Journal of Composite Materials

In situ synchrotron radiation computed tomography (SRCT) was used to compare the fibre damage progression in five configurations of (90₂/0₂)_s carbon-epoxy coupons loaded to failure. The effects of different sizing types, surface treatments and fibre diameters on the macroscopic properties, for example, ultimate tensile strength (UTS), and on the damage accumulation at a microscopic scale, for example, fibre break accumulation, were assessed. A semi-automated approach was adopted to process the large amount of data obtained from the SRCT scans and further method applicability areas can be envisaged. Single fibre break accumulation was seen to be influenced by the fibre type, while the formation of interacting fibre break groups by the surface treatment and the sizing type. For the materials presented, it can be suggested that an increased defect tolerance can be obtained by moving from stronger to weaker fibre-matrix adhesion, with sub-critical multiplet behaviour emerging as independent of the average UTS value.

Nowadays, the application of the engineered cementitious composites(ECC) is expected to highly develop. Due to the lack of access to oiled- polyvinyl alcohol (PVA) fibers in many parts of the world, the implementation of the ECC has contained many difficulties. In this study, to increase the mechanical properties of ECC with the use of un-oiled PVA fibers, the polymers of styrene butadiene rubber (SBR), and ethylene vinyl acetate (EVA) were taken into account to resolve the abovementioned issue. Herein, also in order to enhance the tensile and flexural properties of ECC, the cement was replaced by polymers. Accordingly, a total of 7 mix designs were planned to conduct the proposed tests. The compressive strength, uniaxial tensile strength, and three-point bending tests were performed on the ECC at their 28-day age with consideration of the freeze and thaw cycle. The results of this research illustrated that the use of polymers can enhance the tensile and flexural properties of the ECC with un-oiled PVA fibers. The tensile strain in this study increased by more than 3% after the application of the polymers. Furthermore, the compressive strength increased by more than 47 MPa, and the deflection at the mid-span reached more than 9 mm in the bending test. However, the results showed that the use of polymers was effective on the freeze and thaw cycle and almost preserved the mechanical properties of the ECC. SBR latex has higher compatibility with the ECC in comparison with EVA powder.

The purpose of this paper is to provide a detailed description of a hypoelastic constitutive model. An accurate and robust numerical algorithm is developed and implemented in the Abaqus/Explicit finite element code by means of a vectorized user material (VUMAT) subroutine written in FORTRAN. To validate this model, several elementary tests with different loading conditions were performed on two different types of commingled fiberglass–polypropylene woven composite. The numerical values obtained for the simple tensile test, simple shear test, and objectivity test, were in good agreement with the analytical results of the same tests. The second part of this study was dedicated to the extension of the validation process by performing more realistic simulations of the standard in-plane shear test (picture frame). The numerical responses obtained from the simulation of the picture frame and those from the benchmark curried out by Cao et al. are in good agreement.

A framework using peridynamic theory is developed and demonstrated for deformation and failure analysis of carbon nanotube (CNT) yarn-based structural composites. Experimental work involved tension testing of a CNT yarn/polymer composite resulting in stress–strain response up to and including failure. The as-prepared specimen was characterized using x-ray micro computed tomography (CT), which was then converted into voxel-based data with CNT yarn, polymer, and void phases as well as surface undulation. A Density-Based Spatial Clustering of Applications with Noise algorithm was applied to detect and quantify the clusters of voids, of CNT-rich, and of resin-rich regions. The voxel data, with all microstructural details, were used in peridynamic simulations. These demonstrate the critical roles of resin and void clusters and surface undulation in fracture initiation and propagation. Additional analysis was performed to construct probability density functions (PDFs) of different phases (yarn, resin, and void) with the goal of constructing synthetic virtual composite specimens. The synthetically reconstructed peridynamic models correctly captured the experimental stress–strain response. The similarities and differences between the failure (initiation and propagation) behaviors predicted by x-ray CT-based and PDF-based peridynamic model simulations are presented in detail and discussed.

Nanocrystalline cellulose (NCC) is usually obtained by the acid hydrolysis of microcrystalline cellulose for its use as polymer reinforcement. An ecological alternative to this process, avoiding the use of acids, is a mechanical method. High intensity ultrasonication (HIU) in optimal conditions (time, wave amplitude, volume ratio fiber/solution, cellulose extraction source) can be applied to prepare nanofibrillated cellulose (NFC). In this work, the HIU method was used to mechanically prepare NFC. Ultrasonication time (t) and wave amplitude (A) were optimized seeking for NFC with high crystallinity, strong thermal stability, large aspect ratio (length to diameter) and large surface to volume ratio with diameter in nanometer scale. The morphology and the physical/chemical properties of the NFC prepared at optimal HIU conditions were compared with those of NCC prepared from the same cellulose source at optimal acid hydrolysis (AH) conditions. Similar purity, lower crystallinity, improved thermal stability and larger aspect ratio with diameter in nanoscale were obtained for NFC prepared by HIU. These results can be used as an initial screening for the selection of the optimal process for NCC manufacture focusing on their use as polymer reinforcement.

Natural fiber–reinforced polymer composites offer many advantages over conventional composite materials, such as availability, low cost, inexpensive, lightweight, and high specific mechanical properties. However, the applications of these materials are still limited due to the challenges in achieving a good interface between the fibers and matrix. This is highly influenced by the fiber surface characteristics and the polymer matrix properties. Therefore, in this study, the surface characteristics of ramie fibers were modified using low-pressure plasma treatment in order to improve their interface to the phenolic resin. Furthermore, the effects of using two different curing cycles (acid cure and thermal cure) on the properties of short ramie fiber-phenolic composites were also investigated. A new method for making mats of random short ramie fibers was developed and used for the fabrication of composites containing plasma-treated fibers. The flexural properties of all composites were tested and the obtained fracture surfaces were investigated using LV-SEM. The results indicate that both plasma treatment and cure cycle conditions influence the fiber–matrix interface and consequently the flexural properties of the composites.

The combination of natural fibers and renewable source matrices is an option to replace materials from non-renewable sources used in the manufacture of composites. One example is the use of pinus sawdust and sisal fibers together with a matrix of polyurethane (PU) foam derived from vegetable oils. For the application of composites in sectors such as building or furniture industry, one of the necessary processes is drilling, which allows assembling through different fastening systems. The aim of this work is to investigate the drilling process of the composites of PU foam derived from vegetable oils matrix with only pinus sawdust and hybrid pinus sawdust and sisal fibers taking into account surface damages of the holes and temperature generated during the process. Results showed that drilling parameters influence on the generation of damages mainly at the edges of the holes. Lower cutting speed and feed rate were most appropriate for drilling these types of composites, and temperatures generated during drilling showed relationship with the generation of damages.

The dynamic response of composite sandwich structures with honeycomb-foam hybrid cores subjected to underwater shock waves was investigated by numerical simulations. The deformation process, core compression, momentum transmitting characteristics, and energy absorbing properties of sandwich structures subjected to underwater shock waves with different initial pressures were analyzed. The dynamic responses of the composite sandwich with different core configurations were also compared. The results show that the composite sandwich structures can provide superior protection from underwater shock waves than mass equal laminate plates and the sandwich structures with hybrid cores have better performance than that with empty honeycomb cores when subjected to underwater shock waves. The research can provide reference for the lightweight design and optimization of protective structures against underwater blast loading.

The present research work investigated the influence of biodegradable polymer coatings of hemp fiber on the structural, water absorption, mechanical, and tribological properties of hemp fiber and hemp fiber reinforced epoxy composites (HFREC). Hemp fibers were initially treated with sodium hydrogen carbonate and then coated with biodegradable polymers like polyhydroxybutyrate (PHB) and polylactic acid (PLA). Scanning electron microscopy (SEM) images of the coated fibers showed a visible change in fiber surface and improvement in surface roughness, while; X-Ray diffraction (XRD) analysis indicated the improvement in crystallinity of the coated fibers resulting in enhanced interfacial adhesion between the coated fibers and the epoxy matrix. The experimental results also revealed that both PHB and PLA coatings of the fibers have resulted in improvement of water resistance and mechanical properties such as tensile strength, modulus, and impact strength of coated HFREC. Tribological test results also revealed that the coated HFREC have improved wear and frictional properties in comparison to uncoated HFREC. The best tribological and mechanical properties were exhibited by PLA coated HFREC, which was also confirmed through the SEM images of worn and fractured surfaces of the uncoated and coated hemp fiber composites.

Advanced composite materials used in high-tech fields are widely reinforced with carbon fibers. One of the growing application areas for carbon fibers is their reinforced composites which are used to replace metallic automotive parts. This reduces carbon footprint through weight reduction, which is a strategy pursued globally to reduce the environmental impacts of passenger vehicles. In this study, we assess the reinforcement potential of recycled carbon fibers in a polypropylene (PP) homopolymer with high strength and flowability. The highly crystalline PP homopolymer with low impact properties was used to minimize intrinsic plasticity penalty associated with fiber reinforcement and ascribe the impact strength enhancement solely to extrinsic toughening mechanisms. The reinforced composites are manufactured through extrusion compounding followed by injection molding. Modification of the transition phase connecting the bulk matrix with the bulk carbon fibers led to 78% enhancement in the strength of the composites, compared to the unmodified composites, without any loss in other properties. Compared to a commercial steel bonnet, the compatibilized composites reinforced with recycled carbon fibers exhibited superior specific strength accompanied by ∼87% weight reduction. Morphological analysis showed that all the extrinsic toughening mechanisms are effectively used by the recycled fibers in the reinforced composites.

This article presents the possibility of strength improvement and energy absorption of carbon fibre reinforced polymer composites by matrix modification. In this study, the mechanical properties of bisphenol-A epoxy matrix and carbon fibre reinforced polymer composites were modified with four different wt.% of star-shaped polymer n-butyl methacrylate (Pn-BMA) block glycidyl methacrylate (PGMA). The tensile strength of the epoxy with 1 wt.% star-shaped polymer showed 128% increase in comparison to unmodified epoxy samples. Two different wt.% were then used for the modification of carbon fibre-reinforced polymer composite samples. Tensile tests and low-velocity impact tests were conducted for characterising modified samples. Tensile test results performed showed a slight improvement in the tensile strength and modulus of the composite. Low-velocity impact tests showed that addition of 1 wt.% star-shaped polymer additives increase composite energy absorption by 53.85%, compared to pure epoxy composite specimens. Scanning electron microscopy (SEM) analysis of post-impact specimens displays fracture modes and bonding between the matrix and fibre in the composites. These results demonstrate the potential of a novel star-shaped polymer as an additive material for automotive composite parts, where energy absorption is significant.

This article investigates the dependency of temperature on electrical resistance (R) change in micro carbon fiber polymer composites (MCFPC), for further development as an Internet of Things sensor from previous research works. Three mixtures were prepared using Dow Corning’s Silastic 145 as base polymer and made vary fiber content weight percentages: fiber diameter to length ratio ∅⁄l 0.13 and carbon fiber content of 13%; ∅⁄l:0.66 and carbon fiber contents of 40% and 50%. Composites tested were submitted to temperature loading, with a constant strain of 0.0%, for assessment of R when a change in the composite’s temperature occurs. The composite response was observed to follow an Arrhenius function, for temperatures ranging from −10°C to 40°C. The apparent activation energy was calculated to evaluate further differences between carbon fiber contents and the sensitivity factor, S T due to temperature is determined. The specimens were also tested with a constant strain of 2.86% to assess creep. It was found that creep and R, over the period of time in the analysis, best fit a discrete latent variable model. The sensitivity factor change is determined in regard to stress relaxation, S R . The properties of MCFPC investigated here can be used to establish relationships between electrical resistance outputs and environmental loading conditions for this type of composites, enabling the possibility of deployment as part of a management system network for structural monitoring with real-time data acquisition.

Residual stresses are detrimental to composite structures as they induce processing defects like debonding, delamination, and matrix cracking which significantly decrease their load-bearing capability. In this research, a new in-situ approach using digital image correlation is utilized to analyze the effect of the cure cycle modification on residual stress evolution during processing. It was found that the modified cure cycle comprising abrupt cooling after gelation reduces the residual stresses. Five different layup configurations are investigated to examine the effect of fiber direction. A maximum average residual stress reduction of 31.8% is observed for the balanced unsymmetric [30/-30/60/-60] laminate. The residual stress reduction results in an increase in failure strength between 4 and 12% in the different layups and can lead up to a 22% increase in first-ply failure strength.