Mechanical Performance Of Composites Research Articles

Autogenous healing of Engineered Cementitious Composites (ECC) based on MgO-fly ash binary system activated by carbonation curing

Developing self-healing of concrete cracks represents a critical approach for extending material longevity. If demonstrated on concretes with CO2 stored through carbonation curing, self-healing can further mitigate infrastructure lifecycle emissions. In this study, the self-healing process is investigated on novel Engineered Cementitious Composites (ECC) based on binary blends of reactive MgO cement and siliceous fly ash activated by carbonation. The self-healing was observed under cyclic wetting and drying exposures and was characterized by measurements of resonance frequency, optical microscopy and X-ray computed microtomography (XCT). Thermogravimetric analysis, X-ray powder diffraction and scanning electron microscopy were employed to assist in identifying healing products and mechanisms. It was found that micro-cracks could be autogenously filled in 7 wet-dry cycles, as evidenced by over 95% recovery of resonance frequency and healed crack appearance under optical microscopic observation. Nevertheless, the composite mechanical performance, particularly tensile strength and ductility, did not fully recover with respect to the uncracked specimens. The inadequate post-healing mechanical properties were consistent with XCT observations that indicated low material densities in the cracked area. Based on the chemical and microstructural characterizations, it was determined that nesquehonite crystallites were responsible for the crack filling. Although the nesquehonite filled cracks will be less permeable to invasion of reactive fluids, novel strategies are needed to establish more robust healing capability to completely restore the crack bridging and composite tensile performance.

Effect of film cooling holes on the mechanical properties of 3D braided SiCf/SiC composites at 1350 °C in air

3D braided SiCf/SiC composites are the preferred material for turbine blades of advanced aero engines, but film cooling holes (FCHs) severely destroy the structural integrity and affect the mechanical properties. There are few studies concerning the mechanical performance of composites with FCHs. This paper presents the effect of FCHs on the mechanical properties of 3D braided SiCf/SiC composites at 1350 °C in air. The number of drilled holes were 1, 5, 10 (rectangular) and 11 (triangular), and the average diameter was 0.5 mm. Monotonic tensile tests, microstructure characterization and finite element method were performed to investigate the initiation and evolution of local damage around the FCHs. The results indicated that the coating effectively prevents oxygen penetration in short-term tests and composites with FCHs still maintain excellent ultimate tensile strength (UTS). The UTS of the composites seriously decrease due to stress concentration and unbridged cracking propagation around the FCHs in long-term tests. A triangular arrangement should be avoided in FCHs design of 3D braided composites because specimens with 11-H present low UTS. The failure mechanism of the composites with FCHs was discussed in detail according to the FEM calculation results. The research results of this paper provide a reference for the design of SiC composite turbine blades.

Static and Dynamic Mechanical Performance of Carbon Fiber Reinforced Polyethersulfone Composites

This study has been carried out to demonstrate the effect of short carbon fiber (SCF) loading on static and dynamic mechanical performance of polyethersulfone (PES) composites. Different combinations of SCF/PES composites were prepared by extrusion followed by injection molding. The static mechanical properties such as hardness, tensile and flexural properties of PES based composites were analyzed following ISO standards. As engineering materials, the polymer composites with high modulus as well as excellent damping properties are of great interest in aerospace and automotive industries for severe dynamic environment. Furthermore, in addition to static properties of composites, dynamic mechanical behaviour of PES based composites was evaluated. Mechanical test results showed that increasing the SCF wt. % in the composites increases the hardness, tensile and flexural properties. Furthermore, the optimal SCF loading was found to be 30 wt. % for significantly improving the overall composite mechanical performance. Upon the reinforcing of SCFs, an improvement in the storage modulus was found. Based on the fractographic analysis, orientation and aligned structure of carbon fibers, good bonding of fibers within the matrix and better fiber-matrix interaction were the primary reasons leading to the improvement of mechanical properties. The optimized composite (PES with 30 wt. % of SCF) could be used in automotive components like frames, flap covers and gears of printing machinery.

Rheology, morphological evolution, thermal, and mechanical properties of epoxy modified with polysulfone and cellulose nanofibers

ABSTRACTIn this work, the epoxy systems modified with polysulfone (PSF) and cellulose nanofiber (CNF) cured at different temperatures are prepared to investigate the effect of CNF on curing reaction, morphology evolution, rheology, thermal, and mechanical performance of composites. The reaction rate is increased and the activation energy is decreased with CNF incorporation, implying an accelerating effect of CNF on the epoxy‐amine reaction. The phase separation and gelation of the epoxy/PSF/CNF system start earlier compared with the binary system of epoxy/PSF. While it is displayed by rheology that both the system viscosity and relaxation time are elevated with CNF, presenting an inhibiting effect on phase evolution. Morphologies with smaller domain size are finally freezed by the epoxy gelation. The enhancement of impact performance for the epoxy/PSF/CNF composites is indicated by 40.2% increase in the impact strength, which is attributed to the finer phase‐separated morphology, the uniformly distributed CNF within the polymer matrix and the good load transfer between phases. In addition, the thermal stability of composites is improved as the CNFs existed in the phase‐separated polymer matrix can restrict the thermal motion of molecules during decomposition process. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48628.

Study on Cure Deformation of Metal/CFRP Laminated Composites

During the curing process of composite materials, the differences of the heat transfer ability and mechanical properties of material in various directions result in residual stresses and curing deformation in the composite after curing. Curing deformation has adverse effect on the mechanical performance of composites. The development of internal stress during curing may cause matrix cracking, delamination, warpage and rebound deformation of composites. In this paper, numerical simulation is used to predict the curing deformation of components, thereby reducing production costs and improving production efficiency as well. According to the curing kinetic equation, the HETVAL subroutine was firstly developed to calculate the temperature field and the curing degree field of the curing process. UMAT and UEXPAN subroutines were then applied to solve the mechanical constants and thermal strain and curing shrinkage strain during the curing process. After the proposed model was verified, the deformation of the metal composite co-cured components was studied. It was found that when the thickness ratio of metal to CFRP is one to one the composite gains the greatest geometrical deviation after curing.

Influence of rolling temperature on the interfaces and mechanical performance of graphene-reinforced aluminum-matrix composites

To study the influence of rolling on the interfaces and mechanical performance of graphene-reinforced Al-matrix composites, a rolling method was used to process them. Using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and tensile testing, this study analyzed the micromorphology, interfaces, and mechanical performance of the composites before and after rolling. The experimental results demonstrates that the composites after hot rolling has uniform structures with strong interfacial bonding. With an increase in rolling temperature, the tensile strength and elastic modulus of the composites gradually increase. However, when the rolling temperature is higher than 500°C, granular and rod-like Al4C3 phases are observed at the interfaces and the mechanical performance of the composites is degraded. When the rolling temperature is 480°C, the composites show the optimal comprehensive mechanical performance, with a tensile strength and elastic modulus of 403.3 MPa and 77.6 GPa, respectively, which represent increases of 31.6% and 36.9%, respectively, compared with the corresponding values prior to rolling.

Effect of enzymatic treatment of flax on fineness of fibers and mechanical performance of composites

The application of enzymes as alternative to dew retting of flax was studied in correlation to the characteristics of composites reinforced with these natural fibers. Fiber fineness and mechanical properties of biocomposites were evaluated. Furthermore, moisture absorption by biocomposites was studied and fracture surfaces were investigated using Scanning Electron Microscopy. Compared to dew retted fiber composites, improvements in mechanical performance can be observed for composites impregnated with fibers extracted after enzymatic treatments. All enzymatic treatments resulted in finer fibers than green fibers and led to biocomposites with a reduced equilibrium moisture content and lower diffusion coefficient. This study illustrates the high potential of enzymatic retting, in particular with polygalacturonase. Also, the manual extraction procedure used, produced fibers with an E-modulus up to 84 GPa and strength up to 800 MPa, likely due to reduced fiber damage, which illustrates the hidden potential of flax fibers.

Interfacially-grafted single-walled carbon nanotube / poly (vinyl alcohol) composite fibers

Nanocomposites are critically influenced by interfacial interactions between the reinforcement and matrix. Polyvinyl alcohol (PVOH) of varying molecular weights were prepared and grafted-to single-walled carbon nanotubes (SWCNTs), to improve the interfacial interaction with a homopolymer PVOH matrix. Nanocomposite fibers were coagulation spun across a broad range of loading fractions, controlled by the spinning dope composition. An intermediate grafted-PVOH molecular weight (10 kDa) maximized grafting ratio, and the final composite mechanical performance; the positive effects were attributed to the increased degree of dispersion of the SWCNTs in the dope, as well as the favorable interface. The PVOH grafting increased the stability of the SWCNT loading fractions (up to 45 wt.%), offering increased strength (up to 1100 MPa) and stiffness (up to 38.5 GPa); at the same time, strain-to-failures remained high (up to 23.3%), resulting in high toughness (up to 125 J g−1).

Fabrication and Application of Black Phosphorene/Graphene Composite Material as a Flame Retardant.

A simple and novel route is developed for fabricating BP-based composite materials to improve the thermo-stability, flame retardant performances, and mechanical performances of polymers. Black phosphorene (BP) has outstanding flame retardant properties, however, it causes the mechanical degradation of waterborne polyurethane (WPU). In order to solve this problem, the graphene is introduced to fabricate the black phosphorene/graphene (BP/G) composite material by high-pressure nano-homogenizer machine (HNHM). The structure, thermo-stability, flame retardant properties, and mechanical performance of composites are analyzed by a series of tests. The structure characterization results show that the BP/G composite material can distribute uniformly into the WPU. The addition of BP/G significantly improves the residues of WPU in both of TG analysis (5.64%) and cone calorimeter (CC) test (12.50%), which indicate that the BP/G can effectively restrict the degradation of WPU under high temperature. The CC test indicates that BP/G/WPU has a lower peak release rate (PHRR) and total heat release (THR), which decrease by 48.18% and 38.63%, respectively, than that of the pure WPU, respectively. The mechanical analysis presents that the Young’s modulus of the BP/G/WPU has an increase of seven times more than that of the BP/WPU, which indicates that the introduce of graphene can effectively improve the mechanical properties of BP/WPU.

Examination of voids and geometry of bio-based braided composite structures

Braided composites are formed by interlacing continuous fibers into a textile pre-form and then impregnating the pre-form within a matrix material. Braid mechanical properties are manipulated through the selection of matrix, fiber and braid geometry. Braided composites are produced with conventional materials like carbon, aramid and glass fibers; however, they can also be produced using natural fibers such as jute, hemp, flax or regenerated cellulose. The mechanical properties of conventional and natural braided composites are highly affected by voids within the braided structure. The effect of voids on braided structures must be investigated to improve braided composite performance. A high-resolution micro-computed tomography (μCT) measurement method was utilized to quantify the size and distribution of voids within natural fiber-bio resin braided composite structures. Image processing techniques were employed to quantify void, matrix and fiber content within 35° and 45° braid samples. Accurate quantification of fiber, matrix and void volumes are crucial for evaluating the quality and repeatability of the braided composite manufacturing process. Reduction of voids and pores will improve braided composite mechanical properties and performance. Measurement of the constituents within braided composites is also necessary for the development of accurate models for predicting braid mechanical properties. Measurement of the internal microstructure of braided composites will allow for the development of improved analytical and numerical braided composite models.

Dimensional Scaling and Failure Pattern of the Tensile Properties of Angle-Ply Thermoplastic Composites of Twaron Fiber/Polypropylene

Thermoplastic multilayer composites with different fiber orientations per layer were prepared with polypropylene and aramid fibers as reinforcing material. The prepregs were prepared in a continuous impregnation system using the dry powder method in a fluidized bed. The specimens were laminated by compression molding, tensile tested and their fracture area was analyzed by microscopy. The mechanical performance of the laminates was influenced by the fiber orientation at the different layers. The fibers at 0° conferred high stiffness to the composite, limiting the maximum deformation and promoting failure. The laminates with 0o layers showed a fragile and sudden fracture oriented at 90° to the aplied load, even with low fiber content. The plies oriented at  45° balanced the stress and contributed to higher levels of deformation during the test due to fiber rotation towards the loading direction, also, no post-yield stiffening was found as in thermoset composites due to the ductile nature of the thermoplastic matrix; these layers limited the crack propagation in the transverse direction, canceling the in-plane shear stress. The fibers at 90° acted as filler due to poor interface and did not contribute to the improvement of the composite mechanical performance. The evidence shows no delamination in the materials due to the tenacious nature of the thermoplastic matrix, neither saw-toothed or plateau region was found in the stress-strain curves in contrast to thermoset laminates.

Draping Behavior of Carbon Non-Crimp Fabrics and Its Effects on Mechanical Performance of the Hemispherical Composites

In order to investigate the draping behavior of non-crimp fabrics (NCFs), two types of carbon NCFs with tricot-chain stitches or chain stitches were formed on a hemispherical mould via a stretch forming process. The shear angle and forming defects of the fabrics were measured on the hemisphere, under different blank holder forces (BHFs). The results showed that increasing BHF could enhance the shear angle slightly, reduce the asymmetry for the deformation of the fabrics, and change the main type of the process-induced defects. Besides, compression tests were performed on the corresponding composite components. By analyzing the change of fiber volume fraction and structural parameters of the textile reinforcements, the effects of draping behavior of NCFs on the mechanical performance of the composites were studied. The results reveal that draping process has distinguishable impacts on the mechanical properties of the final components, which is closely related to the stitching pattern of the NCFs.

Effect of manufacturing defect on mechanical performance of plain weave carbon/epoxy composite based on 3D geometrical reconstruction

The investigation on the effect of manufacturing defect on the mechanical performance of composite is essential for the design and application in practice. In this study, the plain weave carbon fiber reinforced polymer (CFRP) laminates are fabricated by the autoclave process and vacuum bag process (VBP), respectively. Uniaxial tensile testes are conducted with a digital image correlation (DIC) system to obtain the macroscopic mechanical performance and local strain distribution. The internal microdefects of composite laminates are captured by micron-resolution computed tomography (μCT) detection technique, including the size and distribution of void, total volume fraction and geometrical parameters of yarns. Based on the Texgen software and Monte-Carlo algorithm, virtual samples with various void contents are constructed to evaluate the impact of defect using finite element solver ABAQUS/Standard. To substantiate this work, we present a comparative study considering both autoclave and VBP. The effect of void defect on the mechanical performances of CFRP laminate is analyzed through finite element method (FEM). The results reveal that the effect of void defect on the surface strain distribution of laminate is significant, especially the value of maximum strain, which will increase obviously with the void defect content. In addition, the overall stiffness predicted by numerical simulation, taking the effect of void defect into account, is lower than that of theoretical.

Enhanced interfacial adhesion between PMMA and carbon fiber by graphene oxide coating

The purpose of this study is to increase the interfacial properties in PMMA/carbon fiber (PMMA/CF) composites Graphene oxide (GO) and brached polyethyleneimine were coated onto the surface of carbon fiber by layer-by-layer assembly in this work. Compared with the origin PMMA/CF composite, the composites reinforced by PMMA/CF–GO showed significant enhancement in interFacial shear strength (IFSS). The improved fiber–matrix adhesion was proved by fracture morphology observation of scanning electron microscopy and almost unaffected mechanical properties of the fiber itself during the coating process. The optimal assembly time was found to be 10 for enhancing the overall composite mechanical performance.

Development and characterization of sugarcane bagasse fiber and nano-silica reinforced epoxy hybrid composites

This paper presents an experimental study on the mechanical performance of sugarcane bagasse fiber reinforced epoxy composite. Tensile and flexural properties of the composites were investigated in this research. Different weightage of short fiber and fiber particulates were utilized to study their effects on the mechanical performance of the composites in terms of tensile and flexural properties. 1% of nano-silica was reinforced to investigate its effect on the mechanical performance of the composites. Hand lay-up composite molding process was used to fabricate the composite samples. During fabrication, ultrasonic mixing was carried out to study the effects on mechanical performance of the fiber particulate reinforced composites. In overall, ultrasonic mixing and addition of nano-silica particles has improved the mechanical performance of the fiber particulate composites. Morphology analysis on surface of composites has shown the removal of air bubbles and deagglomeration. 1wt% of short fiber reinforced composite exhibits the highest tensile and flexural properties among all the samples. Sugarcane bagasse particulates reinforced composites were shown to have better performance compared to short fiber reinforced composites when the wt% of the fiber increase.

Effect of carbon nanotubes and octa-aminopropyl polyhedral oligomeric silsesquioxane on the surface behaviors of carbon fibers and mechanical performance of composites

A kind of carbon fiber/carbon nanotubes/octa-aminopropyl polyhedral oligomeric silsesquioxane (CF/CNTs/POSS for short) reinforcement was prepared by grafting CNTs and OA-POSS to CFs surfaces in order to improve the mechanical properties and interfacial performance. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle testing and analysis were applied to characterize the carbon fibers surface. Tensile testing, bending testing and interlayer shear strength (ILSS) testing were employed to analyze the mechanical properties of composites. The experimental results of SEM and XPS indicate that CNTs and OA-POSS are grafted uniformly on fibers surface with chemical bonding of NH in CNTs and POSS and COOH on CFs surface. The contact angle test and analysis results show that the surface energy of modified CFs decrease compared with that of the unmodified. Furthermore, the mechanical properties of composites after coating with CNTs and OA-POSS are enhanced effectively. Especially, the properties of composites fabricated by CF/1%CNTs/POSS are significantly improved, because OA-POSS increases the interfacial strength and CNTs increases the thickness of the interfacial transition layer, which both improves the interface defects diffusion of composites. Therefore, CF/CNTs/POSS can improve the performance of the composites by forming interface transition layers.

Compressive behaviour of composite columns composed of RAC-filled circular steel tube and profile steel under axial loading

Axial loading tests are conducted on composite columns composed of recycled aggregate concrete (RAC) filled circular steel tube and profile steel. This research primarily aims to investigate the compressive behaviour of composite columns on the basis of the axial compression tests of 11 specimens under uniaxial loading. The design parameters of these columns in the tests are recycled coarse aggregates (RCA) replacement percentage, diameter-thickness ratio of circular steel tube, profile steel ratio and slenderness ratio. The failure process and modes, load-displacement curves, Poisson's ratio of circular steel tube, characteristic loads and ductility of composite columns are presented and analysed. The influence of design parameters on the compressive behaviour of columns is also investigated in detail. Results show that the composite columns present good mechanical performance under axial loading. The profile steel yields ahead of the steel tube and the core RAC exhibits shear failure or crush failure. The axial bearing capacity of composite columns decreases as the magnitude of RCA replacement percentage increases, but the deformability still performs well. The decrease in diameter-thickness ratio and the increase in profile steel ratio are beneficial to the axial bearing capacity and column ductility. In addition, the axial compression behaviour of composite columns decreases significantly as slenderness ratio increases. On the basis of the test and analysis results, a modified AISC design method is proposed to calculate the nominal axial bearing capacity of composite columns composed of RAC-filled circular steel tube and profile steel.

Properties of an industrial extruded HDPE-WPC: The effect of the size distribution of wood flour particles

This work aims understanding the influence of the size distribution of wood flour particles on the physical and mechanical properties of an extruded wood plastic composite (WPC). A industrial-scaled process has been tested for both the wood flour production and the composite forming. Three size distributions of wood flour have been produced from the same batch of wood chips. The analyses of the particle size and form for the three wood flours were carried out by sieve column and by image analysis, revealing the limits of sieving in the case of particles with a high aspect ratio. The present study investigates the influence of the wood flour size distribution on the tensile and flexural behavior of WPC. The Charpy impact behavior of HDPE-WPC is also studied. In addition to the industrial process, the originality of this work lies in relating the microstructure to the mechanical performances of the extruded WPC; especially the orientation of the wood particles that differs according to the size distribution of the wood flour used. In general, mechanical performances of composites are improved by adding large particles. However, in the transverse direction to the extrusion, fine wood flour allows better performances.

Effectively enhanced mechanical properties of injection molded short carbon fiber reinforced polyethersulfone composites by phenol-formaldehyde resin sizing

Abstract This paper reports for the first time the effects of phenol formaldehyde (PF) resin sizing modification of short carbon fiber (SCF) on the mechanical properties of injection molded PF-treated SCF reinforced polyethersulphone (PES) composites. The PF-treated SCFs are fabricated by sizing PF on the SCF surfaces using a conventional sizing process and then cured availing of the high temperature during the extrusion and injection processes. To evaluate the influence of PF sizing on the tensile and flexural properties of PF-sized SCF/PES composites, the PF content relative to SCFs varies in a range of 0.0–30.0 wt%. The results show that the PF sizing on SCF surfaces leads to the improved wettability of the PES on the SCF surfaces and thus an obviously enhanced SCF/PES interfacial adhesion. As a result, both the tensile and flexural properties are effectively enhanced. The optimal PF content relative to SCFs is found to be 20 wt% for effectively improving the overall composite mechanical performance. Compared to the untreated case, the tensile/flexural strength and modulus are improved respectively by 22.2%, 28.4%, 12.9% and 4.4% at this optimal PF coating content. Due to the easy processing and low cost of PF sizing as well as the effectively enhanced mechanical properties of the injection molded composites, the PF-sizing methodology has a great potential for practical applications in short fiber reinforced high performance polymer composites.

Silane-Treated Basalt Fiber⁻Reinforced Poly(butylene succinate) Biocomposites: Interfacial Crystallization and Tensile Properties.

In this work, an economical modifier silane agent—KH550—was used for surface treatment of basalt fiber. Then, a biodegradable poly(butylene succinate) (PBS)/modified basalt fiber (MBF) biocomposite was successfully developed. The effects of silane treatment and fiber mass content on crystalline structure, isothermal crystallization process and mechanical performance of composites were evaluated. The interfacial crystallization of PBS on the surface of MBF was investigated by using a polarized optical microscope (POM). The transcrystalline (TC) structure could be clearly observed and it grew perpendicular to the surface of MBF, which boosted the nucleation ability on PBS crystallization and the strong interfacial interaction between PBS and silane-treated basalt fiber. Under isothermal crystallization kinetics, the incorporation of basalt fiber enhanced the crystallization rate and reduced the crystallization half-time values of composites compared with that of neat PBS due to a heterogeneous nucleation effect. Furthermore, tensile results confirmed that the presence of MBF could greatly improve the tensile strength and modulus. The predicted interfacial shear strength (IFSS) suggested that an enhancement of interfacial bonding could be realized via interfacial crystallization, which was also verified by SEM images. The PBS/MBF biocomposites can be applied in many fields as a low-cost, lightweight, and biodegradable composite material.