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Multi scale analysis by acoustic emission of damage mechanisms in natural fibre woven fabrics/epoxy composites.  [cached]
Bonnafous C.,Touchard F.,Chocinski-Arnault L.
EPJ Web of Conferences , 2010, DOI: 10.1051/epjconf/20100620009
Abstract: This paper proposes to develop an experimental program to characterize the type and the development of damage in composite with complex microstructure. A multi-scale analysis by acoustic emission has been developed and applied to hemp fibre woven fabrics/epoxy composite. The experimental program consists of tensile tests performed on single yarn, neat epoxy resin and composite materials to identify their AE amplitude signatures. A statistical analysis of AE amplitude signals has been realised and correlated with microscopic observations. Results have enabled to identify three types of damage in composites and their associated AE amplitudes: matrix cracking, interfacial debonding and reinforcement damage and fracture. Tracking of these damage mechanisms in hemp/epoxy composites has been performed to show the process of damage development in natural fibre reinforced composites.
Assessment of cumulative damage by using ultrasonic C-scan on carbon fiber/epoxy composites under thermal cycling
Shiino, Marcos Yutaka;Faria, Maria Candida Magalh?es;Botelho, Edson Cocchieri;Oliveira, Pedro Carlos de;
Materials Research , 2012, DOI: 10.1590/S1516-14392012005000062
Abstract: in recent years, structural composites manufactured by carbon fiber/epoxy laminates have been employed in large scale in aircraft industries. these structures require high strength under severe temperature changes of -56° until 80 °c. regarding this scenario, the aim of this research was to reproduce thermal stress in the laminate plate developed by temperature changes and tracking possible cumulative damages on the laminate using ultrasonic c-scan inspection. the evaluation was based on attenuation signals and the c-scan map of the composite plate. the carbon fiber/epoxy plain weave laminate underwent temperatures of -60° to 80 °c, kept during 10 minutes and repeated for 1000, 2000, 3000 and 4000 times. after 1000 cycles, the specimens were inspected by c-scanning. a few changes in the laminate were observed using the inspection methodology only in specimens cycled 3000 times, or so. according to the found results, the used temperature range did not present enough conditions to cumulative damage in this type of laminate, which is in agreement with the macro - and micromechanical theory.
Fracture of Aramid Fiber/Epoxy Resin Micro Composites
Xia WANG,Chunxin ZHANG,Shijiu JIN,Yunzhao YU,

材料科学技术学报 , 1995,
Abstract: Kevlar-49 fiber was modified through cold air plasma treatment and plasma grafting with acrylic monomers. Fracture of aramid fiber/epoxy resin micro composites has been studied by means of single fiber pull-out test. Tow types of pull-out curves are correlated with the different failure modes. A polyacrylic acid-co-ethyl acrylate graft layer can improve the adhesion and protect the fiber from damage caused by interfacial stresses.
Effects of the Contact Geometry on High Strain Rate Behavior of Woven Graphite/Epoxy Composites  [cached]
Fatih Turan,Mohammad R. Allazadeh,Sylvanus N. Wosu
Journal of Materials Science Research , 2012, DOI: 10.5539/jmsr.v1n1p107
Abstract: Effects of the contact geometry on high strain rate failure behavior of woven graphite/epoxy composites are presented. Compressive split Hopkinson pressure bar was used for high strain rate experiments. Woven graphite/epoxy composites were loaded transversely using two different contact geometries at the impact energies of 67 J and 163 J. It is observed that smaller contact area gives higher damage, resulting in higher energy absorption, elastic modulus and strain rate and peak stress in the specimens.
Mechanical and failure bahaviour in carbon/epoxy composites
Stevanovi? Mom?ilo M.,Sekuli?-Pe?ikan Danijela R.
Hemijska Industrija , 2002, DOI: 10.2298/hemind0209361s
Abstract: A review of the mechanical properties and failure initiation and propagation in carbon/epoxy composites is presented. The results of the study of the macromechanical static characteristics, non-linear elastic behavior flexural modulus and shear properties of unidirectional composites (UDC), as well as, of tensile, compression and flexural moduli, strength analysis edge and hybrid effects in multidirectional composites (MDC) were discussed A discussion of the non-linear elastic behavior of carbon/epoxy UDC, the flexural moduli of both UDC and MDC, strength analysis and edge effects of laminates is emphasized.
Mechanical and Abrasive Wear Behavior of Metal Sulphide Lubricant Filled Epoxy Composites  [PDF]
M. Sudheer,N. Karthik Madhyastha,M. Kewin Amanna,B. Jonthan,K. Mayur Jayaprakash
ISRN Polymer Science , 2013, DOI: 10.1155/2013/242450
Abstract: The present work reveals the effect of the addition of commercial MoS2 (10?wt%) particles on mechanical and two-body abrasive wear behavior of epoxy with/without glass fiber mat reinforcement. The composites were fabricated using casting and simple hand lay-up techniques followed by compression molding. The mechanical properties such as density, hardness, tensile, and flexural properties were determined as per ASTM standards. The abrasive wear testing was carried out using pin-on-disc wear tester for different loads and abrading distances at constant speed of 1?m/s. A significant reduction in wear loss and specific wear rate was noticed after the incorporation of MoS2 filler allowing less wear of matrix during abrasion which in turn facilitated lower fiber damage. However the incorporation of MoS2 particles had a detrimental effect on most of the mechanical properties of the composites. The worn surface features were investigated through scanning electron microscopy (SEM) in order to investigate the wear mechanisms. 1. Introduction In recent times, there has been a remarkable growth in large-scale production of fiber and/or filler-reinforced polymer matrix composites for engineering applications [1]. Among various types of fiber reinforcements, namely, short, long (unidirectionally reinforced UD composites), fabric (bidirectionally reinforced BD composites), and the combinations of fabrics or long fibers in various directions (multidirectionally reinforced), BD reinforcement offers a unique solution to ever increasing demands on advanced materials in terms of better performance and ease in processing. Thermoset epoxy resins are extensively studied as a matrix material as they exhibits low shrinkage, higher mechanical properties, easy fabrication, excellent chemical and moisture resistance, good wettability, and good electrical characteristics [2]. One of the well-known reinforcement for polymers is glass fibers. Glass fibers have very high strength and high stiffness. It has been found that size and volume fraction of the fibers/fillers play an important role to improve the mechanical properties such as stiffness and strength. Polymer composites are extensively used in the tribosituations where resistance to abrasive wear is an extremely important criterion. Typical examples are chute liners, conveyor aids, vanes, gears, for pumps handling industrial fluids, sewage and abrasive contaminated water, and so forth. [3]. Polymers filled with solid lubricant (SL) have been extensively studied because of the increasing industrial and material applications.
On the Behavior of Fiberglass Epoxy Composites under Low Velocity Impact Loading  [PDF]
Gautam S. Chandekar,Bhushan S. Thatte,Ajit D. Kelkar
Advances in Mechanical Engineering , 2010, DOI: 10.1155/2010/621406
Abstract: Response of fiberglass epoxy composite laminates under low velocity impact loading is investigated using LS-DYNA?, and the results are compared with experimental analysis performed using an instrumented impact test setup (Instron dynatup 8250). The composite laminates are manufactured using H-VARTM? process with basket weave E-Glass fabrics. Epon 862 is used as a resin system and Epicure-W as a hardening agent. Composite laminates, with 10 layers of fiberglass fabrics, are modeled using 3D solid elements in a mosaic fashion to represent basket weave pattern. Mechanical properties are calculated by using classical micromechanical theory and assigned to the elements using ORTHOTROPIC ELASTIC material model. The damage occurred since increasing impact energy is incorporated using ADVANCED COMPOSITE DAMAGE material model in LS-DYNA?. Good agreements are obtained with the failure damage results in LS-DYNA? and experimental results. Main considerations for comparison are given to the impact load carrying capacity and the amount of impact energy absorbed by the laminates. 1. Introduction Fiber-reinforced composite materials are extensively used in modern aerospace industry because of their low specific weight with high specific modulus. However out of plane loading, such as impact loading, can cause severe drop in load carrying capacity of these laminates. This drop in load carrying capacity is mainly because of the internal damage of matrix or fiber, which in many times is hard to detect just by visual inspection. In the current work a series of experiments were performed to study the effect of increasing impact energy on fiberglass/epoxy composite laminates in terms of their impact load carrying capacity and impact energy absorption. Fiberglass/epoxy composite laminates are particularly considered as they show superior performance under out of plane loading as opposed to carbon/epoxy laminates, which are strong under in-plane loading. In broad sense the study of low-velocity impact loading on a composite material is divided in three categories, (1) experimental study, (2) analytical study, where a failure model of composite material is proposed, and (3) numerical analysis, mainly using finite element analysis. Numerous experimental research efforts have been carried out to understand the behavior of composites under low velocity impact applications. When the composite laminate is impacted with the foreign object, the impact dynamics in the vicinity of the impact region becomes very complex [1]. Wang et al. [2] in his research paper discussed the low velocity
Effect of Particle Size and Dispersion on Dielectric Properties in ZnO/Epoxy Resin Composites
Wenhu Yang,Ran Yi,Xu Yang,Man Xu
Transactions on Electrical and Electronic Materials , 2012,
Abstract: In this paper, ZnO-Epoxy nanocomposites (NEP) were prepared and epoxy composites that contain 5 wt% microZnO (MEP) and deliberately not well dispersed nano ZnO (NDNEP) were also prepared for purpose of comparison.The effects of the particle size and dispersion of ZnO on dielectric properties of epoxy resin were chiefly studied.Test results showed that: at a loading of 5 wt%, the three epoxy composites seem to have no significant difference onresistivity compared to epoxy resin; Dielectric constants of all the epoxy composites are also basically the same butthey are bigger compared to that of the pure epoxy resin (unfilled); Dielectric dissipation factors (tanδ) of NDNEP isgreater than that of NEP and MEP. NEP has the minimum dielectric loss factor, whereas dielectric loss factors of thethree epoxy composites are larger than that of the pure epoxy resin. The decreasing order of electrical breakdownstrength for the three epoxy composites and for the pure epoxy resin is as follows: NEP>MEP>NDNEP>EP. Finally,in order to explain the experimental results the aggregation interface phase was proposed. Furthermore, addition ofwell dispersed nano filler has proved to have a positive effect on the improvement of the dielectric properties of epoxyresin.
Epoxy resins and low melting point alloy composites  [PDF]
J. Stabik,?. Wierzbicki
Archives of Materials Science and Engineering , 2011,
Abstract: Purpose: The goal of this work was to describe manufacturing process of polymer matrix composite materials reinforced with Wood’s alloy particles and to observe changes of structure.Design/methodology/approach: Polymer matrix composite materials reinforced with the Wood’s alloy particles fabricating method was developed during the investigations, making it possible to obtain materials with good mechanical, electrical and thermal properties . Microscopic examination of samples cross- sections in order to search structure of prepared composite materials was done.Findings: The influence of the processing conditions on structure of Wood’s alloy-epoxy composite was observed using microscopic images.Research limitations/implications: Presented research was limited to composites in the form of thin film.Practical implications: Conducted research programmes concerning these materials show their applications possibilities. Polymer composites with low content of a metallic filler can form materials with high thermal conductivity and mechanical strength higher than polymeric matrix.Originality/value: Polymer composites with metallic, low-melting alloys constitute poorly explored group of polymer composites. Most literature describe composites of low-melting-temperature alloys and thermoplastics matrix. Authors of this paper made an attempt to develop composite with thermosetting matrix. Heating was applied to melt metallic alloy but in this same time to cure epoxy resin.
Time dependent response of a rubber-toughened carbon/epoxy composite with damage accumulation
Soriano, E. de A.;Almeida, S. F. Müller de;
Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2003, DOI: 10.1590/S1678-58782003000200010
Abstract: polymeric composites are frequently modeled as linear elastic materials. however, matrix-dominated properties, such as transverse and shear modulus, can display significant nonlinear time-dependence, especially under conditions of high stress and aggressive environment. this behavior is primarily due to the viscoelastic nature of the polymeric matrix. in addition, polymeric composites also present time-dependent damage growth. in this work, nonlinear viscoelastic constitutive equations were used to represent the time-dependent behavior of a rubber-toughened carbon/epoxy composite during damage growth. these equations were originally devised to characterize material response in a stable damage state. in this approach, however, nonlinearities due to damage and viscoelasticity were incorporated by the model stress-dependent functions, allowing its use in the presence of damage accumulation. a procedure was proposed and applied to separate viscoelastic and damage effects. an experimental program consisting of multiple cycle creep and recovery tests was performed to determine the time-dependence of the shear compliance and to verify the theory as well. the results obtained indicated an excellent agreement between theory and experiment. constant stress rate tests were also used to validate the application of the theory.
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