Fiber Reinforced Epoxy Laminates Research Articles

Effect of the loading rate on mode I interlaminar fracture toughness of laminated composites

The objective of the present study is to determine the influence of the loading rate on the critical energy release rate G Ic of fibre-reinforced epoxy laminates. In order to perform pure mode I loading at higher opening velocities, a new test device is developed. The approach is based on a symmetrical opening displacement applied to a DCB specimen. In the data reduction, the influence of the kinetic energy has to be taken into account. The results obtained on the unidirectional carbon–epoxy laminate T300/914 at crack opening rates up to 1.6 m/s show a slight effect of the loading rate on G Ic.

Ballistic Penetration of Compressively Loaded Composite Plates

The effects of ballistic penetration on woven E-glass fiber-reinforced epoxy laminates subjected simultaneously to in-plane compressive loading were investigated. A portable hydraulic press and fixture was designed to apply compressive preloads during ballistic penetration. A civilian version of the US Army ’s M4 carbine was used for the ballistic tests where penetration velocities were well above the ballistic limit for 5.56 mm projectiles. Compression-only data were initially obtained to characterize the various modes of damage. Samples without simultaneous compressive preload were subjected to ballistic penetration alone and then compressively loaded to failure. Finally, samples that had previously undergone ballistic testing at varying levels of compressive preloads were loaded in compression to determine the residual compressive failure strength. For simultaneous loading, samples were subjected to a specified compressive preload while a projectile was fired through the center of the sample. This study finds that the effect of simultaneous preload and ballistic penetration results in a greater extent of damage propagation than for ballistic penetration alone, increasing the possibility of initiating buckling failure of the loaded plate. The equivalent ballistic limit velocity for a given laminate and thickness is also likely to be reduced with increasing preload in composite laminates.

An Investigation on Woven-glass Fiber-reinforced Epoxy Laminate Conveyor Chain Components

This article is concerned with the experimental and numerical results of the stress analysis in woven-glass fiber-reinforced conveying chain components. The effects of various loading conditions on the stress of a pin-loaded composite component are investigated. For the experimental study, an apparatus had been developed to simulate chain components in real motion, and two different loading conditions of the chain component have been investigated. The first condition represents the movement of the chain components without loading, while in the second condition, the chain component tand moves the load. The finite element code ANSYS has been used to perform the numerical analysis using three-dimensional eight-noded layered structural solid elements. The chain tensile forces loaded through pins are chosen to be 300, 600, 900, and 1200 N for the two conditions of the chain components. Comparisons are made between the numerical and the experimental studies for the two different conditions. The experimental and numerical results show that at the second loading condition the stress values increase by increasing the tensile force.

Performance of integrated active fiber composites in fiber reinforced epoxy laminates

Active fiber composite (AFC) composed of lead zirconate titanate (PZT) fibers withinterdigitated electrodes (IDEs) has been integrated into orthotropic glass fiber reinforcedplastic (GFRP) laminates to characterize the performance of AFC as a smart materialcomponent in laminated materials. Monotonic cyclic tensile loading was performed onintegrated specimens at different strain levels. The AFC output was monitored todetermine the effect of applied strain level on the AFC performance. It was found that theAFC sensitivity degraded beyond strains of 0.20% and approached a minimum at 0.50%strain. The degradation in the AFC performance appears to be attributed tothe dominating effect of PZT fiber fragmentation during testing, as opposed todepolarization. Acoustic emission (AE) monitoring was used to detect damage inlaminates during testing and was correlated with crack evidence from microscopyobservations during testing to characterize damage evolution in response to strain levels.

The effect of thermal spiking on moisture absorption, mechanical and viscoelastic properties of carbon fibre reinforced epoxy laminates

Moisture absorption by carbon fibre reinforced epoxy laminates may result in a reduction in mechanical properties and a lower maximum service temperature. Thermal cycling of a laminate coupled with a humid environment, often encountered by military jet aircraft components, results in a higher concentration of absorbed moisture. The effect of moisture absorption as a result of thermal spiking on the mechanical properties of the three composite systems Narmco Rigidite 5245C, Fibredux 927 and Fibredux 924 has been studied. Maximum moisture enhancement occurred at a spike temperature of 140 and 160 °C. For the 5245C laminates, thermal spiking and resultant increased moisture absorption resulted in a reduction in transverse flexural strength relative to un-spiked control specimens. Transverse flexural stiffness was unaffected by thermal spiking in all three systems.

Delamination of laminated composites under the combined effect of nonuniform heating and absorbed moisture

During service exposure, composite structures may be subjected to local heating under which three-dimensional temperature gradients may develop with temperature differences that can exceed 150°C. The different thermal expansion that is associated with such temperature gradients can generate a range of thermal stresses such as compressive thermal stresses around the periphery of the heated zone, leading potentially to delamination. In this article the combined effects of nonuniform heating and moisture in glass- and carbon fiber-reinforced epoxy laminates are presented, detailing the results of the effect of moisture on the mechanical properties, the simulation experiments of nonuniform heating including in situ measurement of temperatures and strains, and a schematic model of the observed delamination by bulging. The main conclusion is that delamination damage in a form of bulging occurs only in the presence of a threshold level of moisture of about 1 wt%. This threshold level corresponds to the critical moisture content found to produce major mechanical property reduction and interlamina separation. The proposed mechanism comprises a chain of consequences induced by moisture, wherein chemical degradation of the interlamina hot region is followed by mechanical interlamina separation and bulging caused by steam pressure. POLYM. COMPOS., 26:770–777, 2005. © 2005 Society of Plastics Engineers

Stress analysis of pin-loaded woven-glass fiber reinforced epoxy laminate conveying chain components

The aim of this study is to examine the effects of various loading conditions on the stress of a pin-loaded woven-glass fiber reinforced epoxy laminate conveying chain component. A numerical and experimental study was carried out to determine the stress distribution of composite conveying chain components used to convey loads. For the experimental study, an apparatus was developed to simulate chain components in real motion. Two different working conditions of the chain component were investigated. The first condition represents the movement of the chain components without loading. In the second condition, the chain component touches and moves the load. The commercial finite element package ANSYS was used to perform the numerical analysis using a three dimensional eight-noded layered structural solid elements. Chain tensile forces were loaded through pins and chosen as 250, 500, 750, 1000 and 1250 N for the two conditions of chain components. Experimental and numerical studies were compared and discussed for two conditions and five different tensile forces. A good agreement between experimental results and numerical predictions is obtained.

Scaling of Structural Strength

Scaling of Structural Strength

Static behavior of CFRPs at low temperatures

Abstract This paper summarizes the results of the tests to determine the effect of the low temperature on the mechanical behavior of carbon fiber reinforced epoxy laminates. Tensile and bending static tests were carried out on two laminate lay-ups (quasi-isotropic and cross-ply laminates), determining properties such as the mechanical strength, stiffness and strain to failure. The results show the changes in the mechanical behavior of this material at different test temperatures (20, −60 and −150 °C).

Bearing stiffness of glass fibre-reinforced polyester: influence of coupon geometry and laminate properties

The bearing stress–strain response of glass fibre-reinforced polyester (GRP) laminates in a single-bolt double lap joint was investigated experimentally and numerically. Six GRP laminate types were tested according to the ASTM D5961 procedures for three coupon geometries. A 2-D finite element model that included material non-linearity, clearance and bolt–hole friction predicted the bearing stiffness very accurately. However, both numerical and experimental data disagreed with existing joint flexibility models developed for metals or carbon fibre-reinforced epoxy laminates with tight fitting bolts. Clearly, some adaptation of the joint flexibility formulae is needed when they are used for design of GRP structures with large bolt–hole clearance. On average, joints with a reduced width ( w/ D=2) were 26% more compliant than three times wider standard joints ( w/ D=6). Doubling the end distance had a smaller effect on the bearing stiffness. Laminates with more axial reinforcement had a clearly higher bearing stiffness for the small coupon width ( w/ D=2). For wider coupons ( w/ D=6), this trend became less apparent.

Laser processing for microelectronics packaging applications

The microelectronics industry is moving toward smaller feature sizes. The main driving forces are to improve performance and to lower cost. From the performance point of view the small distances between chips together with the short interconnection routes have of great importance in order to achieve faster operation. Laser processing applied for via generation, direct pattern processing, image transfer, contour cutting, trimming, etc. has proved to be efficient method for making rapid progress in this direction. On the other hand, smaller spaces between conductive patterns increase the risk of short circuits (caused by pattern faults, solder bridges, migration, etc.), that emphasizes the reliability aspects of applied process technologies. The paper describes the results of research projects that aimed at the application of CO 2 and frequency-multiplied Nd:YAG lasers for drilling and direct patterning of copper clad glass fiber reinforced epoxy laminates, polyester foils and a couple of other structures. The physics of processing using five wavelengths, i.e. 10 600, 1064, 532, 355 and 266 nm, were modeled, examined and evaluated. Laser processing was combined with other – mainly metal coating – processes, e.g. the through contacting of the generated vias were carried out by screen printing with polymer thick films, by wet chemical direct plating and by evaporation of thin metal layers, but the details of metallization are not given here. The conclusion summarizes the results and refers to the possibilities of laser processing of metal layers and polymeric materials in microelectronics packaging applications.

Low Energy Impact Performance of Interleaved Carbon Fibre Reinforced Epoxy Laminates

Cross-ply and quasi-isotropic carbon fibre reinforced epoxy (CF/EP) laminates were toughened by addition of interleaves, which consisted of either a modified epoxy resin or random PET mat embedded in a modified epoxy resin. Impact and multiple impact performances of the laminates were studied using an instrumented falling weight impact tester. A simple model was used to correlate the performance of the laminates under multiple impact.

Failure Behaviour of Cross-Ply Carbon Fibre/Epoxy Laminates Subjected to Transverse Impact and Static Perforation

Cross-ply carbon fibre reinforced epoxy laminates (CF/EP) were toughened with interleaf consisting of random PET fibre mat embedded in a modified epoxy resin. The interleaved laminate had a smaller delamination area but higher energy absorption than the base laminate during transverse impact perforation. In static tests, the interleaved laminate had a higher maximum load and greater deformation at the perforation, compared to the base laminate. The damage development was monitored using acoustic emission technique. The interleaved laminate had less cumulative acoustic emission events than the base laminate. The distribution of the rise time was used to identify the major failure mechanisms.

Impact damage area and interlaminar toughness of modified FRP laminates

Glass fibre reinforced epoxy laminates are improved to enhance their impact tolerance capabilities by modifying the epoxy resin with the addition of CTBN 1300X8 and triphenylphosphine under a controlled atmosphere of inert nitrogen gas. When impacted by a steel projectile, the damage area of a modified laminate is significantly smaller (35-55%) than that of an unmodified laminate for the same impact energy level. The interlaminar energy release rate in Mode I (G Ic) is increased by 41% as a result of the modification while the interlaminar energy release rate in Mode II (G IIc) is enhanced by 47%. No significant adverse effects were found on the modulus or ultimate tensile strength. The modification of epoxy causes precipitation and separation of discrete rubber particles during curing of the epoxy which also enhances the interlaminar toughness and impact tolerance.

The Effect of Water Absorption on Mode I Intterlaminar Fracture Toughness of Aramid Fibre Reinforced Plastics

Mode I interlaminar fracture toughness tests were carried out for aramid fibre reinforced epoxy laminates. Specimens immersed in water were also tested for comparison. The effect of water absorption on interlaminar fracture toughness was small for the aramid/epoxy laminates used in this study.

Effect of Climatic and Radiation Ageing on Properties of Glass Fibre Reinforced Epoxy Laminates

The effect of radiation on the properties of glass fibre reinforced epoxies was investigated. Radiation treatment with a maximum dose of 30 MGy was performed for virgin samples and after 0.5, 1, 2, and 5 years of exposure in cold, moderate and warm damp climates. Evaluation of climatic and radiation resistance was by the change in bending strength, interlaminar shear strength, and Young's modulus. Dynamic mechanical analysis and linear dilatometry were employed to investigate the epoxy matrix during ageing. It has been established that radiation treatment of both virgin and climatically aged samples causes the destruction of the interfacial bond. The large increase in mechanical properties observed is explained by the competing effects of two processes. There is little indication of the occurrence of additional crosslinking of the epoxy binder during irradiation. It is shown that ageing in the reverse order (radiation treatment with subsequent exposure to the climate) is more severe, and intensifies the changes in the properties of the material.

Acoustic Emission from CFRP Laminates during Fatigue Loading

The fatigue behaviour of quasi-isotropic carbon fibre reinforced epoxy laminates under tension-tension cyclic loading is investigated. The acoustic emission technique is used to monitor the different damage mechanisms activated throughout the fatigue life. Filtering of acoustic emission events is performed to reject the events attributed to friction related mechanisms. After appropriate filtering of the AE data, the fatigue damage process can be monitored in terms of cumulative AE counts.

Fracture mechanical characterization of fibre reinforced plastics in the intralaminar crack opening mode (mode I) and in the shear mode (mode II)

Two novel techniques and evaluation procedures for the fracture mechanical characterization of fibre reinforced plastics (FRPs) in the intralaminar mode I (crack opening mode) and mode II (shear mode) based on the fracture energy concept are presented. The splitting (mode I) as well as the punch-through shear (mode II) test are experimentally simple; the loading device and the sample geometries are small and well suited for measurements at cryogenic temperatures on both unirradiated and irradiated samples. The test results are load versus displacement curves, from which the strain-softening behaviour of the FRPs can be evaluated employing finite element calculations (FEM). All material parameters necessary for the FE calculations of the fracture behaviour can be taken directly from the strain-softening diagram and represent characteristic intrinsic material parameters (fracture parameters). Results obtained on a two-dimensionally glass fibre reinforced epoxy laminate are presented.

Effect of Climatic and Radiation Ageing on Properties of Glass Fibre Reinforced Epoxy Laminates

The effect of radiation on the properties of glass fibre reinforced epoxies was investigated. Radiation treatment with a maximum dose of 30 MGy was performed for virgin samples and after 0.5, 1, 2, and 5 years of exposure in cold, moderate and warm damp climates. Evaluation of climatic and radiation resistance was by the change in bending strength, interlaminar shear strength, and Young's modulus. Dynamic mechanical analysis and linear dilatometry were employed to investigate the epoxy matrix during ageing. It has been established that radiation treatment of both virgin and climatically aged samples causes the destruction of the interfacial bond. The large increase in mechanical properties observed is explained by the competing effects of two processes. There is little indication of the occurrence of additional crosslinking of the epoxy binder during irradiation. It is shown that ageing in the reverse order (radiation treatment with subsequent exposure to the climate) is more severe, and intensifies the changes in the properties of the material.

The Effect of Thermal Spiking and Resultant Enhanced Moisture Absorption on the Mechanical and Viscoelastic Properties of Carbon Fibre Reinforced Epoxy Laminates

The Effect of Thermal Spiking and Resultant Enhanced Moisture Absorption on the Mechanical and Viscoelastic Properties of Carbon Fibre Reinforced Epoxy Laminates