd. All rights reserved.

Positive temperature coefficient characteristic and structure of graphite nanofibers reinforced high density polyethylene/carbon black nanocomposites

Abstract: Graphite nanofibers (GNF) and carbon black (CB) filled high density polyethylene (HDPE) hybrid composites were fabricated using a melt mixing method. The effects of the CB and GNF content on the room temperature resistivity and positive temperature coefficient (PTC) behavior of the nanocomposites were examined. The room temperature resistivity of the composites decreased significantly with increasing GNF content, but this was not always the case with the PTC intensity. The incorporation of a small amount of GNF into the HDPE/CB composites significantly improved the PTC intensity and reproducibility of the hybrid nanocomposites. The maximum PTC effect, whose log intensity was approximately 7.2, was observed in the HDPE/CB/GNF (80/20/0.25 wt%) nanocomposite with relatively low room temperature resistivity. The mechanism for the effects of GNF in HDPE/CB/GNF hybrid composites were examined using differential scanning calorimetry, transmission scanning electron microscopy and X-ray diffraction.

Buckling of functionally graded and elastically restrained non-uniform columns

Abstract: Columns with non-uniform distribution of geometrical or material parameters i.e. functionally graded material distribution, varying cross-sectional area and flexural stiffness provide an economical solution to carry the desired higher compressive loads in engineering structures. In this paper, a low-dimensional mathematical model is presented, which is capable of computing the buckling loads of uniform and non-uniform functionally graded columns in the axial direction. The columns with spatial variation of flexural stiffness, due to material grading and/or non-uniform shape, are approximated by an equivalent column with piecewise constant geometrical and material properties. Such a formulation leads to certain transcendental eigenvalue problems where the matrix elements are transcendental functions. This model is further extended in analyzing some uniform and non-uniform elastically restrained or braced axially graded columns with equal or unequal spans. The mathematical modeling, closed-form transcendental functions and numerical solution technique are described and several examples of estimating buckling loads for various boundary configurations are presented. Some of the results are also validated against available solutions, representing the convergence, effectiveness, accuracy and versatility of the proposed modeling and numerical method. Formulation of such low-dimensional eigenvalue problems can also be extended for analyzing, designing and optimizing the static and dynamic behavior of structural components that are made of functionally graded materials.

Improvement of impact property of natural fiber–polypropylene composite by using natural rubber and EPDM rubber

Abstract: In this research, vetiver grass was used as a filler in polypropylene (PP) composite. Chemical treatment was done to modify fiber surface. Natural rubber (NR) and Ethylene Propylene Diene Monomer (EPDM) rubber at various contents were used as an impact modifier for the composites. The composites were prepared by using an injection molding. Rheological, morphological and mechanical properties of PP and PP composites with and without NR or EPDM were studied. Adding NR or EPDM to PP composites, a significant increase in the impact strength and elongation at break is observed in the PP composite with rubber content more than 20% by weight. However, the tensile strength and Young’s modulus of the PP composites decrease with increasing rubber contents. Nevertheless, the tensile strength and Young’s modulus of the composites with rubber contents up to 10% are still higher than those of PP. Moreover, comparisons between NR and EPDM rubber on the mechanical properties of the PP composites were elucidated. The PP composites with EPDM rubber show slightly higher tensile strength and impact strength than the PP composites with NR.

A unit cell approach of finite element calculation of ballistic impact damage of 3-D orthogonal woven composite

Abstract: This paper presents ballistic impact damages of 3-D orthogonal woven composite in finite element analysis (FEA) and experimental. A unit-cell model of the 3-D woven composite was developed to define the material behavior and failure evolution. A user-defined subroutine VUAMT was compiled and connected with commercial available FEA code ABAQUS/Explicit to calculate the ballistic penetration. Ballistic impact tests were conducted to investigate impact damage of 3-D kevlar/glass hybrid woven composite. Residual velocities of conically-cylindrical steel projectiles (Type 56 in China Military Standard) and impact damage of the composite targets after ballistic perforation were compared both in theoretical and experimental. The reasonable agreements between FEA results and experimental results prove the validity of the unit-cell model in ballistic limit prediction of the 3-D woven composite. We believe such an effort could be extended to bulletproof armor design with the 3-D woven composite.

Damage modes in 3D glass fiber epoxy woven composites under high rate of impact loading

Abstract: A qualitative analysis of experimental results from small caliber ballistic impact and dynamic indentation on a 3D glass fiber reinforced composite are presented. Microscopic analysis of the damaged specimens revealed that the current 3D weaving scheme creates inherently two weak planes which act as potential sites for delamination in the above experiments. It is concluded that while the z-yarns may be effective in limiting the delamination damage at low loads and at low rates of impact, at high loads and high loading rates delamination continues to be the dominant failure mode in 3D woven composites. It is shown that dynamic indentation can be used to capture the progression of damage during impact of 3D woven composites.

Numerical simulation of delamination in laminated composite components – A combination of a strength criterion and fracture mechanics

Abstract: An approach for the numerical treatment of delamination in laminated composite components is presented. A first ply failure criterion is employed to predict delamination initiation, while delamination propagation is analyzed using linear elastic fracture mechanics. The combination of initiation and propagation criteria yields a conservative estimation of the load earring capacity of a structure. Furthermore, the growth stability, the sensitivity of the results with respect to a change in the interface properties, and the non-linear structural response caused by the delamination growth process are determined. Two structures are investigated, which show the capability of the proposed approach, a curved laminate and a double lap shear test specimen.

Effect of chemical blowing agent on cell structure and mechanical properties of EPDM foam, and peel strength and thermal conductivity of wood/NR composite–EPDM foam laminates

Abstract: Melt-laminates of wood/natural rubber (wood/NR) composite and ethylene-propylene diene rubber (EPDM) foam were prepared by compression molding technique. Two different forms of 4,4′oxybis(benzenesulfonylhydrazide) (OBSH) blowing agent were used; pure OBSH (designated as OBSH) and ethylene-propylene bound OBSH (designated as EPR–b-OBSH). The effect of the OBSH concentration on the cell structures and mechanical properties of EPDM foam, and the peel strength and thermal conductivity of wood/NR composite–foamed EPDM laminates was examined. It was found that the EPR–b-OBSH gave EPDM foam with greater number of cell structures, higher porosities and resistances to water penetration on the foam surface. However, the EPDM with EPR–b-OBSH agent had worse elastic recovery as compared to that with OBSH due to deformation of cell structures after prolonged compression loading. The recommended concentrations for EPR–b-OBSH and OBSH blowing agents were 3.0 and 5.0 phr, respectively, for the optimum interfacial adhesion and low thermal conductivity.