Glass Fibre Reinforced Polyester Laminates Research Articles

The influence of UV radiation on the properties of GFRP laminates in underwater conditions

Degradation of polymer composites is a significant problem in many engineering aspects. Due to the interaction of various degradation factors during the exploitation of composites, a synergistic effect of destruction is observed. The article describes the phenomena occurring in glass fiber reinforced polyester laminates under the influence of ultraviolet radiation (UV) in an aquatic environment. The laminates were exposed to UV-A, UV-B and UV-C radiation for 1000 h in free-air and underwater conditions. During the test, the materials were immersed at stable depth of 1 mm and 10 mm, respectively. The three-point bending tests performed on the samples after being exposed to UV showed an increase in the flexural strength of the composites. Simultaneously, degradation of the outer surface layer was observed. The degradation removed the thin resin film from the surface which resulted in a direct exposure of the reinforcing fibers to the environment. The transformations taking place in the deeper layers of the composite increased the mechanical strength due to the additional cross-linking reactions excited by the energy arising from the radiation. Moreover, the formation of polymer structures from free styrene remaining after the technological process and the occurrence of free radical reactions as a result of the cage effect was also observed.

Mechanical characterization and validation of biocomposites in small ship hull construction. Life Cycle Assessment.

Nowadays, glass fiber reinforced polyester laminates are widely used in manufacturing small ship hulls by hand lay-up. The main drawbacks of the use of these composite materials are: the dependence of hydrocarbons on the synthesis of resins, the high energy cost to obtain glass fiber and the emission of volatile harmful compounds in the manufacturing process. In this work, the advantages of using flax fiber reinforced bioresins are analyzed. Tensile and flexural standard tests were performanced. After that, a small craft of less than 24 meters in length is designed in accordance with the international norm ISO 12215-5. The results indicate that despite the need for greater thickness, the total weight of the vessel is reduced by 12% using biocomposites. Besides, Finite Element Analysis (FEM) indicates that the structural design can be clearly optimizated. Finally, Life Cycle Assessment (LCA) reveals an environmental improvement of the boat made of biocomposite instead of glass fiber. However, this improvement is limited by land occupation and the high water footprint of flax fiber in its production process.

Relationship between Bending Modulus and Test Sizes of Laminated Glass/Polyester Composites

The effect of span-to-thickness ratio (L/h) on the bending modulus was investigated in warp, 45°, 67.5° and weft directions in woven glass fiber reinforced polyester laminates. Using classical beam theory the results of the bending tests carried out for L/h = 5,..,50 were extended to the total range of definition (0≤L/h<∞) by applying rational fractional and exponential fractional functions. The extensions take the asymptotic behavior of the bending test for L/h = 0 and L/h = ∞ in account while providing the best fitting to the measured data. It has been shown that the exponential fractional estimations give better results regarding the form of functions that is independent from the directions.

Low-velocity impacts on preloaded GFRP specimens with various impactor shapes

The simultaneous effect of impactor shape and biaxial preload on the impact response of thin glass fibre reinforced polyester laminates is investigated herein. Using a specially designed drop weight test rig, specimens were impacted at initial impact energies of 4 J and 6 J using steel flat, hemispherical, ogival and conical impactors, all 12 mm in diameter. Biaxial tension of 500 and 1000 microstrain was applied to the specimens. The applied levels of preload were found to have little effect on the impact response of the GFRP specimens. Due to the stiffening effect of the biaxial tension, the contact duration and deflection were found to decrease with increasing preload. However, the peak force, absorbed energy and damage area were largely unaffected by the preload. The indentation depth produced by the conical impactor at 4 J increased significantly as preload was applied. However, this did not correspond to an increase in damage area.

Machining of Fiber-reinforced Thermoplastics: Influence of Feed and Drill Size on Thrust Force and Torque during Drilling

Polymer-based composite materials possess superior properties such as high strength-to-weight ratio, stiffness-to-weight ratio, and good corrosive resistance and therefore, are preferred for high-performance applications such as in the aerospace, defense, and sport goods industries. Drilling is one of the indispensable methods for building products with composite panels. Drilling tests have been conducted on glass fiber-reinforced plastic composite GFRP laminates using an instrumented CNC milling center. Machining parameters such as drill size, feed rate, and cutting speed have been observed for damage-free drilling of GFRP materials. A series of drilling experiments have been conducted on glass fiber-reinforced polyester laminates and the responses experienced such as thrust force and torque as functions of feed rate and drill size have been characterized to develop a semiempirical relationship which correlated well with an established model in terms of cutting parameters. Results indicated that experimental values correlated better with the model of thrust for 6 mm drill size than for 10 mm and torque correlated better for lower feed ranges than for the higher feed ranges.

Use of acoustic emission to characterize corrosion fatigue damage accumulation in glass fiber reinforced polyester laminates

AbstractThe acoustic emission technique has been used to characterize fatigue damage accumulation in glass fiber woven roving (0/90°) polyester laminates after prolonged exposure in sea water. Comparisons were made with fatigue tests of “as‐received” laminate under similar loading conditions. Pre‐exposure has been found to substantially reduce the fatigue strength of the composite. Acoustic emission monitoring during fatigue testing has shown that the amplitude distribution of the acoustic events shifts from predominantly low amplitude (40–55 dB), associated with matrix cracking, in as‐received specimens, to intermediate amplitude (55–75 dB) associated with delamination and debonding after pre‐exposure. Optical microscopy of fatigued samples has verified these failure mode changes. The number of recorded high amplitude events (≥ 80 dB) associated with fiber fracture is the same in both cases, which indicates that the glass reinforcement is unaffected by pre‐exposure.

An application of experimental design to the development of glass fibre reinforced polyester laminates with enhanced mechanical properties

The use of experimental design in the development of unsaturated polyester resins is described. The process conditions, which are critical in order to achieve an unsaturated polyester with good delamination strength, have been identified and optimised. Qualitative data was obtained by using response surface modelling, and the delamination strength was estimated using a wedge test and the double cantilever beam method. From the response surfaces, the most optimal process conditions can be identified.

Damage Mechanisms in Composite/Composite Bonded Joints Under Static Tensile Loading

This paper presents an experimental study of the initiation and development of damage in composite/composite joints. The materials studied are glass fibre reinforced polyester laminates and these are bonded together using an epoxy adhesive. Two types of joint interface are examined, assemblies between woven roving layers and between mat layers. The experimental techniques employed are dye impregnation, extensometry, visual observation and photoelasticimetry. It is shown that the nature of the surface layer does not influence the damage initiation load but does affect subsequent crack propagation.

Impact response of thick glass fibre reinforced polyester laminates

Thick glass/polyester woven roving laminated plates subject to low-velocity impact have been investigated using a guided drop-weight test rig in ascending energy order up to 1500 J. The impact response and energy-absorbing characteristics have been determined by impact-forces and absorbed-energy histories, and by force-displacement relationships. Impact damage is examined by visual inspection, ultrasonic C-scan and an optical microscope so that a three-staged sequential damage model is proposed to characterize damage growth. Static tests are also conducted to examine strain rate effect. It is demonstrated that the maximum impact forces are increased by 36% for the thin plates and by 22% for the thick plates, although the initial threshold forces are less strain-rate sensitive. Two thicknesses of laminated plates are used to study the thickness effect, and the scaling rules are developed for the delaminated plates. It is shown that both the maximum static and impact forces, and the incident kinetic energy can be scaled by the thickness ratio if these laminates have the same diameter and their behaviour is dominated by shear. The finite element modelling is carried out for relatively low energy cases, the impact structural response is well captured by linear elastic solution.

Fatigue damage—compliance relationship for GRP

This paper presents an analytical relationship between the propagation of damage and the change in compliance of the notched glass fibre reinforced polyester laminates subjected to tension—tension fatigue. Two types of laminates; (0) 3 and (0/90/0) were laid-up by hand and two sizes of specimens having either a slit or a circular hole were tested. The damage extent was found to be directly proportional to the change in compliance of these laminates. The initiation and propagation of damage on all the specimens were closely monitored, a description of which is also presented.

Fatigue damage-compliance relationship for GRP

This paper presents an analytical relationship between the propagation of damage and the change in compliance of the notched glass fibre reinforced polyester laminates subjected to tension-tension fatigue. Two types of laminates; (0) 3 and (0/90/0) were laid-up by hand and two sizes of specimens having either a slit or a circular hole were tested. The damage extent was found to be directly proportional to the change in compliance of these laminates. The initiation and propagation of damage on all the specimens were closely monitored, a description of which is also presented.

Effects of temperature on stressrupture times in glass/polyester laminates

The stress-rupture times of glass fibre-reinforced plastics in water are temperature-dependent. Increasing the temperature increases the diffusion coefficient of a liquid in a given matrix, and may also increase the fracture toughness of the resin. The effects of these two parameters on the rupture lifetimes oppose each other, and so the overall outcome could be either an increase or a decrease in failure time. This problem is illustrated by experiments with glass fibre-reinforced polyester laminates in water. The failure times were greater at 45°C than at either 60°C or 30°C. Acoustic emission experiments suggested that resin microcracking was extensive at 30°C but was much less at the higher temperatures, although the glass transition temperature was outside the experimental range. The stress-rupture results are explained by reference to the effect of temperature on diffusion coefficients and fracture toughness parameters, and by considering the transition temperature of the wet resin. The sequence of events leading to failure is described.

Flammability tests for glass-fibre reinforced polyester laminates

Flammability tests for glass-fibre reinforced polyester laminates

The fatigue damage process of FRP laminates with U and V type notches.

This paper deals with the fatigue damage process of glassfiber reinforced polyester laminates with U and V type notches. It is shown from experimental results that the relationship between the applied stress/tensile strength ratio and fatigue life is the same on the whole, regardless of fiber content. In order to explain these fatigue behaviors, a simple fatigue and residual strength degradation model is proposed to predict the fatigue life under pulsating tensile loadings. The prediction of fatigue life by a numerical approach using the proposed fatigue damage model agrees well with the experimental data.

Mechanical Properties of FRP

Glass fiber reinforced polyester laminates (GRP) have recently found a wide industrial application and the mechanical properties of the laminates have often been reported. However, few are really studied based on a well-organized experimental method.The purpose of our investigations is to study the following effects using the orthogonal array table type L81.(1) The effects of the kinds of base materials in each layers on mechanical properties of GRP.(2) The effects of the molding conditions on mechanical properties of GRP.The test samples were prepared by the hand lay-up molding method with three kinds of base materials which are shown in Table I and Fig. 3.Using the test pieces from the samples, tensile strength, tensile modulus, flexural strength, flexural modulus and thickness were measured in the atmosphere of 20±°C, 65±2% R.H. and the following results were obtained.(1) The force applied to a tensile test piece seems to be uniformly distributed into each layer of the laminates.(2) When the laminates is used as a bent member, the effects of the kinds of base materials are scarcely influenced by the adjacent base materials, and the farther the base material is located from the central layer, the larger become the effects. In ten plies of laminate, the effects of the kinds of the interior four base materials can be neglected.(3) It is advisable not to use woven roving on compression side of bent members.(4) The slower the rate of resin curring is, the stronger products can be obtained.(5) Differences of breaking stresses and moduli are not noticeable between the samples molded by the man of experience and one of inexperience.(6) The screw roller brought a good result in lamination of satin-like weavings, and mohair and wool rollers brought good results in lamination and resin impregnation of the woven rovings. The washer roller gave only bad result for all base materials.(7) After-curring of the sample caused lower tensile strength and modulus with higher flexural strength and modulus. After-curring of the test pieces subsequent to machining caused higher strength and modulus than curring prior to machining.(8) Wider specimens improve apparent breaking stress and modulus.