Ester Laminates Research Articles

Prediction of temperature and structural properties of fibre-reinforced polymer laminates under simulated fire exposure using artificial neural networks

Load-bearing fibre reinforced polymer laminates soften and decompose when exposed to high temperature fire which may cause significant deformation and weakening, ultimately leading to failure. A combined experimental and modelling study is presented to predict the fire structural survivability of laminates using artificial neural networks based on machine learning. Multiple experimental fire-under-tension load tests are performed under identical conditions to determine the average values and scatter to the surface temperatures, deformation rates and rupture times for an E-glass/vinyl ester laminate. A data-driven modelling strategy based on artificial neural networks is presented that can predict the temperatures and fire structural properties for the laminate when subject to combined fire exposure and tension loading. It is shown that the model gives excellent agreement to the measured surface temperatures, deformations, and time-to-failure of the laminate when exposed to one-sided heating at a constant heat flux. It is envisioned that the ANN based model could be used to assess the fire structural survivability of load-bearing composite structures exposed to fire.

A Study of the Moisture Absorption Characteristics of Vinyl Ester Polymer and Unidirectional Glass Fibre Vinyl Ester Laminates

A Study of the Moisture Absorption Characteristics of Vinyl Ester Polymer and Unidirectional Glass Fibre Vinyl Ester Laminates

Stress Analysis of ASME Section X Flanges Using Classical Lamination Theory

AbstractThe increased usage of fiber reinforced plastic (FRP) composite pressure vessels and piping components in the past decades in the residential and industrial sectors is attributed to the FRP material resistance to corrosion and chemical attacks. FRP composite flanges are, however, known for their anisotropic behavior. In the ASME code section X, FRP composite flanges are treated using an analytical approach derived from that metallic flanges in addition to the fact that the geometries are made to fit them as much as possible and not designed independently. This is known to have caused structural flaws for certain FRP flange classes and sizes. Using a recently developed anisotropic FRP flange approach, it is proposed to identify the most critical flanges by analyzing the flange parameters such as flange ring rotation and stresses in their different parts; gasket, flange ring, hub, and shell subjected to pressure loading. The study on the strength of flanges described in ASME section X RD-620.1 table, will reveal the most critical size and class flanges and their highly stressed locations. To conduct such a study, the selected flange material is an E glass/Vinyl Ester laminate composite. The study shows that FRP flanges of classes 25 and 50 are most vulnerable and should comparatively be less loaded. The stresses are found to reach 50 MPa in the shell and 58 MPa in the flange ring while the maximum flange rotation is 0.83 deg.

Effect of repeated thermal cycle on compressive properties of cyanate ester/quartz-based composites

The continuous fibre reinforced polymer composites are used in electronic circuits and radar radomes of defence aircraft due to lower transmission loss in the broadband microwave frequency region. Quartz fibre-reinforced cyanate ester composites are one of the best-suited materials for the radome structure of an aircraft offering exceptional electromagnetic transparency in varying operational temperatures. Moreover, this material possesses high-temperature capability with excellent mechanical and dielectric properties. The radome structure usually undergoes multiple thermal cycles during fabrication. In this work, to determine the compressive strength, a quartz/cyanate ester laminate was prepared with repeated thermal infusion followed by final curing (CE/Q_M) using resin film infusion (RFI) technique. The volume fraction of fibre, resin and void fraction were evaluated using the resin-burn off method. Finally, Ultrasonic C-scanning, a non-destructive quality evaluation and raster scanning using a multi-axis squirter system was carried out to detect and characterize the defects induced in the laminate. These data were compared to a sample produced with regular infusion followed by a curing cycle (CE/Q_S). The compressive strength of CE/Q_M (372.48 MPa) is measured to be 12% more than that of CE/Q_S (332.084 MPa). This is attributed to increased crosslink density in CE resin and strong interfacial adhesion between the resin and the fibre in the latter due to multiple thermal infusion cycles.

Analysis of scatter in the compression properties of fibre-polymer laminates in fire

Previous research has shown that large scatter can occur in the failure loads and failure times of load-bearing fibre reinforced polymer laminates when exposed to fire. This scatter causes uncertainty in quantifying the structural survivability of composite structures in fire. A combined experimental and modelling study is presented to determine the cause of the scatter and to present a statistical-based model to predict the scatter in the structural survivability of laminates under combined compression loading and one-sided heating by fire. Multiple fire-under-load experimental tests are performed under identical conditions to quantify the magnitude of the scatter for a glass-vinyl ester laminate. The scatter to the deformation rate and time-to-failure of the laminate increased when the heat flux or applied compression load were reduced. A model is presented that can predict the scatter to the compressive failure stress and time-to-failure of a fibreglass laminate when subjected to combined fire exposure and compression loading. The analysis reveals that multiple factors cause the scatter, including small variations in the thickness and fibre content of the laminate.

Low Velocity Impact Response of Laminate Rectangular Plates Made of Carbon Fiber Reinforced Plastics

The paper aims to present an experimental study on low velocity impact behavior of composite materials reinforced with carbon fibers. The objectives of investigations are to assess the main characteristics of impact response such as the energy absorbed by the laminate plate, the contact force as well as the indentation corresponding to different initial kinetic energies of the projectile. The experimental tests were conducted on rectangular plate specimens with dimensions of 150x100x2.5mm3, cut off from a symmetric laminate made of 8 unidirectional carbon/epoxy vinyl ester laminate that are stacked in a lay-up configuration of [0/-45/45/90]s. The energy that induced the specimen’s complete perforation as well as the energy corresponding to the level of BVID were determined with regard to typical testing conditions, such as the time varying acceleration, displacement as well as the absorbed impact energy. Moreover, for comparison purposes, the analytically results obtained for the case of an elastic impact with a projectile velocity of 1m/s, by making use of a complete model based on Kirchhoff plate theory, is presented. Within the range of elastic impact, the analytical results demonstrated their good agreement with the experimental testing data in terms of the absorbed impact energy, displacements and contact force time histories.

Finite element modelling of the explosive blast response of carbon fibre-polymer laminates

A finite element (FE) modelling methodology is presented to analyse the dynamic response of carbon fibre reinforced polymer laminates when loaded by the shock wave generated by an airborne explosive blast. An FE model is developed to calculate the out-of-plane deformation of laminates over the entire duration of an explosive blast loading event. The FE model can also predict the initiation and propagation of delamination cracking and ply rupture in laminates. The response of the composite target plates to explosive blast loading was modelled in the FE program Abaqus using an explicit solver. The explosive air blast load was modelled using the ConWep algorithm. The accuracy of the FE model is assessed using experimental data obtained from small-scale far-field and near-field explosive blast tests performed on carbon-polyester and carbon-vinyl ester laminates. The FE model can predict the dynamic deformation of the laminates to within an accuracy of ~10%. The model can also accurately determine delamination cracks and broken plies.

Basalt Fibres in Vinyl Ester Resin Laminates Under Low Velocity Impact Conditions

A study was conducted to investigate the impact strength of basalt fibres in vinyl ester resin, a composite laminate material used for the design of marine vessels. The basalt/vinyl ester laminate material was dynamically loaded with a Ceast/Instron falling weight machine, using a 3.6 kg cylindrical impactor with a 19.8 mm diameter hemispherical nose. Impact tests were conducted at various energy levels—up to complete penetration—to obtain the full load–displacement curve, identify the material’s penetration energy, and investigate damage initiation and propagation. After the impact tests, the internal damage of each specimen was evaluated using the non-destructive Ultra Sound technique.

Modeling the damage of composite materials subjected to fatigue loading

A two-parameter damage model based on residual strength, applied stress and cycle ratio is presented in this paper to predict progression of damage at different stress levels. Using the proposed model, damage factor progression was predicted for E-glass/vinyl ester laminate at three different stress levels. It is observed that proposed model predicts the damage progression closely even though it is not reporting the type of damage. Also, the damage is reported even at low cycles of loading because of anisotropic nature and inherent damages present in the composite materials.

Damage evolution in VARTM-based carbon fiber vinyl ester marine composites and sea water effects

Carbon fiber-reinforced vinyl ester composite facings are being considered by the US Navy for sandwich structures with either low-density polyvinyl chloride foam or balsa wood as the core materials manufactured using Vacuum-Assisted Resin Transfer Molding process. In this paper, experimental techniques are developed to evaluate the variation of surface strain spatially using three-dimensional Digital Image Correlation technique and internal damage evolution using radiation-based tomography. Both X-ray and neutron radiation was utilized to evaluate the microstructure of composite laminate facings in three dimensions at high resolution. Since naval structures are exposed to harsh sea environment, samples were soaked in simulated sea water at 40℃ for long duration, well beyond saturation stage of Fickian diffusion ascertained using weight gain measurements. Results for a series of mechanical tests on fiber dominated samples of [0/90]2S and matrix dominated samples of [±45]2S orientation are reported. Variable specimen sizes (12.5 mm wide by 100 mm long, 25 mm by 200 mm, and 25 mm by 300 mm, all with an average uniform thickness of 2.8 mm) for laboratory tests are utilized in order to evaluate the applicability of results for large ship structures. Different carbon fiber-reinforced vinyl ester failure mechanisms of matrix crack interactions, such as matrix dominated transverse tension, tension along fibers, and fiber delamination were observed. Digital Image Correlation technique was useful to track the existence of localized damage for both fiber and matrix dominated carbon fiber-reinforced vinyl ester laminates. High resolution X-ray and neutron tomography under in-situ mechanical loading were used to investigate interior microstructure evolution and damage at chosen stress levels. The new techniques presented in this paper can enable a comparison between interior specimen damage and surface damage (readily observable using Digital Image Correlation). Use of different modality of radiation (neutrons versus X-rays) was very useful to probe damage resulting from moisture diffused in the matrix resin and fiber interface/interphase and shows a lot of promise for studying the failure modes and damage evolution in polymeric composites and sandwich structures.

Comparative assessment of the explosive blast performance of carbon and glass fibre-polymer composites used in naval ship structures

An experimental investigation is presented into the explosive blast response of fibre-reinforced polymer laminates used in naval ship structures. Blast tests using plastic explosive charges were performed in air on square target plates made of carbon-polyester, glass-polyester, carbon-vinyl ester or glass-vinyl ester laminates, which are composite materials used in naval ships. The laminates were dynamically loaded by shock waves of increasing pressure and impulse, and the deformation, damage and residual mechanical properties were determined. The amount of blast-induced damage and the post-blast mechanical properties depend on both the fibre reinforcement and polymer matrix. E-glass laminates have higher resistance to blast-induced delamination cracking and tow rupture than carbon fibre composites. Furthermore, glass or carbon fibre laminates with a vinyl ester matrix have superior blast damage resistance compared to composites with a polyester matrix. The higher damage resistance is attributed to the higher flexural strain energy capacity and interlaminar fracture toughness properties of laminates containing glass fibres or vinyl ester matrix.

Synergistic effects of marine environments and flexural fatigue on carbon fiber–vinyl ester composites protected by gelcoat

The current process for designing reliable and enduring naval composite crafts and structures is instrumentally dependent upon utilizing protective coatings to shield composite materials against environmental based degradation. However, as coatings can be vulnerable to corrosion and/or erosion in harsh marine environments, they may gradually lose their protective abilities, leading to damage accumulation in the protected composites. To demonstrate the criticality of this process, gel-coated carbon fiber–vinyl ester laminates are subjected to a simulated marine environment consisting of ultraviolet (UV) radiation, moisture, and cyclic mechanical loading. Next, degradation in composite laminates is probed through measuring the flexural strength. Damage in gelcoat is further characterized by digital microscopy of its surface. Correlation between degradation of the gelcoat surface and loss in the mechanical properties of coated composite laminates is also investigated.

Study of damage induced by extreme thermal cycling in cyanate ester laminates and sandwich panels

Composite materials are sensible to temperature variations which can lead to the development of internal stresses. The induced stresses may be large enough to damage the material. The objective of this study is to evaluate the effects of extreme temperature cycles on three cyanate ester laminates and one sandwich panel. Thermal cycles going from −170℃ to 145℃ were conducted up to 360 cycles. Microscopic observations of the edges and the middle section of the specimens were performed to evaluate damage growth. Three types of damage were observed in the laminates: transverse microcracks, debonding between the fibers and the matrix and to a limited extent delamination. However, debonding between the fibers and the matrix were only visible on the edges of the laminates. The effect of the observed damages on the mechanical properties of the laminates was studied. Results show that properties influenced by matrix behavior were affected by thermal cycling.

Experimental Test of Compressive Strength after Impact Damage of Natural Composite Laminate

In this study, structural design and analysis of the automobile bonnet is performed. The flax/vinyl ester composite material is applied for structural design. The Vacuum Assisted Resin Transfer Molding (VARTM) manufacturing method is adopted for manufacturing the flax fiber composite bonnet. A series of flax/vinyl ester composite panels are manufactured, and several kinds of specimens cut out from the panels are tested to obtain mechanical performance data. Based on this, preliminary structural design of the automobile bonnet is performed. Finally, this study is to investigate the residual compressive strength of the flax/vinyl ester laminate due to impact damages. Through investigation on compressive strength, design allowable of flax/vinyl ester laminate is determined by the experiment to address design criteria of the composite structure.

Deterioration of the fire structural resistance of sandwich composite under tension due to water absorption

The effect of water absorption on the fire structural resistance of a sandwich composite is investigated. A sandwich material consisting of E-glass/vinyl ester laminate skins and balsa wood core was environmentally aged in hot (70°C) and humid (85% relative humidity) conditions for an increasing period up to and exceeding the saturation time. The face skins displayed Fickian diffusion behaviour in the absorption of water whereas the core exhibited significant mass loss due to water causing hydrolysis of bioorganic compounds in the wood. Water absorption decreased the fire structural resistance of the sandwich composite under tensile loading. The saturated sandwich composite exposed to fire failed at lower tensile stresses and within shorter times compared to the dry composite. The reduction in fire resistance was primarily due to moisture-induced weakening of the laminate skins. The reduction to the fire structural resistance caused by water absorption was predicted using a thermal–mechanical model.

Durability of Hybrid Composite Beam Bridges Subjected to Various Environmental Conditioning

AbstractThe hybrid composite beam (HCB) is a novel idea that combines conventional construction materials (i.e., steel and concrete) with fiber-reinforced polymer (FRP) composites in a new configuration. This hybridization aims to optimize the beam’s structural performance and produce a structural element that is more durable than conventional members. This study examined the durability of a commercial glass FRP (GFRP) laminate that was used to encase the HCB elements in a recently constructed HCB bridge. The E-glass/vinyl ester laminate was subjected to five aging regimes. These conditioning regimes simulated an alkaline attack, a salt attack, a salt attack that was preceded by ultraviolet (UV) irradiation exposure, and sustained stresses that were accompanied by controlled thermal cycles and natural weathering. The durability of the E-glass/vinyl ester laminate was examined in terms of changes that occurred in the ultimate tensile strength. A microstructural analysis was performed on both unconditioned ...

Joint Strength Optimization of Bi-Adhesively Bonded Composite-Aluminum Sandwich Structure

Adhesively bonded joint strength optimization can be obtained through the modification of the overlap length and bi-adhesively bonded technique. In this technique, the joints have two different types of adhesive in the overlap length. In the present paper, the effects of bi-adhesively bondline on the shear stress, peeling stress and von-Mises stress of tongue and groove joints were investigated by using finite element analysis. The joint models were consisted of thick woven E-glass/vinyl ester laminate composite groove geometry together with aluminum 5083 tongue geometry. Finite element analyses were performed for three different tongue lengths (75, 150, 225 mm). The distribution of shear and peeling stresses were investigated on adhesively bonded tongue and groove joints subjected to longitudinal tensile loads. The results indicated that the joint strength can be improved by selecting appropriate design parameter values with bi-adhesive bonded technique.

Technical Diagnostics of the State of Composite Tanks of the Evaporators of Sulfuric Acid

The recycling of wastes of hydrolytic sulfuric acid (concentrated and purified in special evaporators) returns them into the technological process of production of mineral fertilizers. In this case, the main structural element of the technological equipment (the tank of the evaporator) suffers intense degradation and requires efficient diagnostics. It is shown that the service life of the evaporator strengthened with glass fibers of polymeric vinyl ester laminate and operating under the conditions of variable mechanical and thermal loads manly depends on the properties of the material of wear-resistant coating protecting the inner surface of the tank against abrasion by hard precipitates of the salts of monohydrates, iron sulfates, and magnesium sulfates.

Post-fire mechanical properties of sandwich composite structures

A thermal–mechanical model for calculating the residual stiffness and strength of fire-exposed sandwich composite structures is presented. The model computes the unsteady-state heat flow and decomposition of a sandwich composite exposed to one-sided radiant heating representative of a fire scenario. The model also computes the residual tension and compression properties of a fire-exposed sandwich composite at room temperature. The accuracy of the model is assessed using post-fire stiffness and failure stress property data for a sandwich composite beam consisting of face skins of E-glass/vinyl ester laminate and a core of balsa wood. Experimental testing reveals that the residual tension and compression properties of the sandwich composite decrease rapidly due mainly to thermal decomposition to the fire-exposed skin. It is demonstrated that the model can accurately predict the residual stiffness and strength properties of fire-exposed sandwich composites. The model reveals that the post-fire tension properties are controlled by char damage to the entire sandwich composite whereas the post-fire compression properties are only dependent on charring to the front skin, resulting in a more rapid loss in stiffness and strength than the tension properties.

Tension modelling and testing of sandwich composites in fire

A thermal–mechanical model is presented for calculating softening and failure of flammable sandwich composites under combined tension loading and one-sided unsteady-state heating by fire. The thermal model calculates the temperature rise of the sandwich composite when exposed to fire. The mechanical model computes the reduction to the tensile modulus and strength of the laminate face skins caused by thermal softening of the fibre reinforcement and polymer matrix and weakening of the core. The numerical accuracy of the model was assessed using data obtained from fire structural tests performed on a combustible sandwich composite consisting of thin woven glass–vinyl ester laminate skins and a thick core of balsa wood. Tests were performed at different tension stress levels and heat fluxes. The model can determine the temperature rise, tensile failure stress and failure mechanism of the sandwich composite in fire. The experimental results presented in the paper also provide new insights into the structural survivability of tension-loaded sandwich composites in fire.