Glass-epoxy Composite Laminates Research Articles

EFFECT OF FILLER CONTENT AND SIZE ON THE FLEXURAL STRENGTH AND HARDNESS OF PURE IRON POWDER FILLED LAMINATED FIBERGLASS EPOXY COMPOSITES

The aim of this work is to evaluate the effect of the amount of pure iron powder (99.9987%), introduced as a filler in a glass-epoxy composite laminate, as well as the variation of its grain dimensions, on its flexure strength and hardness. Contact molding was used to produce laminate plates of 15, 20, and 25% of weight content with three different dimensions 92, 64, and 32 μm, and the fiberglass content was set at 30%. For the bending test, the specimens were prepared according to ISO 14125 standard specification, the test was carried out with three different speeds, and the required number of specimens were manufactured according to Taguchi's orthogonal array L9 (3 × 3) by varying three parameters (iron powder content, grain size, and test speed). The results were studied with the Taguchi method; however, the hardness was measured on plates with the same iron powder content while varying the dimensions of its grains (92, 64, and 32 μm). The results show that the pure iron powder content and dimension variations have a direct and clear influence on the composite material's mechanical characteristics, in such a way that: a specific percentage of filler and grains size reduction could widely increase the hardness as well as the material flexure strength. The results of the elaborated composite material's bending test were compared to a 45% glass-epoxy laminate. Whereas the hardness of the elaborated laminate was compared to a resin plate and the 45% glass-epoxy laminate.

Effects of seawater and acidic environment on mechanical properties of iron powder-loaded glass-epoxy composite laminates: Experimental and analytical investigation

This study assesses the impact of seawater and acidity on a glass epoxy composite filled with pure iron powder. Plates with varying iron content (15%, 20%, and 25%) were created using contact molding, with 30% glass fiber content. After dividing the plates into samples, a three-point bending examination was conducted following ISO14125 standards. The samples were immersed in saltwater (Group A), an acidic solution (Group B), or kept dry for comparison (Group C). Each subgroup had 15 specimens (5 for each iron %), immersed for over 60 days before undergoing bending tests. Results showed a significant decline in flexural strength, with a maximum reduction of 29.7% in Group A and 37.9% in Group B, while Young's modulus decreased up to 34.8% in Group A and 45.6% in Group B. The two-way ANOVA approach confirmed these findings, and microscopic examinations and FTIR analysis after immersion elucidated physical alterations and chemical reactions. Despite certain advantages, such as specific applications, the composite's limitations in corrosion resistance, durability, and production cost may restrict its relevance in various industrial and real-world applications. Consideration of these factors is essential before choosing this material for a specific project.

Experimental and Numerical Study on Vibration-Based Damage Detection and Localization in Laminated Composite Plates

Damage detection in composite materials is crucial for ensuring the safety and reliability of engineering structures. Conventional methods often face challenges in accurately identifying damage in plate-like structures, particularly in scenarios involving multiple damages or small-scale delamination. This study focuses on investigating the detection and localization of delamination in composite plates by employing both experimental and numerical modal analysis. An eight-ply woven Glass-Epoxy composite laminate with and without damage was prepared with the aid of hand lamination technique. Laminate was fixed to a Clamped-Free-Free-Free (CFFF) boundary condition for experimental modal analysis by introducing controlled damage to examine its impact on modal properties. To validate the natural frequencies (NFs) of damaged and undamaged composite laminates, a numerical analysis was conducted using ANSYS Parametric Design Language (APDL). Further, to advance the understanding of using modal shapes and their spatial derivatives for damage localization in composite plates under various damage situations, post-processing of simulation results was conducted using MATLAB. Finite Difference Method has been employed to calculate the derivatives, and a novel damage index (DI) is proposed to enhance damage localization capabilities. The results affirm that the proposed DI is effective and precise in identifying damage in plate-like structures, both for individual and multiple damage scenarios. This research study presents a novel approach for identifying and pinpointing damage in composite plates, thereby making a valuable contribution to the field of structural health monitoring (SHM) applications

Moisture Absorption, Desorption and Reabsorption Effects on Mechanical Properties of Glass-Epoxy Composites

The glass-epoxy composite laminates were fabricated using BID glass fabric and RT cure epoxy matrix by Room Temperature Vacuum Bag Moulding (RTVBM) Technique. The Inter laminar shear strength (ILSS), compression and flexural strength values were determined at room temperature for their dry mechanical property evaluation. The test specimens were exposed to a temperature/humidity condition at 45° C/95% RH for moisture absorption studies. The moisture desorption studies were carried out in a temperature oven at 45° C and 85° C. The mechanical properties of the exposed specimens were evaluated during absorption and desorption conditions. Scanning Electron Microscopy (SEM) studies were carried out on the dry and exposed specimens to determine the effect of moisture on the fracture behaviour of glass-epoxy composites. Results show that, moisture reabsorption and full desorption are faster than the absorption and partial desorption. This may be due to, change of material properties after a cycle of moisture absorption and desorption phenomenon. The mechanical strength (ILSS, compression and flexural) has been found to reduce continuously with increased duration of environmental exposure, but a slight shift back of the strength has been observed for desorbed samples.

Experimental and numerical study of mode I interlaminar behavior of carbon nanotube reinforced glass–epoxy composite: A multiscale approach

In this paper, the effect of adding carbon nanotubes (CNTs) between glass–epoxy composite laminate in the mode I interlaminar behavior was investigated by experimental and numerical methods. Mode I interlaminar fracture toughness of epoxy matrix modified by 0.5 wt%, and 1 wt%, CNTs were compared with an unmodified epoxy matrix using the double cantilever beam (DCB) specimen. By adding a 1% weight ratio of CNT, the mode I interlayer fracture toughness increases by about 50%. A multiscale approach was used for modeling the DCB test. At the micro-scale, toughness mechanisms, including CNT pull-out, its breaking and bridging, and the separation of the nanotube from the surrounding resin were modeled. The separation of the nanotube from the surrounding resin was modeled with a cohesive element. The cohesive element around the nanotube was embedded in the three-dimensional elements of the resin and according to the weight percentage of the nanotube to the resin, a representative volume element (RVE) was created. The orientation, length, and diameter of CNT were considered randomly in the RVE. In the mesoscale, according to the percentage of glass fibers to resin, an RVE was created randomly. By using the damage model whose parameters were extracted from the micro-scale, crack growth was simulated. According to the Hill-Mendel conditions, the relationship between the meso and macro scale was established and the amount of effective quantities of traction and separation from the micro-scale was used as the parameter of the cohesive element in the macro-scale. To consider the bridging effect of glass fibers and its effect on interlayer fracture toughness, random distribution of interlayer beam elements was created. At the macro-scale, the DCB test simulated and cohesive elements were considered for modeling lower-scale mechanisms and beam elements for fiber bridging simultaneously. A favorable agreement between the experimental and simulation results was obtained.

Compressive Failure Behaviour of Kevlar Epoxy and Glass Epoxy Composite Laminates Due to the Effect of Cutout Shape and Size with Variation in Fiber Orientations

The increasing trendof constructing componentsmade of composite laminates is due tothe flexibility intailoring their properties and high strength-to-weight ratio. Nevertheless, most practical components involve cutout features for fastening and these cutouts could significantly reduce the strength of the laminate. Due to its importance, many studies were conducted to study the effect of circular cutouts however, there is lack of information regarding the effect of various cutout shapes. Therefore, this study aims to investigate the compressive failure behaviour of Kevlar Epoxy and Glass Epoxy composite laminates due to different cutout shapes and sizes with variation in fiber orientations. Finite element software, ANSYS were used to simulate the deformation and failure behaviour of the laminates under compressive load. Prior to that, mesh convergence analysis and numerical validation were performed. Failure analysis was conducted for various cutout shapes (square cutout, diamond cutout, and circular) and size, based on Maximum Stress Theory. The results show that the existence of the cutouts on the composite laminates have reduced up to ten times the strength of the laminated composite plates. This information regarding the failure behaviour is important when designing components made of composite laminates under compression.

Comparative analysis between co-curing and adhesive bonding of glass-epoxy composite laminates and AA5083 aluminium sheets for Maritime application: effect of surface pattern

Co-curing and secondary bonding are effective techniques to join not only composite structures but also dissimilar materials such as metals and composites whose combined use is increasing in several industrials fields where lightness is strategic to reduce fuel consumption and, consequently, greenhouse emissions (i.e. transports). In particular, the aim of this research is to investigate the effect of different patterns both on co-cured glass-epoxy composite/aluminium joints and on the same joints made with adhesive as third material to bond the aluminium and the laminate preliminary realized by vacuum infusion. These configurations and the materials to join were used typically in maritime applications, i.e. the composite can be used for the main deck and the aluminium for the superstructures. The patterns were made with a controlled milling machine equipped with an engraver with a 45° cutting angle. In both cases, the results showed that the mechanical treatment affected the mechanical properties, i.e. the joint with the best pattern had a higher mechanical strength than the joint where the surface was not treated. Moreover, this influence was more significant for co-curing. Finally, a statistical analysis was performed to evaluate the significance of both the selected factors: i.e. joining process and treatment, and their interaction. The novelty of the work lay both in the materials used to make the joints, which are employed in marine applications, in the use of macroscopic pattern to treat the metal surface for co-cured joints, and in the manufacturing process, which used a CNC milling machine.

Comparison and identification of efficient nanoparticles to improve the impact resistance of glass/epoxy laminates: Experimental and numerical approaches

This research has studied the low-velocity impact (LVI) response of glass-epoxy composite laminates reinforced with different percentage of carbon nanotube (CNT) and nanoclay particles. The obtained results facilitate industrialists’ decision-making on selection of high-performance and cost-effective nanoparticles. Through quasi-static indentation (QSI) tests, the optimal percentages of nanoclay, and CNT were identified, and the impact test was performed on them at wide range of energies. Three key indexes were presented to evaluate the composite resistance against impact loads. The results indicate that both types of nanoparticles have contributed to an improvement in impact resistance. Moreover, a finite element analysis was performed using Abaqus/Explicit package, in which the results were in good agreement with experimental values.

Compressive failure behaviour of glass epoxy and graphite epoxy composite laminates due to the effects of different cut-out sizes and variations in fibre orientation

Composite laminates consisting epoxy are widely used in major industries. Hence, the mechanical property of these materials needs to be fully understood. Currently, there is limited studies on the effect of various square cut-out sizes related to glass epoxy and graphite epoxy composite laminates, therefore, the behaviour of these laminates is not fully understood. This paper aims to study the effect of the square cut-out sizes on the failure performance of glass epoxy and graphite epoxy composite laminates with various fibre orientations. Prior to the compressive failure analysis, convergence and numerical validation were conducted. The failure analysis is conducted by using the finite element method (FEM) using ANSYS with maximum stress theory as the failure criteria. The results show a substantial difference in the strength of the laminates without and with cut-outs. The main finding that can be deduced from the study is, the presence of cut-out reduces the strength of the composite laminates. Different fibre orientations effected graphite epoxy composite laminate at a considerable amount compared to glass epoxy laminates. From the results, it is proven that the present study is important in understanding the compressive failure behaviour of the composite plate in which can be useful in contributing the knowledge for further study.

The effects of cutout size and fibre orientation to the failure behaviour of glass epoxy and boron epoxy composite laminates

The composite laminate was widely used in aerospace, marine and automobile structure. The application of glass epoxy composite widely uses because of the lightweight demand from aerospace industry. The implementation of boron epoxy on the helicopter blade structure is one of the examples the of boron epoxy composite material. This research is to study the effect of square cut-out to failure behaviour of Glass Epoxy and Boron Epoxy composite laminates with various fibre orientations. The research is being conducted in two stages, which is numerical validation of the software used and failure analysis. The method of determining the failure analysis is accomplish by using the finite element method (FEM) with Maximum stress theory as the failure criteria. As the results, a significant variance of strength character between without cut-out and cut-out. The results for all three types of cut-out are somehow different with no cut-out results. The gap in between no cut-out and A1 cut-out is around 96.8% of percentage difference at 0° fibre orientation but at 90° fibre orientation, the different is reduce to 38.3% of percentage difference. By varying the result, the main finding for the research is that material removal effect due to cutting has an impact on the strength of composite laminates. The cut-out size and the direction of fibre orientation also does affect the failure behaviour of the composite laminates research result. Results gaps for all three cut-out sizes on 0-degree also different by around 5% in between A1 and A2 and decrease to 25.32% in between A2 and A3. Consistency is found on the results at 90-degree with different by 38.3% and 20.45%. Although it is not much, all the failure curves for cut-out shows gradually decrease by the increase of degree in fiber orientation after 50°. As the conclusion, it is proven that the current study is important in understanding the failure behaviour of the composite plate in which can be useful in contributing the knowledge for further study.

Assessment of delamination growth due to matrix cracking in hybrid Glass-Kevlar composite laminates using experimental, numerical and analytical methods

In this study, the growth of induced delamination in off axes composite laminates has been investigated. Glass-Epoxy composite laminates and Glass-Kevlar-Epoxy hybrid composite laminates with cross-ply [04/90n]s and angle-ply [304/90n]s and [454/90n]s composite layup, containing a low density matrix crack in 90° layers have been made. Then they have been subjected to tensile loading in experimental tests in order to investigate the growth delamination from the location of the matrix cracking and to measure the stiffness degradation. The experimental observations reflect the effects of hybridization and staking sequences on the induced delamination growth for the first time. In addition, the growth of delamination in the considered composite laminates have been studied numerically in ABAQUS software using the cohesive zone method and the required fracture energy for the analysis was obtained using relative characterization test. Finally, using a simple analytical model, the stiffness degradation due to the growth of delamination was calculated and compared with the experimental and numerical results. The obtained results reveal the employing the Glass-Kevlar-Epoxy hybrid laminate enhances the stiffness as well as the capacity of delamination growth in comparison with Glass-Epoxy with the same thickness.

Evaluation of E glass epoxy composite laminate as an electromagnetically transparent aerospace material

The performance of E glass reinforced epoxy composite laminate as an aerospace material with least loss in transmission of signals, transmitted from aerospace and defence vehicle’s communication devices is evaluated in this work. As a protective covering to an antenna has to endure various environmental conditions, the fabricated E glass epoxy laminates, with a variation in the hardening agent used, is studied for tensile, flexure, shear, and impact properties. The most important function of the protective layer apart from protecting the antennas, is to allow the signals to be transmitted and received without deterioration in its quality. To evaluate the transparency to signals, the dielectric properties such as the dielectric constant and loss tangent are studied. In addition to this, the thermal expansion coefficient is also calculated. This paper gives a comparison of the findings between the mechanical, thermal and dielectric properties of the two hardening agents triethylenetetramine and diethyltoluenediamine of the epoxy resin when used for electromagnetically transparent applications.

Assessment of Cyclic Load Induced Energy Dissipation and Damping on GFRP Composite Laminate

Polymeric composites exhibit load sensitive stiffness unlike the case of homogeneous metallic material. Composites are widely used in dynamic loading environment and hence it is necessary to study their response in terms of structural properties. Behavioural changes of glass epoxy composite laminate on exposure to cyclic loading has been assessed in terms of energy dissipation (Ed) and Damping factor (DF) by hysteresis loop. GFRP composite specimens (UD-0, 0/30/60/0, 0/45/0/-45, 0/90/90/0, and 0/90/0/90) are exposed to low velocity constant amplitude cyclic loading using a laboratory arrangement (by an eccentric disc) at 4.6 Hz and 8.6 Hz frequencies. In fibre-reinforced composites apart from the fibre volume fraction, the fibre interaction angle significantly influences their dynamic properties on loading. Unidirectional (UD-0) laminate exhibits low damping/energy dissipation, while 0/90/0/90 laminate with large fibre interaction angle shows highest damping/energy dissipation. Whereas, symmetric cross ply (0/90/90/0) laminate acts as a performance demarcation among the chosen laminates. Thus, optimum Ed/DF properties of GFRP laminate in dynamic environment is attributed to symmetric lay-up, smaller fibre orientation interaction angle in the lay-up sequence and 0 fibre layer at the boundary.

Glass fiber-reinforced polymer nanocomposite adhesive joints reinforced with aligned carbon nanofillers

In this paper, the effect of aligning multi-walled carbon nanotubes (MWCNTs) and graphene oxide nanoplatelets (GONPs) on the fracture behavior of glass-epoxy nanocomposite adhesive joints was studied experimentally. The nanofillers were aligned using an AC electric field along the adhesive thickness in double cantilever beam (DCB) specimens. A unidirectional carbon fiber layer was embedded as the second ply of each laminated substrate as an electrode inside the glass-epoxy composite laminates. Reinforcing the composite adhesive joints with randomly dispersed MWCNTs and GONPs resulted in the maximum improvements of 82% and 155% in the initiation fracture energy and the improvements of 19% and 69% in the maximum load, respectively. Furthermore, aligning MWCNTs and GONPs resulted in considerably higher improvements of 179% and 349% in the initiation fracture energy and 66% and 127% improvements in the maximum load, respectively and yet changed the failure pattern. The toughening mechanisms due to the addition of the nanofillers were investigated using scanning electron microscope (SEM).

Effect of incident microwave frequency on curing process of polymer matrix composites

Microwave assisted curing of aerospace and structural polymer matrix composites depends on several factors such as dielectric properties of the curing substrate, type of tooling used, thickness of the composite part, kind of applicator chosen and so on but one of the most important factors is the frequency of radiation used for the purpose of curing. Majority of the work reported on microwave curing of polymer composites is restricted to the commonly utilized frequency of 2450 MHz, whereas 915 MHz frequency is extensively employed chiefly for food processing and wood drying applications. This paper evaluates the potential of 915 MHz frequency for curing polymer matrix composites.2 mm thick glass-epoxy composite laminates were prepared using bi-directional glass fiber reinforced epoxy resin system. These composites were then cured in three different ways: microwave curing with 915 MHz as incident microwave frequency; microwave curing with 2450 MHz as incident microwave frequency and conventional thermal (oven) curing. Comparison between microwave and thermal cure process times as well as energy consumption revealed the significant time and energy savings realized by microwave curing. Further, mutual comparison of the cured laminates was drawn in terms of attainment of lamination quality, glass transition temperature and mechanical properties. The results obtained showed that the 915 MHz microwave cured laminate had superior inter-laminar shear strength (ILSS) and flexural strength as compared to 2450 MHz microwave cured and thermally cured laminates. This, in essence, implies that incident microwave frequency plays a crucial role in designing cure process parameters for polymer matrix composites.

Fatigue damage model of woven glass-epoxy fabric composite materials

Based on the Stiffness degradation rule of woven glass fiber composite under fatigue loading, a phenomenological fatigue damage model containing two material parameters in which first is directly proportional to the fatigue life and second is inversely proportional to fatigue loading level is presented in this paper by analyzing damage development effects with very nice result as fatigue modulus is inversely proportional to fatigue strain. Experimental data from Tensile Fatigue Test were employed to verify the model, and the results show that the model can describe the damage evolution of woven glass-epoxy composite laminates under different fatigue loading by verifying the predicted fatigue life of composites. Degradation of Young’s Modulus at different loading cycles, damage development corresponding to Normalized life, its accumulation subjected to constant amplitude fatigue loading including its verifications are well discussed.

The study of hybrid composite plates under transverse sinusoidal load using ANSYS

Composite materials have been widely used in many applications but understanding their failure behavior is always challenging. For years, numerical investigation has been the effective alternative, even though the underlying theories related to composite materials are complicated. This study aims to investigate the improved strength of hybridization by comparing the failure behavior of glass-epoxy composite laminate and hybrid glass-graphite-epoxy laminate under transverse sinusoidal load. The composite and hybrid composite laminates with various aspect ratios were modelled using ANSYS. The plates were simply supported and transverse sinusoidal load were applied until failure occurs. Initially, numerical validation was performed and the simulated results are found to be close to the 3D elasticity analytical results. In general, most simulated parameters produced error less than 2% and thus proving the reliability of the finite element models and implementation. The first ply failure (FPF) and last ply failure (LPF) curves were plotted to compare the failure trend of glass-epoxy composite laminate and its hybrid laminate. The results showed no significant difference in the FPF trend but hybridization could withstand up to 80% more normalized load in terms of the LPF. In conclusion, the present study has shed new knowledge about the failure behavior of hybrid laminate and thus, this knowledge could be applied in designing hybrid composite laminates.

Effect of displacement loading rates on mode-I fracture toughness of fiber glass-epoxy composite laminates

Size-effect method is used in determining mode-I fracture characteristics of woven fiber glass/epoxy composite laminates for varying loading rates. Tensile testing of geometrically similar single-edge notch (SEN) specimens with three widths 30 mm, 40 mm and 50 mm is carried out for four different displacement loading rates namely 1, 10, 100, 500 mm/min. For each width D and loading rate, the crack-length a is varied as 0.125D, 0.25D, 0.375D and 0.5D. A total of 186 specimens are tested. The peak stresses σNu, the initial Youngs Modulus Exx and the shear modulus Gxy are calculated. The fracture toughness KIC, critical strain energy release rate Gf and material characteristic length Cf are calculated using linear regression analysis of non-linear fracture mechanics equations. The values of Gf and Cf first decrease and then increase monotonically as loading rate changes from 1 to 500 mm/min. This behavior was explained using Bažant size-effect equation relating nominal strength and specimen size. The study revealed change in modes of failure characterized by a jump in brittleness number as loading rate increases from 1 mm/min to 10 mm/min followed by decrease in brittleness number as loading rate increases from 10 mm/min to 500 mm/min. This conclusion was supported by highly magnified images of failed specimens using scanning electron microscope. A numerical algorithm to determine crack growth resistance curves (R-curves) from peak load is also implemented. The R-curves are geometry as well as loading rate dependent and give Gf,Cf values which agree qualitatively and to some extent quantitatively with the linear regression approach.

Optimization of acoustic emission parameters to discriminate failure modes in glass–epoxy composite laminates using pattern recognition

In this article, to overcome the challenges encountered during the discrimination of various failure modes in post impacted/indented glass-fiber-reinforced plastic, techniques like pattern recognition method and advanced signal processing were employed. The significant acoustic emission parameters such as amplitude, rise time, counts, energy, duration, and peak frequency that are acquired during compression after impact test are considered as inputs to cluster validity index and for various clustering techniques such as k-means, fuzzy C-means, and Kohonen’s self-organizing map. The acoustic emission count–frequency and amplitude–frequency have no overlapping, whereas other combinations of acoustic emission parameters result in overlapping with four clusters. The clustering techniques are validated by discrete wavelet transform of acoustic emission signals. The discrete wavelet transform was performed on the clustered acoustic emission signals to identify the percentage of energy and frequency content of each level which correlates the different failure modes. The results infer that k-means, fuzzy C-means clustering, and Kohonen’s self-organizing map are 94.5%, 97.1%, and 98.6% reliability, respectively, clearly suggesting Kohonen’s self-organizing map as the most appropriate technique for the classification of acoustic emission signature.

Interlaminar stresses in Glass-Cellulose Epoxy L Bend Hybrid Composites

Huge inter laminar stresses are induced in complex geometry of composite structural joints, for example, those utilized as a primary part of the aircraft structures. An inverted V shaped open mould covered with top plate was used to make L shaped complex geometries using unidirectional (UD) Glass with small amount of Cellulose as fillers at the curvature region in L shaped UD Glass and epoxy composites. But an understanding of the achieved mechanical property is required to improve the technology further and introduced it into industry.Initially tensile test was carried out to know the elastic modulus in the direction of 00 and 900 of UD Glass epoxy composite laminates followed by a four-point bend test was conducted on various L shaped specimen as per ASTM D6415 standard. The experimental results revels that the L shaped specimen made with 7.5wt% of Cellulose fillers in UD Glass gave higher inter-laminar stresses with respect to pristine UD Glass epoxy composite. Further, it is noticed that the UD Glass Cellulose epoxy composite showing increased fiber bridging at the curvature during loading. Finally, it is observed that an improved delamination in L bend composite specimen is achieved by incorporating Cellulose in UD Glass epoxy composite system