Interlaminar Shear Strength Results Research Articles

Influence of Interfacial Interaction and Composition on Fracture Toughness and Impact Properties of Carbon Fiber-Reinforced Polyethersulfone.

In this study, the interlaminar fracture toughness and impact strength of polyethersulfone reinforced with continuous carbon fibers were studied. Interlaminar fracture toughness tests were performed using the double cantilever beam method. It was shown that surface modification using the thermal oxidation method of the carbon fibers can strongly increase the interlaminar fracture toughness of the obtained composites. Thus, the maximum value reached 1.72 kJ/m2, which was 40% higher than the fracture toughness of the composites reinforced with initial carbon fibers. Moreover, fractographic analysis using a scanning electron microscope allowed us to highlight the main reasons for the dependence of fracture toughness on fiber content and surface modification conditions of the carbon fibers. It was shown that the main factor that allowed for an increase in fracture toughness was the enhanced interfacial interaction between the fibers and polymer matrix. Additionally, it was found that expectedly, there was a good correlation between interlaminar fracture toughness and interlaminar shear strength results. However, a negative influence of surface modification on the impact properties of composites was found. Such behavior occurred because of higher structural stability and lower exposure to delamination in multiple layers of the composites reinforced with the modified carbon fibers. It was found that impact energy reached ~150 kJ/m2 for the polyethersulfone-based composites reinforced with initial fibers, while the composites reinforced with modified carbon fibers showed impact energy values of only ~80 kJ/m2. Nevertheless, surface modification of carbon fibers using the thermal oxidation method can be an effective method for improving the performance properties of polyethersulfone-based composite materials.

Adhesively- and hybrid- bonded joining of basalt and carbon fibre reinforced polybenzoxazine-based composites

Polybenzoxazines-based composites are an excellent alternative in lightweight design due to their outstanding properties in terms of chemical stability, inherent flame resistance, as well as mechanical performance. The present work provides an investigation of different joining techniques for polybenzoxazine-based composites, namely adhesively - and hybrid bonded joining. The effects of fibre reinforcement (carbon or basalt), and substrate thickness (2 or 3 mm) on the lap-shear strength of joints are taken into consideration. Here, basalt (BFRP) and carbon fibre reinforced plastics (CFRP) were manufactured by vacuum infusion technique followed by a convection oven curing. Mechanical characterisation of substrates included tensile and interlaminar shear strength testing. Hybrid joints were fabricated by rivet insertion in cured joints bonded with a structural adhesive. Adhesive bonding showed to be a proper joining technique presenting a good adhesion with substrates, and adequate cohesive strength. Hybrid bonded joints had a fail-safe fracture and higher energy absorption prior to failure than their adhesively bonded counterparts. No effect of substrate thickness on lap-shear strength was observed. The dominating failure mechanism for the joints was the delamination of the topmost-layer due to peel stresses. CFRP joints exhibited higher lap-shear strength than BFRP joints, which was consistent with interlaminar shear strength results.

Thermal and mechanical properties of carbon fiber-reinforced resin composites with copper/boron nitride coating

Copper and hexagonal boron nitride filler (Cu/hBN) were incorporated into carbon fiber-reinforced polymer (CFRP) composites by electrophoretic deposition (EPD) to maximize their thermal conductivity. The results show that the thermal conductivity increased to 1.68 and 5.15 W/mK in the through-thickness and in-plane directions, respectively, when the concentration of hBN particles in the deposition solution was increased to 5 g/L. Moreover, the interlaminar shear strength results of various composites exhibited the same trend as the thermal conductivity. However, the tensile test results showed that the tensile strength was reduced as the hBN concentration was increased.

Simultaneous reinforcement of matrix and fibers for enhancement of mechanical properties of graphene‐modified laminated composites

Fiber and matrix‐dominant properties of fiber‐reinforced polymer composites are important in many structural applications. Pre‐mixing the polymer matrix with nanoparticles could enhance the through‐thickness or matrix‐dominant properties. Surface treatment of fiber reinforcements with nanoparticles, on the other hand, could improve the in‐plane or fiber‐dominated properties of laminated composites, as well as interfacial adhesion. In this article, a novel low‐cost manufacturing method, combining surface treatment of fibers with matrix modification techniques, was devised to incorporate nanoparticles for the simultaneous reinforcement of matrix and fibers without increasing the viscosity of the epoxy matrix. Several graphene‐based nanomaterials, including graphene oxide (GO) and its thermally reduced version (rGO), graphene nanoplatelets (GNPs), and multi‐walled carbon nanotubes (MWCNTs) were employed to modify the epoxy matrix and the surface of glass fibers. Unmodified and modified epoxy and fibers were used for fabricating multiscale glass fiber‐reinforced composites following the vacuum‐assisted resin transfer molding process. The composites obtained combined improvements in both the fiber and matrix‐dominant properties, resulting in superior composites. We investigated the morphological, rheological and mechanical properties of the glass fiber‐reinforced multiscale composites. The results from testing for tensile properties and interlaminar shear strength (ILSS) of the glass fiber‐reinforced composites indicate that the introduction of GNPs, GO, rGO, and MWCNTs enhanced mechanical properties. The fracture surfaces of the fiber‐reinforced composites were examined by scanning electron microscopy and we used the micrographs to explain the tensile and ILSS results. POLYM. COMPOS., 40:E1732–E1745, 2019. © 2018 Society of Plastics Engineers

Effects of hydrothermal aging on carbon fibre/epoxy composites with different interfacial bonding strength

This paper presents an investigation on the effects of hydrothermal aging on carbon fibre reinforced polymer (CFRP) composites with different interfacial bonding strength. The combination of electrochemical oxidation and sizing treatments effectively enhanced the long-term interlaminar shear strength (ILSS) retention from 0.24–0.38 to 0.74–0.86 for CFRP in hydrothermal environment, which basically met the specified environmental reduction factor CE (0.85) given in ACI 440.2R-08. The improved durability of fibre/epoxy interface was also evidenced by the moisture absorption and desorption tests and scanning electron microscopy (SEM). In addition, the dynamic mechanical thermal analysis (DMTA) was directly used to characterize the degradation of interface adhesion for CFRP, and the damping at fibre/epoxy interface (tan δin) was evaluated and finally linked with the ILSS results.

Irradiation dose control for polymer‐matrix composites fabricated by in situ curing with low‐energy electron beam

ABSTRACTThe electron beam (EB) with emitting energies lower than 150 keV is applicable in in situ curing of polymer‐matrix composites; however, being poor in penetration ability, it leads to significant attenuation of irradiation dose along the prepreg thickness. In this study, polymer‐matrix composites were fabricated by low‐energy EB irradiation curing, and the effect of dose control of double‐sided irradiation was systematically investigated. Experimental results showed that laminates fabricated by single‐sided irradiated prepregs were low in interlaminar shear strength (ILSS) owing to incomplete curing after being post cured at 180 °C for 30 min. A double‐sided irradiation method which included irradiation of equal dose and different doses on both sides of the prepreg was proposed to overcome this difficulty. Analysis showed that under a total dose of 70 and 100 kGy, the ILSS results were high owing to the low curing degree of two adhesive surfaces; under a total dose of 130 and 160 kGy, laminates fabricated with different EB irradiation doses on both sides exhibited enhanced ILSS compared to those with equal dose on both sides, owing to physical adhesion and chemical crosslinking between layers. The ILSS results exhibited the largest increase of 18.9 and 60.5%, respectively, by tuning the dose differences between both sides of the prepregs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44944.

Inter Laminar Shear Strength (ILSS) of Nano Al2O3 Filled Glass Fiber Reinforced Polymer (GFRP) Composite - A Study on Loading Rate Sensitivity

The objective of the research article is to study the loading rate sensitivity on ILSS of nano Al2O3 filled GFRP composite. Nano Al2O3 filler is impinged into the epoxy matrix at different volume fraction (Vf) of glass fiber. The GFRP composite is fabricated by hand- lay-up techniques. Inter laminar shear strength (ILSS) has been investigated at different loading rate or cross head velocity of 1, 50, 100, 500 and 1000mm/min. The results indicate that ILSS increases when loading rate increase from 1 to 100 mm/min and decreases further with increase in loading rate. This may be because of micro crack does not have sufficient time to propagate the weakest path and rather it has to propagate through the strong covalent bond between the matrix and nano particle or need to break the fiber for crack propagation for which ILSS increases. Experimental results showed that nano Al2O3 filler does not have any effect on glass transition temperature (Tg). Scanning electron microscope is used for fracture surface analysis to study the mode of fracture at different loading rate and correlate them with the ILSS results.

An approach to identify complex CNT reinforcement effect on the interlaminar shear strength of prepreg composites by Taguchi method

Several factors affect the interlaminar shear strength of carbon nanotube reinforced carbon fiber composites in multi-scale. A combined route of CNT toughening through manufacturing a custom made prepreg system with CNT dispersion in epoxy and integrating vertically aligned CNTs as nanofibers to bridge in between prepreg plies is applied to achieve enhanced interlaminar shear strength (ILSS). Depending on the CNT loading, effectiveness of dispersion and CNT bridging between prepreg plies, the mechanical enhancement is achieved up to 15%. A new approach of identifying the critical parameters of nano-engineered and nano-reinforced composites through Taguchi method is a novel route for investigating the combined effects of several factors in a complex mechanical enhancement problem with reduced number of experiments as studied in here. Taguchi L8 orthogonal array is used to obtain maximum ILSS by short beam shear (SBS) test. The parametric study has shown that the most significant parameters affecting the ILSS results are type of epoxy, fabrication procedure and CNT loading.

Role of matrix modification on interlaminar shear strength of glass fibre/epoxy composites

Interlaminar shear properties of fibre reinforced polymer composites are important in many structural applications. Matrix modification is an effective way to improve the composite interlaminar shear properties. In this paper, diglycidyl ether of bisphenol-F/diethyl toluene diamine system is used as the starting epoxy matrix. Multi-walled carbon nanotubes (MWCNTs) and reactive aliphatic diluent named n-butyl glycidyl ether (BGE) are employed to modify the epoxy matrix. Unmodified and modified epoxy resins are used for fabricating glass fibre reinforced composites by a hot-press process. The interlaminar shear strength (ILSS) of the glass fibre reinforced composites is investigated and the results indicate that introduction of MWCNT and BGE obviously enhances the ILSS. In particular, the simultaneous addition of 0.5 wt.% MWCNTs and 10 phr BGE leads to the 25.4% increase in the ILSS for the glass fibre reinforced composite. The fracture surfaces of the fibre reinforced composites are examined by scanning electron microscopy and the micrographs are employed to explain the ILSS results.

Influence of voids on interlaminar shear strength of carbon/epoxy fabric laminates

The effects of voids (void content, void shape and size) on the interlaminar shear strength of [(±45) 4/(0,90)/(±45) 2] S and [(±45)/0 4/(0,90)/0 2] S composite laminates were investigated. Specimens with void contents in the range of 0.2%–8.0% for [(±45) 4/(0,90)/(±45) 2] S and 0.2%–6.1% for [(±45)/0 4/(0,90)/0 2] S were fabricated from carbon/epoxy fabric through varying autoclave pressures. The characteristics of the voids were studied by using optical image analysis to explain the interlaminar shear strength results. The influences of voids on the interlaminar shear strength of the two stacking sequences were compared in terms of the void content and size and shape of the void. The effect of voids on the initiation and propagation of interlaminar failure of both stacking sequence composites was found.

Interlaminar Shear Property of Modified Glass Fiber-reinforced Polymer with Different MWCNTs

The interlaminar shear property of composites remains a serious concern in application. In this article, five different multiwalled carbon nanotubes (MWCNTs) are tried to improve the interlaminar shear property of composites, including two MWCNTs (MWCNTs-A and MWCNTs-B) different with diameters and lengths, an orientated MWCNTs (MWCNTs-C), a film-shaped MWCNTs-A (MWCNTs-D), and a surface-treated MWCNTs-B (MWCNTs-E). The interlaminar shear strength (ILSS) of the composites, filled with one of the above-mentioned materials as a constituent is investigated. The best ILSS increases by 8.16% from 24.5 MPa to 26.5 MPa with MWCNTs-E. In addition, the dispersion of MWCNTs in a glass fiber-reinforced polymer (GFRP) is researched by a scanning electron microscopy (SEM) in association with the ILSS results.

Aging Effects on the Interlaminar Shear Strength of High-Performance Composites

The effect of isothermal aging on interlaminar shear strengths of quasi-isotropic composites laminates were evaluated by using ASTM D 3846-94, Standard Test Method for In-Plane Shear Strength of Reinforced Plastics. Thermoset bismaleimide (IM7/5260) and thermoplastic polyimide (IM7/K3B) were investigated to determine the aging degradation in different matrix materials. The laminates were 24 plies and had a lay up of [-45/90/45/0]3S. Aging temperatures were 300, 350, and 400°F and aging time varied from a few hours to 28 months. Nonaged specimens were also tested for baseline values. Significant differences were noted between these two different matrices. Isothermal aging for IM7/5260 initially caused posteuring effects prior to an overall decrease in interlaminar shear strength. Strength degradation was directly dependent on both aging temperatures and times. In addition, accelerated aging effects at 400°F were observed. For the IM7/K3B specimens no postcure effects were observed. The interlaminar shear strength decreased for longer aging times, but showed little variation for different temperatures. Aging at 400°F did not show any accelerated aging effects. The interlaminar shear strength results were compared with previously obtained compression after impact data. Similar trends in strength degradation were observed.

Resistência ao Cisalhamento Interlaminar de Compósitos com Resina Epóxi com Diferentes Arranjos das Fibras na Presença de Vazios

A presença de vazios em compósitos estruturais pode ter efeitos significativos. Em geral, os vazios diminuem a resistência estática e a vida em fadiga de laminados. Essa influência é bastante pronunciada na resistência ao cisalhamento interlaminar, compressão, entre outras, onde as propriedades mecânicas da matriz exercem maior influência sobre o comportamento do compósito. O presente artigo descreve o estudo do efeito da porosidade na resistência ao cisalhamento interlaminar de sistemas de compósitos de tecido e tape (fitas unidirecionais) de carbono aglutinados com matriz epóxi. Os laminados foram produzidos de maneira semelhante, bem como o processo de introdução de vazios (na faixa de 0a 12% de porosidade).Os compósitos foram avaliados por análises microscópicas e inspeção ultra-sônica e os valores de atenuação medidos foram convertidos em coeficientes de absorção para permitir uma normalização dos dados. O critério de fratura de Mar-Lin apresentou bom ajuste, mostrando-se adequado para o estudo de porosidade em compósitos. Por meio desse critério foi determinado que somente os laminados com porosidade acima de 0,9% para tecido de carbono/epóxi e acima de 0,75% para laminados de tape de carbono/epóxi é que apresentam redução de suas propriedades mecânicas

Comparison of the short beam shear (SBS) and interlaminar shear device (ISD) tests

The Short Beam Shear (SBS) and Interlaminar Shear Device (LSD) tests are compared as methods for determining interlaminar shear strength of thermoplastic composite rings. The rings were manufactured using laser-assisted on-line consolidation and the interlaminar shear strength is taken as a measure of the quality of parts subjected to various processing conditions. Although a number of shear test methods have been developed for use with composite materials over the years, none provide pure uniform shear, or provide the entire stress-strain response to failure from a single specimen [Adams, D.F. and Lewis, E.Q., Current status of composite material shear test methods. SAMPE 31, 1994,6,32-401. Hence, a testing technique is required to provide efficient interlaminar shear strength results. Through the test results, it can be seen that a different mode of failure is acting in each of the tests. Finite Element Analyses (EEA) of the test procedures show that the stress state at the failure site for SBS is not interlaminar shear whereas it is the stress state in the failure zone of the ISD. Therefore, it is concluded that the ISD provides a better measure of the interlaminar shear strength of these specimens. 0 1997 Elsevier Science Limited

Failure mechanisms in carbon-fibre-reinforced poly(ether sulphone)

This paper examines the fracture behaviour of carbon-fibre-reinforced polyethersulphone (PES) and compares the results with carbon-fibre-reinforced polyetheretherketone (PEEK). Tests were carried out over a range of temperatures between −60 and +100°C using the double cantilever beam geometry, and cracks were sent both parallel to the individual laminates (interlaminar) and perpendicular to the laminates (intralaminar). Although the total interlaminar toughness of the PES composite was lower than the PEEK-based material, the crack propagation was stable independent of the testing temperature, whereas the PEEK composite showed a change to unstable fracture at low temperatures. Experiments on the bulk PES polymer reinforced the link between the ductility of the matrix and the stability of cracking of the composite. The weaker fibre/matrix bond for the PES composite, shown by the interlaminar shear strength results, reduced the amount of matrix deformation but aided the composite crack stability. Fibre/matrix debonding was also responsible for a large increase in intralaminar toughness with crack length which eventually passed that of the PEEK material.

Carbon fiber‐reinforced composites: Effect of fiber surface on polymer properties

AbstractDynamic mechanical measurements in a torsional (shear) mode have been used to characterize an unfilled epoxy (Epon 828/m‐phenylene diamine) and A series of uniaxial graphite fiber (Hercules types A and HM) composites. In unfilled resins containing an excess of the epoxy component, Mc—the average molecular weight between crosslinks—decreases with increasing temperature and duration of cure, suggesting a temperature‐dependent side reaction. In fiber‐reinforced composites, the dynamic mechanical response is sensitive to fiber type and curing schedule; elevation of Tg by as much as 45°C has been observed. Comparison of the dynamic data with properties predicted by micromechanical models shows only a fair agreement at room temperature, which rapidly worsens at higher temperatures. Surface treatment of type A fibers gives enhanced interlaminar shear strength (ILSS), both at ambient conditions and after hydrothermal aging. Dynamic data for surface‐treated systems during hydrothermal aging show a sharper drop in G′ and increase in tan δ. The dynamic data and ILSS results are interpreted in terms of a balance of polymer‐fiber interactions, a weak but widespread preferential adsorption of epoxy oligomers on the graphite basal planes at the fiber surface, and a low concentration of covalent bonds between polymer and fiber‐surface‐functional groups.