Interlaminar Shear Strength Of Composites Research Articles

Effects of irregular pores on the shear properties of the plane

Through section analysis and optical microscope observation of thick-section composite materials, it is found that there are significant differences in pore micro-characteristics of samples with different thicknesses. It is pointed out that the difference in pore micro-characteristics in the composite matrix is one of the reasons for the change in the interlaminar shear strength of composite materials. In this paper, irregular pore profiles are obtained through image processing, and the parameters to quantitatively characterize the microscopic characteristics are proposed. A randomly generated three-dimensional representative volume element (RVE) model including fiber, matrix, fiber/matrix interface, and pores. The effect of irregular pores with different sizes and distributions on the interlaminar shear strength of composite materials is given. The RVE numerical analysis results show that the interface failure between the fiber and the matrix near the pore causes damage. At the same porosity, the shear strength decreases with the increase of the maximum pore size. At the same time, the porosity concentration also has a significant effect on the interlaminar shear strength of thick section composite. The numerical results verify that the influence of pores on the interlaminar shear properties of thick-section composites is related to the microscopic characteristic parameters of pores.

Asymmetric Four Point Bend Test Method for Interlaminar Shear Strength in Ceramic Matrix Composites

Asymmetrical Four Point Bend test method is proposed for measurement of interlaminar shear strength in continuous fiber reinforced ceramic composites. The current standard ASTM test method (ASTM C1425) for interlaminar shear strength of composites uses a double edge notched compression (DNC) coupon. Large variation in measured strength is observed with the standard ASTM test method, possibly due to machining variability and damage at the notches. The proposed test AFPB method for ILSS is adapted from ASTM C1469 Standard Test Method for Shear Strength of Joints of Advanced Ceramics. This test method does not require any machining of notches and the sample size requirement is much smaller than the ASTM test method. The shear loading in this method is similar to the standard short beam shear test (ASTM D2344) with higher shear to tensile ratio compared to SBS with AFBP. Using finite element analysis, coupon geometry and the distance between the loading and support pins was optimized to maximize shear and minimize tensile and compressive stresses on the specimen. It was found that the variability in the measured ILSS strength was lower with this method compared to the ASTM standard method using the DNC specimen. In addition, the value of ILSS measured using AFPB method was found to be consistently higher than that measured using DNC coupons. It was also found that specimen preparation (cutting, polishing, etc.) did not have significant effect on the measured strength.

Experimental and finite element study on high-velocity impact resistance and energy absorption of hybrid and non-hybrid fabric reinforced polymer composites

High-velocity impact resistance of FRP composites consisting of Kevlar, carbon and glass in hybrid and non-hybrid stacking sequences was studied through experimental and finite element analysis. Neat Kevlar/epoxy and Kevlar/glass/epoxy sandwich composites have the 1st and 2nd highest impact energy absorption percentage (100% and 97.99%, respectively). Carbon/epoxy composite exhibited the least energy absorption (38.78%). Other hybrid composites showed intermediate values of energy absorption in the range 38.58%–44.11%. Hybridization did not show any improvement in interlaminar shear strength of composites either. However, hybridizing Kevlar based composites with glass in the middle layer offered impact resistance close to Kevlar/epoxy composite while offering a 21% saving in material cost. Thus, such Kevlar and glass fabric-based sandwich composites possess a great potential as protective structures due to their ability to withstand impacts up to 200 m.s−1 velocity. These composites may also be considered for development of protective armor that are light-weight compared to conventional materials and more affordable. Finite element simulation results are in good agreement with that of experimental results with differences below 14%.

Influence of Elevated Temperature on the Mechanical Properties of Hybrid Flax-Fiber-Epoxy Composites Incorporating Graphene.

Natural fibers are now becoming widely adopted as reinforcements for polymer matrices to produce biodegradable and renewable composites. These natural composites have mechanical properties acceptable for use in many industrial and structural applications under ambient temperatures. However, there is still limited understanding regarding the mechanical performance of natural fiber composites when exposed to in-service elevated temperatures. Moreover, nanoparticle additives are widely utilized in reinforced composites as they can enhance mechanical, thermal, and physical performance. Therefore, this research extensively investigates the interlaminar shear strength (ILSS) and flexural properties of flax fiber composites with graphene at different weight percentages (0%, 0.5%, 1%, and 1.5%) and exposed to in-service elevated temperatures (20, 40, 60, 80, and 100 °C). Mechanical tests were conducted followed by microscopic observations to analyze the interphase between the flax fibers and epoxy resin. The results showed that a significant improvement in flexural strength, modulus, and interlaminar shear strength of the composites was achieved by adding 0.5% of graphene. Increasing the graphene to 1.0% and 1.5% gradually decreased the enhancement in the flexural and ILSS strength. SEM observations showed that voids caused by filler agglomeration were increasingly formed in the natural fiber reinforced composites with the increase in graphene addition.

The effect of graphene oxide modified short carbon fiber on the interlaminar shear strength of carbon fiber fabric/epoxy composites

Fiber-reinforced polymer composite laminate is weak in the Z-direction, which limits its application. Herein, short carbon fiber (SCF) was decorated with graphene oxide (GO) to form GO@SCF, which was used to improve epoxy matrix and thereby the interlaminar shear strength (ILSS) of carbon fiber fabric (CFF)-reinforced epoxy composites. The effect of GO@SCF on the ILSS of the composite has been examined. It showed that the optimal content of GO@SCF was 0.1 wt%, and the maximum value of ILSS reached 59.4 MPa, which was 14.7% higher than the pure CFF/epoxy composite. The neat SCF was also employed to enhance the ILSS for the purpose of comparison. The results indicate that GO@SCF has better effect on reinforcing the ILSS than the neat SCF. This study provides an effective approach for the reinforcement of the ILSS of CFF-reinforced epoxy composites.

Research on Influence mechanism of composite interlaminar shear strength under normal stress

Abstract The normal stress along the shear plane has great effect on the composite intralaminar shear strength. However, the influence mechanism on composite interlaminar shear strength under the normal stress along the shear plane was not truly reflected by the double-notch shear experiment. In this paper, the interlaminar shear strength of composite specimens under different external normal stresses was first obtained using the improved double-notch shear experiment. Furthermore, to research the influence mechanism on interlaminar shear strength under normal stress along the shear plane, the characteristic curve method based on the double-notch shear specimen was studied. Finally, the experimental results analyzed by the characteristic curve method were compared with a range of failure criteria presented in the literature. The experimental data obtained in this study agreed best with the NU theory criterion, with a maximum numerical difference of 4%. And the NU theory criterion can reflect the influence mechanism of the composite interlaminar shear strength best.

Revelation of catalytic reduction process affecting the morphology and properties of CNTs/carbon fabrics and their composites

Carbon nanotubes/carbon fabrics and their reinforced resin matrix composites were manufactured by chemical vapor deposition and molding method, respectively. Different catalytic reduction processes with different catalyst types and reduction temperatures had different effects on their morphology and properties. It was found by a series of characterization methods that the catalytic activity of the bimetallic catalyst was higher than that of the single metal, and the surface uniformity of CNTs catalyzed by Fe-Co was the best. When the reduction temperature reached the growth temperature, the uniformity of CNTs and the interlaminar shear strength of composites increased obviously. The influence mechanism of these parameters was discussed in depth, which provided a fundamental engineering basis for understanding of catalytic reduction process, optimizing of CNTs growth process and the application of high-performance composite materials.

On the Inter-Laminar Shear Strength of Composites Manufactured via a Stepped-Concurrent UV Curing and Layering Process

In this paper, we set to examine the inter-laminar shear strength of a fiber-reinforced composite part manufactured via a stepped-concurrent ultraviolet curing and layering process. This process was specifically proposed for making epoxy-based thick parts, whereby a layer-by-layer, model-based, optimal layering time and ultraviolet control scheme is set up with the objective of minimizing the degree of cure deviation across the final thick part. We focus on a cationic curing process wherein additional energy savings are possible by switching off the ultraviolet source after initiating the curing reaction with the ultraviolet source at each layer addition. Since the inter-laminar sheer strength of parts made via a layering process is often a concern, we consider the application of in-situ consolidation pressure in the layering process. We then characterize the inter-laminar shear strength by manufacturing samples with application of different in-situ consolidation pressures and measuring the inter-laminar shear strength of each sample by the short-beam shear test. The results showed that the inter-laminar shear strength of composite parts fabricated with the proposed stepped-concurrent curing, and layering process increases with the applied consolidation pressure up to a point. Scanning electron microscopy of samples cured at different in-situ consolidation pressure showed that the sample with optimum consolidation pressure has relatively uniform fiber to resin distribution and hence improved inter-laminar shear strength.

Improved interlaminar shear strength of glass fiber/epoxy composites by graphene oxide modified short glass fiber

Improving the interlaminar shear strength (ILSS) of composites is vital for the application of laminated composites. In this work, graphene oxide (GO) modified short glass fibers (GO-modified SGFs) was employed to intercalate into glass fiber/epoxy (GF/EP) composites to improve their ILSS. The effects of GO-modified SGFs and SGFs on the ILSS of composites were compared. The GF/EP composites were prepared by compression molding. The results showed that the ILSS of GF/EP composites increased by 12.5% and 18.4% after intercalation of SGFs and GO-modified SGFs, respectively. GO significantly increased the surface roughness of SGFs, and improved the interfacial adhesion between SGFs and EP.

Effect of Alkali Treatment on Mechanical and Morphological Properties of Pineapple Leaf Fibre/Polyester Composites

In this study, our aim is to analyze the influence of fibre treatments and different fibre loading on mechanical, physical and chemical properties of pineapple leaf fibre reinforced polyester composites (PALF/PE). Fibre treatments were carried out with 1 N NaOH and KOH for 1 h. The untreated and treated PALF/PE composites were fabricated with 25 wt%, 35 wt% and 45 wt% fibre loadings by compression molding technique. Fourier Transform Infrared Spectroscopy (FTIR) was used to understand the effects of chemical treatment on PALF mechanical test results revealed that 45 wt% of PALF/PE composites treated with NaOH showed a 35% increase in tensile strength compared to untreated PALF/PE composites. The tensile modulus and the flexural module are also the highest at 45 wt% of KOH treated composites. The highest impact strength of 70 J/m was obtained for PALF/PE composites with NaOH treated fibres at 25% fibre loading. The results show that the fibre treatments in terms of the flexural and inter-laminar shear strength of composites were not effective. SEM of the tensile fractured specimen of PALF/PE composites revealed the changes in fibre characteristics due to the alkali treatment and less fibre pull-out at higher fibre loading. Overall we conclude that 1 N NaOH, 45 wt% treated PALF/PE composites satisfactorily and effectively improved both the mechanical and morphological properties. Obtained composites would be promising for construction materials, furniture and automotive components due to their superior strength and modulus at higher fibre loading.

Influence of Areca Nut Nano Filler on Mechanical and Tribological Properties of Coir Fiber Reinforced Epoxy Based Polymer Composite

The present study is aimed at investigating the effect of incorporating arecanut nano filler on the tribological behaviour of coir reinforced epoxy based polymer matrix composite. Areca nut nano filler is produced by grinding followed by ball milling. Particle size analyzer confirmed the size of nano fillers obtained are in the range of 20-100 nm. Composites with different weight percentage of nano filler (0%, 5%, and 10%) were studied for their mechanical and tribological behaviour using pin on disc rig. Tensile, Flexural, Interlaminar shear and impact tests are carried out on the proposed composite. Taguchi’s technique is used for analysing effect of various factors on the tribological behaviour of the composite. The results showed that inclusion of arecanut nano filler enhanced the microhardness of the composite, with inclusion of arecanut filler the tensile strength increased up to 5 %, later there is a decrease in tensile strength. Flexural strength significantly increases with increase in filler percentage from 0% to 5%, but the variation of flexural strength from 5% to 10% is negligible. Inclusion of filler has negligible effect on the interlaminar shear strength of composites. Impact strength and wear resistance of the composite is enhanced with incorporation of filler.

The Effect of Nano-Fillers on the In-Plane and Interlaminar Shear Properties of Carbon Fiber Reinforced Composite

In this study, the interlaminar region of a carbon fiber composites was reinforced with silica nano-particles, and its effect on the in-plane mechanical response was investigated. Also, the effect of particles on the dynamic interlaminar shear strength of composites was studied. Two batches of composite specimens, one batch made of only fiber and matrix and the other with nano-silica added as a third phase, were fabricated. The composite specimens were prepared through a high-temperature molding process, where the nanoparticles were dispersed on the surface of the prepreg layers before stacking. For in-plane properties, standard tensile test coupons were made with fibers oriented at a different angle relative to the loading direction. For interlaminar shear properties, a V-notch bending and three-point bending specimens were prepared. It was found that the nanoparticles have a sound influence on the in-plane mechanical response mainly on the in-plane shear property of the composite. On the other hand, the nano-filler has shown a significant effect on the dynamic interlaminar shear strength of the laminate.

Improvement of aramid fiber III reinforced bismaleimide composite interfacial adhesion by oxygen plasma treatment

Domestic Aramid Fiber III (DAF III) was modified by oxygen plasma treatment. The effects of oxygen plasma treatment power on fiber surface and DAF III reinforced bismaleimides (BMI) composite interfacial properties were investigated, respectively. The fiber surface characteristics were analyzed by X-ray photoelectron spectroscopy, Scanning Electron Microscopy, Atomic Force Microscopy and Dynamic Contact Angles Analysis, respectively. The results showed that oxygen plasma treatment introduced new oxygen containing groups such as C=O and –COO on to the fiber surfaces, changed the fiber surface morphologies and enhanced surface roughness by oxidative reactions and plasma etching. Finally, the fiber surface wettability was effectively improved. The total free energy increased from 49.8 to 71.7 mJ/m2 at maximum with 300 W oxygen plasma treatment. The composite interlaminar shear strength (ILSS) was evaluated by short beam shear measurement. The ILSS value increased from 49.3 to 59.8 MPa (by 21.3%) within 300 W plasma treatment.

The interfacial adhesion of wood fiber–reinforced UHMWPE composite filled with acid‐treated clay

Wood fiber–reinforced ultrahigh molecular weight polyethylene (wood fiber/UHMWPE) composites have been filled with acid‐treated clay to enhance the adhesion. According to the modification, the interlaminar shear strength of composites has been greatly improved. X‐ray photoelectron spectroscopy and scanning electron microscopy are used to examine the microscopic properties of resultant composites. The enhanced interlaminar shear strength is attributed to the clay interlock, which improves the wetting between wood fibers and resins.

Interface characteristic of aramid fiber reinforced poly(phthalazinone ether sulfone ketone) composite

Interface is an important microstructure for advanced polymer‐matrix composite. The composite interface is the bridge and the link for stress transferring between the fiber and the matrix resin. In this work, oxygen plasma treatment was used for modification of aramid fiber surface. The effects of plasma treatment power on interlaminar shear strength of composite were evaluated by short‐beam shear test. The morphologies of both the aramid fiber surface and its composite interface fracture were observed by SEM. The chemical structure and surface chemical composition of the plasma‐treated and separated fibers were analyzed by Fourier transform infrared (FTIR) and XPS, respectively. The results showed that the interlaminar shear strength of composite was enhanced by 33% with plasma treatment power of 200 W. The FTIR and XPS results indicated that the active functional groups were introduced onto the aramid fiber surface by plasma treatment forming chemical bonds with the poly(phthalazinone ether sulfone ketone) resin. The SEM results proved that the aramid fiber surface was roughened by plasma treatment enhancing the mechanical bond with the poly(phthalazinone ether sulfone ketone) resin. The composite rupture occurred from the composite interface to the fiber or the matrix resin. Copyright © 2017 John Wiley & Sons, Ltd.

Improvement of interfacial adhesion in PP/PS blends enhanced with supersonic atmosphere plasma spraying surface‐treated carbon fiber

The effects of surface treatment of a carbon fiber (CF) by supersonic atmosphere plasma spraying (SAPS) on the interfacial adhesion behavior and morphology of polypropylene/polystyrene (PP/PS) matrix blends filled CF composites were investigated. Effects of surface treated a commercial CF on mechanical properties are studied. Contact angle was measured to examine the changes in wettability of the CF. The chemical and morphological changes were characterized by using X‐ray photoelectron spectroscopy and scanning electron microscopy. PP/PS/CF composites were fabricated with and without SAPS treatment, and their interlaminar fracture toughnesses were compared. The results showed that the interlaminar shear strength of composites has been greatly improved filled SAPS modification CF. The water contact angle of resin sample decreased 50% after addition of SAPS surface‐treated CF. Scanning electron microscopy results on the fractured surface exhibited PP/PS blends adhered well around the CFs of the SAPS‐treated specimen compared with that of the untreated specimen. This attributed to the CF interlock, and it improves the wetting between fibers and resins. Copyright © 2017 John Wiley & Sons, Ltd.

Flexural properties, interlaminar shear strength and morphology of phenolic matrix composites reinforced with xGnP-coated carbon fibers

Abstract In the present study, exfoliated graphite nanoplatelets (xGnP) with different particle sizes were coated onto polyacrylonitrile-based carbon fibers by a direct coating method. The flex-ural properties, interlaminar shear strength, and the morphology of the xGnP-coated carbon fiber/phenolic matrix composites were investigated in terms of their longitudinal flexural strength and modulus, interlaminar shear strength, and by optical and scanning electron mi-croscopic observations. The results were compared with a phenolic matrix composite coun-terpart prepared without xGnP. The flexural properties and interlaminar shear strength of the xGnP-coated carbon fiber/phenolic matrix composites were found to be higher than those of the uncoated composite. The flexural and interlaminar shear strengths were affected by the particle size of the xGnP, while the particle size had no significant effect on the flexural modulus. It seems that the interfacial contacts between the xGnP-coated carbon fibers and the phenolic matrix play a role in enhancing the flexural strength as well as the interlaminar shear strength of the composites.

Effects of Graphene Oxide Modified Sizing Agents on Interfacial Properties of Carbon Fibers/Epoxy Composites.

A kind of graphene oxide (GO) modified sizing agent was used to improve the interfacial properties of carbon fibers/epoxy composites. The surface topography of carbon fibers was investigated by scanning electron microscopy (SEM). The surface compositions of carbon fibers were determined by X-ray photoelectron spectroscopy (XPS) and the interfacial properties of composites were studied by interlaminar shear strength (ILSS). The results show that the existence of GO increases the content of reactive functional groups on carbon fiber surface. Thus it enhances the interfacial properties of carbon fibers/epoxy composites. When GO loading in sizing agents is 1 wt%, the ILSS value of composite reaches to 96.2 MPa, which is increased by 27.2% while comparing with unsized carbon fiber composites. Furthermore, the ILSS of composites after aging is also increased significantly with GO modified sizing agents.

Synergistic reinforcement effect of aramid nonwoven fabrics and PVDF on mechanical and damping properties of bismaleimide matrix composites

A new type of structural damping composite was prepared by interleaving aramid nonwoven fabrics (ANF) modified with semi-crystalline polyvinylidene fluoride (PVDF) between carbon-fibre-reinforced bismaleimide (BMI) laminae. The co-cured composite exhibited an increase of 108% and 2.72% in loss factor and flexural modulus, respectively, compared with the original carbon-fibre-reinforced BMI composite. The damping behaviour of the co-cured composites was experimentally investigated using the single cantilever beam test and dynamic mechanical analysis. Furthermore, the composite interlaminar shear strength and flexural strength and modulus were also investigated. The results indicated that the composite interleaved with ANF/PVDF possessed higher flexural modulus and loss factor than the composites interleaved with ANF or PVDF films alone as a result of synergistic reinforcement of ANF and PVDF. Finally, the reinforcement mechanism of ANF/PVDF was investigated by analyzing the composite microstructure and the dynamical mechanical properties of ANF, PVDF, and ANF/PVDF interlayers.

Effect of TEOS Electrospun Nanofiber Modified Resin on Interlaminar Shear Strength of Glass Fiber/Epoxy Composite

 Abstract —Interlaminar shear strength (ILSS) of fiber reinforced polymer composite is an important property for most of the structural applications. Matrix modification is an effective method used to improve the interlaminar shear strength of composite. In this paper, EPON 862/w epoxy system was modified using Tetraethyl orthosilicate (TEOS) electrospun nanofibers (ENFs) which were produced using electrospinning method. Unmodified and nanofibers modified resins were used to fabricate glass fiber reinforced polymer composite (GFRP) using H-VARTM method. The ILSS of the Glass Fiber Reinforced Polymeric Composites (GFRP) was investigated. The study shows that introduction of TEOS ENFs in the epoxy resin enhanced the ILSS of GFRPby 15% with 0.6% wt. fraction of TEOS ENFs.