An experimental investigation on the repeated impact response of glass/epoxy composites subjected to thermal ageing

In this study, the effect of thermal ageing on low velocity impact response of E-glass/epoxy composites was investigated. Together with single impact case, repeated impact response of the composite samples was also investigated. Impact energies were chosen as 20 J, 40 J, 60 J, 80 J and 100 J for single impact tests while 20 J was chosen for repeated impact tests. The test coupons were cut out from composite panels with stacking sequence of [0/90]_4S and the dimensions of the specimens were 100 mm × 100 mm, with the nominal thickness of 4.2 mm. The conditioning humidity and temperature were chosen respectively as 70% and 95 °C, considering the glass-transition temperature (T_g) of the intact composites which was determined as 78 °C. The samples were exposed to ageing durations of 100, 400, 700, 1000 and 1300 h by using a climatic test cabin. Along with images of damaged samples, variations of the impact characteristics such as absorbed energy, maximum contact force, maximum deflection and contact duration for successive impacts until perforation of the samples are provided. As a result of the study it is found that in addition to the mechanical properties, damage resistance of the E-glass/epoxy composites is significantly affected by the thermal ageing.     

Effect of hydrothermal pretreatment on the properties of moso bamboo particles reinforced polyvinyl chloride composites

Bamboo plastic composites were fabricated from polyvinyl chloride (PVC) and moso bamboo particles (BP). In order to improve the interfacial interaction between BP and PVC, as well as to obtain composites with outstanding mechanical properties, the roles of hydrothermal treating temperatures (120, 140, 160, 180, 200, 220, 240, 260 and 280 °C) on characteristics of BP and properties of the PVC/BP composites were investigated. Results showed that hydrothermal modification improved the surface property of BP and wiped off hemicelluloses and pectin. A uniform dispersion of BP in PVC matrix was observed by SEM with hydrothermal treatment. Tensile strength, tensile modulus and flexural strength of the composites achieved their maximal values of 15.79 MPa, 6702.26 MPa and 39.57 MPa, respectively, with 180 °C hydrothermal treatment. The highest values of elongation at break and flexural deformation were 3.75 ± 0.20% with 200 °C hydrothermal modification and 36.22 ± 2.70% with 140 °C hydrothermal modification, respectively. Due to more decomposition of hemicellulose, the composites expressed lower water absorption and higher thermal stability when the hydrothermal treating temperature exceed 160 °C.     

Thermal cycles effects on interlaminar shear strength (ILSS) and impact behaviour of carbon/PEI composites

In this paper, the effect of thermal cycle on the interlaminate shear strength (ILSS) and impact behaviour of unidirectional carbon fibre reinforced polyetherimide (PEI) matrix composites were studied. Samples were subjected to 100 thermal cycles (by immersing from boiling water (100°C) to ice water (0°C). The effects of thermal cycles were characterized by short beam shear and instrumented impact testers. Also Fractographic investigations were done using a scanning electron microscope (SEM). It is observed that the plastic deformations at the fibre/matrix and interlaminar interface as well as residual stresses lower the ILSS and flexural modulus of the material proportional with the number of thermal cycles. Up to the first 20 thermal cycles the material shows a brittle fracture with lower fracture energy, but after the 20th thermal cycles it is possible to observe that the material fractures with higher fracture energy at longer fracture time. A remarkable difference in the fracture morphology between the thermal cycled and un-treated materials has been observed. It is found that thermal cycles strictly affect the fracture morphology.     

Polydimethylsiloxane–barium titanate composites: Preparation and evaluation of the morphology,moisture, thermal,mechanical and dielectric behavior

Polydimethylsiloxane-α,ω-diols were used as matrix for barium titanate particles to obtain electroactive elastomeric composites. Filler particles were previously treated with a surfactant to improve the compatibility with and dispersibility in the matrix. The composites, processed as films and crosslinked with methyltriacetoxysilane, were investigated from point of view of the morphology, moisture sorption and thermal properties, as well as mechanical and dielectric behavior. Maximum strain value of 850% at 0.32 MPa and dielectric permittivity of 4.41 at 10 Hz and 20 °C were obtained. Two parameters of interest for potential future application of such materials in electromechanical devices (actuation or harvesting), electromechanical sensitivity and harvesting energy capacity, were estimated and discussed in correlation with the molecular mass of the polymeric matrix and the content of the active filler.     

Influence of compatibilizing system on morphology,thermal and mechanical properties of high flow polypropylene reinforced with short hemp fibers

Simultaneous influence of polypropylene-graft-maleic anhydride (MAPP) and silane-treated hemp fibers (HF) on morphology, thermal and mechanical properties of high-flow polypropylene (PP) modified with poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) was studied in this paper. The addition of SEBS reduced the efficiency of MAPP in PP composites with HF, thus silane-treated fibers (HFs) were used to improve polymer–fiber interface. Thermal stability of HF was improved after silane treatment and less than 2% weight loss was observed at 240 °C in composites with 30 wt% HF. Better dispersion of fibers and better efficiency in enhancing static and dynamic mechanical properties of PP, doubling its strength and stiffness were observed in composites with treated fibers compared to untreated ones. High ability to absorb and dissipate energy and well-balanced strength and stiffness were showed by PP modified with SEBS and MAPP containing 30 wt% HFs. These composites were studied as an alternative to conventional PP/glass fibers composites for injection molding of small to medium auto parts.     

Elevated temperature low cycle fatigue of grey cast iron used for automotive brake discs

This paper evaluates the fatigue life properties of low carbon grey cast iron (EN-GJL-250), which is widely used for automotive brake discs. Although several authors have examined mechanical and fatigue properties at room temperatures, there has been a lack of such data regarding brake discs operating temperatures. The tension, compression and low cycle fatigue properties were examined at room temperature (RT) and at brake discs’ working temperatures: 500 °C, 600 °C and 700 °C. The microstructure of the material was documented and analysed. Tensile stress–strain curves, cyclic hardening/softening curves, stress–strain hysteresis loops, and fatigue life curves were obtained for all the above-mentioned temperatures. It was concluded, that Young’s modulus is comparable with both tension and compression, but yield its strength and ultimate strength are approximately twice as great in compression than in tension. All the mechanical properties remained quite stable until 500 °C, where at 700 °C all deteriorated drastically. During fatigue testing, the samples endured at 500 °C on average at around 50% of cycles at room temperature. Similar to other materials’ properties, the cycles to failure have dropped significantly at 700 °C.     

Experimental and FEM study of thermal cycling induced microcracking in carbon/epoxy triaxial braided composites

The microcrack distribution and mass change in T700s/PR520 and T700s/3502 carbon/epoxy braided composites exposed to thermal cycling was evaluated experimentally. Acoustic emission was utilized to record the crack initiation and propagation under cyclic thermal loading between −55 °C and 120 °C. Transverse microcrack morphology was investigated using X-ray computed tomography. The differing performance of two kinds of composites was discovered and analyzed. Based on the observations of microcrack formation, a meso-mechanical finite element model was developed to obtain the resultant mechanical properties. The simulation results exhibited a decrease in strength and stiffness with increasing crack density. Strength and stiffness reduction versus crack densities in different orientations were compared. The changes of global mechanical behavior in both axial and transverse loading conditions were studied. By accounting for the obtained reduction of mechanical properties, a macro-mechanical finite element model was utilized to investigate the influence of microcracking on the high-speed impact behavior.     

Electrical and thermal conductivities of porous SiC/SiO2/C composites with different morphology from carbonized wood

Porous SiC/SiO₂/C composites exhibiting a wide range of high thermal and electrical conductivities were developed from carbonized wood infiltrated with SiO₂. As a pre-treatment, the samples were either heated at 100 °C or kept at room temperature followed by sintering in the temperature range 1200–1800 °C. The microstructure, the morphology, and the electrical and thermal conductivities of the composites were investigated. Pre-treatment at room temperature followed by sintering up to 1800 °C produced composites exhibiting a greater size of carbon crystallites, a higher ordering of the microstructure of carbon and β-SiC and a smaller amount of SiO₂, resulting in electrical and thermal conductivities of 1.17 × 10⁴ Ω⁻¹ m⁻¹ and 25 W/mK, respectively. The thermal conductivity could be further improved to 101 W/mK by increasing the density of the composite to 1.82 g/cm³. In contrast, the pre-treatment at 100 °C produced composites possessing a lower thermal conductivity of 2 W/mK.     

Investigation of microstructure and mechanical properties of nano MgO reinforced Al composites manufactured by stir casting and powder metallurgy methods: A comparative study

In the present work, Al–nano MgO composites using A356 aluminum alloy and MgO nanoparticles (1.5, 2.5, and 5 vol.%) have been fabricated via stir casting and powder metallurgy (PM) methods. Different processing temperatures of 800, 850, and 950 °C for stir casting and 575, 600, and 625 °C for powder metallurgy were considered. Powder metallurgy samples showed more porosity portions compare to the casting samples which results in higher density values of casting composites (close to the theoretical density) compare to the sintering samples. Introduction of MgO nanoparticles to the Al matrix caused increasing of the hardness values which was more considerable in casting samples. The highest hardness value for casting and sintering samples have been obtained at 850 and 625 °C respectively, in 5 vol.% of MgO. Compressive strength values of casting composites were higher than sintered samples which were majorly due to the more homogeneity of Al matrix, less porosity portions, and better wettability of MgO nanoparticles in casting method. The highest compressive strength values for casting and sintered composites have been obtained at 850 and 625 °C, respectively. Scanning electron microscopy images showed higher porosity portions in sintered composites and more agglomeration and aggregation of MgO nanoparticles in casting samples which was due to the fundamental difference of two methods. Generally, the optimum processing temperatures to achieve better mechanical properties were 625 and 850 °C for powder metallurgy and stir-casting, respectively. Moreover, casting method represented more homogeneous data and higher values of mechanical properties compare to the powder metallurgy method.     

The effect of temperatures on hybrid composite laminates under impact loading

The present experimental investigation deals with the impact responses of hybrid composites (carbon–glass fiber/epoxy) under various temperatures. A number of samples were subjected to increasing impact energy at the temperature range of ?20 to 60 °C until complete perforation of samples. With this use of increasing impact energies, it was possible to examine the impact response and failure mechanisms of hybrid composites until perforation of sample. An Energy Profiling Diagram (EPD) was used to obtain the penetration and perforation thresholds of hybrid composites. Besides, the temperature effects on impact characteristics such as load, contact time and permanent deflection were also presented in figures. Test results showed that temperature variations affect the impact characteristics of hybrid composites and they get their maximum values at ?20 °C or 60 °C.     

The effects of the injection moulding temperature on the mechanical properties and morphology of polypropylene man-made cellulose fibre composites

Composites made of polypropylene and man-made cellulose fibres that are intended for injection moulding applications show potential for use in sustainable and light weight engineering with high energy absorption capacity. Due to the thermal sensitivity of the cellulose fibres, process parameters play an important role during the injection moulding process. A polypropylene and a man-made cellulose fibre were chosen for this investigation. Effective melt temperatures between 200 °C and 269 °C were used to process the compounds into test specimens. Tensile, impact and colorimetric tests, as well as an SEM analysis, and a measurement of the fibre length distribution were carried out in order to characterise the mechanical and optical properties of the composites. It was observed that the fibre length becomes shorter above 256 °C and elongation at break and Charpy strength (notched) of the composites already decrease at lower temperatures than tensile strength. A direct correlation between mechanical properties and discoloration was not observed. Therefore, melt temperatures up to 250 °C are suitable for these composites.     

Influence of fibre treatment and glass fibre hybridisation on thermal degradation and surface energy characteristics of hemp/unsaturated polyester composites

The effect of fibre treatment on the thermal degradation and surface energy characteristics of hemp fibre reinforced unsaturated polyester (HFRUP) composites was investigated by means of a thermogravimetric analyser (TGA) in a nitrogen atmosphere and contact angle measurement. In order to modify the fibre/matrix interface, NaOH treatment and glass fibre hybridisation were employed. HFRUP composites were compared to the unreinforced UP, NaOH treated hemp and glass fibre hybridised hemp/UP composites. TGA test results show that the weight loss for all samples occurred between 200 and 415 °C. The unreinforced UP had a maximum weight loss of 1.011%/°C. For the HFRUP composites, the maximum rate of weight loss was 0.81%/°C. For the NaOH treated and glass fibre hybridised hemp/UP composites, the maximum rate of weight loss was 0.78%/°C and 0.79%/°C, respectively. The effect of fibre treatment on the surface energy of studied samples and their dispersive and polar components were also investigated. Surface energy characteristics obtained from contact angle measurement revealed that for unreinforced UP, the contact angle measured with glycerol is 49.37°. For hemp/UP composites, the contact angle is 76.05°. For NaOH treated hemp/UP composites sample, the contact angle was recorded 78.89°, higher than untreated one. For hemp/CSM/UP specimen, the contact angle was recorded 69.80°. Both TGA and contact angle results indicated that surface treatment and glass fibre hybridisation led to better thermal stability and the wetting behaviour of hemp/UP composites.     

Viscoelastic interpretations of erosion performance of short aramid fibre reinforced vinyl ester resin composites

Short aramid fibre reinforced vinyl ester resin based isotropic composites are fabricated with varying fibre weight fractions (20–50 wt%). The composites were evaluated for their erosion performance under a dynamic set of variables such as impingement angle (30°–90°), impact velocity (43–76 m/s), erodent size (250–600 μm) and stand-off distance (55–85 mm) following design of experiments (DOE) based on Taguchi analysis approach. The thermo-mechanical attributes such as storage modulus, loss modulus and damping properties as viscoelastic responses of the composites were investigated in the temperature range of 0–180 °C for their possible interpretations regarding reinforcement efficiency and energy dissipation aspects relevant to erosion process. An interrelation between the full-width half-maxima (FWHM) of loss modulus peak and erosion rate has emerged indicating the erosion to be mainly controlled by the fibre–matrix interfacial characteristics. The eroded surface morphology investigation by scanning electron microscopy (SEM) revealed the nature of wear-craters, material damage mode and other qualitative attributes responsible in facilitating erosion of the composites.     

Effects of Steam Environment on Fatigue Behavior of Two SiC/[SiC+Si<Subscript>3</Subscript>N<Subscript>4</Subscript>] Ceramic Composites at 1300°C

The fatigue behaviors of two SiC/[SiC+Si₃N₄] ceramic matrix composites (CMC) were investigated at 1,300°C in laboratory air and in steam. Composites consisted of a crystalline [SiC+Si₃N₄] matrix reinforced with either Sylramic™ or Sylramic-iBN fibers (treated Sylramic™ fibers that possess an in situ BN coating) woven in a five-harness satin weave fabric and coated with a proprietary boron-containing dual-layer interphase. The tensile stress–strain behaviors were investigated and the tensile properties measured at 1,300°C. Tension–tension fatigue behaviors of both CMCs were studied for fatigue stresses ranging from 100 to 180 MPa. The fatigue limit (based on a run-out condition of 2 × 10⁵ cycles) in both air and steam was 100 MPa for the CMC containing Sylramic™ fibers and 140 MPa for the CMC reinforced with Sylramic-iBN fibers. At higher fatigue stresses, the presence of steam caused noticeable degradation in fatigue performance of both composites. The retained strength and modulus of all run-out specimens were characterized. The materials tested in air retained 100% of their tensile strength, while the materials tested in steam retained only about 90% of their tensile strength.     

Impact performances of steel tube-confined recycled aggregate concrete (STCRAC) after exposure to elevated temperatures

The impact behaviours of steel tube-confined recycled aggregate concrete (STCRAC) following exposure to elevated temperatures of 20 °C, 200 °C, 500 °C and 700 °C were experimentally investigated using a 100 mm-diameter split Hopkinson pressure bar (SHPB). The recycled coarse aggregate (RCA) replacement ratios were set as 0, 50% and 100%. The effect of RCA replacement ratio and exposure temperature on the impact properties of STCRAC were analysed in terms of failure modes, stress-strain time history curve and dynamic increase factor (DIF). The results show that the fire-damaged STCRAC can maintain its integrity during impact load. However, there were evident degradations in the dynamic behaviour of STCRAC after exposure to high temperatures of 500 °C and 700 °C. The ultimate impact strength, impact secant modulus and residual impact strength of STCRAC obviously decreased because of the damage due to high temperature exposure. But the degradations of both the ultimate impact strength and impact secant modulus of STCRAC under impact loading were less severe than those under quasi-static loading. The remaining strength factor and the DIF tended to increase with the raise of the elevated temperatures. Overall, during the impact loading, the fire-deteriorated STCRAC exhibited excellent impact behaviour.     

Flexural behaviour of CNT-filled glass/epoxy composites in an in-situ environment emphasizing temperature variation

The paucity of structural defects in carbon nanotube (CNT) with unrivalled mechanical properties has always posed an interest to material scientists for its potential incorporation in soft polymer resins to achieve superior mechanical stability. Present investigation focuses on the assessment of flexural behaviour of glass/epoxy (GE) and multiwalled carbon nanotubes (MWCNT) embedded glass/epoxy (0.3 wt. % of epoxy) (CNT-GE) composites at different in-service environmental temperatures. In-situ 3-point bend tests were performed on GE and CNT-GE composites at −80 °C, −40 °C, room temperature (20 °C), 70 °C and 110 °C temperatures at 1 mm/min crosshead speed. The results revealed that at 110 °C temperature, the flexural strength of GE and CNT-GE composites was significantly decreased by 67% and 81% respectively in comparison to their strength at −80 °C temperature. Similarly, 38% and 77% decrement in modulus was noted for GE and CNT-GE composites respectively. Dynamic mechanical thermal analysis (DMTA) was carried out in the temperature range of −100 °C to 200 °C to correlate the mechanical and thermo-mechanical response of both the material systems. Addition of 0.3 wt. % MWCNT in GE composite resulted in lowering of glass transition temperature (T_g) by 12 °C. Furthermore, to understand various possible deformation and failure mechanisms, the post failure analysis of the fractured specimens, tested at different temperatures, was carried out using scanning electron microscope (SEM). The critical parameters needed during designing composite structures were calculated and modelled using Weibull constitutive model.     

The effect of graphene presence in flame retarded epoxy resin matrix on the mechanical and flammability properties of glass fiber-reinforced composites

The effect of adding graphene in epoxy containing either an additive (MP) or reactive-type (DOPO) flame retardant on the thermal, mechanical and flammability properties of glass fiber-reinforced epoxy composites was investigated using thermal analysis; flexural, impact, tensile tests; cone calorimetry and UL-94 techniques. The addition of MP or DOPO to epoxy had a thermal destabilization effect below 400 °C, but led to higher char yield at higher temperatures. The inclusion of 10 wt% flame retardants slightly decreased the mechanical behavior, which was attributed to the poor interfacial interactions in case of MP or the decreased cross-linking density in case of DOPO flame retarded resin. The additional graphene presence increased flexural and impact properties, but slightly decreased tensile performance. Adding graphene further decreased the PHRR, THR and burning rate due to its good barrier effect. The improved fire retardancy was mainly attributed to the reduced release of the combustible gas products.     

Influence of carbon fibre treatment and filler addition on porosity and structure change of carbon fibres reinforced phenolic matrix composites during carbonization

The transformation during pyrolysis of ex-cellulose carbon fibres/phenolic matrix 2D composites is investigated. The amount and the dimensions of pores and micro-cracks created after heat treatment are characterized and described from 600 °C (resin pyrolysed matrix) to 1,000 °C (carbonized matrix). Characterization of samples was performed using mercury intrusion porosimetry at different stages of thermal treatment. Three different composites were prepared in order to study the influence of fibre surface properties and the role of carbon filler addition in matrix, on the porosity emergence. Inter-laminar shear strengths of these materials were recorded. On the investigated materials, the lowest fibre/matrix bonding is found to preserve material cohesion by promoting interfacial debonding and thus limiting consequences of shrinkage during matrix carbonization.     

Mechanical and thermal properties study of glass fiber reinforced polyarylene ether nitriles

Glass fiber (GF) reinforced phenolphthalein-based polyarylene ether nitrile composites were prepared through melt blending, and the composites were characterized by various methods to find that both the mechanical and thermal properties of the silane coupling agent treated GF reinforced composites were improved with the increase of GF content. Tensile strength, flexural strength and Izod impact strength got their highest values with GF content at 35 wt.%, 30 wt.% and 25 wt.% respectively. The heat distortion temperature (HDT) of 30 wt.% GF reinforced composite is 284 °C, more than a 100 °C increase compared to the pristine resin.     

Anisotropic thermal conductivity of three-layer laminated carbon-graphite composites from carbonized wood

Composites with characteristics of anisotropic thermal conductivity for thermal management in Solar Power Satellite (SPS), to discharge the heat that was generated when solar energy was not converted to electricity, were developed by alternating layers of laminated graphite and carbonized wood. The effects of the weight fraction of carbonized wood, particle size, interlayer interfaces, and environment temperature on the thermal conductivity and the ratio of thermal conductivity between horizontal and vertical directions (H/V ratio) to the plain surface of samples were discussed. The thermal conductivities of carbon–graphite (C/G) composites were measured using the laser flash method. Laminated C/G composites improved the anisotropic thermal conductivity. The highest H/V ratio of 10.17 was obtained at 10 wt% of carbonized wood. Particle size and interlayer interfaces were found to affect the anisotropic thermal conductivity. The thermal conductivity of C/G composites increased with increasing temperature from 25 °C to 150 °C.