Mostefa Bourchak

Analytical and experimental investigation of tensile properties of cross-ply and angle-ply GFRP composite laminates

Abstract The static tensile properties in the form of ultimate failure stress, ultimate failure strain and Young’s modulus of a cross-ply glass fiber-reinforced polymer (GFRP) composite laminate [904, 04]s and an unconventional angle-ply GFRP composite laminate [+67.54, -67.54]s were investigated using the netting analysis, the laminate mixture rule (Hart-Smith 10% rule) and the classical laminate theory (CLT). The findings were then compared to experimental results to determine the accuracy of each analytical technique. It was found that the netting analysis was the best overall method for estimating the cross-ply laminate tensile properties, whereas neither the CLT nor the 10% rule were appropriate for estimating the tensile properties of the unconventional ply angle laminate.

Damage assessment of random multiwalled carbon nanotube-reinforced polymer nanocomposites

Abstract The paper presents a numerical procedure to evaluate the mechanical properties and predict the damage initiation of random multiwalled carbon nanotube-reinforced polymer nanocomposites (MWCNT-RPNC). The Hashin-Shtrikman (H-S) random prediction model is used to compute the properties of the reinforced polymer matrix, whereas the Chamis model is used to compute the lamina properties and the Hashin progressive damage model within the ABAQUS environment is used as a finite element analysis (FEA) tool to predict the damage initiation in the reinforced composite material. Experimental testing is employed to validate the numerical results and to adjust the H-S prediction model for MWCNT-RPNC.

Polymer composite reinforced with nanoparticles produced from graphitic carbon-rich fly ash:

Carbon nanotubes and graphene are considered effective reinforcement materials for various polymers because of their superior properties. However, they are expensive and difficult to separate and incorporate individually into matrix systems because of their tendency to exist in clustered form. In this work, carbon nanoparticles produced from graphitic carbon-rich fly ash by high-energy ball milling are evaluated as a reinforcement in a high-performance epoxy matrix system. They were used in various weight fractions ranging from 0.1 to 2 wt.%. The obtained carbon nanoparticles have an average particle size of around 20 nm, while XPS spectrum shows active carbonyl groups on their surfaces. The mechanical tensile properties of the carbon nanoparticles/epoxy nanocomposite, including their Youngs modulus, stiffness, and load at fracture, were investigated. Moreover, the effect of ethanol as a dispersion medium was studied. The obtained results indicate that the Youngs modulus and load at fracture changed only slightly upon the addition of carbon nanoparticles to the epoxy matrix system. On the other hand, the stiffness was improved by 60% over that of the pure epoxy matrix system. This improvement was obtained at 0.6 wt.% carbon nanoparticle content. The test results indicate that ethanol is effective in modifying the nanocomposite mechanical properties. Additionally, results show that low-cost CNPs might be useful as a reinforcement material for high-stiffness products.

LEFM to Investigate the Impact of Deteriorated Particles in Composite Material

Due to its distinguished properties especially being isotropic, particulate reinforced composite is considered as one of the attractive material for wide range of applications, where the relatively low manufacturing cost is a desirable advantage. In the present analysis, deteriorated particles embedded in particulate reinforced composite have been investigated. The impact of the fractured particles is studied through the principles of fracture mechanics using finite element method. Mainly the stiffness variation of the composite due to the presence of the fractured particles is mainly predicted, since it is considered as an important factor especially from the view point of the damage-tolerant design of composite structures. A representative volume element (RVE) has been selected to represent the particulate composite with different particle volume fractions. It is important to point out that based on a previous investigation and comparison between two and three dimensional finite element analysis for a particulate reinforced composite, two-dimensional, plane strain finite element analysis is used to estimate the stresses and deformation that taken place. Uniaxial tensile stress perpendicular to the crack face of the fractured particle has been applied to the representative volume element. Due to symmetry of the studied geometries, quarter of the representative volume element is modeled via finite element method with a consistent mesh as possible to maintain reliable results. Linear elastic fracture mechanics (LEFM) is adopted through estimating stress intensity factor (SIF) of the cracked particles. Basically, the investigation covers the assessment of fractured particles with different crack lengths, where the particle’s stiffness is considered as a substantial parameter in the analysis in combination with others. Moreover, various particles volume fractions are taken into account to figure out their influence on the effective Young’s modulus of the representative volume element chosen for the studied cases. Multiple point constraints (MPC) technique is adopted in the finite element model to calculate the effective stiffness of the fractured particle. In general, it has been shown that there is a considerable influence of the deteriorated particles on increasing stress intensity factor levels at the crack tip as long as the crack length increases with respect to the particle size, and this basically depends on the stiffness ratio of the matrix/particle considered in the analysis. In the other hand, it has been noticed that a significant reduction in the effective stiffness of the particulate composite which is calculated based on the modeled representative volume element as a function of the crack length.Copyright

Failure Analysis in Hybrid Composite Laminates Using Acoustic Emission and Microscopy

Fiber Reinforced Plastic (FRP) composite materials are widely used in many applications especially in aircraft manufacturing because they offer outstanding strength to weight ratio compared to other materials such as aluminum alloys. The use of hybrid composite materials is potentially an effective cost saving design while maintaining strength and stiffness requirements. In this work, Woven Carbon Fibers (WCFs) along with Unidirectional Glass Fibers (UDGFs) are added to a an aerospace-rated epoxy matrix system to produce a hybrid carbon and glass fibers reinforced plastic composite plates. The manufacturing method used here is a conventional vacuum bagging technique and the stacking sequence achieved consists of a symmetric and balanced laminate (±451WCF, 03UDGF, ±451WCF) to simulate the layup usually adopted for helicopter composite blades constructions. Then, tensile static tests samples are cut according to ASTM standard using a diamond blade and tested using a servohydraulic test machine. Acoustic Emission (AE) piezoelectric sensors (transducers) are attached to the samples surface using a special adhesive. Stress waves that are released at the moments of various failure modes are then recorded by the transducers in the form of AE hits and events (a burst of hits) after they pass through pre-amplifiers. Tests are incrementally paused at load levels that represent significant AE hits activity which usually corresponds to certain failure modes. The unbroken samples are then thoroughly investigated using a high resolution microscopy. The multi load level test-and-inspect method combined with AE and microscopy techniques is considered here to be an innovation in the area of composite failure analysis and damage characterization as it has not been carried out before. Results are found to show good correlation between AE hits concentration zones and the specimens damage location observed by microscopy. Waveform analysis is also carried out to classify the damage type based on the AE signal strength energy, frequency and amplitude. Most of the AE activity is found to initiate from early matrix cracking that develops into delamination. Whereas little fiber failure activity has been observed at the initial stages of the load curve. The results of this work are expected to clear the conflicting reports reported in the literature regarding the correlation of AE hits characteristics (e.g. amplitude level) with damage type in FRP composite materials. In addition, the use of a hybrid design is qualitatively assessed here using AE and microscopy techniques for potential cost savings purposes without jeopardizing the weight and strength requirements as is the case in a typical aircraft composite structural design.Copyright