Unidirectional Glass Fiber Reinforced Plastics Research Articles

An Experimental Procedure to Study the High-Speed Orthogonal Cutting of Unidirectional GFRP

The aim of this paper is to establish a valid procedure for better understanding all of the phenomena associated with the high-speed machining of glass fiber-reinforced plastic (GFRP) composites. Both rectangular and circular specimens were machined at high cutting speeds (up to 50 m/min) in order to understand what occurred for all values of fiber orientation angles during machining operations. An innovative testing methodology was proposed and studied to investigate the phenomenon of burr formation and thus understand how to avoid it during machining operations. To this end, the forces arising during the machining process and the roughness of the resulting surface were carefully studied and correlated with the cutting angle. Additionally, the cutting surface and chip morphology formed during cutting tests were examined using a high-speed camera. Close correlations were found between the variations in the cutting forces’ signals and the trends of the surface roughness and the morphology of the machined surface.

Size effect in flexural behaviour of unidirectional GFRP composites

In this paper, the size effect in unidirectional (UD) laminated glass-fibre reinforced plastic (GFRP) composites subjected to quasi-static bending loading was investigated: the sensitivity of a specimen’s mechanical behaviour and failure mechanism to its geometry was studied. Composite beams with different numbers of 0° unidirectional plies were tested and their post-deformation structures were analysed microscopically. In the subsequent simulations, the intraply damage was modelled using continuum damage mechanics, implemented as a user-defined VUMAT subroutine in ABAQUS/Explicit, while cohesive zone elements were employed to characterize the delamination between different plies. It was observed that the flexural failure triggered the multiple delaminations; their location was studied. The influence of the size effect on the bending response of the UD composite beams was analysed in depth. The findings of the current study can be used to design modern structures made of composite materials.

Enhancement of open hole tensile strength via alignment of carbon nanotubes infused in glass fiber - epoxy - CNT multi-scale composites

Cut-out or holes are unavoidable features in composites for structural assembly and functionality. To enhance the strength of the unidirectional glass fiber reinforced plastic (UD-GFRP) laminates around the cut-outs, multi-walled carbon nanotubes (MW-CNTs) were locally aligned at the periphery of the cut-outs via non-uniform electric field. These multi-scale UD-GFRP composites were fabricated in two configurations based on CNT alignment in parallel and perpendicular directions to the glass fiber orientation. The performance was compared with composites containing randomly oriented MW-CNTs in epoxy matrix and composites without MW-CNTs. The damage evolution was investigated using digital image correlation (DIC) techniques during open hole tensile (OHT) tests. The presence of aligned MW-CNTs around the hole perpendicular to the fiber orientation was able to arrest the pertinent damage modes leading to an increase of the tensile strength by 27% as compared to the control samples fabricated using neat epoxy resin.

Design of composite members with curvilinear fiber trajectories

The design possibility of shaped constant area composite tensile test specimen and leaf spring is shown and the last can provide by chosen geometry threefold mass reduction for the given level of stored elastic energy. The use of unidirectional GFRP (glass fiber reinforced plastic) makes it possible to reduce the mass by approximately 15 times in compare with the steel analog for the same strength and stored energy requirements. The curvilinear trajectories of fibers tracing around the hole or rivet/bolt connection make it possible to increase load carry capacity many times.

A numerical approach to determine fiber orientations around geometric discontinuities in designing against failure of GFRP laminates

PurposeDetermining fiber orientations around geometric discontinuities is challenging and simultaneously crucial when designing laminates against failure. The purpose of this paper is to present an approach for selecting the fiber orientations in the vicinity of a geometric discontinuity; more specifically round holes with edge cracks. Maximum stresses in the discontinuity region are calculated using Classical Lamination Theory (CLT) and the stress concentration factor for the aforementioned condition. The minimum moment to cause failure in a lamina is estimated using the Tsai–Hill and Tsai–Wu failure theories for a symmetric general stacking laminate. Fiber orientations around the discontinuity are obtained using the Tsai–Hill failure theory.Design/methodology/approachThe current research focuses on a general stacking sequence laminate under three-point bending conditions. The laminate material is S2 fiber glass/epoxy. The concepts of mode I stress intensity factor and plastic zone radius are applied to decide the radius of the plastic zone, and stress concentration factor that multiplies the CLT stress distribution in the vicinity of the discontinuity. The magnitude of the minimum moment to cause failure in each ply is then estimated using the Tsai–Hill and Tsai–Wu failure theories, under the aforementioned stress concentration.FindingsThe findings of the study are as follows: it confirms the conclusions of previous research that the size and shape of the discontinuity have a significant effect on determining such orientations; the dimensions of the laminate and laminae not only affect the CLT results, but also the effect of the discontinuity in these results; and each lamina depending on its position in the laminate will have a different minimum load to cause failure and consequently, a different fiber orientation around the geometric discontinuity.Originality/valueThis paper discusses an important topic for the manufacturing and design against failure of Glass Fiber Reinforced Plastic (GFRP) laminated structures. The topic of introducing geometric discontinuities in unidirectional GFRP laminates is still a challenging one. This paper addresses these issues under 3pt bending conditions, a load condition rarely approached in literature. Therefore, it presents a fairly simple approach to strengthen geometric discontinuity regions without discontinuing fibers.

Scale Effect on Impact Performance of Unidirectional Glass Fiber Reinforced Epoxy Composite Laminates.

As a result of the increasing use of glass fiber reinforced plastic (GFRP) composites in engineering fields, the investigation of scale effect on impact performance for this kind of composite is essential for large scale structure design. The effects of scaling on the impact response of simply supported unidirectional GFRP were investigated through drop weight impact (DWI) tests in this study. Impact tests were undertaken over a wide range of energies to generate damages between barely visible and initiated penetration on four scale size GFRP laminates. The main impact responses including impact force, contact duration, displacement, energy absorption and damage area of scaled specimens were normalized to compare with the full-size specimen. It was found that the impact response of large sample with elastic deformation and small area of delamination can be predicted accurately according to a geometrical similar scaling law. Scale effect was found in the damage threshold force and absorbed energy of the laminates when significant internal damage occurs due to the microstructural effect becoming important in resisting impact force and absorbing impact energy. Moreover, the energy partition and effective stiffness were calculated according to the energy balance model to reveal the contribution of different modes of deformations on energy absorption for the GFRP laminates.

Prediction method of electrical conductivity of nano-modified glass fibre reinforced plastics

Glass fibre reinforced plastics (GFRP) is non-conductive construction material, however with carbon nanotubes (CNT) modifying it can get additional functionality due to its gained electrical conductivity. Main aim of the study is to check functionality of the prediction method of electrical conductivity of GFRP with nano-modified epoxy matrix using structural approach. GFRP composites under investigation were based on unidirectional (UD) Glass fiber and two matrixes modified with carbon nanotubes. Electrical conductivity of epoxy resin modified by CNT (concentrations < 1%) was modelled using structural approach. Electrical conductivity of unidirectional GFRP layer was measured experimentally and modelled based on conductivity of polymer matrix and assuming non-conductive fibres. It was supposed that epoxy matrix and composite on different structural levels follow the Ohm’s law. Two components of tensor of electrical conductivity for monotropic material in main axis of symmetry were calculated for composites by several different ways. Control experiment was performed on a sample of GFRP monolayer cut from the unidirectional plate under different angles. The calculated data are in a good agreement with the experimental values.

Fracture Toughness and Strength of the Interface of an Intrinsic Hybrid Laminate

Unidirectional glass fiber reinforced plastic (U-GFRP) represents itself as an excellent lightweight structural material due to its high tensile strength Rm and its low density ρ. A major drawback, however, is the relative weakness of the matrix under more complex, multi-axial loading conditions. Therefore, a local hybridization of U-GFRP seems to be an adequate measure to enhance the robustness of the material. First, the material testing program sets the focus on the investigation of the strength of the interface between U-GFRP and the additional constituent steel. Hence, the energy release rate GI, the static shear strength ts as well as the cyclic shear strength τs,cyclic of the considered interface have been determined at room temperature RT and at an elevated temperature of T = 80° Additionally, aged specimens have been statically tested as well. The results show up that primers, such as silane, are leading to a good adhesion between the constituents. Furthermore, a fiber bridging effect is apparent which leads to an increase of the energy release rate GI with the growth of the length a of the crack. A power law is well suited to describe this strengthening and its exponent n serves as a further measure to describe the strength of the interface. Generally, ageing of the material and straining at an elevated temperature harm the performance of the intrinsic hybrid material.

Interlaminar properties of GFRP laminates toughened by CNTs buckypaper interlayer

The interlaminar property is essential to the application of fiber reinforced composites for the overall performance. For the purpose of enhancing the interlaminar properties, the unidirectional Glass Fibre Reinforced Plastics (GFRP) laminates were fabricated by adding carbon nanotubes (CNTs) buckypaper to the mid-plane layers under different curing pressures (1 MPa, 2 MPa, 3 MPa). In order to study the enhancement mechanism of the CNTs buckypaper, a series of experiments were designed and conducted based on double cantilever beam (DCB), end notch flexure (ENF) and interlaminar shear strength (ILSS) tests followed by scanning electron microscope (SEM) examination to study the surfaces of the specimens. It was observed that the modes I and II interlaminar fracture toughness of GFRP embedded with CNTs buckypaper were relatively higher than those without CNTs buckypaper. Considerable improvements in interlaminar shear strength of the laminates were obtained with the integration of the CNTs buckypaper between the interlayers. The micro-structure of the enhanced mixed interface of fiber-resin-CNTs responsible for interlaminar strengthening was further studied with the help of SEM. It was found that the higher curing pressure could increase the inter-diffusion of the resin and CNTs offering a stronger interfacial adhesion. The interlaminar characteristics of the specimens cured at 2 MPa pressure were found to be relatively superior with optimal interlaminar fracture toughness and interlaminar shear strength.

Influence of specimen type and reinforcement on measured tension–tension fatigue life of unidirectional GFRP laminates

It is well known that standardised tension–tension fatigue test specimens of unidirectional (UD) glass-fibre-reinforced plastics (GFRP) laminates tend to fail at end tabs. The true fatigue life is then underestimated. The first objective of this study was to find for UD GFRP laminates a test specimen that fails in the gauge section. The second objective was to compare fatigue performance of two laminates, one having a newly developed UD powder-bound fabric as a reinforcement and the other having a quasi-UD stitched non-crimp fabric as a reinforcement. In the first phase, a rectangular specimen in accordance with the ISO 527-5 standard and two slightly different dog-bone shaped specimens were evaluated by means of finite element modelling. Subsequent comparative fatigue tests were performed for the laminates with the three specimen types. The results showed that the test specimen type has a significant effect on the failure mode and measured fatigue life of the laminates. A significantly higher fatigue life was measured for the laminate with the powder-bound fabric reinforcement when compared to the laminate with the stitched reinforcement.

Effects of curing pressure on mode II fracture toughness of uni-directional GFRP laminates

The purpose of this work is to investigate the effect of curing pressure on the Mode II interlaminar fracture toughness behaviour of uni-directional glass fibre reinforced plastics (GFRP). Investigation was carried out experimentally on uni-directional GFRP specimens using end notched flexure (ENF) tests to find out the changes in the material and geometric properties due to the application of pressure. Stiffness of the different laminates cured under different pressure was studied and it was shown that both material and geometric stiffness accounts for the total stiffness of the laminate, but their contribution to total stiffness varies. It is shown that fracture toughness values, GIIC, remain unaffected by stiffness since it is only related to the new surfaces created due to crack initiation and propagation. It is shown that the thickness of the matrix layer influences all the properties, including the fracture toughness. The laminates cured at 5 Psi, 400 Psi and 800 Psi exhibit different fracture toughness. Optimum thickness of matrix layer offers both adhesive and cohesive resistance to the crack propagation and thus offers high fracture resistance.

NDE of Low-Velocity Impact Damage in GFRP Using Infrared Thermography Techniques

In this study, low-velocity impact damage (LVID) in glass fiber reinforced plastic (GFRP) was investigated using pulse thermography (PT) and lock-in thermography (LIT) techniques. The main objective of this study was to evaluate the detection performance of each technique for LVID in GFRP. Unidirectional and cross-ply GFRPs were prepared with four energy levels using a drop weight impact machine and they were inspected from the impact side, which may be common in actual service conditions. When the impacted side was used for both inspection and thermal loading, results showed that the suggested techniques were able to identify the LVID which is barely visible to the naked eye. However, they also include limitations that depend on the GFRP thickness at the location of the delamination produced by the lowest impact energy of five joule.

Multiple-response optimization of cutting forces in turning of UD-GFRP composite using Distance-Based Pareto Genetic Algorithm approach

This paper presents the investigation of cutting forces (tangential and feed force) by turning of unidirectional glass fiber reinforced plastics (UD-GFRP) composite. Composite materials are used in variety of engineering applications in different fields such as aerospace, oil, gas and process industries. Process parameters (tool nose radius, tool rake angle, feed rate, cutting speed, depth of cut and cutting environment) are investigated using Taguchi's robust design methodology. Taguchi's L18 orthogonal array is used to conduct experimentation. The experimentation is carried out with Carbide (K10) Tool, covering a wide range of machining conditions. Analysis of variance (ANOVA) is performed for significant parameters and later regression model is developed for the significant parameters. The relative significance of various factors has also been evaluated and analyzed using ANOVA. Distance-Based Pareto Genetic Algorithm (DBPGA) approach is used to optimize tangential and feed force. Predicted optimum values for tangential force and feed force are 39.93 N and 22.56 N respectively. The results of prediction are quite close with the experimental values.

Machining Unidirectional Composites using Single-Point Tools: Analysis of Cutting Forces, Chip Formation and Surface Integrity

The need for high quality machining of composite materials is rising due to the increased utilisation of these materials across several applications. This paper presents experimental findings of orthogonal cutting of unidirectional glass fibre reinforced plastic (UD-GFRP) composites using HSS single-point cutting tools. Key process indicators including cutting forces, chip formation and surface integrity were evaluated. Full factorial design is employed with fibre orientation, depth of cut, cutting speed and rake angle as process control variables. Fibre orientation and depth of cut were found to be the most significant factors affecting the investigated responses. Lower cutting forces and better surface quality were obtained at 0o fibre orientation and lower depth of cut. Cutting at 45o fibre orientation generated extremely damaged surfaces with relatively high average surface roughness values and should be avoided in practical applications.

Investigation of surface roughness and MRR for turning of UD-GFRP using PCA and Taguchi method

This paper investigates the machinability of unidirectional glass fiber reinforced plastics (UD-GFRP) composite in turning process. Taguchi L18 orthogonal array is used for experimental design. The six parameters i.e. tool nose radius, tool rake angle, feed rate, cutting speed, cutting environment (dry, wet and cooled) and depth of cut are varied to investigate their effect on output responses. An attempt has been made to model the two response variables i.e. surface roughness and material removal rate using Principal Component Analysis. PCA is a technique of great practical importance in many applications of statistical inference, when it becomes difficult to relate a large number of independent variables with a number of dependent outcomes without having enough observations to carry out the analysis in a reliable way. Correlated responses are transformed into uncorrelated or independent quality indices called principal components. From the experimental results, it is evident that the surface roughness increases as feed rate increases. It is found that feed rate is more significant factor followed by depth of cut and cutting speed. Feed rate = 0.2, depth of cut = 1.4 mm and speed = 159.66 m/min produces the optimum value of surface roughness μRa = 1.498 μm and the optimum material removal rate MRR = 330.267 mm3/s.

Multiple-response optimization of turning machining by the taguchi method and the utility concept using uni-directional glass fiber-reinforced plastic composite and carbide (k10) cutting tool

This paper presents a utility concept for multi-response optimization in turning uni-directional glass fiber-reinforced plastics composite using Carbide (K10) cutting tool. The single response optimization resulted in the non-optimization of other responses. The Taguchi method (Orthogonal L18 array) was employed in the experimental work. The process parameters selected for this study were tool nose radius, tool rake angle, feed rate, cutting speed, depth of cut, and cutting environment. Statistically significant parameters were found to simultaneously minimize surface roughness and maximize the material removal rate by ANOVA. The results were further verified by confirmation experiments.

Prediction of cutting forces in machining of unidirectional glass fiber reinforced plastics composite

Machining of plastic materials has become increasingly important in any engineering industry subsequently the prediction of cutting forces. Forces quality has greater influence on components, which are coming in contact with each other. So it becomes necessary to measure and study machined forces and its behavior. In this research work, experimental investigations are conducted to determine the effects of cutting conditions and tool geometry on the cutting forces in the turning of the unidirectional glass fiber reinforced plastics (UD-GFRP) composites. In this experimental study, carbide tool (K10) having different tool nose radius and tool rake angle is used. Experiments are conducted based on the established Taguchi’s technique L18 orthogonal array on a lathe machine. It is found that the depth of cut is the cutting parameter, which has greater influence on cutting forces. The effect of the tool nose radius and tool rake angles on the cutting forces are also considerably significant. Based on statistical analysis, multiple regression model for cutting forces is derived with satisfactory coefficient (R 2). This model proved to be highly preferment for predicting cutting forces.

Prediction of cutting force in turning of UD-GFRP using mathematical model and simulated annealing

Glass fiber reinforced plastics (GFRPs) composite is considered to be an alternative to heavy exortic materials. According to the need for accurate machining of composites has increased enormously. During machining, the obtaining cutting force is an important aspect. The present investigation deals with the study and development of a cutting force prediction model for the machining of unidirectional glass fiber reinforced plastics (UD-GFRP) composite using regression modeling and optimization by simulated annealing. The process parameters considered include cutting speed, feed rate and depth of cut. The predicted values radial cutting force model is compared with the experimental values. The results of prediction are quite close with the experimental values. The influences of different parameters in machining of UD-GFRP composite have been analyzed.

Fractographic analysis of tensile failures of aerospace grade composites

This paper describes fractographic features observed in aerospace composites failed under tensile loads. Unidirectional Carbon Fibre Reinforced Plastic (UD CFRP) and Unidirectional Glass Fibre Reinforced Plastic (UD GFRP) composite specimens were fabricated and tested in tension. The morphology of fractured surfaces was studied at various locations to identify failure mechanism and characteristic fractographic features. CFRP composites displayed transverse crack propagation and the fracture surface showed three distinct regions, viz., crack origin, propagation and final failure. Significant variations in the fractographic features were noticed in crack propagation and final failure regions. Crack propagation region exhibited brittle fracture with chevron lines emanating from the crack origin. The entire crack propagation region exhibited radial marks on the individual fibre broken ends. On the other hand, the final fracture region revealed longitudinal matrix splitting and radial marks in majority of locations, and chop marks at some locations. The change in fracture mode in the final fracture was attributed to superimposition of bending loads. GFRP composites exhibited broom like fracture with extensive longitudinal splitting with radial marks present on individual fibre broken ends. Transverse fracture was observed at a few locations. These fracture features were analyzed and correlated with the loading conditions.

Cutting Forces in Orthogonal Turning of Unidirectional Glass Fibre Reinforced Plastic Composites

Experimental investigation of machining is cost prohibitive. The number of parameters to control, the exhaustive material characterisation and the time consuming procedure to determine the mechanical responses like cutting forces restricts experimental studies. In this context, mathematical modelling can be a feasible tool for studying the various responses in machining. This paper presents an attempt to investigate orthogonal machining of unidirectional Glass Fibre Reinforced Plastic Composite (UD-GFRP) materials using mathematical modelling. The model entailing fibre orientation, shear strength, depth of cut, feed, friction angle and rake angle is constructed for investigating the tangential cutting and feed cutting force developed during machining. The numerical results are compared to the experimental results. The comparison indicates that the model provides satisfactory prediction of the cutting forces. The relations between process parameters are discussed.